91P4D148-1-31T ORGANOMETALLIC COMPOUNDS OF
BORON AND SOME TRANSITION METALS
A Thesis submitted for the Degree of
Doctor of Philosphy
in the University of London
by
APAR SINGH
Imperial College of Science and Technology, London, SOV.7. December, 1959. DEDICAT7D TO MY PROF7,SSOR. ABSTRACT.
Part I describes the preparation and properties of tristr:Lalkyl- silyl esters of boron. The most convenient method was, howeve:7, by the silanolysis of trisdiethylamino boron. Bistriethylsilyl phenyl boronate [(2t3Si0)2BPh)] and triethylsilyldiphenyl borinate
[(Tqt3Si0BPh21 have been prepared. These compounds undergo slow hydrolysis and rapid dealkylation with halogen acids, and are thermally very stable. The trisalkylsilyl metaborates have been formed :from bori oxide and the corresponding orthoborates. They are trimeric
(cryoscopic measurement) and possess cyclic boroxole structure, which is supported by the presence of a doublet at 720 and 735 cm. in the infrared structure recently assigned to the out-of-plane vibration of boroxole skeleton.
Part II describes a number of substituted binuclear cyclopentadienyl carbonyls of molybdenum, tungsten and iron, which have been made by the direct interaction of the metal carbonyls with fulvones. The corres- ponding mononuclear iodides and some alkyl derivatives have been obtained. n-Cyclopentadianyl molybdenum 7-cyclopentadienyl tungsten hexacarbonyl, 7t-05115Mo(C0)6W.n-05H5, is the first reported complex compound with a metal-metal bond between different transition metal atoms. Abstract (continued).
Triphenylphosphonium cyclopentadienylide metal complexes of
molybdenum, tungsten, chromium and iron have been prepared by the direct
interaction of the metal carbonyl with triphenylphosphonium cyclopenta-
dienylide in which the five-membered carbocyclic ring (cyclopentadienyl
ring) has a sextet of electrons and acts as a six-electron donor ligand
comparable to aromatic hydrocarbons. N.M.R. studies have shown beyond
doubt that the -M(C0)3 residue is attached to the cyclopentadienyl ring
and not to one of the phenyl groups, since there is no change in the
resonances of the phenyl group protons whereas the line due to the protons
on the cyclopentadienyl ring shifts to higher fields in the metal
complexes compared to the original ligands.
Molybdenum(II) dibenzoate, a novel type of oxygen chelatate complex, where, in addition, the arene nucleus is bound to the metal atom by a
sandwich-type bond, as in arene-metal carbonyls, is described. From
physical and chemical data, the structures of molybdenum(II) dibenzoate
and related compounds have been assigned.
C ONTENT S.
Chapter PART I Page,
Historical
I The Esters of Boron 1
II The Trialkyl/aryl Siloxy Inorganic Compounds 4
Discussion
III Preparation of Trialkylsilyl Esters of Boron 10
IV Properties of Trialkylsilyl Esters of Boron (Chemical and Physical) 14
Experimental
V Preparation and Techniques 16
Preparation of Trialkylsilyl Esters 17
Hydrolysis of Trialkylsilyl Esters 18
Dealkylation of Trialkylsilyl Esters 21
Formation of Silylmetaborates 22
References 23
Contents (continued)
Chapter PART II Page
I Introduction
(a) Fulvenes and related compounds, their preparation, reactions and theoretical importance 27
(b) n-Cyclopentadienyl metal carbonyls and their special characteristic features 31
II Discussion
(a) 7c-Substituted cyclopentadienyl carbonyls of molybdenum, tungsten, chromium and iron 36
(b) Triphenylphosphonium cyclopentadienylide metal complexes 42 (c) Molybdenum(II) dibenzoate and related compounds 44
III Experimental
Preparations and Reactions: 48
Preparation of substituted di-cyclopentadienyl metal carbonyls of iron, tungsten and molybdenum 50 Preparation of substituted I-cyclopentadienyl molybdenum tricarbonyl iodides 53 Preparation of metal alkyl derivatives of certain substituted cyclopentadienyl molybdenum tricarbonyls 54 Preparation of 7t-cyclopentadienyl molybdenum 7-cyclopentadienyl tungsten hexacarbonyl 54 Preparation of triphenylphosphonium cyclopentadienylide metal complexes of molybdenum, tungsten, chromium and iron 55
Contents, Part II (continued)
Chapter III. Page
Infrared Spectra 57
Ultraviolet Spectra
Preparation of Molybdenum(II) Dibenzoate and Related Compounds 60
References 62 PART I
TIE TR 'ALKYL SILYL E ST.ER S OF BORON HISTORICAL 1.
CHAPTER I.
The Esters of Boron.
(1) The Orthoborates.
In the present study we are mainly concerned with the organic derivatives of boric acid. The best known and most stable of these compounds are the trialkyl and triaryl orthoborates. These have now been
prepared by a large variety of methods.
The first mention of orthoborates was made by Ebelman and
Bouquet (1), who utilised the reaction between boron trichloride and the respective alcohols to prepare trimethyl, triethyl and triamyl borates.
3ROH BC13---+ B(003 3HC1
This method has now been found to be of very wide application (2,3,4,5,6,7).
It was found, however, that in the cases where the alcohol had a powerfully electron-releasing group (e.g. tort-butyl and 1-phenylethyl alcohols). the products were mainly the alkyl halides and boric acid. This has been interpreted as being due to the rapid SN1 dealkylation of the borate by the hydrogen halide (8,9) also formed, this rapid SN1 reaction being characteristic of powerful electron-releasing groups. Quantitative yields of these borates have been obtained, however, by the reaction of the alcohol and boron trihalides in the presence of pyridine (8,10).
BC13 + 3ROH + 5C5H5N B(OR)3 + 3C5H5N.HC1
Um.mmoire sie 4iet-errr-tri-i-err-44te—peepara..t.i.a41--- -er+itebrrvItes 2.
The use of boron trioxide in the preparation of orthoborates was introduced by Schiff (11), who prepared a number of borates from the oxide, and alcohols in an autoclave. Though boric oxide is now widely used for the preparation of borates, there has been no report of the fission of dialkyl or diaryl ethers by boron trioxide to produce borates.
The preparation of tristrimethylsilyl borate in this way by the fission of hexamethyldisiloxane has, however, been reported (12).
B203 + 3(CH3 )3SiOSi(CH3 )3.,.4 2[(CH3)3Si0]3B
Boric acid has recently become widely used (13,14,15,16,17) for
the preparation of the orthoborates.
B(OH)3 + 3ROH --+B(OR)3 + 3H20
Although the method was first utilised by Cohn (18), who carried out the reaction in the presence of concentrated sulphuric acid to remove the water formed, later workers removed the water as it was formed — as a binary azeotrope of the alcohol being used (17); a further modification (19) now incorporates an inert solvent like benzene or toluene, and the water is removed as a ternary azeotrope.
Easily obtained borates have been used as starting materials for the preparation of those less readily obtained, by an alcoholysis reaction.
B(OR)3 + 3R'OH -4 B(OR' 3 3ROH
This method has now been shown to have a wide application to the esters of boron (20). 3.
(2) The Metaborates.
Until recently the existence of alkyl metaborates has been in some doubt (20). Goubeau and Keller (21) obtained methyl metaborate by heating the orthoborate and boron trioxide in a sealed tube in equi- molecular quantities. They found the product to be trimeric.
B203 (CH30)3B (CH30B0)3
The Raman spectrum of this compound (22) was evidence for a ring formulation (I) of the trimer.
CH3 Lappert (23) has recently prepared an extensive
0 series of these compounds by the interaction of 1 boric oxide and the corresponding orthoborate, and
0 0 also by the decomposition of the corresponding
B B aialkylchloroborinate. Neither of these methods / / 0 0 0\ worked for the preparation of tert-butyl metaborate, CH3 CH3 however, and to date this compound has not been
(I) reported.
(3) The Phonylboronates and Diphenylborinates.
These compounds are respectively the esters of phenylboronic and diphenylborinic acids. The alkyl and aryl esters have been prepared and extensively studied (24,25,26,27) and shown to have parallel preparative methods to those of the orthoborates, and further to be similar in many of their reactions. 4.
CHAPTER II
The Trialkyl/aryl Siloxy Inorganic Compounds.
Here we are mainly concerned with the methods used for the preparation of trialkyl/aryl siloxy compounds, and at the end of this chapter a complete list of these compounds known to date, along with their physical properties, is given in Table I. A glance at the periodic table will give one an impression as to the very little progress made in these compounds (especially the siloxy compounds of transition metals) as com— pared to the corresponding known metalalkoxides, because the two elements in question show considerable differences in their chemical properties.
Moreover the siloxy compounds undergo very easily curious side reactions such as polymerisation, dehydration, etc.
The trialkyl/aryl siloxy compounds can chiefly be prepared by the following methods:
(1) By the interaction of the alkali metals or their hydroxides with
trialkyl silanols (1,2,3).
2R3SiOH + 2Na 2R3SiONa + H2
R3SiOH NaOH R3SiONa + H20
(2) By the interaction of silyl ethers with sodium hydroxide in the
presence of methanol (4,5).
(R3S020 + 2NaOH > 2R3 SiONa + H20 5.
(3) By the interaction of alkali metal silanolates with various metal halides (1,6).
2R3SiONa + [R3Si0]2 Eg + 2NaC1
4R3SiONa + 4 [R3SiO]4Ti + 4NaC1
(4) By the fission of silyl ethers with acidic oxides (7,8,9,10,11).
3R3SiO—Si—R3 + P205 —4 2[R3Si]3PO4
2[R3SiO]3B
(5) By the interaction of silanol with metal halides in the presence of ammonia or an amine (12,13).
(CH3 )3SiOH + TiC14 + 4NH3 4NH4C1 C(CH3 )3Si0L.Ti
However, Bradley and Thomas (14) have claimed almost quantitative yields of the trialkyl siloxy derivatives of Ti, Nb, Zr and Ta by reactions involving either silanol or trialkylsilyl acetate and the appropriate metal alkoxide.
nR3SiCH + M(0R'}n4.--4nR 1 OH + M(0-SiR3 )n
nR3Si0Ao + M(OR')n---) nR'OAc + M(OSiR3)n
In addition to the methods described above, various individual methods have been used for their preparation. PERIODIC TABLE
0 I II III IV V VI VII V III a b a b a b a b a b a b a b a b ./ // He Be B C 0 F
/ , , Ne ,Na /111;p Al Si Cl
/ Cr Mn Fe Co Ni A , K Ca Sc ;Ii/// ' /
Cu Zn Ga Ge As/ Se Br /// Kr Rb Sr Y / Mo Tc Ru R h Pd
Cd In // / Sri/ Sb Te I
/ //// r 57-71 'if VSS W Re Os Ir Pt Xe Cs Ba ft rare earths" ,i,,,, a Au 7 T1 7// i f //yP Bi Po At
/ 4 k// Rn Fr Ra Ac Th Pa U 7
TABLE I.
Yield M.p. B.p. 20 20 Gp. Compound di. D References % o c o c
I 1.Lithium trimethyl - no sharp sublimed at - - 1 silanolate m.p. 180/1 mm.
2.Sodium trimethyl 80-87 sublimed under high - - 1,2,4,5 silanolate vacuum, 130-150
3. Sodium triethyl 80 - - - - 1,3,23,24 silanolate
4. Sodium dimethyl 76 87-94 4,5 phenylsilanolate 5.Sodium methyl di- 76 - - - 4,5 phonylsthnolate
6.Sodium triphenyl 80 Carbonised without - - 4,16 silanolate melting at 300-350 in vacuum 7.Potassium tri- 80-87 d - - - 1,2,4,5 methyl silanolate 131-135 II 8. Trimethylsiloxy - - - - - 10 magnesium iodide 9. Mercury trimethyl - - - - - 1 silanolate III 10. Aluminium tri- - 159 - - - 6,25 methyl silanolate
11.Tris(trimethyl- 20-25 - 184.5/776 0.8285 1.3860 8 silyl) borate
12.Tris(methyldiethyl 73 - 131-33/5mm. 0.8751 1.4225 8 silyl) borate 13.Tris(triethylsily1) 100 - 134-136/1mm 0.8918 1.4379 18 borate 14.Tris(methyl-di-n- 74 - 157-160/imm 0.8668 1.4332 8,17 propylsilyl)borate 8.
20 Yield M.p. B.p. References Gp. Compound °C sc 4
15.Methyl bis(triethyl 100 3,26 silyl) boronate 16.Dimethyl(triethyl 100 3,26 silyl) borinate
17.Bis(triethylsilyl) 100 70/5 mm. 3,26 bromo boronate
18.Monomethoxy bis 100 115/2.5 mm. 3,26 (triethylsilyl) borate
IV 19.Tetra kis(tri- 90.0 151 60/0.1 mm. 6,12,13,14 methyl) siloxy titanium 20.Tetra kis(tri- 100 0.9078 1.428 14 ethylsiloxy) titanium 21.Tetra kis(tri- 100 501-503 1.215/ 1.648/ 13,14 phenylsiloxy) 29° 114° titanium 22.Tetra kis(ti- 60.0 151 14 methylsiloxy) zirconium 23.Bis (trimethyl- 1 siloxy) tin 24.Bis (trimethyl- 1.56/ 1 siloxy) dimethyl 25 tin 25. Tetra kis(tri- 1.419/ 1 methylsiloxy) tin 25 26.Bis (trimethyl- d 180 18,27 siloxy) lead
V X27. Penta kis(trimet- 74 80 84/0.05 mm. 14 1 hylsiloxy)tantalum
28. Penta kis(trimet- 14 hylsiloxy) niobium
9. (Trimethylsiloxy) -39 35-36/1 mm. - 11.5186 9 vanadyl dichloride 9.
Yield M.p. B.p. 20 20 Gp. Compound d4 References °C oc D
30.Bis(trimethylsil-. 53/1.0 mm. - 9 oxy) vanadyl mono chloride 31.Tris(trimethyl- -18 100/9.5 mm. - 1.4578 9 siloxy) vanadium
32.Tris(trimethyl- 80.0 97/6 mm. 0.9591 1.4089 7,8,10,28 silyl) phosphate
33.Tris(methyldiethyl 40.0 145-47/1mm. 0.9474 1.4302 7,8 silyl) phosphate 34.Tris(triethyl- 80 166.5/1 mm. 0.9670 1.4457 7,8 silyl) phosphate
35.Tris(methyl-di-n- 50 221-224/ 0.9326 1.4380 7,8 propylsilyl) 10 mm. phosphate 36, Tris(n-propyl- 55 215-225/5mm 7,8 silyl) phosphate 37. Tris(n-butylsily1) 55 260-270/5mm 7,8 phosphate
38.Tris(trialkylsily1)25-30 19 phosphites
39.(Trimethylsiloxy) nitrite 40.(Dimethylsilyl) 9 dinitrate 41.(Trimethylsilyl) -15 76/77 mm. 1.4249 20 orthoarsenate
42.(Trimethylsily1) 20 meta-arsenate VI 43. Bis(trimethyl- 69 45-46 87-90/4 mm. - 18,11,29,30 silyl) sulphate
44. Bis(triethylsily1)150.0 170/12 mm. 1.4421 21,22 sulphate DISCUSSION 10.
CHAPTER III
Preparation of the Trialkylsilyl Esters of Boron.
The direct reaction between boric acid and numerous alcohols is known to give the corresponding trialkyl borates (1). We have found that triethylsilanol and boric acid gave tristriethylsilyl borate in good yield.
5(C2H5)3 Si0H + H3B03 [(C2H5)3SiO]3 B + 3H20
The reaction was carried out in boiling benzene, and water of esterification was removed continuously as the benzene/water azeotrope. This reaction is much more simple than that reported for the corresponding preparations leading to the tertiary alkyl borates (2). This reaction was not attempted with trimethylsilanol, owing to its very rapid acid catalysed formation of hexamethyldisiloxane.
The silanolysis of tris-trimethylsilyl borate with triethylsilanol has produced tris-triethylsilyl borate
[(CH3 S10]3B + 5(C 2H5 )3Si011 --->[(C05)3SiOLB + 3(CH3 )3SiOH
The reaction mixture was kept at 150°, and the trimethylsilanol distilled off as it was formed. The silanol as such, however, was not isolated, owing to its rapid condensation to hexamethyldisiloxane.
2(CH3 )3SiOH (CH3 )3SiOSi(CH3 )3 + H2O
Owing to this condensation reaction, the silanolysis of triethyl borate with triethylsilanol resulted in considerable formation of hexaethyl- disiloxane as a by-product. Only a 38% yield of the product was obtained.
(C2H50)3B + 3(C2H5 )3Si0H---4 3C21150H + [(C2H5)3SiO]3B 11.
Interaction of the boron halides and organoboron halides with
alcohols and phenols has been shown to give good yields of the alkyl and aryl
borates (1). In the case of certain alcohols with powerful electron-
releasing groups, however, this reaction was found to give the alternative
reaction products of boric acid and alkyl halide. This difficulty was
overcome by the use of a tertiary base such as pyridine (3).
3ROH + 3C5H5N +BX3 (R0)3B + 3C5H5N.HC1
Preliminary experiments showed that tristrialkylsilyl borates
were rapidly dealkylated by hydrogen halides to boric acid and trialkylsilyl
halides.
Triethylsilanol reacted with boron trichloride in the presence of
pyridine to give tristriethylsilyl borate. The yield (34%), however, was
not good, and considerable amounts of boron trichloride- pyridine complex
and hexaethyldisiloxane were isolated as by-products.
A much improved yield of borate from boron trichloride is obtained
if the trialkylsilanol is first treated with sodium to obtain the sodium
salt.
(C2H5 )3SiOH + (C2H5 )3SiONa + H
Direct reaction in benzene of this sodium salt with the stoichiometric
amount of boron trichloride results in a good yield of the borate.
BC13 + 3(C2H5 )3SiONa---4 [(C2115 )3 Si0]3B + 3NaCl
In a similar manner sodium triethylsiloxide reacted with phenyl- boron dichloride and diphenylboron chloride, respectively, to give bis- triethylsilyl phenylboronate and triethylsilyl diphenylborinate. 12.
2(C2H5)3SiONa + PhBC12---* PhB[OSi(C2H5 )3]3 + 2NaC1
(C2115 )3SiONa + Ph?BC1 Ph2BOSi(C2H5)3 + NaC1
The most convenient preparation of the tristrialkylsilyl borates was the silanolysis of trisdiethylaminoboron.
3(C2H5 )3 SiOH + [(C2H5 )2N]3B -4 [(005)3sio]3B + 3(c2115),NH
This reaction required no solvent, and the reaction between stoichiometric quantities was instantaneous in the cold. Removal of diethylamine at reduced pressure gave the pure borate, in such a high state of purity that it distilled completely and unchanged at constant temperature.
Boric oxide has been reported to cause the fission of hexamethyl- disiloxane to produce tristrimethylsilyl borate (4). We have found that phenylboronic anhydride did not cause fission of the siloxane to give a phenylboronate, as might have been expected. It was possible, however, to cause the fission of ethoxytrimeth,71silane with boric oxide.
3(CH3 )3S10C2H5 + B2O3 -.._) (C2H50)3B + [(CH3 )3Si0]3B
The two borates forme' could be quite easily separated by fractional distillation.
The existence of organic metaborates has been in doubt until recent years. Now, however, considerable work has been done on these compounds and their preparations and properties have been well studied (5,6,7).
The interaction of molar proportions of boric oxide and alkyl borates has given good yields of the metaborates (7), and a similar reaction between tris-trimethylsilyl borate and tris-triethylsilyl borate and boric oxide respectively has produced the corresponding metaborates. Both trimethyl- silyl metaborate and triethylsilyl metaborate were found to be trimeric by 13.
direct ebullioscopic determination of their molecular weights. This is in accordance with the cyclic structure for these compounds which has been concluded from measurements of Raman spectra (6).
It is interesting to note that although a large number of meta- borates have been made, it has not proved possible to isolate the structural analogues of the herein mentioned alkylsilyl compounds, namely the tertiary alkyl metaborates. This appears to be owing to the formation of butene by an elimination reaction. It is Tocsible that the reason the silyl compounds exist, as opposed to the non-existence of their purely organic analogues, is the complete absence of a tendency to form double-bond compounds in silicon.
Thus any elimination reaction would be prevented. 14.
CHAPTER IV
Properties of the Trialkylsilyl Esters of Boron.
Chemical.
The tris—trialkylsilyl borates are not hydrolysed rapidly by water, over fifty per cent being recovered after violent shaking with a
large excess of water for long periods. The steric hindrance to the
hydrolysis of organic borates has been very extensively investigated (1),
and although in the present work this may possibly be used to explain the rather faster hydrolysis of the phenylboron esters of the trialkyl silanols, it seems unlikely that the remarkable resistance to hydrolysis is purely
steric. The powerful water—repelling properties of the silanols and
disiloxanes formed on hydrolysis may account, on purely physical grounds, for the slow hydrolysis rate, each drop of ester being coated instantly with a layer of water—repelling material thus preventing further hydrolysis.
Hydrogen chloride and bromide reacted rapidly and completely with
tris—temethylsilyl borate to produce boric acid and the corresponding
trimethylhalogenosilanes. Here the trialkylsilyl group behaves in a
similar manner to that of the tert—butyl group, as only tert—alkyl and other
borates with strongly electron—releasing groups undergo this rapid reaction with hydrogen halides (2).
(R0)3B + 3HX 3RX + H3B03 15.
The thermal stability of the tris—trialkylsilyl orthoborates is
considerable and they may be refluxed (up to 260°C) in an anhydrous atmos—
phere unchanged. The metaborates, however, decompose to orthoborate and
boric oxide under high temperature conditions. These metaborates may,
however, be heated at 250° for 50 hours in a sealed tube and remain unchanged.
Physical.
With the exception of refractive index and density, for
characterisation purposes the only physical property of the trialkylsilyl
esters of boron studied has been the measurement of the infrared spectra of
these compounds.
No unexpected trends were noted in these spectra, but the doublet
band at 720 and 735 cm. observed in the spectra of both trimethyl and
triethyl silylmetaborates supports the trimeric boroxole structure which we have allocated to these compounds. This doublet has recently been assigned
to the out—of—plane —ibrations of the boroxole skeleton (3).
The strongest bands in all the spectra observed are due to the
B-0 stretching modes in the 1300-1400 cm. region, with the absorption
maxima at 1334 ± 5 cm. except in the metaborates whore the maximum occurs
1 at about 1380 cm. • (4,5). EXPERIMENTAL 16.
CHAPTII V
Experimental.
Preparation of Hexaethyldisiloxane.
The method used was that described by Di Giorgio, Strong,
Sommer and Whitmore (1).
In a two—litre thre —necked flask fitted with a mercury—sealed stirrer, reflux condenser and dropping funnel was prepared ethyl magnesium bromide (22 mol.) from magnesium (52.8 g.) and ethyl bromide (240 g.) in anhydrous ether (1.5 litres). To the cooled Grignard solution was added dropwise ethyl orthosilicate (145 g., 7 mol.) with vigorous stirring. After standing (1 hr.) the ether was removed and the product heated on a steam bath for twelve hours. After the ether was returned to the flask the contents were hydrolysed with dilute hydrochloric acid. After separation of the ether layer, solvent was distilled from the product.
Then with constant cooling the product was dissolved in concentrated sulphuric acid (150 cc.), and poured into cold water (1 litre). The organic layer which separated was dried over calcium chloride; fractional distillation gave hexaethyldisiloxane (57.0 g., 60%), b.p. 2380/760 mm., 20 n D 1.4340. 17.
Preparation of Triethylchlerosilanec
[By the method of Di Giorgio et al. (1)]
Hexaethyldisiloxane (53.0 g., 1.1 mol.) was dissolved in con-
centrated sulphuric acid (55 ml.) with cooling. To this was added with
stirring ammonium chloride (35.0 g., 3.1 mol.), over a period of two hours.
The separated upper layer was fractionally distilled to give triethyl-
chlorosilane (50.0 g., 85%), b.p. 145°/760 mm., n;2 1.4314.
Preparation of Triethylsilanol.
[By the method of Sommer, Pietrusza, and Whitmore (2).]
Triethylchloresilane (17.0 g., 1 mol.) in ether (80 cc.) was kept
ice-cold while caustic soda (N solution) was added with vigorous stirring
to the neutral point (phenolphthalein). The ether layer was separated off,
and the aqueous layer was extracted with ether (3 x 20 cc.). The ethereal
layer was dried over anhydrous potassium carbonate, and subsequent
fractionation gave triethylsilanol (1400 g., 95%), b.p, 154°/760 20 n D 1.4315.
Interaction of Tris-trimethylsilyl Borate and Triethylsilanol.
The borate (2.94 g., 1 mol.) and the silanol were maintained at
150° and trimethylsilanol was allowed to distil off; this underwent rapid 20 change to bistrimethylsilyl ether (2.38 g., 91.2%), b.p. 100, n D 1.3779,
and water (0.25 g., 80%). Distillation of the residual liquid gave 18
20 0 tris-triethylsilyl borate (3.60 g-,, 85%), bop. 184 /20 mmo, n D 1.4370 (Found: B, 2.71%).
Interaction of Triethyl Borate and Triethylsilanol.
The borate (1.60 g., 1 mol.) and silanol (4.32 g., 3 mol.) were
slowly fractionated (3 hr.) to yield ethanol (1.19 g., 77%), b.p. 75-80°, 20 n D 1.3640. Distillation of the residue produced bistriethylsilyl ether 20 0 1.4260, and tris-triethylsilyl borate (2.03 g.), bop. 120 /25 mm., n D 0 20 (1.67 g., 38%), b.p. 184 /20 mm., -n D 1.4370 (Founds B, 2.74%).
Attempted Fission of Hexamethyldisiloxane with Phenylboronic Anhydride.
After the compounds had been heated in a sealed tube at 2500 (40 hr.) and then cooled, the siloxane (96%) and anhydride (94%) were recovered unchanged.
Hydrolysis of Tris-trimethylsily1 Borate.
The borate (4.5 g., 1 mol.) was shaken violently (2 hr.) with
water (3.0 g., 10 mol.), and the mixture then extracted with ether. Unchanged tris-trimethylsilyl borate (2.74 g., 61%), b.p. 840/20 mm., 20 n 1.3680 (Found: B, 3.8%) was obtained. After similar treatment D tris-triethylsilyl borate (67%) was also recovered.
Interaction of Boric Oxide and Ethoxytrimethylsilane.
The silane (18.67 g.) was refluxed (5 hr.) with boric oxide
(7.40 g.). After removal of unchanged boric oxide by filtration, 19.
distillation gave triethyl borate (7.87 g., 99%), b.p. 118-120°, 20 D 1.3741 (Found: B, 7.3. Cale. for %I-11503B: B, 7.4%), and 20 tris-trimethylsilyl borate (11.0 g., 75%), b.p. 1860, n D 1.3840 (Found: B, 3.97%. Calc. for C9H2703BSi3: B, 3.89%); a glass-like residue (3,83 g.) remained.
Interaction of Boron Trichloride (1 mol.) and Triethylsilanol (3 mol.) in the Presence of Pyridine (3 mol.).
The trichloride (3.46 g.) in light petroleum (15 cc.) was added
(30 min.) to the silanol (11.65 g.) and pyridine (6.97 g.) in light petroleum (30 cc.) at -800, with constant shaking. After 24 hr. at 20°, the precipitate was filtered off and washed with light petroleum, and excess of solvent removed (200/0.5 mm.). Pyridinium chloride (2.35 g.) was washed from the precipitate with water (3 x 20 cc.) to leave (after being dried at 200/1.01 mm.) pyridine-boron trichloride (3.70 g.), m.p. 114° (Found: N, 7.3%. Cale. for C5H5N,BC13: N, 7.1%). Removal of solvent from the filtrate (00/20 mm.) and subsequent distillation gave a forerun (7.0 g.) (unchanged pyridine and hexaethyldisiloxane) and then 20 tris-triethylsilylhorate (4.0 g., 34%), b.p. 1850/20 mm.9 n D 1.4378
(Found: B, 2.72%).
Interaction of Boric Acid and Triethylsilanol.
The acid (0.51 g., 1 mol.), triethylsilanol (5.32 g., 5 mol.), and hen:-ene (20 ml.) were heated slowly, and the water benzene azeotrope allowed to distil off (2 hr.). Careful fractionation of the residue gave 20.
20 hexaethyldisiloxane (1.38 g.), b.p. 600/1 mm., n D 1.4340, and tris- triethylsilyl borate (2.94 g., 89% on H3B03 taken), b.p. 1200/1 mm., 20 n 1.4370 (Found: B, 2.68. Calc. for C 03BS13 2 B, 2.73%). D 18H45
Interaction of Diphenylboron Chloride and Sodium Triethylsiloxide.
The chloride (645 g., 1 mol.) in benzene (20 cc.) was added with constant shaking to sodium triethylsiloxide (4.96 g., 1 mel.) in benzene (25 cc.); heat was evolved during the addition (15 min.), and shaking was continued for 2 hr. Removal of benzene (200/20 mm.), and subsequent distillation gave triethylp_ly1 diphenylborinate (9.20 g., 97%),
20 20 b.p. 1350/0.5 mm., d 0.974, n D 1.5270 (Found: C, 72.7; H, 8°39
B, 3.6. C 1811250BSi requires C, 73.0; H, 8.8; B, 3.7%).
Interaction of Sodium Triethylsiloxide and Boron Trichloride.
The siloxide (from 6.18 g. of silanol and 1.10 g. of sodium) in light petroleum (30 cc.) was treated with boron trichloride (1.84 g.) in light petroleum (10 cc.) at -70c. After being warmed to 20° the mixture was set aside (2 hr.) and sodium chloride was filtered off. Removal of solvent from the filtrate (200/0.1 mm.) and subsequent distillation of the residue gave tris-triethylsilyl borate (4.62 g., 73%), b.p. 1830/17 mm., 20 D 1.4370 (Found: B, 2.69%). 21.
Interaction of Phonylboron Dichloride and Sodium Triethylsiloxide.
In the same manner as that described above for triethylsilyl diphenylborinate, the ester bistriethylsilyl phenylboronate (6.30 g., 56%), 2 b.p. 1200/0.2 mm., d2 4 0.928, n D 1.4370 (Founds C, 62.0; H, 10.4;
B, 3.2. C18H3502BSi2 requires C, 61.7; H, 10.0; B, 3.1%) was prepared.
Interaction of Tris-diethylaminoboron and Triethylsilanol.
The silanol (4.46 g., 3 mol.) was added to tris-diethylamino- boron (2.56 g., 1 mol.); during the addition heat was evolved and the vessel was kept at 0°. After 30 min., diethylamine (1.84 g., 75%), b.p. 20 55°, n D 1.3860, was removed (20°/15 mm.). The remaining tris-triethyl- 20 silyl borate (4.45 g., 984), b.p. 182°/15 mm., n D 1.4370 (Found: B, , 20 2.70%), distilled unchanged cn D 1.4371).
Action of Hydrogen Halides on Tris-trimethylsilyl Borate.
(a) Hydrogen chloride. The gas was passed through the ester in a very slow stream at 0°. There was an immediate evolution of heat and the products set to a solid white mass. Passage of the gas was continued for a further 10 min., then volatile matter was removed (20°/20 mm.). The residue was boric acid (0.497 g., 98%) (Founds B, 17.6. Calc. for
H3B03: B, 17.7%), Distillation of the condensate gave trimethylchloro- silane (2.47 g., 95%), b.p. 57°, n;2 1.3874 (Found: Cl, 31.9. Cale. for C3H9 C1Si: Cl, 32.7%). 22.
(b) Hydrogen bromide, In a similar manner to that described above we
obtained boric acid (0.768 g., 88%) (Found; B, 17.9%) and trimethylbromo—
silane (6.28 g,, 98%), 13 .1) 81°, hi; 1.4132 (Found: Br, 51.7. Calc. for C3H9BrSi: Br, 52.3%).
Formation of the Silyl Metaborates.
(a) Trimethylsilyl metaborate. Tris—trimethylsilyl borate (5.16 g., 1 mol.
and boric oxide (1.41 g., 1.1 mol.) were heated (30 hr.) in a sealed tube at
225°. Only small traces of solid boric oxide then remained, and the mixture was poured into ether (20 cc.) and stored (24 hr.) in a stoppered
flask. After filtration, solvent was removed (200/0.1 mm.) to leave , 2 trimethylsilyl metaborate (5.63 g., 87%), d2 4 0.988, n D 1.4101 (Found:
C, 30.4; H9 7.4; B, 9.5%; M9 331. C9H2706B3S13 requires C, 31.0;
H, 7.8; B, 9.3%; M, 348), as a slightly viscous liquid.
(b) Triethylsilyl metaborate. Tris—triethylsilyl borate and boric oxide reacted as described in (a) to produce triethylsilyl metaborate (7.65 g., 20 20 8 1.4360 (Found: C, 46.2; H, 8.9; B, M, 450. 4%), d 4 0.955' a D 6.9%; C18114.506B3Si3 requires C, 45.5; H, 9.5; B, 6.8%; M, 474). REF.ERENCES 23.
REFERENCES
Chapter I
1. Ebelman and Bouquet, Ann. chfm. phys., 1846, 3, 54.
2. Michaelis and Hillringhaus, Ann., 1901, 315, 41. 3. Gerrard and Lappert, J. Chem. Soc., 1951, 2545.
4. Idem, ibid., 1955, 3084. 5. Wiberg and Sfitterlin, Z. anorg. u. allgem. Chem., 1931, 202, 1.
6. Colclough, Gerrard and Lappert, J. Chem. Soc., 1955, 907. 7. Idem, ibid., 1956, 3006.
8. Gerrard and Lappert, J. Chem. Soc., 1951, 1020. 9. Brindley, Gerrard and Lappert, J. Chem. Soc., 1956, 824. 10. Lappert, J. Chem. Soc., 1953, 667.
11. Schiff, Ann. Suppl., 1867, 5, 158. 12. Voronkov and Zgounik, Zhur. obshchei Khim., 1957, 27, 1476.
13. Ballard, U.S. Patent 2,217,354; C.A., 1941, 1071. 14, Haider, Khundkar and Siddiqulah, J. Appl. Chem., 1954, 4, 93. 15, Johnson and Tompkins, Org. Synth., 1933, 13, 16. 16. Scattergood, Miller and Gammon, J. Amer. Chcm, Soc., 1945, 67, 2150. 17. Wuyts and Duquesne, Bull. soc. chim. Belg., 1939, 48, 77. 18. Cohn, Pharm. Zentr., 1911, 52, 479. 19. Thomas, J. Chem. Soc., 1946, 820.
20. Lapperty Chem. Rev., 1956, 959. 24.
Chapter I (contd.)
21. Goubeau and Keller, Z. anorg. u. allgem. Chem., 1951, 267, 1.
22. Idem, ibid., 1953, 272, 303. 23. Lapperty J. Chem. Soc., 1958, 2790, 3256. 24. Abel, Gerrard and Lappert, J. Chem. Soc., 1957, 112.
25. Idemy ibid., 1957, 3833. 26. Brindley, Gerrard and Lappert, J. Chem. Soc., 1955, 2956.
27. Idem, ibid., 1956, 1540.
Chapter IT
1. Tatlock and Rochow, J. Org. Chem., 1952, 1/, 1555. 2. Sommer, Green and Whitmore, J. Amer. Chem. Soc., 1946, 68, 2282. 3. Wiberg and Kruerkey Z. Naturforsch., 1953, 8b, 609.
4. Hyde, Johanson, Daudt, Fleming and Rochey J. Amer. Chem. Soc 1953 75, 5615.
5. Hyde, U.S,P. 2,472,799 [1946/49]; C.A., 1949, 7500. 6. Andrianov, Zhdanov and Dulova, Doklady Akad. Nauk S.S.S.R., 1957, 112, and 1050. 7. Voronokov /Zgonnik, Zhur. obshchei Khim., 1955, 25, 437.
8. Idem, ibid., 1957, 27, 1476. 9. Schmidt and Schmidbaur, Angew. Chem., 1959, 71, 220. 10. Sauer., J. Amer. Chem. Soc., 1944, 68, 1707. 11. Sommer, Kerr and Whitmore, ibid., 1948, /2, 445. 12. 7nglish and Sommer, ibid., 1955, 77, 170. 25.
Chapter II (contd.)
13. Zeitler and Brown, J. Amer. Chem. Soc., 19579 4616. 14. Bradley and Thomas, Chem. and Ind., 1958, 1264. 16. Namatkin, Topcieve and Macus, Doklady Akad. Nauk S.S.S.R., 1952 [2], 83, 705.
17. Dow Corning Ltd. B.P. 694,526, 1953; C.A. 1954, 10765. 18. Patnode and Schmidt, J. Amer. Chem. Soc., 1945, .§.1, 2272. 19. Voronokov and Skorik, Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk, 1958, I, 119,
20. Schmidt and Schmidbaur, Angew. Chem., 1959, 71, 553. 21. Sommer, Pietrusza and Whitmore, J. Amer. Chem. Soc., 1946, 68, 2282. 22. Anderson and Stainslov, J. Org. Chem., 1953, 18, 1716. 23. Ladenburg, Ber., 1871, 4, 901. 24. Idemy Lieb. Ann., 1872, 164, 300. 25. Andrinov and Ganina, Izvest. Akad. Nauk S.S.S.R., Otdel. khim. Nauk, 1956, 74. 26. Kruerkey Diss. Mlinchen, 1953.
27. Patnode, U.S. Patent 2,455,880 (1945).
28. Voronokov, J. Gen. Chem. (U.S.S.R.), 1955, 25, 437. 29. Patnode and Wilcock, J. Amer. Chem. Soc., 1946, 68, 358. 30. Sommer, Pietrusza, Kerr and Whitmore, ibid., 1946, 68, 156. 26.
Chapter III
1. Lappert, Chem. Rev., 1956, 959.
2. Idem, J. Chem. Soc., 1953, 662.
3. Gerrard and Lappert, J. Chdb. Soc., 1951, 1020.
4. Voronkov and Zgonnik, Zhur. obshchei Khim., 1957, 22, 1476.
5. Goubeau and Keller, Z. anorg. u. allgem. Chem., 1951, 1.
6. Idem, ibid., 1953, 272, 303.
7. Lappert, J. Chem. Soc., 1958, 2790, 3256.
Chapter IV
1. Steinburg and Hunter, Ind. Eng. Chem., 1957, Ai, 174. 2. Gerrard and Lappert, J. Chem. Soc., 1951, 2545.
3. Lappert, J. Chem. Soc., 1958, 2790, 3256.
4. Webster and Brien, Austral. J. Chem., 1955, 8, 355.
5. Bellamy, Gerrard, Lappert and Williams, J. Chem. Soc., 1958, 2412.
Chapter V
1. Di Giorgio, Strong, Sommer and Whitmore, J. Amer. Chem. Soc., 1946, 68, 1380.
2. Sommer, Pietrusza and Whitmore, ibid., 1946, 68, 2282. TART II 27.
CHAPTER I
Introduction
(a) Fulvenes and related compounds, their preparation, reactions and theoretical importance. Fulvenes are characterised by the presence of a cross-conjugated system within a five-membered ring in which the groups R and R' may be hydrogen, /R alkyl, aryl and other groups. = C R' They were first prepared by Thiele (1), by the condensation of cyclopenta- diene with aldehydes and ketones. They are bright yellow-red coloured compounds, very reactive and add to maleic anhydride, hydrogen, oxygen and halogens and are easily polymerised (especially the simpler fulvenes) by heat. Fulvenes are most simply prepared by condensing monomeric cyclo- pentadiene (and its derivatives containing a free methylene group) with ketones and aldehydes in the presence of a small amount of base (alcoholic sodium or potassium hydroxide (2), sodium ethoxide (3), aqueous or alcoholic ammonia (3) and occasionally piperidine (4). Grignard and Courtot (5) prepared fulvenes by the interaction of cyclopentadiene with Grignard reagents to give cyclopentadienyl magnesium halide which on treatment with ketone in the cold yields a mixture of fulvene and the fulvanols; the latter on dehydration with substances like dry hydrogen chloride in glacial acetic acid, phosphorus pentoxide in absolute benzene give fulvenes (6).
This method, however, fails with aliphatic aldehydes and yields no pure products, only resins. Special synthetic methods have been used 28.
occasionally (7). The reactivity of the -CH2 group in cyclopentadiene, indene and fluorane decreasosas the ethylenic linkage of the five-membered ring becomes double linkage in benzene nucleus because of the decrease of the hyperconjugation of the methylene groups and of the symmetry of the ion. Cyclopentadiene condenses extraordinarily easily with ketones while fluorene does not condense at all under the influence of alkali condensing agents. A lot of difficulty is experienced inihe purification of the fulvenes since those tend to absorb oxygen from the air and in general resinify rather easily. Moreover, condensations are often accompanied by curious side reactions.
The formation of the negatively charged cyclopentadienide ring was recognised by Thiele in 1900 (1) when he prepared the potassium cyclo- pentadienide. According to Goss and Ingold (8) the ion has six / electrons distributed over five equivalent CH groups, thus constituting a stable aromatic system. Later, Ingold and Jessop (9) reported - that the negatively charged cyclopentadienide ring could be achieved not only by an anion formation but also in dipolar molecules such as fluorenes bearing either
-SMe, or -NR3 groups in position 9, and the corresponding negative charge in the central five-membered ring. This was in agreement with the dipole measurements, the molecule being highly polar in character (10). In recent years, the novel molecules of Lloyd and Sneezum (11)2 Ramirez and Levy (12), and Doering and DePuy (13),and dicyclopentadienyl iron have established beyond doubt the remarkable stability of the C5H5 ion with six 7 electrons. 29.
The tendency of the cyclopentadiene system to accept electrons and thus
achieve aromatic stability is also shown by fulvenes. Recently fulvenes
have aroused great interest from the theoretical standpoint because the valence—bond method and molecular—orbital method, when applied, give
different results: the first does not lead to a polar structure for the fulvenes while the latter does. According to Coulson (14) and
Longuet—Higgins (15), all molecules containing conjugated double bonds arranged within or adjacent to a ring of odd number of C—atoms should be charge polar. The direction of the moment of/is towards the ring, so that
C—atom(l) exhibits the same negative charge which expresses itself in tire
tgoatiammu to cyclopentadiene (and its benzo—homologues, indene and fluorene) and pyrrol(and its benzo—homologues indole, carbazol6e, etc.).
Dimethyl fulvene (R = R' = Me) has a dipole moment of 1.44 D, the ring being negative and C—atom 6 positive (16). This clearly indicates the electron—attracting nature of the ring which tends to acquire a stable sextet of electrons, but the charge separation is opposed by coulombic attraction and the actual structure of dimethylfulvene is intermediate between (III) and (IV).
3
\"/ 2 \ /5 CH 2 CH C 11 6 1 + ' ' IN
I II III IV V VI 30.
— P — P+ /'N
** N I
Diazocyclopentadiene (13) and triphenylphosphoniumcyclopentadienylide (12) are resonance hybrids of structures (V) and (VT), and structures (VII) and (VIII), respectively. Since the positive charge is more easily accommodated either by a nitrogen or phosphorus atom than by a carbon atom as in fulvenes (IV), the forms VI and VIII contribute more to the hybrid. The dipole moment of triphenylphosphonium cyclopentadienylide measured in benzene solution at 25° is 7.0 D, which corresponds roughly to equal contributions from the pentacovalent structures (VII) (calc. moment nearly zero) and the tetracovalent structure (VIII) (calc. moment
14.0 D) (17).
Recent physical measurements such as dipole moment and absorption spectra of fulvenes are in accord with the predictions of the theory and lead to the observation of a polar molecule. This is further borne out by chemical evidence in reactions with lithium aluminium hydride, a reagent typical for polar double bonds, organometallic compounds and sodium metal. 31.
In fact, the distribution of the negative charge over the cyclopentadienide ring confers a higher degree of stability, in line with recent views on the non-benzencAdaramatic systems.
(b) Substituted n-cyclopentadienyl metal carbonyls.
Since the first preparation by Wilkinson (18) of the binuclear cyclopentadienyl compounds of molybdenum and tungsten, a large number of different types of compound with n-mono- and di-n-cyclopentadienyl and arene metal complexes have been prepared; up-to-date and comprehensive reviews of these compounds have been published by Cotton and Wilkinson (19), and by Fischer and Fritz (20), respectively. However, a brief review of these compounds is discussed here. Monocyclopentadienyl metal carbonyls, in contrast to pure cyclopentadienyl compounds, are formed only by the transition elements of group V to group VIII, i.e., metals which can enter into ferrocene-type bonding. Moreover, transition elements of odd atomic number (V, Mn, Co) yield readily volatile compounds of the formula
C5H5Me(C0)x while the even-membered (Mo, W, Cr) numbers form dimers of composition [C5H5Me(C0)x3 2. The actual value of x, the number of ligand carbon monoxide molecules, corresponds to the number of pairs of electrons required for the attainment of the next inert-gas configuration, assuming
(a) that a five-membered aromatic ring is bonded to the central metal atom with all six of its 1 electrons, (b) that a metal-metal bond contributes in the case of a dimeric compound, and (c) that carbon monoxide, N0+ ion, and an olefinic bond contribute two electrons, nitric oxide three, and hydrogen, halogen, alkyl group, etc., one electron each. 32.
metal carbonyl The n—cyclopentadienyl%compounds may be classified as follows:
(i ) n—cyclopentadienyl metal carbonyls and nitrosyls, e.g.
n—COn(C0)3, 1—CpCr(NO)2C1, n—CpMo(00)2N0.
(ii)n—cyclopentadienyl metal carbonyl halides or other salts, hydrides,
alkyls and aryls, etc., for example n—CpFe(C0)2C1,
n—CpMo(C0)3H, n—CpFe(C0)2Si(CH3 )3.
(iii)Binuclear n—cyclopentadienyl metal carbonyls, e.g. [n—CpMo(C0)3]2.
The n—cyclopentadienyl metal carbonyls can be prepared in a number of ways
and a brief sketch of some preparations and reactions of those compounds
is represented in the table below (p. 33). The structural features of
these compounds are well characterised by physical measurements like
infrared and ultraviolet absorption spectra, nuclear magnetic resonance
and dipole moment. For the mononuclear species, simple carbonyls, nitrosyl
halides, alkyls, etc., the structures are fairly simple, with the n—05H5
group bound to the metal atom as in, say, ferrocene, with other ligands or
groups on the opposite side of the metal atom, the geometry of the molecule
depending of course on the formulas. Infrared studies of many of these
compounds have shown that there is negligible interaction between the n—05H5
group and other ligands, as would indeed be expected if the 1—05H5 groups
were freely rotating about the metal ring axis as in ferrocene. The
disposition of other ligands can therefore be ascertained by merely
considering the local symmetry of these groups (21,22). This evidence
is consistent with the structure of n—CplAn(C0)3 in which the three
carbonyl groups are disposed symmetrically about the metal—ring axis (23).
330
Co2(C0)8 C5H6 _4 1-CpCo(C0)7 25°C Higher su- (C5115 )3Ni3 (C0)2 blimation/temp. Ni(C0)4 + n(C5H5 )2Ni in benzene ---“C5H5Ni(C0)1 2 + 2C0
/ / (C5H5)2ReH + CO 250 atm. k,C5H5)2ReHt.00)2 90°
100-200 atm. HC1 + 02 n-Cp,V + CO n-CpVC0()4 n-CpV0C1, 200° elevated temp. „ Mn(C5H5)2 + CO ,c5H5mn( c0 )3
.F. Mo(CO)6 + NaC5H5 -* n-CpMo(C0)3NaHgC1 [it -CpMo(C0)3 ]2Hg C10E:12 I CH "OOH''---,,_RI _cpmo(c0)3],) heat or air 3 [n -CpMo(C0)3H -----4.n-CpMo(C0)3R oxidation NO / bromosuccinimide n-CpMo(C0)210 CBr 4 52/IgBr RMe;Br n-CpMo(C0)3X
reflux or r __heat Fe(C0)5 + C1011 12 /n-CpFe(C0)2 autoclave ' L 2 't Cp,Fe at 200° / HC1 + 0 N 12 , Br2 [n-CpFe(C0)2]2 HFC144 n-CpFe(C0)2Na
(CH3 )3 SiC1 j RX
n-CpFe(C0)2Si(CH3 ):(r n-CpFe(C0)2R el°'el-c—n-CpFo(C0)2X-49--*.[I-CpFe(COIH2Or [NaC5H5 n-CpFe'(C0)20T5H5 34.
On the basis of a completed three-dimensional X-ray diffraction study of the binuclear molybdenum and tungsten compounds, Wilson and Shoemaker
(24) have been able to rule out a structure proposed by the earlier workers (18) in which the metal atom and the ring centres in the sequence
C5H5-M(C0)61FC5H5 lie on a straight line normal to the planes of the two cyclopentadienyl rings and the plane of a ring of six carbonyl groups.
They have suggested a non-linear arrangement with a metal-metal bond and with non-bridging independently-coordinated carbonyl groups that form no rings. This structure provides for a completed 18-electron shell for the metal atom, in accord with the diamagnetism of the compound. The molecular shape, the rather long metal-metal bond, and some rather short intramolecular non-bonded contacts suggest that the molecule is under considerable strain. Moreover, this finds support from the structure of
I-CpMn(C0)3 (23) which possesses a monomeric structure in which the carbonyl groups occupy three of the six approximately octahedral positions and the cyclopentadienyl ring centre is equidistant from the other three.
The molybdenum and the analogous (w, Cr) compounds must assume a dimeric structure because of having one less valence electron than manganese; the molybdenum atom is under compulsion to form an additional electron-pair bond in order to complete its 18 shell.
The binuclear iron compound [n-051-15Fe(C0)2]2 is an example of a compound whose structures in the crystal and as a free molecule in solution are not the same. According to infrared studies (21) there are both non-bridging and bridging carbon monoxide groups present but the number 35.
of C-0 stretching frequencies is not consistent with the presence of a centre of symmetry in the molecule. Mills (25) from detailed X-ray analysis has shown that there exists a metal-metal bond together with bridging and non-bridging carbonyl groups. The metal-ring distance of
2.12 2. is longer than that in ferrocene and is comparable to di(,-indenyl)iron, as a result of which both the di(n-indenyl)iron and the binuclear iron compound are of lower stability. Further infrared and Raman measurements (26) suggest that in solution the molecule cannot have a centre of symmetry in accord with the original views.
36.
CHAFT2R II
Discussion
(a) n-Cyclopentadienyl carbonyls of molybdenum, tungsten and iron.
Molybdenum and tungsten have been shown (18) to form binuclear
cyclopentadienyl hexacarbonyls [n-05H5M(C0)3]2, and a methyl-substituted
derivative was prepared (22) from methylcyclopentadiene. In our studies
with metal carbonyls and fulvenes we have been able to prepare a large
number of other substituted binuclear cyclopentadienyl metal carbonyls of
molybdenum, tungsten and iron by the direct interaction of simple carbonyls
with various fulvenes (Table I). Fulvenes were recently shown to be
starting materials for the preparation of substituted ferrocene
derivatives by the reaction of the lithium derivatives with iron halides (270
Whereas the formation of the n-cyclopentadienyl compounds from cyclo-
pentadiene required the loss of hydrogen in a manner as yet not fully
understood, the formation of the substituted n-cyclopentadienyl metal
compounds from the fulvenes requires the uptake of hydrogen according to
the equation R R C = C + 2M(C0)6 + 2H --4 R C - C5H4M( CO )3 600 ....(1) R H z Since high yields are obtained only when using solvents such as ethylene- glycol dimethyl ether or dimethyl cellusolve, from which it is known that 37.
TABLE I
Di-substituted 7-cyclopentadienyl metal tricarbonyls obtained by direct interaction_of metal carbonyls and the corresponding fulvene.
R in [R-05F4M(C0)x]2 M m.p. Colour Yield
n-propyl Mo d. 200 red 20
isopropyl Mo 163 red 42 1-methyl-n-propyl Mo 170 red 70 1-ethyl-n-propyl Mo 152 red 45 1-methyl-n-butyl Mo 117-1-19 red 62
1-phenyl ethyl Mo d. 125 dark red 30 diphenyl methyl Mo 203-205 brown 30 anisyl-methyl Mo d. 103 brown 60
cyclohexyl Mo 180 red 20
isopropyl W 195 red 10
1-ethyl-n-propyl W 184 red 8 isopropyl Fe liquid dark red -
1-ethyl-n--propyl Fe II II -
If 1-phenyl ethyl Fe If - 38.
hydrogen can be abstracted, the hydrogen is most likely derived from the
solvent used, though some hydrogen abstraction from the excess fulvene
used is also possible,
Dimethyl fulvene and diethyl fulvene reacted with tungsten hexacarbonyl
only at elevated temperature requiring the use of dimethyl carbitol as the
solvent. However, no such product could be isolated while using ethylene-
glycol dimethyl ether as the solvent. Chromium hexacarbonyl with dimethyl
fulvene gave a red product, very unstable to air,and this could not be
isolated in the pure state. It may, however, be mentioned that the
compound does not appear to be binuclear (substituted n-cyclopentadienyl)
carbonyl which is dark green in colour (28). It may be substituted
dicy1Dpentadienyl chromium like the dicyclopentadienyl chromium which is
red in colour and very unstable to air.
Iron pentacarbonyl with fulvene, however, gave binuclear substituted R twk n-cyclopentadienyl carbonyl H - C C51-14Fe(C0)2 in very small yield 2 which could not be obtained iri- the pure state because of its unstable
nature (22) in organic solvents, but its presence was confirmed by its
infrared spectrum.
The n-cyclopentadienyl molybdenum tricarbonyl halides have previously
been made by indirect methods (29) but it is now found that the metal-metal
bond (21) in di(n-cyclopontadienylmolybdenum tricarbonyl) undergoes
immediate fission with iodine in solution. In this way we have prepared
a number of monomeric iodides of the general formula R-05H4Mo(C0)3I
(Table II).
[R-05110go(C0)3]2 + 2R-051-142go(C0)3I (2) 39
TABLE II
Substituted n-cyolopentadienyl molybdenum tricarbonyl iodides.
R in R-0511Mo(C0)3I map. j Colour Yield
isopropyl 92-94 dark red 69
1-methyl-n-propyl 75 red 70
1-ethyl-n-propyl 45 red 43 1-phenyl ethyl 76 brown 59 anisyl methyl 78 brown 70
1-methyl-n-butyl oil red 40
TABLE III Alkyl derivatives of substituted n-cyclopentadienyl molybdenum tricarbonyls.
R-C;11,MO-R' CO map. Colour Yield R R'
isopropyl methyl -25 yellow 70 isopropyl ethyl -15 yellow 60
1-ethyl-n-propyl methyl oil yellow 60 1-ethyl-n-propyl ethyl oil yellow - 1-phenyl ethyl methyl oil yellow - 40.
The metal-metal bond can also be cleaved by sodium shot in tetrahydrofuran
to give the corresponding sodium salts.
A large number of compounds are now known in which an alkyl group is
Cr-bonded to the metal atom of n-cyclopentadienyl molybdenum
tricarbonyl residue (29). No compounds were known) however, in which alkyl groups were attached directly to the metal and also substituted on the
n-cyclopentadienyl ring. A number of these compounds have been prepared
by the interaction of the sodium salts of the substituted cyclopentadienyl molybdenum tricarbonyls and alkyl halides (Table III).
In physical and chemical properties the ring-substituted compounds
described above are very similar to the parent cyclopentadienyl compounds; for instance, they are readily soluble in chloroform, rather less soluble in carbon tetrachloride, alcohol, acetone, benzene, etc., and are sparingly soluble in light petrol. They are insoluble and unaffected by water, dilute acids or bases. The monomeric iodides are insoluble in water and do not give yellow precipitataswith silver nitrate in aqueous medium. Thus there is no evidence for the formation of cationic species in aqueous solution. In acid solution the precipitation with silver nitrate solution is rapid. The resulting solution after filtration gives no precipitate with silicotungstic acid and Reinecke's salt, showing the
absence of [CpMo(C0)3]+ cations. There is a general tendency, however, for the ring substituents to cause a lowering in melting point and increase instability of the compounds. The alkyl derivatives of substituted n-cyclopentadienyl molybdenum tricarbonyls were generally 41.
yellow oils thermally very unstable and forming on decomposition the corresponding binuclear compound. This trend has already been noted on methyl substitution (22).
The infrared spectra of all the compounds have only two strong modes in the metal-carbonyl CO stretching region (2,200 to 1700 cm. .). This is despite the presence of substituent groups on the cyclopentadienyl ring and confirms the view (21,22) that the number of infrared-active modes is
0 pendent upon the local symmetry of the -M(C0)3 groups and not on the total symmetry of the molecule, owing essentially to free rotation about the metal-ring bond (19,30). The small variations observed in CO stretching frequency may be explained by the variations in electron density on the ring and metal atom, caused by substituents on the n-cyclopentadienyl ring. The CO stretching modes of all these compounds are given in Table VII.
Interaction of the sodium salt of cyclopentadienyl molybdenum tricarbonyl and cyclopentadienyl tungsten tricarbonyl chloride has produced a n-cyclopentadienyl tungsten cyclopentadienyl molybdenum hexacarbonyl. n-051.15Mo(C0)3Na + n-05H5W(C0)3C1-4 NaC1 + n-05H5(C0)3Mo-W(C0)37C5H5
So far as we are aware, this is the first example of a complex with a metal-metal bond between different transition metals. As an equimolar mixture of the corresponding Mo-Mo and W-177 compounds would have the same analysis, the compound was carefully chromatographed twice (as a single band) and then shown to analyse unchanged. Further, the ultraviolet 42.
spectra of the binuclear 3-cyclopentadienyl molybdenum and tungsten
carbonyls have sharp absorption maxima at 386 and 360 m4, respectively.
An equimolar mixture of the compounds exhibits both these peaks (387 and
364 m4) whereas the mixed molybdenum-tungsten compound has only one
maximum at 374 mµ.
According to Day and Lukman (31) the absorption spectra of 6',6'—
disubstituted fulvenes are practically identical and show a strong
absorption peak at 265-71 m4 and a weaker peak at 352-60 m4. The
conjugation of the phenyl group with the fulvene group at the 6—position of stron1,er absorption shifts the maximum/about 30 mp towards longer wavelengths and decreases
the amount of absorption; a new peak appears at 230-240 m4 while that near the 360 m4 disappears. These peaks are further shifted 25 mp towards
the visible for diphenyl fulvene„ etc. All the compounds show two strong
absorption peaks at 390-400 mp and 510-517 mp with the exception of the
unsubstituted derivatives or the derivatives of the tungsten metal where
these are found at longer wavelengths (360-365 mp and 490-494 mµ)•
These slight shifts in the absorption maxima may be due to the presence
of the substituents on the cyclopentadienyl ring.
(b) Triphenylphosphoniumcyclopentadienylide metal complexes.
The cyclopentadienylides formed by the triphenylphosphonium (12) and
pyridinium (11) groups can be considered to have resonance forms in which the five-membered carbocyclic ring has a sextet of electrons. In
such a form it should be possible for the cyclopentadienyl ring to act
43.
as a formal six-electron donor and act as a ligand comparable to aromatic
hydrocarbons which are well known to be able to replace carbon monoxide
in metal carbonyls to give compounds such as C61-16Cr(C0)3 (32).
By the direct interaction of chromium, molybdenum and tungsten
hexacarbonyls with triphenylphosphonium cyclopentadienylide in refluxing
ethyleneglycol dimethyl ether, we have obtained good yields (ca. 60%) of
the corresponding metal tricarbonyl derivatives as fine yellow crystals
from chloroform-light petroleum.
The compounds are readily soluble in chloroform, slightly soluble in
benzene and insoluble in light petroleum. They are unaffected by water,
dilute alkalies or mineral acids. There seems little doubt that the
-M(C0)3 residue is bound to the five-membered ring as in (I) and not to one
of the phenyl groups, C 61-15
\C6H5 ;MO 7 N, CO I CO CO
since high-resolution N.M.R. measurements show no change in the resonances
of the phenyl group protons, whereas the line due to the protons on the cyclopentadienyl ring shifts to higher fields in the metal complex compared
to the original ligand. Such high-field shifts on the sandwich bonding
of a ring system to a metal have been observed in n-cyclopentadienyl compounds (29) and in arene metal compounds (33), e.g. in dibenzene- chromium the proton resonance lies 2.94 p.p.m. on the high-field side with respect to benzene; in benzene-iron cyclopentadiene the value is
3.09 p.p.m.
44.
The infrared spectra of these compounds show only two strong bands
in the C-0 stretching region, suggesting, as in other cases (32), the
probably free rotation of the -M(C0)3 group about the metal ring axis.
Triphenylphosphoniumcyclopentadienylide on direct interaction with
iron pentacarbonyl gave a yellow crystalline compound, C231119Fe2(C0)4
(from analytical data and molecular-weight determination), which we think
contains one -Fe(C0)2 residue attached to the five-membered ring and the
other -Fe(C0)2 to the phenyl group. The compound shows three strong bands
in the C-0 stretching region in solution. The compounds prepared in this
manner are listed in Table VIII, together with some of their properties.
CO stretching modes, Compound Colour oc cm-1 (all strong)
1. MO(C0)3-triphenylphosphonium- cyclopentadienylide 170d yellow 1923, 1810
2. W(C0)3-triphenylphosphonium- 184d cyclopentadienylide orange 1919, 1817
3 Cr(C0)3-triphenylphosphonium- 200d yellow 1915, 1810 cyclopentadienylide
Fe2(C0)4-triphenylphosphonium- 4 yellow cyclopentadienylide 205 2060, 1982, 1943
(c) Molybdenum(II) benzoate.
Recently a number of workers have reported (32, 34, 35, 36) the reaction between substituted aromatic compounds and chromium hexacarbonyl
to produce tricarbonyl aromatic chromium compounds. It has been noted,
however (32), that certain substituents (COOH, CN, CHO, NO2) on the 45•
aromatic nucleus cause decomposition, without the formation of a metal-tricarbonyl compound.
In the process of reacting molybdenum he-acar'enyl with a variety of compounds, we have obtained molybdenum dibenzoate, (C6H5C00)Mo, by the direct interaction of benzoic acid and the hexacarbonyl in dimethyl carbitol. This compound we believe is a novel type of oxygen chelatate complex [I] and [II], where, in addition, the arene nucleus is bound to a the metal atom by/sandwich type bond, as in the arene-metal carbonyls.
co oc
I II 46.
The absence of the COOH group is confirmed by the insolubility of the substance in alkali and the failure to liberate any hydrogen chloride on warming with either phosphorus pentachloride or thi nyl chloride. Further, there are no hydroxyl frequencies observable in the infrared spectrum, either in the free OH or hydrogen—bonded OH regions.
There is also a complete absence of absorption in the metal carbonyl and carboxylic acid regions, but the presence of the —C N140 groups is confirmed by very strong absorption at 1404 and 1494 cm. , these two regions being very characteristic (37) of the symmetrical and asymmetrical vibrations of the C00 structure.
From the structures proposed it can be seen that it is possible for the aromatic ring to coordinate to the same (I) or different (II) metal atom from its carboxylate group, the latter giving chain formation. This polymerisation is confirmed by the solubility properties of the compound.
A very small portion of the initial product is soluble in chloroform to give a bright yellow solution which undergoes rapid decomposition; the residual yellow crystals, however, are completely insoluble in any solvent.
These possess remarkable thermal stability and have been recovered unchanged after heating at 350° for 24 hours in the absence of air. Those crystals on boiling with concentrated nitric acid, give benzoic acid; however, the compound is stable towards dilute hydrochloric acid. The polymeric structure does break down at higher temperature, however,and it is possible to sublime molybdenum dibenzoate at 4200/0.01 mm. The crystalline yellow condensate has identical analysis and infrared spectrum to an unsublimed sample. Again the condensed compound appears to be mainly polymeric and has the same solubility properties as it had before sublimation. 47.
Similar compounds with the same properties have also been obtained from o-toluic acid and anisic acids. These also have very strong infrared absorptions in the COO regions, viz.
molybdenum o-toluate 1384 and 1500 cm.-1 and molybdenum anisate 139 0 and 1504 cm. .
All the three compounds are diamagnetic. The reaction of nitrobenzene with molybdenum hexacarbonyl gives a blue insoluble, presumably polymeric material, perhaps of a rather similar nature to the benzoate; we have been unable to purify the material or to obtain reliable analyses. 48.
CHAPTER III
Experimental
Many of the compounds and intermediates prepared in this work are rapidly decomposed by atmospheric oxygen and moisture. Therefore all preparations, reactions and purifications were carried out either in an atmosphere of nitrogen or in vacuum using standard methods of crystallisation, vacuum sublimation and chromatography on alumina. In addition all metal carbon monoxide derivatives are light sensitive; however, such decomposition is insignificant in diffuse daylight although direct sunlight must be avoided.
Microanalyses of elements, and molecular weights, were performed by the Microanalytical Laboratory of Imperial College.
Preparations and Reactions.
The various fulvenes used in this work with their methods of preparation and properties are given in Table IV. Since the methods of preparation given are mostly similar, with slight modifications, the preparations of dimethyl fulvene, diphenyl fulvene, and cyclohexylidine— cyclopentadiene as a representative of each class are given below. 49.
TABLE IV
20 Me thod Fulvene b.p. n t Yield Colour I) of prep.
1. Dimethyl fulvene 54/17 mm. 1.5450 60.0 (38) yellow 2. Methyl ethyl fulvene 66/17 mm. 1.542 35.0 (38) yellow
3. Diethyl fulvene 68-72/17mm. 1.520 40.0 (38) yellow 4. Methyl phenyl fulvene 130/10 mm. - 10-15 orange
5. Diphenyl fulvene m.p. 82 - 40.0 (1) orange
6. Anisilidene fulvene m.p. 70 - 32.0 (2) yellow
7. Cyclohexylidene- 78-80/17mm. 1.5478 40.0 (39) yellow cyclopentadiene
8. Ethyl fulvene 68-70/17mm. - 40.0 (40) pale yellow
Prparation of dimethyl fulvene.
Freshly distilled cyclopentadiene (110 g., 5 mol.) and an equivalent
amount of acetone (97.0 g., 5 mol.) were placed in a three-necked flask
fitted with a stirrer, a reflux condenser and a dropping funnel, cooled
in ice. To this was added 20% solution of potassium hydroxide (35 ml.)
in ethanol slowly with constant shaking and cooling of the reaction
mixture. When the vigorous reaction was complete, the flask was stoppered
and kept cooled overnight. The water layer was separated and low-boiling
materials were removed on pump at 20°/20 mm. The residue on fractional
distillation gave dimethyl fulvene (50.0 g., 60%), b.p. 54-57/17 mm. 7.20 = 1.545. 50.
Preparation of diphenyl fulvene.
Benzophenone (18.20 g., 1 mole) was dissolved in sodium (2.30 g.,
1 gm. atom) in absolute alcohol (200 ml.). To this was added freshly
distilled cyclopentadiene (6.60 g., 1 mole) and the reaction mixture was
warmed. The condensation product first separates out as an oil which soon
becomes solid on stirring. The crude product was filtered, washed with
alcohol and finally crystallised from petroleum ether (40-60) in red
crystals (9.0 gm., 40.0%), m.p. 82".
Preparation of cyclohexylidenecyclopentadiene.
A mixture of freshly distilled cyclopentadiene (22.0 g., 1 mol) and
cyclohexanone (32.7 g., 1 mol.) was added slowly with constant shaking and
cooling (when necessary) to a solution of sodium metal (7.70 g., 1 gm. atom)
dissolved in dry methanol (100 ml.). The resulting mixture was immediately
diluted with water as soon as the addition was over and the condensation
product extracted with chloroform. The chloroform extract was dried and
fractionated under reduced pressure. Fractional distillation at
76-78/17 mm. gave cyclohexylidene cyclopentadiene (20.0 g., 40%).
Interaction of fulvenes with molybdenum hexacarbonyl.
Dimethyl fulvene (3.18 g., 1.5 mol) and molybdenum hexacarbonyl
(5.28 g., 1 mol) in ethyleneglycol dimethyl ether (50 ml.) were refluxed
(6 hours), keeping an atmosphere of nitrogen above the reaction mixture.
During this period considerable carbon monoxide was evolved and the reaction mixture became deep red. Volatile material was removed 51.
(60A0-3 mm.), and the rod residue extracted with petrol/`benzene mixture.
After purification by chromatography on an alumina column di(isopropylcyclopentadienyl molybdenum tricarbonyl) was crystallised from light petrol as fine red crystals (3.0 g., 42.0%), m.p. 163-164°. The analytical data for the various substituted di(cyclopentadienyl molybdenum tricarbonyl) are given in Table V.
TABLE V
R in Mol. weight Found Required
[C5H4RMo(C0)3]2 Found Required C H Mo 0 C H 1 Mo 0 n-propyl 588 574 46.0 3.7 33.2 - 45.9 3.8 33.5 - isopropyl 619 574 45.5 4.2 33.6 16.9 45.9 3.8 33.5 16.7 1-methyl-n-propyl 614 602 48.30 4.1 32.8 15.9 47.8 4.31 31.9 15.9 1-ethyl-n-propyl 678 630 50.0 4.8 30.9 14.90 49.5 4.8 30.5,15.2
1-methyl-n-butyl 645 630 50.4 5.10 30.5 15.20 49.5 4.8 30.5 15.2 1-phenyl ethyl 702 698 55.42 4.0 27.8 13.8 55.0 3.7 27.5 13.8 diphenyl methyl 862 822 61.5 4.30 22.90 - 61.3 3.7 23.4 - anisyl methyl 717 730 53.2 4.1 26.4 - 52.6 3.6 26.3 - cyclohexyl 670 654 51.5 4.9 29.1 14.5 51.4 4.6 29.4 14.70 52.
Interaction of fulvenes with tungsten hexacarbonyl.
In the same way as described above for the molybdenum analogues, we have prepared di(isopropy1-1-cyclopentadienyl tungsten tricarbonyl)
(10%) [Found: C, 34,6; H, 3.4; W, 48.2%. M.W. 723. C22H2206W2 requires C, 35.2; H, 2.9; W, 49,10%. M.W. 750] and di(1-ethyl-n-propyl-
I-cyclopentadienyl tungsten tricarbonyl) (8.0%) [Found: C, 38.8; H, 2.8;
W, 46,1%, M.W. 806. C26H3006W2 requires C, 38.6; H, 3.7; W, 45.7%.
M.W. 795) using dimethyl carbitol as the solvent. It may be mentioned, however, that no reaction took place when ethyleneglycol dimethyl ether was used as the solvent.
Interaction of dimethyl fulvene with iron pentacarbonyl.
Iron pentacarbonyl (11.8 g., 1.5 mol) was refluxed in petrol (100-120°)
(50 ml.) with dimethyl fulvene (4.20 g., 1 mol) for 24 hours. There was considerable evolution of carbon monoxide and solution soon turned deep red.
Volatile material was removed (20/1 mm.) and the residue extracted with chloroform and centrifuged. The solution was concentrated and chilled in a dry-ice acetone bath; no crystals were obtained. The solvent was removed and the residue chromatographed on alumina. The semi-solid residue could not be crystallised but was confirmed to be di(isopropylcyclopenta- dienyl iron dicarbonyl) by infrared spectra. This was further confirmed by the preparation of monomeric iodide by reaction with iodine in chloro- form. 53.
Preparation of the substituted cyclopentadienyl molybdenum tricarbonyl iodides.
The substituted di(I-cyclopentadionyl molybdenum tricarbonyl)
(1 mol.) in chloroform was added dropwise to iodine (1 mol.) in chloroform with constant shaking, After completing the addition the chloroform solution was shaken with aqueous sodium thiosulphate to remove any poly- iodides formed; after separation, the chloroform was removed (20/10 mm.) and the residual brown mass recrystallised from light petrol to yield the pure product (Table VI). All these preparations were carried out on approximately 0.005 molar scale.
TABLE VI.
R in Mol. wt. Found Required
R-05H4Mo(C0)3 I Found Required C H 1 Mo I 1 0 C H 1 Mo I
'11.5 Isopropyl 422 414 32.1 2.6 23.5 31.9 2.7 23.2 -
1-methyl-n-propyl 450 428 32.7 2.8 22.6 29.7 33.7 3.0 22.4 29.7 1-ethyl-n-propyl 476 442 34.6 3.5 22.0 29.2 35.3 3.4 21.7 28.7 1-phenyl-n-ethyl 488 476 40.8 3.2 20.0 27.5 40.3 2.7 20.2 26.7 anisyl methyl 510 492 39.5 3.2029.5 25.8 39.0 2.70 19.5 25.8
1-methyl-n-butyl 416 442 34.0 3.80122.1 29.0 35.3 3.4 21.7 28.7 54.
Preparation of the metal-alkyl derivatives of certain substituted cyclo- ipentadienyl molybdenum tricarbonyls.
Di(isopropyl-n-cyclopentadienyl)dimolybdenum hexacarbonyl (1.7 g.,
1 mol.) in tetrahydrofuran (25 ml.) was added to sodium shot (0.4 g., 5 mol) suspended in tetrahydrofuran (75 ml.), and the solution refluxed gently with stirring (3 hours); during this time a yellow coloration developed owing to formation of the sodium salt. After cooling the reaction mixture, methyl iodide (2 ml.) was added dropwise and the mixture was refluxed for a further hour. Removal of volatile matter (20/10 mm.) left a dark oil which on sublimation gave pure isopropyl-n-cyclopentadienyl methyl molybdenum tricarbonyl (70.0%) [Found: C, 48.1; H, 4.73;
Mo, 30.8%; M.W. 295. 0121111Mo03 requires C, 47.7; H, 4.6; Mo, 31.7%.
M.W. 302]. In a similar manner we prepared iso-propy1-7-cyclopentadienyl ethyl molybdenum tricarbonyl (60%) [Found: C, 50.2; H, 5.2; Mo, 29.8%.
M.W. 298. C131113Mo03 requires C, 49.4; H, 5.1; Mo, 30.4; M.W. 316] and 1-ethyl-n-pEopyl-n-cyclopentadienyl methyl molybdenum tricarbonyl
[Found: C, 52.1; H, 5.9; Mo, 28.2%, M.W. 315. C141115Mo03 requires
C, 50.9; H, 5.5; Mo, 29.1%, M.W. 330].
Preparation of Tc-cycle entadienE1 molybdenum n-cyclopentadienyl tungsten hexacarbonyl.
Di(cyclopentadienyl-molybdenum tricarbonyl) (1.30 g., 1 mol) was added to sodium shot (0.49 g., 4 mol) in tetrahydrofuran (100 ml.) and the mixture refluxed (2 hours). After cooling, the yellow solution of the sodium salt was filtered off from the excess metal and added to 55.
I-cyclopentadienyl tungsten tricarbonyl chloride (1.96 g., 1 mol) in
tetrahydrofuran (30 ml.). The yellow reaction mixture gradually became
red and after refluxing (2 hours) and subsequent cooling the volatile
matter was removed (20/10 mm.) and the crude product crystallised from
chloroform/petrol. After chromatographing twice in benzene-chloroform
mixture, pure red crystals of I-cyclopentadienyl molybdenum 1-cyclopentadienyl
tungsten hexacarbonyl (1.0 g., 65%), mop. 250° [Found: 0, 32.0; H, 1.81;
Mo, 16.75; W, 32.10%, M.W. 528. C/61110MoW04 requires C, 33.2; H, 1.71; Mo, 16.6; W, 31.8%; M.W. 578] were obtained.
Preparation of triphenylphosphoniumcyclopentadienylide (12).
Cyclopentadiene (2.7 g., b.p. 40-42°) in chloroform was treated with a
solution of bromine (6.6 g.) in chloroform (10 ml.) under nitrogen atmos-
phere at -50 to -40°. When the bromination was complete, the solution was
diluted with chloroform (10 ml.) and was treated at -40° with triphenyl-
phosphine (21.6 g.) in chloroform (100 ml.). The solution was heated
slowly and was maintained at its reflux temperature for six hours and at room temperature overnight. The cooled mixture was shaken with 100 ml. of
1.3N aqueous sodium hydroxide. The chloroform extract was dried,
distilled and the residue washed with methanol and dried. It was finally crystallised from chloroform ethanol mixture (5.0 g., yield 40%), m.p.
228-231°. 56.
Interaction of triphenylphosphoniumcyclopentadienylide with molybdenum hexacarbonyl.
Molybdenum hexacarbonyl (1.0 g.) and triphenylphosphonium-
cyclopentadienylide (0.5 g.) in ethyleneglycol dimethyl ether (30 ml.) were refluxed (4 hours), keeping an atmosphere of nitrogen above the reaction mixture. When there was no more evolution of carbon monoxide gas, .-3 the volatile material was removed (60/10 mm.) and the residue on crystal- lisation from a mixture of dichloromethane and light petrol gave triphenyl-
phosphoniumcyclopentadienylide molybdenum tricarbonyl (0.5 g., 60%) in fine lemon yellow needles, m.p. 170°d. [Found: C, 61.7; H, 3.8; Mo, 19.7;
P, 6.3%. C261119 PM003 requires C = 60.6; H, 3.8; MO, 19.0; Py 6.1%]. In a similar manner were prepared triphenylphosphoniumcyclopentadienylide tungsten tricarbonyl, m.p. 184°d (60%) [Found: C, 52.60; H9 3.08f. C261119WP03 requires C, 52.52; H, 3.20]; triphenzlphosphoniumcyclopenta- dienylide-chromium tricarbonyl, m.p. 200°d. (50%) [Found: C, 67.16;
H, 4.43; Cr, 11.26%. C26H19Cr(C0)3 requires C, 67.53; H, 4.11; Cr, 11.26%] and triphenylphosphoniumcyclopentadienylidedi-iron tetracarbonyl, m.p. 205° (45%) [Found: C, 57.82; H, 3.72; Fe, 20.05; C271119Fe204P requires C, 58.90; H, 3.46; Fe, 20.37%]. 57.
Infrared Spectra.
Infrared spectra were recorded on a Perkin-Elmer Model 21 double beam recording spectrophotometer, using sodium chloride optics. The scale was
spread to 0.1 micron per inch and the machine was programmed to obtain
maximum resolution. The spectra were measured in reagent-grade chloroform
in C-0 stretching region 1700-2200 cm.-1 and the principal absorption bands
are listed in Tables VII and VIII.
TABLE VII
R in CO stretching R-05I-1 4.Mo-RqC0)3 CO stretching; M modes (cm.-1) modes (cm. ) [R-05H4M(C0)3]2 (all strong) (all strong) n-propyl IVIo 1967, 1916 isopropyl methyl 2030, 1938 iso-propyl Mo 19649 1916 isopropyl ethyl 2025, 1931
1-methyl-n-propyl Mo 1964, 1913 1-ethyl-n-propyl methyl 2028, 1931 1-ethyl-n-propyl Mo 1962, 1916 1-ethyl-n-propyl ethyl 2021, 1927
1-methyl-n-butyl Mo 19 62 , 1912 1-phenyl ethyl methyl 2021, 19 31
1-phenyl ethyl Mo 1962, 1912
diphenyl methyl Mo 19 61, 1916 anisyl-methyl Mo 19 61 , 1911 cyclohexyl Mo 19 61, 1911 isopropyl w 1958, 1906 1-ethyl-n-propyl W 1960, 1905 58
TABLE VIII
R in CO stretchin ) R in ! CO stretchin M modes (cm.-1 M modes (cm.-1 ) [R-051.14M(C0)2]2 R-05H4Mo(C0)xI (all strong)
Isopropyl Fe 2050(w), 2005(s) isopropyl Mod 2052, 1974 1953(s), 1765(s)
1-ethyl-n-propyl Fe 1-methyl-n-propyl Mo 2051, 1974
1-phenyl ethyl Fe 2064(w), 2009(s), 1-ethyl-n-propyl Mo 2050, 1976 1959(s), 1764(s)
1-phenyl ethyl Mo 2052, 1974
anisyl methyl Mo 2055, 1975
1-methyl-n-butyl Mo 2050, 1973
isopropyl Fe 2048, 2001
Ultraviolet Spectra.
The spectra presented in Table IX were obtained using a Spectracord recor6.'n
spectrophotometer. The solvent used in each case was chloroform. All
these compounds show two strong absorption peaks at 390-400 mp and
510-517 mp which are characteristic of the parent di(7-cyclopentadienyl)
metal tricarbonyls of molybdenum and tungsten and do not show any independent absorption of the conjugated diene system found in fulvenes. 59.
TABLII: IX.
R in Absorption maximum Absorption maximum M [R-05HI.M(C0)3]2 wavelength E wavelength C (mu) max. (n111) (-max.
H Mo 386 22,000 510 2150 isopropyl Mo 393 15,070 510 3123
1-ethyl-n-propyl Mo 395 15,05o 515 1645 1-methyl-n-propyl Mo 400 18,060 517 1982
1-methyl-n-butyl Mo 398 19,240 512 3436 diphenyl methyl Mo 394 13,900 512 2978
1-phenyl ethyl Mo 390 18,750 513 2360 anisyl methyl Mo 395 16,340 513 2340
H W 36o 16,700 490 1540 isopropyl W 365 26,250 492 4000 l-ethyl-n-propyl W 365 31,300 493 3793 n-C 5H5 C13 Mo- - 374 17,000 498 2540 w co 3n-05H5 60.
Interaction of molybdenum hexacarbonyl and benzoic acid.
Molybdenum hexacarbonyl (5.0 g., 1 mol) and benzoic acid (4.7 g., 2 mol) in freshly distilled diethyleneglycol dimethyl ether (50 ml.) were heated at
160° until there was no further evolution of carbon monoxide (about 9 hours).
Crystals separated out during the reaction and after cooling volatile matter was removed (60°/10-3 mm.). Washing with warm alcohol (4 x 20 cc.) and subsequent vacuum drying left a mass of lemon yellow needle crystals of molybdenum(II) dibenzoate (2.72 g., 38%) [Found: C, 49.7; H, 3.1; MO9 28.0;
0, 19.20; C141110Mo04. requires C, 49.7; H9 3.0; Mo, 28.4; 0, 18.9%].
In a similar manner molybdenum di-o-toluate (41%) [Found: C, 52.7;
H, 4.5; Mo, 26.2; 0, 17.45. C16H14m004. requires C, 52.5; H, 3.8;
Mo, 26.2; 0, 17.5%] and molybdenum di-anisate (38%) [Found: Cy 48.1;
H, 4.30; Mo, 24.3; 0, 23.7; C16H14Mo04 requires C, 48.2; H, 3.5; Mo, 24.1; 0, 24.1%] were prepared as yellow crystalline solids.
Sublimation of molybdenum benzoate.
The salt was placed under a thick pad of glass wool in a small sublimer with an air-cooled probe. After evacuating (0.01 mm.), the sublimer was slowly heated in a Woods metal bath. At 350° the pale yellow crystals becane orange (but returned to yellow on cooling), and then at about 420° yellow crystals started to condense on the probe. The temperature was kept at this value until most of the benzoate had sublimed. On cooling, the probe was removed and the condensate (78%) was unchanged molybdenum benzoate [Found: C, 49.6; H, 3.05; MO, 28.2; 0, 19.0%] (strong infrared absorptions at 1404 and 1494 cm. ). 61.
Infrared spectrum of molybdenum(II) dibenzoate.
Infrared spectra, in nujol and hexachlorobutadiene mulls and potassium bromide discs, were recorded: 677(s), 707(s), 717(s), 842(m), 930(w), 1026(m), 1067(m), 1137(m), 1172(w), 1404(vs), 1442(m), 1494(vs), 1583(m), 3020(w). 62.
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I am greatly indebted to my supervisor, Professor G. Wilkinson, for his constant guidance, keen interest, unstinted support and encouragement during the course of this study.
I would like to thank Dr. To W. Abel for his ungrudging support and constant advice in the fulfilment of this work.
My thanks are due to Dr. D.F. Evans, Dr. L. Pratt, and to my colleagues Mr. W.P. Griffith, Mr. M.A. Bennett and others for many helpful discussions and their enjoyable company, and to Miss C.M. Ross for her care in typing this material in a very short time.