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A Bell & Howell Information Company 300 North Zeeb Road. Ann Arbor. Ml 48106-1346 USA 313/761-4700 800/521-0600 REACTION CHEMISTRY OF
FISCHER-TYPE RHENACYCLOBUTADIENE
AND
t|3-TRIMETHYLENEMETHANE PLATINUM COMPLEXES
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree of Doctor of Philosophy
in the Graduate School of The Ohio State University
By
Vdronique Plantevin
The Ohio State University
1995
Dissertation Committee: Approved by:
Dr. Bruce Bursten
Dr. Viresh Rawal « -
Dr. Andrew Wojcicki Adviser / Department of Chemistry UMI Number: 9526075
UMI Microform 9526075 Copyright 1995, by UMI Company. All rights reserved.
This microform edition is protected against unauthorized copying under Title 17, United States Code.
UMI 300 North Zeeb Road Ann Arbor, MI 48103 To My Parents
ii ACKNOWLEDGMENT
I would like to express my sincere gratitude to my advisor, Professor A.
Wojcicki, for his support and guidance.
The completion of my experimental work would have been impossible without the collaboration of Carl Engleman (NMR), David Chang (mass spectrometry), and Judith
Gallucci (X-ray diffraction analysis).
I would like to acknowledge as well the financial support provided by The Ohio
State University and the Lubrizol Co. for a graduate fellowship.
Thanks to all the members of the Wojcicki group, past and present: Laura L.
Padolik, Patrick W. Blosser, Richard R. Willis, Dean E. Rende, Mark W. Baize, Todd
R. Dunsizer, Kirsten L. Daniel, and Christopher M. Beck. In addition to constructive chemistry-related discussions, I am appreciative of their moral support and friendship.
Finally, I would like to express my gratitude to my parents whose love, patience, and unconditional support have contributed to the completion of my graduate studies.
This dissertation is dedicated to them. VITA
January 29, 1968 Bom, Rognac, France
1985 Baccalaurdat C, Lycde Vauvenargues, Aix-en-Provence, France
1985-1987 Mathdmatiques Supdrieures-Mathdmatiques Spdciales, Lycde Paul Cdzanne, Aix-en-Provence, France
1987-1989 ESCIL, Lyon, France
1989-1993 Teaching Assistant and Research Assistant The Ohio State University
1994 Lubrizol, Co. Industrial Fellow, The Ohio State University
PUBLICATIONS
- Plantevin, V.; Blosser, P. W.; Gallucci, J. C.; Wojcicki, A. "ti3-Trimethylenemethane Complexes of Platinum", OrganometaUics 1 9 9 4 , 13, 3651.
- Plantevin, V.; Gallucci, J. C.; Wojcicki, A. Inorg. Chim. Acta 1994, 222, 199.
FIELDS OF STUDY
Major Field: Chemistry Studies in Organic Chemistry Professor Andrew Wojcicki
iv TABLE OF CONTENTS
DEDICATION...... ii
ACKNOWLEDGMENT...... iii
VITA...... iv
LIST OF TABLES...... vii
LIST OF FIGURES...... viii
LIST OF SCHEMES...... x
CHAPTER PAGE
I. INTRODUCTION ...... 1
PART A: ORGANORHENIUM COMPLEXES...... 2 I- Fischer-type carbene complexes ...... 2 II- Schrock-type metallacyclobutadiene complexes ...... 19 III- Fischer-type rhenacyclobutadiene complexes ...... 21 IV- Objectives of the project ...... 25
PART B: ORGANOPLATINUM COMPLEXES...... 26 I- T)3-Propargyl transition metal complexes ...... 26 II- Use of trimethylenemethane transition metal complexes in organic synthesis...... 32 III- ti3-Trimethylenemethane complexes of platinum ...... 42 IV- Objectives of the project ...... 42
II. DISCUSSION ...... 44 PART A: ORGANORHENIUM COMPLEXES...... 44 I- Fischer-type properties o f ...... rhenacyclobutadiene complexes 1 ...... 44 II- Attempts to diversify die substitution pattern onthemetallacycle ...... 53 III- Exploration of the novel reaction chemistry of rhenacyclobutadiene complexes ...... 70 IV-Summar y...... 132
v PART B: ORGANOPLATINUM COMPLEXES...... 133 I- Spectroscopic data ...... 133 II- X-Ray diffraction analysis of complex 7 8 ...... 137 III- Reactivity of complex 7 8 with unsaturated reagents 144 IV- Attempt to change the nature of the substituent on C 2 163 V- Attempts to change the terminal substituent ...... 168 VI- Study of the reactivity of complex 150 toward olefins ...... 188 VII- Summary...... 192
III. EXPERIMENTAL PART...... 193
PART A: GENERAL PROCEDURES...... 193 I- General experimental conditions ...... 193 II- Instrumentation ...... 194 III- Reagents and chemicals ...... 196
PART B: ORGANORHENIUM COMPLEXES...... 197 I- Preparation of rhenacyclobutadiene complexes ...... 197 II- Deprotonation of complex la and deuteration/alkylation studies ...... 203 III- Aminolysis reactions ...... 207 IV- Reactions involving P(CH 3 )2Ph ...... 210 V- Rhenium cyclopentadienyl complexes ...... 213 VI- Oxygen-atom insertion reactions ...... 222 VII- Nucleophilic attack by carbanions ...... 224 VIII- Rearrangements in organonitriles and pyridine ...... 227 IX- NH-Insertion reactions ...... 230
PART C: ORGANOPLATINUM COMPLEXES...... 236 I- Synthesis of propargyl tosylate starting materials ...... 236 II- Attempts to isolate -propargyl Pt tosylate complexes ...... 238 III- Synthesis of various heteroatom-substituted platinum allyl complexes ...... 240 IV- Synthesis of various trimethylenemethane complexes of platinum ...... 245 V- Reactivity of substituted trimethylenemethane complexes of platinum ...... 251
REFERENCES...... 257
APPENDIX...... 272
vi LIST OF TABLES
TABLE PAGE
1. Product ratios: naphthols versus indenones ...... 19
2. Selected 13C{ 1H} NMR chemical shifts of complexes 1 ...... 22
3. IR data of complex la and its conjugated base ...... 49
4. Selected 13C{ 1H} NMR chemical shifts of complexes 8 7 ...... 57
5. Chelation effect ...... 81
6. IR data of complexes 116 and 117 ...... 89
7. Rearrangement in various organonitriles ...... 91
8. Spectroscopic data for complexes 125 and 1 1 7 ...... 116
9. Selected bond distances and angles for 1 2 5 ...... 121
10. Spectroscopic data of complexes 126 and 1 1 8 ...... 125
11. Selected bond distances and angles for complex 7 8 ...... 139
12. 3ip{lH} NMR chemical shifts and coupling constants resulting from
reactions of complex 7 8 with electron-deficient alkenes
andalkynes ...... 145 13. One-pot synthesis of T|3-allyl Pt complexes ...... 173
14. One-pot synthesis of trimethylenemethane Pt complexes ...... 179
15. Crystal data and data collection and refinement detail for 125 ...... 273
16. Positional and equivalent isotropic thermal parameters for 125 ...... 275
17. Crystal data and data collection and refinement detail for 7 8 ...... 277
18. Positional and equivalent isotropic thermal parameters for 7 8 ...... 279
vii LIST OF FIGURES
FIGURE PAGE
1. 1H NMR spectrum of the deuteration reaction product of la ...... 52
2. 1H NMR spectrum of complex 87a ...... 59
3. 1H NMR spectrum of complex 1 0 0 ...... 68
4. 13C{ 1H> NMR of complex 1 0 0 ...... 69
5. l H NMR spectrum of complex 10 5 ...... 75
6. 13C{ 1H} NMR spectrum of complex 105 ...... 76
7. 1H NMR spectrum of complex 1 1 9 ...... 92
8. 13C{1H} NMR spectrum of complex 119 ...... 93
9. 1H NMR spectrum of complex 1 2 0 ...... 98
10. 13C{1H} NMR spectrum of complex 120 ...... 99
11. 1H NMR spectrum of complex 1 2 5 ...... 114
12. 13C{1H} NMR spectrum of complex 125 ...... 115
13. ORTEP drawing of complex 125 ...... 120
14. Selected examples of azametallacycles ...... 118
15. 1H NMR spectrum of complex 1 2 7 ...... 127
16. 3ip{lH} NMR spectrum of complex 7 8 ...... 134
17. 1H NMR spectrum of complex 7 8 ...... 135
18. ORTEP drawing of complex 7 8 ...... 137
19. 1H NMR spectrum of cycloadduct 1 3 4 ...... 149
20. 13C{ 1H} spectrum of cycloadduct 1 3 4 ...... 150
21. 3ip{lH} NMR spectrum of complex 1 3 7 ...... 155
viii 22. 1H NMR spectrum of complex 1 3 7 ...... 156
23. 1H NMR spectrum of cycloadduct 1 4 0 ...... 160
24. 13C{1H} spectrum of complex 1 4 0 ...... 161
25. In-situ 31P{ 1H> NMR spectrum of complex 145 ...... 174
26. 3ip{iH> spectrum of complex 147b ...... 175
27. 1H NMR spectrum of complex 147 b ...... 176
28. 31P{1H} spectrum of complex 149b ...... 177
29. 1H spectrum of complex 149 b ...... 178
30. 3ip{ 1H} spectrum of complex 1 5 0 ...... 180
31. 1H spectrum of complex 150 ...... 181
ix LIST OF SCHEMES
SCHEME PAGE
1. Basic reaction chemistry of Fischer carbene complexes ...... 3
2. Mechanism of Michael addition to Fischer carbene complexes ...... 5
3. Intramolecular Diels-Alder reaction - Preparation of precursors ...... 8
4. Intramolecular Diels-Alder reaction - Results ...... 9
5. Reactivity of vinylketene intermediates ...... 13
6 . Benzannulation reaction - General ...... 17
7. Original synthesis of rhenacyclobutadiene complexes ...... 22
8 . Reaction of complex la with phosphines ...... 24
9. Original synthesis of complex 6 9 ...... 29
1 0. Preparation of transition metal trimethylenemethane complexes ...... 33
11. Preliminary mechanistic studies ...... 35
12. Proximal approach ...... 37
13. Distal approach ...... 38
14. Possible regiochemistry ...... 39
15. Reaction with aldehydes ...... 41
16. Reaction of complex la with P(/?-tolyl >3 and PEt 3 ...... 46
17. Reaction of complex la with P(CH 3)2P h ...... 47
18. Diversification of the metallacycle substituents ...... 54
19. Aminolysis mechanism ...... 56
20. Proposed mechanism for the aminolysis of complex la ...... 56
21. Activation of carbon C 3 ...... 62
x 22. Deprotonation/alkylation of Fischer carbene complexes ...... 65
23. Proposed mechanism of alkylation ...... 67
24. Expected metathesis reaction ...... 70
25. Attempted coordination of a double bond or a heteroatom ...... 83
26. Proposed mechanism for the formation of cylopentadienyl
complexes ...... 85
27. Expected insertion of organinitriles ...... 88
28. Examples of 1,2-shifts of dialkyl-substituted alkylidene complexes. 95
29. Examples of alkyl migration ...... 95
30. Proposed mechanism for the rearrangement promoted by pyridine.. 101
31. Reaction of Fischer carbene complexes
with sulfur-stabilized carbanions ...... 104
32. Reaction of complex la with sulfur-stabilized carbanions ...... 106
33. Alternative mechanism ...... 107
34. Proposed mechanism of NH-insertion ...... 113
35. Expected [3+2] cycloaddition involving complex 7 8
and electron-defcient olefins ...... 144
36. I3C{1H} spectrum of cycloadduct 1 3 4 ...... 152
37. Synthetic approach to prepare complex P ...... 163
38. Possible mechanisms of oxidative additions ...... 169
39. Design of a one-pot synthesis ...... 171
40. In-situ 3 ip{ 1H} NMR spectrum of complex 145 ...... 173 41. Mechanism of nucleophilic attack on r^-propargyl
Pt complexes proposed by Chen and coworkers ...... 184
42. Acid-promoted propargyltrimethylsilane to
allene rearrangements ...... 184
xi Protodesilylation reaction: proposed mechanism 1
Protodesilylation reaction: proposed mechanism 2 CHAPTER I
INTRODUCTION
The growing use of transition metal complexes in organic synthesis that has been
observed over the past three decades is related to a better understanding of their reactivity.
The coordination of a ligand to a transition metal center modifies its properties. The metal
center can either directly participate in the reaction or increase the stability of the
coordinated ligand or its reactivity and consequently afford improved selectivity or give
access to new types of reactions.1 Two factors can be invoked: steric constrains and
electronic properties. Geometrical restrictions can lead to a specific alignment of reacting
species, therefore promoting their reactivity. Donor-acceptor relationship between ligand and metal center may provide stabilization or activation, hence allowing new
transformations to occur, transformations that do not have any counterpart in the absence of the metal fragment. Among the multitude of examples available in the literature,2 two illustrations have been selected that are relevant to the present dissertation topics: Fischer- type carbene and trimethylenemethane complexes. As it will be explained in more details,
Fischer-type carbene complexes can be envisioned as carboxylic ester analogues.
However, the replacement of the carbonyl oxygen atom with a metal center is responsible for enhanced reactivity that is illustrated in cycloaddition reactions in addition to rearrangements. The coordination of a trimethylenemethane ligand to a transition metal center has allowed its isolation, otherwise impossible, and an exploration a different aspect of its reactivity, namely cycloadditions to unsaturated substrates. 2 PART A: ORGANORHENIUM COMPLEXES
I- Fischer-type carbene complexes
Carbene complexes are defined by the presence of a transition metal to carbon
atom double bond. This family of compounds can be subdivided into 2 groups:3 Fischer-
type and Schrock-type complexes.
1-1 Presentation of Fischer-type carbene complexes
Fischer-type complexes are characterized by a late transition metal center in a low oxidation state that is coordinated to 3i-acceptor ligands stabilizing the M(dji).electrons,
such as carbon monoxide. Moreover, the carbenic center is substituted with at least one
heteroatom-containing group such as alkoxy (OR), thio (SR) or amino group (NR'R")
stabilizing the carbenic center. This combination is responsible for a polarization of the M(6-)=C(6+) bond, which explains some of the fundamental properties and reactivity
trends of the complexes including electrophilicity and acidity of a methyl substituent.
-6 J* ,R LnM —CC +6 ► LnM'— cT X X+
X=OR\ NR'R", SR'
The basic reaction chemistry that can be anticipated from these considerations is summarized in scheme 1. A methylene or methine group attached to the carbenic carbon atom is acidic and can be easily deprotonated and alkylated (path a). The carbene center bearing a partial positive charge, is sensitive to nucleophilic attack by a wide variety of nucleophiles (path b). The heteroatom-containing substituent can be complexed by Lewis acids, giving access to carbyne complexes (path c). Finally, labilization of a CO ligand can be followed by coordination of various ligands that can undergo insertion into the
M=C bond (path d).
Scheme 1: Basic reaction chemistry of Fischer carbene complexes
OC / O C R 2
X(CO)4C r = C C R 2H OC— c'r— C Electrophile Base y v \ OC CO o R (BX3) H ™ I (a) / r 2 OC— C r = C \ OC4 CO \ O R
H SNucleophile H + L (d) I (b) \ OC vCO ,CR2 / ° / R* \ ^ / oc— cV=c OC— -Cf—C— Nu+ / V \ 4 ^ \ L CO O R OC CO o R
This limited number of reactions related to the electronic and steric properties of
the complex is the basis for a large number of applications to organic synthesis, which
can be divided into two categories. First, there is a group of reactions in which the role of
the transition metal fragment can be considered as "passive". This group comprises the
reactions in which the metal fragment provides a source of activation of the ligand
(therefore facilitating known reactions in carbon chemistry) as well as the transformations
where it helps to stabilize a reactive fragment and opens a new area of its reaction chemistry. The second domain of applications of Fischer carbene complexes concerns reactions in which the metal fragment LnM is directly involved as, for example, in the case of a CO ligand incorporation. 4 The reactions that take advantage of the activation provided by the MLq fragment
and make the alkoxy-substituted carbene an equivalent of carboxylic ester, will be first
presented.
1-2 Reaction chemistry of Fischer-type carbene complexes
Preliminary remarks
Based on the isolobal analogy,4 the M=C bond can be envisioned as an equivalent
to a carbonyl fragment.
-8 /R -5 /R LnM=C^+8 0=C +6 X \)R * 1
This comparison is supported by reactions such as aminolysis,5 in which the alkoxy substituent is replaced with a primary or secondary amino group as illustrated in equation
1.
.CH3 ch 3 (CO)5C r=Q + HN(CH3)2 THF ». (CO)5Cr=<^ OCH3 N(CH3)2 2 3 (eq 1)
The acylation of amines by carboxylic esters is known. Unsubstituted, monosubstituted and disubstituted amides can be easily synthesized by this method provided a good leaving group R' such as p-nitrophenyl is used. However, simple esters (R1 = Me, Et...) are much less reactive and require the use of basic catalysis, cyanide-ion catalysis or high pressure.6 5 The replacement of the carbonyl oxygen atom with a transition metal fragment is
also responsible for an increase in the acidity of a methyl group. The pKa of methyl acetate is about 25.7 In contrast, the pKaof complex 2 has been calculated to be about
8.8
^CH3 pKa=8 ^CH3 pKa=25 (CO)5C r= C v versus o = C \ \ o c h 3 o c h 3
Michael addition
Scheme 2: Mechanism of Michael addition to Fischer carbene complexes
+
Et HN R1 o v f " ' ) k fast R2 h 3 » > ■ ■ I O Et O 5 B Compared to a,p-unsaturated esters, the electron withdrawing properties of the
(COJsM fragment provide a better delocalization of the electron density than those of the carbonyl oxygen atom. Therefore, the nucleophilic attack on the end carbon atom is
facilitated. The Michael addition of amines and the parameters favoring this process over
the 1,2-addition have been studied in detail.9 The proposed mechanism consists of two steps: nucleophilic attack on the end carbon followed by rapid proton transfer. A polar
transition state is assumed to result in the formation of a zwitterionic intermediate.(Scheme 2) The stereochemical outcome of the reaction was also examined
since vinyl carbene complexes are unable to undergo Lewis-acid chelation as traditional
Michael acceptors. The studies showed that the syn-diastereoselectivity is independent of the geometry or counterion of the enolate. It was concluded that the products must result from an open transition state.10
Diels-Alder cycloaddition reactions
Owing to the electron withdrawing property of the metal fragment, vinyl Fischer carbene complexes have found applications in Diels-Alder cycloaddition reactions.
Improvements in terms of rate, stereo- and regioselectivity have been observed, that are in the order of Lewis acid-catalyzed cycloaddition reactions as illustrated in equation 2.11
o c h 3 (CO)5Cr= >-
92 8 ,OCH3 < r ( 70 30 25°C, 3 months (eq 2)
Interestingly, because of the absence of Lewis acid, a wide range of functional groups is tolerated on the ligand. The scope of the reaction has been investigated by varying the 7 degree of substitution on the diene and dienophile and by changing the metal.12 It was found that the geometry of the double bond is retained. Tungsten carbonyl complex 9 has been preferable in some cases because of its higher thermal stability. The choice of the metal is also crucial in those cases where [4+2] cycloaddition is in competition with cyclopropanation reaction as illustrated in equation 3.
,OCH3 TBDMSO, TBDMSO,
,OCH3 TBDMSO, H TBDMSO, (CO)5W
(CO)4 (eq 3)
The intramolecular [4+2] cycloadditions promoted by tungsten carbenes was studied in detail by Dotz.13 A straightforward addition/substitution sequence afforded both kinds of complexes for X = O, N, S according to Scheme 3. Results are summarized in Scheme
4. Whereas thiocarbene complexes failed to undergo cycloaddition, alkoxy-substituted carbenes decomposed owing to their propensity to undergo thermal decarbonylation or facile cycloreversion. On the other hand, amino carbenes displayed a lower activation barrier for [4+2] cyclization and were less prone to cycloreversion than analogous amides. Therefore, they provided an efficient route to lactams after cleavage of the metal fragment by using standard oxidative conditions. Scheme 3; Intramolecular Diels-Alder reaction - Preparation of precursors
U PR IK^
PR
2.R'
A comparative study, carried out between MeCp(CO) 2Mn=C(NR 2)R' and
(CO)sW=C(NR2)R' complexes confirmed that the increasing acceptor capacity of the
metal fragment is crucial in the promotion of the cycloaddition,14 MeCp(CO) 2Mn being
less efficient.
[2+2] cycloadditions
[2+2] cycloadditions between electron rich alkenes such as dihydropyran or
propenyl ethyl ether and alkynyl tungsten carbene 20 have been observed. The reactions
proceeded efficiently at room temperature within 6 h (97% yield in the case of
dihydropyran). As illustrated in equation 4, the corresponding reaction of dimethyl
acetylenedicarboxylate required more forcing conditions (180°C, toluene, 16 h). Only a
60% yield of a 3:2 mixture in favor of the [2+2] adduct can be obtained.15 For non-cyclic
olefins, the reaction was stereospecific. The cycloadduct derived from propenylethyl
ether converted spontaneously into a diene complex with complete retention of configuration during the ring opening. 9
Scheme 4: Intramolecular Diels - Alder reaction-Results
Vjj-sSV toluene, (CO)5W = ^ (CO)5W O / reflux, 3h, 60% CH3\"V'
(CO)5W toluene (CO)5W + (CO)4W
N ,NH
,NH
N. (CO)5W
Ph 19 Ph 10
c h o CH3On .W(CO)5 3 H \ ____ W(CO)5 ,o 25°C, 6h LT ► 97%
20 H 21
c o 2c h 3 c o 2c h 3 o c o 2c h 3
/\ toluene, 180°C ► 16h, 60% c o 2c h 3 v_A c o 2c h 3 C02CH3 (eq 4)
A second example has been observed by treatment of vinylidene complex
Cp(CO)PPh 3Fe=C=CH2]+BF4" 22 with the imine PhC(H)=N(CH 3 ). Oxidation of the resulting carbene 23 afforded the corresponding p-lactam.(equation 5)
.Ph / Ph
Ph Cpv Ph \ = N C H 3 \ PhIO (eq 5) Addition of the imine reagent to tosylate carbene 2 4 also yielded a {3-lactam precursor 2 5 via deprotonation promoted by the imine and elimination of the tosylate.(equation 6) OTs ph =NCH3 (GOlsCr: Ph (CO)5 Cr: N CH2- 24 25 CH3 (eq 6) 11 Disubstituted vinylidene complexes prevented the incorporation of a second equivalent of imine.16 1,3-dipolar cycloaddition The 1,3-dipolar cycloaddition of diazoalkanes with alkynyl carbene complexes was the first example of such a process to be reported for Fischer-type complexes.17 Diazomethanewas found to be non-chemoselective, attacking both the double bond and the M=C bond of complex 26 (equation 7). However, a synthetic equivalent such as trimethylsilyldiazomethane attacked selectively the conjugated double bond of complexes 28 yielding complexes 29 (equation 8). OEt 4eqC H 2N2 (CO)5W W(CO)5 (eq 7) OMe OEt Me3SiCHN2 (CO)sM R (CO)5M hexane, 25°C M=Cr, R= Mfc, ra, l ivio R 28 57-87% (eq 8) Similar results were obtained with a , (1-alkenyl carbene complexes.18 Diazoalkanes, with the exception of diazomethane19 reacted rapidly and regioselectively. Cyclic alkenyl 12 carbenes such as 30 were studied more specifically in order to evaluate how geometric constraints would affect the reactivity of the double bond.18 (equation 9) ,CH3 c h 3 (CO)5 Cr 30 (CO)5Cr (eq 9) Results suggested that the reactivity of a double bond in a five or six-membered ring, was decreased compared to that of a linear alkenyl carbene. Stabilization ofvinylketene complexes Transition metal vinylketene complexes have attracted the attention of many research groups. In particular, they have been postulated to be a key intermediate in the reaction between Fischer carbenes and alkynes.20 A complex of this nature was first characterized by Wulff and coworkers21. They isolated vinylketene complex 33 in 52% yield upon heating amino carbene complex 3 2 in benzene. R (CO)5 Cr 32 33 (CO)3 (eq 10) The complex was stable enough to be purified by chromatography on silica gel. Its structure was confirmed by X-ray diffraction analysis. The product ratio obtained from treatment with one equivalent of alkyne was very close to the one pot-reaction outcome. 13 This observation supported the involvement of this type of structure in a benzannulation reaction. These reactive intermediates have also been exploited in the preparation of (3- lactams (see previous section), cyclobutanones and a-amino acids by reaction with imines,22 alkenes23 and alcohols,24 respectively (scheme 5). Scheme 5; Reactivity of vinylketene intermediates X R (CO)4C r ^ (CO)5Cr=<; R (CO)4Cr -Y C O 35 II O R'OH X= NR‘ R R OR' NR O Stabilized phosphorus ylides also reacted with the transient vinylketene complex. Inert toward Cr alkoxy carbenes, they yielded captodativeallenes, under an atmosphere of CO or in strongly coordinating solvents, (equation 11) OCH2CH3 CH3CH2Ov C 02CH2Ph / riv, U J \ s (CO)5Cr=Y + Ph3P=CHC02CH2Ph ► N = c= ^ C(CH3)3 benzene,60% (CH3)3C H M +Cr(CO)s + Ph3PO (eq 11) The allenes could be readily hydrolyzed into Z oc,p-unsaturated ketones. The reaction failed with amino carbene 37 owing to the prevalent proton transfer that prevented the elimination of one equivalent of phosphine oxide and afforded the corresponding carbamate 3 8. (equation 12)25 14 O- NHC02tBu P+Ph3 (CO)sCr + Ph3P=CHC02CH2Ph tBu02C C 02R kC(CH3)3 tBuC^C PPh3 38 (eq 12) Aldol-type condensation As it has already been mentioned, the electronic properties of the MLq fragment are responsible for the enhanced acidity of a methyl group attached to the carbene center. According to the Fischer carbene-carboxylic ester analogy, the anion generated by treatment with a base such as nBuLi or LDA can be considered as an enolate equivalent. However, as suggested by the pKa value, this conjugated base was unreactive toward most electrophiles. To circumvent this problem, the enolate (e.g. 39) was treated with a carbonyl type electrophile that had been activated with a Lewis acid (equation 13) or was activated itself by substituting one carbon monoxide ligand with a phosphine. (equation 14)26 (CO)5Cr nBuLi, Et2Q (COJsCr’ -78°C 1.10 eq acetone, Lewis Acid 2. H20 (CO)5Cr (eq 13) The p-alkoxy carbene complex 40 could be isolated owing to the strength of the O-Lewis acid bond involved in the addition mechanism. Since the ligand could be oxidatively cleaved, generating a carbonyl center, this method gave access to (3-hydroxy esters otherwise synthesized by aldol condensation. ,o c h 3 ,o c h 3 1. nBuLi, 2. PhCHO (CO)4Cr < (CO)4Cr ► - < CH3 -78°C -78°C to 0°C (n-Bu^P 41 ,OCH3 (CO)4Cr 42 (86%) Ph (eq 14) Pauson-Khand reaction2 7 Treatment of amino alkynyl Fischer carbene complexes 43 with one equivalent of Co 2(CO)8 at room temperature in THF afforded the corresponding cyclopentenone complex 4 4 in 70-82% yields in spite of the presence of an electron-withdrawing metal substituent on the disubstituted alkyne. (equation 15) The reaction proceeded under mild conditions with good stereoselectivity owing to the involvement of two metal centers. Furthermore, the resulting complexes could then be used in other cycloadditions, thus giving access to complex carbon skeletons. Co2(CO)8 (CO)sM 16 Benzmnulation reaction Benzannulation reaction has received a great deal of attention since its first report by Dotz in 1975.28 (equation 16) This powerful reaction has been applied to the synthesis of numerous natural products. R ‘(R2) 40-60°C + R1 ■R2 ^ R2(R*) (CObCr 45 46 (eq 16) It involves the reaction of an aryl-substituted carbene complex with alkynes and results, in one pot, in the formation of a highly-substituted aromatic ring from the combination of the carbene center, the aromatic substituent, one equivalent of alkyne and a CO ligand of the initial complex. OH O Ph Ph / \ Ph (CObCr oc;^ Important mechanistic studies have been carried out by Wulff and coworkers while the authors investigated the scope of this complex reaction. The conditions are versatile since a variety of substituents are tolerated both on the complex and the alkyne. Even though several products have been observed (naphthols, furans, indenes and cyclobutenones), their distribution can be controlled to some extent. 17 Scheme 6 ; Benzannulation reaction - General 1. Solvent ■B ------2. Oxidation R O + OMe B + N OMe R A possible pathway involves a cis CO-ligand dissociation as the rate-determining step. This promotes the coordination of the acetylene reagent which is responsible for the regioselectivity of the transformation, the less sterically demanding substituent ending up in the vicinity of the carbene ligand. Indene and cyclobutenone are formed preferentially to naphthols if coordinating solvents such as acetonitrile or dimethylformamide are used, instead of non polar solvents such as hexane or toluene .29 The metal center is also a determining factor in the product distribution: for instance, indene product becomes the major product when molybdenum or tungsten are substituted for chromium. The increasing strength of the M-CO bond has been invoked by Geoffroy .3 0 The reaction of thio- and amino-carbene complexes has also been examined .3 1 18 The reaction can be promoted by ultraviolet irradiation, as can be expected from the assumption that CO dissociation is the rate determining step. Contrary to the thermally-induced reaction, the formation of the indene product is favored. It was later discovered that the concentration of alkyne and/or the mode of addition influence the product distribution. Indeed, the presence of an excess of alkyne might promote a carbonyl insertion at a determining point of the mechanism hence favoring the formation of the CO-insertion product (quinone) over the non-insertion product (indene). Other carbene complexes have been considered in an attempt to change the product distribution. Hence, treatment of (triphenylstannane)tricarbonylcobalt carbene complexes with alkynes allowed the exclusive isolation of furan-type products as illustrated in equation 17 for the formation of 48 promoted by complex 4 7 ,32 OC >PO QCH3 3 equiv. of 2 -butyne Ph 3 Sn— Co ►- nBu 11011 benzene, 50°C OCH3 4 days o c h 3 48 (eq 17) The mechanism is assumed to involve the formation of a cobaltacyclobutene complex, favored by the presence of the triaryltin ligand, followed by a CO insertion. Similarly, amino-stabilized carbenes have been reported to yield furans under the same conditions. The reaction has been extended to heteroaryl carbenes as well as alkenyl carbenes. Although the initial reports were not encouraging, the reaction seems to be more selective since the formation of the six-membered ring is highly favored, (equation 18) (CO)5M Et 49 50 51 (eq 18) Table 1: Product ratios: naphthols versus indenones M 50 51 Cr 99% 1% Mo 12% 88% W 98% 2% In contrast, Schrock-type alkylidene complexes usually contain an early transition metal complex in a high oxidation state, coordinated to non-n acceptor ligands. These characteristics in addition to the absence of electron-donor subtituent on the carbene center, are responsible for the opposite polarization of the M=C bond, making the complex nucleophilic. II- Schrock-type metallacvclobutadiene complexes With the exception of the two complexes reported by Weaver in 1970 (complex 52)33 and Frisch in 1979 (complex 53 ) ,3 4 metallacyclobutadiene complexes had not received much attention. (CH3)3P Ph + PhfCH^hP Ph (CH3)3P Ph Ph(CH3)2P Ph 52 53 Complexes 52 and 53 were obtained by oxidative addition of C 3 Ph 3 +Cl' on trans- IrCl(CO)[P(CH3 )3 ]2 and RhCI(CO)(PR 3)2 , respectively. Whereas no clear conclusion 20 could be drawn from the X-ray structure of complex 52, substantial degree of electron delocalization over the four-membered metallacycle in complex 53 was evidenced. However, these two complexes are structurally very different from the "Schrock-type" complexes discussed thereafter. Since the involvement of Schrock-type metallacyclobutadiene complexes in the mechanism of alkyne metathesis was suspected, their synthesis, isolation, characterization and applications have been reconsidered .35 By analogy with the formation of an unstable metallacyclobutane complex as the key step in alkene metathesis, the formation of a metallacyclobutadiene complex according to equation 19, was anticipated before being observed experimentally. H R R M = CR + R C = C R ' (eq 19) The nature of the ligands on the metal fragment appeared to be determinant in the success of the metathesis, probably relating to the efficiency of the polarization W( 6 +)=C(6 -). The metallacycle could be isolated when OR = 0 -2 ,6 -C6H3 -iPr2 (DIPP), OCH(CF3)2 , andOCMe(CF3)2. Et -tBuCCEt (DIPP)3W=CtBu + 2 EtC=CEt > . (DIPP)3W Et Et 54 55 (eq 20) 21 The structure of complex 5 5 was determined and showed that the WC 3 ring is essentially planar and symmetrical .3 6 Both W-C bond lengths have an intermediate value between a single and a double bond. These complexes promote metathesis of internal alkynes. Depending on the ligands, the reaction can go through an associative or dissociative mechanism (planar metallabenzene). No terminal alkyne metathesis could be observed for different reasons: possible degeneracy of the reaction ,37 loss of a proton affording deprotiocycles 38 lower stability of methylidyne complexes. The r)3-cyclopropenyl complexes derived from addition of nitrogenous bases to W(C 3tBuMe2 )Cl3 was shown not to be involved in alkyne metathesis. Alternatively, i^-cyclopentadienyl complexes are formed upon treatment of W(C 3 R3 )Cl3 with dialkyl alkynes. The irreversible collapse of a metallabenzene was invoked .39 Because of the high oxidation state of the metal and the absence of heteroatom- containing substituent, such complexes have been classified as alkylidene-type metallacyclobutadiene complexes referring to the distinction between the two types of carbene complexes. Examples of high-oxidation state rhenacyclobutadiene complexes are known .4 0 However, until rhenacyclobutadiene complexes I were prepared and characterized, no Fischer-type metallacyclobutadiene complexes had been reported in the literature.41 Ill- Fischer-type rhenacyclobutadiene complexes III-l Preparation and properties41 These compounds are derived from rhenacyclobutenones, unexpected products of reaction between Re(CO) 5 " and activated alkynes. Their synthesis is effected in three steps. A THF solution of the anion Na+Re(CO) 5', obtained by reduction of the commercially available Re 2(CO) 10 complex, is treated with one equivalent of activated 22 alkyne R-OC-CO 2CH3 (R = H, CH3 , CO2CH3). The presence of an electron withdrawing group on the alkyne is believed to stabilize the negative charge that results from the nucleophilic attack on the triple bond. A rhenacyclobutenone results from ring closure on one of the carbon monoxide ligands. This anionic complex, inert toward methyl iodide, can be alkylated with more powerful reagents such as triethyloxonium hexafluorophosphate salt. The sequence is summarized in Scheme 7. Scheme 7t Original synthesis of rhenacyclobutadiene complexes Re2 (CO)io + Na THF' 2NaRe(CO) 5 COR NaRe(CO> 5 + R C0 2 CH3 COR COR C0 2 CH; Na+ + E t3 OPPF6 ReCZ»-C02CH3 CO OCH2 CH3 I The 13C{1H} chemical shifts of the carbon attached to the metal in all three complexes suggested their Fischer character; typical values range between 200 and 400 ppm .42 Table 2: Selected lie 11H> NMR chemical shift of complexes I 6 c in ppm R s CH3 (la) R = CO2CH3 R = H (Ic) (lb) M-C(R) 246.39 210.54 219.81 M-C(OEt) 243.71 253.78 251.89 23 In addition to the chemical shifts values, the bond distances observed in the X-ray structure of complex la (R = CH 3 ) indicate that both carbons attached to the metal fragment display some carbenic character. Moreover, the electrons are delocalized over the metallacycle even though the delocalization is not as substantial as in the Schrock-type carbene complexes. The ring is planar and the difference in bond distances reflects the unsymmetrical substitution pattern. Hence, whereas the two M-C bonds differ by only 0.05 A, the C-C bond distances are more different [C(OCH 2CH3 )-C(CC>2CH3 ) = 1.45 A, C(CC>2CH3 )-C(CH3 ) = 1.36 A]. A similar Re complex was reported in the literature soon after complexes I, (CO) 4Re(ri2 -C3 Ph 3 ) (56).43 It was prepared by photochemically-, chemically-or thermally- induced ring opening of the cyclopropenyl ligand of the complex (CO) 5 Re(t|l-C3Ph 3 ). (equation 21) Whereas both complexes display similar M-Ca bond distances, the metallacycle is totally symmetrical. Ph NaRe(CO)5- + (CO)4Re£33>— Ph Ph 56 (eq 2 1 ) III-2 Preliminary reactivity studies The electrophilic properties of Fischer carbene complexes have been evidenced by their reactivity toward nucleophiles such as tertiary phosphines, the electronic and steric properties of which can be easily adjusted .4 4 -2 The detail of the results will be discussed in chapter II. However, the reactions are summarized in scheme 8 . 24 Scheme 8 ; Reaction of complex la with phosphines CO ? H3 I p Ra Re " CO2CH3 0CX|°T co°ch 2 c h 3 co 9H3 oc \ R1 e'C = 3> - co 2ch 3 oc / c 0 OCH2 CH3 RT,CH2C12 CO och 2ch 3 la The carbenoid character of the complex was supported by the oxygen atom insertion observed upon treatment of complex la with (NH 4)2Ce(NC>3)6 in acetone. Instead of a cleavage of the organic ligand, an oxygen atom insertion into Re-C(CH 3 ) bond is obtained as the major reaction (5 7). (equation 22) c h 3 -A . Acetone, (CO)4 Rev T l 5 > — C 0 2 CH3 + 3 Ce(NOj)6 (NH4 ) 2 ------► RT, 1 h OCH2 CH3 la 0 CH3 (CO)4Re = y ^ ' CH3 + (CO)4Rc^ \ - C° 2CH3 V / ch 3ch 2o/ co 2ch 3 ° = \ OCH2 CH3 57 58 (eq 22) Some aspects of the reactivity of (CO) 4 Re(r]2-C3Ph 3 ) (5 7) parallel the reactivity of complexes I. Hence attempts to chemically labilize a CO ligand using Me 3 NO resulted in the insertion of an oxygen atom into a Re-C bond. However, the nature of the metallacycle substituents might be responsible for the equilibrium between 25 rhenacyclobutadiene and rj3-cyclopropenyl complex (equation 2 1) on the NMR scale, since no dynamic behavior is observed on complexes I. IV- Objectives of the project Fischer-type metallacyclobutadiene complexes being novel compounds, the investigation of their reaction chemistry was undertaken in order to ascertain to what extent they would follow the trends observed for classical Fischer carbene complexes. It was also expected to evaluate the consequences that would result from the cyclic/double carbenic nature. The development of this research project has followed three steps: - The confirmation of the Fischer-type reactivity of rhenacyclobutadiene complexes illustrated by the electrophilic properties of the carbene centers (sensitivity to nucleophiles, acidity). - The generalization of the synthetic pathway in order to have access to a wide range of substituted metallacyclobutadienes and to adjust their reactivity by modifying the initial sequence and derivatizing known rhenacyclobutadiene complexes. - The exploration of their potential use in organic synthesis, including cycloadditions and novel insertion reactions. 26 PART B; ORGANOPLATINUM COMPLEXES I- nl-Propargvl transition metal complexes 1-1 General considerations4 5 tjI- and r|3-allyl complexes have been thoroughly studied mainly owing to their importance in organic synthesis .4 6 On the other hand, transition metal propargyl complexes have received much less attention. While 1,3-shift isomerization reactions and [3+2] cycloaddition reactions with neutral unsaturated electrophiles have been explored for Tjl-propargyl complexes for quite a while, T^-propargylic complexes have been isolated only recently. Several synthetic strategies have been developed for these compounds. Butenynyl-type complexes are obtained through the coupling of two alkynyl fragments, (equation 23)47 4 (PMe3 )4 O s (C = C P h ) 2 + AgPF6 PF* Os(PMe3)4 59 60 (eq 23) Only a limited number of actual r| 3-propargyl/allenyl complexes are known. Molybdenum and tungsten examples have been synthesized by Krivykh 48 by photolyzing a metal carbonyl precursor in presence of propargyl alcohol and treating the resulting v\2- acetylene complex with HBF 4 .(equation 24) Casey synthesized Cp*(CO)2Re(r]3- CH2CCCH3 )+ (64) by hydride abstraction from Cp*(CO) 2Re(r)2 -CH3 -CsCH) (63) 49 (equation 25) 27 Me. h c = c c h 2o h oC / OC CO CO oc 61 62 (eq 24) CH CH3 H3C^ CH3 Ph 3 CPF6 ► PF* -Ph3CH Re HsC Re C H 3 - CH3 OC CO o c 7 \ oc 63 64 (eq 25) Although it has not been isolated, a rj^-propargyl Pd species has been invoked by Chen and coworkers to rationalize the formation of zwitterionic complex 6 6. It is thought to result form the treatment of ira/is-Pd(r|l-HCsCCH 2 )Br(PPh 3 )2 (65) with one equivalent of NaCH(CC>2 CH3 )2 . This is based on the synthesis and reactivity of [(Ph 3 P)2 PtCn3- CH2CCH)]BF4.50 (equation 26) H Ph 3 P, sy= c = c v L 1 \ NaCH(C02 CH3 ) 2 Pd / \ Br PPh 3 Pd' 65 I 4 Pd Ph3PX PPh3 (eq 26) 28 1-2 Representation Based on spectroscopic and crystallographic data the rp-propargyl complexes complexes can be represented by either resonance forms a and b or the delocalized form c. Either representation will be used thereafter. h 2c ' T ^ C R 'c h 2 h 2c CR < ? \/M M M M= Pd, R= H M= R , R= aryl a 1-3 Synthesis of T]3-propargyl platinum complexes In an attempt to elucidate the mechanism involved in the transformation illustrated in equation 27, complex 6 8 [(Ph 3 P)2Pt(ii3-CH2CCPh)]OTf was prepared 51 as a plausible intermediate in the isomerization. PPh 3 Ph (CH3 )3 P ^ \ c — c = c h 2 Br— P t— C- •ph P,CH% Br- H2 Pt PPh 3 N p(C h 3 ) 3 67 68 (eq 27) The synthetic sequence is summarized in scheme 9. It involves the oxidative addition of Ph-CaC-CH 2 Br to (Ph 3 P)2Pt(q2 -CH2=CH2). Conversion of cw-(Ph 3 P)2Pt(ri1- CH2CeCPh) complex into the trans -isomer by heating the mixture to reflux temperature of CH 2CI2 . The formation of the t|3-propargyl complex is then achieved by halide abstraction promoted by AgOTf. 29 Scheme 9: Original synthesis of complex 69 PPh 3 P t + Ph Ph 3 P— P t— C Ph PhjP^ Br + cis isomer CH2 C12, reflux + PPh 3 AgOTf I Ph O T f <4 . Br— P t— C Ph -AgBr | 3 Ph3P PPh 3 PPh 69 67 The Tj3-propargyl complex is isolated as a yellow solid and is stable when maintained under an inert atmosphere. The method showed some drawbacks. Thus, attempts to apply the same sequence to achieve the synthesis of the non-substituted propargyl ligand failed. While the Tjl-allenyl complex 70 (Ph 3 P)2Pt[r|!-HC=C=CH2]Br52 was isolated after treatment of (Ph 3 P)2Pt(ii2-CH2=CH2 ) with 3-bromopropyne, the subsequent halide abstraction step carried out at room temperature led to an intractable mixture of compounds. The isolation of the titled compound was reported by Chen and co-workers: the halide abstraction reaction afforded complex (Ph 3 P)2Pt[ri3-C3 H3 ][BF4 ] (71) in good yield (80%) but had to be performed at -30°C.53 (equation 28) 4 CH2 C12, -30°C 70 71 (eq 28) 30 Although the halide-abstraction route appeared to be cleaner, phenyl-substituted r]3- propargyl complex 7 3 could also be prepared by cleavage of the methoxy group of (Ph 3 P)2Pt(Ti2 -Ph-CsC-CH 2-OCH3 ) using one equivalent of BF 3 -Et2 0 according to equation 29. OCH, Ph 3P. Ph 3Pv THF, \ Pt + Ph- -C OCH3 ------>■ Pt Hz -78°C to RT Ph3P Ph3P 72 Ph BF3.Et2 0 Ph BF3 OMe" Pt Ph 3 P ^ PPh 3 73 (eq 29) The preparation reported by Stang and co-workers was not as general .5 4 It consisted of the treatment of (Ph 3 P)2PtCn 2 -H2 C=CH2) with alkynyl(phenyl)iodonium triflates, involving the unexpected incorporation of the ethylene ligand to afford complex 7 4. (equation 30) PhaP^ tBu CH2 C12 Pt + t-Bu C=C IPhOTf ► car RT, 30 min PhsP^ Pt PPh 3 74 (eq 30) 31 1-4 Reactivity of T|3-propargyl complexes In light of the few reports regarding the reaction chemistry of these complexes, the coordination mode of the propargyl ligand to the transition metal center is believed to enhance the electrophilic character of the central carbon. Hence, Mo complex 6 2 reacted with H 2 O to form the hydroxyallyl complex 7 5. (equation 31) OH 62 75 (eq 31) Cationic Re complexes 64 also underwent attack at the central carbon upon treatment with Nu = PMe 3 , LiCsCtBu, and CH(CC>2CH3 )2'. Whether the nucleophile is anionic or neutral, the formation of a rhenacyclobutene 76 was observed. n+ Nu OC— Re—CO Nu n= 0 , 1 64 76 (eq 32) Platinum complexes have been reported to yield allyl complexes by addition across the triple bond.51- 55 Interestingly, even upon treatment with NaCH(C 0 2 CH3 )2 , the overall neutral complex has an allylic structure. Whereas neutral platinacyclobutene complexes 32 have been prepared and characterized by X-ray crystallography ,56 no derivative from r|3- propargyl complex has yet been isolated. Nu n+ RO-H, Ph3P PPh 3 R!R2 N-H, ph3p PPh3 n=0,1 NaCH(C02 CH3 ) 2 69 77 c h 3 o 2c c o 2 c h 3 NaCH(C02 CH3 ) 2 Ph3P PPh 3 69 78 (eq 33) II- Use of trimethvlenemethane transition metal complexes in organic synthesis Trimethylenemethane transition metal complexes have been extensively studied 57 since the report of the first complex Fe[rj 4 -C(CH2)3](CO)3 in 1966 by Emerson .58 Envisioned as a stabilization method of a fragment otherwise unisolable, these complexes are of theoretical and structural interest. Their synthetic potential has received considerable attention since these complexes were shown to participate in [3+2] cycloaddition reactions with unsaturated compounds .59 Indeed, among the methodologies developed to build cyclopentanoid units (frequent in natural products), cycloadditions have been greatly improved by the use of transition metals (cycloadditions of TMM units to olefins proceed in very poor yields). With the exception of a few specific examples ,6 0 transition metal trimethylenemethane complexes can be prepared via four main routes as it is illustrated in scheme 1 0 : 33 Scheme 10: Preparation of transition metal trimethylenemethane complexes K X ML, -XY MLnY Thermal extrusion MLn MLn Elimination of Ring opening TMSX Me3 S i' X = 0 A c,0 S 0 2 M e ,a Bifunctional Conjunctive Reagents ("BCR") that have been used more recently to synthesize r^-trimethylenemethane (TMM) complexes of Ir, Rh, and Os61, were first designed to participate in [3+2] cycloaddition reactions with electron deficient olefins promoted by a catalytic amount of Pd .62 (equation 3 4) EWG (CH3)3Si ^OAc Pd(PPh 3 ) 4 ► EWG (eq 34) II-l General conditions used in BCR-promoted cycloadditions48 The reaction typically involves an electron deficient olefin (i.e. containing at least one electron withdrawing group) and a catalytic amount of palladium (3-9 mol% Pd(PPh 3 )4 , 1-4 mol% dppe). The use of l,2-bis(diphenylphosphino)ethane (dppe) prolongs the lifetime of the catalyst and prevents the precipitation of Pd black. The 34 reaction can be performed in hot toluene or in THF at reflux. However, as the reaction proceeds through a polar intermediate, THF reduces the reaction time and enhances the yield. Conversion even proceeds at room temperature in DMF. The reaction displays a moderate to high stereospecificity: E olefins yield E adducts while Z olefins lead to a mixture of products, (equation 35) EWG Pd(PPh 3 ) 4 (CH3)3Si EWG (CH3)3Si Pd(PPh 3 ) 4 (eq 35) The method shows some limitations: no cycloaddition takes place with either too unstable olefins such as tetracyanoethylene (TCNE), 1,4-naphthoquinone, and chloroacrylonitrile (oxidation of Pd catalyst via electron transfer) or alkynes such as methylphenyl propiolate or methyl tetrolate (Ph-CsC-CC> 2CH3 , CH3 -CSC-CO2CH3). II-2 Nature of the TMM-Pd complex63 TMM-Pd complexes have not been isolated until recently by Chen and co workers .50 However, earlier on, the nature of the intermediate had been experimentally established. For example, through deuteration of the TMM ligand and protonation experiments, the non-equivalence of the three CH 2 groups had been demonstrated. When a good trap such as a very acidic compound was involved, the 35 protonation of a specific methylene group was selectively observed. However, scrambling took place upon treatment with weaker acids. II-3 Mechanistic studies6 4 Existence o f a TMM-Pd complex: Allylic alkylation studies initially supported the formation of a TMM-Pd complex. If a good nucleophile such as sodium dimethyl malonate was involved, the T)3-allyl complex was trapped before desilylation reaction took place. However, if the nucleophile was less reactive, desilylation occurred, followed by protonation owing to residual activated methylene compound. Nucleophilic attack then took place on the T^-allyl complex. (Scheme 11) Scheme 11: Preliminary mechanistic studies ^ S i(C H 3 ) 3 Si(CH3 ) 3 ,OAc PdLn _ ^ ^ OAc Pd L •Me^iOAc (CH3)3Si Reactivity toward carbonyl compounds has also been investigated. Methyl ketones are deprotonated by the TMM-Pd complex. The resulting cationic r|3-allyl platinum complex is then nucleophilically attacked by the generated enolates.(equation 36 36) In contrast, nucleophilic attack on the carbonyl group of aldehydes takes place. However, because alkoxides are poor nucleophiles and a cyclization would involve a sterically strained 5-endo-trig process, trapping of the alkoxide by the TMS group prevails, (equation 37) Si(CH3 ) 3 OAc (eq 36) OTMS Pd+LsOAc’ OTMS ,OAc Ph R (eq 37) Structure o f TMM-Pd complexes involved in catalytic reactions In spite of the numerous efforts to establish the bonding mode of the trimethylenemethane ligand involved in the intermediate, no experiment clearly allowed to rule out a q3- versus a q 4 -structure. For example, deuteration results demonstrated the nonequivalence of the three methylene groups of the ligand. However, such a phenomenon is not characteristic of a re structure if a slow rotation of the q4- trimethylenemethane ligand is involved. On the other hand, deuterium scrambling observed with weaker acids could be compatible with a q3-structure where the Pd unit could migrate by syn-anti interconversion or Jt-olefin diyl intermediate. 37 Syn-anti interconversion: < Pd+L2 Pd+L2 Pd+L2 ji-olefin diyl species: < < Pd+L2 Pd+L2 Pd+L2 Mechanism ofcycloaddition: Two mechanisms were considered to account for the stereochemical outcome of the reaction. i. Proximal approach: A proximal approach is unlikely since it would involve the attack of the electrophilic acceptor on the electrophilic end of the TMM-Pd complex.(Scheme 12) Scheme 12: Proximal approach EWG 38 ii. Distal approach: Two possible pathways can be envisioned from an approach of the alkene from the opposite side of the metal. (Scheme 13) Scheme 13: Distal approach R EWG EWG EWG EWG EWG A proximal approach was definitively ruled out upon analyzing the stereochemistry of the product derived from a chiral TMM precursor .6 5 (equation 38) The net retention of stereochemistry with respect to the allyl unit indicates a distal approach since the t]3-allyl complex is formed by initial inversion of configuration. ,TMS (eq 38) Regiochemistry o f the cycloaddition66 Owing to the importance of these synthons in natural product synthesis, the regiochemistry of the cycloaddition has been addressed. (Scheme 14) Scheme 14: Possible regiochemistry EWG = / R and/or Pd+L* EWG EWG Bimolecular trapping Calculations showed that for a methyl-substituted TMM-Pd complex, form 1 is much more stable than II or III. The carbon farthest from Pd carries the largest negative charge. 40 Experimentally, it was found that whatever the nature of the substituent the negative charge is localized on the substituted carbon: if R is an electron-withdrawing group it corresponds to the thermodynamically most stable position. However, surprisingly, in the case of an electron-releasing group, the carbonation is positioned on the most electron-rich carbon of the TMM ligand, (equation 39) EWG EWG + (eq 39) Intramolecular version of the cyclization 67 ,TMS EWG THF.dppe, reflux EWG OAC 51% The intramolecular version of the reaction was also examined. The formation of the expected product showed that: - the nucleophilic attack is initiated by the carbon atom of the TMM moiety bonded to the electron-releasing group as observed for the intermolecular cycloaddition. - the first step proceeds preferentially cis (formation of the five-membered ring): the strain involved is compensated by the minimization of the charge separation developed after the first step of the cycloaddition. Several investigations toward the functionalization of the TMM ligand have been reported. For instance, CN or SC^Ph 6 8 groups can be conveniently introduced taking 41 advantage of the acidity of a methylene group a to these electron-withdrawing groups, (equation 40) (eq 40) The catalyst can be modified in order to achieve efficient addition of TMM ligand to aldehydes. A comparative study has been carried out between tin- and silicon- containing precursors .69 In contrast with silyl ethers, Sn ethers are excellent nucleophiles and lead to cyclization products, (scheme 15). Scheme 15: Reaction with aldehydes R' LnPd R3M, OAC R'CHO Pd+L2 + R3MOAc Pd+La R' o - M=Sn M= Si AcO 42 II-5 Reactions promoted by a stoichiometric amount of TMM-Pd complex The involvement of a Pd-TTM complex in these cycloadditions reactions was further confirmed by the preliminary reactivity studies of (PPh 3)2Pd(T)3- CH2 CC(CQ2CH3 )2CH2) conducted by Chen and coworkers.5o The detail of their results will be presented in the discussion part. III- ni-Trimethvlenemethane complex of platinum As it has already been mentioned, until recently no TMMd10MLn complex had been isolated. The structure of the intermediate involved in the Pd-promoted [3+2] cyclization was inferred from reaction chemistry. The phenyl-substituted t]3- trimethylenemethane complex of platinum, whose synthesis has been reported earlier ,70 is the first example of a Pt complex to be structurally characterized. The presence of a substituent and the possibility to replace it with group of different electronic and steric nature led to examine its reactivity. IV- Objectives of the project The overall goal of the project was to determine whether complex 7 8 would be an adequate model to study the mechanism and the parameters influencing [3+2] cycloaddition reactions of Pd, or whether its increased stability compared to the palladium complex would give access to an entirely new reaction chemistry. rp-Trimethylenemethane complex 78 is prepared from the corresponding r)3- propargyl triflate, common precursor of alkoxo- and amino-allyl Pt complexes. Allyl complexes are versatile intermediates in organic synthesis, but are accessible through only a limited number of routes . 1 2 The presence of a phenyl substituent, responsible for the relative stability of complex 78 was anticipated to be a drawback. It is not a synthetically interesting group because of lack of reactivity of the derivatives. The difficulties encountered upon trying to make the parent propargyl complex led to design a one-pot synthesis of T^-propargyl complexes (Ph 3 P)2Pt{ri3 -CH2CCR}{X} (without Lewis acid assistance) that would allow its in situ trapping with nucleophiles. The versatility of this new approach was demonstrated by the preparation of various T]3-allyl complexes and rp-trimethylenemethane complexes. The consequence on cycloadditions of the presence of a different substituent on the terminal carbon of the ligand was also examined. CHAPTER II DISCUSSION PART A: ORGANORHENIUM COMPLEXES I- Fischer-type properties of rhenacvclobutadiene complexes 1-1 Electrophilicity of the carbenic centers As it has previously been pointed out in the literature^ the classification of carbene complexes as Fischer-type or Schrock-type complexes is artificial: indeed, some complexes characterized as nucleophilic carbene complexes may display some reaction chemistry of electrophilic Fischer carbene complexes and vice versa. Moreover, some examples of amphiphilic carbene complexes have been reported by Casey .7 0 Hence, (CO)2CpRe=C(H)(CH 2)3 C(CH3)3 79 acts as a nucleophile toward HC1, but can also be deprotonated with a base such as K-Ot-Bu. Re . Re “ ,, OC- ' / VH o c - 7 V oc }- OC I ° c I 79 44 45 In light of this observation and because rhenacyclobutadienes I were the first examples of Fischer-type metallacyclobutadiene complexes ever synthesized (low oxidation state of the transition metal, Jt-acceptor ligands, presence of a heteroatom-containing substituent on the metallacycle, downfield chemical shift of both carbon atoms attached to the metal, M-C bond lengths indicating a partial double bond character), the first objective of the project was to confirm the Fischer-type properties of the complexes through the study of their basic reaction chemistry. As reported previously ,41 the electrophilic character of complexes I was supported by their reactivity toward tertiary phosphines. R R=CH3 la (CO)4R c r^ 5 > - C02CH3 R= C 0 2CH3) lb R= H, Ic OEt A difference of reactivity was observed between complex la and lb. Complex lb, bonded to an electron-withdrawing substituent CO 2 CH3 , undergoes electrophilic addition to triethylphosphine and tri-/?-tolylphosphine affording a zwitterionic complex that can be converted into a CO-substitution complex under thermal conditions. Unlike la, lb reacts with PEt 3 to give a zwitterionic complex at room temperature, whereas the more sterically demanding phosphine, P(p-tolyl) 3 , undergoes CO-substitution reaction affording metallacyclobutadiene complex. (Scheme 16) An intermediate was detected by 31P{1H} NMR, but its nature could not be determined. This reactivity pattern is believed to illustrate the studies reported by Fischer 71 stating that the equilibrium constant of the reversible addition of tertiary phosphines on the carbenic carbon of (CO) 5M=C(OMe)Me (M = Cr, W) depends on the metal, the phosphine, and the reaction conditions. In the case of rhenacyclobutadiene complexes, the equilibrium is also influenced by the stabilizing nature of substituent R. 46 Scheme 16: Reaction of complex la with Pfp-tolyl)^ and PfEt^)^ CO c h 3 c o 2c h 3 P(p-tolyl) 3 , RT CO CH3 ■3 c o 2c h 3 p r 3 R=Et CO o c h 2c h 3 c o 2c h 3 % P OCH2CH3 3 This selectivity was further illustrated by the reaction of complex la with PPhMe 2 . Even though the reaction proceeds at room temperature, the reaction mixture is cleaner if the addition is performed at -78°C. Hence, treatment of a CH 2 CI2 solution of complex la with one equivalent of PMe 2Ph at -78°C followed by warming of the reaction mixture, results in the formation of the ylide-type complex 80. Whereas total conversion was observed by 3ip{lH} NMR of the reaction solution, the complex was isolated in only 53% yield owing to the purification method (slow extraction at low temperature). The structure is supported by the spectroscopic data: the upfield value of 6 [(Re)-C-P+R3] (- 4.3 ppm) suggests a high electron density of the carbon center; the large coupling constant 3Jpn = 20 Hz between the phosphine substituent and the methyl group agrees with a nucleophilic addition on Re-C-CH 3 carbene center. This complex can be thermally converted into a CO-substitution product 81 in 80% yield, restoring the metallacyclobutadienic character of the complex: d(Re-C-OEt) = 258.62 Hz, 6 (Re-C- CH3) = 252.90 Hz. Only three CO doublets are observed by 13C{1H} NMR, the 2Jpc value of which suggests a facial geometry (J~7-8 Hz for the two CO's that are cis to the 47 phosphine ligand, 7~68 Hz for the CO that is trans to P(CH 3)2Ph ligand). The loss of the ylide character is also apparent in the shift observed in the 31P{1H} NMR spectrum (from 32.34 to -26.17 ppm). The Fischer carbene nature of complex 81 was confirmed by the addition of a second equivalent of phosphine on the Re=C(CH 3 ) carbenic center, yielding complex 8 2. Interestingly, the only site of attack that was detected was carbon Ci even though 13C{ 1H} NMR chemical shifts suggest a slightly greater carbenic character for the heteroatom-stabilized center [ 6 (=C(OEt)) = 243.71 ppm versus 6 (=C(CH3 )) = 246.39 ppm)]. As it has already been suggested ,72 the site of nucleophilic attack is thought to result from the location of the lowest unoccupied molecular orbital. Scheme 17; Reaction of complex la with P(CHV)»Ph CO c h 3 CO c o 2 c h 3 oc. OC. | J< ^-P +(CH3)2Ph P(CH3 )2 Ph, CH 2 C12 .Re c o 2 c h 3 > .R e:- c o 2 c h 3 OC' -78°C to RT OC CO OCH2 CH3 CO OCH2 CH3 la 80 IA CO C 0 2 CH3 CO CH3 oc^ I ^J^-p^cftOzPh OC. Re: C 0 2 CH3 P(CH3 )2 Ph, CH 2 C12 ^Re c o 2 c h 3 o c ' o c ' J -78°C to RT Ph(CH3)2P 0CH 2 CH3 Ph(CH3)2P OCH 2 CH3 82 81 On the other hand, if one envisions rhenacyclobutadiene complex la as being mainly represented by resonance form B, then the attack of tertiary phosphines occurs in a 1,4- mode. (CO)4Re c o 2c h 3 (CO)4Re —c o 2 c h 3 o c h 2 c h 3 OCH2 CH3 A B 48 The reactivity of complex la toward several nucleophiles was also investigated, but will be analyzed later. 1-2 Acidity of the methyl group substituent of complex la Early in the exploration of the reaction chemistry of Fischer carbene complexes, it was observed that the methyl substituent in the chromium complex (CO)5Cr==C(CH3 )OCH3 2 displays some unexpected acidity .7 3 -8 A rapid hydrogen/deuterium exchange is obtained by stirring complexes (CO)5M=C(CH3 )(OCH3) in MeOD (99%) in presence of a catalytic amount of NaOCHb. Complex 2 can be deprotonated by strong bases such as n-BuLi, but also milder bases such as potassium t-butoxide or sodium methoxide. By studying the equilibrium between the bis(triphenylphosphine)iminium (PPN) salt of its conjugated base and acidic phenols, the pKa was determined to be 8 . Owing to ion pairing effect, the value was shown to reach approximately 12 for the lithium salt. The unexpected thermodynamic acidity is attributed to the stabilization of the anion by the presence of the heteroatom-containing substituent and the transition metal fragment bearing ^-acceptor ligands. One of the consequences of this high acidity of Fischer carbene complexes is the lack of reactivity of their conjugated bases, which represents a drawback from a synthetic standpoint. Complex la contains a methyl group attached to the carbenic center Ci which is remote from the heteroatom-stabilized center. Deprotonation conditions had to be investigated, since this reaction was anticipated to be a possible side reaction upon treatment with nucleophiles such as carbanions. While the acidity of the methyl group in complex la was addressed, Casey and coworkers reported the reactivity of rhenium complexes C 5H5 (CO)2Re=C(H)CH2R (79) (R = H, alkyl). They showed that, even though the carbenic center is not stabilized by a heteroatom-containing center, the methylene group can be deprotonated by t-BuOK and deuterated. (equation 41) 4 9 OC (eq 41) While complex la does not react with sodium methoxide, it can be deprotonated by strong bases such as lithium diisopropylamide in THF at low temperature and tBuOK, but also by weaker bases such as the sodium salt of dimethyl malonate. Although no pKa determination has been attempted, the fact that it is deprotonated by NaCH(C 0 2 CH3 )2 (pKa[CH 2(CC>2CH3)2] = 12), suggests that at most the pKa of la equals 12. Before investigating the alkylation possibilities of the conjugated base, isolation of the anion was attempted. As it has already been mentioned, PPN[(CO) 5 Cr=C(OCH3 )CH2] (83) is stable enough to be characterized by spectroscopy.73b Therefore, the same isolation method was applied to complex la. Deprotonation of complex la with one equivalent of commercially available LDA solution at low temperature in THF was confirmed by comparison of the CO region in the infrared spectrum of the reaction mixture with that of starting material la. As expected for an anionic complex, a net shift in the absorptions values toward lower energy was observed of the same order as in the case of Cr Fischer carbene complexes. (Table 3) Table 3: IR data of complex la and its conjugated base v(CO) in cm' 1 of starting material 2082 (w), 1991 (s), 1937 (s), 1704 (w) o(CO) in cm' 1 of deprotonated v , species V 2058 (w), 1960 (s), 1901 (s), 1630 (m) 50 The THF solution was transferred to a flask containing one equivalent of PPNC1 under argon and stirred at room temperature for one hour. The metathesized product 84 was separated from salts by filtration and precipitated out by by the addition of hexane. An orange solid was collected and examined by NMR. (equation 42) (CO)4 R e'cZ}>- C0 2 CH3 (CO)4jRe C 0 2 CH3 to 84 2. PPNCI OCH2 CH3 la 84 (eq 42) The yield is assumed to be slightly lower than 94% since all solvent could not be completely removed and the purity could not be ascertained owing to solubility problems. The low solubility of the solid also prevented an acquisition of 13C{1H} NMR data. However, the 1H NMR spectrum indicated the disappearance of the singlet at 8 = 3.07 ppm assigned to the methyl substituent, and the presence of two doublets at 6 = 6.3 ppm and 8 = 4.67 ppm, 7hh = 4.5 Hz. The presence of two inequivalent vinyl hydrogens was also reported for Cr complex 8 3 (two singlets at 3.78 and 4.52 ppm). The spectrum of la suggests that the negative charge is not located on the methylene group but either on the metal or delocalized over the rest of the metallacycle. It can be rationalized by the stabilization provided by the (CO) 4 Re fragment as well as the electron-withdrawing group CO2CH3 . (resonance forms C and D) (CO)4Re C 0 2 CH3 (CO)4Re OCH2CH3 OCH2 CH3 c D The reactivity of the PPN salt was not investigated in depth but will be mentioned later on. These spectroscopic pieces of evidence were confirmed by deuteration and alkylation studies. Deuteration of the methyl group was achieved by quenching the low temperature solution of the conjugated base with deuterium chloride (commercially available solution of 20% DC1 in D 2O). A mixture of three complexes was isolated after work-up. The *H NMR spectrum (Figure 1) indicated the presence of starting material and monodeurated ( 8 5) and dideuterated ( 8 6 ) products that could not be separated, (equation 43) 1. LDA.THF, -78°C Ia Ia + (C 0)4 R e tV 3 X > — C° 2 CH3 + (CO)4 RelV^V>-- co 2CH3 OCH2CH3 OCH2CH3 85 8 6 (eq 43) Casey reports a similar problem upon deuteration of (CO) 5 Cr=C(OCH3 )CH2". In addition to 90% monodeuterated complex, 7.3% of starting material, 2.4% dideuterated and 0.6% trideuterated complexes were observed as contaminants (equation 44). (CCOsCr (CCOsCr 1. nBuLi THF (CO)5C r= C : (COJjCr + (CO)5 Cr 0.6 % C° 3 (eq 44) The deuteration of complex 84 is so fast that this problem could not be solved even by changing the conditions (temperature, addition of the deprotonated carbene to a THF j j jntegh*l .5 54.5 5.05.5 Figure 1 :1H NMR spectrum of the deuteration reaction product of la of product reaction deuteration the of spectrum NMR :1H 1 Figure . . 1.53.5 2.5 3.0 4.0 PPM —r— i-n— -|— 2.0 1.0 0.0 53 solution of DC1). The fact that deuteration occurs exclusively at the methylene carbon is not surprising because it restores the aromaticity of the metallacycle. The reactivity of this anion was disappointingly limited, a problem that will be discussed in section II. II- Attempts to diversify the substitution pattern on the metallacycle The initial synthesis of the complexes was reported in the literature .2 It involves the reduction of the commercially available Re 2(CO)io using a suspension of sodium in THF at room temperature. The resulting anion is then reacted with one equivalent of activated alkyne, i.e. bearing at least one CO 2CH3 group. The nucleophilic attack is followed by cyclization on one of the carbon monoxide ligands, affording an overall [2+2] rhenacyclobutenone cycloadduct. O-alkylation can be achieved by using strong alkylating agents such as triethyloxonium reagents, e.g., Et 3 0 PF6 . Therefore, this sequence requires very specific reagents which restricts the substitution pattern on the metallacycle. Because of the limitations it would represent in terms of applications to organic synthesis, several options were considered to solve this problem. As it is illustrated in scheme 18, efforts were directed in two directions. One option was to modify the synthetic sequence in order to introduce different substituents. In addition to changing the nature of the substituent attached to Q at the [ 2 +2 ] cycloaddition step (path a) (synthesis of phenyl-substituted rhenacyclobutadiene complex 53), methods to activate C3 were also examined (path b). Alternatively, possibilities to alter the substituent on the already-prepared rhenacyclobutadiene complexes were considered. As it has already been mentioned, complex Ia undergoes CO-substitution reaction upon treatment with phosphines (path c). The products of this transformation show differences in reactivity owing to a modification of their electronic properties. The exchange of the heteroatom- containing substituent was expected to alter the electron delocalization and change the Scheme 18: Diversification of the substituent pattern on the metallacycle E+ OC CH OC o c oc, pathc oc r-V Pam path a oc oc oc OC R OC R OC OC Re! Re! pathe OC OC OC V* OC OR LG NuH OC R OC, Re^Z5>"C02CH3 OC L x 55 steric characteristics of the ligand (path d). Finally, the prospect to derivatize complex Ia though a deprotonation/alkylation sequence seemed promising (path c). II-1 Substituent on C3 Reaction with amines The electrophilicity of the carbene center has been used to derivatize Fischer carbene complexes. For example, early in the study of this class of compounds, amino carbenes were synthesized by exchange of the alkoxy group. The initial procedure involves treatment of the alkoxy-substituted carbene with one equivalent of non-hindered mono or dialkylated amines .7 4 This method not only gives access to a wide range of substrates but also provides a way to tune the reactivity of carbene complexes. For instance, the conjugated base is anticipated to be more reactive than in the alkoxy case. Indeed, the electron-donor properties of the nitrogen-containing substituent being superior, the negative charge generated on the a carbon cannot be stabilized as much by the metal fragment 75 It was anticipated that reaction with amines would be an effective route to a different class of metallacyclobutadienes provided that the nucleophilic attack would occur selectively on C 3 . Treatment of complex Ia with one equivalent of primary (aniline, p- toluidine, 2-amino ethanol) or secondary amine (diethyl amine) at low temperature (-78°C for 1° amines, 0°C for 2° amine) followed by warming to room temperature, results in a clean conversion to the corresponding amino complex. It is interesting to note the absence of competition between O- and N- attack in the case of 2-amino ethanol as could be anticipated from their difference in nucleophilicity. The products do not crystallize easily. The mechanism has not been investigated but the transformation is believed to proceed similarly to the conversion of Fischer-carbene complexes. Since the initial kinetic studies reported by Werner and coworkers in 1971 76 only one thorough mechanistic study has 56 been published .77 (Scheme 19) The reaction with primary amines has been shown to be stepwise and to follow a general base-catalysis mechanism: a nucleophilic attack yielding a zwitterionic complex is followed by deprotonation. A neutral complex is obtained by elimination of the alkoxy substituent, through a general acid-catalyzed process. Scheme 19; Aminolvsis mechanism OCH, _ (CO)5 C r = C + RNH2 ^ ^ (CO)5Cr': C— Ph Ph I NRH2+ NHR CH30 ’ + (CO)5Cr=C A similar mechanism can be proposed for the present system. (Scheme 20) Scheme 20; Proposed mechanism for the aminolvsis of complex Ia c h 3 c h 3 (C O )4R e^— C0 2CH3 + r !r 2NH ^ (C O )4 R e^ ^ > — C0 2CH3 OT12CH3 CHjCHjO^hTHR'R2 CH3 57 No indication of attack on the other carbenic center was detected. Studies on alkynyl carbene complexes (CO) 5 M=C(OR)-CsC-R' have been carried out. Hence, when phenylacetylenyl(ethoxy)carbene is treated with one equivalent of dimethylamine, control of the temperature affords selectively addition to the triple bond or aminolysis.9a However, if this path cannot be ruled out, attack on Re-C-(CH 3 ) would be responsible for a loss of the aromatic character of the metallacycle and a reversal of the addition would probably be favored. The spectroscopic data agree with the observations reported for Cr carbene complexes. The 13C{1H} NMR chemical shifts of the carbon atoms indicate a greater shielding of the carbene centers and an increased localization of the electrons over the metallacycle (T able 4). Table 4: Selected 13r flH} NMR chemical shifts of complexes 87 X = X = OEt (Ia) X = NHCH 2 CH 2 X = NHPh NEt2(87a) OH (87b) (87c) a[C(CH3)] 246.4 193.7 197.8 197.3 6 [C (X )] 243.7 210.1 224.1 230.5 A significant difference can be noticed when the spectra of complexes Ia (X = OEt) and 87a (X = NEt2) are compared. The singlet assigned to the methyl group is also shifted upfield upon substituting NEt 2 group for OEt group ( 6 = 2.69 ppm instead of 5 = 3.07 ppm) suggesting a significant localization of the electrons on the metallacycle (Figure 2). A partial double bond character of (Re)-C-N is indicated by the pattern observed for the methylene groups of the ethyl groups. Whereas the methyl groups are not equivalent (6 - 1.37 ppm, 5 = 1.26 ppm, J= 7.2 Hz), the methylenes resonate as a multiplet at 5 = 3.70 ppm showing the lack of free rotation around C-N bond. This observation was expected: 58 Fischer and coworkers reported that amino carbenes such as RR'N(CH 3 )C=Cr(CO)5 display a C-N double bond character greater than do carboxyl ic amides and acids. Monosubstituted aminomethyl carbene complexes exist essentially in the cis form based on 1H NMR coupling constants .78 A cis/trans isomerization can be promoted via deprotonation. The lesser delocalization of the electrons leads one to consider amino-substituted rhenacyclobutadiene complexes 87 as cyclic a,|3-unsaturated amino carbene complexes. Such compounds are well documented in the literature .79 A brief screening of the properties of aminorhenacyclobutadiene complexes was then undertaken. Complex 87a undergoes CO-substitution reaction upon treatment with one equivalent of P(CH 3 )2Ph (addition at low temperature, followed by warming of the reaction mixture), to afford carbenic complex 8 8 . (equation 45) CH2 C12 (CO)4Re C 0 2 CH3 + PMe2Ph c o 2 c h 3 Me2PhP NEt 2 NEt2 87a 8 8 (eq 45) The nature of the product was inferred from the spectroscopic data and comparison with the various phosphine-addition or phosphine-substitution products. The 31P{1H} NMR spectrum displays only one singlet at 6 - -25.2 ppm. This low value is consistent with the trend observed for phosphine-substituted complexes.4i The coupling constants observed in the 1H NMR are more diagnostic. The methyl group resonates as a doublet at 2.43 ppm Jph = 2.0 Hz, a value that is significantly smaller than the value typical for ylide-type complexes (7pn~20Hz). The carbene carbon atoms are shifted downfield compared to those of the starting material (223.1, 201.4 ppm), but are coupled to the phosphorus atom (12-13 Hz). The now inequivalent carbonyls show some characteristic Figure 2: 1H NMR spectrum of fC0)djte=CfCH^-CrC07CH^=CrNfCH7CH2)2l 60 coupling constants. The value for cis-CO ligands is relatively small (ca. 7-8 Hz). The value for the trans ligand is significantly larger (62 Hz). Attempts to deprotonate the complex with one or two equivalents of LDA followed by quenching at low temperature with DC1 in D 2 O were unsuccessful, (equation 46) (CO)4Re C 0 2 CH3 -► (CO)4Re 2.DC1/D20 NEt2 NEt2 87a (eq 46) The localization of the double bond is responsible for a much lower acidity of the methyl group. Additional reactions involving amino-substituted rhenacyclobutadiene complexes will be discussed later in this chapter. Reaction with alcohols and thiols Fischer carbene complexes are known to readily undergo exchange reaction of heteroatom-containing substituent upon treatment with alcohols or thiols .8 0 (equation 47) SR' RT / (CO)5 M = C (CO)5 M = C ^ + CH3 0 H R M= Cr, W; R= CH3, Ph; R'= CH3, C 2 H5, Ph (eq 47) Rhenacyclobutadiene complexes are much less reactive. For example, when complex Ia was stirred in neat methyl alcohol for two days at room temperature, only a minor conversion into the methoxy-substituted rhenacyclobutadiene complex was observed (1/20 by integration of the 1H NMR spectrum), (equation 48) 61 CH, CH3 (CO)4Re c o 2 c h 3 CH3OH ^ (CO)4 Re c o 2 c h 3 RT, 2 days o c h 2 c h 3 5% conversion o c h 3 Ia 11 (eq 48) However, no thiolysis was achieved by stirring complex Ia in presence of 50 equivalents of PhSH at room temperature for 48 h. (equation 49) (CO)4Re^33>— C0 2 CH3 No Reaction OCH2 CH3 Ia (eq 49) Diversification o f the alkoxy group The initial synthesis involves O-alkylation of the acyl group of the rhenacyclobutenone complex. The lack of reactivity of the complex precludes the use of alkylating agents other than oxonium salts which do not allow the introduction of a large variety of groups. For instance, earlier studies showed that alkylation with milder alkylating agents such as methyl iodide could not be achieved. Fischer carbenes have also recently been prepared by alkylation of acylmetalates with alkyl iodides using phase- transfer catalysis conditions (CH 2CI2/H2O in presence of a catalytic amount of n- Bu4NBr) .81 The sensitivity of the rhenacyclobutenone complexes would not allow the use of aqueous conditions. Connor reported earlier an alternative synthesis of the complexes that consists in the activation of the acyl group by treating it with acetyl chloride to form as an intermediate an acyloxy carbene complex. The leaving group ability of the acetate substituent precludes its isolation but activates it toward nucleophilic attack.82 Hence, a wide variety of alkoxy carbene complexes could be synthesized using 62 this method .83 This strategy was applied to the synthesis of rhenacyclobutadiene complexes. (Scheme 21) Scheme 21: Activation of carbon Cj 1. AcCl, CH2CI2, -15°C ------► (CO)4Re C0 2CH3 2.ROH OR 90 (CO)4Re r O > - CO2CH3 CH3 1. A ca,C H 2Cl2, -15°C (C O )4 R e ^ ^ > - CO2CH3 2 . CH3CONH2 nr NHCOCH3 90 95 c h 3 1. AcCl, CH2CI2, - 15°c JL Na ------► (CO)4 R c ^ ^ > — c o 2c h 3 2 . cf 3ch 2oh nr OCH2CF3 90 96 Hence, rhenacyclobutenone complex 90 in CH 2CI2 solution is reacted at -15°C with one equivalent of acetyl chloride. After 30 min, without raising the temperature, the intermediate can be treated with one equivalent of alcohol to generate the desired alkoxy- substituted rhenacyclobutadiene. This sequence was used to prepare various alkoxy- substituted rhenacyclobutadiene complexes the synthetic potential of which will be discussed later. (ROH = EtOH (la), MeOH (89), CH 2=CHCH2OH (91), 63 CH3 OCH2CH2OH (92), C H 3 SCH2CH2 O H (93), HCbC(CH 2)3 0 H (94)) Disappointingly, this methodology could not be applied to the introduction of carboxylic amides such as acetamide or less nucleophilic alcohols such as trifluoroethanol. These conditions led to no reaction or the formation of an intractable mixture of compounds. Incorporation o f a different alkyne The presence of a methyl group is of interest because of the possibility to derivatize the complex by deprotonation/alkylation. However, a phenyl group was thought to be a valuable substituent in electrophilic reactions where deprotonation could interfere, or in cyclization reactions with alkynes where the resulting extended conjugation might also modify the reactivity.(see benzannulation reaction Chapter I, p. 15) The formation of rhenacyclobutenone complexes requires the presence of only one activating group (CO 2CH3 ). It was anticipated that the reaction of Re(CO) 5- with Ph- C3 C-CO2CH3 should not raise any problem. The THF solution of Re(CO) 5 ~ was treated with one equivalent of PI 1-CSC-CO2 CH3 for 48 h at room temperature. Rhenacyclobutenone complex 97 can be easily crystallized from Et 2 0 -THF/hexane and isolated in 80% yield. The spectroscopic data of the complex show values similar to those of the previously characterized rhenacyclobutenones (6[Re-(C=0)-] = 225.67 Hz). Alkylation using one equivalent of Et 3 0 PF6 afforded the expected phenyl-substituted rhenacyclobutadiene complex 98 in 77% yield, (equation 50) The chemical shifts of both carbon atoms attached to the metal display some carbenic character: 6 [=C(Ph)] = 227.371 ppm, 6 [=C(OEt)] = 243.53 ppm. The reaction chemistry has not been fully investigated. However, the influence of the phenyl group will be discussed in section III-1 where reactions with alkynes are reported. 64 Ph THF.RT NaRe(CO) 5 + Ph-CC-C0 2 CH3 Na+ (CO)4 Re c o 2 c h 3 2 d, 80% o 97 Ph Ph Et3 OPF« Na+ (CO)4 Re c o 2 c h 3 (CO)4 Re C 0 2 CH3 CH2 C12 , 77% OCH2 CH3 97 98 (eq 50) II-2 Substituent on Ci Among the three complexes first synthesized, the methyl-substituted complex la appeared to be the most versatile owing to the prospect of potential functionalization via deprotonation. The deprotonation studies conducted on complex la were explained in section 1-2. Complex la can be deprotonated quantitatively with LDA. Based on the work done on Cr carbene complexes, the conjugated base of complex la was thought to be strong enough to react with a wide range of electrophiles. (Its pKa was estimated to be lower than or equal to 12). The anions (CO) 5M=C(OCH3 )CHR" were reported to react with strong alkylating reagents such as methyl fluorosulfonate, acylating reagents such as acetyl chloride, benzaldehyde, 73c epoxide, 84.5 a,(3-unsaturated compounds .85 (Scheme 22) However, these studies reveal a lack of reactivity or selectivity depending upon the reagents. For example, owing to their stability, they do not react effectively with non activated halides or tosylates. With more activated alkylating agents, the problem of dialkylation when R = H is a serious drawback against their synthetic use .730 They do not react with ketones, and treatment with enolizable aldehydes leads to the formation of aldol condensation products, the intermediate p-alkoxy addition product being unstable. This restricts the use of Fischer carbene in aldol condensation reactions and has motivated extensive research to solve this problem. Activation of the carbonyl-containing reagent by coordination to Lewis acids, activation of the complex by changing the heteroatom- 65 Scheme 22: Deprotonation/alkvlation of Fischer carbene complexes OCH3 OCH3 ? / 1 n-BuU / I -CH3O’ (CO)5Cr=C l n » (CO)5Cr=C J ^ (CO)5Cr CHCH,3 >------' 2 . ethylene oxide Z 0 0 1 ’ l.n-BuLi i 3™3 (CO)5Cr:=C ______^ (CO)5Cr=C C02CH3 + dialkylated . \ / product c h 3 2. BrCH2 C0 2 CH3 >------' y P C K l l.n-BuLi ,OCH 3 (CO)5 W = C ^ ^ (CO)5 W = C CH3 2.Benzaldehyde ^ Ph Z 0 ™ 3 l.n-BuLi (CO)5W = C ______^ (CO)5W = C v ,ch 3 2 . Acetyl chloride 2 3 % (CCOsCr O l.nBuLi ( C O ) s C r = ^ 7 > . q C(0)CH 3 2. Acrolein containing substituent 86 or by replacing a CO ligand with a phosphine87’ 26 are some of the most efficient modifications elaborated to circumvent this problem. By substituting a ji-acceptor ligand with a trialkyl- or even a triarylphosphine, an increase in pKa of more than 6 units is observed (under the same conditions pKa was measured to be 18.8).26a The enhanced reactivity that results from charge destabilization is such that the carbanion can then be alkylated with non-activated alkyl halides. Complex la was known to be less acidic than Cr carbene complexes. Therefore, it was expected to be more versatile. Disappointingly, only strong alkylating agents such as oxonium salts are capable to alkylate the anion. Reactions with Mel failed. On the other hand, the problem of dialkylation could not be avoided in spite of the greater steric 66 hindrance of the carbenic center or attempts of optimization (temperature, reverse addition technique). However, the difference among monoalkylated complex 9 9, starting material la, and dialkylated product 1 0 0 is such that the components of the reaction mixture could be separated by chromatography on silica gel. Kinetic and thermodynamic studies have been conducted to rationalize the dialkylation observed upon alkylation of Cr carbene complexes .740 The authors concluded that an equilibrium between a monoalkylated and a dialkylated carbenes was established owing to the fact that proton transfer is faster than alkylation. Unexpectedly, the more substituted carbanion reacts faster than the less substituted one, leading to a mixture of mono, dialkylated, and parent complexes. A similar phenomenon could explain the complexity of the reaction mixture obtained in the case of the alkylation of complex la. (Scheme 23) Attempts to react the anion with acyl halides (acetyl chloride) or a,p-unsaturated ketones (methylvinyl ketone) were not successful and were not pursued. Scheme 23; Proposed mechanism of alkylation B+ OCH2 CH3 (CO)4Re OCH2CH3 99 CHCH2CH3 (CO)4Re OD2CH3 OCH2CH3 I B' CH(CH2CH3)2 c h 3 (CO)4Re 002CH3 + (CO)4Re 002CH3 OCH2CH3 o c h 2c h 3 100 la AJ. Figure 3; iH NMR spectrum of (CO)4Re=CrCH(C%CH^?1-CrCO?.CH^=C(OCHiCH^ JWfWU V4~ ) ""...I...... I...... I...... I...... I...... 'I...... "T".... I...... 260 240 220 200 180 160 140 120 100 80 60 40 20 0 PPM I I Figure 4: 13C{lH> NMR spectrum of (COURe^rCHrCHiCHaHl-CrCOTCH^sCfOCHiCH^) o\ VO 70 III- Exploration of the novel reaction chemistry of rhenacyclobutadiene complexes Having confirmed the Fischer-type character of the complexes through their reactions with phosphines and amines (electrophilicity) and the possibility to diversify the substituents by derivatizing complex la or by modifying the synthetic sequence, the authors then investigated the potential applications of the complex in organic synthesis. III-l Reaction of rhenacyclobutadiene complexes with alkynes Background Metallacyclobutadiene complexes of Shrock type have been proven to be intermediates in alkyne metathesis. The substitution pattern on the metallacycle and the option to tune the electronic and the steric properties of the system were anticipated to give access to a wide variety of substituted alkynes. (scheme 24) Scheme 24; Expected metathesis reaction (CO)4Re (CO)4Re^3>-R R-CC-CO2CH3 OR' OCH2CH3 Simultaneously, Berke and co-workers 43 reported the synthesis of a triphenyl- substituted rhenacyclobutadiene complex (5 6 ) and preliminary reactivity studies on 5 6 including reaction toward alkynes. They showed that no metathesis occurs, but a cyclopentadiene complex (18) is formed irrespective of the nature of the alkyne reagent.(equation 51) 71 Ph Ph Ph (C0)4Re Ph + r R Ph R= Ph, CO 2CH3 R Re R I O C ^ I CO CO 56 101 (eq 51) The formation of cyclopentadienyl complexes was also observed by Schrock and co-workers, upon studying alkyne metathesis reaction promoted by tungstenacyclobutadiene complexes.39a (equation 52) tBuO }Bu -Me2C=CMe2 (eq 52) Although no clear evidence of the mechanism of formation was provided, they suggested that an acetylene inserts into an alkylidene-Iike W-C bond of a non-planar tungstenacyclobutadiene complex. The tungstenacyclohexatriene complex or planar metallabenzene that results is then susceptible to an irreversible collapse to a cyclopentadienyl complex. The last example of five-membered ring formation that is relevant to the present discussion is that of indene products under benzannulation reaction conditions. [3+2] cycloadducts have been isolated as the major products if the formation of the six- membered ring is precluded (equation 53). 72 Ph Ph toluene (CO)5W + Ph Ph ► Ph 100°C,90% OCH3 OCH3 (eq 53) Substituting W for Cr seems to favor the formation of the five-membered rings, as does as the use of polar coordinating solvents such as DMF. (equation 54) OCH3 Et (CO)5Cr 2. air.TsOH 67 % O >8 8 : 1 2 six-membered ring (eq 54) General conditions When complex la is treated with one equivalent of dimethylacetylene dicarboxylate, it is cleanly converted into a cyclopentadienyl complex. Unlike for the triphenyl-substituted metallacyclobutadiene complex, the reaction requires the reflux temperature of toluene to proceed. Refluxing the mixture of reagents in THF did not result in any conversion. Only a partial conversion was observed over 4 h when the reaction was carried out in refluxing heptane. The completion of the reaction was monitored by IR. The four characteristic carbonyl absorptions of the starting material (2082 (w), 1991 (vs), 1937 (vs), 1704 (w) cm-1) were slowly replaced with three lower frequency bands (2032 (s), 1960 (vs), 1952 (vs) cm-i) in addition to carbomethoxy bands at 1732 and 1743 cm-l. The products are stable to air and can be purified by hexane extraction followed by chromatography over grade III AI 2Q3. (equation 55) 73 c o 2 c h 3 c o 2c h 3 CH3 toluene (CO)4 R e ^ ^ ^ > — C 0 2 CH3 + reflux CHaOjC Re COzCHa OCH2 CH3 ~ " > v ~ c o 2 c h 3 OC' I CO CO la 102 (eq 55) The reaction proceeds equally well with electron-deficient alkynes such as DMAD and electron-rich alkynes such as diphenylacetylene (complex 103) or 2-butyne (complex 104). The reaction in the latter case has to be performed in a closed vessel and in presence of an excess of alkyne owing to the volatility of the alkyne. However, a selectivity is observed upon conducting the following competition reaction, (equation 56) C 0 2 CH3 CH3 CH ^C- ■ c o 2 c h 3 CH3Y V ° c h 2ch3 (CO)4 R e ^ ^ ^ > — C 0 2 CH3 +•( toluene ► Ph- -Ph reflux CH 3 0 2 C> d C 0 2 CH3 OCH2 CH3 Ke o c x I CO CO la 102 (eq 56) Thus , when complex la is treated with one equivalent of DMAD and one equivalent of diphenylacetylene, the only observed product results from insertion of DMAD into Re=C bond. Characterization of the cyclopentadienyl complexes The CO stretching region of the IR spectra shows very specific values whatever the substituent pattern on the ligand is. The starting material is characterized by four 74 bands including the CO stretching frequencies relating to the carbomethoxy groups on the metallacycle;they occur around 2082, 1991, 1937, and 1704 cm-1. The conversion of starting material to product is accompanied by a shift of the wave-number values to lower energy. Typical absorption band values for the various synthesized complexes are 2025, 1975, and 1720 cm-1. The 1H NMR spectra of products exhibit the following common features: the resonance of the methyl Cp substituent is shifted upfield to about 23-2.1 ppm; the ethoxy methylene resonating as a quartet in the starting material shows additional coupling upon formation of the cyclopentadienyl ligand; for Cp resulting from the incorporation of a terminal alkyne, the hydrogen atom is associated with a singlet at around 8 = 4.9-S.3 ppm. (Even in cases where this hydrogen was shown by nOe experiments to be vicinal to the methyl substituent, no coupling could be observed.) By 13C{1H} NMR, all three CO ligands are equivalent and resonate as a singlet at around 193 ppm. The carbon atoms of the Cp ligands are spread from 8~70 ppm to 8~140 ppm depending on the electronic properties of the substituent. Regioselectivity o f the reaction Preliminary studies were carried out with symmetrical alkynes. The regioselectivity of the cycloaddition was first examined by using a terminal alkyne, phenyl acetylene, before testing internal unsymmetrical ones. Surprisingly, only one isomer (105) was obtained (Figures 5 and 6 ). The absence of coupling that could have indicated the proximity of the methyl substituent did not allow to draw any conclusion about structure. A nOe experiment was used to establish the structure of the isomer. By irradiating the Cp proton singlet at 8 = 5.29 ppm, a 6% enhancement was observed on the methyl group singlet at 8 = 2.49 ppm. XKTCSfUL (COHR e fn3- Cg (CHO (CO ?CH i) i) ?CH (CO e Cg fn3- (CHO (COHR Figure 5: 1H NMR spectrum of of spectrum NMR 1H 5: Figure ( OCfibCHV) OCfibCHV) ( PhH H ) ) > H PhH ft# f w v m m ~r~ -~r- ~T~ ’T’ ~r~ •"rT"r 200 too 180 170 160 150 140 130 120 110 PPH 100 go eo 70 60 SO 40 30 20 10 Figure 6: jjC llH I NMR spectrum of fCOkRein3-CgfCHoUCO^CH^(OCHiCH^(PhHH)> 0 \ 77 H c o 2c h 3 CH3 H3C>v ^#:^ n v - . o c h 2c h 3 (CO)4Re C ^ > - C0 2CH3 + - w o c h 2c h 3 H Re Ph Ph o c ^ I CO CO la 105 (eq 57) The regioselectivity is dependent on the difference of bulkiness of the two alkyne substituents. Hence, when complex la was treated with 1-phenyl-1-propyne, a 1:3 mixture of unseparable regioisomers (106 and 107) was isolated. The spectroscopic data do not allow to establish the structure of the major isomer, (equation 58) c h 3 c o 2c h 3 c o 2c h 3 CH3 H3c °CH2CH3 s ^ o c h 2c h 3 (CO)4R e t ^ ^ > — COzCH3 + OCH2CH3 H3C Re Ph Ph' Re CH3 Ph O C ^ I ^C O o c ^ I CO CO CO la 106 107 (eq 58) The influence of the nature of the substituent on Ci was illustrated by the loss of selectivity occurring by treating (C 0 )4Re=C(Ph)-C(C 0 2 CH3 )=C(0 CH2CH3) ( 1 2) with one equivalent of phenylacetylene. A 2:1 mixture of regioisomers (108 and 109) was obtained, (equation 59) c o 2c h 3 c o 2c h 3 Ph ^ ^ r \ r O C H 2CE3 Ph-^^V^.OCH 2CH3 (CO)4R e ^ — C0 2CH3 + - m + OCH2CH3 H Re Ph Ph Re H Ph OC^ I CO o c ^ I CO CO CO 53 108 109 (eq 59) 78 This result cannot be rationalized exclusively by steric considerations. Indeed, the 13C{1H} NMR data of the starting material suggest a lesser delocalization of the electrons over the metallacycle (S(Re-C(Ph)) = 227.37 ppm versus S(Re-C(CH 3 )) = 243.71 ppm). On the other hand, since the chemical shifts of the second carbene center Re-C- OCH2CH3 are not really different between the two complexes, it seems reasonable to assume that the selectivity stems from some interaction between Re-Ci-R carbene center and the alkyne. Attempts to alter the outcome o f the reaction The reaction requires elevated temperature, and this suggests that the loss of a CO ligand may be involved in the rate determining step. In the event that the mechanism goes through a metallacyclohexatriene complex 88 that would collapse to form a Cp complex under these conditions, it was thought that the use of milder conditions might prevent the occurrence of this irreversible step. Alternatively, the presence of CO in the reaction mixture might then promote an insertion or a stabilization of the intermediate, if not metathesis. a. Photochemical conditions The photochemistry of (CO) 5W{C(OMe)Ph) was investigated by Geoffroy .89 Upon irradiation of the complex, CO loss was the only detectable reaction. When the reaction was performed in presence of an alkyne, the adduct that was observed at low temperature decomposed at room temperature to afford polymerization products. Benzannulation reactions are known to proceed under photochemical conditions. Even though the yields are not as high as for the thermally-promoted transformations, the conditions allow to perform the reaction even at -78°C as illustrated in equation 60.90 In each case, however, a substantial amount of decomposition products is observed. 79 ,OCH3 l.THF, -78°C, 13.5 h,UV Et 44% O (eq 60) UV-visible spectrum of complex la in hexane ( 10-4 M solution) shows absorption at four wavelengths: 223, 247, 271, and 308 nm. Reactions with DMAD and diphenylacetylene were attempted by treatment of a hexane solution of complex la (104 M) with one equivalent of alkyne under irradiation at 300 nm (Rayonnet reactor). A large amount of decomposition (unidentified solid) was observed upon reaction with DMAD after one hour of irradiation. The residual solution was shown to contain a large amount of starting material contaminated with baseline impurities and a small amount of cyclopentadienyl complex 102 already characterized. Reaction with diphenylacetylene did not produce as much decomposition, and a slow conversion could be observed by IR spectroscopy. After overnight irradiation, the solution was filtered and analyzed by 1H NMR. A mixture of 60% cyclopentadienyl complex and 40% starting material was observed. In light of these discouraging preliminary results, a further study of photochemical conditions was abandoned. b. Chemical labilization of a CO ligand As reported by Berke, attempt to dissociate a CO ligand from (CO) 4Re{r]2“ C3Ph3} (56) with trimethylamine A-oxide91 resulted instead in the formation of a rhenafuran-type complex by oxygen atom insertion. The use of Rh[P(C 6 H5)3]3 Cl92 was also precluded owing to the liberation of one equivalent of PPh 3 that was expected to be trapped by the coordinatively unsaturated species. A certain number of chemical decarbonylations have been reported in the literature.93 Among them, the efficiency of 80 transition metal oxides, such as palladium o x id e ,3 0 has been demonstrated and successfully used in CO-substitution reactions. The mechanism is assumed to involve catalytic electron transfer between the catalyst and the substrate. This seemed to eliminate the possibility of an oxygen atom transfer involved in the mechanism of reagents such as (n-Bu) 3 PO. Complex la was therefore submitted to analogous conditions (one equivalent of PdO, CH 3 CN, RT, leq alkyne). In each case, the total conversion of starting material required two days at room temperature, but afforded the corresponding Cp complex 105 in comparable yields as under thermal conditions.(equation 61) OCH2 CH3 (CO)4Re C 0 2 CH3 + CH3 CN,RT 2 days, 90% OCH2 CH3 Ph oc^ I N''co CO la 105 (eq 61) c. Intramolecular coordination The advantages of the intramolecular coordination of a heteroatom were illustrated in benzannulation reactions. Not only was it expected to participate in the dissociation of a CO ligand hence promoting the coordination of one equivalent of alkyne, but also to stabilize any unsaturated intermediate. In benzannulation reactions, chelation by a methoxy substitutent of the phenyl group was shown to affect the product distribution. Hence, the formation of cyclobutenone is highly favored over naphthol when the metal is coordinated by two external molecules: the solvent (THF) and a methoxy substituent. These elements are believed to stabilize the vinylketene key intermediate. 81 l.solvent Et Et OMe + 2 . oxidation Et (eq 61) Table 5: Chelation effect R - o-OMe c h 3c n <2 % 43% R= p-OMe THF 85% - The chelation strategy has also been examined by Dotz, who studied the reactivity of an acylamino carbene complex .9 4 He prepared A-acylamino carbenes of Cr, Mo and W by JV-acylation of the corresponding amino carbene in presence of DMAP (A,/V-dimethyl amino pyridine). A spontaneous decarboxylation afforded a five-membered chelate ring through the oxygen of the amido substituent. This system was very chemoselective affording either indene/naphthalene derivatives or pyrrol/pyrrolone derivatives depending on the metal and the nature of the chelate. The intramolecular coordination of a double bond has also been considered as a means to activate the carbene precursor toward alkyne coordination .9 5 More generally, the formation and reactivity of heteroatom-containing chelates have been extensively reviewed.96 The possibility of activation of the rhenacyclobutadiene complex la toward alkyne coordination by removing a CO ligand and stabilizing the intermediate with a heteroatom was considered. The variation of the synthesis discussed in part II.l.c allows the introduction of various OR 1 groups. Hence, reaction of rhenacyclobutenone with one equivalent of acetyl chloride at -15°C followed by treatment with one equivalent of HOCH2X (X = CH2 OCH3 (92), CH2SCH3 (93), CH=CH2 (91), (CH2 )2C=CH (94)) afforded the following rhenacyclobutadiene complexes. However, in situ treatment with one equivalent of acetamide resulted in decomposition of the complex, (equation 63) CH3 vt+ l.AcCl, -15°C, CH2 C12 2 3 CO CH Na ------► (CO)4 Re c o 2 c h 3 2. HO-CH2-X o c h 2x (eq 63) c h 3 c o 2 c h 3 OCH3 - s c h 3 92 93 c h 3 (CO)4 R e ^ ^ > — C 0 2 CH3 O— 91 94 The results obtained for the heteroatom-tethered complexes and the allyloxy-substituted complex were disappointing. When complex 91 was heated in toluene for 4 h, no coordination of the double bond could be detected by IR. Upon heating in presence of one equivalent of phenylacetylene, starting material was converted into the corresponding Cp complex. A similar reactivity was observed for complexes 92 and 9 3. (Scheme 25) 83 Scheme 25: Attempted coordination of a double bond or a heteroatom C 0 2 CH3 toluene, C H 3 0(CH 2 )2 XCH3 reflux, 4h \ f ) / le q phenyl acetylene ^ CH3 H Ph Re (CO)4Re c o 2 c h 3 o c y | CO CO CH3 o toluene x=o,s reflux, 4 h —XCH3 (CO)/3 R T e ^ ^ — C0 2 CH3 h 3c Heating complex 94 in toluene, however, resulted in its complete conversion within 2 h into a dihydropyran-Cp fused ring complex 110 (equation 64). The rate of the conversion seems to be enhanced. The facile coordination of the triple bond is a reasonable promoting factor in this particular reaction. c o 2 c h 3 toluene, reflux 1 2.5 hours □ Re OC/ | ^ C O CO 94 110 (eq 64) d. Electronic nature of the metallacvcle In 1992, Finn reported that whereas (CO) 2(Me-Cp)Mn=C(Ph)(OCH 3 ) was inert toward benzannulation reaction, the reactivity was greatly enhanced in (CO)2(Me-Cp)Mn=C(Ph)(OTiCp 2Cl) . 97 (equation 65) 84 O OTiCpaCI ,n-Bu / 1 . 1 -hexyne (Me-Cp)(CO)2Mn = C\ Ph hu, THF, 20°C 2. Ce(IV) oxidation 30% O (eq 65) The option of changing the electronic properties of the ring through variation of the substituent on C 3 was then investigated. However, attempts to make starting materials 111 and 96 failed. (CO)4 Re CO2 CH3 (CO)4 Re C 0 2 CH3 OTiC^Cl OCH2 CF3 111 96 Proposed mechanism Despite efforts to elucidate the mechanism of formation of cyclopentadienyl complexes (page 73), no definite path can be proposed. Attempts to trap an intermediate metallabenzene with a two-electron donor such as pyridine resulted in decomposition. Attempt to add one equivalent of PPI 13 to the PdO-catalyzed reaction mixture prevented the formation of the Cp complex. This seems to indicate that a CO-dissociation step is involved, and the unsaturated intermediate species can be trapped by an alkyne, or a phosphine or that it decomposes. Based on extensive work done on benzannulation reaction and regioselectivity observed with unsymmetrical alkynes, the following sequence of steps is proposed: CO-dissociation, coordination of one equivalent of alkyne governed by steric demand, insertion of the alkyne into a Re-C(R) bond, and collapse of the metallabenzene-type complex to form a Cp complex, (scheme 26) 85 Scheme 26: Proposed mechanism for the formation of cyclopentadienyl complexes R1 CO OCH2 CH3 4 2 3 (CO) R e ^ ^ > - C 0 CH + C 0 2 CH3 OCH2 CH3 Rs Rs CO2 CH3 OCH2 CH3 (COfcRe Attempts to cleave the highly substituted Cp ligandfrom the metal The access to a wide range of substituted cyclopentadienyl complexes motivated the search of conditions to cleave the ligand from the metal to use the diene part in synthesis. Unfortunately, attempted cleavage under acidic conditions failed (CH 3 CO2 H, CF3 CO2H, HBF4 , CF3 SO3 H (decomposition)). Based on extensive work reported on ring slippage of transition metal cyclopentadienyl complexes, the alternative to reduce the hapticity of the Cp ligand and react it then seemed reasonable. The factors influencing the reactions have been investigated by Casey .9 8 The slippage from ^5 to iq 3 is facilitated when the steric hindrance is kept low and in presence of an electron-withdrawing group. The effect of substituents have been examined more systematically by Basolo, who studied CO substitution on (T]5-C5H4X)Rh(CO)2 complexes (1 1 2 )." Acceleration was observed for X = NMe 2 and Cl owing to the stabilization of the r^-intermediate. 8 6 Another encouraging report was the slippage of (CO) 3Re(ii5-Cp) (113) to (PMe3 )2(CO)3 Re(til-Cp) (36) promoted by excess trimethylphosphine . 100 (equation 6 6 ) PMe3 o c oc— Re—CO Me3 P/ \ : 0 (eq 6 6 ) In spite of the steric hindrance of the substituents on the Cp ring, the presence of an electron donating group [N(CH 2CH3)2] adjacent to an electron-withdrawing group (CO2 CH3) on complex 115 was expected to favor the localization of a double bond resulting from the slippage. Unfortunately, the complex is inert under these conditions, probably owing to steric hindrance, (equation 67) The less sterically crowded Cp complex 105 was then reacted with a three-fold excess of PMe 3 in a sealed tube at 50°C in a mixture of hexane /toluene. While the temperature was maintained for 1.5 h, a white thick precipitate formed. Because of its limited stability, it could not be fully characterized. However, the 3ip{lH} NMR and 1H NMR spectra seem consistent with a CO substitution complex: the 31P{!H} NMR spectrum shows a singlet at 18 ppm. The 1H NMR spectrum indicates the presence of a PMe 3 ligand and the coupling of the Cp 87 proton at 5.89 ppm (7hp = 4.46 Hz). The ethoxy methylene pattern is also affected by the presence of the phosphine. (equation 6 8 ) C02 CH3 H3C> ^ j ^ ^ N(CH2CH3)2 PE> h e x a n e CH3 O2C Re CO2 CH3 O C^ I ^C O CO 115 CO2CH3 C02 CH3 N (C H 2C H 3) 2 (CH 2CH 3 ) 2 CH 3 0 2 C c o 2c h 3 CH3 O2C CO2 CH3 O C R e C O OC - R e - CO Et3 P/ \ o Et3 P/ \ o (eq 67) C02 CH3 C02 CH3 o c h 2c h 3 H3CW OCH2CH3 PMe3 hexane/toluene w ? H m Re Ph H & Ph o c ^ I ^C O O C ^ I PMe3 CO CO 105 (eq 6 8 ) III-2 Rearrangement reactions Insertion oforganonitriles into Fischer carbene complexes Whereas Fischer carbene complexes undergo benzannulation reactions upon treatment with alkynes, they undergo insertion when reacted with a carbon-nitrogen triple bonds . 101 (equation 69) 8 8 OCH3 R2 / benzene, 80C / (CO)5 C r = C + 1 4 eq R 2CN ------► (C0)5Cr=C OCH3 \ > 2411 \ = Rl (eq 69) Owing to the cyclic structure of complex I, the hypothetical insertion of organonitrile was anticipated to be a versatile route to heterocycles. Scheme 27: Expected insertion of organonitriles CH3 EtO BO BO Complex la is stable in acetonitrile at room temperature. However, when it is heated at reflux temperature for several hours, it is converted to a new product 116 that does not contain the organonitrile. It can be isolated by slow extraction into hexane as a yellow- green oil, the stability of which is only moderate. The experiment was repeated with deuterated acetonitrile. The product that was isolated showed no evidence of deuterium incorporation. och 3 CH3CN or (CO)4Re COzCH3 ► CD3CN, 80°C 2 hours c o OCH2CH3 K 70% isolated CH3CH20 116 (eq 70) Spectroscopic data IR, 1H NMR and 13C{1H} NMR data were collected. The IR spectrum showed some similar absorptions to those of the oxygen insertion product 117.(Table 6 ) Table 6 : IR data of complexes 116 and 117 / ° \ ^ O C H 3 (CO)4 R e ' y - “U CH3 CH2 O CO2 CH3 c h 3 c h 2o > ------ (THF) (hexane) 2 1 0 1 2092 1999 2039 1942 1997 1727 1944 1703 1726 The most important feature of the 1H NMR spectrum was the loss of the CH 3 singlet at 8 = 3.07 ppm standing for the Cj methyl group substituent in la. On the other hand, three vinyl multiplets each accounting for one proton were present in the product ( 8 = 4.95 ppm, dd, Jgem = 2.67 Hz, Jcis = 12.1 Hz; 8 = 5.58 ppm, dd, Jgem = 2.67 Hz, Jtrans = 17.99 Hz; 8 = 6.43 ppm, dd, yds = 12.1 Hz, J ^ = 17.99 Hz). The 13C{1H} NMR spectrum confirmed the presence of a vinyl group with two singlets at 8 = 110.75 ppm (~CH=CH2) and 8 = 114.9 ppm (~CH=CH 2). The singlet at 8 = 159.43 ppm, assigned to the uncoordinated carbomethoxy carbonyl group in the starting material, is replaced with a singlet at 8 = 186.36 ppm, a value that had previously been reported for the ester- coordinated five-membered metallacycle 118. 90 / ° s ^ o c h 2ch 3 / x ^ o c n 3 (CO)4Re (CO)4Re ^ \\ - /*'■ A c h 3 'c o 2 c h 3 CH3 CH20 C p 184.60 ppm Cj= 186.37 ppm C3= 233.70 ppm C3= 234.307 ppm 118 116 Finally, the presence of a resonance at 6 = 234.31 ppm suggests at least a partial delocalization of the electrons over the ring. Several examples of metallafurans, including manganacycles, can be found in the literature. The aromatic character of these complexes, apparent in the values of bond distances, was confirmed by reactivity studies. Hence, complex 119 undergoes electrophilic aromatic substitution upon treatment with N- bromosuccinimide . 102 (equation 71) O ►Mn(CO ) 4 -►Mn(CO )4 4-Bromosuccinimide -► II3C Ph H3CAA.- Ph r Br 119 (eq 71) Even though acid-promoted demetallation as well as insertion of isocyanates 103 could be achieved on metallafuran-type complexes (M = Mn, Re ) , 104 acyl-coordinated five- membered metallacycles are known to be extremely stable. They generally do not undergo acyl displacement , 105 multiple alkyne insertion, or (3-elimination reaction. Generality o f the reaction The rearrangement was first identified on methyl-substituted rhenacyclobutadiene complex la. However, the reaction is not always clean. It was anticipated that the instability of the product might be due to the presence of the double bond. Indeed, this is 91 I one of the major structural differences between complex 116 and (CO) 4 Re=C(CH3)- C(C0 2CH3 )=C(0 CH2CH3 )-0 , 118, its oxygen-atom insertion product. The rearrangement product of the corresponding propyl-substituted complex was thought to give rise to two possible stereoisomers owing to the possible formation of cis and trans double bonds of the resulting rhenafuran. The reaction was attempted, however, and provided evidence for a similar rearrangement, with the presence of a vinylic singlet in the 1H NMR spectrum. On the other hand, the 3-pentyl substituted rhenacyclobutadiene complex 1 0 0 was shown to convert slowly, but more cleanly, to a single product, rhenafuran complex 119. (equation 72) c o CH(CH 2 CH3 ) 2 RCN - c o 2 c h 3 80°C c o o c h 2 c h 3 5 days 100 119 (eq 72) Table 7: Rearrangement in various organonitriles R Conversion c h 3 >90% c h 3 c h 2 >90% Ph >90% (CH3)3CN <40% The reaction requires five days at reflux temperature of acetonitrile to be complete. The product can be isolated by slow extraction of the crude oil using 20 mL of hexane. It crystallizes upon evaporation of the extraction solvent. Although the conversion is greater than 90%, the extraction steps necessary to purify the compound are responsible for a substantial loss of product (isolated yield: 55%). The proposed structure is supported by spectroscopic evidence (!H and 13C{lH> NMR) as well as analytical data. I I 4.4 PPH 4.3 J______1 /U_ y | " l ■ I T | ■ . , » | , | 1T I I | 1 11 I » | ' 1* 1 I » | I ' l I » | I 1 I I | I I I T | I I I T "|"» I I I I I I I* I I I *l~| » » <* ■ I ' • i ■ ■ i ■ I—; .rt-|- , | Tm, , , I 9 .6 9 .0 3.5 8.0 7.5 7.0 6.5 6.0 5.5 5 .0 PPH4.5 4.0 3 .5 3.0 2.5 2.0 1.5 i.O .5 0.0 Figure 7: 1H NMR spectrum of (CO)£Re=C(OCH?CH^-C(CH=CrrCH*CH*ni1=C(OCH^O S3 1 "I"" ""I"" 240 220 200 1B0 160 140 120 100 BO 60 40 20 PPH Fi2 ure 8 : 11CI1H} NMR spectrum of I 1 (C 0 URe=C(0 CH 7 CH^C(CH=Cr(CHiCHa) 2 l)= C (0 CHg) 0 u>VO 9 4 In particular, the 1H NMR spectrum (figure 7) shows a single olefinic proton at 5.36 ppm as a broad singlet. The splitting of the vinyl ethyl groups was predictable: the methylene groups resonate as two quartets at 6 = 2.08 and 1.92 ppm, J- 7.5 Hz. The quartet of the methylene that is cis to the olefinic proton is further split into a doublet J = 1.34 Hz. However, the methyl groups are equivalent and appear as a triplet at 1.02 ppm with a coupling constant of 7.5 Hz. Finally, the 1 3 C{1H} NMR spectrum (figure 8 ) confirms the chelation of the carbomethoxy carbonyl oxygen with a downfield shift from about 165 to 188.33 ppm. The metallacycle exhibits some residual Fischer-type carbene character, since the carbon bonded to the metal resonates at 249.2 ppm. The cleanness and reproducibility of this reaction made this compound a good substrate for a study of the generality of the rearrangement in terms of organonitriles RCN. Several aliphatic organonitriles as well as benzonitrile were tested. It was found that the conversion is greater than 90% in acetonitrile, propionitrile, and benzonitrile after five days at 80°C. However, when the electron-rich but bulkier trimethylacetonitrile was involved, only 40% conversion was observed after five days, suggesting that even though the organonirile is not incorporated in the final product, an activation of some sort has to be involved in the mechanism of rearrangement. The temperature at which the reaction is performed is not the only influencing factor, since no conversion was observed upon heating the substrate in benzene at 80°C. Similar but spontaneous 1,2-shifts of dialkyl-substituted alkylidene complexes have been reported in the literature . 106 Among alkylidene complexes containing a p- hydrogen atom, only a limited number undergo rearrangement at room temperature. Selected examples are presented in Scheme 28.107 Alkyl migration has also been observed and thought to be favored by the presence of a particularly electrophilic carbene center (cationic complex, late transition metal, no stabilization by phosphines), the absence of p-hydrogen, and the achievement of strain 95 relief. 108 Competition experiments were designed to evaluate the relative migratory aptitude of various subtituents. (Scheme 29) The following order was established, all other promoting factors being minimized: H>Ph>Me . 109 Similarly, the electrophilic nature of the alkylidene-part of the complex combined with the strain relief accompanied by the rearrangement could be invoked as the driving force in the isomerization/rearrangement reaction of rhenacyclobutadiene complexes. Scheme 28: Examples of 1.2-shifts of dialkvl-substituted alkylidene complexes CD2 C12 H Fp Scheme 29: Examples of alkvl migration CH2 C12, -78°C 30min Ph H 96 An alternative mechanism that was considered was an acid/base type process. The acidic behavior of acetonitrile during the reaction was ruled out by the absence of deuterium incorporation upon carrying out the reaction in deuterated acetonitrile. In contrast, the occurrence of the rearrangement under basic conditions was demonstrated by the formation of a related product by heating in pyridine. Rearrangement in pyridine Pyr (eq 73) Pyridine was reported by Casey and coworkers to react with Fischer-type carbene complexes, cleaving the ligand from the metal . 110 (equation 73) More recently, Hegedus observed that a similar cleavage could be achieved by treatment of the carbene complex with an equivalent of sodium phenoxide in phenol . 111 (equation 74) A more general mechanism for such base-promoted transformations was then proposed. 97 "* 0 a*- a \ I (COJsCr Ph (CO) 5 Cr (eq 74) When 3-pentyl-substituted rhenacyclobutadiene complex 100 was heated in pyridine, instead of a complete cleavage of the ligand from the metal, all starting material was converted into a rhenafuran-type complex. The rearrangement was also accompanied by the substitution of a CO ligand with a pyridine ligand. With the exception of IR data, the spectroscopic data relating to compound 1 2 0 show a lot of similarities with those for complex 119. (Figures 9 and 10) c o CH(CH 2 CH3 ) 2 r ] C ^ c o , c h 3 | 80°C CO o c h 2 c h 3 w* c h 3 c h 2 c / 100 120 (eq 75) The possibility that CO-substitution by pyridine occurs prior to deprotonation/rearrangement can not be ruled out. A similar coordination of an equivalent of acetonitrile could be invoked in the rearrangement leading to complex 116. Acetonitrile is not as good a coordinating ligand as pyridine. However, if CO-dissociation occurred at 80°C, the release of an equivalent of ligand would be expected to be irreversible. Therefore, it should not be present in solution to afford the tetracarbonylrhenafuran complex. To prove that organonitriles would act as bases and promote the establishment of an equilibrium, complex la was 4.7 PPH ■ i i ■! i i ■» i i i i i » i I i i i » I i * i i I i I—(-1—|-t- i i i | i i » i j i i i i | i i-n-jTn-i-[irr. ■ i 1 ■ ■ ■ l ■ 1 ■ ■ t 1 ' 1 ’ l 1 1 ■ 1 I ' ■ ' 1 l ' 1 J ' I 1 ' ; 1 I M 1 ' I * ' ' L I S 9 0 8 5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 .5 PPH f ------[ Figure 9: 1H NMR spectrum of PvfCO^Re=CfQCH7 CH^-CfCH=CrfCH 7 CH1 H 1)=CfO CH ^O 99 ) 0 4 Pv(CO)3Re=CfOCH2CHg)-CfCH=CffCH2CH^)2l)~C(QCHa spectrum spectrum of NMR NMR © -raAl in» in» 13p.|1JH> P ipurp P ipurp 1 0 0 treated with hindered bases such as Hunig's base (i-Pr 2NEt). However, an intractable mixture of products was isolated, and no conclusion could be drawn, (equation 76) Starting material + R e X l 3 > — C0 2 CH3 + i-Pr2NEt Mixture of unknown products c o OCH 2 CH3 la (eq 76) Protonation studies presented earlier in the discussion (section 1-2 page 48) were performed with strong acids such as DC1. The idea behind the following experiment was to test whether the use of a weaker acid such as Et 3NH+BPh 4 - would favor reprotonation at the metal center rather than at the methylene group. This alternative pathway might promote the isomerization/rearrangement reaction. The conjugated base of complex la was generated by treatment with one equivalent of LDA in THF. Disappointingly, its reaction with one equivalent of Et 3 NH+BPh 4 % only starting material was recovered, (equation 77) After treatment of the conjugated base of la with one equivalent of pyridinium chloride, the 1H NMR spectrum indicated a mixture that could not be identified, (equation 78) CO 9 H3 Starting material OCH2 CH3 (eq 77) Mixture of products Re t = > - C0 2 CH3 2. Pyridinium chloride c o OCH2CH3 (eq 78) 1 0 1 Proposed mechanism (Scheme 30) Scheme 30: Proposed mechanism for the rearrangement promoted bv pyridine CO CH(CH2 CH3 ) 2 CO C(CH2 CH3 ) 2 • QQ :° OCH2CH3 c o OCH2CH3 I i 1 (CH3 CH2 )2 C, H C(CH2 CH3 ) 2 (CO)4Re (CO)4Re c o 2 c h 3 c h 3 c h 2o (CH3 CH2 )2 Ct Py(CO)3 Re, Pyridine (CO)4Re ,CH2 CH3 c h 3 c h 2o c h 3 c h 2 o-* O c h 2 c h 3 Based on the mechanism formulated by Casey, the rearrangement observed in pyridine is proposed to involve a partial deprotonation of the methyl or substituted-CH attached to Cl on the metallacycle. The equilibrium might then be driven to completion if reprotonation occurs at the metal instead of regeneration of the starting material. This unstable metal hydride complex could then undergo reductive elimination, affording an 18 e- complex by coordination of the double bond. Next, a bond rotation has to be invoked in order to account for the chelation by coordination of the oxygen atom of the carbomethoxy substituent of the metallacycle. The occurrence of this bond rotation might be favored, since it results in the formation of a metallafuran known to be very stable . 112 1 0 2 A similar kind of rearrangement affording a chelate-type structure was reported for the following ruthenium and osmium systems . 113 The conversion, slow under thermal conditions, is assumed to proceed through a reduction of the C=C bond order brought about by the presence of an electron-withdrawing group. The polarization of the ligand promotes a bond rotation responsible for the coordination of the ester carbonyl group, (equation 79) PPfrj—-►|KU ►[!*« ^ pph3PPh3------—► L tRujl JVUJ ^"* c 0 2CH3 [Ru]. H ^ C0 2CH3 c o 2ch 3 — pphv \ 4 ( \ H3CO o O o c h 3 o o c h 3 [Ru]= Ru(CO)Cp (eq 79) In the rearrangement observed in the rhenacyclobutadiene case, this polarization is even more favored by the "push-pull" effect promoted by the alkoxy and carbomethoxy groups. To support the involvement of the deprotonation at Cl substituent, the following experiment was attempted. If pyridine partially deprotonates complex 100, heating complex 1 0 0 in presence of an equivalent ^/-pyridinium tetraphenylborate should lead to some substantial deuterium incorporation at the olefinic position. Disappointingly, the reaction was not clean, and no deuterium incorporation could be ascertained, (equation 80) 103 c o CH(CH 2 CH3 ) 2 I CH3 CN, ^.RA. e^3> -C 02CH3 + BPh4’ (X T I 80°C, 3.5 days c o OCH 2 CH3 / ° \ ^OMe PyCCObRe^ > (CO)4 Re + Impurities EtO' < RO a (eq 80) III-3 Reactions with stabilized-carbon nucleophiles The prospect of utilizing two electrophilic carbon centers to undergo insertion reactions or cleavage of the organic ligand from the metal was considered as soon as the Fischer-type structure of the metallacycle was established. Dimethyl sulfoxide has been observed to be a good oxygen transfer reagent for Fischer carbene complexes. Following insertion of the oxygen atom into M=C, a cleavage of the organic fragment released as a carboxylic ester takes place. The generation of one equivalent of dimethyl sulfide, a good leaving group, probably favors this reaction. Based on the same idea , 114 imidates have been prepared by insertion of NR into Fischer carbene M=C bond by use of sulfilimines RN--S+R'2. Ketone enolates or carbanions derived from dialkyl malonates could not be used owing to the acidity of the methyl group attached to Cl. Wittig reagents were expected to be too basic to undergo nucleophilic attack over deprotonation as observed in the case of Fischer-type carbene complexes. Indeed, Casey observed only deprotonation of (CO)5 W=C(OCH3 )(CH3 ) upon treatment with one equivalent of phosphorane CH2=PPh 3 (equation 81), instead of vinyl ether formation as in the case of treatment with diazoalkanes . 115 104 o ch 3 (CO)5W + H2 C = = P P h 3 (C0)5w c h 3 (eq 81) Less basic reagents, such as dimethyl sulfide ylides, were then considered. Alcaide116 in 1992 reported that the ligand of Fischer carbene complexes could be cleaved as a vinyl ether upon treatment with an equivalent of sulfur-stabilized carbanions. The reaction was performed in acetonitrile under photochemical or thermal conditions. The mechanism is illustrated below. (Scheme 31) Nucleophilic attack is followed by the formation of a C=C bond promoted by the elimination of a good leaving group such as dimethyl sulfide (DMS). In spite of the presence of a methyl group that was more acidic than in complex la, no deprotonation Scheme 31; Reaction of Fischer carbene complexes with sulfur-stabilized carbanions (CO)sCr (CCOsCr. occurred. In light of these encouraging results, two sulfur stabilized carbanions were prepared: (CH 3 )2S+-C-(CN) 2 and (CH 3)2S+-CH-(C(0)Ph). The sulfur ylide derived from malononitrile was first prepared and tested. It was chosen because of its low 105 basicity. The pKa of its precursor (CH 3 )2 S+CH(CN)2 is lower than 5. It was prepared using a literature method . 117 (equation 82) H3C ^ _ CH2C12 H3C CH2(CN)2 + N j— o + soci2 ► c h ( c n ) 2 cr h 3 c / -15°C H3C aq. NaHCGj (eq 82) Upon reproducing the conditions described by Alcaide, only partial conversion was observed. Reflux temperature of CH 3 CN had to be maintained for 6 h to complete the reaction. A mixture of two products was obtained, (equation 83) CO CH3 o / \ ^ o c h 3 (CO)4 Re c o 2 c h 3 c h 3c n + c o o c h 2 c h 3 /\ c h 3 c h 2o NC CN major la 121 (eq 83) The major product 43 could be separated and identified by spectroscopic techniques. The carbene methyl substituent is converted into an allylic methyl group as illustrated by the chemical shift values ( 8 = 2.32 ppm instead of 3.07 ppm in complex la). The 13C{1H} NMR spectrum shows two distinct singlets assigned to the nitrile substituents at 8 = 112.3 and 113.3 ppm. The carbon atom still attached to the metal center resonates at 239.8 ppm suggesting some residual carbenic character of the complex. The presence of two electron-withdrawing groups was thought to be responsible for the slow transformation. Moreover, the absence of any protons on the inserted group made the identification of the insertion-rearrangement product difficult at first. That is the reason 106 why complex la was then reacted with one equivalent of (CH 3)2S+-C-(H)C(0 )Ph .118 The reaction proceeded at room temperature and was complete after 30 min. The product (122) was isolated by extraction of the crude residue with hexane in 48% yield, (equation 84) CO 9 « 3 h3c c h 3 OC. I I \ / (CO)4Re \ c h 3c n R eX l5 > -co 2cH3+ —— ► ,C(0)Ph O C ^ l ^ r c - RT, 30 min M c o OCH2CH3 _ _ / \ CH3CH20 ' H C(0)Ph la (eq 84) 1H NMR spectroscopy revealed that one isomer was selectively formed (figure 11). NOe experiment support the cis geometry of the double bond (4% enhancement). The following mechanism, consistent with the formation of these two products, is proposed (Scheme 32). Scheme 32: Reaction of complex la with sulfur-stabilized carbanions CO c h 3 h 3c c h 3 o o c ^ I JL (CO)4Re C 0 2 CH3 OC + c - 2 3 CO OCH CH j j / n r c h 3 c h 2o 4 3 c o 2 c h 3 (CO) Re. ,OCH CO o c h 2c h 3 c h 3 c h 2 o + ° Nucleophilic attack occurs at Re=C(CH 3). The intermediate zwitterionic structure then leads to the cleavage of the Re-C bond, a step that is driven by the elimination of an equivalent of dimethyl sulfide. This intermediate is stabilized by the coordination of the 107 resulting double bond. A more stable structure is however obtained by bond rotation bringing the carbomethoxy group in closer proximity to the metal and allowing the formation of a five-membered chelate structure. Such a bond rotation had already been invoked to explain the rearrangements observed in organonitriles. An alternative mechanistic pathway involves a cyclopropanation reaction. Sulfur- stabilized carbanions such as dimethylsulfonium phenacylide undergo 1,4-addition to a,p-unsaturated carbonyl compounds affording cyclopropane adducts.119 (equation 85) PhCH=CH-C(0)Ph + (eq 85) If complex la is considered as a a,p~unsaturated ester equivalent, a 1,4-addition of the carbanion might yield a highly strained cyclopropane, which is likely to rearrange and form a rhenafurantype structure as observed.(Scheme 33) Scheme 33; Alternative mechanism C S(CH3 ) 2 2 3 c o c h (CO)4 Re C 0 2 CH3 2 3 OCH CH OCH2 CH3 (CO)4Re (CO)4Re C 0 2 CH3 CH3 CH20 OCH2 CH3 108 III-4 Heteroatom Insertion Reactions Oxygen atom insertion The organic ligand of Fischer carbene complexes can be easily cleaved as carboxylic esters under a wide variety of oxidative conditions. The reagents include (NH4)2Ce(N0 3 )6, DMSO, and (CH3)3N 0.12°. llb (equation86) OR /R O (CO)sM:[ C^ + Oxygen transfer ► II X RI reagent OR Oxygen-tianferreagent; ( N H ^ C e ^ O ^ , DMSO, MegNO (eq 8 6 ) More recently, dimethyldioxirane reagents have shown to effect decomplexation of the organic fragment in comparable or better yields.121 (equation 87) OCH2 CH3 0 . / acetone, 3h ■■ < + |N < : ------► 11 Ph ( j / X 20°C, 97% Ph^ ^ OCH2 CH3 (eq 87) The first attempts to cleave the metallacycle under oxidative conditions (three equivalents of (NH 4 )2 Ce(N0 3 )6 , acetone, room temperature) resulted in the insertion of an oxygen atom in one of the Re=C carbene bonds.41 The composition of the mixture was determined to be 3:1 in favor of the keto-coordinated rhenafuran 117. The two components could be separated by chromatography on silica gel, and the major product was characterized by X-ray diffraction analysis. The present research showed that rhenacyclobutadiene complex la undergoes oxygen atom insertion under a wider range of conditions: for example, upon carrying out a control reaction in DMSO at room temperature, the same mixture of rhenafuran complexes was isolated. Upon attempting to react la with one equivalent of nitroethane in presence of an equivalent of triethylamine, oxygen insertion was observed instead of nucleophilic attack. Finally, complex la showed the same reactivity toward trimethylamine W-oxide as (CO) 4Re(r|2 -C3 Ph 3 ) ,43 affording a rhenafuran-type complex. The ratio of keto-coordinated (117) versus ester- coordinated complex (118) varied slightly depending upon the conditions, (equation 8 8 ) CH3 o c h 2 c h 3 c h 3 c h 2o c o 2 c h 3 0 \ OCH2 CH3 la 117 118 (eq 8 8 ) Oxygen atom transfer reagent: (NH^CefNO^g, DMSO, (CH 3 )3 NO, EtN02 /Et3N NH-group insertion reactions To extend the synthesis of rhenafuran-type complexes to analogous insertion- derived compounds, the preparation of a rhenapyrrole complex was attempted. a. Unsuccessful trials The first strategy to be considered was a ring expansion type of reaction. In 1972, Connor 122 reported the synthesis of an imine by the base-promoted proton transfer reaction as illustrated in equation 89: ph y v + |j ^ hexanc r fac(Pyr) 3 Cr(CO) 3 1 1 0 Similar conditions applied to a primary amine-derived rhenacyclobutadiene complex were anticipated to favor ring expansion leading to complex 123. However, refluxing the complex in hexane for as along as 18 h in presence of an excess of pyridine led to no reaction. While heating the complex in neat pyridine to 60°C overnight did not result in any reaction either, use of reflux temperature led to decomposition, (equation 91) CH3 CH3 I I excess pyridine I (CO)4Re‘^ — C02CH3 — ^ ► (CO)4ReX /^ 5y ^ ' C° 2CH3 m orneat / H p-tolyl ^ H 87d 123 (eq 91) b. Nucleophilic attack route Several examples of NH insertion into M=C bond of Fischer-type carbene complexes have been reported in the literature. They include the nucleophilic attack of the carbene center by hydroxylamine H 2NOH123 or sulfilimines NH=SPh 2 . 124 (equation 92) och 3 OCH3 (CO)5 C r = C + H2NOH (CO)5 C r N = C c h 3 c h 3 (eq 92) The treatment of fischer carbene complexes such as 2 affords nitrile complexes . 125 (equation 93) OCH3 (CO)5 C r = C + H2 N-N(CH3 ) 2 ► (CO)^Cr-----NCCH3 CH3 + CH3OH + (CH3)2NH (eq 93) Ill The insertion of a NH group into the M=C bond was observed in only one case illustrated in equation 94. OCH2 CH3 OCH2 CH3 OCH2 CH3 OCH2 CH3 (CO)4 C r ^ N S— \ + H2 N-N(CH3 ) 2 -► (CO)4Cr s -J 30% n h 2 OEt c h 3 c h 2 o ^ . c n NH .OEt .OCH2 CH3 / (CO)4Cr (CO)sCr S ^ + (COljCr------1 S + s 4% 7 % (eq 94) In light of these literature precedents, the product of the reaction was expected to be a rhenafuran complex 47. A subsequent bond rotation would result from chelation of the carbomethoxy substituent, (equation 95) i (CO)4R e ^ C 0 2 CH3 + H2 N-NR2 c o OCH 2 CH3 o c h 3 47 (eq 95) 112 c. General conditions 126 The first hydrazine that was considered for the proposed synthesis was 2,4- dinitrophenyl hydrazine. The presence of two electron-withdrawing groups on the phenyl substituent was anticipated to favor the N-N bond cleavage necessary in the insertion step. Indeed, the reaction proceeds at room temperature and is complete within 2 days. All starting material is converted into a single product 12 5, isolated by hexane extraction. Further purification can be achieved by chromatography through alumina (grade III). An orange precipitate, insoluble in hexane, was identified as 2,4-dinitroaniline (side product resulting from the N-N bond cleavage), (equation 96) H THF.RT (CO)4Re (CO)4Re C 0 2 CH3 + 2,4-N02 C6 H4 -NH-NH2 OCH2 CH3 c h 3 c h 2o c o 2 c h 3 la 125 (eq 96) d. Proposed mechanism Unlike in the case of linear Fischer carbene complexes, the nucleophilic attack does not occur at the heteroatom-stabilized carbene center. Instead, the proposed mechanism (scheme 34) involves nucleophilic attack at the Re=C(CH 3 ) center followed by a proton migration from one nitrogen atom to the other. This enhances polarization of the N-N bond. The formation of a three-membered ring is promoted by the presence of a good leaving group such as 2,4-dinitroaniline. Such a strained metallacycle was invoked to rationalize the N-N bond cleavage involved in the NR insertion into M=C bond using sulfilimines . 127 113 Scheme 34; Proposed mechanism of NH-insertion co 9H3 00 (f°^ ^ ’NH2+‘NH'Ar Rl e XA l A , > — C 0 2 CH3 + H2 N-NH-At c o 2 c h 3 OCX | Y OCH2 CH3 OCH2 CH3 CH3 CO c h 3 -NH2 +At (CO)4Re > - c o 2ch 3 C 0 2 CH3 O C ^ I o c h 2 c h 3 c o OCH 2 CH3 (CO)4 Re/ % CH3 CH20 c o 2 c h 3 e. Identification of the product The product was first identified by infrared and NMR spectroscopy. The presence of a NH group was confirmed by a broad absorption band at around 3350 cm-1. Four bands in the CO-stretching region were identified: 2095 (w), 1994 (s), 1943 (s) and 1695 (w) cm-i. These values are comparable to the wavenumbers recorded for the analogous oxygen-insertionmetallacycle 117 (IR spectrum in THF: 2101(w), 1999 (s), 1942 (s), 1727 (w), 1703 (w) cm-1). in the 1H NMR spectra (figure 11), the main differences between starting material and product are the following: the singlet corresponding to the methyl substituent is shifted upfield at 2.38 ppm and is split into a doublet (7<1 Hz). (For comparison, the methyl substituent in (CO) 5WHN=C(CH3 )OCH2 CH3 resonates at 2 .2 1 ppm.128) A broad singlet at 5 = 6.80 ppm accounting for one proton is assigned to the NH resonance. The proximity of the methyl and the NH groups was confirmed by the JL I Av_ n 1 ' 1 1 ' ■ • ■ ■ ■ I ■ ■ ■ ' I ‘ 1 ■ 1 I 1 1 ■ 1 I I ' ■ ■■ I 1—1 r I I I I I I—I I I I I | I I I |-| I T-I- I I J-I I I | I I I i | i * I I | I ■ I I [ > I I |- | I l-l I | I I I' I ( 1-1 I I I—T-T I < ■ 9-5 9-° 8-s ®-° 7-5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 .5 0.0 f ‘I'M Figure 11: 1H NMR spectrum of (CO)£Re=C(OCH 1 C H ^-C (C Q 2 CH 3 )=C fC H ^)N H — ..I... '— I— " "1.. '""I..... ” T ~ ™r~ 300 260 260 240 220 200 160 160 140 120 100 SO 60 40 20 PPH I I Figure 12: HCIlHI NMR spectrum of (COldRe^fOCHiCH^CfCOiCH^sCfCH^NH 116 Table 8 : Spectroscopic data of complexes 125 and 117 0 (CO)4 R e ^ j T ^ C^ ~ f c ~ c h 3 c h 2o c o 2 c h 3 c h 3 c h 2o c o 2 c h 3 IR ;n cmii (hexane) 3350 (mw), 2095 (m), (THF) 2101 (m), 1999 (s),1942 (s), 1994 (s), 1943 (s), 1695 (w). 1727 (w), 1703 (w). iHNM B 1-46 (t, J= 7.1 Hz, OCH2 CH3, 1.50 (t, J= 7.07 Hz, OCH2CH3 , WMK 2.38 (d, J- 0.3 Hz, CH3 ), 2.38(d,7=0.3Hz,CH3), 6 in ppm 3.74 (s, CO 7 CH1 ). 3.75 (s, CO2 CK3), fCDCl?! 4.41 (q, J= 7.1 Hz, OCH7 CH3 ), 4.53 (q, J= 7.07 Hz, OCHjCHa). 1 3} 6 . 8 (s, NH) 239.3 (s, C-OEt), 191.7, 258.53 (s, C-OEt), 191.10, iSCNMR tongas risCOV 189.97 (2s, cis CO), 8 in ppm 190.4 (s, C-CH3), 211.81(s,C-CH3), 0 2 f r n r t \ 1 8 5 8 (trans c o )> 1 6 6 3 £ °2 CH3). 185.19 (trans CO), 165.64 (s, C CH3), m 3 (s C.C0 2 CH3), 127.53 (s, C-C02 CH3), 67.8 (t, OCH 2 CH3), 51.0 (q, COzCHj), 78.15 (t, OCH 2 CH3), 51.25 (q, C O ^ H ^ , 26.2 (q, C-CH3), 15.6 (q, OCH2 CH3 ) 26.0 (q, C-CH3), 15.23 (q, OCH2 CH3) 117 collapse of the doublet at 8 = 2.38 ppm into a singlet upon selective irradiation of the NH signal. The 13C{1H} NMR spectrum (figure 12) confirmed a partial delocalization of the electrons over the metallacycle ( 8 (Re-C(OEt)) = 239.3 ppm). The presence of a free carbomethoxy substituent is confirmed by a singlet at 166.3 ppm, chelation being usually accompanied by a downfield shift to about 185 ppm. To illustrate the analogy between the two heteroatom insertion products, IR and spectroscopic data have been gathered in table 8. f. X-rav diffraction analysis The structure of 125, confirmed by X-ray diffraction analysis, supports the analogy between the two heteroatom insertion products. The crystals were grown by slow evaporation of solvent from CH 2CI2 solution of complex 125 saturated with hexane. An ORTEP drawing of the complex is presented in Figure 13. The crystals contained two independent molecules, different by the orientation of the carbomethoxy substituent. A hydrogen-bonding interaction between the ester carbonyl group and the NH group was supported by the average value of the N-C( 0 )0 CH3 bond distance, 2.936 A. The metallacycle was found to be almost planar. For example, if one considers the best four-atom plane in each of the two molecules of the crystal, the fifth atom is displaced by at most 0.16 A away from it. HH (CO)4 Re CH3CH2O C0 2CH3 CH3CH2O CO2CH3 E F A substantial delocalization of the electrons over the metallacycle is indicated by the following bond distances, even though resonance form F seems to be a more accurate representation of the complex. Indeed, Re-C 3 average bond distance of 2.182(6) A is 118 intermediate between typical values of Re-Csp2 (2.22 A) and Re=C sp2 (2.09 A ).129 The recorded average Re-N distance of 2.146 A is close to the values reported for the delocalized six-membered azarhenacycle J (2.145 A) and the non-delocalized five- memberedring H (Ar = P-C6 H4 OCH3 , R = 2,6-xylyl). However, the average value of Ci-N 1.296(7) A is closer to a typical C=N bond distance (1.27 A ) than a single bond (1.44 A ) .130 The sum of angles of 360° around the nitrogen atom supports a sp2 hybridization of the atom. Bond distances, and angles are provided in Table 9. A summary of the crystal data and the details of the intensity data collection and refinement are given in Tables 15 and 16 of the appendix. C C 1.390(7) This complex represents one of the few examples of five-membered ring azametallacycles (figure 14). R G OCH2 CH3 H I J Figure 14: Selected examples of azametallacycles 119 DeMeijere131 prepared some azachromacycles G, precursors of highly substituted cyclopentadienes. A series of non-delocalized azarhenacycles H was synthesized by thermal reaction of (CO) 4 Re(CH2 C6H4 X-p)(CNR) (X = Cl, OCH 3 , R = P-C6H4OCH3 , 2,6-xylyl) with triethylphosphine in acetonitrile . 132 Finally, tungsten azacycles I were isolated after treatment of a tungsten qM-azaallyl complex with alkyl isocyanides .133 However, no azametallacycles had been prepared by ring expansion reaction promoted by hydrazines. g. Reactivity of azarhenacvcle 125 The contribution of the resonance form E suggests an analogy between complex 125 and organic pyrroles. The pKa of the non-substituted pyrrole has been measured to be 17.5. The presence of CO ligands on the metal fragment and electron-withdrawing group CO 2 CH3 was anticipated to enhance the acidity of the NH proton. Moreover, non- cyclic imidate complexes such as (CO) 5WNH=C(OCH3)Ph were shown to be deprotonated by bases such as NaH, LiBu, NaOEt, and NaSEt. Surprisingly, however, the NH proton of complex 125 does not exchange with deuterium upon stirring in D 2 O, but can only be deprotonated with strong bases such as LDA. Attempts to alkylate the anion were unsuccessful. However, the solution of the deprotonated species could be quenched with a solution of 20% DC1 in D 2O at low temperature, (equation 97) H D (CO)4Re (CO)4Re THF, -78°C 2. DCI/D2 O CH3 CH20 C 02CH3 125 (eq 97) 120 06A 05A CUA N1A C4A C10A RE1A C9A C2A 01A C12A C3A C5A 07A 03A 02A C7A C8A C6A O* Figure 13: ORTEP drawing of fCOl£Re=CrOCH1CHO-CfCQ7CH2)=CfCH1lNH (125) Table 9: Selected bond distances (A) and angles (dea) for complex 125 Bond distances (A) Re(lA)-N(lA) 2.136(5) Re(lB)-N(lB) 2.133(5) Re(lA)-C(3A) 2.178(6) Re(lB)-C(3B) 2.185(5) 0(1A)-C(5A) 1.201(7) 0(1B)-C(5B) 1.188(6) 0(2A)-C(5A) 1.342(7) 0(2B)-C(5B) 1.326(7) 0(2A)-C(6A) 1.437(8) 0(2B)-C(6B) 1.446(7) 0(3A)-C(3A) 1.339(7) 0(3B)-C(3B) 1.345(6) 0(3A)-C(7A) 1.459(7) 0(3B)-C(7B) 1.440(6) N(1A)-C(1A) 1.287(7) N(1B)-C(1B) 1.304(7) C(1A)-C(2A) 1.439(7) C(1B)-C(2B) 1.438(7) C(1A)-C(4A) 1.496(7) C(1B)-C(4B) 1.495(8) C(2A)-C(3A) 1.394(7) C(2B)-C(3B) 1.385(7) C(2A)-C(5A) 1.467(8) C(2B)-C(5B) 1.488(7) _ ^ 122 Table 9; Selected bond distances (A) and angles (deg) for complex 125 Bond angles (deg) N( 1 A)-Re( 1 A)-C(3A) 73.9(2) N( 1B)-Re( 1B)-C(3B) 73.9(2) Re( 1A)-N(1A)-C(1A) 119.7(4) Re( 1B)-N( 1B)-C( IB) 120.0(4) N(1A)-C(1A)-C(2A) 116.8(5) N( 1A)-C( 1 A)-C(2A) 115.5(5) N(1A)-C(1A)-C(4A) 119.2(5) N(1B)-C(1B)-C(4B) 120.6(5) C(2A)-C( 1A)-C(4A) 124.0(5) C(2B)-C( 1B)-C(4B) 123.9(5) C(1A)-C(2A)-C(3A) 114.3(5) C( 1B)-C(2B)-C(3B) 115.4(5) C( 1A)-C(2A)-C(5A) 118.8(5) C( 1B)-C(2B)-C(5B) 122.6(5) C(3A)-C(2A)-C(5A) 126.9(5) C(3B)-C(2B)-C(5B) 122.0(5) Re( 1 A)-C(3A)-0(3A) 130.6(4) Re( 1B)-C(3B)-0(3B) 131.6(4) Re(lA)-C(3A)-C(2A) 115.3(4) Re(lB)-C(3B)-C(2B) 115.0(4) 0(3A)-C(3A)-C(2A) 114.1(5) 0(3B)-C(3B)-C(2B) 113.4(4) 123 Deuterium enrichment was confirmed in the 1H NMR spectrum by the disappearance of the broad singlet at 8 = 6 .8 ppm assigned to the NH proton as well as of the coupling on the methyl group. The 2H NMR spectrum contained a singlet at 8 = 6.98 ppm providing evidence for the deuteration of the NH group. h. Generality of the insertion reaction The same product can be obtained by treatment with two other electron-poor hydrazines: tosylhydrazine and hydrazine hydrochloride. The reaction in the latter case is slower, probably owing to solubility problems. Indeed only 50% conversion was observed after 24 h at reflux temperature of THF. (equation 98) THF C 02CH3 + R-NH-NH2 R-NH-NH2= Ts-NH-NH2i THF, RT, 2d R-NH-NH2= p-CH3-C 6 H4 -NH-NH2, THF, reflux, 24h (eq 98) However, when complex la was reacted with one equivalent of hydrazine monohydrate, a mixture of two complexes was observed. A major product 126 was contaminated with traces of complex 125. Purification could be effected by extraction of the impurities into hexane at 0°C. The product was isolated as a white solid only in 26% yield owing to losses sustained during the extraction step and handling of this static powder, (equation 99) 124 c h 3 c h 3 C 0 2 CH3 THF, 0°C to RT (CO)4R e ^ (CO)4Re f C 0 2 CH3 + H2 O.NH2 -NH2 overnight, 26% isolated / \ OCH2 CH3 H o c h 2 c h 3 126 + traces of complex 125 (eq 99) Characterization of the structure was achieved by IR, 1H and 13C{1H} NMR spectroscopy and analytical techniques. Upon comparing these data with those of the analogous oxygen atom insertion complex 118, it was concluded that complex 126 results from insertion of NH into Re-C(OCH 2CH3 ), Table 10 illustrates the analogy between the two compounds. The significance of the following chemical shifts will be pointed out: the carbon bonded to the metal resonates at 212.86 ppm. This value, although at higher field than for the oxygen-atom insertion product, indicates some partial carbenic character of the compound. The NH-C-OEt center resonates at slightly higher field than the carboxylic ester center, which is also a common trend for the free fragments. The 1H NMR spectrum confirms the partial carbenic character of the Re-C- CH3 center. Indeed, the singlet assigned to the methyl substituent is only shifted by 0.25 ppm to 2.82 ppm (3.07 ppm for complex la). In contrast, it was shifted by 0.69 ppm in the case of complex 125. Selective irradiation of the NH proton did not result in any change in the spectrum. 125 Table 10: Spectroscopic data of complexes 126 and 118 c h 3 c h 3 (CO)4 R e ^ j V ^ ' C°2 CH3 / \ H j26 OCH2 CH3 118 OCH 2 CH3 1.43 (t, J- 7.0 Hz, OCH2CH3 , 1.35 (t, J= 7.12 Hz, OCH2 CH3 , i l l NMR 2.82 (s, CH 3 ). 2.91 (s, CH 3 ), " 3.79 (s, CO 2CH3 ), 3.78 (s, C O ^K ,), 5 in ppm 4 . 1 3 (q, j= 7 . 1 Hz, OCH2 CH3 ), 4.39 (q, 7= 7.10 Hz, OCH 2 CH3). (CDCI3 ) 5.9 (s, NH) 212.86 (s, Re-CCH3), 191.34, 233.70 (s,Re-CCH3), 191.29, 12r NMR 191.02 (2s, cisCO), 189.56 (2s, cisCO), - C NMR l g 6 ? 4 (trang c0)> 187.55 (trans CO), 6 in ppm 179.65 (s,ReNHCOEt), 184.60 (s,ReOCOCH 2 CH3), fCDClil 166.21 (s, CO2 CH3 ), 165.25 (s, C0 2 CH3), K 3' 131.49 (s,C-C0 2 CH3), 128.62 (s, C-C 0 2 CH3), 62.62 (t,OCH2 CH3), 64.32 (t,OCH 2 CH3), 51.41 (q.C O ^H s), 51.60 (q.COjCHa), 33.82 (s, Re-C-CH3), 34.13 (s, Re-C-CH3), 13.69 (q, OCH2CH3) 14.05 (q,OCH2 CH3) 126 In many aspects, amino-substituted rhenacyclobutadiene complexes do not exhibit the same reactivity as alkoxyrhenacyclobutadiene complexes. For instance, upon treatment with PMe 2Ph, diethylamino-substituted rhenacyclobutadiene complex 87a undergoes CO-substitution reaction, and no ylide-type complex could be detected even by performing the reaction at low temperature. It cannot be deprotonated under the same conditions as the corresponding ethoxy complex. However, it reacts with alkynes such as dimethylacetylene dicarboxylate and affords [3+2] cycloaddition product 115 (experimental page 218). Upon investigating insertion reaction of diethylamino complex 87a, the following results were obtained. No reaction took place upon treatment with one equivalent of 2,4-dinitrophenyl hydrazine even after heating the reaction mixture to reflux temperature overnight, (equation 1 0 0 ) CH3 THF, reflux (CO)4 Re CO2 CH3 + 2,4-dinitrophenyl hydrazine No Reaction N(CH2 CH3 ) 2 87a (eq 1 0 0 ) However, when the complex was reacted with one equivalent of hydrazine monohydrate atO°C and the reaction mixture was slowly allowed to warm to room temperature, it was totally converted to a single product within 24 h. Complex 127 resulting from insertion into Re-C(CH 3 ) bond was isolated as a solid in 84% yield, (equation 101) CH, H THF, 0°C to RT (CO)4Re (CO)4Re C 0 2 CH3 + NH2 -NH2 H 2 O N(CH2 CH3 ) 2 (CH2 CH3)2N c o 2 c h 3 87a 127 (eq 101) pN TEG Ril 0 8. 0 6. 0 4. 0 2. . 0.0 0 1.0 .0 2 .0 3 .0 4 .0 5 .0 6 .0 7 .0 8 .0 9 iue 5 1 NR pcrm f (CO)£Re=CrN(CH of spectrum NMR 1H 15: Figure _AL u PI'H* OK J 2 r CH^)il-C(CO^CH^)=C(CHg)NH 128 The composition of the complex was determined by elemental analysis and mass spectrometry, and its structure elucidated by spectroscopy. The IR spectrum shows the presence of a band at 3380 cm -1 confirming the incorporation of a NH fragment. A broad band of medium intensity at 1685 cm -1 was assigned to a C=N stretching mode, supporting resonance form L. (CO)4Re (CO)4Re (CH3CH2)2N C02CH3 (CH3CH2)2N c o 2c h 3 K L The carbonyl region contains three bands at 2087,1990 and 1938 cm-1. According to the !H NMR spectrum (figure 15), the ethyl groups became equivalent upon insertion of the NH fragment. Indeed, whereas the two methyl groups in the starting material resonate as two distinct triplets at 6 = 1.26 and 6 = 1.37 ppm, only one triplet at 6 = 1.22 ppm, accounting for six protons, is observed for complex 127. A possible rationalization of this observation is that upon insertion the double bond character of (Re-)C=NEt 2 decreases. The chemical shift of NH proton ( 6 = 5.85 ppm) is comparable to the value observed for complex 126. The absence of coupling between the NH and the methyl group did not allow to rule out the insertion of the NH group into Re-C(CH 3 ) bond. However, the downfield shift of the methyl resonance compared to starting material (from 8 = 2.69 ppm to 6 = 2.85 ppm) was unexpected. A compound that is related to the other regioisomer 128 is reported in the literature. It results from the insertion of dimethylcyanamide into the metal-carbene bond of tungsten and chromium alkoxy carbene complexes . 134 However, no ^C^H} NMR data are available on these complexes. 129 CH3 c o 2 c h 3 (CO)4Re H N(CH2 CH3 ) 2 128 N(CH3) (CO)5 Cr— c: At (CO)5 C r = C . + (CH3)2N C = N VN = < OR (eq 1 0 2 ) The regiochemistry of the insertion is given support by a nOe experiment. Indeed, upon selective irradiation of the methyl singlet at 6 = 2.25 ppm a 4.4% enhancement of the NH singlet was observed. The singlet at 6 = 218.43 ppm was assigned to Re-C(NEt 2). Similar chemical shifts have been reported for the carbenic center in complexes I (page 118) (R = Me, 8 = 222.6 ppm; R = Et, 8 = 221.8 ppm ) . 134 i. Reactivity studies on rhenapvrrole complexes Most of the reactivity studies undertaken involved complex 125. Some of the transformations are presented below. As it has already been mentioned, the nitrogen atom could not be alkylated either by mixing the complex with a CH 2CI2 solution of triethyloxonium hexafluorophosphate or by using EtsOPFg after deprotonation reaction with LDA. (equation 103) H N, (CO)4Re Et3 OPF6 ,CH 2Cl2 NR or LDA, THF, -78°C then Et 3 OPFg, CH2 C12 c h 2 c h 3o c o 2 c h 3 (eq 103) 130 Attempts to cleave off the organic ligand under oxidative conditions were unsuccessful. For example, treatment of an acetone solution of the complex with 1.5 equivalents of cerium ammonium nitrate at room temperature did not affect the complex, (equation 104) Ce(Np3)6(NH4)2 ------► NR acetone, RT (eq 104) The unsaturated metallacycle is also inert toward cycloaddition to cyclohexadiene. When a toluene solution was treated with 2 equivalents of 1,3-cyclohexadiene and heated at reflux temperature for 16 h under argon or in a sealed tube, only starting material was observed.(equation 105) H .N. toluene, (co>4t r c:3 r ^ i ► NR /\ reflux, 16h c h 2 c h 3o c o 2 c h 3 (eq 105) In an attempt to cleave the organic fragment as a heterocycle arising from the insertion of one equivalent of alkyne, the complex was submitted to the following conditions. A THF solution of complex 125 was heated at reflux temperature of the solvent for 2.5 days in presence of one equivalent of 4-pentyn-l-ol. No transformation resulted. When a toluene solution of the complex was treated with one equivalent of phenylacetylene, and the mixture was heated at 100°C in a sealed tube for 12 h, starting material decomposed into an intractable mixture of products, (equation 106) 131 toluene, 16h _ - 1 h ► Decomposition reflux, sealed tube (eq 106) 132 IV- Summary The preliminary studies of the reaction chemistry of rhenacyclobutadiene complexes I (C0 )4 Re=C(R)-C(C0 2CH3 )=C(0 R') have ascertained the Fischer-type nature of these new compounds. Both carbons attached to the metal center exhibit electrophilic properties. The synthesis of a wide variety of complexes I was made possible by the modification of the original synthetic pathway and the derivatization of complex la. An investigation of novel aspects of the reactivity of I has not revealed any direct applications to organic synthesis that would complement the reactivity of Fischer carbene complexes. However, the uniqueness of the system was illustrated in the observation of [3+2] cycloadditions with alkynes and the characterization of various 5- membered ring expansion rhenacycles via rearrangement or insertion reactions. 133 PART B: ORGANOPLATINUM COMPLEXES The characterization of neutral complex 7 8 as a trimethylenemethane complex (TMM) of platinum opened a new area of possible applications to synthesis. The zwitterionic structure of the complex was anticipated from the nature of the substituents on the ligand. The spectroscopic data of the compound suggested its zwitterionic structure. The first objective of the project was to establish the hapticity of the ligand by X-ray diffraction techniques. Indeed, all transition metal trimethylenemethane complexes isolated to this point showed a q4-bonding mode instead of a rj3_type structure.56a Moreover, no group 10 LnM(trimethylenemethane) transition metal complex was structurally characterized in spite of the implication of such an intermediate in palladium- promoted [3+2] cycloadditions to electron-deficient olefins. 1- Spectroscopic characterization of complex 78 The 1H and 13C{1H) NMR spectroscopic data suggest an intermediate structure between a q 3-allyl M and a platinacyclobutane structure N . Indeed, while the 1H NMR spectrum (figure 17) displays three allylic resonances at 5.38, 4.00, and 2.60 ppm, the CH2 group exhibits a coupling constant of 4.2 Hz, a value that would be compatible with a platinacyclobutane-type structure . 135 The broad singlet at 8 = 5.38 ppm, assigned to C/2Ph, and the absence of platinum satellites support an overall syn addition of the carbanion across the coordinated triple bond. The mechanism of addition has not been elucidated. Attempted labeling experiment involving NaCD(C 0 2 CH3>2 (>98% deuterium) did not result in any substantial deuterium incorporation at the CPh center. The two CO2CH3 groups resonate as a sharp singlet at 8 = 3.49 ppm. The presence of a single resonance in the 13c{1H} NMR spectrum confirmed the existence of a fluxional phenomenon. In order to establish the nature of the fluxionality and calculate the energy I ' T i J ’■' I ’ ’ I * i • I ’ ■ r ■ ~-r* I i ’I1-- "T™ "T“ ~ r ~ 30.0 34.0 32.0 30.0 26.0 24.0 2 2 .0 18.0 16.0 14.0 12.0 10.0 6 .0 4.0 2.0 Figure 16: 31PI1H> NMR spectrum of (PPh^frPt^-’CHgCfCfCOiCH^glCHPh} to A Figure 17: 1H NMR spectrum of fPPh^HptlT1- CHl crCfCQl CH^ l1CHPh> 136 barrier value, a CH 2 CI2 sample of the complex was prepared, and a variable temperature 1H NMR experiment was conducted. As the temperature was lowered, no broadening was observed until 223 K. Coalescence was found to occur at around 173 K. Even at 163 K, no complete separation could be obtained, but two broad singlets were overlapping. Based on the frequency values recorded on the spectrum at 163K, a free energy of activation AG$ = 8.4 kcal/mol was calculated . 136 The splitting pattern on the other allylic protons was not altered, indicating that the equivalence of the two groups likely results from a rapid rotation around the C-C bond instead of an inversion of the trimethylenemethane ligand as reported for oxatrimethylenemethane by Kemmit and coworkers.57c For comparison, the value calculated for the analogous azatrimethylenemethane complex (PPh 3 )2 Pt(rj3 -CH2CNArCHPh) (129) is 13.5 kcal/mol, the coalescence being observed at 278 K . 137 The room-temperature 13C{lH} NMR spectrum of complex 78 is better interpreted by a r]3-allyl type structure than a platinacyclobutane-type structure. Indeed, the chemical shifts and coupling constants observed for the three allyl carbon atoms are closer to typical values for allyl carbon centers 138 than to typical values for platinacyclobutane carbon atoms. The two doublets at 6 - 70.7 and 46.6 ppm (Jptp = 227 Hz and Tptp = 159 Hz) are assigned to CHPh and CH2 , respectively. The central carbon is associated with a resonance at 6 = 149.2 ppm with a coupling constant of 91 Hz. CII3 O2 C . .C 0 2 CH 3 CH 3 O 2 C co 2ch 3 / \ / \ Ph3P PPh3 Ph3P PPh3 M N 137 II- X-Rav diffraction analysis of complex 78 139 Crystals suitable for X-ray diffraction studies were grown by slow evaporation of solvent from a CH 2CI2 solution of the complex saturated with toluene. Each asymmetric unit was shown to contain two platinum complexes, a molecule of toluene, and a half of a molecule of THF, residual solvent from the synthesis. The two crystallographically independent molecules differ in the orientation of the CO 2CH3 groups. Bond distances, and angles are provided in Table 11. A summary of the crystal data and the details of the intensity data collection and refinement parameters are given in Tables 17, and 18 in the appendix. A ORTEP drawing of the compound is presented in figure 18. While several trimethylenemethane transition metal complexes had been structurally characterized, no group 10 LnM(trimethylenemethane) complex had been isolated and fully characterized .563 The hapticity of the ligand is the first feature to be pointed out. Bond lengths confirm that the trimethylenemethane (TMM) ligand is attached to the metal in a t]3- rather than a r^-fashion as it had been suggested by Trost 6 1 1 4 0 and Albright141. The phenyl substituent is anti to the central substituent as expected from the 1H NMR spectrum pattern observed for the CWPh. Moreover, it is pointing away from the metal center. However, as it was suggested by spectroscopic data, the structure is intermediate between that of aT]3-allyl and a platinacyclobutane complex. For instance, the average angle Ci- C2-C3 is 107.0(9)°, a value that is intermediate between that of a rp-allyl complex (1 2 0 ° )142 and the platinacyclobutane complex (Et 3 P)2Pt(Ti2-CH2C(CH3 )2 CH2) (97.5(5 ) ° ) . 143 The average value of the dihedral angle between the Ci-Pt-C 3 and C 1-C2- C3 planes is 59.9°, that is close to the values observed for Y]3-allyls (61-720)144, rj3- oxoallyls (Ph 3 P)2Pt(T)3 -CH2 C(0 )CH2) (51.0°)145, ( P h 3 P)2 Pt(Ti3- CH(C0CH3)C(0)CH(C0CH3)), 48.0(4)°146, and (Ph 3 P)2Pt(ri3- CH(C0 2 CH3)C(0 )CH(C0 2 CH3)) 50.4(4)° 147, or Tp-iminoallyls Figure 19: ORTEP drawing of complex 78 139 Table 11: Selected bond distances (A.) and angles (deg) for (78V>.PhMe.l/2 THF Bond distances Pt(lA)-P(lA) 2.279(3) Pt(lB)-P(lB) 2.280(3) Pt(lA)-P(2A) 2.307(2) Pt(lB)-P(2B) 2.31192) Pt(lA)-C(lA) 2.126(9) Pt(lB)-C(lB) 2.149(9) Pt(lA)-C(2A) 2.348(10) Pt(lB)-C(2B) 2.352(9) Pt(lA)-C(3A) 2.146(11) Pt(lB)-C(3B) 2.146(10) C(1A)-C(2A) 1.45(1) C(1B)-C(2B) 1.46(1) C(1A)-C(9A) 1.52(1) C(1B)-C(9B) 1.50(1) C(2A)-C(3A) 1.43(1) C(2B)-C(3B) 1-47(1) C(2A)-C(4A) 1.44(2) C(2B)-C(4B) 1.38(1) C(4A)-C(5A) 1.42(2) C(4B)-C(5B) 1.46(2) C(4A)-C(7A) 1.62(2) C(4B)-C(7B) 1.47(2) C(4A)-C(7AA) 1.37(2) 0(1B)-C(5B) 1.2 0 (1 ) 0(1A)-C(5A) 1.2 2 (2 ) 0(3B)-C(7B) 1.2 1 (2 ) 0(3A)-C(7A) 1.13(3) 0(3AA)-C(7AA) 1.27(3) Table 11; Selected bond distances (A1 and angles fdeel for 140 f78^.PhMe.l/2 THF Bond angles P( 1 A)-Pt( 1 A)-P(2 A) 100.31 (9) P(lB)-Pt(lB)-P(2B) 99.19(9) P( 1 A)-Pt( 1 A)-C( 1 A) 100.2(3) P( 1B)-Pt( 1B)-C( IB) 100.5(3) P(1A)-R(1A)-C(2A) 132.1(3) P(lB)-Pt(lB)-C(2B) 131.4(2) P( 1 A)-Pt( 1 A)-C(3A) 165.8(3) P(lB)-Pt(lB)-C(3B) 166.7(2) P(2A)-Pt( 1 A)-C( 1 A) 159.4(3) P(2B)-Pt( 1B)-C( IB) 160.2 (3) P(2A)-R( 1 A)-C(2A) 123.2(3) P(2B)-R(1B)-C(2B) 124.0(2) P(2A)-Pt( 1 A)-C(3 A) 93.7(3) P(2B)-Pt(lB)-C(3B) 94.1(2) C( 1 A)-Pt( 1 A)-C(2A) 37.5 (4) C(lB)-Pt(lB)-C(2B) 37.4(3) C(lA)-Pt(lA)-C(3A) 65.9(4) C(lB)-Pt(lB)-C(3B) 66.3(3) C(2A)-Pt( 1 A)-C(3 A) 36.7(4) C(2B)-Pt(lB)-C(3B) 37.8(3) Pt( 1 A)-C( 1 A)-C(2A) 79.6(5) Pt(lB)-C(lB)-C(2B) 78.9(5) Pt( 1 A)-C( 1 A)-C(9A) 116.3(7) Pt(lB)-C(lB)-C(9B) 115.8(6) C(2A)-C(1A)-C(9A) 116.1(9) C(2B)-C(1B)-C(9B) 119.0(8) Pt( 1 A)-C(2A)-C( 1 A) 62.9(5) R( 1 B)-C(2B)-C( IB) 63.7(5) Pt( 1 A)-C(2A)-C(3 A) 63.9(6) R(1B)-C(2B)-C(3B) 63.5 (5) Pt( 1 A)-C(2A)-C(4A). 124.9(7) R( 1B)-C(2B)-C(4B) 126.7(7) C( 1 A)-C(2A)-C(3 A) 107.4(9) C( 1B)-C(2B)-C(3B) 106.7(8) C( 1 A)-C(2A)-C(4A) 123.0(9) C( 1B)-C(2B)-C(4B) 125.9(9) C(3A)-C(2A)-C(4A) 127.0(10) C(3B)-C(2B)-C(4B) 125.7(9) Pt( 1 A)-C(3 A)-C(2A) 79.3 ( 6 ) R(1B)-C(3B)-C(2B) 78.8(5) C(2A)-C(4A)-C(5A) 1 2 0 (1) C(2B)-C(4B)-C(5B) 1 2 1 (1) 141 Table 11 (continued) C(2A)-C(4A)-C(7A) 117(1) C(2B)-C(4B)-C(7B) 1 2 1 ( 1) C(2A)-C(4A)-C(7AA) 125(1) C(5B)-C(4B)-C(7B) 118(1) C(5A)-C(4A)-C(7A) 123(1) 0( 1B)-C(5B)-0(2B) 1 2 1 ( 1 ) C(5A)-C(4A)-C(7AA) 1 1 1 ( 1) 0(5B)-C(5B)-C(4B) 126(1) 0(1A)-C(5A)-CX2A) 119(1) 0(2B)-C(5B)-C(4B) 113(1) 0( 1 A)-C(5A)-C(4A) 127(1) 0(3B)-C(7B)-0(4B) 1 2 0 ( 1) 0(2A)-C(5A)-C(4A) 114(1) 0(3B)-C(7B)-C(4B) 126(1) 0(3A)-C(7A)-0(4A) 125(2) 0(4B)-C(7B)-C(4B) 113(1) 0(3AA)-C(7AA)-0(4AA) 117(2) 0(3A)-C(7A)-C(4A) 126(2) 0(3AA)-C(7AA)-C(4A) 128(2) 0(4A)-C(7A)-C(4A) 109(2) 0(4AA)-C(7AA)-C(4A) 115(2) 142 [(Ph 3 P)2P t^ 3-CH2 C(NMe2)CH2 ]BF4j 54(2)° and [(Ph 3 P)2PtCn 3 -CH2 C(NHi- Pr)CH2 ]Br, 57(2)°148. For comparison, the puckering in platinacyclobutanes is illustrated by dihedral angles ranging between 0 and 30°.149 Calculations for a rp-TMM-transition metal complex where the TMM ligand would be planar indicated a dihedral angle of 96°. Electron-delocalization, as expected inat]3-allyl type complex, is indicated by the average value for the C-C bond distance on the allyl skeleton of 1.45 A. Whereas this bond distance averages ca. 1.40 A for typical allyl complexes, it is significantly longer in platinacyclobutane complexes (C-C single bonds). The contribution of the r^-allyl form is also obvious from the value of the Pt-Ci (2.138(9) A) and Pt-C 3 (2.146(10) A) distances that are close to the typical values for platinum rp-allyl [(PCy 3 )2Pt(r|3- CH2CHCH2)]PF6 (2.17(5)A)150 and Tp-oxoallyl (Ph 3 P)2Pt(il3-CH2-C(0 )-CH2) (2.132(12) A) complexes. In contrast, the average value for the platinacyclobutane complex (Et 3P)2Pt(T]2-CH2-C(CH3 )2-CH2) is 2.083(6) A. On the other hand, the Pt-C 2 bond distance 2.350(10) A, 0 2 1 A longer than the Pt-C(terminal) bonds, is comparable to the value measured on the r^-allyls or rj3-oxoallyls, and shorter than the non-bonding distance characteristic for platinacyclobutane complexes, e.g., (Et 3 P)2Pt(r|2-CH2- C(CH3 )2-CH2) (2.76 A). This is consistent with the observation of a Jptcvalue of 91 Hz for the allylic central C atom ( 6 = 149.2 ppm). The coordination around the platinum center is nearly square planar with a dihedral angle between the Ci-Pt-C 3 and Pi-Pt-P 2 planes of only 3.2°. This type of coordination is favored for l^M ^-allyl) complexes according to calculations carried out by Albright and co-workers . 151 However, the partial pyramidalization of various centers of the ligand shows the presence of a hybrid structure. Thus, the sum of the angles around Ci and C 3 (347°) and around C 2 (357.8°) provides evidence for the metallacyclobutane resonance form. The pyramidalization of C 2 is substantial based on 143 the fact that C 4 is located about 0.31 A away from the C 1-C2-C3 plane and the torsion angle between the planes C 1-C2 -C3 and C 5 -C4 -C7 is 18.2°. Shortly after the structure of (Ph 3P)2 Pt0 i3-CH2 CC(CO2CH3)2CHPh) (7 8 ) was elucidated, Chen and coworkers published the structure of the related Pd complex (Ph 3 P)2 Pd(r)3-CH2CC(C0 2 CH3 )2CH2) (1 3 1).50 The compound was prepared similarly to the platinum one. However, the proposed rp-propargyl complex intermediate was neither isolated nor characterized, (equation 107) CH30 2 C C0 2CH3 4 Ph 3 P. PhaP^ \ Bf CH(C0 2CH3)2 Ph3P Br PPh 3 \) Ph3P PPh 3 130 131 (eq 107) A brief discussion of the X-ray diffraction analysis was provided in the communication. It illustrated the similarities between the two compounds 78 and 131. Indeed, the average C-C bond distance is shorter than 1.45 A, the dihedral angle between the planes C 1-C2 -C3 and Pi-Pd-P 2 is 62.5 (1)°, and the ligand arrangement around the metal center is nearly square planar. All these support a r|3-allyl type representation of the complex. The value of Pd-C 4 distance (3.38(6) A) rules out any bonding interaction between the metal center and the fourth atom of the TMM ligand. The average value of C 2 -C4 of 1.41 A in 7 8 , intermediate between a Csp 2-Csp2 single bond (1.48 A) and a Csp 2=Csp2 double bond (1.32 A ), 152 indicates partial localization of the negative charge on C 4 . This was expected based on the presence of the two electron-withdrawing groups and the low barrier to rotation around C 2-C4 bond observed by variable temperature NMR experiment. It was thought that the zwitterionic structure would enhance the reactivity of the complex toward activated alkenes and make 144 it a good substrate for cycloaddition reactions. Preliminary studies on 7 8 , based on the extensive work carried out by Trost and coworkers59b with palladium, were then undertaken. HI- Reactivity of (Ph^PhPtfni-CHiCaCOiCH^CHPh) (781 with unsaturated reagents III-l Preliminary results Based on literature precedence, the expected outcome of the reaction was a cycloadduct combining the allylic moiety and the unsaturated substrate which might stay coordinated to the platinum fragment if only one equivalent of alkene or alkyne is used. (Scheme 35) Scheme 35: Expected f3+21 cycloaddition involving complex 78 and electron-deficient olefins Ph EWG Ph Ph Ph EWG Complex 7 8 was treated with several electron-deficient alkenes and alkynes such as diethyl fumarate, fumaronitrile, malononitrile, phenyl vinyl sulfone and 145 dimethylacetylene dicarboxylate. No reaction was initiated by stirring the reactants at room temperature. However, upon refluxing a solution of the reactants in benzene for an average of 18 h, all starting metal complex was consumed. The reactions were monitored by 3ip{lH} NMR spectroscopy. In each case, the characteristic broad singlets with platinum satellites were replaced with a singlet with platinum satellites for symmetrical reagents, and two doublets with platinum satellites for unsymmetrical reagents. The observed coupling constants are summarized in Table 12. Table 12; HPIIHI NMR chemical shifts and coupling constants of fPPh^l^Ptfnl-olefin) complexes resulting from reactions of complex 78 with electron-deficient alkene and alkvnes Reagents Chemical Shift 6 in Coupling Constant ppm JvtV* J w Hertz Dimethylacetylene dicarboxylate 24.8 3834 (Jptp) Maleic Anhydride 23.34 3722 (JptP) Diethyl Fumarate 25.8 3863 (Jptp) Phenyl Vinyl Sulfone 30.45, 27.45 3540 (7PtP), 3945 (Jptp), 32.5 Gfo) The platinum-containing compounds were isolated, purified by recrystallization, and analyzed by NMR spectroscopy. The 1H NMR chemical shifts and integration indicated the formation of a bis(triphenylphosphine)Pt^-alkene/alkyne) complex. For example, the dimethylacetylene dicarboxylate-derived complex was characterized by a singlet at 6 = 3.3 ppm accounting for six protons which was assigned to the two carbomethoxy groups. In addition, there was a multiplet in the aromatic region. The 146 assignments were confirmed by comparison with NMR data (chemical shifts and coupling constants) available in the literature.69153 C 0 2 CH3 Ph 3 P, pt 31P NMR: 23.8 ppm, Jw = 3722 Hz Ph3P c o 2 c h 3 CE&Q H Ph 3P ^ Pt 31P NMR: 23.8 ppm, J*P = 3869 Hz H C 0 2 CH3 PhsP. Pt 31P NMR: 27.4 ppm, 28.5 ppm, Ph3P JPP= 39.7 Hz, yp,p= 4089 Hz, 3575 Hz. H' COzCH3 Even upon reacting complex 78 with one equivalent of alkyne or alkene, no other platinum-containing complex was identified. This suggested that the alkene or alkyne was not incorporated in the organic product of the reaction. Since all of these reagents appeared to react similarly with complex 78, only one system was selected for full characterization of its products. III-2 Reaction of complex 78 with diethyl fumarate The reaction attempted in several solvents (THF, CH 2 CI2 , benzene, DMF) was found to be clean in benzene at reflux temperature, even though it proceeds very slowly at room temperature. Monitoring the reaction by 31P{ 1H} NMR showed that conversion of the starting material to the bis(triphenylphosphine)platinum( 0 ) complex 132 (equation 108 page 148) takes typically about 18 h. The transformation is complete by 31P{1H} NMR spectroscopy. However, when the reaction was conducted on a small scale, the complex was isolated in only ca. 75% yield after precipitation from Et 2 0 solution and 147 recrystallization from CH2Cl2/Et20- The nature of the platinum complex was confirmed by NMR and mass spectrometry. The 1H NMR spectrum exhibits characteristic resonances of a coordinated olefin, in addition to a multiplet in the aromatic region: the olefinic protons resonate at 4.18 ppm as a doublet (Jpn = 3.5 Hz, JptH = 56 Hz). The ethyl methylene groups are accounted for by two multiplets at 5 = 3.92 and 3.43 ppm. The methyl groups, however, are equivalent as a lone triplet at 6 = 0.75 ppm, J = 7.06 Hz. The 13C{tH> NMR resonances of the olefinic carbon and the carbomethoxy carbonyl group provide evidence for some interaction with the metal: 173.0 (t, 7pt-c = 39.6 Hz, CO 2CH3 )) and 49.01 (t, JP.C = 13.5 Hz, 7Pt.c = 215.6 Hz, =CH(OEt)). The isolation of the organic product 133 in this reaction required several extraction steps to achieve complete separation from the platinum complex. This procedure resulted in a low yield of the compound (53%). A mixture of two cycloadducts is usually obtained after precipitation of the complex with a 1:1 mixture of Et 2 0 /hexane followed by extraction with hexane. The analysis of the !H NMR spectrum showed that they both result from the dimerization of the trimethylenemethane ligand. One contains two exo double bonds (133), and the other corresponds to its isomer with two endo double bonds (134). [Pt] CH3 O2 C C 0 2 CH3 CH3 O2 C . C0 2 CH3 Ph ^ c o 2 c h 3 Ch3 The ratio of the two products varied depending on the trials. It was found that the isomerization occurs partially during the reaction (thermal conditions) or can be promoted by elution of the mixture through a silica gel column . 154 148 CHaOiC.^COjCHg H C 0 2 CH2 CH3 Benzene, ► + Reflux, 18h ^ Ph CH3CH202C Pt / \ Ph3P PPh 3 H C°2CH2CH3 ci ^QjC C 0 2 CH3 CH3 O2 C c o 2 c h 3 Ph Ph Ph 3 P,\ IPt- / Ph3P Ph H3C CH3CH202C h CH30 2 C c o 2 c h 3 c h 3 o 2c SiO-? 132 133 134 (eq 108) The 1H NMR spectrum of dimer 133 exhibits two vinylic doublets at 6 = 6.23 ppm and 6 = 4.65 ppm with Jgem - 2.9 Hz and an allylic triplet at 8 = 5.77 ppm, Jallylic = 2.6 Hz, assigned to -CHPh. The isomerization of the double bond results in the presence of a singlet at 8 = 2.65 ppm. In both compounds, the carbomethoxy groups resonate as two singlets, at 8 = 4.02 and 3.78 ppm for cycloadduct 133, and 8 = 4.16 and 3.83 ppm for cycloadduct 134 (figure 19). The electron impact (El) mass spectrum of the compound confirmed the dimerization of two trimethylenemethane ligands with the presence of a parent peak at 492 and an intense peak at 246 corresponding to M+/2. The 13C{1H} spectrum of complex 134 is in agreement with the proposed structure. (Figure 20) Upon reviewing the literature, no example of such a transition metal-promoted coupling could be found. The only reaction that can be related to this coupling is the dimerization of two oxoallyl fragments . 155 (equation 109) Upon attempts at isolation of oxallyl 13 5 at low temperature, only a dimerization product 136 was observed. n 1 1~-T' T "1T TTT t T* T"r T 1 1 1 1 r-j—• 9.5 ■ l * *rT * « I ' I r T _1 r T ~ 1 » I » » 1 »1 1 1 1 I .... 1 1 ! 1 1 ' 9.0 6.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.0 3.53.0 2.5 2.0 1.5 1 .0 .5 0.0 Figure 19; 1H NMR spectrum of cycloadduct 134 in CDsCN *r*r i h i vmurf ^vn>»«iivw'i»»> 1 , . ,--- -r 220.0 200.0 100.0 160.0 140.0 120.0 100.0 BO.O 60.0 40.0 20.0 Figure 20; IlCflHV NMR spectrum of cycloadduct 134 in CD 3 CN 151 + PPN+Cr(CO)4 NO‘ -90°C c h 3 135 136 (eq 109) The observed connectivity in 136 is rationalized by consideration of the rules of pericyclic cycloadditions. Two mechanisms are proposed to account for the dimerization of the fragment: either an oxyallyl-oxyallyl combination or the interaction between one oxyallyl and a precursor. The latter, however, was ruled out based on the stereochemical consideration of 136. The influence of the external olefin in the process was illustrated by the stability of the starting material when it was heated to the reflux temperature of benzene in the absence of diethyl fumarate. Whether it actually initiates the dimerization of the trimethylenemethane ligand or prevents the retrodimerization process by irreversibly complexing the platinum fragment was not ascertained. Scheme 36 shows a possible mechanism: 152 Scheme 36: Proposed mechanism of dimerization of the TMM ligand ,C02Et / Et02C C 0 2 CH3 Co 2Et Ph3P PPh 3 4 P t X CH3 O2C- W Ph/ w N pph,COjEl h 3 c o 2c . c o 2 c h 3 ,co 2 c h 3 c h 3 o 2c ,co 2 c h 3 Diethyl fumarate Pt(PPh 3 ) 2 ► CH30 2 C c o 2 c h 3 CH30 2 C c o 2 c h 3 + (PPh 3 )2 Pt(ri2 -Et02 C(H)C=C(H)C02 Et) + 2 (PPh 3 )2 Pt(ri2 -Et02 C(H)C=C(H)C02 Et) Chen and coworkers published some preliminary reaction chemistry of the analogous palladium zwitterionic complex 131.50 Among the few examples presented, it was shown that maleic anhydride reacts differently with the palladium system than with the platinum system, undergoing a [3+2] cycloaddition reaction. However, the versatility of the palladium system was not obvious from the selection of substrates. The conditions necessary to perform cycloadditions on complex 7 8 are not substantially more forcing than those used in the cycloadditions promoted by palladium (Bifunctional Conjunctive Reagents or "BCR"). Some Pd-promoted cycloadditions 153 indeed require reflux temperature of dioxane or xylene over a longer reaction time to be complete. It was anticipated that the use of a more electron poor olefin or a more polarized double bond might be sufficient to initialize a polarized stepwise cycloaddition. An example is the use of a polarized imine in the palladium-catalyzed cycloaddition of TMM precursors to imines (equation 1 1 0 ) :156 Si(CH3 ) 3 Pd(OAc) 2 (i-PiO)3P,THF,65°C 84% c o 2 c h 3 (eq 1 1 0 ) III-3 Reaction of complex 78 with tetracyanoethylene The first electrophile tested was tetracyanoethylene (TCNE). This highly activated olefin had been successfully used in various cycloaddition reactions , 157 even though electron transfer processes had precluded its use in TMMpalladium-catalyzed cycloaddition reactions . 158 The reaction was found to proceed at room temperature in benzene, (equation 111) Complete conversion of the starting material is observed within 1.5 h. The formation of a small amount of dark solid has been attributed to some electron transfer decomposition process. This material forms even upon using freshly sublimed TCNE and protecting the reaction mixture from light. C 0 2 CH3 CttjOzr <^o2 c h 3 C H ^C NC CN ,CN CH2 C12, Ph CN + CN RT, 1.5h Ph I CN NC CN Pt Ph 3 P / ^ P P ^ 137 (eq 111) 154 The completion of the reaction was monitored by 3ip{lH} NMR spectroscopy. The starting material was converted into a compound containing two inequivalent phosphines resonating at 8 = 21.1 ppm, Jptp = 3430 Hz, and 8 = 21.9 ppm, Jptp = 3930 Hz, Jpp = 22.2 Hz (figure 21). The presence of two inequivalent phosphines was indicative of a different reactivity from that of diethyl fumarate, since q 2. (TCNE)bis(triphenylphosphine)Pt(0) is symmetrical and shows only one 3lp{lH} NMR signal ( 8 = 15.3 ppm, 7ptp = 3745 Hz ) . 159 However, the chemical shift values and the coupling constants suggested the formation of a platinum olefin complex. The reaction was found to be clean when one equivalent of electrophile is involved. The product was isolated in 58% yield, after removal of decomposition solid by filtration and precipitation from Et 2 0 . The structure of the compound was shown by IR, NMR and elemental analysis to result from [3+2] cycloaddition involving the centers "C(C 0 2 CH3 )2 " and "CH2 " of the TMM ligand. The !H NMR spectrum (Figure 22) indicated the presence of two inequivalent carbomethoxy groups at 8 = 3.68 and 2.52 ppm. The unexpected upfield chemical shift value, 2.52 ppm, was rationalized by the proximity of one of the carbomethoxy substituents to the metal . 160 In addition to a multiplet in the aromatic region assigned to the two phosphine ligands and the phenyl substituent of the exo double bond, three resonances account for the three other protons of the complex. A doublet at 6 = 6.19 ppm with Jpn = 9 Hz and JptH = 25 Hz corresponds to the ethylenic proton. The coupling constants associated with the other two broad resonances at 8 = 3.04 and 2.16 ppm were inferred from selective decoupling experiments. Upon irradiation of the multiplet at 8 = 3.04 ppm, the multiplet at 8 = 2.16 ppm collapsed to a doublet with Pt satellites allowing to calculate the coupling constants Jpn = 12 Hz and JptH = 45 Hz. Upon irradiation of the multiplet at 8 = 2.16 ppm, a doublet with Pt satellites was obtained (Jpn = 30 Hz). The value of JptH could not be calculated. These 55.0 50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 -5.0 -10.0 -15.0 PPM I------1 Figure 21: 3jp OH> NMR spectrum of fPPh 1 )1 PtlT|2 -CfPh)H=CCH 1 CfC N )1 C(CN)2 C(C 0 2 CH 3 ) 2 > & i ------1- I ...... I 3.0 2,0 1.0 0.0 e.o 7.0 o.o 5.0 PPM 4.0 > ~ 1 Figure 22: IH NMR spectrum of rPPh^nPUriZ-CfPhm^CH^CfCN^CfCNl^CrCO^CH^ & 157 two patterns correspond to the inequivalent protons of the methylene group of the cycloadduct. The 13C{1H} NMR spectrum provides strong support for the proposed structure. Among the two distinct resonances at 6 = 171.14 and 170.54 ppm assigned to the carbomethoxy carbonyl groups, only one of them displays platinum coupling. The inequivalence of the subtituents is confirmed by the presence of two singlets at 50.03 and 51.68 ppm. The incorporation of one equivalent of TCNE is evidenced by the presence of four CN resonances at 8 = 112.19, 111.58, 110.95, and 110.8 ppm as well as the presence of two quaternary carbons at 44.8 and 43.85 ppm. III-4 Reaction of complex 78 with p-toluenesulfonyl isocyanate (TSI) If the charge separation in complex 7 8 is significant, a stepwise cycloaddition would be favored with more polarized unsaturated reagents. For example, pyrrolidines have been successfully prepared by palladium-promoted cycloaddition reactions of TMM precursors with activated imines . 156 Isocyanates have been involved in cycloadditions to oxatrimethylenemethane complex of palladium . 161 Where oxatrimethylenemethane palladium complex 138, (PPh 3 )2Pd(-q3 -(CH3 )2CC(0 )CH2), fails to react with olefins bearing an electron-withdrawing group owing to the low nucleophilicity of the negative oxygen, it does react with aryl isocyanates on a catalytic scale, (equation 1 1 2 ) 5 mol% Pd(PPh3)4 toluene reflux (eq 112) Phenyl isocyanate had also been used in the Pd(0)-catalyzed cycloaddition of activated vinylcyclopropanes . 162 Disappointingly, phenyl isocyanate is inert toward complex 78. Even after heating the reaction mixture overnight at reflux temperature of benzene, starting material was left unreacted. p-Toluenesulfonyl isocyanate (TSI), a more reactive 158 isocyanate, was then considered. It had previously been shown to participate in cycloaddition reactions to Tjl-propargyl transition metal complexes. I57d Treatment of complex 7 8 with three equivalents of TSI overnight at room temperature results in the formation of a platinum-containing complex 139 and an organic cycloadduct 140. (equation 113) 140 + (Ph 3 P)2 Pt(TSI) 2 139 (eq 113) In the in situ 31P{1H} NMR spectrum of the CH 2 CI2 reaction solution, starting material has been replaced with a complex containing only one phosphine or equivalent phosphines (5 = 5.03 ppm, s, Jptp = 3704 Hz). Compound 139 was found to be insoluble in THF. Therefore, it could be isolated as a white solid by stirring the crude mixture in a small volume of THF at room temperature. The 1H NMR spectrum of the complex indicates the presence of a singlet at 6 = 2.28 ppm and a multiplet in the aromatic region in a ratio 3:19 that corresponds to one PPI 13 to one p-toluenesulfonyl isocyanate. The 13C{1H} NMR spectrum of the complex shows the presence of a tolyl group with a singlet at 6 = 21.3 ppm. However, no definite carbonyl resonance of a TSI ligand could be assigned. The same compound was previously observed in a totally different reaction mixture . 163 (equation 114) Mononuclear Ru complex Benzene, RT + TSI ► + Mononuclear Pt complex 139 ''R u — Pt(PPh3)2 ocr (eq 114) 159 The mass spectrum of complex 139 contains its highest peak at m/e 1087 that most likely corresponds to the loss of a CO from the molecular ion of (PPh 3 )2Pt(TSI)2 (m/e 1114). The mode of coordination of the TSI ligands in complex 139 has not been elucidated. Attempts to grow crystals of the complex have been unsuccessful. When the reaction is performed in presence of only one equivalent of TSI, a second product is detected by 31P{1H} NMR. It contains two inequivalent phosphines at 8 = 14.0 ppm (d, 7pp = 13.4 Hz, Jptp = 3836 Hz) and 6 = 14.5 ppm (Jptp = 3959 Hz). Its structure could not be elucidated: no information could be obtained from the broad 1H NMR spectrum that probably resulted from decomposition of this intermediate. The organic product (140) is insoluble in hexane. The THF extracts, separated from precipitate 139, were pumped down to dryness. Compound 140 was subsequently purified by washing the residue in a 10-mL portion of hexane. Further purification could be achieved by chromatography on silica gel. The repeated extraction steps were responsible for the low yield (33%). An analysis of the NMR spectra revealed the formation of a cycloadduct involving centers "(CH 3 0 2 C )C and "CHPh". Thus, the 1H NMR spectrum (figure 23) indicates the presence of an exocyclic double bond ( 6 = 5.60 ppm, dd, 7gem = 1.93 Hz; 8 = 5.33 ppm, dd, Jgem = 1.98 Hz) and an allylic proton ( 8 = 5.83 ppm, t, Jgem = 2.25 Hz). As expected, the two carbomethoxy groups are not equivalent and resonate as two separate singlets at 6 = 3.79 and 3.77 ppm. The 13C{1H} NMR spectrum (figure 24) is characteristic of a five-membered lactam subtrate: three carbonyl resonances are present, at 6 = 165.34 and 165.19 ppm for the two carbomethoxy groups and at 8 = 164.50 ppm for the amide carbonyl g r o u p . 162 The existence of an exocyclic double bond was confirmed by two olefinic resonances at 8 = 144.90 and 118.60 ppm for the non-substituted C sp2 carbon atom. l-m - i —I'i'i 11 I ■ ■■■'■ | > ■ ■ ■ | i i ■ i f i-i i i ! i i ■ . | i * '■ 'T—! “t i [ill. i-■-'! ■ ■■■ [ ■ ■■■■■ |- f . [ ■ . ■ i | ■ ■ ■ | 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 .5 0.0 PPM Figure 23; 1H NMR spectrum of cycloadduct 140 Figure 24: HCXjHI NMR spectrum of cycloadduct 140 162 Similar cycloadducts have been synthesized from the analogous azatrimethylenemethane complex 129 (PPh 3)2 PtCq3 -CH2 C(NAr)CHPh) and TSI . 164 (equation 115) 'N- Benzene, RT R • -Ts + =o A Ph O H Ph R= 4-N0 2 C6 H4,4-MeQH4 141 + (Ph 3 P)2 Pt(TSI) 2 139(eq 115) The reason why these two [3+2] cycloadditions (equations 111 and 113) do not involve the same positive pole is not known. Also, these results demonstrate the low reactivity of the system under investigation. Even though this low reactivity stems in part from the nature of the metal center, other features of the complex were thought to contribute. For example, the electron-delocalization provided by the phenyl substituent on the terminal carbon atom might prevent cycloaddition to moderately activated alkenes. On the other hand, the presence of two electron-withdrawing groups to stabilize the anionic pole might be responsible for the stability of the complex for either electronic or steric reasons. EW< PPI13 O P 163 IV- Attempt to chance the nature of the substituent on C-> To increase the reactivity of the platinum complex by facilitating nucleophilic attack of the anionic pole on the activated alkene, one option was to replace the malonate fragment with a substituent bearing a single electron-withdrawing group, (complex P) The synthesis involves nucleophilic attack of the r^-propargyl complex 69. (Scheme 37) Scheme 37; Synthetic approach to prepare complex P E W G ^ Ph , Pt + CH2 EWG Ph 3 P/ N PPh 3 p t 4 Ph3P'/ ' PPh 3 69 P IV-1 Reaction with Li(CH2 N 0 2) The first carbanion that was considered was the conjugated base of nitromethane. Indeed, the pKa of CH 3 NO2 equals 10.7, which is slightly lower than the pKa of dimethyl malonate (12).7 The anion was generated prior to reaction since nitromethane is not reactive enough to react with complex 6 9. Moreover, addition of the preformed anion was thought to minimize a side reaction involving the possible addition of residual base with the electrophilic propargyl substrate. So, a stock solution of IJCH 2 NO2 was prepared by reaction of CH 3 NO2 with one equivalent of a commercial solution of LDA. It was then added at low temperature to a solution of rp-propargyl complex 69, and the mixture was stirred at low temperature for one hour, (equation 116) 164 + Ph Mixture of two complexes + IiCH 2 NO2 Ph3P PPh 3 69 (eq 116) The 3ip{lH} NMR spectrum of the reaction mixture indicated a mixture of two complexes that could not be purified. To minimize the amount of the second product thought to result from reaction between r]3-propargyl complex and i-Pr 2 NH, a solution of r]3-propargyl complex was added to a mixture of CH 3 NO2 and Et 3 N. Under these conditions, a single compound identified as the oxoallyl complex 142, (PPh 3 )2Pt(T)3- CH2 C(0 )CHPh), was observed . 138 Its formation was explained by the ability of alkyl nitronates to undergo nucleophilic attack through the carbanion or the oxygen atom . 165 (equation 117) + CH3 N0 2 /Et3N Pt Ph 3P^* ^PPhs 142 (eq 117) IV-2 Reaction with the lithium enoiate of t-butyl acetate To circumvent the problem of residual base present in the reaction mixture, the enoiate of t-butyl acetate was used. Indeed, t-butyl acetate can be deprotonated with an equivalent of LDA and the product isolated and stored under inert atmosphere with only minor decomposition . 166 A THF solution of complex 69 was added to an equivalent of the anion at low temperature, then warmed to room temperature and stirred for an additional hour. Two platinum-containing compounds were detected by 31P{1H} NMR. 165 None of them, however, corresponded to the desired complex based on the absence of t- butyl singletin the 1H NMR spectrum, (equation 118) t-Bu02C | + Ph y, Pt OTf + UCH2 C 0 2 t-Bu ~ " jr - PfcjP^ \ p h 3 Ph3P PPh 3 69 (eq 118) Unfortunately, t-butyl acetate is not acidic enough to undergo nucleophilic addition on the central carbon. This had been considered as the first step of an alternative route to the zwitterionic complex, followed by the deprotonation of the generated cationic allyl complex, (equation 119) n+ tBuC^C tBu02CL Ph Pt + tBu02 CCH3 BaSC ^ Ph Ph Ph-jP^ \ p h 3 Pt P t 4 Ph 3 P/ ^ P P h j Ph 3 P/ X PPh 3 69 143 (eq 119) This general strategy had been successfully used for the preparation of N-aryl azatrimethylenemethanecomplexesl29.137 (equation 120) n Ph Pt + ArNH2 Ph3P \ p h 3 Pt / \ Pl^P PPh 3 69 129(eq 120) 166 IV-3 Reaction with enoiate equivalents The formation of two products was observed upon reaction of r|3-propargyl platinum complex with enolates. It was thought that enolates might be too reactive and give rise to two products. Fischer-type carbene complexes have found extensive applications in organic synthesis. A widely explored area has been the reaction of the conjugated base of methyl-substituted Fischer carbene complexes. For instance, this has been successfully used in the development of aldol-type alkylations (see chapter 1). The alkylation of Fischer carbene conjugated base has been extended to the nucleophilic attack on transition metal containing substrates. Thus, the conjugated base of (CO)5W=C(OCH3)CH3 undergoes condensation with Fischer carbene complexes according to equation 1 2 1 167. .OCH3 ,OCH3 2.TMSCl,Et20,-78°C 3. Si02,58% W(CO)5 W(CO)5 OCH3 (eq 1 2 1 ) Another example of their behavior is the electrophilic addition undergone by cationic (t]6- arene)tricarbonylmanganese complexes treated with the lithium salt of (CO)5M=C(X)(CH3) (M = Cr, W; X = OCH3 , OCH2CH3, NHt-Bu)***. (equation 122) 167 M(CO) 5 Q CH2Ii Mn(CO ) 3 (eq 1 2 2 ) The preparation of (CO) 5Cp=C(OCH 3 )CH3 169 (2) and its deprotonations were achieved by the following literature procedures, (equations 123 and 124) OCH, 1. McLi, Et2 0 , reflux Cr(CO)s ------i (COfcCr 2.Me£>BF4 i,H 20 c h 3 (eq 123) ,OCH3 (CO)5 Cr " (CCOsCr n-BuLi, THF, PPNC1 (CCOsCr ► PPN4 -78°C //\ c h 3 h 2c o c h 3 h 2c A cx:h 3 83 (eq 124) A solution of complex 69 was treated with the anion of Cr complex 2 under several sets of conditions. A mixture of decomposition products was observed upon treatment of a THF solution of qS-propargyl complex at 0°C with one equivalent of (CO)5Cr=C(OCH3 )(CH2 ')Li+ or by addition of the PPN salt 83 to a solution of the propargyl complex at room temperature. None of these preliminary studies appeared promising, and the approach was abandoned even though the Fischer carbene complex could be modified to alter its reactivity. 168 V- Attempts to change the terminal substituent V-l Design of a one-pot synthesis The attempt to extend the same synthetic sequence (oxidative addition of a propargyl halide followed by halide abstraction using AgOTf) to the preparation of the parent ri3-propargyl platinum complex was unsuccessful, (equation 125) The bromide abstraction step carried out at room temperature led to a mixture of decomposition products. 170 Ph3P, \ H- IPt* Br- P/ Br Ph3P T \ PPh3 AgOTf Decomposition 70 (eq 125) The same compound was later isolated by Chen and coworkers by running the reaction at low temperature .53 Therefore, an alternative route avoiding this halide-abstraction step was investigated. The oxidative addition of R-X to platinum(O) species can involve several pathways . 171 For simple alkyl halides, two different mechanisms have been invoked: (1) an Sn 2 attack by platinum(O) fragment to form a intermediate cationic complex, followed by coordination of the anion; ( 2 ) the formation of a radical pair by halide abstraction by the Pt(0) fragment, which can result in the observation of the expected oxidation product or the dimerization of the two alkyl radicals and the formation of a Pt(II)X 2 species. (Scheme 38) 169 Scheme 38: Possible mechanisms of oxidative additions A third pathway may be considered if the organic halide contains a functional group capable of coordination to the metal. This hypothesis was supported by the stepwise alternative route to r)3-propargyl complexes illustrated in equation 126.51 Moreover, upon performing the oxidative addition of ArCaC-CFkBr to (PPh 3)Pt(ri2 -CH2=CH2) in presence of a radical chain inhibitor 2,6-di-t-butyl-4-methyl phenol (BHT), no change in rate or product distribution was observed. This strongly provides support for the ionic pathway . 172 These observations led to design a reagent that would favor a stepwise mechanism. Ph 3 P, \ Pt1 _ Pt — Ph / Ph3P OCH3 72 73 (eq 126) Alkyl sulfonates have been extensively used in organic synthesis in nucleophilic displacement steps. Sulfonic ester groups are better leaving groups than halides . 173 Alkyl triflates and tosylates have been shown to undergo facile oxidative additions via an Sn 2 pathway, including reactions with platinum(O) reagents.174- 54 However, whereas the preparation of alkyl triflates or vinyl triflates does not cause any problems , 175 the purification and storage of propargyl triflates is more challenging owing to facile 170 rearrangements. On the other hand, propargyl tosylates 176 are not as sensitive and can be isolated as solids and stored under inert atmosphere for extended periods of time without any sign of major decomposition. This is the reason why propargyl tosylates were first examined. The process of oxidative addition of organotosylates is believed to go through an ionic-type pathway rather than a radical mechanism . 177 The consideration of the propargylic nature of the substrate and the good leaving group ability of the tosylate were thought to favor the last mechanistic pathway (equation 126): treatment of (PPh 3)2 PtCn2- CH2=CH2) with an equivalent of R-CeC-CH 2 0 Ts (145) is likely to undergo coordination of the triple bond of the propargyl fragment followed by nucleophilic displacement of the tosylate group. Moreover, even though a tosylate anion is a better ligand than a triflate anion, it is not expected to be coordinated to the metal like bromide anion in the oxidative addition of (PPh 3 )2Pt(T]2-CH2=CH2) with Ph-CsC-CH 2-Br. Therefore, the replacement of R-CsC-CH 2-Br with R-CsC-CH 2 -OTs was anticipated to afford the synthesis of [(PPh 3 )2PtCn 3-CH2-CC-CR)]OTs in a one-pot sequence, making the use of a Lewis acid unnecessary. Finally, the possibility of rearrangement of the propargyl tosylate into an allenyl substrate was not a concern. In the hypothesis that the complex would be formed by nucleophilic attack, an Sn 2 ' versus an Sn 2 process would have yielded a rjl-allenyl instead of a rjl-propargyl complex, which should not present a problem. Indeed, Chen and coworkers demonstrated that the allenyl complex tratis- Br(PPh 3 )2Pt(rjLCH=C=CH2) (7 0) forms the corresponding rj3-complex upon treatment with AgBF 4 which is susceptible to nucleophilic attack at the central carbon .53 The Sn2 1 pathway should be minimized by the steric hindrance of the phenyl-substituted propargyl substituent. 171 Scheme 39: Design of a one-pot synthesis R Ph3P, Ph 3 P, \ R- \ IPf IP f OTs / Ph3P Ph3P 144 OTs Pt 14S V-2 Attempt to isolate T)3-propargyI Pt complexes The method was first tested on phenylpropargyl tosylate, since the tosylate salt of the ri3-propargyl platinum complex was expected to exhibit similar spectroscopic data to the fully characterized triflate salt. Among the various conditions that have been investigated, treatment of a CH 2 CI2 solution of the complex (PPh 3 )2Pt(r]2-CH2=CH2) at low temperature with one equivalent of methylpropargyl tosylate dissolved in a minimum amount of solvent results in the conversion of starting material into a product that could be detected by 3 1 P{1H} NMR of the reaction mixture. However, in spite of all the precautions taken to avoid contamination with air and moisture (flame-dried glassware, manipulation of all reaction solutions inside the dry-box, careful purification of any solvent or reagent) the complex whose chemical shifts and coupling constants agreed with a formulation of an r)3-propargyl complex 145, [(PPh 3 >2Pt(r)3-CH2CCCH3 )]OTs, could not be isolated (figure 25). The structure of the decomposition product has not been elucidated. The properties of the anion may be involved in the process. On the other hand, the nature of the intermediate is not known. The anticipated rp-propargyl complex 145 might be in equilibrium with a minor species that undergoes decomposition. The 172 complexity of the mechanism was suggested in the following reaction: a mixture of three phosphorus and platinum-containing complexes was formed upon treatment of a solution of (PPh 3P)2Pt(Ti2-CH2=CH2) with one equivalent of trimethylsilylpropargyl tosylate. The chemical shifts and coupling constants obtained from the 31P{1H} NMR spectrum of the reaction mixture were indicative of the presence of very dissimilar complexes. However, treatment of the reaction mixture with an excess of diethylamine led to the formation of the same two amino-substituted allyl complexes 148b and 14?b, also obtained from the appropriate one-pot sunthesis. V-3 Trapping of the intermediate ri3-propargyl complex In contrast to their reactions with -propargyl transition-metal complexes, nucleophiles attack the central carbon of the T)3-coordinated ligand in the complex [(PPh 3 )2Pt('n 3-CH2CCPh)]OTf (145). Thus, treatment of a CH 2CI2 solution of complex (PPh 3 )2Pt(Ti2 -CH2=CH2 ) at room temperature with one equivalent of R-CsC-CH 2-OTs in presence of an excess of alcohol or amine affords the corresponding heterosubstituted platinum allyl complexes. It was thought that the facile addition of the nucleophile across the triple bond would provide further evidence for the formation of an intermediate r)3- propargyl complex. Furthermore, it would illustrate the convenience of the method to generate in one step a wide variety of platinum allyl complexes from (PPh3)2Pt(r|2- CH2=CH2). A s expected, treatment of a solution of (PPh 3)2Pt(ii2 -CH2 =CH2) with one equivalent of phenylpropargyl tosylate or methylpropargyl tosylate in presence of excess methyl alcohol or diethylamine results in the formation of the corresponding heterosubstituted allyl complex. (Scheme 40) 173 Scheme 40; Trapping of the ni-propargyl intermediate Nu Ph 3P, NuH \ R IP f OTs- / Ph3P Table 13: One-pot synthesis of nl-allvl Pt complexes R MeOH Et2NH Ph 146a, 58% 147a, 61% Me 146b 61% 147b, 45% * 7 The initial mechanism of addition/proton migration on the isolated T)3-propargyl complex is not known apart from the fact that the proton actually comes from the alcohol. 178 However, no labeling experiment could be designed to ascertain whether an intramolecular or intermolecular transfer takes place. It is to be pointed out, however, that in both cases (stepwise or one-pot synthesis) the same mode of addition is observed, i.e. formal syn addition of amines and formal anti addition of alcohols. In contrast, the trapping of the trimethylsilyl propargyl-derived intermediate is not as straightforward. In addition to the expected TMS-substituted allyl complexes (NuH = MeOH, 148a; NuH = Et2NH, 148 b), a complex resulting from protodesilylation becomes predominant (NuH = MeOH, 149a; NuH = Et2 NH, 149 b). Complexes 149a and 149b could be separated and characterized. (Figure 29) i.... I.... 50.0 40.0 30.0 20.0 10.0 0.0 - 10.0 PPM Figure 25: In-sitn 31P{IH> NMR spectrum of {(PPh^P^Ptfnl-CHiCCCH-QVOTs i i (----,--- 1----:———r-—r—'—~i- 1—"'i■ ■ ■ ■ ■— ...... —'i■ ■ —r~ 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 -5.0 -10.0 -15.0 PPM Figure 26: 3jp |lH>NMR spectrum of fPPfoP^Ptfn 3 -CIF>CrN(CH 7 C H ^ 7 lCHCH^>OTs JU i i | -i | . | r ' ■ ~ i 1 i > t " - i < 11 ■1'— ■ i ...... i 1 • i • i 11.0 10.0 9.0 B.O 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 -1.0 PPM Figure 27: iHNMR spectrum of (PPh^P^Ptfnl-CH^CfNfCHiCHaHlCHCHbVOTs -j o\ , p ...... I I I I I I ...... 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 -5.0 PPN Figure 28: IIP -flH>NMR spectrum of (PPh^P tfn3 -CH 7 C [ N (CH? CHV)7 1C H?> O T s 3 Figure 29: 1HNMR spectrum of (PPfoPWPt{Ti3.CH?CrN(CH?CH^?lCH?>OTs 179 V-4 Application of this new route to the synthesis of various trimethylenemethane complexes The purpose of the development of this method was to prepare various trimethylenemethane complexes with enhanced reactivity toward activated alkenes. So, an excess of NaCH(C 0 2CH3 ) 2 was used as the nucleophile to trap in situ the rj3-propargyl intermediate. The sequence was successfully used to prepare (PPh 3 )2Pt(Ti3 - CH2CC(C0 2 CH3)2CHPh) (78) and (PPh 3 )2Pt(q3 -CH2CC(C0 2 CH3 )2CHCH3 ) (150). (equation 127) CH3O2C.W ^ C 0 2CH3 _ Ph 3P, xs NaCH(C0 2 CH3 ) 2 \ P f R- CH2 C12 / OTs L 2 Ph,P Pt ■* / \ Ph3P PPh 3 (eq 127) Table 14; One-pot synthesis of trimethylenemethane Pt complexes R Ph, 78 Me, 150 Yield (%) 80 77 The same stereochemistry of addition of the nucleophile as in the stepwise reaction was observed (formal syn addition based on the coupling constants obtained from the 1H NMR spectrum). The use of this method to prepare complex 78 represents an improvement in terms of yield and reaction time (one step, 5 h, greater than 80% yield instead of three steps, 2 days, 60% overall yield). The structure of complex 150 was established by comparison with the data collected for complex 7 8 . The presence of a methyl substituent is responsible for additional couplings that support the formation of an i x .1 X ___ I___ _I_ XXX± 55.0 50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 -5.0 - 10.0 -15.0 PPM Figure 30: ilP-flHVNMR spectrum of (PPh^P)?Pt fn-i-CH?CTC ( CQ?CHV)^1CHCH^> J V . A i / l ■ I * • T 1 ■ I1' ■ I 1 ■ I 1 T* ■■■!■■ ■ r'~ ~'T ' ■ I ■ "rT"r ^ ■ ' 1 ' ■ I ■ 0.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 3.5 3.0 1.5 1.0 .5 0.0 PPH Figure 31: 1HNMR spectrum of rPPfoP^PUni-CHTCrCfCOiCH^lCHCHhl 182 anti allyl complex. Thus, the methyl substituent resonates as a septet at 6 = 1.01 ppm. Selective decoupling experiments revealed that it is coupled to the syn CHCH 3 proton (multipletat 5 = 4.05 ppm). Irradiation at 6 = 4.05 ppm (assigned to the two syn protons) results in the collapse of the septet to a doublet. This provides evidence for its coupling with a phosphine ligand and, therefore, for its anti position relative to the central substituent. The anti proton resonates as a doublet with platinum satellites at 2.40 ppm. Moreover, as in this case of complex 7 8 , the two carbomethoxy methyl groups are equivalent, resonating as a sharp singlet at 8 = 3.52 ppm. (Figure 31) Attempt to extend this methodology to the preparation of a trimethylsilyl- substituted trimethylenemethane complex resulted in the formation of a mixture of complexes owing to a predominant deprotection of the TMS-substituted terminal carbon atom (151). (equation 128) Si(CH3 ) 3 CH3 0 2 C ^ .CO 2 CH3 C H aO zC ^ . c o 2 c h 3 c _ c _ PhsP xs NaCH(C0 2 CH3 ) 2 + + Ph3P CH2 C12 R PPhs PPh 3 TsO Ph3P Ph3P major 151 152(eq 128) Investigation of conditions that minimize or favor the deprotection pathway were unsuccessful. However, complex 151 was separated from 152 and characterized by NMR spectroscopy. There again, the TMS-substituted complex 152 could not be further converted into the parent complex under the reaction conditions (excess NaCH(CC>2CH3 )2 , room temperature, CH 2CI2). The *H and 3lp{lH} NMR spectra of complex 151 are characteristic of a very symmetrical complex. The two equivalent phosphines resonate at 8 = 19.9 ppm (Tptp = 3066 Hz). The 1H NMR spectrum, 183 although contaminated with signals of organic impurities, indicated the absence of a TMS signal and the presence of a singlet at 8 = 3.45 ppm, accounting for the two ester groups, and a broad multiplet at 8 = 3.0 ppm of the allylic protons. The compound was not further characterized because of difficulties in isolation and separation from unidentified organic impurities. Moreover, it was of limited interest since Chen and coworkers had already reported its synthesis .53 Upon repeating this reaction, it was found that the ratio of products is not predictable, and the difficulties to separate the components by recrystallization made it inconvenient from a preparative standpoint. V-5 Insight into the mechanism of deprotection of TMS-propargyl precursor. The formation of a TMS-substituted r^-propargyl complex was achieved by Stang and coworkers through the migratory insertion of an ethylene ligand into a Pt- acetylide a-bond. This complex was found to be stable in the absence of any nucleophile.54 To understand the occurrence of the deprotection, the possibility of cleavage at every step of the proposed mechanism was examined. Most of the following discussion is based on the product distribution observed for NuH = Et 2NH. Terminal alkyne can be regenerated 179 from the organosilicon-protected alkyne (R-CsC-Si(CH3)3) by treatment with hydroxide ion, or silver(I) ion followed by cyanide ion, fluoride ion, or methyl lithium/lithium bromide complex. Methanolysis can also be effected but involves forcing conditions (MeOH, dilute aqueous NaOH ) . 180 Therefore, deprotection should not take place under the reaction conditions. Allenyl silanes are relatively inert: they neither react with organocuprates nor undergo electrophilic reactions under mild conditions. Although there is no literature precedence for the reaction 184 chemistry of transition-metal allenyl silane complexes, it is anticipated that a rjl-allenyl silane complex should not undergo deprotection at that stage. The formation of two allylic complexes 148-149 and 151-152 may rationalized through one of the two intermediates invoked by Chen and coworkers.55c (scheme 41). Since no experiment run so far has allowed to rule out one of the pathways, either intermediates may be operative. Scheme 41: Mechanism of nucleophilic attack on n-L-propargyl Pt complexes proposed by Chen and coworkers D PPh3 B r ' Nu On the one hand, free propargyl trimethylsilanes are known to afford terminal allenes upon electrophilic attack via a cationic transition state. (Scheme 42) The substrate is stable in presence of a mild acid, but undergoes complete conversion upon treatment with strong acids such as trifluoroacetic acid . 181 Scheme 42: Acid-promoted propargyl trimethvlsilane to allene rearrangements Si(CH3 ) 3 R Si(CH3 ) 3 r c h = c = c h 2 R 185 The isolation of a mixture of two r|3-allyl complexes 148 b and 149 b can be related to this observation. Indeed, the cleavage of the TMS group might be facilitated by coordination of the propargyl ligand resulting in the formation of a cationic complex. The cationic complex responsible for the isomerization/deprotection can not be the TMS- substituted Pt allyl complex 148b, since no further conversion to complex 149b is observed upon treatment of the mixture with an additional equivalent of nucleophile NuH. (equation 129) (NuH = Et 2NH) Nu Nu NuH Si(CH3 ) 3 + Pt OTs / \ O T s ' Ph3P PPh 3 i NuH (eq 129) Based on pathway 2, a reaction route can be proposed that involves an allene intermediate resulting from the coordination of the nucleophile to the metal followed by protonation of the terminal carbon. The presence of a trimethylsilyl group is then likely to stabilize the partial positive charge on the central carbon. This is based on the p-effect characteristic of organosilicon compounds . 180 Silicon-carbon bonds better stabilize carbocations in p position than do C-C or C-H bonds. The Si-C bond is therefore made weaker, and the silicon atom is more sensitive to nucleophiles. This would make the deprotection of the trimethylsilyl center competitive with the intramolecular transfer of the nucleophile to the central carbon. (Scheme 43) The alternative pathway, pathway 1, involves a metallacyclobutene-type intermediate. Although no platinacyclobutene complex has been isolated as the result of 186 nucleophilic attack on a ^-propargyl platinum complex, this type of complex is known for platinum . 182 Moreover, a related complex has been obtained from nucleophilic addition to r]3-propargyl rhenium complexes .4 9 The deprotection of free vinyl silanes typically requires forcing conditions (HBF 4 , hot CH 3 CN). However, the presence of the transition metal center might favor the protodesilylation at this stage. Indeed, if the addition of NuH across the coordinated triple bond is stepwise, the presence of the trimethylsilyl group should stabilize the developing negative charge owing to the a effect. This is responsible for a weakening of the C-Si bond and may make the group more susceptible to nucleophilic attack and protodesilylation. (Scheme 44) The competition between the two pathways may be influenced by the strengths of the Nu-Si bond formed upon desilylation. Thus, whereas the bond strength of N-Si (320 kJ/mol) and C-Si (318 kJ/mol) is comparable, the formation of a Si-O should be highly favored (Si-O bond strength: 500-800 kJ/mol ) . 179 Hence, it was noticed that in presence of an excess of methyl alcohol only the protodesilylated species is formed. In contrast, upon reaction with diethylamine the deprotected allyl is contaminated with some trimethylsilyl-substituted allyl Pt complex. Even upon treatment of (PPh 3 )2PtCn2- CH2=CH2)/(CH3 )3 Si-CsC-CH2 -OTs with one equivalent of Et 2NH, a mixture of the two complexes 148b and 149b is obtained. The 3ip{lH} NMR spectrum of the reaction mixture indicates complete conversion of the starting material to these two platinum-containing species. However, based on the isolated yields, a platinum species that does not appear in the 31P{1H} NMR spectrum might also be present and account for this discrepancy. While conditions to form predominantly and consistently the trimethylsilyl-substituted allyl complexes could not be established, the protodesilylated complex could be isolated in fair yields (~ 75%). These complexes have also been prepared by Chen and coworkers via nucleopilic attack of [(PPh 3)2PtCn3- CH2 CCCH)]BF4 at low temperature.53 187 Scheme 43; Protodesilvlation reaction: proposed mechanism 1 Si(CH3 ) 3 ~ r H— < -PPh 3 Si(CH3 ) 3 Ph3p\ / C = C H 2 Pt OTs" Pt Ph3P PPh 3 / \ TsO Nu NuH H -NuTMS. H — C + PPh 3 ph3\ y ^ C = C H 2 pt / TsO Nu +pph 3 Nu Nu OTs' Scheme 44: Protodesilvlation reaction: proposed mechanism 2 NuH Pt Nu H OTs* Pt 188 V I- Study of the reactivity of complex (PPhg.HPtfnl- CHgCCfCO?CHVWCHCH^l (150) toward olefins To evaluate the importance of the electron delocalization on the stability of complex 78, the reactivity of complex 150 toward activated alkenes was examined. The presence of an alkyl group instead of an aryl group was expected to promote the cycloaddition of the zwitterionic complex to olefins. Possibly, however, owing to the electron-releasing properties of the methyl substituent, the positive charge on the terminal carbon should be partially neutralized. As a result, [3+2] cycloadditions might be disfavored. VI-1 Reaction with fumaronitrile The first alkene with an electrophilic double bond to be considered was fumaronitrile. (equation 130) Even though the reaction proceeds at room temperature, it takes several days for completion. The reaction performed on an NMR scale in deuterated benzene was monitored by 31P{1H} and *H NMR spectroscopy. The conversion of the starting material into a complex containing two equivalent phosphines at 6 = 22.97 ppm (Tptp = 3709 Hz) and 6 = 23.5 ppm (Jptp = 3705 Hz) 153a was indicative of the formation of (PPh 3 )2Pt(T]2-(CN)HC=CH(CN)). The absence of [3+2] cycloaddition was confirmed by the 1H NMR spectrum of the worked-up reaction mixture. The organometallic product contained a characteristic olefinic proton at 6 = 2.57 ppm with coupling constants /ph = 5.9 Hz and Jptn = 113 Hz. The organic product was difficult to obtain pure. However, the spectrum provided evidence for the formation of a dimerization cycloadduct, analogous to that derived from the phenyl-substituted trimethylenemethane complex: olefinic protons at 6 = 5.49 and 4.88 ppm (d, 7hh =1-3 Hz), two inequivalent methyl esters at 5 = 3.25 and 3.0 ppm, an allylic proton at 6 = 2.27 ppm (q), and a methyl split 189 ppm (q), and a methyl split by the allylic proton at 6 = 0.75 ppm (d, Jhh = 7.1 Hz). Attempt to chromatograph this organic product on silica gel resulted in decomposition. CH3n . r ,c o 2 c h 3 H ,CN + RT,44h X NC H CN c h 3 o 2c h 3c . Ph3P, + Ph3P CH3 c o 2 c h 3 153 154 (eq 130) In conclusion, the replacement of the phenyl group with a methyl group did not change the reactivity trend of the system, even though a slight rate increase could be noted. Vl-2 Reaction with tetracyanoethylene The reaction of complex 150 with one equivalent of tetracyanoethylene (TCNE) results in the formation of a platinum-olefin complex 155 as a result of a [3+2] cycloaddition between the centers "(CH 3 0 2 C)2C" and "CH 2 " and the olefin. When one equivalent of TCNE is used, no decomposition occurs. The composition of the complex was based on analytical data showing the incorporation of one equivalent of TCNE into the product, (equation 131) The 3ip{lH} NMR spectrum contains two inequivalent phosphines ( 6 = 21.46 ppm, Jpp = 18 Hz, Jptp = 3839 Hz; 6 = 20.15 ppm, Jptp = 3560 Hz) as expected from the coordination of an unsymmetrical alkene. 190 NC. .CN .CN \/ benzene CN CN RT, 1.5h 'CN NC CN / V 150 (eq 131) The 1H NMR spectrum exhibits similar features to the cycloaddition product obtained from complex 78. Thus, the coordination to the metal center is responsible for the couplings that appear on the inequivalent methylene allylic proton signals ( 8 = 3.20 ppm, Jhh = 14.8 Hz; 8 = 2.3 ppm, Jhh = 14.7 Hz, Jhp = 9.3 Hz). In addition, the cyclic character of the olefin substituent makes the two methyl esters inequivalent, with an upfield shift of one of them owing to the proximity of the metal center. The methyl substituent of the alkene resonates at 1 .0 2 ppm as a doublet resulting from the coupling with one of the phosphines (7hp = 7.35 Hz). The 13C{1H} NMR spectrum shows the presence of two olefinic carbon atoms at 8 = 63.3 ppm (Jpc = 4 Hz, Jpc = 59 Hz, Jptc = 405 Hz) and 8 = 53.07 ppm (Jpc = 5 Hz, Jpc = 38 Hz, Jpc not calculated). The incorporation of one equivalent of TCNE was confirmed by the presence of four resonances around 110 ppm accounting for the four CN groups, as well as two quaternary carbon atoms at 48.15 and 43.6 ppm. Finally, the allylic methyl group is split by one phosphorus atom (Jpc = 4.6 Hz), as was the resonance in the 1H NMR, and is coupled to the metal (Jptc = 31 Hz). VI-3 Reaction with p-toluenesulfonyl isocyanate (TSI) The reaction proceeds cleanly to completion within 3 h at room temperature in the presence of three equivalents of TSI. The 31P{1H} NMR spectrum indicates the conversion of the starting material into complex 7 8 analyzed as (PPh 3 )2Pt(TSI)2 (139). 191 The organic products were isolated in low yield owing to necessary repetitive extractions. However, the spectroscopic data agree with the formation of a cycloadduct 156 resulting from C-C bond formations between "(CH 3Q2C)2C''-"CO" and "Ts-N"-"CHCH 3 n as in the phenyl-substituted complex and in contrast with the TCNE reaction, (equation 132) 9 c o 2c h 3 II CHaOiC^ / 3 I ^ ^ ^ RT overnight \ ^ x N . S Ts Ts H3C 156 + (PPh3)2Pt(TSI)2 150 139 (eq 132) 192 VI- Summary The t]3 structure of trimethylenemethane complex 78 was confirmed by X-ray diffraction analysis. However, as it is illustrated by the low reactivity of the system toward electron-deficient olefins, complex 78 does not represent an adequate model for mechanistic studies relating to Pd-promoted [3+2] cycloadditions. Efforts to design a TMM ligand with an enhanced reactivity toward unsaturated substrates led to the develop a one-pot synthesis of various substituted r|3-allyl and trimethylenemethane complexes. The accessibility of TMM ligands with substituents exhibiting different electronic and steric properties should allow the promotion of cycloadditions and a study of the factors involved in the mechanism of reaction. CHAPTER III EXPERIMENTAL PART PART A: GENERAL PROCEDURES 1- General experimental conditions All reactions and manipulations described in this chapter were carried out under inert atmosphere of argon using either a double-manifold Schlenk line providing high vacuum (<0.5 mm Hg) and high purity Ar according to standard procedures183. The Schlenk line was equipped with a P 2O5 column designed to adsorb traces of water and with an oxygen scavenger to trap traces of oxygen (Ridox catalyst regenerated with a 5% H2 in N 2 at 160 °C for 24 h). Especially air-sensitive reactions, such as the preparation of complex 6 9 [(PPh 3)2Pt(r|3 -CH2CCCHPh)][OTf], the attempts to isolate [(PPh 3)2Pt(r|3- CH2CCR)] [OTs], and the purifications and isolations of various Pt allyl complexes were performed in a Vacuum Atmospheres dry-box under an atmosphere of Ar. Solutions were transferred using gas-tight Hamilton syringes or stainless-steel cannulae. Purification of compounds was achieved by either extraction, recrystallization under inert atmosphere, or chromatography using silica gel or grade III alumina under argon. The chromatography support was packed under Ar by transferring the solvent from a Schlenk flask under Ar via cannula. The separated bands were collected in Schlenk flasks under inert atmosphere and isolated after evaporation of the solvent of elution under reduced pressure. The organic products that were purified by chromatography were handled in air, and the 193 194 i------separation was monitored by TLC. Crystals of (CO) 4 Re=C(OCH2 CH3)- C(C0 2CH3 )=C(CH3)-NH were grown in a Vacuum Atmospheres dry-box at room temperature by slow evaporation of a CH 2 CI2 solution of the compound saturated with hexane. On the other hand, crystals of (PPh 3)2Pt('n 3 -CH2 CC(C0 2 CH3 )2 CHPh) were obtained by slow evaporation of a CH 2 CI2 solution of the complex saturated with toluene in air. The removal of residual amounts of solvents from platinum complexes was achieved by drying the compounds under high vacuum. NMR samples were prepared under Ar by syringing the sample dissolved in the appropriate deuterated solvent into a screw-cap NMR tube placed in a large Schlenk tube. Alternatively, the solvent was introduced into the NMR tube containing the sample as a solid. NMR scale experiments were performed in a 5-mm screw-cap NMR tube in regular or deuterated solvents. Purification and isolation could be achieved by either transferring the sample into a Schlenk flask or working up the reaction mixture inside a dry-box. NMR was also used to monitor reactions of organoplatinum complexes by syringing an aliquot of the reaction solution into a screw-cap NMR tube under argon. With the exception of CDCI 3 and C6 D6 , deuterated solvents (CD 2CI2, CD3 CN, C7 D8 , C4 Q8 O) were bought from Cambridge Isotopes Co. and used without further purification. CDCI 3 was dried over P2O5 and transferred under vacuum into a vial maintained under Ar. A similar procedure was used to collect C 6D6 dried over sodium/benzophenone. II- Instrumentation II-1 Infrared spectroscopy All spectra were recorded on Perkin-Elmer model 283B or 1600 infrared spectrophotometers. Reactions of the organorhenium complexes were monitored by infrared spectroscopy. An aliquot of the reaction solution was syringed into a NaCl liquid 195 cell, previously flushed with argon. The carbonyl region of the IR spectrum was also used in the identification of the compounds, and the spectra were run in hexane when solubility properties allowed it The data are reported in cm - 1 as s (strong), m (medium), and w (weak). II-2 NMR spectroscopy Identification of the organometallic as well as the organic compounds involved the use of 1H, tiC-pH}, and 3ip{lH} NMR spectrometry. Elucidation of some structures required *H selective decoupling experiments. A variable temperature !H experiment was also performed to establish the presence of a fluxional process on (PPhs^PtCn3- CH2 CC(CC>2CH3)2CHPh) (78). Spectra were run on a Brucker AC-200, AM-250, AC- 300, or AM-500 spectrometer. NOE and 13C{1H} DEPT experiments were carried out by Mr. Carl Engleman on the same instruments. Reports of the !H NMR spectra consist of the following data: chemical shift (ppm) [multiplicity (b = broad, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constant (Hertz), assignment). II-3 Mass spectrometry Mass spectra were obtained by Mr. D. Chang on Kratos VG70-250S instruments using either electron impact (El) or fast atom bombardment (FAB) techniques. II-4 Elemental analysis Combustion analyses were performed by M-H-W Laboratories, Phoenix Arizona and Guelph Chemical Laboratories Ltd., Ontario, Canada. 196 II-5 X-Ray diffraction analysis Both X-ray diffraction analyses were performed by Dr. Judith C. Gallucci on a Rigaku AFC5S diffractometer. III- Reagents and chemicals Reagent grade solvents were distilled under Ar prior to use over the appropriate drying agent: THF over potassium, Et 2 0 over n-BuMgBr, hexane over potassium, CH2CI2 over P 2 O5 , and benzene and toluene over sodium. Reagent grade chemicals were purchased from Aldrich Chemical Co., Inc. or Lancaster Chemical Co. Re 2 (CO)io was purchased from Strem Chemical Co. and purified by sublimation prior to reduction. Reduction of Re 2(CO)io was performed by using a suspension of Na in mineral oil, washed three times in hexane prior to reaction. All reagents with the exception of methyl- 2 -butynoate, 4-pentyl-l-ol, acetyl chloride, solution of lithium diisopropyl amide, triethyloxonium hexafluorophosphate, dimethylphenylphosphine, triphenylphosphine, diphenylacetylene, phenylacetylene, 2 -butyne, 1-phenyl- 1-propyne, 1-pentyne, cerium ammonium nitrate, dimethylsulfoxide, trimethyl acetonitrile, 2,4-dinitrophenyl hydrazine, and p-toluenesulfonyl isocyanate (TSI) were purified by distillation or recrystallization before reaction according to known procedures . 184 p-Toluidine, tetracyanoethylene (TCNE), and fumaronitrile were sublimed under vacuum prior to reaction. Ph-CsC- CO2CH3 was prepared by esterification of Ph-CeC-CC^H in methyl alcohol catalyzed by p-toluenesulfonic acid at reflux temperature of methyl alcohol. Sulfur-stabilized carbanions (CH 3 )2S+C-(CN)2 and (CH 3 )2 S+C-(H)(COPh) were prepared according to standard p ro ced u res.117-1^ . Phenylpropargyl tosylate, methylpropargyl tosylate, and trimethylsilyl propargyl tosylate were prepared from the corresponding propargyl alcohols . 1 7 7 The preparation of (rj2-ethylene)bis(triphenylphosphine)platinum(0), 197 (PPh 3)2Pt(T|2-CH2=CH2), starting with platinum metal, was performed according to literature procedures . 185 PART B: ORGANORHENIUM COMPLEXES I- Preparation of rhenacvclobutadiene complexes 1-1 Preparation of Na[(C0)4 Re-C(CH3 )=C (C 0 2 CH3 )-C(0)J 41(90) The titled compound was synthesized according to a procedure already reported in the literature. However, carrying out the reduction step on a larger scale resulted in better yields (minimization of the formation of the polynuclear impurity side product). Reduction of 2.000 g of Re 2(CO)io (3.065 mmol), freshly sublimed under vacuum, was performed by adding it as a solid under a flow of argon to a suspension of excess sodium (ca. lg) in 60 mL of THF. The reaction mixture was stirred for 18 h at room temperature, during which time the solution turned orange. The completion of the reaction was checked by IR. The excess sodium was then decanted, and the bright red solution transferred into another flask by cannula. The polynuclear impurity that was detected by IR was not removed at this point but was be eliminated by recrystallization at the end of the second step. At room temperature, one equivalent of methyl tetrolate (0.615 mL, 0.601 g, 6.13 mmol) was added. The solution was stirred at room temperature for 12 h. Solvent was removed under reduced pressure. A dark gray precipitate formed upon addition of 10 mL of THF and 10 mL of Et 2 0 , and was removed by filtration. Rhenacyclobutenone was recrystallized overnight by dissolving the crude product in 4 mL of THF and 4 mL of Et 2 0 and adding a layer of hexane. Large orange crystals of complex 90 were collected in 78% yield (2.156 g). In some cases, a second crop could 198 be obtained by recrystallizing the solid obtained from the supernatant solution (Owing to the presence of residual solvent, the yield reported in only approximate). 1-2 Preparation of (C0 )4 Re=C(CH3 )-C(C 0 2 CH3 )=C(0 CH2 CH3) (la) Method 1.41 Rhenacyclobutenone complex (1.376 g, 3.080 mmol), placed in suspension in 20 mL of CH 2CI2 , was reacted at room temperature with one equivalent of Et 3 0 PFg (0.770 g, 3.08 mmol) in solution of 5 mL of CH 2CI2 , and the mixture was stirred for one hour. The product went into solution upon reaction. The insoluble solids were then removed by filtration and the filtrate was pumped down to dryness. Extraction using 20-mL portions I of hexane resulted in the isolation of complex (CO) 4 Re=C(CH3)- C(C0 2CH3 )=C(0 CH2CH3 ) (la) as a bright yellow solid in 48% yield (670 mg). Further purification, when necessary, could be achieved by chromatography on silica gel using a 1:1 mixture of hexane/CH 2Cl2 as the eluent. IR (v, THF): 2082 w, 1991 s, 1937 s, 1704 w cnr*. 1H NMR (CDCI3 ): 6 4.69 (q, J = 7.2 Hz, OCH2CH3 ), 3.70 (s, CO2CH3), 3.06 (s, CH3), 1.58 (t, J = 7.2 Hz, OCH2CH3 ). 13C{1H} NMR (acetone-d6): 6 246.39 (s, Re-C-CH3), 243.71 (s, Re-C- OCH2 CH3 ), 194.46 (s, CO), 192.99 (s, CO), 191.25 (s, trans CO), 159.43 (s, CO2CH3 ), 156.87 (s, C-CO 2CH3), 81.10 (s, OCH 2CH3 ), 50.60 (s, CO2CH3 ), 35.24 (s, CH3), 14.97 (s, OCH 2CH3 ). Anal. Calcd for C ^ H n ^ R e : C, 31.79; H, 2.44. Found: C, 31.63; H, 2.23. Method 2: Rhenacyclobutenone complex obtained from the reduction of 1.00 g of Re2(CO)io (1.53 mmol) was placed in suspension in 20 mL of CH 2CI2 and cooled to -15°C before being reacted with one equivalent of acetyl chloride (0.130 mL, 0.118 g). 199 The solution turned bright yellow within minutes. The reaction mixture was stirred for 20 min. Two equivalents of ethanol (0.359 mL, 0.432 g) were added, and the temperature was slowly allowed to rise to room temperature. Following a work-up identical to that described in Method 1, complex (CO) 4 Re=C(CH3)-C(C0 2 CH3)=C(OCH2CH3 ) (la) is isolated in 80% yield (0.650 g). The purity was checked by NMR spectroscopy. 1-3 Preparation of (C0 )4 Re=C(CH 3 )-C(C 0 2 CH3 )=C(0 CH3 ) (89) The method is similar to l.a Method 2. Rhenacyclobutenone complex 90 (0.434 g, 0.990 mmol) was placed in suspension in 20 mL of CH 2 CI2 and cooled to -15°C for 15 min before one equivalent of acetyl chloride (0.070 mL, 0.078 g) was added. The mixture was maintained at this temperature for 2 0 min, during which time the product went into solution (clear orange solution). This solution was reacted in situ with 50 equivalents of methyl alcohol (2.10 mL, 49.5 mmol). The temperature of the bath was maintained at -15°C for 2.5 h. The color turned bright yellow, and a white precipitate formed, probably NaCl. This solid was removed by filtration, and the solution was pumped down to dryness. The yellow residue was then extracted with 20-mL portions of hexane, yielding a bright yellow solid. The product could be further purified by filtration on silica gel using CH 2CI2 as the eluent, and was isolated as an air-stable green solid. Yield: 333 mg, 76%. IR (u, hexane): 2081 w, 1995 s, 1951 s, 1719 w cm-L 1H NMR (CDCI 3): 5 4.44 (s, OCH3 ), 3.71 (s, CO2CH3 ), 3.08 (s, CH3).13C{1H> NMR (CDCI 3 ): 5 249.56 (s, Re- C-OCH3), 246.61 (s, Re-C-CH3), 193.16, 192,21 (s, cis CO’s), 189.88 (s, trans CO), 158.93 (s, CO 2CH3 ), 155.45 (s, C-C02CH3), 68.98 (s, OCH 3 ), 50.60 (s, CO2 CH3), 35.79 (s, CH 3 ). Anal. Calcd for CnHgOyRe: %C, 30.07; %H, 2.06. Found: C, 30.23; H, 2.06. 2 0 0 1-4 Preparation of (C0)4 Re=C(CH 3 )-C (C 0 2 CH3 )=C (0C H 2 CH=CH2) (91) Rhenacyclobutenone complex 90 was prepared by using the procedure described previously starting with 0.250 g of Re 2 (CO)io (0.385 mmol) . The red solid was placed in suspension in 10 mL of CH 2CI2 , and the suspension was cooled to -15°C. A small excess of acetyl chloride (0.055 mL, 0.060 g, 1.06 eq) was then added. After stirring the mixture at that temperature for 2 0 min, the bright red solution was treated with one equivalent of allyl alcohol (0.055 mL, 0.045 g). The reaction mixture turned cloudy yellow while it was stirred at that temperature for 2.5 h. The solvent was evaporated, and the residue was extracted with hexane (10*mL portions) affording complex 91 in 76% yield (270 mg) as a yellow crystalline solid. (If necessary, further purification could be achieved by filtration on SiC >2 using CH 2CI2 as the eluent). IR (v, hexane): 2080 w, 1994 s, 1949 s, 1717 w cm-1. lH NMR (CDCI3 ): 6 6.11 (m, 7cis = 10.6 Hz, Ttrans = 17.2 Hz, TaUyiic = 4.7 Hz, CH 9 -CH—CH?), 5.52 (dq, «/t|-ans = 17.2 Hz, ./allylic = 1.5 Hz, 0 -CH2-CH=CH2), 5.42 (dq, = 6.7 Hz, 0-CH2- CH=CH2), 5.13 (dq, ./allylic = 0.7 Hz, ./allylic = 0.7 Hz, 0-CH2-CH=CH2), 3.70 (s, CO2CH3 ), 3.07 (s, CH3 ). 1 3 C{1H} NMR (CDCI3 ): 8 249.8, 244.5 (2s, Re-C-CH3, Re-C-OCH2CH=CH2), 193.1. 192.3, 189.9 (3s, CO), 159.9, (s, CO 2CH3 ), 155.7 (C- CO2CH3), 130.6 (s, 0-CH2-CH=CH2), 1 2 0 .2 (s, OCH2-CH=CH2), 83.6 (s, OCH2- CH=CH2), 50.6 (s, CO2CH3 ), 35.8 (s, CH3). MS (FAB): m/z 467 (M++1), 452 (M++ 1-CH3), 369 (M++l-CO-OCH 2CH=CH2), 341 (M++l-2CO-OCH2 CH=CH2). Anal. CalcdforCi 9 Hi7 0bRe: C, 33.55; H, 2.38. Found: C, 33.4; H, 2.53. 1-5 Preparation of (C0 )4 Re=C(CH 3 )-C(C 0 2 CH3 )=C[0 (CH2 ) 3 CeCH] (94) Rhenacyclobutenone complex 90 was prepared by using the procedure described previously starting with 0.250 g (0.385 mmol) of Re 2 (CO) iq. This red solid was then placed in suspension in 20 mL of CH 2C12, and the suspension was cooled to -15°C. One 2 0 1 equivalent of acetyl chloride (0.055 mL, 0.060 g) was then added. After stirring the mixture at that temperature for 2 0 min, the bright red solution was treated with one equivalent of 4-pentyn-l-ol (0.070 mL, 0.065 g) and was stirred at this temperature for 2.5 h. The crude product obtained after evaporation of the solvent was extracted several times with 10-mL portions of hexane. Rhenacyclobutadiene complex 94 was further purified by cooling a saturated solution in hexane. Yield: 312 mg, 83%. IR (u, hexane): (CO) 2066 w, 1982 s, 1950 s, 2011 m, (CC) 1995 cm '1. 1H NMR (CDC13): 6 4.73 (t, 7 = 6.31 Hz, OCH2 ), 3.69 (s, CO 2 CH3), 3.06 (s, CH3 ), 2.44 (d of t, 7 = 6 .8 , 2.5 Hz, CH2 -CC-H), 2.16 (quintet, 7 = 6.5 Hz, HCC-CH2-CH2 -CH2), 2.03 (t, 7 = 2.5 Hz, CC-H). 1 3 C{1H} NMR (CDCI3): 6 249.05 (s, Re-C-OR), 244.1 (s, Re-C-CH3), 193.14, 192.08 (2s, cis CO), 189.99 (s, trans CO), 158.92 (s, CO 2CH3 ), 155.63 (s, C-CO2CH3 ), 82.08 (s, OCH2), 82.01 (s, CCH), 69.93 (s, CCH), 50.5 (s, COzCHs), 36.6 (s, CH3), 27.8 (s, CH2), 14.8 (s, CH 2CCH). MS (FAB): m/z 492 (M+), 464 (M+-CO), 436 (M+-2CO), 380 (M+-4CO). 1-6 Preparation of (C0) 4 Re=C(C 6 H5 )-C (C 0 2 CH3 )=C (0C H 2 CH3) (98) Preparationof (CO)Me=C(C«H<)-C(CO,cin^C(OCH,CH,)(97) T h e THF solution obtained by reduction of 2 .0 0 0 g of Re 2 (CO)jo (3.065 mmol) was reacted with one equivalent of Ph-CsC-C 0 2 CH3 (0.850 mL, 0.981 g) at room temperature for 36 h. The solution turned lighter red. Solvent was then removed under reduced pressure, and the crude residue was purified in a similar fashion as the methyl-substituted rhenacyclobutadiene complex la. A dark precipitate that formed upon addition of 5 mL of Et20 and 2 mL of THF was removed by filtration. The volume of the filtrate was reduced to ca. 3 mL, and 60 mL hexane was added. After a few hours, large orange crystals of complex 97 appeared and were isolated in 80 % yield (2.500 g) by removal of the supernatant solution with a cannula. 2 0 2 IR (-u, THF): (CO) 2054 w, 2005 s, 1940 s, 1904 m, 1608 w cn r1. 1H NMR (acetone-^): 6 7.4-7.2 (m, Ph), 3.63 (s, CO 2 CH3). 13C{lH> NMR (acetone-4;): 5 225.67 (s, Re-C(=0)-), 202.36 (s, Re-C(Ph)-), 199.55, 197.41, 196.91 (3s, CO), 161.7 (s, CO2CH3 ), 149.27 (s, C-C0 2CH3), 128.06, 127.76, 126.96, 126.55 (4s, Ph), 49.62 (s, CO 2CH3 ). Preparation of( CO)^Re-C( CaH*)-C( CO^CHo )=C( OCH^CHo ):(98) O-alkylation was performed by using Method 2. A suspension of 0.500 g of I------1 Na[(C0)4 Re-C(C6H5)=C(C02CH3 )-C(=0)] (97) (0.980 mmol) in 5 mL of CH 2 C12 was cooled to -15°C and reacted with one equivalent of AcCl (0.070 mL, 52 mg). The orange suspension turned dark red. Upon adding an excess of EtOH (0.200 mL), the color turned dark orange. After 2 h of stirring at RT, the solvent was removed under reduced pressure, and the crude product was extracted with 10-mL portions of hexane. A bright orange solid was obtained in 11% yield (387 mg, 0.760 mmol). IR (v, hexane): 2079 w, 1995 s, 1946 s, 1725 w cm-1. 1H NMR (CDCI3 ): 6 7.49-7.41 (m, Ph), 4.76 (q, 7 = 7.2 Hz, OCI^CHs), 3.64 (s, C 0 2CH3 ), 1.63 (t, J = 7.2 Hz, OCH^Hs). 13C{1H} NMR (CDCI3): 6 . 243.53 (s, Re-C-OCH2 CH3), 227.37 (s, Re-C-Ph), 193.28, 191.51 (2s, cis CO's), 189.89 (s, trans CO's), 160.54 (s, CO 2CH3), 152.07 (s, C-C0 2 CH3 ), 145.54 (s, ipso carbon), 130.58 (s, p-Ph carbon), 128.62, 128.10 (2s, Ph carbons), 79.70 (s, OCH 2CH3), 50.83 (s, CQjCHs), 14.76 (s, OCH2 CH3 ). MS (El): m/z 516 (M+), 488 (M+-CO), 460 (M+-2CO), 429 (M+-2CO- OCH3 ), 401 (M+-3CO-OCH3), 374 (M+-4CO-OCH3). 203 II- Deprotonation of complex la and alkvlation/deuteration studies II-l Preparation of Li[(C0)4 Re-C(=CH 2 )=C (C 0 2 CH3 )-C (0C H 2 CH3)] by deprotonation of (C0)4 Re=C(CH 3 )-C (C 0 2 CH3 )=C (0C H 2 CH3) (la) with LDA Deprotonation was performed using a commercially-available 0.8 M LDA solution in hexane. To a solution of 349 mg of (C 0 )4 Re=C(CH3 )-C(C0 2CH3)=C(0 CH2CH3 ) (la) (0.770 mmol, 0.038 M) in 20 mL of THF cooled to -78°C, one equivalent of LDA solution was added (0.970 mL). The solution color turned orange immediately. The reaction mixture was stirred at low temperature for 1 h. The completion of the reaction was checked by IR. The anion solution was then quenched or metathesized without purification as described in the following procedures. IR (uCO, THF): 2058 w, 1960 s, 1901 s, 1630 m cm-*. II-2 Deuteration of (C0)4 Re=C(CH3 )-C (C 0 2 CH3 )=C(0CH 2 CH3) (la) Complex (C 0 )4 Re=C(CH3 )-C(C0 2 CH3 )=C(0 CH2CH3) (la) was deprotonated by using the procedure described previously. After checking the completion of the reaction, the reaction mixture was treated at low temperature with ca. 5-fold excess of deuterium chloride (20% w/w in D 2O). A white precipitate formed and was removed by filtration. The filtrate was pumped down to dryness and extracted with 20-mL portions of hexane. A bright yellow solid was obtained upon evaporation of hexane in yields typically higher than 95% as a mixture of monodeuterated rhenacyclobutadiene complex (85) (up to 87% D incorporation calculated by integration) and starting material. Depending on the trials, evidence of the formation of dideuterated complex ( 8 6 ) has been observed. The components of the mixture could not be separated. 204 1H NMR (CDCI3 ): 6 4.69 (q, J = 7.10 Hz, OCH2 CH3 ), 3.69 (s, CO 2CH3 ), 3.06 (s, CH3 ), 3.02 (t, J - 2.2 Hz, CH2 D), 1.58 (t, J = 7.10Hz, OCH2CH3 ). 2H NMR (CH2C12): 6 3.04 (t, J= 2.3 Hz, CH2D). II-3 Deprotonation of (C 0 )4 Re=C(CH 3 )-C(C 0 2 CH 3 )=C(0 CH 2 CH 3 ) (la) with NaCH[(C0 2 CH3)2] A suspension of 950 mg (1.10 eq, 7.70 mmol) of NaH in 20 mL of THF was prepared and cooled to 0°C. One equivalent of dimethyl malonate (0.800 mL, 0.923 g, 6.99 mmol) was then slowly added. When foaming stopped, the ice bath was removed and the reaction mixture was stirred at room temperature for another ten minutes. The supernatant solution was filtered. The solvent was removed under reduced pressure, and the resulting white solid was used without further purification. Complex (C0) 4 Re=C(CH3 )-C(C02CH3 )=C(0CH2CH3) (la) (0.113 g, 0.250 mmol) was dissolved in 15 mL of THF, and the solution was cooled to 0°C. Then, 1.2 equivalent of NaCH[(C 0 2CH3 )]2 (39 mg) in solution of 5 mL of THF was slowly added. The reaction mixture was stirred for 30 min after the addition was completed. The color of the solution turned yellow. The IR spectrum of the reaction solution indicated that all starting material had reacted. The solution was then concentrated to ca . 2 mL, and 50 mL of hexane was added to induce precipitation. 1H NMR data indicated chemical shifts characteristic of deprotonated rhenacyclobutadiene. This was further supported by partial deuteration of rhenacyclobutadiene complex la upon quenching the reaction mixture with DC1 (20% w/w in D 20). An impure product was obtained (96 mg) after extraction of the crude reaction mixture into hexane. 205 II-4 Preparation of PPN[(C0)4 Re-C(=CH 2 )-C (C 0 2 CH3 )=C (0C H 2 CH3)] (84) metathesis of Li[(C0)4 Re-C(=CH 2 )-C (C 0 2 CH3 )=C (0C H 2 CH3)] with PPNCI The THF solution of Li[(C 0 )4Re-C(=CH2)-C(C0 2 CH3 )=C(0 CH2CH3 )] (prepared according to II-3 using 0.770 mmol (350 mg) of complex la and one equivalent of 0.8 M solution of LDA (0.97 mL)) was added to one equivalent of PPNCI (0.442 g) under argon. The mixture was allowed to warm to room temperature while stirring for 1 hour. Insoluble excess PPNCI and LiCl were removed by filtration. The orange filtrate was then concentrated. Addition of ca. 60 mL of hexane induced the precipitation of an orange solid. The flask was then cooled to 0°C. The supernatant solution was decanted, and the solid washed with 20-mL portions of hexane to eliminate traces of amine. The orange powder was collected and dried in vacuo for 24 h (Yield: 330 mg, 94%). The complex slowly decomposed in solution. 1H NMR (THF-rfg): 6 7.8-7.2 (m, Ph), 6.3 (d, J = 4.5 Hz, =CH2), 4.67 (d, J = 4.5 Hz, =CH2 ), 4.02 (q, J = 7.02 Hz, OCH2 CH3 ), 3.36 (s, CO2CH3 ), 1.21 (t, J = 7.06 Hz, OCH2 CH3 ). II-5 Preparation of(CO)4 Re=C(CH 2 CH2 CH3 )-C (C 0 2 CH3 )=C(OCH 2 CH3) (99) A solution of 0.205 g of complex la (0.450 mmol) in 15 mL of THF was cooled to -78°C and treated with one equivalent (0.135 mL) of LDA (1.5 M) . The solution was stirred for 1 h at low temperature, and them for 20 min at room temperature. The solvent was pumped down, and the brown oil was dissolved in 15 mL of CH 2 CI2 . One equivalent of Et 3 0 PF6 (0.112 g) in solution of 5 mL of CH 2CI2 was added, and the mixture was stirred at room temperature for 1 h. After evaporation of the solvent, the residue was stirred in 10 mL of hexane. The extracts yielded 109 mg of a yellow oil 206 containing a mixture of starting material and alkylated products after removal of the solvent A partial separation of these could be obtained by chromatography on silica gel, and a pure fraction of complex 99 was isolated in 29% yield. 1H NMR (CDCI3 ): 64.69 (q, 7 = 7.2 Hz, OCH 2 CH3 ), 3.70 (s, CO2CH3 ), 3.17 (t, J = 7.3 Hz, CH2CH2CH3 ), 1.85 (septet, J- 7.55 Hz, CH2CH2 CH3 ), 1.58 (t, J = 7.2 Hz, OCH2CH3 ), 1.05 (t, J = 7.3 Hz, CH2CH2 CH3). 13C {1H} NMR (CDCI3 ): 6 253.6 (s, Re-C-OCH2CH3), 243.07 (s, Re-C- Pr), 193.44 (s, CO), 191.91 (s, CO), 190.1 (s, trans CO), 159.16 (s, CO 2CH3 ), 155.12 (s, C-CO2CH3 ), 79.77 (s, OCH 2 CH3), 50.59 (s, CO2CH3 ), 47.79 (s, CH 2CH2CH3), 24.13 (s, CH2CH2 CH3 ), 14.8 (s, OCH 2 CH3), 14.4 (s, CH2CH2 CH3 ). MS (El): m/z482 (M+), 454 (M+-CO), 426 (M+-2CO), 398 (M+-3CO), 370 (M+-4CO), 339 (M+-4CO-OCH3), 311 (M+-4CO-C0 2 CH3). II - 6 Synthesis of (C0) 4 Re=CH [(CH 2 CH 3 ) 2 ]-C (C 0 2 CH 3 )= C (0C H 2 CH3) ( 100) A solution of 204 mg of complex (CO) 4 Re=C(CH3)-C(C0 2 CH3 )=C(OCH2CH3 ) (la) (0.450 mmol) in 15 mL of THF was cooled to -78°C for 15 min. One equivalent of a commercial solution of LDA (1.5 M solution in cyclohexane) was then added (0.300 mL), and the reaction mixture stirred at low temperature for 1 h. THF was evaporated to afford a brown orange oil that was placed in suspension in 10 mL of CH 2CI2. In the meantime, a solution of one equivalent of Et 3 0 PF6 (0.112 g) was prepared in 5 mL of CH2 CI2 and added at RT with a cannula to the above suspension. The suspension turned into a clear solution within a few minutes and was stirred at RT for an hour. Then, dichloromethane was evaporated and the sequence repeated, using 0.5 equivalent of LDA and alkylating agent (LDA: 0.15 mL; EtsOPF^: 0.056 g). The crude product was dissolved in about 1 to 2 mL of a mixture of hexane/CH 2Cl2 (2/1) and loaded on top of a silica gel column packed with the same solvent mixture. The product was then eluted and 207 collected as a homogeneous yellow band. The dialkylated product 100 was obtained as a yellow oil that solidified upon pumping down. Yield: 60 mg, 44%. IR (vCO, hexane): 2079 w, 1993 s, 1948 s, 1719 w cm-1. 1H NMR (CDCI 3 ): 8 4.71 (q, J= 7.2 Hz, OCH2CH3), 3.70 (s, CO2CH3 ), 3.53 (m, CH(CH2 CH3)2), 160 (t, J = 7.15 Hz, OCH2 CH3 ), 1.77-1.26 (m, CH(CH2CH3)2), 0.87 (t, J = 7.4 Hz, CH(CH2CH3 )2). 13C{1H> NMR (CDCI3 ): 8 255.66, 242.90 (s, carbene’s C), 193.42, 191.4 (s, cis CO), 190.3 (s, trans CO), 159.55 (s, CO 2CH3 ), 156.7 (s, C- CO2CH3), 79.65 (t, OCH 2 CH3 ),54.29 (d, CH(CH 2 CH3)2), 50.53 (q, CO2CH3 ), 29.26 (t, CH(CH2CH3 )2 ), 14.77 (q, OCH2CH3), 12.48 (q, CH(CH 2 CH3)2). MS (El): m/z 510 ( M+), 482 (M+-CO), 424 ( M+-2CO-C 2H4). Anal. Cald for CisHigOyRe: C, 37.72; H, 3.76. Found: C, 37.64; H, 4.00. Ill- Aminolvsis reactions III-l Synthesis of (C0) 4 Re=C(CH 3 )-C (C 0 2 CH3 )=C[N (CH 2 CH3)2] (87a) A solution of 480 mg of complex (CO) 4 Re=C(CH3 )-C(C0 2 CH3 )=C(OCH2CH3 ) (la) (1.06 mmol) in 20 mL of THF was cooled to 0°C. One equivalent of Et2NH (0.11 mL, 0.078 g) was added and the mixture was stirred for 2 h at this temperature. The IR spectrum showed a shift of the CO absorptions toward lower energy. Evaporation of the solvent yielded a bright yellow oil. The crude product was then dissolved in 1 mL of CH2CI2, layered with hexane, and stored at -23CC for 24 h: the impurities oiled out while complex 87a diffused into the solution. Typical yields ranged from 74 to 85%. IR (vCO, hexane): 2066 w, 2004 s, 1974, s 1924 m, 1712 w cm'1. 1H NMR (CDC13): 8 3.70 (m, 4H, N(CH2CH3)2), 3.71 (s, CO2CH3 ), 2.69 (s, CH 3 ), 1.37 (t, 3H, J = 7.2 Hz, N(CH2CH3 )2), 1.26 (t, 3H, J = 7.2 Hz, N(CH2CH3 )2). 13C{1H> NMR (CDC13): 8 13.98, 13.71 (q, N(CH 2CH3)2), 31.31 (q, C-CH3), 56.78 (s, C 0 2CH3), 208 147.90 (s, C-CO 2CH3), 163.70 (s, CO2CH3 ), 193.24, 191.31, 191.14 (s, CO), 193.7 (s, Re-C-CH3), 210.1 (s, Re-C-NEt2). MS (FAB): m/z481 (M+), 453 (M+-CO), 425 (M+-2CO). III-2 Synthesis of (C0) 4 Re=C(CH 3 )-C (C 0 2 CH 3 )=C[N H (CH 2 )2 0 H ] (87b) A solution of 254 mg of complex (C 0 )4Re=C(CH3 )-C(C0 2CH3)=C(0 CH2CH3 ) (la) (0.560 mmol) in 10 mL of THF was cooled to -78°C. One equivalent of 2- aminoethanol (0.034 mL, 0.034 g) was added, and the mixture was stirred for 2 h at this temperature. The IR spectrum showed a shift of the CO absorptions toward lower energy. Evaporation of the solvent yielded a bright yellow oil. The crude product was then dissolved in 1 mL of Et 20 , layered with hexane, and stored at -23°C for 24 h: the impurities oiled out while complex 87b diffused into the solution. Typical yields ranged from 75 to 95%. IR (vCO, hexane): 2060 w, 2000 s, 1975 s, 1930 m, 1675 w cm-1. 1H NMR (CDCI 3): 6 3.94 (t, 4H, OCH 2 ), 3.72 (s, C0 2 CH3 ), 3.69 (m, NCH 2 ), 2.92 (s, CH 3 ), 1.88 (br s, NH). 13C{1H} NMR (CDCI3 ): 6 32.7 (s, C-CH3 ), 50.4 (s, C0 2 CH3 ), 58.9 (NH- CH2), 61.8 (s, CH 2 -OH), 145.02 (s, C-C02CH3), 162.5 (s, CQ2CH3 ), 190.1 (s, trans CO), 192.7, 193.5 (s, CO), 197.8 (s, Re-C-CH3), 224.1 (s, Re-C-NEt2). MS (FAB): m/z 470.9 (M+), 442 (M+-CO), 414 (M+-2CO), 386(M+-3CO), 358 (M+-4CO), 327 (M+-4CO-OCH3), 299 (M+-4CO-OCH 3 -CO). III-3 Synthesis of (C0) 4 Re=C(CH 3 )-C (C 0 2 CH 3 )=C(NHPh) (87c) A solution of 0.376 g of the complex (CO) 4 Re=C(CH3)- C(C0 2CH3 )=C(0 CH2CH3) (0.83 mmol) (la) in 10 mL of THF was cooled to -78°C. One equivalent of aniline (0.075 mL, 35 mg) was added, and the mixture was stirred for 1 h at this temperature, then overnight while slowly warming to room temperature. 209 Evaporation of the solvent yielded a bright yellow oil.. The crude product was dissolved in 1 mLof Et 2 0 , layered with hexane, and stored at -23°C for 24 h. The impurities oiled out while clean complex 87c diffused into the solution, affording a green solid in 70- 80% yield after evaporation of the solvent. IR faCO hexane): 2060 w, 2002 s, 1975 s, 1935 m , 1710 w cm'1. 1H NMR (CDC13): 5 7.4 (m, Ph), 3.77 (s, CO 2CH3 ), 2.99 (s, CH 3 ). 13c {1H> NMR (CDCI3): 5 33.5 (s, C-CH3), 50.8 (s, CO 2 CH3), 140.4 (ipso), 129.4, 128.0, 123.1 (Ph), 145.8 (s, C-CO2CH3), 162.8(s, CO 2CH3 ), 1993.6, 191.4, 190.9 (CO), 197.4 (Re=C(CH3), 230.5 (s, =C(NHPh). MS (FAB): m/z 501 (M+), 473 (M+-CO), 417 (M+-2CO), 389(M+-4CO). III-4 Synthesis of (C0) 4 Re=C(CH 3 )-C (C 0 2 CH 3 )=C(N H p-C 7 H7) (87d) A solution of 100 mg of complex la (0.221 mmol) in 10 mL of THF at 0°C was treated with one equivalent of p-toluidine (24 mg) in solution (1 mL) of THF. The temperature was allowed to rise over 5 h. The solvent was then removed under reduced pressure, and the residue was extracted with hexane (10-mL portions). The beige precipitate was removed by filtration. Complex 87d was isolated as a solid in 95% yield (128 mg) upon removal of the solvent. IR (v , THF): 2052 w, 1953 s, 1914 s, 1651 w cm '1. 1H NMR(CDC13): 6 12.31 (br s, NH), 7.4-7.29 (m, Ph), 3.78 (s, CO 2CH3 ), 2.99 (s, CH 3 ), 2.41 (s, Ph-CH 3). 13C{1H> NMR (CDCI3): 5 229.78 (s, Re-C-NR), 196.45 (s, Re-C-CH3), 193.69, 191.59 (2s, CO), 191.04 (s, trans CO), 162.91 (s, CO 2CH3), 145.8 (s, C-CO 2 CH3), 138.03, 137.91 (2s, Ph), 130.0, 1 2 2 .8 (2d, Ph), 50.53 (q, CO 2 CH3 ), 33.45 (q, CH3 ), 21.13 (q, tolyl CH3). MS (El): m/z 515 (M+). A nal. Calcd for Ci 7Hi4 N0 6Re: C, 39.69; H, 2.74. Found: C, 39.86; H, 2.95. 2 1 0 IV- Reactions involving PfCH^sPh IV-I Preparation of (CO)4 Re-C(CH 3 )(PM e2 Ph)- C (C 0 2 CH 3 )= C (0C H 2 CH3) (80) by reaction of (CO) 4 Re=C(CH3)- C (C 0 2 CH 3 )= C (0C H 2 CH3) (la) with P(CH3)2Ph To a solution of complex (C 0 )4Re=C(CH3 )-C(C0 2 CH3 )=C(0 CH2 CH3 ) (la) (0.117 g, 0.258 mmol) in 10 mL of CH 2CI2 cooled to -78°C, one equivalent of PMe 2Ph (0.058 mL, 0.054 g) was added. The yellow color faded while the solution was stirred for one hour. The solvent was removed under reduced pressure without allowing the temperature to rise. The heterogeneous crude mixture was recrystallized from 0.5 mL of B 2O, 0.5 mL of THF, and a layer of hexane at -23°C. After 3 days, the solid was separated from the supernatant solution and identified as complex 80. Yield: 0.122 g, 53%. IR (vCO, THF): 2059 m, 1969 s, 1943 s, 1919 s, 1649 w cnr*. 1H NMR (CDCI 3 ): 5 7.68-753 (m, Ph), 4.01 (q, J- 7.1 Hz, OCH2 CH3 ), 3.66 (s, CO2 CH3),2 . 1 0 , 1.89 (d, J = 11.8 Hz, J- 12.07 Hz, CH3 -P), 2.28 (d, J- 19.9 Hz, CH 3 -C-Re), 1.36 (t, J = 7.09 Hz, OCH2CH3 ). 13C{1H} NMR (CDCI3 ) : 6 -4.3 (d, J- 14.9 Hz, C-PMe 2Ph), 8.25 (d, J- CH3 -P), 10.87 (d, CH 3 -P), 15.21 (s, OCH2CH3 ), 27.24 (d, J = 6 . 6 Hz, CH3- C-P), 50.29 (s, CO 2CH3 ), 73.37 (s, OCH2 CH3), 114.01 (d, J= 5.5 Hz, C-CO2 CH3), 164.55 (s, CO2CH3 ). 31P{1H}NMR (CDCI3 ) : 6 32.34 (s). MS (FAB): m/z 592 (M+). IV-2 Conversion of C0) 4 Re-C(CH 3 )(PM e2 P h)-C (C 0 2 CH 3 )= C (0C H 2 CH3) (80) to (PMe 2 P h )(C 0 ) 3 Re=C(CH 3 )-C (C 0 2 CH 3 )= C (0C H 2 CH3) (81) A solution of (C 0 )4 Re-C(CH3)(PMe2Ph)-C(C 0 2CH3 )=C(0 CH2CH3 ) (80) (0.122 g, 0.206 mmol) in 15 mL of THF was heated at reflux for 1 hour. The pale 2 1 1 yellow color turned bright yellow after a few minutes. The solvent was then evaporated, and the residue was extracted with hexane. The yellow oil obtained by evaporation of the extracts solidified overnight. Complex 81 was isolated in 80 % yield (90 mg). IR (vCO, hexane): 2007 s, 1939 s, 1904 s, 1708 m cnr1. 1H NMR (CDCI 3): 8 7.4- 7.27 (m, PMe2Ph), 4.37 (q, 7 = 7.2 Hz, OCH 2CH3), 3.63 (s, CC^Cfcb), 2.73 (d, 7 = 1.8 Hz, P(CH 3 )2Ph), 1.43 (t, 7 = 7.2 Hz, OCH 2CH3 ). 1 3 C{1H} NMR (CDCI3): 8 14.6 (s, OCH^Hs), 16.25 (d, 7 = 30.9Hz, (CH 3)2Ph), 17.25 (d, 7 - 31.3Hz, (CH3 )2Ph), 34.67 (s, C-CH 3), 50.04 (s, CO ^H s), 78.55 (s, OCH 2CH3), 159.074 (d, 7 = 3.83Hz, CO 2CH3 ), 152.80 (d, 7 = 8.43 Hz, C-CO2CU3), 200.84 (d, 7 = 8 . 2 Hz, CO), 199.31 (d, 7 = 7.2 Hz, CO), 197.55 (d, 7= 58.31 Hz, CO), 258.62 (d, 7 = 12.21 Hz, carbene carbon), 252.90 (d, 7 = 12.20 Hz, carbene carbon). 3 1 P{1H} NMR (CDCI3 ): 8 -26.17. MS (FAB): m/z 564 (M+). IV-3 Preparation o f (PMe2 Ph)(CO)3 Re-C(CH 3 )(PMe2 Ph)- C (C 0 2 CH3 )=C (0C H 2 CH3) (82) by reaction of complex (PMe2 Ph)(C 0)3 Re=C(CH 3 )-C (C 0 2 CH3 )=C(0CH 2 CH3) (81) with PMe2Ph A solution of the complex (PMe2Ph)(CO) 3 Re=C(CH3)- C(C02CH3 )=C(OCH2CH3) (81) (90 mg, 0.16 mmol) was prepared in 20 mL of CH2C12 and cooled to -78°C before one equivalent of PMe2Ph (0.024 mL, 22 mg) was added. The solution was stirred for one hour while its color turned pale yellow. The product was recrystallized by dissolving the crude product in 0.5 mL of CH 2C12 and adding ca. 50 mL of hexane. A fraction of complex 8 2 slowly crystallized as pale yellow needles (43 mg, 38%). However, the total yield could not be calculated since much of the product remained in solution. IR Cu, CH2C12): 1989 s 1889 m, 1870 m, 1636 w cm'1. 3 1 P{1H} NMR(CDC13): 6 29.8 (s), -30.48 (s). NMR (CDCI3 ): 8 7.66-7.34 (m, P(CH3 )2Ph), 4.17-3.94 (m, 2 1 2 OCH2 CH3), 3.5 (s, CO2CH3 ), 1.62 (dd, 7PH = 21.4 Hz, 7PH = 1.5 Hz, Re-C-CIL,), 1.94 (dd, 7PH = 11.80 Hz, JPH = 3.69 Hz, P(CH 3 )2 Ph), 1.77 (dd, JPH = 23.75 Hz, JPH = 7.5 Hz, P(CH3 )2Ph), 1.36 (t, J=7.1 Hz, OCH2CH3 ). 1 3 C{1H> NMR (CDCI3): 5 -4.3 (d, 7PC = 20.9 Hz, CH 3 -C-P), 9.93 (d, 7PC = (CH 3)2P-Re), 18.88 (d, d, J= 15.03 Hz, (CH3 )2P-Re), 10.84 (d, JPC = 3.77 Hz, (CH 3 )2P-Re), 16.24 (d, J?c = 3.96 Hz, (CH3)2P-Re), 15.99 (s, OCH 2 CH3 ), 23.50 (d, JPC = 6.92 Hz, CH3), 49.48 (s, C0 2 CH3 ), 72.54 (s, OCH2CH3), 137.50 (d, JPC = 3.65 Hz, C-C02CH3), 164.22 (s, COzCHs). IV-4 Reaction of (CO^ResCfC^J-CtCOjCHg^CtNCCHjCH^] with PMe2Ph 1------A solution of 0.197 g (0.410 mmol) of (CO)4 Re=C(CH3)- C(C0 2CH3 )=C[N(CH2CH3 )2] (87a) in 5 mL of CH 2C12 was cooled to -78°C. One equivalent of PMe2Ph (0.060 mL, 0.057 mg) was syringed into the reaction flask. The reaction mixture was then stirred at low temperature for 2 h. The solvent was pumped off. The product was isolated by cooling a 5 mL of hexane solution of the oil to -78°C. Complex 8 8 precipitated out and was separated from the supernatant solution (42 mg, 18%). No attempts were made to obtain further product. IR (u, hexane): 2000 m, 1923 s, 1890 s, 1680 w cm'1. 3ip{lH} NMR (CDCI3): 6 -25.2(s). 1H NMR (CDCI3): 6 7.6-7.1 (m, Ph), 3.68 (s, C 0 2 CH3 ), 3.48 (q, J =7.2Hz, NCH2 CH3 ), 3.37 (m, NCH2 CH3), 1.78 (d, 7 HP = 7.8Hz, P(CH 3 )2Ph), 1.72 (d, JHP = 7.8Hz, P(CH 3 )2Ph), 1.32 (d, J = 7.2Hz, NCH2 CH3 ), 1.15 (d, J = 7.2Hz, NCH2CH3 ). 13CUH} NMR (CDCI3 ): 8 223.1 (d, 7PC = 13.1 Hz, =C(NEt2)), 201.4 (d, JPC = 12.0 Hz, =C(CH3)), 201.1 (d, 7PC = 7.8 Hz, trans CO), 200.1 (d, 7PC = 7.1 Hz, CO), 197.6 (d, 7PC = 61.58 Hz, CO), 163.9 (s, CO 2CH3 ), 145.11 (d, JPC = 8.5 Hz, C-C0 2CH3 ), 137.9 (d, yPc = 40.1 Hz, ipso carbon on the phosphine ligand), 213 129.8-128.1 (Ph carbon), 55.3, 46.9 (s, N(CH 2 CH3)2), 50.5 (s, C O ^H s), 30.6 (s, CH3), 16.6 (d, JPC = 30.1 Hz, P(CH3)2), 15.6 (d, JPC = 29.5 Hz, P(CH3)2), 13.7, 13.1 (s, N(CH2CH3)2). Anal. Cald for C 22H28 0feNPRe: C, 42.71; H, 4.40. Found: C, 42.79; H, 4.50. V- Rhenium cyclopentadienvl complexes V-l Preparation of (C0 )3 Re[Tj5 -C5 (CH3 )(C 0 2 CH3 )(0 CH2 CH3 )(Ph)(Ph)] i------(103) from dipheny lacetylene and (CO)4 Re=C(CH3)- C(C 0 2 CH3 )=C(0CH 2 CH3) (la) A solution of 100 mg of (C 0 )4 Re=C(CH3 )-C(C0 2CH3 )=C(0 CH2CH3) (la) (0.221 mmol) in 10 mL of toluene was transferred into a flask containing one equivalent of diphenylacetylene (40 mg) under argon. The solution was heated at reflux temperature for 3 h. The color turned brown within 15 min. The completion of the reaction was followed by IR. The solvent was removed under reduced pressure, and the brown oil was extracted with 10-mL portions of hexane. The remaining gray solid was discarded. The filtrate was collected and pumped down to dryness. To remove any excess diphenylacetylene, the complex can be chromatographed on alumina (grade III) using a mixture of CH 2Cl2/hexane as eluent. Yield: 107 mg, 80%. IR (v, hexane): 2016 m, 1971 s, 1720 w cm-l. 1H NMR (CDC13): 6 3.9 (s, CC^CFb), 2.43 (s, O la), 3.70 (m, OCthCHs), 1.17 (t, J = 7.01 Hz, OCH2CHj). 13C{1H> NMR (CDC13): 6 194.0 (s, 3 CO), 165.6 (s, C p 2CH3), 123.3, 103.7, 100.1, 97.2, 89.3 (s, Cp C), 75.0 (t, OCH 2CH3), 52.0 (q, C O ^ H ^ , 15.1 (q, CH3), 1 2 .8 (q, O C H ^H ^. 214 V - 2 Preparation of (CO )3 Re[qs - C5 (CH3 )(C 0 2 CH3 )( 0 CH2 CH3 )(CH 3 )(CH3)] (104) from 2-butyne and (C 0)4 Re==C(CH3 )-C (C 0 2 CH3 )=C(0CH 2 CH3) (Ia) Attempt to drive the reaction to completion by using the same methodology as above was unsuccessful probably owing to the low boiling point of 2-butyne. Therefore, the reaction was conducted in a sealed tube in presence of 5 equivalents of the alkyne, the excess being easily pumped off during work-up. A toluene solution (2 mL) of 100 mg of complex Ia (0.221 mmol) was treated with 5 equivalents of 2-butyne (0.090 mL, 0.060 g). The sealed tube was heated overnight in an oil bath to 110°C. The solution was then cooled to room temperature, transferred into a Schlenk flask, pumped down to dryness, and extracted with two 10-mL portions of hexane. A bright yellow solution and a beige insoluble material were obtained from this extract. Upon removal of hexane under reduced pressure, a yellow oil was isolated in 83% yield ( 8 8 mg). Further purification could be achieved by chromatography on AI 2 Q} by using CH 2CI2 as the eluent. The pale yellow oil solidified under vacuum overnight (collected 60 mg, 57%) IR (u, hexane): 2098 m, 1977 s, 1726 w cm-1. NMR (CDCI3 ): 6 3.97, 3.88 (m, OCH2CH3 ), 3.80 (s, CO 2CH3), 2.41, 2.16, 2.15 (3s, CH3 ), 1.33 (t, J = 7.0Hz, OCH2CH3 ). 13C{1H} NMR (CDCI3): 5 194.8 (s, CO), 165.64 (s, CO 2 CH3), 137.55, 75.16 (2s, C-CO2 CH3 , C-OCH2CH3), 98.27, 95.28, 92.38 (3s, C-CH 3), 75.26 (s, OCH2 CH3), 51.7 (s, CO2 CH3), 15.4 (s, OCH2CH3 ), 11.84, 10.49, 9.44 (3s, CH3). MS(EI): Rel87 m/z480(M+). 215 V - 3 Preparation of (CO )3Re[r|5- C5 (CH3 )(C 0 2 CH3 )(0 CH2 CH3 )(C 0 2 CH3 )(C 0 2 CH3 ) ] (102) from i------dimethylacetylene dicarboxylate and (CO)4 Re=C(CH3)- C (C 0 2 CH3 )=C (0C H 2 CH3) (Ia) The reaction was performed in an open system at reflux temperature of toluene or in a sealed tube for 4 h. A solution of 60 mg of complex Ia (0.13 mmol) in 2 mL of toluene was treated with one equivalent of dimethylacetylene dicarboxylate (0.016 mL, 19 mg). The reaction mixture was heated at reflux temperature of the solvent for 4 h. The solvent was removed under reduced pressure and the crude product was extracted with 10-mL portions of hexane. A pale yellow-green oil was isolated in 65% yield (49 mg) upon removal of the solvent IR (v, toluene): 2031 m, 1952 s, 1732 w, 1743 w cm-1. 1H NMR (CDCI 3): 6 4.07, 3.92 (m, OCH 2 CH3), 3.83, 3.82, 3.80 (s, CO 2 CH3 ), 2 .6 8 (s, CH3 ), 1.31 (t, J = 7.01 Hz, OCH2 CH3). 13C{1H} NMR(CDC13) (DEPT): 6 192.06 (s, 3CO), 163.78, 163.72, 163.5 (s, CO2CH3 ), 139.96 (s, C-OCH 2CH3), 105.64 (C-CH3 ), 84.23, 84.14, 79.37 (C-CO 2CH3), 73.72 (t, OCH2CH3), 53.05, 51.18, 51.75 (q, CO 2CH3), 14.97 (q> CH3), 12.72 (q, OCH2 CH3 ). MS (FAB): m/z 568 (M+), 537 (M+-CO), 481 (M+- 2 CO-OCH3 ). V-4 Synthesis of substituted cyclopentadienyl complexes 106 and 107 1------from 1-phenyl-l-propyne and (CO)4 Re=C(CH3)- C(C 0 2 CH3 )=C (0C H 2 CH3) (Ia) The reaction was performed in toluene under argon either in an open system at reflux temperature of the solvent or in a sealed tube. A solution of 60 mg of complex Ia (0.13 mmol) in 5 mL of toluene was treated with one equivalent of 1-phenyl-l-propyne (0.017 mL, 15 mg). The solution was heated at reflux temperature for 5 h. The solvent 216 was removed under reduced pressure and the residue extracted with 1 0 -mL portions of hexane. A small amount of beige precipitate was removed by filtration and a yellow oil was collected and identified as a mixture of two regioisomers (106 and 107) in a 1:3 ratio. The mixture was further purified by chromatography on AI 2Q3 (grade III) with CH2CI2 as the eluent affording an oil. Yield: 44 mg, 56%. lH NMR (CDCI3 ): 8 3.97, 3.88 (m, OCH 2CH3), 3.80 (s, CO 2 CH3 ), 2.40, 2.16 (s, CH3 ), 1.32 (t, J = 7.0 Hz, OCH2CH3 ). V-5 Preparation of (C 0 )3 Re[q5 .C 5 (CH 3 )(C 0 2 CH 3 )(0 CH2 CH 3 )(Ph)(H)] 1------(105) from phenylacetylene and (CO)4 Re=C(CH3)- C (C 0 2 CH 3 )= C (0C H 2 CH3) (Ia) General method To a solution of complex (C 0 )4Re=C(CH3 )-C(C0 2 CH3 )=C(0 CH2CH3 ) (Ia) (0.244 g, 0.548 mmol) of 20 mL of toluene, one equivalent of phenylacetylene was added (0.054 mL, 0.056 g). The solution was then heated at reflux temperature. After 4 h, the solution was brown. The solvent was then evaporated under reduced pressure, and the residue was extracted with hexane. A brown residue was removed by filtration and discarded. The hexane extracts were then pumped down to yield a brown oil that partially solidified overnight upon storage at room temperature (Yield: 349 mg). Further purification, when necessary, could be achieved by filtration through deactivated alumina (grade III) using first hexane (250 ml) and then a mixture of hexane/CH 2 Cl2 as the eluent. Yields were typically higher than 90%. IR (ucq> hexane): 2025 m, 1945 s, 1729 w cm-1. 1H NMR (CDCI 3 ): 8 7.7-7.1 (m, phenyl group), 5.29 (s, C-H), 3.87 (s, CO 2CH3 ), 3.80 (m, OCH 2 CH3 ), 2.49 (s, CH 3), 1.25 (t, 7 = 7.0 Hz, OCH2 CH3). 13C{1H> NMR (CDCI3 ): 8 192.53 (s, CO’s), 217 165.26 (s, CO2CH3 ), 137.48, 130.78, 101.64, 95.26, 79.17 (s, Cp’s C), 128.87, 128.56, 128.36,127.85 (s, Ph), 74.88 (t, OCH 2 CH3), 51.94 (q, CO 2CH3), 15.26 (q, C-CH3 ), 14.78 (q, OCH 2 CH3 ). MS (FAB): m/z 528. (M+). Anal. Calcd for CigHnQjRe: C, 43.26; H, 3.25. Found: C, 43.42; H, 3.12. Alternative syntheses 1. Synthesis of complex 105 by using PdO in CH 3 CN: Complex (C0) 4 Re=C(CH3 )-C(C02CH3)=C(0CH2 CH3) (Ia) (162 mg, 0.357 mmol) was combined with one equivalent of PdO (44 mg) and placed under argon. Then, 7 mL of CH 3 CN were added yielding a yellow solution with black solid particles in suspension. One equivalent of phenylacetylene was syringed into the flask (0.040 mL, 37 mg). The suspension turned green within an hour. Two days of stirring at RT were necessary to drive the reaction to completion. At this point, the solvent was evaporated after or without filtration of the black Pd species. About 20 mL of hexane was then added to extract the product. A NMR of the orange oil obtained after evaporation of the solvent showed a clean product. The product could not be crystallized. Typical yields were in the range of those obtained through method 1. 2. Reaction in a sealed tube Complex (C 0 )4 Re=C(CH3 )-C(C0 2CH3)=C(0 CH2 CH3) (Ia) (300 mg, 0.662 mmol) in a sealed tube under argon was dissolved in 1.5 mL of toluene and reacted with one equivalent of phenylacetylene (0.075 mL, 6 8 mg). The tube was sealed and heated at 120°C overnight. The crude product was then transferred to a Schlenk flask, pumped down to dryness, and extracted with 10-mL portions of hexane. The product was isolated as a brown oil in 90% yield (0.315 g). 218 V - 6 Preparation of (CO )3 Re['rls " C5 (CH3 )(C 0 2 CH3 )(0 CH2 CH3 )(C 3 H7 )(H)] from 1 -pentyne and (CO)4 IU=C(CH 3 )-C(CO 2 CH3 )=C (0C H 2 CH3) (i«) A solution of 176 mg of complex Ia (0.39 mmol) in 20 mL of toluene, was treated with 5 equivalents of 1-pentyne (0.192 mL, 27 mg) and heated at reflux temperature for 5 h. The brown solution was cooled to room temperature, pumped down to dryness, and extracted with 10-mL portions of hexane. A yellow oil was obtained after elution through an AI 2 Q3 (grade III) column with hexane in almost quantitative yield (200 mg). IR (u, hexane): 2026 m, 1989 s, 1729 w cnr1. 1H NMR (CDCI 3 ): 5 4.92 (s, Cp's CH), 4.2-3.74 (m, OCH2 CH3 ), 3.83 (s, CO 2CH3), 2.41 (s, Cp's CH3), 2.5-2.0 (m, CH2 CH2CH3 ), 1.55 ( quintet, CH 2 CH2 CH3), 1.35 (t, OCH2 CH3 ), 0.9 (t, CH2CH2CH3 ). 13C{1H} NMR(CDC13) (DEPT): 6 194.03 (s, CO), 165.39 (s, CO2CH3 ), 137.8, 101.26, 97.38, 76.5 (4s, Cp), 78.37 (d, Cp CH), 75.95 (t, OCH2 CH3 ), 51.81 (q, CO 2 CH3), 27.39 (t, CH 2 CH2CH3), 24.78 (t, CH 2 CH2 CH3), 15.44 (q, Cp's CH 3 ), 14.76 (q, OCH2 CH3 ), 14.0 (q, CH2CH2 CH3). V - 7 Preparation of (CO )3 Re[r]5 . C5 (CH3 )(C 0 2 CH3 )[N(CH 2 CH3 ) 2 ](C 0 2 CH3 )(C 0 2 CH3 ) ] (115) from I'" .... dimethy (acetylene dicarboxylate and (CO)4 Re=C(CH3)- C (C 0 2 CH3 )=C[N(CH 2 CH3)2] (87a) To a 0.05 M solution of (CO) 4 Re=C(CH3 )-C(C0 2 CH3 )=C[N(CH2 CH3 )2] (87a) (125 mg, 0.260 mmol) in toluene, 1.5 equivalents of DMAD (0.048 mL, 37 mg) were added. The yellow reaction mixture turned orange almost immediately upon refluxing. The temperature was maintained for 2 h. The solvent was then removed under reduced 219 pressure, and the residue was extracted with hexane. Complex 115 was isolated as a green solid in 6 6 % yield ( 1 0 2 mg). IR (u, toluene): 2025 m, 1978 s, 1730 w cm-1. 1H NMR (CDCI 3 ): 5 3.84, 3.83, 3.81 (s, CO2CH3 ), 3.05 (m, N(CH2 CH3)2) 2.62 (s, CH3 ), 1.06 (t, 6 H, J = 7.2 Hz, N(CH2CH3 )2). 1 3 C{1H> NMR (CDCI3 ) (DEPT): 8 12.18 (q, N(CH 2CH3)2), 12.84 (q, C-CH3), 53.61, 53.35, 52.45 (3s, C0 2 CH3), 83.04, 82.69, 82.56 (3s, C- C0 2 CH3), 106.25 (s, C-CH3 ), 134.38 (s, C-(NEt2)), 165.22, 164.59 (s, CO 2CH3 ), 192.44 193.24, 191.31, 191.14 (CO). MS (FAB): m/z 595.2 (M+). A nal. Calcd for Ci9 H22N0 9 Re: C, 38.38; H, 3.73. Found: C, 38.51; H, 3.91. V- 8 Competition reactions 1. Competition between DMAD and diphenylacetylene for reaction with complex Ia. Complex (CO) 4Re=C(CH3)-C(C0 2CH3 )=C(OCH2CH3 ) (Ia) (50 mg, 0.11 mmol) dissolved in 10 mL of toluene was reacted with one equivalent of dimethylacetylene dicarboxylate (0.014 mL, 16 mg) and one equivalent of diphenylacetylene (20 mg). The mixture was kept at reflux for 4 h. Solvent was removed under reduced pressure, and the crude product was extracted with 10-mL portions of hexane. The extracts showed the exclusive formation of DMAD-derived Cp complex (102) by 1H NMR spectroscopy. 2. Competition between diphenylacetylene and phenylacetylene for reaction with complex Ia. Complex (CO) 4Re=C(CH3 )-C(C0 2 CH3 )=C(OCH2CH3 ) (Ia) (50 mg, 0.11 mmol) dissolved in 10 mL of toluene was reacted with one equivalent of phenylacetylene (0.014 mL, 12 mg) and one equivalent of diphenylacetylene (20 mg) in 10 mL of toluene. 2 2 0 The mixture was kept at reflux for 4 h. Solvent was then removed under reduced pressure, and the crude product was extracted into hexane. The extracts showed the exclusive formation of phenylacetylene-derived Cp complex (105) by 1H NMR spectroscopy. V-9 Preparation of (C 0 )3 Re{ti5 -C5 (H)(CH 3 )(C 0 2 CH 3 )[0 (CH 2 )3 ]} (HO) A solution of 312 mg of (C 0 )4 Re=C(CH3 )-C(C0 2CH3 )=C[0 (CH2)3 C3 CH] (94) (0.640 mmol) in 20 mL of toluene was heated at reflux temperature for 4 h. After evaporation of the solvent, the crude product was dissolved in a minimum volume of hexane and cooled to -78°C. Yellow-green crystals were isolated by filtration in 56% yield. (166 mg). IR (u, toluene): 2065 m, 2006 s, 1972 m, 1935 m, 1720 w cm'1. l H NMR (CDC13): 5 5.01 (s, Cp's H), 3.84 (s, CO 2CH3 ), 2.65 (t, CH2 (CH2)2 0 ), 2.47 (s, CH3 ), 1.95 (m, CH2 of the pyrane ring).13C {tH} NMR (CDCI 3 ) DEPT: 6 193.97, 190.87 (2s, CO), 165.58 (s, CO 2 CH3 ), 139.32(s, Cp carbon), 100.17 (s, Cp carbon), 82 49 (s, Cp carbon), 71.94 (s, Cp carbon), 78.03 (d, Cp carbon), 68.61 (t, OCH 2), 51.81 (q, CO2 CH3 ), 21.61 (t, 0 (CH2)2 CH2), 19.89 (t, OCH 2-CH2-CH2), 14.62 (q, CH3). MS (FAB): m/z464(M+), 433 (M+-CO). V ■ 1 0 Preparation of (CO)3 Re{r|5- C s(H )(C H 3 )(C 0 2 CH 3 )[0 (CH 2 ) 2 0 CH3 ]Ph} A solution of 224 mg of (CO)4Re=C(CH3)-C(C02CH3)=C[0(CH2)20CH3](92) (0.460 mmol) in 20 mL of toluene was treated with one equivalent of phenylacetylene (0.050 mL, 47 mg). The solution was heated at reflux temperature for 3 h. Solvent was then removed under reduced pressure, and the residue was extracted with 10-mL portions of hexane. The product was isolated as a brown oil in 8 6 % yield (220 mg), and could be 2 2 1 further purified when necessary by filtration through an AI 2Q3 (grade III) column using a 2 /1 mixture of hexane/CH 2 Cl2 . IR (v, hexane): 2068 m, 1982 s, 1948 m, 1729 w cnr1. 1H NMR (CDCI 3 ): 6 8 .1-6.7 (m, Ph), 5.3 (s, Cp H), 4.0 (m, OCH 2 ), 3.88 (s. CO 2CH3 ), 3.54 (m, CH2OCH3 ), 3.29 (s, OCH3 ), 2.31 (s, CH3 ). 13C{1H} NMR(CDC13) (DEPT): 6 193.46 (s, CO), 165.2 (s, CO2CH3 ), 130.0 (s, d, phenyl), 128.94, 128.57, 128.45 (d, Phenyl), 77.50 (s, Cp), 78.86 (d, Cp), 95.82 (s, Cp), 102.01 (s, Cp), 137.12 (s, Cp), 51.95 (q, CO2CH3 ), 77.88 (t, OCH 2CH3 ), 71.21 (t, OCH2 CH3 ), 58.95 (q, , CH 2 QCH3), 14.84 (q, CH3). V-ll Preparation of (C0 )3 Re[q5 -C 5 (Ph)(C 0 2 CH3 )[ 0 CH2 CH3 ](Ph)(H)] I------(108 and 109) from phenylacetylene and (CO)4 Re=C(Ph)- C (C 0 2 CH3 )=C (0C H 2 CH3) (98) A solution of 100 mg of complex 9 8 (0.190 mmol) in 2 mL of toluene in a sealed tube was treated with one equivalent of phenylacetylene (0.021 mL 20 mg). The reaction mixture was heated at reflux temperature overnight, and then transferred into a Schlenk flask under argon. Solvent was removed under reduced pressure. The product was isolated by extraction into hexane (10-mL portions). The extracts were separated from a beige solid (discarded) and pumped down to dryness. The resulting orange oil was identified by 1H NMR as a 2:1 mixture of regioisomers 108 and 109. The yield was 58% (75 mg). 1H NMR (CDCI3): 6 7.6-6.91 (m, Ph), 5.62 (major), 5.32 (minor) (2s, Cp's CH), 3.74 (major), 3.62 (minor) (2s, CO 2CH3 ), 4.2-3.91 (m, OCH 2 CH3 ), 1.48 (minor), 1.32 (major) (2t, J= 7.05 Hz, OCH2CH3 ). 2 2 2 VI- Oxygen-atom insertion reactions VI-1 Oxygen-insertion reaction effected by nitroalkanes An equimolar mixture of nitroethane (0.040 mL, 0.55 mmol) and triethylamine (0.084 mL, 41.3 mg, 0.55 mmol) was added to 15 mL of THF solution of 250 mg (0.55 mmol) of complex (CO) 4Re=C(CH3)-C(CO2CH3)=C(0 CH2CH3 ) (Ia). The reaction mixture was stirred overnight at room temperature. The solvent was evaporated under reduced pressure. The residue was extracted with 10-mL portions of hexane. The extract was evaporated to lead to the isolation of 211 mg of a yellow oil. This oil contained a i------mixture of starting material I a and the oxidation product (CO) 4 Re(0)=C(CH3)- 1 C(C02CH3)=C(0CH2CH3) (117). The two components were separated by chromatography on silica gel. The starting material was first eluted by using 3 x 250 mL of hexane. The oxidation product was then collected by washing the column with 10 mL of CH 2 CI2 . Compound 117 was isolated as green needles in 43% yield (110 mg) by evaporation of the solvent. IR (uCO, hexane): 2096 w, 2000 s, 1949 s, 1726 w, 1709 w cm'1. 1H NMR (CDCI3 ): 6 4.54 (q, 7= 7.1 Hz, OCH2 CH3), 3.76 (s, CO2CH3 ), 2.40 (s, CH3 ). 1.51 (t,7 = 7.1 Hz, OCH2 CH3). 13C{1H} NMR (CDCI3) DEPT: 6 258.5 (s, C(OCH 2CH3), 191.1, 190.0, 185.2 (s, CO), 165.7 (q, CO 2CH3), 127.6 (q, C-CO2CH3), 78.1 (t, OCH 2 CH3), 51.2 (q, CO2CH3), 25.9 (q, CH 3 ), 15.1 (q, OCH2CH3 ). MS (FAB): m/z 471 (M+), 443 (M+-CO+2), 413 (M+-2CO+2), 383 (M+-3CO+2). VI-2 Cerium nitrate oxidation of complex (CO)4 Re=C(CH3)- C (C 0 2 CH3 )=C (0C H 2 CH3) (Ia) at 0°C A 5-mL solution of three equivalents of (NH 4)2 [Ce(N0 2 )e] (180 mg) cooled to 0°C was added to a 5-mL solution of the complex (CO) 4 Re=C(CH3)- 223 C(C02 CH3)=C(0CH2CH3) (Ia) (50 mg, 0.11 mmol) at 0°C. The reaction mixture was stirred at 0°C for 6 h and then allowed to warm to room temperature overnight. The solvent was removed under reduced pressure, and the crude product was extracted into 10 mL of CH 2 CI2 . The extract was placed on top of a silica gel column and was eluted using the same solvent followed by Et 2 0 . A yellow oil was obtained after evaporation of the solvent. The yield was not calculated. The results were analyzed by 1H NMR spectroscopy. Integration of the methyl-substituent protons indicated a ratio of 1/7 in favor of the keto-coordinated complex 117. A similar ratio was observed when one equivalent of cerium nitrate was used under the same conditions. These compounds have been characterized previously and are reported in the literature .41 VI-3 Cerium nitrate oxidation of (CO)4Re=C(CH3)- C(C02CH3)=C(0CH2CH3) (Ia) at reflux temperature of acetone. Complex (C 0 )4 Re=C(CH3 )-C(C0 2CH3 )=C(0 CH2CH3) (la) (50 mg, 0.11 mmol) and three equivalents of (NH 4 )2 [Ce(N0 2 )6l (180 mg) were combined as solids and then dissolved in 10 mL of acetone. The solution was refluxed for 1 hour. The solvent was removed under reduced pressure, and the crude product was extracted into 10 mL of CH 2 CI2 . The extract was placed on top of a silica gel column and eluted using the same solvent as the eluent. A yellow oil was obtained after evaporation of the solvent. The yield was not calculated. The product mixture was analyzed by 1H NMR spectroscopy, which indicated a 1/4 ratio in favor of the ester-coordinated complex 118. VI-4 Oxygen-insertion reaction effected by DMSO A sample of 50 mg of (C 0 )4Re=C(CH3)-C(C0 2CH3 )=C(0 CH2CH3 ) (Ia) (0.11 mmol) was dissolved in 0.5 mL of deuterated DMSO. The reaction was monitored by *H NMR. After one hour, a mixture of the starting material, are keto-coordinated 117 and 224 ester-coordinated 118 oxygen insertion products in a ratio 2.6:23 :1 was observed. After 5 h at room temperature, starting material was totally converted into a 3:1 mixture of keto- (117) and ester-coordinated (118) oxygen insertion products. After extraction of the sample into hexane, 75 mg of the mixture was isolated (same ratio). VII- Nucleophilic attack by carbanions VII-1 Preparation of sulfur-stabilized carbanions Synthesis of(CH3)2S+-C-(CN)2 A two-neck flask equipped with a reflux condenser and a dropping funnel was charged with 0.1 mol of DMSO (7.10 mL, 7.80 g), 0.1 mol of malononitrile (6.60 g), and 15 mL of CH 2CI2. Then, one equivalent of thionyl chloride (SOCI 2 , 7.3 mL, 11.9 g) was added dropwise over one hour while the temperature was maintained below -15°C. A thick yellow precipitate appeared during the addition. The mixture was allowed to warm up, and the precipitate was filtered off. It was washed with small portions of dichloromethane and dried overnight to give a sand-like powder (8.06 g). Deprotonation was achieved by dissolving the solid in a few milliliters of water and treating with NaHCQ3 . Excess NaHCQ 3 was filtered off and the product was extracted with small portions of CH 2CI2. The crude mixture was recrystallized from isopropyl alcohol. Yield: 3.03 g, 24%. 1H NMR (CDCI3): 52.80 (s, 6 H, S+(CH3 )2. 13C{1H} NMR(CDC13): 6 15.68 (s, C-(CN)2, 31.39 (q, CH 3 ’s), 116.62 (s, CN’s). MS (El): m/z 126.18 (M+). Synthesis of(CH3)2S+-CH -CO-Ph Chloroacetophenone can be purified by recrystallization from ethanol to give white needles. A solution of 5.40 g of 2-chloroacetophenone (35.0 mmol) in 5 mL of 225 dimethyl sulfide (DMS) was stirred overnight at RT. A thick white precipitate was obtained. Excess DMS was removed in vacuo. About 40 mL of distilled water was added, and an insoluble white solid was filtered off. A volume of 75 mL of 10% aqueous NaOH solution was then added. The mixture first turned cloudy orange and then yellow upon stirring. The product was extracted several times with chloroform. The combined organic phases were dried over MgSQ 4 for 1 h. The drying agent was then filtered off, and chloroform was evaporated. The orange oil obtained was recrystallized from a minimum amount of benzene and a layer of hexane on top. Orange needles were collected in 13.5 % non-optimized yield (850 mg). 1H NMR (CDC13): 5 7.8-7.3 (m, Ph’H), 4.31 (br s, =CH-), 2.96 (s, S(CH 3)2). 13C{1H> NMR(CDCI3 ): 6 183.14 (s, CO), 140.9 (s, ipso C), 129.27 (d, para Ph’C), 127.82 (d, ortho Ph’C), 126.27 (d, meta Ph’C), 50. 6 6 (d, =CH-), 28.14 (q, S(CH3)2). 1------VII-2 Preparation of complex 121 by reaction of (CO)4 Re=C(CH3)- C(C 0 2 CH3 )=C(0CH 2 CH3) (Ia) with (CH3 ) 2 S+ C-(CN ) 2 A mixture of (C 0 )4Re=C(CH3)-C(C0 2CH3)=C(0 CH2CH3 ) (Ia) (0.231 g, 0.510 mmol) and one equivalent of ylide (0.063 mg) was placed under argon and dissolved in 10 mL of acetonitrile. The yellow solution was heated at reflux temperature for 5.5 h. The solvent was removed under reduced pressure, and the crude product extracted with hexane. The 1H NMR of the resulting oil indicated a mixture of three products. The major one (121) was isolated by further extraction of the residue by using 2 mL of THF and a layer of hexane at room temperature. The remaining dark oil was removed and discarded. The product diffused into the hexane layer, and was isolated after evaporation of the solvent. Yield: 63 mg, 24%. IR (v, CH2C12): 2102 w, 2067 s, 2004 s, 1972 m, 1943 m, 1723 w cm-l. 1H NMR (CDCI3 ): 6 1.48 (t, J= 7.09 Hz, OCH 2CH3), 2.32 (s, CH3 ), 3.91 (s, C 0 2CH3 ), 4.46 226 (q J = 7.07 Hz, OCH2 CH3). 13C{1H> NMR (CDCI3 ) (DEPT): 5 15.2 (q, CH3), 23.25 (q, allylic CH3 ), 54.14 (q, CO2 CH3 ), 76.8 (t, OCH 2CH3), 87.02 (s, ethylenic C), 114.3 (s, ethylenic C bound to CN’s), 112.3, 113.3 (2s, CN’s), 185.5 (Re-O- C(OCH3)=), 189.7, 190.3, 194.1 (3s, CO *s), 239.8 (s, COCH 2CH3). MS (El): m/z 518 (M+), 490 (M+-CO), 462 (M+-2CO), 434 (M+-3CO), 406 (M+4CO). VII-3 Preparation of complex 122 by reaction of (CO)4Re=C(CH3)- C (C 02CH3)=C(0CH 2CH3) (Ia) with (CH3)2S+-CH--CO-Ph A solution of the complex (C 0 )4 Re=C(CH3)-C(C0 2 CH3)=C(0 CH2CH3 ) (Ia) (0.123 g, 0.270 mmol) and one equivalent of (CH 3 )2S+-CH‘-CO-Ph (49 mg) was prepared in 12 mL of CH 3 CN. This reaction mixture was heated at reflux temperature for 30 min. Within 15 min, the color turned orange. An IR spectrum of the solution run after 30 min showed a total conversion. Acetonitrile was pumped down, and hexane was added to extract the product. The extracts were separated from the residue. The solvent was removed under reduced pressure, affording complex 122 as a yellow oil in 49% yield (75 mg) that slowly decomposes even upon storage under inert atmosphere. IR (uco. hexane): 2096 w, 2001 s, 1996 s, 1941 m, 1665 w cm-l. 1 h NMR (CDCI3 ): 6 7.82-7.24 (m, Ph H), 6.59 (d, J= 1.08 Hz, =CH(COPh)), 4.20 (q, J= 7.07 Hz, O O ^ C ^ ), 3.72 (s, C0 2CH3 ), 2.05 (d, J = 0.8 Hz, CH 3 ), 1.29 (t, J = 7.06 Hz, OCH2CH3 ). 13C{1H} NMR (CDCI3 ): 6 214.71 (s, C-OCH2CH3), 191.88, 191.71, 190.74 (3s, CO), 185.142, 186.52 (2s, CO(Ph), CO 2 CH3 ), 147.45 (s, C-CH3), 132.1, 128,17, 128,25 (d, Ph CH), 138.91 (s, ipsoC), 124.29 (d, =C(H)-), 117.36 (s, C-C(CH3)=), 74.73 (t, OCH2CH3), 53.37 (q, C O ^H s), 25.04 (q, CH3 -C(R)=), 15.38 (q, OCH2 CH3). 227 VIII- Rearrangement in organonitriles and pyridine VIII-1 Preparation of complex 116 by rearrangement of (C0 )4 Re=C(CH 3 )-C(C 0 2 CH3 )=C(0 CH2 CH3 ) (la) in CH3CN A solution of 105 mg of complex Ia (0.232 mmol) in 10 mL of CD 3 CN in a screw-cap NMR tube was heated at reflux temperature for 2 h, the reaction being monitored by 1H NMR spectroscopy. The solvent was removed under reduced pressure, and the residue was extracted with 10 mL of hexane. A green oil was isolated (74 mg, 70% yield) upon removal of the solvent from the extracts. The proposed structure of the product is based on 1H and 13C{1H} NMR spectroscopy. The product was too unstable to submit for analytical data. IR (v, hexane): 2096 w, 1998 s, 1947 s, 1624 w cm-l. 1H NMR (CDCI3 ): 6 6.43 (dd, ycis = 12.1 Hz, /tran s = 17.99 Hz, -CH=CH2), 5.58 (dd, Jgem = 2.67 Hz, /trans = 17.99 Hz, -CH=CH2 ), 4.95 (dd, Jgem = 2.67 Hz, 7 ^ = 12.1 Hz, -CH=CH2 ), 4.38 (q, J = 7.07 Hz, OCH2CH3 ), 3.89 (s, CO 2CH3), 1.50 (t, J= 7.07 Hz, OCH2 CH3). 13C {1H } NMR (CDCI3 ): 6 234.31 (s, Re-C-OCH2CH3), 186.37, 190.47, 191.51 (3s, CO), 186.36 (s, CO 2CH3 ), 114.9 (s, -CH=CH2), 110.75 (s, -CH=CH2), 75.42 (s, OCH2 CH3), 53.37 (s, CO2CH3), 15.34 (s, OCH2CH3 ). VIII-2 Preparation of complex 119 by rearrangement of (C 0 )4 Re=C[CH(CH 2 CH3 ) 2 ]-C(C 0 2 CH3 )=C(0 CH2 CH3)] (100) in CD3 CN 3-pentyl-substituted rhenacyclobutadiene (51 mg, 0.10 mmol) (100) was dissolved in 0.5 mL of CD 3 CN, placed in a screw-cap NMR tube, and heated at 78-80°C for a total of 4 days, the reaction being monitored by 1H NMR. About 84% conversion was obtained after 4 days (NMR integration). The sample was transferred to a flask and pumped down to dryness. The product was extracted with 0.5 mL of CH 2 CI2 and a layer 228 of hexane. A resulting yellow oil was obtained after evaporation of the solvent. It was crystallized after having been stirred in 10 mL of hexane, the flask kept at 0°C for a few hours. Complex 119 was isolated as a solid in 55% yield (28 mg). IR (v, hexane): 2018 m, 1938 s, 1899 s cm-1. 1H NMR (CD 3 CN): 6 5.34 (br s, CH=), 4.35 (q, J- 7.07 Hz, OCH2CH3 ), 3.78 (s, CO 2CH3 ), 2.08 (q of d, J = 7.5 Hz, J= 1.34 Hz, allylic ethyl goup CH?), 1.92 (q, 7=7.6 Hz, allylic ethyl group CH?). 1.32 (t, J= 7.07 Hz, O CH2CH3), 1.02 (t, J= 7.5 Hz, allylic ethyl group CH 3 ), 0.98 (t, J = 7.5 Hz, allylic ethyl group CH 3 ). 13C{1H} NMR (CD3CN) (DEPT): 6 242.2 (s, Re- C-OCH2CH3 ), 199.44, 197.44, 194.69 (3s, CO), 188.33 (s, CO 2CH3), 146.02 (s, C- CO2 CH3 ), 114.52 (s, =CEt2), 116.08 (d, CH=CH2), 74.37 (t, OCH 2 CH3), 53.68 (q, OCH3 ), 29.03. 25.44 (2t, =C(CH 2CH3)2), 16.31 (q, OCH2CH3 ), 13.24, 12.5 (2q, =C(CH2 CH3)2). MS (El): m/z 510 (M+), 482 (M+-CO), 452 (M+-CO-CH 20), 424 (M+-2C0-CH20), 396 (M+-4CO-2). Anal. Cald for CisHigC^Re: C, 37.72; H, 3.76. Found: C, 37.63; H, 3.80. The following reactions were performed on a small scale to evaluate their generality. The product was extracted from the crude mixture into hexane. The residual oil was checked by JH NMR spectroscopy to establish the absence of any identifiable complex. The yields range from 15 to 20 mg owing to possible loss of complex 119 during transfer or to partial decomposition under the reaction conditions. VIII-3 Rearrangement in EtCN 3-pentyl-substituted rhenacyclobutadiene (20 mg, 0.039 mmol) (100) was dissolved in 0.5 mL of EtCN, placed in a screw-cap NMR tube and heated at 78-80°C for a total of 4 days.The mixture was then transferred into a flask and pumped down to dryness. About 5 mL of hexane was added to the green oil to extract the product over 229 several hours. The green supernatant solution was separated from the residue and pumped down to dryness. The NMR spectrum showed the presence of rearrangement product 119 contaminated with propionitrile. VI1I-4 Rearrangement in PhCN 3-pentyl-substituted rhenacyclobutadiene (20 mg, 0.039 mmol) (100) was dissolved in 0.5 mL of PhCN, placed in a screw-cap NMR tube, and heated at 78-80*0 for a total of 4 days. The solution was transferred into a flask, pumped down to dryness, and extracted into 5 mL of hexane over several hours. Only complex 119 slightly contaminated with solvent was observed by NMR. VIII-5 Rearrangement in t-BuCN 3-pentyl-substituted rhenacyclobutadiene (20 mg, 0.039 mmol) (100) was dissolved in 0.5 mL of t-BuCN, placed in a screw-cap NMR tube, and heated at 78-80°C. After a total of 4 days, the contents were transferred into a flask, pumped down to dryness, and extracted into 5 mL of hexane. The supernatant solution was collected and evaporated to dryness in vacuo. The 1H NMR spectrum of the extracts showed that they contained more than 60 % starting material (integration) and two rearrangement products. VIII-7 Preparation of complex 120 by rearrangement of (C0)4Re=C[CH(CH2CH3)2]-C(C02CH3)=C(0CH2CH3)] (100) in pyridine 3-pentyl-substituted rhenacyclobutadiene (20 mg, 0.039 mmol) (100) was dissolved in 0.5 mL of pyridine, placed in a screw-cap NMR tube, and heated at 78-80°C for a total of 2 days. The mixture was transferred into a flask, pumped down to dryness, and extracted by slow diffusion into 5 mL of hexane. The green-yellow solution was 230 i------collected and dried in vacuo, yielding 15 mg of complex (Py)(C0) 3 Re-0=C(0CH3)- C[CH=C(CH2CH3 )2]=C(OCH2 CH3) (120) as a green solid (69%), IR (v , hexane): 2014 w, 1928 s, 1898 w cnr1. 1H NMR (CDC13): 5 8.7-7.3 (m, Py), 5.37 (br s, CH=), 4.54 (m, OCH 2CH3 ), 3.80 (s, CO 2CH3 ), 2.07 (q d, 7 = 7.5 Hz, 7 = 1.3 Hz, allylic ethyl goup CH?). 1.68 (q, 7 = 7.6 Hz, allylic ethyl group CH?), .43 (t, 7 = 7.07 Hz, OCH2CH3 ), 1 .0 2 (t, 7= 7.5 Hz, allylic ethyl group CH 3 ), 0.80 (t, 7 = 7.5 Hz, allylic ethyl group CH 3 ). 13C{1H> NMR(CDC13): 5 247.4 (s, Re-C-OCH2CH3), 200.86, 198.57, 194.72 (3s, CO), 187.39 (s, CO 2CH3 ), 153.73, 137.69, 125.38 (3d, Py CH), 145. 82 (s, C-C(H)=), 144.28 (d, C(H)=), 113.97 (s, C(CH 2CH3)2), 73.76 (t, OCH2 CH3 ), 53,18 (q, OCH 3), 28.32, 24.7 (2t, =C(CH 2CH3)2), 15.77 (q, OCH2 CH3), 12.78, 12.14 (q, =C(CH 2CH3)2). MS (El): m/z561 (M+), 533 (M+-CO), 504 (M+- CO-Et), 476 (M+-2CO-EI), 448 (M+-3CO-2), 369 (M+-3CO-Py-Et). Anal. Calcd for CisHigOyRe: C, 42.85; H, 4.31. Found: C, 42.87; H, 4.15. IX- NH-Insertion reactions IX-1 Preparation of (C 0 )4 ReNH=C(CH 3 )-C(C 0 2 CH 3 )=C(0 CH 2 CH 3 ) (125) A solution of complex (C0) 4Re=C(CH3 )-C(C02CH3)=C(0CH2CH3) (Ia) (150 mg, 0.331 mmol) and 2,4-dinitrophenyl hydrazine (65 mg, 0.33 mmol) in 15 mL of THF was stirred at room temperature for 2 days. Solvent was removed under reduced pressure. The residue was treated with hexane, and the resulting suspension was stirred overnight The mixture was filtered to remove an orange solid. The filtrate was pumped down to dryness to afford yellow crystalline complex 125 in 90% yield (140 mg). Further purification could be effected by chromatography on alumina (grade III) eluting with 1:1 CH 2Cl2/hexane. Single crystals, suitable for X-ray diffraction analysis were 231 obtained by slow evaporation of a dichloromethane solution saturated with hexane under inert atmosphere. IR (u, hexane): (NH): 3350 w-m br; (CO): 2095 w, 1994 s, 1943 s; (C=N): 1695 m br cm-1. 1H NMR (CDC13): 6 6 . 8 (br s, NH), 4.41 (q, J= 7.1 Hz, CH2CH3), 3.74 (s, CO2 CH3), 2.38 (d ,J = 0.3 Hz, CH3 ), 1.46 (t, J= 7.1Hz, CH2CH3). 13C {1H} NMR (CDCI3 ): 6 239.3 (s, C-OEt), 191.7, 190.9 (2s, cis CO), 190.4 (s, C-CH 3), 185.8 (s, trcms COs), 166.3 (s, C-C02CH3), 124.3 (s, C-CCO2CH3 ), 67.8 (t, OCH 2CH3), 51.0 (q, C 0 2CH3), 26.2 (q, C-CH3), 15.6 (q, OCH2CH3). MS (El): m/z (187R e) 468.95 (M+), 441 (M+-CO), 411.93 (M+-2CO-H), 384 (M+-3CO-H), 356 (M+-4CO-H), 325 (M+-4CO-H-OCH3). Anal. Calcd for Ci 2Hi2N0 7 Re: C, 30.77; H, 2.58; N, 2.99. Found: C, 31.00; H, 2.39; N, 2.93. IX-2 Structure determination of (C 0 )4 ReNH=C(CH 3 )-C(C 0 2 CH 3 )=C(0 CH 2 CH3) (125) Crystals of complex 125 suitable for X-ray diffraction analysis were obtained by slow evaporation of the solvent from a CH 2C12 solution saturated with hexane. The data collection crystal was a yellow-gold plate with well formed faces. Examination of the diffraction pattern on a Rigaku AFC5S diffractometer indicated a triclinic crystal system so that the space group is restricted to Pi or P\. The cell constants were determined by a least-squares fit of the diffractometer setting angles for 25 reflections in the 20 range 28 to 30° with Mo K a radiation (X(Ka) = 0.71073 A). The intensities of six standard reflections, which were measured after every 150 reflections, decreased slightly during the course of the data collection. The average change in intensity was 5.3%, and a linear decay correction was applied to the data. An analytical absorption correction was also applied to the data . 186 232 The structure was solved by using the Patterson method in SHELXS 8 6 in space group PI . 187 There are two molecules in the asymmetric unit, and these are labeled A and B. The two Re atoms were located on the Patterson map, and the rest of each molecule was elucidated by standard Fourier method. Full-matrix least-squares refinements were done in TEXSAN ;188 the function minimized was £u)(IF 0 l-IFcl)2 with to = l/o2(F0). The hydrogen atoms bonded to carbon atoms were included in the model as fixed contributions in calculated positions with C-H = 0.98 A and Bh = 1 .2 B (eq) (attached carbon atom). The methyl hydrogen atoms were idealized to sp3 geometry based on positions located in various difference electron density maps. The set of methyl hydrogen attached to C(4A) has two orientations, and each is included in the model with occupancy factors set to 0.5 . The same is true for the set of methyl hydrogen atoms bonded to C(6 B). The hydrogen atom bonded to nitrogen atoms were initially located on a difference electron density map, and then added to the model and refined isotropically. The final refinement cycle for the 5120 reflections with F 02 > o(FQ2) and the 387 variables resulted in agreement indices of R = 0.031 and Rw = 0.032. The maximum and the minimum peaks in the final difference electron density map are 0.90 and -0.82 e / A3. Scattering factors for neutral atoms were used and included terms for anomalous scattering . 189 A summary of the crystal data and the details of the intensity data collection and refinement are provided in Table 15 in the appendix. Final position and equivalent isotropic thermal parameters are given in Table 16 in the appendix . The lists of bond distances and angles are given in Table 9 in Chapter II. 233 IX-3 Reactivity of (C0)4ReNH=C(CH3)-C(C02CH3)=C(0CH2CH3) (125) Reaction of(CO)4ReN(H)=C(CH3)-C(C02CH3)=C(OCH2CH3) (125) with LDA A solution of complex (C 0 )4 ReN(H)=C(CH3 )-C(C0 2 CH3 )=C(0 CH2CH3 ) (125) (50 mg, 0.11 mmol) in 5 mL of THF at -78°C was treated with one equivalent of LDA (0.075 mL, 1.5 M solution in cyclohexane). The mixture was stirred for 30 min. The color turned from yellow to brown. The reaction solution was then quenched by addition of an excess of DC1 in D 2O(2 0 % by wt., 99.5%) at -78°C. The original yellow color reappeared almost immediately. After 30 min, the solvent was removed under reduced pressure, and the residue was extracted into hexane. After filtration of the extracts and evaporation of the solvent, a yellow-green solid was obtained. IR (v, hexane): (CO): 2095 w, 1994 vs, 1943 s; (C=N): 1695 (m br) cnr1. 1H NMR (CDCI3 ): 6 4.41 (q, J- 7.1 Hz, CH2CH3), 3.74(s, CO2 CH3 ), 2.38 (s, CH 3 ), 1.46 (t, J = 7.1 Hz, CH2 CH3 ). 2H NMR (CH2C12): 6 6.98 (s, ND). Oxidation A solution of 70 mg of the complex (CO) 4 ReN(H)=C(CH3)- C(C02CH3)=C(0CH2CH3XI 25) (0.14 mmol) and 1.5 equivalent of cerium ammonium nitrate (115 mg, 0.21 mmol) in 10 mL of acetone was stirred at room temperature overnight. The ^H NMR spectrum of the residue obtained by evaporation of the solvent indicated no conversion of the starting material. No conversion was observed when the solution was refluxed for 24 h, either. Reaction with dimethylphenylphosphine A solution of 40 mg of the complex (CO) 4 ReN(H)=C(CH3)- C(C0 2CH3 )=C(0 CH2CH3) (125) (0.085 mmol) in 5 mL of CH 2 CI2 was reacted with 234 one equivalent of P(CH 3)2Ph (12 mg) at room temperature overnight. The reaction solution was then heated at reflux temperature for 2 h. The crude mixture was checked by 31P{1H} NMR spectroscopy and showed no conversion of starting material. Attempt to prepare a phosphine-substituted rhenapyrrole A solution of (p-tol) 3 P-substituted rhenacyclobutadiene complex (0.225 g, 0.309 mmol) in 10 mL of THF was reacted with one equivalent of dinitrophenyl hydrazine (95.5 mg). After no conversion had been observed at room temperature, the mixture was kept at reflux in toluene for 2 days During this time, the amount of the starting material decreased as shown by the 31P{1H} NMR spectrum (5 = 12.95 ppm) while a new singlet was growing at 16.4 ppm. However, no product could be identified. IX-4 Preparation of (C0)4ReNH=C(CH3)-C(C02CH3)=C(0CH2CH3) (125) by reaction of (C0)4Re=C(CH3)-C(C02CH3)=C(0CH2CH3) with tosyl hydrazine A solution of 312 mg of complex (C 0 )4Re=C(CH3 )-C(C0 2 CH3 )=C(0 CH2CH3 ) (Ia) (0.688 mmol) in 20 mL of THF was reacted with one equivalent of tosylhydrazine (0.128 mg) with stirring at room temperature for 2 days. After evaporation of the solvent, 20 mL of hexane were added. A yellow-green oil was obtained after evaporation of the solvent. tH NMR analysis of the crude product (200 mg) showed 50% conversion of the starting material into complex 125. 235 IX-5 Preparation of (C0)4Re-C(CH3)=C(C02CH3)-C(0CH2CH3)=NH (126) by reaction of (C0)4Re=C(CH3)-C(C02CH3)=C(0CH2CH3) (la) with hydrazine monohydrate A solution of 350 mg of (C 0 )4 Re=C(CH3 )-C(C0 2 CH3 )=C(0 CH2CH3) (Ia) (0.770 mmol) in 10 mL of THF cooled to 0°C was treated with one equivalent of hydrazine monohydrate (0.040 mL, 40 mg). The reaction mixture was stirred overnight while slowly warming to room temperature. The solvent was then evaporated, and the residue dissolved in a minimum amount of CH 2 CI2. A first purification was carried out by slow extraction into hexane from a concentrated CH 2 CI2 solution. The extracts were separated from the residue and pumped down to dryness. Complex 126 was isolated as a white solid by washing the resulting oil in hexane.Yield: 120 mg, 33% . IR (u, CH2C12 ): (NH): 3390 w; (CO): 2090 m, 1990 s, 1935 s cm-l. iH NMR (CDCI3 ): 5 5.9 (br s, NH), 4.13 (q, J = 7.0 Hz, OCH2 CH3 ), 3.79 (s, CO 2 CH3 ), 2.82 (s, CH3 ), 1.43 (t, J = 7.0 Hz, OCH2 CH3 ). 13C{1H} NMR (CDCI3 ): 6 13.69 (q, OCH2 CH3 ), 33.82 (q, CH3), 51.41 (q, OCH 3 ), 62.62 (t, OCH2CH3), 131.49 (s, C- C02CH3), 166.21 (s, CO2CH3 ), 179.65 (s, Re-NH-C(OCH 2CH3), 186.74 (s, trans CO), 191.34 (s, CO), 212.86 (s, Re-C-CH3). M S (El): m/z469 (M+), 441 (M+-CO), 413 (M+-2CO), 385 (M+-3CO), 357 (M+-4CO), 325 (M+-4CO-MeOH). IX-6 Preparation of complex 127 by reaction of (C0)4Re=C[N(CH2CH3)2]-C(C02CH3)=C(CH3) (87a) with hydrazine monohydrate A solution of the complex (C 0 )4 Re=C[N(CH2CH3 )2]-C(C0 2CH3 )=C(CH3 ) (87a) (0.192 g, 0.400 mmol) in 10 mL of THF was cooled to 0°C before addition of a slight excess of hydrazine monohydrate (0.020 mL, 20 mg). The reaction mixture was slowly allowed to warm to room temperature and stirred for a total of 24 h. After 236 evaporation of the solvent, the product was extracted into hexane. The oil resulting from this extraction, slowly crystallized under vacuum to give a bright yellow solid in 84% yield (166 m g). IR (u, hexane): (NH): 3380 w; (CO): 2087 s, 1990 s, 1938 s; (C=N): 1685 br m cnr1. lH NMR (CDC13): 6 5.85 (br s, NH), 3.63 (q, 7=7.1Hz, N(CH 2 CH3)2), 3.65 (s, CO2CH3 ), 2.25 (s, CH3), 1.22 (t, 7 = 7.1Hz, N fC H ^ H ^ ). NOe experiment: irradiation of the singlet at 2.25 ppm resulted in a 4.4% enhancement of the broad singlet at 5.85ppm suggesting a spatial proximity of NH and CH 3. 13C p H } NMR (CDC13): 6 14.34 (q, N(CH2CH3)2), 26.13 (s, CH3), 52.30 (q, N(CH2CH3)2), 50.47 (s, C0 2 CH3), 168.51 (s, C 0 2 CH3), 186.7, 113.37 (s, quaternary carbon of the ring ), 187.19, 190.83 , 192.38 (s, CO), 218.43 (s, Re-C). MS (El) (187Re) m/z: 496 (M+), 468 (M+-CO), 440 (M+-2CO), 410 (M+-3CO), 384 (M+-4CO), 352 (M+-4CO- CH3 OH). Anal. Calcd for C^H^NOyRe: C, 33.93; H, 3.46; N, 5.65. Found: C, 33.88; H, 3.66; N, 5.54. PART C: ORGANOPLATINUM COMPLEXES I- Synthesis of propargyl tosvlate starting materials176 1-1 Preparation of phenylpropargyl tosylate A solution of 2.29 g of TsCl (10.0 mmol) in 40 mL of Et20 was cooled to -5°C. One equivalent of phenylpropargyl alcohol was then added (1 mL, 1.32 g, 10 mmol). A 10-fold excess of finely powdered KOH (5.52 g) was added over 15 min by using an addition tube under a flow of argon. After the addition was completed, the reaction mixture was stirred for an hour, during which time a white precipitate formed. The reaction mixture was then hydrolyzed by pouring it into 100 mL of ice-cold distilled 237 water. After separation of the layers and further extraction into Et 2 0 , the organic phase was dried over MgSO,*. A white solid was obtained in 64% (1.83 g) after recrystallization from Et 2 0 /hexane. 1H NMR (CDC13): 6 7.85 (d, Ts Ph), 7.2-7.0 (m, PPh3), 4.96 (s, CH 2 -OTS), 2.39 (s, Ts's CH3 ). 13C{1H> NMR (CDCI3 ): 6 145 (s, SO2-C (Ar)), 121.0 (s, CH3 -C(Ar)), 88.9 (s, CC-Ph), 80.6 (CC-CH2), 58.6 (CH2), 21.5 (s, Ar-CH3). 1-2 Preparation of methylpropargyl tosylate A solution of 2.29 g of TsCl (10.0 mmol) in 50 mL of Et 2 0 was cooled to -5°C. One equivalent of methylpropargyl alcohol was then added (0.750 mL, 2.24 g, 10.0 mmol). A 10-fold excess of finely powdered KOH (5.52 g) was added over 15 min by using an addition tube under a flow of argon. After the addition was complete, the reaction mixture was stirred for an hour, during which time a white precipitate formed. The reaction mixture was then hydrolyzed by pouring it into 100 mL of ice-cold distilled water. The two layers were separated, and the aqueous part was further extracted with 10-mL portions of Et 2 0 . The combined organic fractions were dried over MgSC> 4 . A white solid was obtained in 60% yield after recrystallization from Et 2 0 /hexane (1.36 g). 1H NMR (CDCI3 ): 6 7.8-7.3 (2d, Ts Ph), 7.2-7.0 (m, PPh3), 4.65 (q, J = 2.4 Hz, CH2 -OTS), 2.43 (s, Ts's CH3 ), 1.70 (t, J = 2.4 Hz, CH3 -CC). 13C{1H) NMR (CDCI3 ): 6 144.8, 133.4 (s, ipso carbons of OTs group), 129.7, 128.1 (s, Ph's H), 86.1, 71.04 (s, triple bond carbons), 58.06 (s, CC-CH 2), 21.55 (s, CH3 -PI1), 3.5 (s, CH3 -CC). 1-3 Preparation of trimethylsilylpropargyl tosylate A solution of 6 8 6 mg (3.60 mmol) of TsCl and 0.465 mL (0.385 g, 3.00 mmol) of 3-trimethylsilyl-2-propyn-lol in 5 mL of Et 2 After filtration, Et 2 0 was removed under reduced pressure. The impure oil could be purified by the following extraction and purification procedure. The crude product was dissolved in a minimum amount of Et 2 0 and layered with ca. 50 mL of hexane. The product was slowly allowed to diffuse into the hexane layer over a few hours. The slightly colored top layer was separated from the brown oil. Its volume was then reduced to ca. 1 mL, and the flask was stored overnight at -23°C. The propargyl tosylate crystallized as a white solid (130 mg). A second crop could be obtained the same way. Total yield: 250 mg, 45%. lH NMR (CDCI3 ): 6 7.80, 7.32 (2d, Ts Ph), 4.70 (s, CH 2 OTS), 2.44 (s, Ts's CH3), 0.078 (s, (CHsbSi). 13C{1H} NMR (CDCI 3 ): 5 144.93, 133.29 (s, Ts ipso carbons), 129.7, 128.12 (2s, Ar), 96.19, 94.95 (2s, CC), 58.29 (s, OCH2), 21.58 (s, Ts's CH 3), -0 .6 6 (s, (CH3bSi). 11- Attempt to isolate n3-propargvl platinum tosylate complexes The reaction was first attempted with phenyl propargyl tosylate in order to check the versatility of the method, since the r]3-phenylpropargyl Pt complex has been fully characterized as the triflate salt. However, whereas the isolation of the complex has been unsuccessful for all R-substituted propargyl tosylates tried, the best evidence of an intermediate q3-propargyl complex has been observed for methylpropargyl tosylate. Both 239 (Ph 3 P)2Pt0 l2-CH2=CH2) a°d methylpropargyl tosylate were recrystallized from CH2CI2/hexane and Et 2 0 /hexane, respectively, prior to use. The "solv-seal" glassware was flame-dried before being taken into the dry-box where the solution was prepared. The solvent, CH 2CI2 , was dried over P 2O5 and degassed by three "freeze-pump-thaw" cycles on the vacuum line, and then taken into the dry-box. The completion of the reaction was monitored by in situ 3 1P{1H} NMR, after the sample had been prepared in the dry-box by concentration of the reaction solution and transfer into a screw-cap NMR tube. A solution of 50 mg of (Ph 3 P)2Pt(ri2 -CH2 =CH2) (0.067 mmol) in 2 mL of CH2CI2 was prepared in the dry-box . A solution of one equivalent of methylpropargyl tosylate (15 mg) in 1 mL of CH 2CI2 was placed in an addition flask connected to the reaction flask. The set-up was sealed in the dry-box and taken outside of the dry-box. The reaction flask was cooled to -78°C before starting dropwise addition of the propargyl tosylate. The reaction mixture was stirred for 3 h during which time the temperature was allowed slightly to rise. The flask was taken into the dry-box. The volume of the reaction solution was reduced under vacuum. An aliquot was placed in a screw-cap NMR tube and checked by in situ 31P{1H} NMR spectroscopy. The sample was taken back into the dry-box for work-up. The product decomposed into an unidentified compound upon isolation attempt 31P{1H> NMR: 6 12.6 (d, JPP = 17.4 Hz, JPtP = 3754 Hz), 18.8 (d, JPtP = 4240 Hz). 240 III- Synthesis of various heteroatom-substituted platinum allvl complexes III-I Preparation of [(PPh3)2Pt(T)3-CH2C(OCH3)CHPh)](OTs) (146a) A solution of 50 mg of (PPh 3 )2Pt(ri2 -CH2=CH2) (0.067 mmol) in 5 mL of CH2 CI2 was cooled to -78°C. An excess of methyl alcohol (2.00 mL, 1.58 g, 49.0 mmol) was added to the solution. With the temperature maintained at -78°C, one equivalent of Ph-CsC-CH2OTs (20 mg) in 1 mL of CH 2CI2 was slowly added to this solution. The temperature was allowed to rise over a period of 6 h. The completion of the reaction was ascertained by 31P{1H} NMR. After evaporation of the solvent, the residue was dissolved in 2 mL of CH 2CI2 . An off-white solid was precipitated upon addition of 40 mL of hexane. It was collected by filtration, washed with 5-mL portions of Et 2 0 , and isolated in 58% yield (40 mg). Since the triflate salt had been fully characterized^ 1 the tosylate salt was identified only by 31P{1H} NMR and 1H NMR spectroscopy. 31P{1H} NMR (CDCI3 ): 6 18.45 (d, JPP = 11.1 Hz, 7P.Pt = 3779 Hz), 13.96 (d, JP_ Pt = 3789 Hz). 1H N M R (CDCI3): 6 7.95-6.65 (m, Ph), 4.65 (d, 7PH = 10.5 Hz, 7PtH = 38 Hz, CHPh), 3.48 (s, OCH 3 ), 3.61 (m, Hsyn), 2.91 (m, Hanti, 2.31 (s, Ts's CH 3 ). III-2 Preparation of [(PPh3)2Pt(Ti3-CH2C(OCH3)CHCH3)](OTs) (146b) A solution of 50 mg of (PPh 3 )2PtCq2-CH2=CH2 ) (0.067 mmol) in 5 mL of CH2CI2 was cooled to -78°C. An excess of methyl alcohol (2.00 mL, 1.58 g, 49.0 mmol) was added to the solution. With the temperature maintained at -78°C, one equivalent of CH 3 -CeC-CH2OTs (15 mg) in 1 mL of CH 2CI2 was slowly added. The temperature was allowed to rise over a period of 4.5 h. The completion of the reaction was ascertained by 3ip{lH} NMR spectroscopy. After evaporation of the solvent, the residue was dissolved in 2 mL of CH 2CI2. An off-white solid was obtained upon 241 addition of 40 mL of hexane, collected by filtration, and washed with 5-mL portions of hexane. It was isolated in 61% yield (40 mg). 3 IP {1H} NMR (CDC13): 6 20.64 (d, Jpp = 9.6 Hz, Jp.pt = 3753 Hz), 15.2 (d, 7p.pt = 3126 Hz). 1H NMR (CDCI3): d 7..5-7.0 (d, Ts's Ph), 7.35-7.22 (m, Ph), 3.49 (s, CO2CH3), 3.48 (m, CHCH 3 ), 3.02 (dd, Jgem = 10.7 Hz, J HP = 9.6 Hz, J HPt = 33 Hz, CH2 syn), 2.71 (br m, CH 2 anti), 2.28 (s, Ts's CH 3 ), 0.88 (m, CHCH 3 ). 13C{1H > NMR(CDCl3): 5 152.6 (t, Jptc and Jpc not calculated), 145-126 (m, Ph), 6 6 . 6 (d, Jpc = 37 Hz, 7ptc = 178 Hz, CHCH 3), 55.35 (s, OCH3 ), 51.5 (d, JPC = 35 Hz, 7Ptc = 122 Hz, CH2), 21. 89 (s, Ts's CH 3 ), 9.99 (s, allylic CH3). HI-3 Preparation of [(PPh 3 )2 Pt(Ti3 -CH2 C[N(CH 2 CH 3 ) 2 ]CHPh)](OTs) (147a) A solution of 50 mg of (PPh 3 )2Pt(Ti2 -CH2=CH2) (0.067 mmol) in 5 mL of CH2C12 was cooled to -78°C. With the temperature maintained at -78°C, one equivalent of Ph-CsC-CH2OTs (20 mg) in 1 mL of CH 2C12 was slowly added to this solution. Immediately, four equivalents of diethylamine were added (0.030 mL, 20 mg). The temperature was allowed to rise over a period of 6 h. The completion of the reaction was ascertained by 31P{1H} NMR spectroscopy. After evaporation of the solvent, the residue was dissolved in 2 mL of CH 2 C12. An off-white solid was precipitated upon addition of 15 mL of hexane. It was isolated by filtration and washed with 5-mL portions of hexane. Yield: 45 mg, 61%. Since the triflate salt had been fully characterized ,51 the tosylate salt was identified by 3ip{lH} NMR, 1H NMR and 13C{1H} NMR spectroscopy. 31P{1H} NMR (CDCI3): 6 18.0 (d, Jpp = 8.5 Hz, Jp.pt = 3023 Hz), 14.6 (d, Jp.pt = 3368 Hz). 1H NMR (CD 2 C12): 6 7.9-6.9 (m, Ts), 4.35 (br m, CHPh), 3.32 (d, N(CH2 CH3)2), 3.05, 2.60 (2 br s, C lk), 2.30 (s, Ts's CH 3 ), 1.31 (t, N(CH2CH3 )2). 13C {1H} NMR (CD2 C12): 5 155.25 (t, 7PC = 4.2 Hz, CH2C), 145.125 (m, Ph), 59.4 242 (dd, J PC = 51 Hz, J p c = 2.4 Hz, 7PtC = 238 Hz, CHPh), 44.3 (br s, N(CH 2 CH3)2), 37.4 (dd, JpC ~ 49 Hz, JPC= 3 Hz, 7Ptc = 182 Hz, CH2), 20.9 (s, Ts’s CH3), 13.1 (br s, N(CH2£H3)2). III-4 Preparation of [(PPh 3 )2 Pt(Ti3 CH 2 C[N(CH 2 CH 3 )2 ]CHCH 3 )](OTs) (147b) A solution of 50 mg of (PPh 3)2Pt('n 2 -CH2=CH2) (0.067 mmol) in 5 mL of CH2C12 was cooled to 0°C. To this solution, 2.2 equivalents of diethylamine was added (0.015 mL, 11 mg). With the temperature maintained at 0°C, one equivalent of CH3- C=C-CH2OTs (15 mg) in 1 mL of CH 2C12 was slowly added. The reaction mixture was stirred at 0°C for one hour. The solvent was removed under reduced pressure. Upon addition of 5 mL of CH 2C12 and 5 mL of Et 20 , a yellow oil coated the bottom of the flask. The clear and colorless supernatant solution was collected and pumped to dryness. This residue was recrystallized from benzene/hexane, and yielded 30 mg of pure complex (45% yield). The product was also present in the yellow oil, but was impure and no attempts were made at its purification. 31P{1H> NMR (CDC13): 8 18.2 (d, JPP= 7 Hz, JP.Pt = 3420 Hz), 15.35 (d, 7P.pt = 2910 Hz). 1H NMR (CDC13): 8 7.9-7.05 (2d, Ts), 7.4-7.1 (m, Ph), 3.15 (m, N(CH2 CH3)2), 2.92 (m, CH synCH3), 2.66 (m, CH2syn), 2.35 (m, C H ^ri), 2.27 (s, Ts's CH3 ), 1.14 (t, JpH = 7.0 Hz, CHfCfb)), 1.01 (t, J = 7.1 Hz, N(CH2CH3)2). 13C{1H} NMR (CDC13): 8 156.26 (t, JPC = 8 Hz, JPtc = 120 Hz, CH2-C), 145-126 (m, Ph), 50.06 (d, JPC = 52 Hz, JPiC = 230 Hz, CH(CH3)), 44.06 (s, N(CH2 CH3)2), 36.25 (d, JpC = 47 Hz, JPtC - 186 Hz, CH2), 21.2 (s, Ts's CH3), 16.57 (d, JPC = 6 Hz, yPtc = 48 Hz, CH(CH3)), 13.4 (br s, N(CH 2CH3)2). 243 III-5 Preparation of [(PPh3)2Pt(Ti3-CH2C(OCH3)CH2))(OTs) (149a) A solution of 100 mg of (PPh 3 )2Pt(,n 2-CH2=CH2) (0.134 mmol) in 3 mL of CH2CI2 was prepared and cooled to -30°C. A solution of one equivalent of TMS-CsC- CH2-OTS (38 mg) in 1 mL of CH 2CI2 was added. The resulting solution was stirred at this temperature for 1 h before being reacted with an excess of methyl alcohol (1.00 mL, 0.790 g, 24.7 mmol). The reaction solution was checked by in situ 31P{ 1H} NMR of an aliquot. A mixture of four products was observed. This mixture slowly converted to a singlet with satellites over 12 h at room temperature. Complex 149a was precipitated by addition of ca. 60 mL of hexane to a concentrated benzene solution. It was isolated as a yellow solid in 74% yield (95 mg). 31P{1H> NMR (CDCI3): 8 15.9 (s, JPPt = 3673 Hz). 1H NMR (CDCI 3): 8 7.9-7.05 (m, Ph), 3.42 (s, OCH 3 ), 3.07 (br s, allylic CH 2 ), 2.27 (s, Ts's CH3 ). 31C{1H> NMR (CDCI3 ): 8 156.33 (t, JPC = 4 Hz, JPtc = 29 Hz, CH 2-C-CH2), 145-126 (m, Ph), 55.6 (s, OCH3), 53.07 (dd, JPC = 4.5 Hz, JPC = 40 Hz, JPtC = 108 Hz, CH2), 21.21 (s, Ts's CH3 ). MS (FAB) m/z: 790.4 (M+), 719 ((PPh 3 P)2Pt+). Alternative procedure A solution of 50 mg of (PPh 3 )2Pt(r)2-CH2=CH2) (0.067 mmol) in 1 mL of CH2 CI2 was cooled to -78°C. A solution of one equivalent of TMS-C=C-CH2-OTs (19 mg) in 1 mL of CH 2CI2 was added. A 50-fold excess of methyl alcohol (0.135 mL, 0.107 g) was syringed into the flask. The resulting reaction mixture was maintained at low temperature for one hour. The reaction mixture was then stirred at room temperature for 30 min. The completion of the reaction was checked at this point by 31p{lH} NMR spectroscopy. The major product was isolated by recrystallization from benzene/hexane in comparable yields (70-75%). 244 III-6 Preparation of [(PPh3)2Pt(ri3<:H2C[N(CH2CH3)2]CH2)](OTs) (149b) A solution of 100 mg of (PPh 3)2Pt(ri2-CH2=CH2) (0.134 mmol) in 2 mL of CH2 CI2 was cooled to -78°C. A solution of one equivalent of TMS-OC-CH 2 -OTS (38 mg) in 1 mL of CH 2CI2 was added. From a stock solution of Et2NH in CH 2CI2 (0.48 M), one equivalent of nucleophile (0.21 mL) was added. The resulting solution was stirred overnight while it was slowly allowed to warm to room temperature. A mixture of two products was observed by in situ 31P{1H} NMR. A fraction of the major product could be isolated pure in 27% yield (35 mg) by recrystallization from CH2Cl2/Et20- The filtrate was identified as a mixture of two products. No attempts were made to obtain further product. 31P{1H> NMR (CDCI3 ): 6 16.7 (s, JPPt = 3256 Hz). 1H NMR (CDCI3 ): 6 7.89, 7.11 (2d, J= 8 .1 Hz, Ts), 7.86-6.4 (m, Ph), 3.07 (q, J = 7.0 Hz, N(CH2 CH3)2), 2.30 (br s, CH 2), 2.26 (s, Ts's CH3 ), 0.99 (t, J= 7.0 Hz, N(CH2CH3 )2). 13C {1H} NMR (CDCI3): 5 158.01 (t, Jpc = 4.1 Hz, CH2 -C-CH2), 44.2 (s, N(CH2 CH3 )2), 40.8 (d, JpC = 47 Hz, CH 2-C), 21.2 (s, Ts's CH3), 13.04 (s, N(CH2CH3)2). MS (FAB): m/z 831.5 (M+), 719 ((PPh 3 )2Pt+). Alternative procedure A solution of 100 mg of (PPh 3)2Pt(Ti2-CH2=CH2) (0.134 mmol) in 3 mL of CH2CI2 was cooled to -30°C. A solution of one equivalent of TMS-C 3 C-CH2-OTS (38 mg) in 1 mL of CH 2CI2 was added. The resulting solution was stirred at this temperature for 1 hour before being reacted with an excess of Et 2NH (0.10 mL, 71 mg, 0.97 mmol). The solution was slowly allowed to warm overnight, and was checked by in situ 31P{1H} NMR. A mixture of two products was observed. The reaction mixture was evaporated, and the residue was washed successively with a mixture of 1 mL CH 2CI2/ 15 245 mL hexane, 15 mLEt 2 0 , and 2 mL Et20/15 mL hexane. The washings were discarded. The solid residue was then recrystallized from 2 mL of benzene and 15 mL of hexane. Complex 145b was isolated in 71% yield (80 mg) as a white powder. IV- Synthesis of various trimethvlenemethane complexes of platinum IV-1 Preparation of (PPh 3 )2 P t h 3 *CH 2 C(C(C 0 2 CH 3 )2 )CHPh] (78) Method 1:51 The reaction was performed in the dry-box owing to the sensitivity to moisture of the propargyl precursor. A solution of 980 mg of the propargyl complex [£PPh 3)2Pt(Ti3- CH2 CCPh)](OTf) (69) (0.996 mmol) in 100 mL of CH 2CI2 was added to one equivalent ofNaCH(C0 2CH3) 2 (153 mg, 0.996 mmol). The resulting solution turned from yellow green to orange almost immediately. The solution was stirred at room temperature for 1 h. The solvent was then removed under reduced pressure. About 20 mL of benzene was added to extract the product from the triflate salts. The extracts were then concentrated to about 5 mL, and precipitation of the product was induced by addition of ca. 100 mL of hexane. The complex (PPh 3)2Pt|/n 3-CH2C(C(C0 2 CH3)2)CHPh] (7 8 ) was isolated as a yellow solid, washed with hexane, and dried under vacuum for a day. Yield: 800 mg, 83%. 31P{1H} NMR (CD2CI2): 6 20.1 (Jpp = 3.6 Hz, 7p.pt = 3359 Hz), 18.6 (7p.pt = 3126 Hz). 1H NMR (CD2C12): 6 7.5-7.0 (m, Ph), 5.38 (m, 1H, CHPh), 4.00 (s, 1H, Hsyn), 3.49 (s, 6 H, CO2CH3), 2.60 (dd, 1H,7ph = 11.3 Hz, 7gem = 4.2 Hz, 7PtH = 55 Hz, Hanti). 13C{1H} NMR(CD 2C12): 6 170.7 (s, 7Ptc = 21 Hz, C0 2 CH3), 149.2 (t, JPC = 3.4 Hz, 7PtC = 91 Hz, H 2CC), 144-122 (m, Ph), 88.4 (s, 7PtC = 25 Hz, C=(C0 2 CH3)2), 70.7 (d, 7PC = 47 Hz, 7PtC = 227 Hz, CHPh), 50.3 (s, CC>2 CH3), 246 46.6 (d, Jpc = 42 Hz, Jptc = 159 Hz, CH 2). Anal. Calcd for C so H ^ ^ O ^ P t: C, 62.17; H, 4.59. Found: C, 61.97; H, 4.79. Method 2: A batch of 10-fold excess NaCH(C 0 2 CH3 )2 was freshly prepared by reaction of 0.18 mL of CH 2(C0 2 CH3 )2 with 16 mg of NaH in 20 mL of THF at room temperature. After stirring for an hour, the solvent was removed under reduced pressure, and the white solid was used without further purification. A solution of 50 mg of (PPh 3 )2Pt(r]2 -CH2=CH2) (0.067 mmol) in 5 mL of CH2CI2 was cooled to -78°C and transferred by cannula to the flask containing the carbanion. While the temperature was maintained at -78°C, one equivalent of Ph-CsC- CH2OTS (20 mg) in 1 mL of CH 2CI2 was slowly added. The temperature was allowed to rise over a period of 2 h. The reaction mixture turned pale cloudy yellow owing to the presence of salts. All starting material was converted into (PPl^Ptfri3- CH2C(C(C0 2 CH3)2)CHPh] (78) as indicated by 3ip{lH} NMR spectrum of the reaction mixture. The solvent was removed under reduced pressure. A gel-like residue was formed upon addition of ca. 10 mL of benzene. It was filtered off, washed with 5 x 5 mL of benzene, and discarded. A yellow filtrate (combined with the washings) was collected and concentrated to about 3 mL. The precipitation of a yellow solid was induced by addition of 10 mL of hexane. The product was collected by filtration and dried for 24 h. It was isolated as a pure solid in 80 % isolated yield (35 mg, 0.036 mmol) and was identified by 31P{1H} NMR and 1H NMR spectroscopy as the complex (PPh 3)2Pt[r|3 - CH2C(C(C02CH3 )2)CHPh] (78). 247 IV-2 Structure determination of (PPh3)2Pt[T]3‘CH2C(C(C02CH3)2)CHPh] (78)2.PhMe.l/2THF Crystals were grown by slow evaporation of solvent from a saturated solution of 78 (prepared in THF) in CH 2Cl2/toluene. The data collection crystal was a yellow pyramidally-shaped piece which had been cut from a larger crystal. As a check of crystal stability, six standard reflections were measured after every 150 reflections during the data collection. Their intensity decreased slightly, with the average change in intensity being 3.2%. Data processing was done with the TEXSAN software package . 188 A linear decay correction was applied to the data. There are two Pt complexes in each asymmetric unit. The position for the two Pt atom were found via the Patterson method, and the rest of the atoms were obtained by the DIRDIF procedure 190 and by standard Fourier methods. The two Pt atom are labeled A and B. The asymmetric unit also contains a toluene molecule (C(151)-C( 157)) which was modeled through a rigid group . 191 There appears to be a disordered THF molecule located about an inversion center. One of the atoms of the THF molecule resides on the inversion center, which makes it common to both sites of the molecule. All atoms in the THF atoms are labeled as (C(201)-C(205)) and given occupancy factors of 0.5. Thus, the asymmetric unit is composed of two Pt complexes, one toluene molecule, and a half of a THF molecule. Full-matrix least-squares refinements were done in TEXSAN; the function minimized was £to(IFol-IFcl)2 with to = l / o 2 ( F 0 ) . The data were corrected for absorption by using the empirical V scan method . 192 One of the esters groups in the Pt complex A is disordered over two sites and modeled in terms of two sets of atoms: C(7A), 0(3A), 0(4A), C(8 A) and C(7AA), 0(3AA), 0(4AA), C( 8 AA). The occupancy factor for one of these atoms was refined while the occupancy factor of the other atoms was constrained accordingly. As a result, fragment A has an occupancy factor of 0.56 while fragment AA 248 is at 0.44. Because of the disorder, the geometry for this portion of molecule A is not as well defined as in molecule B. The disordered ester group, the THF molecule, and the rigid toluene group were all kept isotropic. All of the other non-hydrogen atoms were refined anisotropically. The hydrogen atoms for the Pt complexes were included in the model as fixed contributions in calculated positions with C-H = 0.98 A and # h = 1 .2 #(eq) (attached carbon atom). The three trimethylenemethane hydrogen atoms for each complex were refined isotropically (H(71)-H(76)). One of these, H(75) acquired a large B value. Its B value was then fixed at 3 A2 for subsequent refinements, and only its positional parameters were refined. Methyl hydrogen atoms were idealized to sp 3 geometry based on positions located in different electron density maps. No hydrogen atoms were added to the toluene and THF molecules. Scattering factors for neutral atoms, along with terms for anomalous dispersion, were used. 189 Several reflections with uneven backgrounds were removed from the data set: (0, 3, 20), (2, 1, 25), (2, 1, 15), (1, 1, 12), (0, 3, 22), (3, 2, 17), and (4,4, 12). A summary of the crystal data and the details of the intensity data collection and refinement are provided in Table 19 in the appendix. Final positional and equivalent isotropic thermal parameters are given in Table 20 in the appendix. The list of bond distances and angles is given in Table 11 (Chapter II). IV-3 Synthesis of (PPh3)2Pth3-CH2C(C(C02CH3)2)CHCH3] (150) A solution of 100 mg of (PPh 3 )2PtCq2 -CH2=CH2) (0.134 mmol) in 5 mL of CH2CI2 was added to a flask containing a 10-fold excess (153 mg, 0.996 mmol) of NaCH(C0 2 CH3 )2 as a solid, and the mixture was cooled to -78°C. One equivalent of CH3 -CHC-CH2-OTs (30 mg) in a solution of 1 mL CH 2CI2 was then slowly added. The mixture was stirred for 4.5 h while the flask was slowly allowed to warm to room temperature. Solvent was removed under reduced pressure. The residue was extracted 249 with 20-mL portions of benzene. The extract was filtered and concentrated. Addition of ca. 60 mL of hexane induced the precipitation of a pale yellow powder which was collected on a filter frit, washed with hexane, and dried under vacuum for several hours (90 mg, 77% yield). 31P {1H} NMR (CDC13): 6 21.4 (d, JPPt = 3382 Hz), 18.45 (s, 7PPt = 3003 Hz). 1H NMR (CDCI3): 5 7.5-7.0 (m, Ph), 3.52 (s, CO 2CH3 ), 4.05 (m, CH2), 2.40 (d, J Hp = 9.5 Hz, 7HPt = 61.5 Hz, anti CH2), 1.05 (septet, allylic CH3). 13C{lH} NMR (CDCI3 ): 8 170.3 (t, Jp c = 11.7 Hz, CQ2CH3 ), 153.75 (s, 7PC = 84 Hz, CH 2-C), 135- 125 (m, Ph), 88.09 (s, C(C0 2CH3)2), 61.8 (d, JPC = 37 Hz, JPtC = 178 Hz, CHCH 3 ), 50.03 (s, C O ^H s), 42.5 (d, JPC = 40.5 Hz, 7Ptc = 171 Hz, CH2), 16.8 (d, 7PC = 6.01 Hz, Jptc = 48 Hz, CH 3 ). Anal. Calcd for C 45H4 2 0 4 P2Pt: H, 59.8; H, 4.68. Found: C, 60.53; H, 4.99. IV-4 Attempt to prepare (PPh3)2Pt[T|3-CH2C(C(C02CH3)2)CHSiMe3] (152) The procedure described below was used in order to prepare complex 152 using the method described for the synthesis of complexes 78 and 150. Preliminary results provided evidence for the occurrence of a side reaction affording complex 151. Optimized conditions for the preparation of complex 152 could not be established. The variation in product ratio and the difficulty in separation of the two components of the reaction mixture (151 and 152) prevented a complete characterization of the complexes. A solution of 100 mg of (Ph 3P)2Pt('n 2-CH2=CH2) (0.134 mmol) in 1 mL of CH2C12 was cooled to 0°C. A solution of one equivalent of Me 3 Si-CsC-CH2-OTs (38 mg) in 1 mL of CH 2C12 was added. A THF solution (4 mL) of 2.5 equivalents of NaCH(C0 2CH3 )2 (prepared from 50 pL (58 mg) of CH 2(C0 2 CH3 )2 and 1 0 mg of NaH) was then added. The reaction mixture turned cloudy while it was stirred at 0°C for 20 250 min. The solvent was then removed under reduced pressure. The residue was extracted with 10-mL portions of benzene. The salts were filtered off, washed with 5-mL portions of benzene, and discarded. The rest of the work-up was performed in the dry-box. The residue remaining after evaporation of the benzene extracts and washings was dissolved in a minimum amount of benzene (ca. 2 mL), and 20 mL of hexane was added to the resulting solution. A small amount of solid containing impure complex 152 was filtered off. The filtrate was collected, pumped down to dryness, and the residue dissolved in a minimum amount of benzene (ca. 0.5 mL). An off-white solid precipitated out upon addition of 20 mL of hexane and was collected by filtration. The solid was dried under vacuum. It was identified by 1H NMR and 31P{1H} NMR spectroscopy as the complex (PPh 3 )2Pt[r|3 -CH2C(C(C0 2 CH3 )2)CH2 ] (151). Complex 151 was the major product in most of the trials and was isolated in yields as high as 37% (44 mg). The presence of residual organic impurities as well as complex 152 prevented the acquisition of 13C{1H} NMR data. Complex 151: 31P{1H> NMR (CDC13): 6 19.9 (JptP = 3066 Hz). 1H NMR (CDCI 3 ): 5 7.5-7.0 (m, Ph), 3.45 (s, CO 2CH3 ), 3.0 (m, CH2). In-situ data for complex 152: 31P{1H} NMR (CDCI3 ): 6 19.88 (7Ptp = 2936 Hz), 22.49 (JPtp = 2933 Hz). 1H NMR (CDCI3 ): 6 6.7-7.8 (m, Ph), 4.5 (br s, allylic CH 2), 4.15 (m, allylic CH2), 3.6 (s, CO2CH3 ), 1.96 (m, allylic CH2), 0.1 (s, Si(CH3)3) . 251 V- Reactivity of trimethvlenemethane complexes of platinum V-I Reaction of (PPh3)2Pt[ri3-CH2C(C(C02CH3)2)CHPh] (78) with diethyl fumarate Complex (PPh 3)2Pt[r]3-CH2C(C(C0 2 CH3 )2)CHPh] (75 mg, 0.078 mmol) was dissolved in 5 mL of benzene and reacted with one equivalent of diethyl fumarate (0.020 mL, 14 mg) for 18 h at reflux temperature. The completion of the reaction was monitored by 3ip{lH} NMR spectroscopy. The slightly cloudy reaction solution was then filtered, and the filtrate was pumped down to dryness. The residue was washed with 10 mL of Et20. The undissolved complex (PPh 3 )2Pt[Ti2-CH3CH2 0 2 C(H)C=C(H)C0 2 CH2CH3 ] (132) (an off-white solid) was collected by filtration, washed with 5-mL portions of Et20, and dried under vacuum (51 mg, 73% yield). All the washings were combined and pumped down to dryness. The resulting residue was extracted into 10 mL of hexane at -78<>C for 1 h. The extract was filtered. The oil obtained after evaporation of the solvent from the filtrate contained a mixture of two products 133 and 134 as indicated by its 1H NMR spectrum. Purification by filtration through a short column of silica gel (eluent: CH2CI2) afforded complex 134 (off-white needles) in 53% yield (10 mg). In some instances, isomer 134 was the only one observed in the 1H NMR spectrum of the reaction solution, indicating that the isomerization was complete at the end of the reaction. Data for complex 132: IR (o, C6H6): (COOMe): 1753 s; (Ph C=C): 1617 m, 1528 m, 1435 m cm-L 3 lp {1 h > NMR (C6H6): 625.8 (s,JP.Pt = 3862 Hz). 1H NMR (C6D6): 6 8.0-6.5 (m, Ph), 4.18 (d, 2H, /ph = 3.5 Hz, JptH = 56 Hz, =C(H)C0 2CH2CH3), 3.92, 3.43 (m, 4H, =C(H)C02CH2CH3)> 0.75 (t, 6 H, J = 7.06 Hz, =C(H)C0 2CH2 CH3 ). 13C {1h> NMR (C6 D6): 6 173.0 (t, M -c - 39.6 Hz, CO^CH^), 136-127 (m, Ph), 58.5 (s, C0 2 CH2CH3), 49.01 (t, Jp.c = 13.5 Hz, J?t.c = 215.6 Hz, =CH(OEt)), 13.95 252 (CO2 CH2CH3 ). M S (FAB): m/z 892 (M+), 818 (M+-CH 3 CH2OH-CO), 719 t(PPh 3 )2Pt+]. Selected data for compound 133: 1H NMR ( CeHe) selected data: 5 4.65 (d, Jgeminal= 2.4 Hz), 5.77 (t, ./allylic = 2.6 Hz), 6.23 (d, /geminal = 2.9 Hz). Data for compound 134: 1H NMR (CDCI3 ): 6 2.41 ppm (s, allylic CH 3 ), 3.83, 4.16 (s, CO 2 CH3), 7.54-7.00 (m, phenyl group). 1 3 C{lH> NMR(CDC13): 5 164.08, 161.8 (s, CO 2CH3 ), 139.5 (s,_C(CH3)=), 130. 5 (s), 128.4, 126.7, 125.4 (d, Ph’C), 118.02 9 (s, C(Ph)=), 93 06 (s, C(C02CH3)2), 57.5, 50.8 (q, C O ^H s), 10.9 (q, CH3). MS (El): m/z 492.178 (M+), 461 (M+-OCH3 ), 434 (M+-OCH3 -CO), 402 (M+-20CH3 -CO), 374 (M+- 2 OCH3 -2 CO), 246 (M+/2). V-2 Preparation of complex 137 by reaction of (PPh 3 )2 Pt[r|3 - CH2 C(C(C 0 2 CH 3 )2 )CHPh] (78) with tetracyanoethylene (TCNE) A solution of complex 7 8 (200 mg, 0.207 mmol) and one equivalent of freshly sublimed TCNE (28 mg) was prepared in 5 mL of benzene. During the entire reaction time, the flask was protected from light by aluminum foil. The solution was stirred for 1.5 h, during which time it turned darker orange and a small amount of gelatinous residue formed. The reaction mixture was then filtered and the solid was discarded. After evaporation of the filtrate, the crude product was washed with 10 mL of Et 20. The resulting yellow solid was then recrystallized from CH 2 C12/Et20 while the Et20 washings were discarded. Complex 137 was dried under vacuum for 2 days. Yield: 132 mg, 58%. IR (v, C6H6): (CN): 2196 w; (COOMe): 1704 s; (C=C): 1600 m, 1481m, 1435 m cm'1. 31P{1H> NMR (CDCI3 ): 6 21.1 (d, JP.P = 22.2 Hz, 7P.Pt = 3430 Hz), 21.9 (d, JP.Pt 253 = 3930 Hz). 1H NMR (CDCI 3 ): 6 3.68, 2.52 (s, 6 H, CO2CH3 ), 6.19, 3.04, 2.16 (s, 1H, ethylenic protons, 8.0-7.0 (m, Ph). 13C{1H} NMR (CDCI 3 ): 6 171.5 (m, CO2CH3 ), 170 (m, CO2CH3), 140-127 (m, Ph), 111.9 (s, CN), 111.4 (s, CN), 110.7 (s, 2 CN), 57.0 (dd, 7PC = 57 Hz, 3.4 Hz, CHPh), 55.3 (d, C(C 0 2 CH3)2), 51.9 (s, CO2 CH3), 50.1 (s, CO2CH3), 44.7 (d, C(CN)2), 44.5 (d, C(CN)2), 43.8 (d, JPC = 47 Hz, CH2). Anal. Calcdfor Cs 6 H44N4 0 4 P2Pt: C, 61.48; H, 4.05; N, 5.12. Found: C, 61.31; H, 4.21; N, 4.99. V-3 Reaction of complex (PPh 3 ) 2 Pt[Tl3 -CH 2 C(C(C 0 2 CH 3 ) 2 )CHPh] (78) with p-toluenesulfonyl isocyanate (TSI) A stock solution of TSI was prepared in the dry-box, just before reaction, by dissolving 0.250 mL of TSI (commercial reagent opened in the dry-box) in 2.25 mL of CH2C12 (0.656 M). Alternatively, TSI reagent was weighed in the dry-box. A solution of 0.200 g of complex 7 8 (0.202 mmol) was dissolved in 5 mL of CH2C12 and treated with one equivalent of TSI (40 mg or 0.305 mL of the stock solution). As the solution was stirred at room temperature for 3 h, it turned darker, then lighter orange. The solvent was removed under reduced pressure, and ca. 10 mL of THF was added. The solution was stirred for 30 min, during which time a large amount of white precipitate formed (139) and was collected by filtration (42 mg). It was washed with 5-mL portions of THF. The filtrate was combined with the THF washings of the precipitate and concentrated. A yellow-orange solid formed upon addition of hexane, but could not be purified further. The slightly colored supernatant solution was pumped down to dryness, and the residue was washed with hexane to eliminate organic contaminants. Compound 140 (off-white solid) was then collected and dried under vacuum for 2 days. Isolated yield: 33 mg, 0.074 mmol, 36%. Compound 139: 2 5 4 lR(v, C6 H6): (C=C): 1598 m, 1550 m, 1481 m, (SO): 1020 s cn r1. 3 ip {lH } NMR (CDCI3 ): 8 (crude mixture) major product 12 5.03 (s, Jp.pt = 3704 Hz) and a minor product 13: 14.0 (d,7p_p= 13.4 Hz,Jp_pt= 3836 Hz), 14.5 (d^/p.pt= 3959 Hz). 1H NMR (CDCI3 ): 8 (complex 12:) 8.0-6.5 (m,19 H, Ph), 2.28 (s, 3H, CH 3 -PI1). 13C{1H> NMR (CDCI3): 8 (complex 12) 141.0, 139.98 (ipso carbons), 134-127 (Ph), 21.27 (Ph-CH3). Anal. Calcd. for C 52H44N2Q;P2PtS2: C, 56.06; H, 3.98; N, 2.51. Found: C, 55.70; H, 4.13; N, 2.61. Compound 140: 1R (u, C6H6) (compound 14): 1773 (CO of esters), 1679 (CO of amide), 1570, 1549, 1436 (C=C), 1377, 1176 (S02). *H NMR (CDCI 3): 8 (compound 14) 8.0-6.5 (m, Ph), 5.83 (t, 1H,Jh_h = 2.25 Hz), 5.60 (d of d, 1H,/h.h = 1.93 Hz), 5.33 (dd, 1H,7h.h = 1.98 Hz), 3.79 (d, 3H, CC^CHs), 3.77 (s, 3H, CC^Q b), 2.40 (s, 3H, PI 1-CH3). 13C{1H> NMR (C6De): 8 165.34, 165.19 (s, CO 2CH3 ), 164.50 (s, CO-N), 144.90 (s, C=CH2), 136-126 (m, Ph), 118.60 (s, =CH2), 67.99 (s, ^(CC^CHs)^, 66.43 (s, CHPh), 53.38, 53.13(s, C 0 2 CH3 ), 21.12 (s, Ph-CH3). MS (El): m/z 443 (M+), 412 (M+-OCH3 ), 384 (M+-OCH 3-CO), 288 (M+-Ts). Anal. Caicd for C 22H2 i0 7 NS: C, 61.81; H, 4.95. Found: C, 62.00; H, 4.94. V-4 Reaction of (PPh 3 )2 Pt[ri3 CH2 C(C(C 0 2 CH 3 >2 )CHCH 3 ] (150) with fumaronitrile A solution of the complex (PPh 3)2Pt[ri3-CH2C(C(C0 2CH3 )2)CHCH3 ] (150) (30 mg, 0.033 mmol) in 0.5 mL of benzene-^ was treated with two equivalents of freshly sublimed fumaronitrile (5 mg). The reaction solution was monitored by 31P{1H} NMR and 1H NMR over 44 h at room temperature. The in-situ spectra showed evidence for the formation of complex 153, which was isolated. The organic cycloadduct 154 that was observed could not be isolated. Decomposition occurred upon work-up. 255 Complex 153. 3ip{lH> NMR (CDCI3): 6 22.97 (JPPt = 3709 Hz). 1H NMR (CDCI3): 5 8.0-7.0 (Ph), 2.57 (d, Jhh = 5.9 Hz, =C(CN)H). Compound 154. 1H NMR (CDCI3): 6 5.49, 4.88 (d, Jhh = 1.3 Hz), 3.25 (s, CO2CH3), 2.27 (q, allylic H), 0.75 (d, 7hh = 7.1 Hz, CH3). V-5 Preparation of complex 155 by reaction of (PPh3)2Pt[ri3- CH2C(C(C02CH3)2)CHCH3] (150) with TCNE A solution of the complex (PPh 3)2Pt[ri3-CH2C(C(C0 2 CH3 )2)CHCH3] (150) (100 mg, 0.110 mmol) in 10 mL of benzene was treated with one equivalent of TCNE (14 mg). The reaction was monitored by 3lp{lH> NMR, and total conversion was observed after one hour. The solvent was then removed under reduced pressure. The residue was washed with 10 mL of Et 2 0 at room temperature. The resulting yellow solid was isolated by filtration and washed with 5-mL portions of Et 20. It was identified by NMR spectroscopy and elemental analysis as complex 155. Yield: 85 mg, 61%. 31P{1H> NMR (CDCI3 ): 6 20.46 (d, 7PP = 18 Hz, 7PPt = 3839 Hz), 20.15 (d, 7PPt=3560 Hz). 1H NMR (CDCI3): 6 8.0-6.8 (m, Ph), 4.48 (m, CH 3 (H)C=), 3.2 (d, 7hh= 14.8 Hz, allylic CH2), 2.3 (dd, 7gem= 14.7 Hz, JHP= 9.3 Hz, allylic CH2), 3,45, 3.05 (2s, CO2CH3 ), 1.02 (d, 7HP = 7.4 Hz, CH3 ). 13C {lH } NMR (CDCI3): 5 170.6, 170.1 (m, CO2CH3 ), 138-125 (m,P(C 6H5)3 ), 112.8, 112.14, 111.8, 111.24 (4s, CN), 63.3 (dd, JPC = 59 Hz, JPC = 4 Hz, 7PtC = 405 Hz, CH3 (H)C=), 53.07 (dd, 7PC = 38 Hz, 7Pc = 5 Hz, Jptc = not readable, olefinic carbon), 51.8,51.2 ( 2 s, CO2 CH3), 48.15, 43.6 (2 s, C(CN)2), 49.7 (s, 7PC = 8.5 Hz, CfCC^CHsh), 43.15 (dd, 7PC = 12 Hz, JPtC = 63 Hz), 20.4 (d, 7PC = 4.6 Hz, 7PtC = 31 Hz, CH3 (H)C=). Anal. Calcd. for C5 iH4 2N4 0 4 P2Pt: C, 59.36; H, 4.10; N, 5.43. Found: C, 59.84; H, 4.92; N, 5.18. 2 5 6 V-6 Reaction of complex £>PPh3)2Pt[t]3-CH2C(C(C02CH3)2)CHCH3] (150) with TSI The complex lPPh 3 )2Pt['n 3-CH2C(C(C0 2CH3 )2)CHCH3 ] (150) ( 1 0 0 mg, 0 .1 1 mmol) was dissolved in 5 mL of THF, and the solution was treated with two equivalents of TSI (60 mg). The resulting solution was then stirred overnight at room temperature. The color turned brighter orange during the reaction, and an abundant white precipitate formed. The precipitate (complex 139) was filtered off, washed with 2-mL portions of THF, and dried in vacuo (107 mg). The filtrate was pumped down to dryness. The bright orange residue was then stirred in ca. 20 mL of Et 2 0. A bright orange solid was separated from a lightly colored washing that contained a small amount of an organic product. A phenyl-containing contaminant was eliminated by washing the orange solid several times with 20-mL portions of Et 20. 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APPENDIX 272 273 Table 15: Crystal data and data collection and refinement details for 125 formula Ci2Hi2NC>7Re fw 468.44 space group PI a, A 8.721(1) b, A 12.172(1) c, A 15.0'3(2) a, deg 86.42(1) P, deg 88.83(1) Y> deg 79.48(1) V,A3 1563.7(4) Z 4 Scaled, gcm-3 1.99 cryst size, mm 0.11 x 0.29x0.38 radiation Mo Kq p, (cm-1) 79.03 temperature ambient 20 limits, deg 4 -5 5 scan speed (4° min-l in oo with max. 4 scans 4 refln-l) transmission factors 0.77 - 0.44 scan type 0) scan range, deg (in u>) 1.30 + 0.35 tan 0 data collected +h, +k, +/ unique data 7185 274 Table 15 (continued) unique data (F02 > o(F02)) 5120 final variables 387 R(F) 0.031 RW(F) 0.032 error in obsn of unit wt, e 1.13 Table 16: Positional parameters and equivalent thermal parameters for 125 Atom X y z B(eq)«(A2) Re(lA) 0.14812(3) 0.21122(2) 0.42805(2) 4.41(2) 0(1 A) 0.4172(5) 0.4900(4) 0.2095(3) 6.4(3) 0(2A) 0.5883(5) 0.3923(4) 0.3034(3) 5.7(3) 0(3A) 0.4343(5) 0.3404(4) 0.4492(3) 5.3(3) 0(4A) 0.1907(7) 0.1488(5) 0.6287(3) 7.3(4) 0(5A) -0.1316(9) 0.0861(6) 0.4240(4) 9.6(5) 0(6A) -0.0953(7) 0.4234(5) 0.4728(4) 7.1(4) 0(7A) 0.391(1) -0.0010(6) 0.3879(5) 11.9(6) N(1A) 0.1274(6) 0.2591(5) 0.2889(3) 4.3(3) 0(1 A) 0.2196(7) 0.3202(5) 0.2519(3) 3.5(3) C(2A) 0.3360(7) 0.3496(5) 0.3079(3) 3.5(3) C(3A) 0.3188(7) 0.3101(5) 0.3967(4) 3.9(3) C(4A) 0.2031(7) 0.3542(6) 0.1546(4) 4.6(4) C(5A) 0.4448(7) 0.4183(5) 0.2686(4) 3.9(3) C(6A) 0.7018(8) 0.4553(7) 0.2672(5) 4.6(4) C(7A) 0.443(1) 0.3038(8) 0.5437(4) 3.9(3) C(8A) 0.579(1) 0.334(1) 0.5802(5) 6.6(5) C(9A) 0.177(1) 0.1734(6) 0.5543(5) 7.2(6) C(10A) -0.027(1) 0.1293(7) 0.4263(5) 10.0(8) C(11A) -0.0042(9) 0.3484(6) 0.4560(4) 5.5(4) C(12A) 0.301(1) 0.0757(8) 0.4027(5) 6.4(5) Re(lB) 0.97175(3) 0.72629(2) 0.14178(1) 4.9(4) 0(1B) 1.1104(6) 0.8121(5) -0.1836(3) 7.0(6) 276 Table 16 (continued) 0(2B) 1.3229(5) 0.8501(4) -0.1278(3) 3.54(1) 0(3B) 0.9052(4) 0.8760(3) -0.0440(2) 6.3(3) CK4B) 0.6276(6) 0.8113(5) 0.1881(3) 5.2(3) 0(5B) 1.0152(7) 0.5848(5) 0.3210(3) 4.0(2) 0(6B) 0.8453(6) 0.5369(4) 0.0527(3) 6.8(3) 0(7B) 1.0600(8) 0.9286(5) 0.2369(4) 7.5(3) N(1B) 1.2098(6) 0.6699(5) 0.1059(3) 5.8(3) C(1B) 1.2630(6) 0.7021(5) 0.0287(4) 8.4(4) C(2B) 1.1510(6) 0.7740(5) -0.0278(3) 4.2(3) C(3B) 1.0040(6) 0.8046(5) 0.0094(3) 3.7(3) C(4B) 1.4293(7) 0.6627(6) 0.0024(4) 3.3(3) C(5B) 1.1893(6) 0.8127(5) -0.1202(4) 3.2(3) C(6B) 1.3664(9) 0.8855(7) -0.2170(5) 5.1(4) C(7B) 0.7481(7) 0.9172(6) -0.0149(4) 3.6(3) C(8B) 0.6741(8) 0.9975(7) -0.0859(5) 6.0(4) C(9B) 0.7570(8) 0.7821(6) 0.1702(4) 4.8(4) C(10B) 0.9972(8) 0.6377(6) 0.2553(4) 4.7(4) C(11B) 0.8978(7) 0.6047(6) 0.0843(4) 4.2(3) C(12B) 1.0308(8) 0.8559(6) 0.2010(4) 5.2(4) aThe form of the equivalent isotropic displacement parameter is: B(eq) = (8jt2/3)q2j2jUa* ja*jaj- aj 277 Table 17: Crystal data and data collection and refinement details for (78)2.PhMe.l/2 THF formula 2(C50H44O4P2Pt).C7H8.l/2(C4H8O) fw 2060.06 space group P2\ln a, A 12.750(2) b, A 18.503(4) c, A 39.648(6) P, deg 94.69(1) V,A3 9322(5) Z 4 Dcalcd, gcm-3 1.47 cryst size, mm 0.38 x 0.38 x 0.58 linear abs coeff, cm-1 31.52 temp, °C 22 diffractometer Rigaku AFC5S radiation (X, A) Mo Kq with graphite monochromator (0.71073) transmission factors 0.77 -1.0 (empirical tp scan method) 26 limits, deg 4 -5 0 scan speed, deg min-1 (in co) 4 (3 rescans) scan type co scan range, deg (in co) 0.90 + O.35tan0 data collected +h, +k, ±1 278 Table 17 (continued) no. of reflns measured 17,795 (total), 16,980 (unique, /?int 0.041) no. of reflns used (7>3a(/)) 9982 no. of variables 1070 R(F) 0.045 Rw(F)a 0.050 error in obsn of unit wt, e 1.56 max peak in final diff map, e A-3 1.57 max peak in final diff map, e A 3 -1.40 aRw(f) = [2co(|F0l - |Fcl)2/2a)F02]l/2j with to= (l/a2)F0 279 Table 18: Positional and equivalent isotropic parameters for C78V>.PhMe.l/2 THFS Atom X y Z Z?eqb o r By A 2 Pt(lA) 0.40685(3) 0.16701(2) 0.09771(1) 3.25(2) P(1A) 0.3064(2) 0.1845(1) 0.14199(6) 3.7(1) P(2A) 0.2786(2) 0.1694(1) 0.05317(6) 3.7(1) 0 ( 1A) 0.6665(7) 0.2413(5) 0.0301(2) 7.8(5) 0{ 2A) 0.6909(7) 0.3497(4) 0.0532(2) 6.5(5) 0( 3A) 0.561(1) 0.3232(8) 0.1346(4) 6.4(4) 0(3AA) 0.775(2) 0.320(1) 0.1163(5) 6.2(5) 0( 4A) 0.724(1) 0.3431(8) 0.1248(4) 5.9(3) 0 (4AA) 0.618(2) 0.317(1) 0.1376(6) 5.8(5) C (lA) 0.5589(7) 0.1617(6) 0.1239(2) 3.9(5) C(2A) 0.5855(7) 0.1889(6) 0.0913(3) 4.4(5) C(3A) 0.5312(8) 0.1452(6) 0.0658(3) 4.0(5) C(4A) 0.6309(8) 0.2590(6) 0.0870(3) 4.5(5) C(5A) 0.6639(9) 0.2795(7) 0.0551(3) 5.3(6) C(6A) 0.733(1) 0.3741(8) 0.0228(4) 9(1) C(7A) 0.628(2) 0.315(1) 0.1185(6) 4.5(5) C(7AA) 0.679(2) 0.300(1) 0.1123(5) 3.2(4) C(8A) 0.734(2) 0.388(1) 0.1539(6) 6.9(5) C(8AA) 0.663(2) 0.364(2) 0.1648(7) 6.1(6) C(9A) 0.5992(8) 0.0868(6) 0.1335(2) 4.1(5) C(10A) 0.6886(8) 0.0591(6) 0.1189(3) 4.9(5) Table 18(continued) 280 C(11A) 0.7345(9) -0.0051(7) 0.1305(3) 5.9(7) C(12A) 0.695(1) -0.0430(7) 0.1562(3) 6.1(7) C (13 A) 0.607(1) -0.0159(6) 0.1711(3) 6.4(7) C(14A) 0.5594(8) 0.0484(6) 0.1600(2) 4.6(5) C (15A) 0.3708(8) 0.1803(6) 0.1845(2) 4.1(5) C (16A) 0.4487(9) 0.2300(6) 0.1937(3) 5.5(6) C(17A) 0.5016(9) 0.2290(7) 0.2265(3) 5.9(7) C(18A) 0.477(1) 0.1780(8) 0.2489(3) 5.9(7) C(19A) 0.400(1) 0.1265(7) 0.2408(3) 5.8(6) C(20A) 0.3475(8) 0.1279(6) 0.2086.(3) 4.9(6) C(21A) 0.2038(8) 0.1163(6) 0.1427(2) 4.1(5) C(22A) 0.240(1) 0.0459(7) 0.1368(3) 5.9(7) C(23A) 0.167(1) -0.0119(7) 0.1366(4) 7.8(9) C( 24A) 0.063(1) 0.002(1) 0.1424(4) 8(1) C (25A) 0.032(1) 0.070(1) 0.1488(4) 8(1) C(26A) 0.0997(9) 0.1273(7) 0.1486(3) 6.2(7) C(27A) 0.2481(8) 0.2749(6) 0.1439(3) 4.4(5) C(28A) 0.279(1) 0.3277(7) 0.1223(3) 6.0(7) C(29A) 0.239(2) 0.3969(9) 0.1236(4) 9(1) C(30A) 0.165(2) 0.412(1) 0.1460(7) 12(1) C(31A) 0.140(1) 0.361(1) 0.1684(6) 11(1) C(32A) 0.181(1) 0.2921(7) 0.1687(4) 7.8(8) C{33A) 0.1391(8) 0.1772(6) 0.0601(2) 4.3(5) C(34A) 0.0699(9) 0.1184(7) 0.0594(3) 6.1(7) C ( 3 5 A) -0.035(1) 0.128(1) 0.0659(4) 8(1) C(36A) -0.072(1) 0.191(1) 0.0728(4) 7.6(9) Table 18(continued) 281 C(37A) -0.009(1) 0.2508(8) 0.0734(3) 7.4(8) C(38A) 0.097(1) 0.2443(7) 0.0672(3) 5.9(7) C(39A) 0.2978(8) . 0.2427(5) 0.0237(2) 4.1(5) C(40A) 0.3837(7) 0.2882(5) 0.0276(2) 4.1(5) C(41A) 0.398(1) 0.3424(6) 0.0046(3) 5.6(6) C(42A) 0.328(1) 0.3518(7) -0.0228(3) 6.4(7) C(43A) 0.240(1) 0.3090(8) -0.0273(3) 7.1(8) C(44A) 0.2249(9) 0.2551(7) -0.0041(3) 5.6(6) C(4 5A) 0.2855(8) 0.0861(6) 0.0287(3) 4.2(5) C(46A) 0.289(1) 0.0215(7) 0.0462(3) 7.0(8) C(47A) 0.291(1) -0.0440(7) 0.0300(4) 8.1(9) C ( 4 8A) 0.291(1) -0.046(1) -0.0049(5) 8(1) C(4 9A) 0.292(1) 0.016(1) -0.0214(4) 10(1) C(50A) 0.288(1) 0.0813(7) -0.0055(3) 7.5(8) Pt(lB) 0.88736(3) 0.19664(2) 0.328333(9) 2.99(2) P (IB) 0.9876(2) 0.1808(1) 0.28384(6) 3.4(1) P(2B) 1.0177(2) 0.1881(1) 0.37222(6) 3.6(1) 0(IB) 0.6297(7) 0.1185(5) 0.3957(2) 7.6(5) 0( 2B) 0.6190(7) 0.0098(5) 0.3720(2) 8.0(5) 0(3B) 0.7056(7) 0.0465(5) 0.2877(2) 7.5(5) 0( 4B) 0.5506(6) 0.0261(5) 0.3066(2) 7.1(5) C(IB ) 0.7336(7) 0.2056(5) 0.3021(2) 3.5(5) C(2B) 0.7082(7) 0.1737(5) 0.3340(2) 3,5(4) C(3B) 0.7645(7) 0.2160(6) 0.3611(2) 3.7(5) C(4B) 0.6621(7) 0.1069(6) 0.3379(2) 4.1(5') Table 18(continued) 282 C(5B) 0.6362(9) 0.0816(7) 0.3710(3) 5.1(6) C(6B) 0.591(1) -0.0195(8) 0.4032(4) 10(1) C(7B) 0.646(1) 0.0565(6) 0.3092(3) 5.4(6) C(8B) 0.539(1) -0.0253(8) 0.2784(3) 9(1) C(9B) 0.6969(7) 0.2811(5) 0.2936(2) 3.7(5) C(10B) 0.7405(8) 0.3219(6) 0.2693(3) 4.7(5) C(11B) 0.699(1) 0.3883(7) 0.2594(3) 6.0(7) C(12B) 0.613(1) 0.4155(7) 0.2743(4) 6.8(8) C(13B) 0.566(1) 0.3750(7) 0.2977(3) 6.3(7) C(14B) 0.6088(8) 0.3085(6) 0.3082(3) 4.7(5) C(15B) 0.9244(7) 0.1881(5) 0.2419(2) 3.8(5) C(16B) 0.9497(8) 0.2406(6) 0.2178(2) 4.5(5) C(17B) 0.8978(9) 0.2430(6) 0.1860(3) 5.2(6) C(18B) 0.820(1) 0.1935(7) 0.1770(3) 5.9(6) C(19B) 0.7952(9) 0.1422(7) 0.1993(3) 5.9(6) C(20B) 0.8462(8) 0.1388(5) 0.2314(2) 4.2(5) C(21B) 1.0909(7) 0.2486(5) 0.2847(2) 3.6(5) C(22B) 1.1940(9) 0.2374(6) 0.2782(3) 5.2(6) C(23B) 1.2662(9) 0.2947(7) 0.2803(3) 6.0(7) C(24B) 1.235(1) 0.3605(7) 0.2895(3) 6.2(7) C{25B) 1.134(1) 0.3735(6) 0.2967(3) 5.6(6) C(26B) 1.0624(8) 0.3178(6) 0.2943(3) 4.6(6) C(27B) 1.0461(7) 0.0913(6) 0.2819(3) 4.2(5) C(28B) 1.1132(9) 0.0740(6) 0.2572(3) 6.1(7) C(29B) 1.156(1) 0.0046(9) 0.2569(5) 9(1) C(30B) 1.131(1) -0.0462(8) 0.2802(5) 8(1) Table 18(coiitinued) 283 C(31B) 1.063(1) -0.0296(7) 0.3041(4) 7.8 ('8) C(32B) 1.0194(9) 0.0391(6) 0.3044(3) • 5.0(6) C(33B) 1.1573(7) 0.1893(6) 0.3650(2) 4.0(5) C(34B) 1.2059(8) 0.1282(6) 0.3548(3) 4.9(6) C(35B) 1.313(1) 0.1280(7) 0.3485(3) 5.9(7) C(36B) 1.369(1) 0.1904(8) 0.3524(4) 7.0(8) C(37 B) 1.323(1) 0.2524(7) 0.3621(3) 6.3(7) C(38B) 1.2167(8) 0.2516(6) 0.3685(3) 5.1(6) C(39B) 1.0064(8) 0.1047(5) 0.3962(2) 4.4(5) C(40B) 1.0842(9) 0.0816(7) 0.4200(3) 6.0(6) C(41B) 1.072(1) 0.0193(8) 0.4376(4) 8.0(9) C(42B) 0.984(1) -0.0223(8) 0.4317(4) 8.0(9) C(43B) 0.906(1) -0.0005(6) 0.4088(3) 5.9(6) C(44B) 0.9171(8) 0.0620(6) 0.3906(2) 4.6(5) C(45B) 1.0034(7) 0.2614(6) 0.4019(2) 4.1(5) C(46B) 0.980(1) 0.3292(7) 0.3897(3) 6.8(7) C(47B) 0.975(1) 0.3900(7) 0.4102(4) 8.3(8) C(48B) 0.991(1) 0.379(1) 0.4441(4) 8(1) C(49B) 1.015(1) 0.313(1) 0.4580(3) 9(1) C(50B) 1.022(1) 0.2545(7) 0.4356(3) 6.5(7) C(201) 0.620(2) 0.038(2) 0.5307(7) 7.0(6) C(202) 0.565(3) 0.046(2) 0.5092(9) 9.0(8) C(203) 0.497(2) 0.066(2) 0.4871(7) 7.9(7) C(204) 0.593(3) -0.037(2) 0.5366(9) 11(1) C(205) 1/2 0 1/2 20(1) C(151) 0.0922(8) 0.1242(8) 0.9215(3) 14.6(3) Table 18(continued) 284 C(152) 0.071(1) 0.1966(8) 0.9139(3) 14.6(3) a a C(153) -0.004(1) 0.2341(5) 0.9307(3) 14.6(3) * * C(154 ) -0.0576(7) 0.1991(6) 0.9553(2) 14.6(3) * A C(155) -0.037(1) 0.1267(6) 0.9630(3) 14.6(3) A A C(156) 0.038(1) 0.0892(5) 0.9461(4) 14.6(3) A A C(157) -0.140(1) 0.2402(9) 0.9738(4) 14.6(3) A A aEstimated standard deviations in the least significant figure are given in parentheses. Atoms 0(3A), 0(4A), C(7A), and C(8A) have occupancy factors of 0.56. 0(3AA), 0(4AA), C(7A), and C(8A) have occupancy factors of 0.5. t>The form of the equivalent isotropic displacement parameter is fl(eq) = (8n2/3)qZi2jUa*ia*jai*aj. Asteriks designate atoms refined isotropically. Double asteriks designate atoms refined as part of a rigid group.