THE QUEST FOR NEW AMINOSTIBINES AND AMINOBISMUTHINES
by
Laura Stark
Submitted in partial fulfillment of the requirements for the degree of Master of Science
Dalhousie University Halifax, Nova Scotia August 2000
O Copyright by Laura Stark, 2000 National Libraiy Bibliothèque nationaie l*l ofCanada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Welington Street 395. rue Wellington OttawaON KlAON4 OttawaON KIAON4 Canada Canada
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Table of Contents ...... iv
List of Figures ...... vi
List of Tables ...... vii
*.* Abstract ...... viii
List of Abbreviations and Symbols ...... ix
Acknowledgements ...... x
Chapter 1. Introduction
The Pnictogens ......
Compounds of antimony and bismuth ......
Arninostibines and aminobismuthines ......
Homoleptic aminostibines and aminobismuthines ......
Reactions of SbC13 and BiC13 with RN(H)Li ......
Cyclic bis(amin0)-stiba and -bismahalides ......
Reactions of [SbClx(NMe2)3-J(x = O - 2) with primary amines ......
Monosilylated amino derivatives of Sb and Bi ......
iv 1 -8 Diethylarninoorganoantimony(m) derivatives ...... 16
1.9 Single versus multiple bonding ...... 17
1.10 Characterization of compounds ...... 19
1.1 1 Summary and concIusions ...... 20
Chapter 2. Expenmental
2.0 Generai procedures ...... 24
2.1 Reactions of EC13 with RNOLi ...... 25
2.2 Reactions of DipN(H)ENDipI2 (E = Sb, Bi) ...... 32
Chapter 3 . Results and Discussion
Objectives ...... 35
Optirnizing reaction conditions ...... 37
Reactions of BiC13 with RN(H)Li ...... 37
Reaction of SKI3+ 3 'BUN(H)L~...... 39
Improved synthetic route to [DipN(H)ENDipl2(E = Sb, Bi) ...... 39
Reactions using [DipN(H)ENDipI2 as starting materid ...... 41
Reactions of EC13 with m(H)Li] and [R'N(H)Li] ...... 43
Conclusions ...... 48
Endnotes (references) ...... 50 List of Figures
Figure 1- Pathway leading to the formation of pipN(H)BiNDipI2 ...... 7
Figure 2 . i3 { pN(2,6-Me2C&) l4 (NH(2,6-Me2C&) )] ...... 9
Figure 3- Reaction of ECb with ~e~si(N'~uLi)~...... 10
Figure 4. Formation of Bi2[(NtBu)2SiMe2]3 ...... 11
Figure 5 . Structure of [S bCl(NHMe2) (p-NtBu)]2 ...... 14
Figure 6. Structures of [Sb(NMe2)(p-NR)]2 (R=mpy, C6H2(OMe)3.3,4, 5) ...... 15
Figure 7 . Cyclodimerization of alkenes ...... 18
Figure 8 . StmcturaIly characterized arninostibines ...... 22
Figure 9 . Structurally characterized amino bismuthines ...... 23
Figure 10- A typical two-chamber reaction vesse1 ...... 26
Figure 11. Monomer-dimer relationship ...... 36
Figure 12. Dissociation of PipN(H)PnNDip];! by addition
of acid (A) or base (B) ...... 36
Figure 13. Crystal structure of mi2(p-NDip)2(NHDip)z(pyr)] ...... 42
Figure 14. Crystal structure of cycfo.[l,3-CI2-S.@ipNH).2,4, 6.(Di~)~@iN)~]...... 44
Figure 15. Comectivity diagram of
cyclo~[173~C12-5-@ipNH).2,4, 6.(Di~)~@iN)]...... 45
Figure 16. Core of cyc10~[I,3~C~~-5~@ip~-2,4,6.(Dip)3(BN)3] ...... 47
Figure 17. Possible products of the reaction BiC13 + DipNOLi t Mes*N(H)Li ...... 47 List of Tables
Table 1. Sorne properties of Sb and Bi ...... 2
Table 2 . Diatomic NPn bond enthalpies ...... 5
Table 3 . Selected 'H and 13cNMR shifts of 1,3-di-tert-butyl-l,3,2,4-
diazadistibetidines ...... 13
Table 4- Calculated enthalpies of cyclodimerization for 1.2.substituted (R)
alkenes Od/mol) ...... +...... 18
Table 5 . Observations from reactions of EC13 with RNoLi in various
stoichiometries ...... 27
Table 6. Observations from reactions of [PipN(H)ENDipI2 with various
reagents ...... 32
Table 7 . Selected bond lengths (A) for Bi2(p-NDip)z(Wip)z(pyr)] ...... 41
Table 8. Selected bond angles (O) for [Bi2(p-NDip)2(NHDip)~(pyr)] ...... 43
Table 9 . Selected bond lengths (A) for cyclo-[1.3-C12-5@ipNH)-
2.4. 6.(Dip)3(BiN)3] ...... 45
Table 10. Selected bond angles (O) for cyclo~[l,3~C1~~5~@ipNH).
2.4. 6.(Di~)~(BiN)~l...... 46
vii Abstract
The synthesis and characterization of aminostibines and aminobismuthines has been Iimited and few exampIes are known- A common synthetic method involves reacting lithium amide salts (RtNLi, R = H, organic group) with EC13 (E = Sb, Bi), resulting in elhination of LiCl and amination of the pnictogen. However, the stoichiometry of these reactions has dways been one equivalent of EC13 to three equivalents of R2NLi, and the variety of amines used has not been extensive. Several homoleptic aminopnictines [E(NRz)~]have been prepared with R groups rnethyl, ethyl, propyl, butyl (E = Sb), and phenyl @ = Bi). Aiso known are the compounds @(NHM~s*)~],(Mes* = 2,4,6-tri-tert-butylphenyl) and several species containing a dimeric E2N2 core. This work systematicaiiy investigated the synthesis of antimony and bismuth amines by varying the size of the R groups on the amine and by varying reaction stoichiometries. Using this approach, the compound cycl0-[1,3-C1?-5-@ipNH)-2,4,6- (D~P)~(B~N)~J, a novel 6-membered ring containing dtemating bismuth and nitrogen atoms, was prepared from the reaction BiCI3 + DipNmLi + Mes*N(H)Li @ip = 2,6- diisopropylphenyl). This is one of only a few examples of a stmcturally charactenzed aminobismuthine containing a Bi-Cl bond. The double bond rule States that heavier main group elernents, including antimony and bismuth, do not normally form rc-bonds because of their preference for a-bonding. Wtiile there are three reported iminoarsines (compounds containing a N=As double bond), there are currently no analogues for antimony or bismuth. In an attempt to isolate
a double bonded bismuth-nitrogen species, the cornpound pipNCH)BiNDip]-7 was reacted with several reagents, incIuding acids such as GaCI3 and HOTf, and a base (pyridine). While none of the attempted reactions gave isolable iminobismuthines, a pyridine adduct of pipNOf)BiNDip]î was observed. hterestingly, although the reaction was performed with an excess of pyridine, only one molecule of pyridine coordinated ont0 one of the bismuth centres. List of Abbreviations and Symbols
A acid Mes* 2,4,6-tri-tert-butylphen yl A mL rnilliliter B base mm millimeter Bu mPY 4-meth ylp yridin-2-y1 C Celcius n principal quantum number cm-' wavenumber NMR nuclear magnetic resonance d doublet (NMEt spec.) OTf triflate, OS 02CF3
Dcalc calculated density Ph phenyf Dip 2,6-diisopropylphenyl Pn pnictogen (group 15 element) E element (Sb or Bi) PPm parts per million Et eth y 1 Pr P~OPY~ FT Fourier transforrn PPt precipitate u b PYr p yridine Hz quint quintet (NMR spec.) 1 nuclear spin quantum number Ri unweighted agreement factor IR sept septet (NMR spec.) J joule t triplet (NMR spec.) k kilo THF tetrah ydrofuran
P bridging TMS trimethy lsilyl m multiplet (NMR spec.) Trip 2,4,6-triisopropylphenyl M v volume Me VDW van der Waals mp- melting point X halogen Mes O degrees Acknowledgements
Firstly, 1 would like to thank my supervisor, Dr. Neii Burford, for accepting me into his Iab and having confidence in my abilities as a chernist. He was always enthusiastic and even when things weren't going as planned he trïed to help me maintain a positive attitude.
1 also need to thank the other rnembers of the Burford research group. They made the laboratory environment a pleasant place to spend the days and were always helpful when 1 had a problem. 1especially need to acknowledge Roland, Andrew, and Denise for their patience and rnany useful and informative discussions.
My friend and roornmate Nicole, 1 thank you for proof reading this thesis, even though it is not in your area of interest. To Nicole, Kathy, and John, rhanks for having confidence in me and for making my free time so much fun.
1 want my parents and grandrnother to know that 1 appreciate the support they have given me over the last two years. They encouraged me to continue when 1 feIt like quitting.
1 also need to acknowledge the fine workmanship of Jurgen Muller, who devoted so much of his tirne to making glassware for the lab. Thanks also to Dr. T.S. Cameron,
Kathy Robertson and Bob McDonald for solving my crystal structures.
Finally, 1thank the department of chernistry for financial assistance. Chapter 1. Introduction
1.0 The Pnictogens
Group 15 of the perïodic table consists of the elements N, P, As, Sb, and Bi, which are colIectively referred to as the "pnictogens". The heaviest member of the group
(Bi) is a heavy metal; in fact, it is the heaviest stable isotope of al1 existing elements (dl nuclides beyond *%i are radioactive). As and Sb are both metdloids while the lighter members of group 15 (N, P) are non-metals. The ground state configuration of each element is ns2np3with an unpaired electron in each of the three p orbitals. While nitrogen can adopt any formal oxidation state between -3 and +5, the most common oxidation States for the heavier pnictogens are +3 and +5. The two heaviest pnictogens, namely antimony and bismuth, are the focus of this thesis.
The existence of antimony has been recognized since ancient times (- 4000 BC).'
It was given the name stibium by PLiny in about AD 50 and the name antimoniurn by
Jabir in about AD 800. It occurs mainly in the gray sulphide mineral stibnite (Sb&) and is also found as several antimonides of the heavy metals including copper, silver, and mercury. Sb has two stable isotopes: I2'sb (57.3%) and '"~b (42.7%). It occurs as several aIlotropes including the stable a-form, which has a lustrous blue-white coIour and flaky crystalline texture, and black, yellow, and expIosive forms. Sorne properties of antimony are listed in Table 1.
The existence of metallic bismuth has been known since at least AD 1480.' The narne "bismuth" is derived fiom the German word "wismut" which was latinized to
"bisemutum" in 1530 by German scientist G. Bauer. It is most commonly found in ores
I 2 containkg copper, lead or M, the rnost important of which are bismuthite (Bi&), bismite (Bif13) and bismutite ((BiO)KO3-H20). Bi exists entirely as the single isotope
209~iUnlike antimony, which has several allotropie foms, bismuth exists as a single allotrope and ha a silver-white colour tinged with red. Some properties of bismuth are shown in Table 1.
AnUmony and bismuth can both be extracted by roasting their sulphide ores in air to convert them into oxides, and then reducing these with carbon. Antimony can also be recovered by liquidating its ores tmder reducing conditions to give Sb& and then treating this with scrap iron to remove the suEde. Both elements exist as grey solids which have corrugated layer lattices with each metal atom surrounded by three nearest neighbours and an interbond angle of approximately 96O. The two elements react readily with oxygen, halogens, and some other nonmetals but are unaffected by non-oxidizing acids.
Table 1: Some properties of Sb and Bi
Sb Bi Atomic Number 51 83 Atomic Mass (glmol) 121-75 208.9804 Electro negativity Pauling 2.05 2.02 Allred-Ro cho w 1.82 1.67 VDR, covalent radii (A) 2.20, 1.41 2.40, 1.52
Isotopes (%), I 121sb (57.3), 512 'O'B~ (100), 9/2 123~b(42.7), 712 1.1 Compounds of antimony and bismuth
There are some well-estabiished compounds of antimony and bismuth including hydrides, halides, oxides, etc. Their syntheses and properties are discussed in several inorganic texts. 'jv4
Binary compounds of antimony and bismuth with other metal atoms are easiiy prepared by reaction with stoichiometric quantities of the elements. The cornpounds Vary greatly and their structures range from simple to very elaborate. Compounds with transition metals generally have compositions m,where n = 1,2 or 3. Most are hard, insoluble, relatively unreactive serniconductors. Antimony and bismuth react with alkali and alkaline earth elements to form what are referred to as "ZintI Phases" which contain
Km-anions. The principal types of Zintl anions that exist are E: and E,~-.
The trihydrides (EH3) of antimony and bismuth can be obtained by reduction of sulfuric acid solutions of the elements with an electropositive metal. They are very thermaIly unstable. The hydrides do not exist for Sb and Bi (V) because the hydnde is readily oxidized.
The tnhdides of antimony and bismuth are well known for al1 of the halides.
They are obtained by direct halogenation, keeping the element in excess. They are dl readily hydrolyzed by water. It is noteworthy that SbF3 molecules are linked together via
F bridges to form polymeric chahs, giving each Sb0a distorted octahedral environment. BiF3, on the other hand, is ionic with tricapped trigonal prismatic coordination of Bi by nine F atoms. The pentahalides SbFc, Bi& and SbC15 also exist 4 and are prepared by direct halogenation, keeping the halogen in excess. The fiuorides are al1 polymenc while SbCls (dong with the trichlorides) is molecular covalent.
The antimony oxides Sba6and Sb20s are weIl known. The trioxide is prepared by the direct reaction of antimony with oxygen. The pentoxide is made by the action of oxygen at high temperature and pressure on Sbf13. Both of these compounds are poIymeric. The only well-known bismuth oxide is Bi203,which is also polymeric.
Chalcogenides of Sb and Bi (ie. E2S3, Ele3, and E2Te3)are synthesized by direct reaction of the elements at high temperature. Sb2S3,which has flarne-retarding properties, has industrial uses in the manufacture of safety matches, military ammunition, explosives, pyrotechnie products, and ruby-coloured glass. Sb2S5,which cm be obtained as a red solid, is used as a pigment in fireworks. Sb2S3,Sb2Ses, and Bi2S3 dl have a rïbbon-like polyrneric structure.
While these are only selected exarnples of compounds formed with antimony and bismuth, they give a good introduction to some of the basic chemistry of these two elements. It rnay appear that much is known about these pnictogens. However, when compared to what is known about the chemistry of carbon, hydrogen, oxygen, nitrogen, and even phosphorus, the study of the chemistry of antimony and bismuth must be considered to be in its infancy.
1.2 Aminostibines and aminobismuthines
The focus of this thesis will be on the synthesis of new aminostibines and aminobismuthines. There is an extensive chemistry of P-N and P=N bonds, but as Group
15 is descended, the number of stmcturally characterized compounds containing 5 pnictogen-nitrogen bonds decreases. This is in part due to the weakness of the Sb-N and
Bi-N bonds compared to N-N, P-N and As-N bonds, as shown in Table 2.'
Table 2: Diatornic NPn bond enthalpies
Bond enthalpy Od/mol)
NAs
NSb
NBi
The bond enthalpies listed are for neutral gas phase diatomic molecules (determined by spectroscopic and mas spectrometric means) and therefore cannot be directly applied to solid-state compounds. However, they do show an obvious trend. There has been no systematic development of the chernistry of aminostibines and aminobisrnuthines, partialIy due to the weakness of the bonds and the consequential diffkulties associated with the preparation of these cornpounds, and partially due to the difficulties in characterking these materials. Presented here is a discussion of what is currently known about the amine chemistry of antimony and bismuth.
1.3 Homoleptic aminostibines and aminobismuthines
~~çdimeth~laminostibine~~~and trisdiethylaminostibine7 cm both be synthesized by the low temperature reaction of the appropnate lithium amide salt with a solution of antimony trichloride in diethyl ether. Mer refluxing for an hour and removing the
solvents, the product is distilled as a colourless liquid. The balanced reaction can be seen
in equations 1 and 2.
(1) Rm+ BuLi --+ R2NLi + + Cal,
(2) SbC13 + 3 R2NLi Sb(N'R2)3+ 3 LiCl
R = Me, Et
Yields are 62-85% for [Sb(NMe2)3] and 75% for [Sb(NEt2)3]. The products have been characterized by elemental analysis and IR and NMR spectroscopies.
The reaction of [Sb(NMe2)3] with secondary amines in 1:3 stoichiometries allows substitution of the three NMe2 groups with NR2 groups as shown in equation 3.'
(3) Sb(NMe2)3+3HNR2-Sb(NR&+3HNMe2
R = Et, Pr, Bu
The reaction was also attempted for R = 'Pr. However, elementai analysis and NMR spectroscopy showed that substitution was not complete and a definite structure could not be assigned to the product. It has been suggested that the isopropyl groups are too bulky to aIlow formation of the trisaminostibine.
Several homoleptic aminobismuthines (Bi(NR& R = Ph, Me, Et, n-~r)'-'O have been successfully prepared following the synthetic route shown in equations 1 and 2, with bismuth replacing antimony. One equivalent of BiC13 is reacted with three equivalents of
LiN& in THF or THF-petroleum ether at low temperature. The LiCl is filtered out and the product is isolated in several different ways depending on the R group. Unlike the antimony compounds, which are aU clear, colourless liquids, the bismuth denvatives are 7 yellow or orange soiïds. Crystalline products suitable for X-ray crystallography have been obtained where R is ~e'*or ph9. The method used for obtaining crystals of
Bi(NMe& involves filtration of the solution to remove LiCI, removal of the solvent in vacuo, and sublimation of the yellow filtrate onto a cold fmger at dry ice temperature.
Crystals of Bi(NPh& can be obtained by filtering out the LiCI, removing the solvent under reduced pressure, and recrystallizing the orange solid from CH2Ch-hexane by solvent diffusion at -30°C. In both compounds, the bismuth atom adopts a tngonal pyramidal coordination environment Bi-N distances of 2.189(18) and 2.180(2 1) A in
~i(??'Me2)a]are comparable to those in Pi(NPh2),] which are 2. I2(2) - 2.28(2) A.
1.4 Reactions of SbC13 and BiCI3 with FtN(H)Li
The reaction of BiC13 with three equivalents of ~i@%fH(2,6-'~r~6~3)](LiNHDip) gives a dimeric cyclic pnictetidine with the formula DipN(H)BWip12.II The reaction is proposed to involve more than one step, as shown below:
BiC13 + 2 RNHLi - 2 LiCI
RNHLi - RNH2
- LiCI I H 2
Figure 1: Pathway leading to the formation of [DipNOr)BiNDip12 8 In this reaction, one +valent of the iithiated aniline serves as litbiating reagent for the intermediate pnictogen-chlonde (l),rather than as an arninating reagent. IntermolecuIar elirnination of LiCl then Ieads to the formation of the dimer (2). The reaction seems to be independent of reaction conditions, so that compound 1 can not be isolated even by carrying out the reaction in a 2:1 ratio. The solid state structure shows that the compound is centrosymmetric and consists of a planar four-mernbered Bi-N-Bi-N ring with pendant
N(H)Dip moieties attached to the bismuth centers. Cyclic and acyclic Bi-N bond Iengths are the same (2.1 B(4) - 2.174(5) A). Cyclic N-B i-N and Bi-N-B i bond angles are
78.5(2)O and 10 1S(2)" respectively while acyclic N-Bi-N bond angles are 93 .O(Z)" and
SbC13 reacts in a 1:3 ratio with the less stencalIy encumbered Li=] (R = 2,6-
Me2(Ca3))to give a similar dimer with the formula [S b2(p-NR)2(NHR)2] '"13 (equation
(4) SbCI3+3Li(NHR) 1/2 I I - 3 LiCl R-N-Sb-N-R - NH2R I
This compound is prepared by adding a solution of SbCl3 in THF to three equivalents of
Liw(2,6-Me2(C&))J in ether. AU volatiles are removed and CH2C12is added to precipitate out LiC1. Filtration and solvent diffusion of hexane at low temperature gives a 9 crystalline product in approximately 25% yield. The centrosymmetric structure consists of a planar 4 rnembered Sb-N-Sb-N ring with pendant NH(2,6-Me2(C6H3))moieties attached to the Sb centers. Cyclic Sb-N bond Lengths are 2.034(4) and 2.057(4) A and acyclic Sb-N bond lengths are 2.042(4) and 2.057(4) A. Cyclic Sb-N-Sb and N-Sb-N bond angles are 102.5(2) and 77.5(2)" respectively.
The analogous reaction with BiC13 gives a mixture of red and orange crystals."
Only the red crystals were suitable for X-ray crystallography, which showed hem to be a unique bicyclic compound pi3{ p-N(2,6-M&&) 14 {m(2,6-MezC&) )] (Figure 2)- In this structure, one of the bismuth centres is bonded to a terminal primary amido group and two bridging imido groups. Each of the irnido groups is further bonded to a second bismuth centre. The bismuth centres are both mutually bridged by two more imido groups. The geomeuy around each bismuth atom is trigond-pyramidal; the nitrogen centres have approximately trigonal plmar geometries. B i-N bond lena& range from
2.15(2) to 2.23(2) A. The orange crystals have not been stnicnirally characterized.
Figure 2: i3{ p-N(2,6-Me2C&) } 4 {NH(2,6-Me2C6H3)} ]
Increasing the size of the R group to [2,4,6-[Bu3Cm (Mes*) and carrying out the reaction of EC13 (E = Sb, Bi) with 3 equivalents of LiNHMes* leads to the formation of the tris-arnino products @~(NHM~S*)~].'~The procedure involves adding the solution of 10
LNHMes* in Et20 to a solution of either SbC13 or BiC13 in Et20. Filtration of the LiCl and slow removal of Et20 in vacuo gives a yellow crystalline solid when E = Sb and a dark orange-red solid when E = Bi. Crystals of [B~(NHM~s*)~]are obtained by dissolving the orange-red solid in hexane and then slowly removing the solvent in v~cuo.
The yield from both reactions is quite low; Sb(NHMes*)3 is obtained in 25% yield while
B~(NHM~S*)~is obtained in only 11%. The structures of both compounds are isomorphous. Steric crowding imposed by the bulky Mes* substituents effects a severe distortion from a pyramidal geometry at the pnictogen centres; N-Sb-N bond angles range from 85.6(2) to 104.4(3)" while N-Bi-N bond angles range from 82.7(6) to 106.7(6)".
Sb-N bond lengths average out to 2.05 1 A and Bi-N bond lengths average out to 2.18 A.
1.5 Cyclic Bis(amin0)-Stiba and -Bisrnahalides
Four-mernbered heterocycles (SfiE) are formed when two of the chlorine atoms in ECl, (E = Sb, Bi) are replaced by the ligand (-N('Bu)s~-~e2-('Bu)N-} ,l5 as illus trated in Figure 3.
Figure 3: Reaction of EC13 with ~e~si(N'BuLi)~
The antimony and bismuth compounds are isotypic and isostructural. The chlorine substituents are almost perpendicular to the EN2Si cycles and their interaction with 11 neighbourïng molecules resuits in the formation of an infinite E-Cl-E chain where the Sb and Bi centres are 4 coordinate. E-Cl'--E-CIbond angIes are 143-5" when E = Sb and
145.7" when E = Bi. Sb-N bond distances are 1.995(6) A and Bi-N bond distances are
2.124(9) A.
A minor product (22% yield) in the synthesis of Me2~i(N'~u)r~i]~~(shown above) is ~i~[(N'Bu)~si~e-&,in which the bismuth atoms are bonded exclusively to nitrogen atoms: 15
y-.:' 'BU Bi. / \~e 'N' 'N' N, I 'BU - 6 LiCl ,
Figure 4: Formation of Bi2[(N'B~)2Si~e2]3
Another cyclic bis(arnin0)-bismachloride is formed in 90% yield by reacting the dilithium salt of N-methyl-N',N"-(trimethylsily1)-die- with bismuth trichloride, as shown in equation 5.16 12
The coordination geometry at Bi approaches a trigond bip yramid with a N-Bi-N angle O f
101.8" and a N+Bi-N angle of 159-6". The Bi-N bond lengths are 2,123(5) and 2.138(6)
A while the coordinative N-Bi bond length is 2.496(6) A
The reaction of S bX3 (X = Cl, Br) with LïN('Bu)SiR3 gives diazadistibetidines with the formula (xs~N'Bu):~ as shown in equation 6.
R = CH, X = CI, Br
A solution of SbX3 in ether is added to a solution of LN('Bu)s~R~in ether. The reaction mixture is stirred for four hours. Filtration and removal of ether in vacuo gives a mixture of 3 and 4. The products are reffuxed in benzene for 2 hours. Removal of solvent gives product 4 with yields of 82% (X = Cl) and 31% (X = Br). The products have been characterized by elemental analysis and NMR spectroscopy, but structural data could no t be obtained. There have been no reports of analogous compounds for bismuth.
[CIS~N'BU]~cm be used as a starting material in the synthesis of other dia~adistibetidines,~~as sho wn in equation 7.
/"\ + 2 R-Metal (7) -Sb, ,Sb-Cl /N\ - 2 Metal-Cl t -2, ,Sb-R N N I I R R-Metal 6 OMe MeONa 7 OPh PhONa 8 OtBu 'BUOK 9 N(TMS)* (TMS)&Li 10 P(TMS)2 (TMS)2PLi 11 Me MeLi 12 'Bu 'BuLi
NMR spectroscopy showed that most of the reaction products (7,8,9,12) were mixtures of geometrical isomers. Cis and tram isomers have different NMR signals; trans isomers have lower 6 values in the 13cNMR and slightly higher 6 values in the 'H NMR (Table
Table 3: Selected 'H and 13cNlMR shifts of 1,3-di-tert-butyl-1,3,2,4diazadistibetidines
7b 66-08 1.O3 cis ~((c~3)3co>sb~(c(cH3)3)~28a 54.0 1 1.18 tram 8b 54-30 1.O6 cis ( [((CH3)3Si)îmSbN(C(CH3)3) 12 9a 54-33 1.33 tram 9b 56.68 1.13 cis [((cH3>3c>sbN(c(cH3>,)12 12a 52-63 1.56 tram 12b 53 -48 1.32 cis
X-ray crystdography was performed on compound 12 (R = tBu), confirming the structure of the trans isomer. Sb-N bond lengths are 2.043(5) and 2.05 l(4) k N-Sb-N and Sb-N-Sb bond angles are 78.3(2) and 101.7(2)". 1.6 Reactions of [SbClx(NMez)sJ (x = O - 2) with primary amines
[S bCl(NMe&] can be generated by the disproportionation reaction between
SbC13 and two equivalents of s~(NM~~)~.'~Reaction with the primary amine 'BUNH~ leads to the formation of the dimeric unit [~b~l(NHMe~)(p-~'~u)12(Figure 5).19
Figure 5: Structure of [S bC1(NHMe2) (p-N'Bu)]~
This structure has a dimeric SbN2Gamework where the Sb centres are bridged by two
N'BU ligands. Sb-N bond lengths of the core are 2.018(3) and 2.028(3) A;Sb-N-Sb and
N-Sb-N bond angles are 101.62(13)0 and 78.38(13)', respectively. Two equivalents of
NHMe2 are produced as a by-product when 'BUNH~undergoes dimetallation; two molecules coordinate to antimony while the other two escape fiom the reaction system- me2is a gas at room temperature but remains coordinated to the antimony centers both in solution and in the solid state. Coordinative Sb-N bond lengths are 2.524(3) A
The presence of Cl substituents increases the Lewis acidity of the Sb(m) centers giving rise to an extensive intermolecular association.
CS b(NMe~)~j,which was earlier shown to undergo substitution reactions with secondary des,can also be a good startïng material for reactions with primary amines. 15
It reacts with 2-amino4methylpyridine and 3,4,5-trimethoxyaniline to produce diazadistibetidines [S~(NM~~(~-NR)]~O as shown in equation 10 and Figure 6.
R=
Me Me0 OMe
Both reactions result in the retention of one of the Mefi groups of Sb(NMe& and complete deprotonation of the primary amines. The dirner molecules formed in both reactions are simüar with almost symmetrical plana SbîNr cores. Sb-N bond lengths average out to 2.060 A in compound 13 and 2.054 A in compound 14. N-Sb-N bond angles are very acute with values of 73.6(2)O in 13 and 75.8(2)" in 14.
Figure 6: Stmctures of [Sb(NMe2)(p-NR) 12 (R = mpy, C&(OMe)3-3 ,4,5) 16
Equation 11 shows that [Sb(NMe2)3]reacts with the sterîcally bulky Dipwto give a cis-diazadistibetidine?
(1 1) 2 [Sb(NMei)3I + 2 CDi~rnd toluene + 4 Me2NH Dip -N N-Dip 'Sb 'Sb
Variable-temperature 'H NMR shows that the cis conformation is retained in solution at and below room temperature. The Sb2N2ring is puckered with a fold angle of 153.4"-
Sb-N bond lengths range between L.983(8) and 2.062(8) A.
1.7 MonosiIylated amino derivatives of Sb and Bi
The reaction of lithium (trimethylsily1)methylamide with alkyl hdogen compounds of antimony and bismuth leads to the formation of monosilylated derivatives
[(CH3)3SiNCH3]nM(CH3)3..(M = Sb, Bi; n = 1-3),= which have been characterized spectroscopically.
1.8 Diethylaminoorganoantimony0m) derivatives
Diethylaminoalkylstibines RnSb(NEt2)3-ncan be prepared by reaction of lithiated diethylamine with halostibines in various stoi~hiornetries.~~ 17
The diethylaminoakylstibines are colourless liquids while the phenyl analogues are slightly yeilow oils. Ali products have been characterized by boiling point, elemental analysis, and IR and NMR spectroscopies. Attempts were made at synthesizing
Me-bNEt?, but the yields were very low (10 - 20%) and elemental analysis was made difficult by the extreme air-sensitivity of the compound.
1.9 Single versus multiple bonding
Multiple bonding is common among elements in the fxst row of the p-block, such as carbon, oxygen, and nitrogen, but becomes less cornmon as the groups are descended.
The most obvious explanation for this is that the atoms becorne larger as n increases. The orbitals become correspondingly larger and more diffuse, resulting in poorer orbital ovedap and weaker bonds. This is descnbed by the "double bond nile" which states that heavier main group elernents will not form rr-bonds because of their preference to G- bond.24 Recently, however, the use of bullcy substituents, such as 2,4,6-tri-tert- butylphenyl (supermesityl, Mes*), has led to the isolation of multiply bonded species of the heavier main group elements.2536 This is attributed to both a thermodynamic and a kinetic effect. From a kinetic point of view, stencally demanding substituents act as a shield, hindering the approach of molecules and preventing oligomerization and attack by other reagents. The thermodynarnic effect, which is much less obvious, has been demonstrated by the use of molecular mechanics and serniempirical calc~lations.'~Using these theoretical calculations, enthalpies of cyclodimerization for a series of trans-1,2- substituted allcenes possessing substituents of varying sizes have been deterrnined. Figure 7: Cyclodimerization of aikenes
The calculated energies of cyclodimerïzation can be seen in Table 4 (taken from ref. 27).
While the dimerization of ethene to cyclobutane is exothedc, as the R groups become larger, the dimerkation becomes less exothemiic and more endothennic due to the increased steric strain.
Table 4: Calculated Enthalpies of Cyclodimerization for 1,2-Substituted (R) Aikenes
@/mol)
R H Me 'Bu Ph Mes Trip Mes*
aHeat of formation of cyclobutane - 2(heat of formation of alkene) vota1 energy of cyclobutane - 2(total energy of alkene)
From Table 4 it can be seen that the enthalpies of cyclodimerization become endothemic when R is Mes and that the endothermicity greatly increases when the R group is changed to the buikier Trip and Mes*. This means that for those substituents, the alkenes are thermodynamically favoured over the cycloalkanes ie. the stenc strain caused by the bulky substituents Mes, Trip, and Mes* destabiiizes the filly o-bonded compounds with respect to the n-bonded monomers. This thesis is concerned with the nitrogen-pnictogen chernistry of antimon y and bismuth, While many double-bonded phosphorus-nitrogen compounds have been characteri~ed,?~there are only three examples for arsenic29-3 1 with no examples for antimony and bismuth. It remains to be discovered whether the use of bulky substituents will lead to the isolation of rnultiply bonded antimony-nitrogen and bismuth-nitrogen compounds.
1.10 Characterization of compounds
The analysis and characterization of compounds containing the heavier pnictogens is often difficult due to the lack of effective techniques available for the analyses. IR and Raman spectroscopies cm be used to identify certain functional groups, such as N-H or Pn-CI, but the assignrnent of peaks is often speculative and the spectra are rnostly used as a 'YingerprintY7of the compounds, W-Vis spectroscopy, which is generally used to detennine the presence of aromatic and unsaturated compounds, is rarely used in the analysis of &-sensitive pnictogen-containing species. For these compounds, it is difficult to prepare solutions with a known concentration and the glassware must be adapted for use with vacuum-line manipulation. 'H NMR and 13c
NMR spectroscopies are usefil for examination of the organic portion but do not give information on the pnictogen centres directly. Phosphorus has a nuclear spin of % and can therefore be conveaiently studied using 31~NMR. As, Sb, and Bi have quadrupolar nuclei with nuclear spins of 3/2,5/2 and 7/2, and 9/2 respectively. These nuclides give broad NMR signals due to quadrupolar relaxation. This creates difficulties in observing multiplet splitting due to couplings with other nuclei and in resolving chernical shifts. By far the most useful method available for characterization of compounds is X-ray crystallography. In order to use this technique, crystals of suitable quality must be obtained, and these crystals must not degrade when exposed to X-rays for extended periods of time. Al1 atoms present in the molecule are detected and the geometry at each atom cm be detennined to a high degree of certainty. Elemental analysis can be used to confirm the molecular composition and mass spectrometry can be used to determine molecular weight and fragment weight information,
1-11 Summary and conclusions
There are few aminobismuthines and aminostibines that have been cornprehensively characterized. Specifically, structural data are only known for eight aminostibines and seven aminobismuthines, which are shown in figures 8 and 9. An interesting observation conceming the antimony compounds is that the majority of them are dimers. These diazadistibetidines have endocyclic bond lengths between 2.0 18 and
2.062 A and the N-Sb-N bond angle (73.6 - 78.4") is much more acute than the Sb-N-Sb angle (101.2 - 106.4O) in ail instances. In the case of bismuth, there is only one known diazadibisrnetidine ([DipN(K)BiNDip]2). The cyclic Bi-N bond lengths (average of 2.16
A) are longer than the Sb-N bond lengths, as would be expected, but as for antimony, the
N-Bi-N bond angle (78.5") is more acute than the Bi-N-B i angle (10 1SO).
Figures 8 and 9 clearly show that the amine chemistry of antimony and bismuth has not been developed in a systematic manner. There are no examples of compounds that contain two or more different amines coordinated to the Sb or Bi centres and there are no examples of species containing a double bond between the pnictogen and nitrogen. The effect of varying the size of the R groups on the amines has also not been fully assessed. CIearly, more work needs to be done in this area in mrder to more completely understand the amine chemistry of the two heaviest pnictogens- Figure 8: Structurally characterized aminostibines '"\"/"'
'BU Bi. I N, 'N' 'N' 'B u
Figure 9:Structurally characterized aminobismuthines Chapter 2. Experimentai
2.0 General Procedures:
Bismuth(m)chloride, 2,4,6-tri-tert-butylaniIine (Mes*=), 2,4,6-trimethylaniline
(MesNJ&), 2,6-diisopropylaniline (Dipm), methyl trifluoromethanesulfonate (methyl trifl ate, MeOTf), trifluoromethanesulfonic acid (triflic acid, HOTf), and n-butyllithium
( 1-6 M in hexanes) were used as received (Aldrich). AntimonyCm)chlonde, diphenylarnine, gallium(m)chIonde, and iodine were sub1imed in vacuo. Tert- butylarnine was dried at reflux over KOH and Cal&. Diethylether, THF, benzene, and toluene were dried over sodium with benzophenone. Hexane was dried over potassium.
Methylene chloride was dried in three steps: first over C&, then over P20s, and finally over CaH2, each for two days. Solids were handled in a VAC VacuumlAtmospheres nitrogen-filed glovebox and Iiquids were manipulated in a nitrogen-filled glovebag.
Reactions were performed in sealed reactors which were evacuated IO-^ Torr) and flame- dned before use?' Infrared spectra were recorded as Nujol mulls on Cs1 plates using a
Nicolet 5 10P FT-IR spectrometer. IR spectra are presented as wavenumber (cm-') maxima with ranked intensities for each absorption, the most intense given a ranking of
1. Solution 'H NMR spectra were recorded on a Bruker AC-250 MHz spectrometer with sarnples flarne-sealed in 5mm Pyrex tubes. Chernical shifts are reported in ppm relative to external standards (TMS for 'H). Crystals suitable for X-ray crystallography were either mounted in thin wall glas capillaries in the dry box and seded under nitrogen or covered with perfluorinated oiI, sealed in a glas sarnple tube under nitrogen, and submitted for analysis to Dr. T.S. Carneron and Kathenne Robertson at the Dalhousie
24 25
Crystallography Centre @AIX) or to Robert McDonald at the Univerïsty of Alberta.
Melting points were obtained on a Fisher-Johns apparatus and are uncorrected. Chernical
analyses were performed by Belier Laboratones, Gottingen, Gerrnany.
2.1 Reactions of EC13 with RN(EI)Li
A typical reaction vessel used for reactions is shown in Figure 10. The reactor
contained two chambers, one of which was fitted with a septum side arm (septum
charnber) and attached to a filter. This type of reactor was modified slightly from those
previously described." In a typical procedure, ECls (E = Sb, Bi) was loaded into the
septum charnber of a two-charnber reactor. NH2R was weighed into a separate one- chamber vessel, also equipped with a septum side arrn. Approximately 20 mL of freshly dried solvent (Et20 or THF) was injected into both chambers through a rubber septum via either a cannula or a syringe. An equirnolar quantity of "BuLi (1 -6 M solution in hexanes) was then introduced via syringe into the solution of NH2R at room temperature
(0°C when R = tBu). After stirring overnight, the solution of lithium amide was slowly added to the cooled (-78OCdry ice/acetone or ethanoVriquid nitrogen bath) solution of
EC13 (via cannula or syringe). The reaction mixture was stirred for aï least 50 minutes at
-78°C and was then slowly warmed to room temperature and stirred for at Ieast one hour.
It was frozen and evacuated and the reaction mixture was filtered into the second chamber of the vessel. Attempts to isolate the product(s) as a crystalline material began by slow removal of the solvent in vacuo. Figure 10: A typical two-charnber reaction vesse1 Many of the reactions of EC13 with RN(H)Li did not give products that could be isolated in a pure form. The obsewations are listed in Table 5.
Table 5: Observations frorn reactions of EC13 with RN(H)Li in various stoichiometrïes
Reactants Observations
- - -- BiC13 + MesNoLi - immediate development of a yellow solution
and red and white ppts
- removal of Et20 Ieft a srnall amount of yellow
solid
- immediate formation of a white ppt and a red
solution
- frothy red oil obtained from &O; redhrown
solid obtained from hexane
- - -- - crearny orange reaction mixture
- red and orange crystals obtained from EtzO
(orange crystals did not contain Bi and the red
ones were not suitable for X-ray analysis)
- irnmediate formation of white ppt and a dark
orange solution
- solution darkened to red upon warming to room
temperature
- red oil obtained from Et20 28
- reaction mixture turned a duil yellow upon addition of DipNOLi
- after stimng for 3 minutes, MesN(H)Li was added causing the reaction mixture to become yello w/brown
- brown oil obtained from EtzO; orange/brown oil from hexane
- immediate development of a white ppt and a pale yellow solution
- removal of Et20 gave a yellow oil which precipitated white powder when left standing
- microcrystalline yellow solid obtained from hexane
- cloudy orange reaction mixture upon addition of Ph2NLi
- addition of DipN(H)Li caused the solution to become bnght yellow
- when warmed to room temp, the reaction mixture darkened to red
- viscous red oil obtained from EtzO; orangefred powder obtained from hexane 29 Reaction of BiCh with DipN(H)Li
DipN(H)Li (5.42 mmol) in Et20 was added to BiCb (1.71 g, 5.43 mmol) in
immediately giving a bright yellow solution. After stirring for 2 hours at -78OC it was slowly wmed up to room temperature, and became orange. Rernoval of the solvents left a viscous, cloudy dark orange oil. CH2C12 was added and precipitated LiC1.
Filtration left a clear red solution from which a mixture of red and orange/brown crystals were obtained by slow removal of CH2C12 in vacuo. The red crystals were not suitable for X-ray analysis. The orangehown crystais were mounted in glas capillary tubes for
X-ray crystallography, but the crystals tumed to powder upon exposure to X-rays. The orange crystals gradually turned purple when heated to 150°C and partially melted at
17 1OC. IR of mixture (ranked intensity): 3274(14), 13 l4(4), 1220(7), 1178(1), 1097(6),
1039(5), 930(16), 886(13), 857(15), 821(11), 805(9), 776(2), 762(3), 743(12), 679(17),
64O(l O), 504(8). Attempts were made to repeat this reaction, but a crystalline producr was not obtained.
Reaction of %Cl3 with 3 'BuN(H)Li
'BuNOI)Li (14 mmol) in EtzO and SbC13 (1.03g, 4.53 rnrnol) in EtzO were combined as outlined. The reaction mixture irnmediately turned beige and cloudy. It was stirred for 60 minutes at -78OC and was then warmed to room temperature and stirred for one how. Filnation yielded a yellow solution. Slow removal of Et20 in vacuo gave yebw crystals coated with yellow oil. The oil was decanted away and the crystals were washed several times with EtzO by cold-spot back disti~ation.~~Mass of product was 30 0.170 g; mp. 2 11-2 14°C; 'H NMR (ppm, CD2CI2): 1.47 (s); IR (ranked intensity):
1356(3), 1182(2), 1007(15), 960(S), 932(4), 909(13), 780(1 l), 770(10), 727(1), 682(7),
579(9), 503(14), 487(18), 478(16), 472(17), 41 1(12), 387(20), 376(19), 255(6), 242(8).
Isolation of cycZ0-[1,3-CZ~-5-(DipNH)-2,4,6-(Dip)~(BiN)~]:
DipN(H)Li (3.3 rnmol) in Et20 and BiCb (1.02 g, 3.24 mol) in Et20 were combined as descrïbed above to give a cloudy orange reaction mixture. It was stirred for
10 minutes and then a solution of Mes*N(H)Li (0.857 g, 3.28 mrnol) in EttO was added
(via syringe, 10 minutes) with no noticeable change in appearance. The reaction mixture was stirred for 50 minutes at -78°C and was then warmed to room temperature and stirred for another 3 hours. Filtration yielded a clear bright red solution from which a mixture of red (30%) crystals and orangelred powder (70%) was obtained, total yield 0.97g. X-ray crystallographic analysis showed the red crystais to be cyclo-[1,3-CI-5-(DipNH)-2,4,6-
@i~)~(BiN)~l.When heated the crystals decomposed gradually and partially melted at
140°C. 'H NMR of mixture (ppm, CD2C12): 1.22 (s), 1.24 (s), 1-25(s), 1.47 (s), 2.9
(sept), 4.1 (s, broad), 7.0 (d), 7.2 (s); IR of mixture (ranked intensity): 3514(16),
3441(13), 1619(4), 1436(1), 1361(2), 1300(9), 1290(10), 1265(5), 1237(3), 1193(12),
1175(8), 1153(15), 1095(1l), 1044(18), 881(7), 816(17), 771(6), 643(14), 505(19);
Crystal data: monoclinic, space group: P2i/a(#14), a = 20.123(2) A, b = 1 1.951 (5) A, c =
27.506(4) A, B = 108.02(1)0, V = 6290(2) A3, Dcdc = 1.664 ~~/rn~,RI= 0.0779. Preparation of [DipN((H)Bi'NDip]2:
Under an atmosphere of nitrogen, LiN(H)Dip (9.9 rnrnol) was added to BiCls
(1.56g,4.95 mmol) in EtzO as outlined earlier to give an orangelred solution and a white precipitate. After stimng for a couple of minutes, a solution of LiN(H)'Bu (4.9 mmol) in
Et20 was added. The reaction mixture was stirred at -78°C for 1-5 hours and was then warmed to room temp and stirred for another 3 hours. Filtration yielded a dark red solution. Removal of solvent gave red crystals of DipNoBiNDipl2 with a yield of
1.35g, 49%; mp. 163OC; spectroscopie confirmation with that previously reported; ' ' R
(ranked intensity): 3360(16), 3043(15), 1426(2), 1381(7), 1327(14), 1262(9), 1242(3),
1221(6), 1182(4), 1175(12), 1097(13), 846(10), 832(8), 767(1), 752(5), 505(11); 'H
NMR (ppm, CD$&): 0.89 (d), 1.21 (d), 1.23 (d), 1.33 (d), 2.70 (sept), 2.91 (sept), 4.42
(sept), 5.7 (s), 6.5 (m), 6.7-7.2 (m), additional minor signals.
Preparation of [DipN(H)SbA?Dip]2
DipN(HJSbNDipJ2 was prepared by the procedure descnbed for the bismuth analogue using SbCI, (5.83 rnmol), L~w(~,~-'P~c~H~)](1 1.6 mmol), and BUNHL~
(5.90 mrnol). A peach oil was obtained upon removal of Et@. The addition of hexane
(20 rnL) resulted in precipitation of a bright yellow powder. Filtration and slow removal of the hexane gave cube shaped yellow crystals, which were spectroscopically identical to the powder, combined yield 1.50 g, 54%; mp. 197499°C; Anal. Caicd.: C, 60.88; H,
7.45; N, 5.92 %; Found C,60.75; H, 7.50; N, 5.96 9%; IR (ranked intensity): 3381(17),
3053(16), 1431(2), 1383(10), 1322(7), 1311(13), 1259(6), 1240(3), 1231(5), 1190(4), 32
1 100(14), 885(20), 858(12), 840(1 l), 794(15), 772(1), 759(8), 697(18), 670(9),5 14(l9);
'H NMR (ppm, CD2C12): 0.9 (d), 1.1 (d), 1.3 (d), 1.4 (d), 2.7 (sept), 4.3 (sept), 5.1 (s),
6-7-7.2 (m), additional minor signals. For X-ray data, see reference 33.
2.2 Reactions of DipN(H)ENDiplz @ = Sb, Bi)
In a typical procedure, [DipN@)ENDip12 was loaded into one of the chambers of a two chamber reaction vessel. The other reactant was weighed or distilled (volatile liquid) into the second chamber. Any chamber that had been opened in the dry box or glove bag was evacuated. Solvent was distilled into each chamber (15 - 20 mL). The reaction was performed by adding the reactant in the second chamber across the reaction vessel into the solution of PipN(H)ENDipl2. If required, the now ernpty chamber was replaced with a clean chamber attached to a filter and the solution was filtered. The solvent was slowly removed in vacuo.
Some of the reactions using [DipN(H)ENDip12 as starting material did not give products that could be isolated. These are descnbed in Table 6.
Table 6: Observations frorn reactions of [DipN(H)ENDipI2 with various reagents
Reactants Observations
[DipN(H)BiNDipJa + excess GaC13 - dark orange reaction mixture in Et20 - derstimng ovemight, a small amount of beige ppt had formed - microcrystalline orange powder surrounded by oil obtained fiom removal of Et201 orange powder obtained fiom hexane [PipN(H)BiNDipJ2 + excess HOTf - red solution of [DipN(H)BiNDipI2 becarne a
in toluene darker red upon addition of HOTf
- red oil obtained upon removal of toluene;
orangelbrown powder obtained from hexane
[DipN(H)SbNDipI2 + excess in - very dark reaction mixture with an orange tinge
CH2C12 - after stirring for 7 hours, it was dark orange with
yellow ppt
- filtration and removal of CH2C12gave yellow
particles surrounded by brown oil
PipNOBiNDipJ2 + excess MeOTf - red solution of PipN(H)BiNDipl2 darkened
in CH2C12 upon addition of MeOTf
- removal of CH2C12 left an oily solid and some
frothy red oil; an oily red solid was obtained from
benzene
Reaction of [D~PN(H)B~'ND~'~]~with pyridine
A solution of pyridine (excess) in CH2CL2(15 mL) was added to a solution of
pipN(H)BïNDip]2 (0.5 15 g, 0.459 mol) in CH2C12 (15 rnL, red solution). There was no irnrnediate change in the appearance of the reaction mixture. After stimng for 2 hours, some orange precipitate had formed. Filtration gave a clear red solution. Slow removal of CH2C12gave red bar-shaped crystais, yield 0.40 g, 68%; mp. 170-171°C; 'H
NMR (ppm, CD2C12):0.89 (d), 1.10 (d), 1.23 (d), 1.Z4 (d), 1.35 (d). 2.7 1 (sept), 2.92 34
(sept), 3.17 (quint), 3.74 (s, broad), 4.43 (sept), 5.32 (s), 5.71 (s), 6.5 - 7.3 (m), 7.68 (t),
8.57 (m), additional minor signals; IR (ranked intensity): 3360(26), 3O43(16), 1588(l3),
1426(1), 1326(9), 1298(11), 1261(7), 1241(3), 1220(5), 1182(4), 1107(12), 1097(10),
1049(24), 1041(22), 847(14), 832(8), 790(23), 767(2), 752(6), 634(17), 019(25), 587(19),
573(21), 563(20), 505(18), 395(15);
Crystal data: orthorhombic, space group: P212121(#19), a = 11.632(2) A, b = 12.1 H(2) A, c = 38.224(7) A, V = 5404.19(1) A3, Dd, = 1.664 ~~/rn~,Ri = 0.1009.
Repeated in toluene, starting material was isolated. Chapter 3. Results and Discussion
3.0 Objectives
The primary objective of this project was to carry out reactions of BiC13 with lithium pnmary amides in a systematic and rational fashion. Four amines were chosen initially, with R groups Mes*, Mes, Dip, and 'Bu. Mes* is a large, bulky substituent, Dip and Mes are moderately bulky and 'Bu is relatively small. Work done by other groups had previously shown that the reaction of 3 DipNHlLi with BiCI3 resulted in the formation of a cyclic bismetidinel' pipN0BiNDipl2and that the reaction of 3 Mes*NHLi with
BiC13 resulted in the formation of the tris-aminobismuthine F~(M~S*NH)~].'~Neither reaction was quantitative, indicating the presence of more than one product in the reaction mixtures. Bulky substituents such as Mes* have been shown to stabilize double bonded compounds of the heavier elements. If we consider that the rnonorneric fom of
[DipN(H)BiNDipJzwould be a double bonded Bi=N species with the formula
[DipN(H)Bi=NDip] (Figure Il), it is curious that when R is the larger Mes* substituent, the tris-arnino product is isolated instead of the dimer. We were interested in determining whether the less bulky Mes and Bu groups would give tris-amino bismuthines or dimeric species. We were also interested in learning if the mono- or bis-amino products could be isolated and used as starting materials in reactions with lithium amides. Once this work was carried out for bismuth, the analogous reactions would be performed for antimony. Dip-N NDip Dip-N=E \ / \ E N-Dip 1 H
D~~H~N~
Figure 11: Monomer-dimer relationship
A secondary objective of the project was to perfom reactions using
[DipN(H)ENDip12 as a starting material. It was proposed that the addition of acid or base could possibly result in the dissociation of the pnictetidine, as shown in Figure 12. By coordinating a base (eg. pyridine, Et3N or quinuclidine) to the pnictogen center, a nucleophilic displacement of the intermonomer bond could occur, leading to the double bonded mononer. The addition of an acid, such as HOTf, would presurnably result in protonation of the nitrogen centres, forming 2 [DipN(H)E@ip)OTfl. A Lewis acid, such as GaC13, could also lead to the dissociation of the dimer by accepting the lone pair of electrons from N, thus stabilizing the double bond.
Dip-NE \ NDip AJ H
Figure 12: Dissociation of [DipN(H)hiNDipI2 by addition of acid (A) or base (B) A final objective was to synthesize heteroleptic aminobismuthines and aminostibines. By reacting EC13 (E = Sb, Bi) with two Merent lithium amides, it should be possible to produce compounds containing two unique amines coordinated to the pnictogen. As discussed in the introduction, very few reactions of EC13 with lithium pnmary amides have given pure and isolable products, and those that are known contain ody one type of amine.
3.1 Optirnizing reaction conditions
The initial procedure followed for reactions of EC13 with RN(H)Li involved adding the solution of lithium amide across a two-charnber reactor into the solution of
EC13 at room temperature, This proved to be probiematic because there was immediate formation of black soIid or oïl, which was presumably elemental bismuth or antimony precipitating out of solution. Although the decomposition products were removed by filtration, when left standing for more than a couple of hours, further decornposition would occur. Several modifications were made in an attempt to prevent this. By cooling the solution of EC13 to -7g0Cand adding the lithium amide using a syringe or a cannula, the reaction mixture was always kept cold and the formation of black solid or oil was prevented. After being warmed to room temperature, the reaction mixture now showed much Iess of a tendency to decompose when left standing.
3.2 Reactions of BiCls with RN(H)Li
Reactions of BiC13 with WoLiin 1: 1 and 1:3 stoichiometries gave products which were difficult to isolate. In some instances, even when a crystalline material was 3 8 obtained, its structure could not be determined. Sorne interesting observations were
nevertheless made.
It had been reported previously that reactions of 8iC13 with DipN(H)Li always gave LDipN(H)BiNDipJz(red), regardless of stoichiometry and reaction conditions.' '
However, it was observed that when the f :l reaction of BiCI3 with DipN(K)Li was carried out at -78", the reaction mixture was yellow and that it darkened to red only when warrned to room temperature. It was proposed that at -78OC, the monoaminobismuthine formed and that as the reaction mixture was wmned to room temperature, the reaction continued on to give the themodynarnicaily favoured product DipN(H)BiNDipJ2. In an attempt to prevent this, the reaction mixture was kept at -78°C for 2 hours and then without warming it up, the solvent was removed with hard vacuum. The resulting orange oil was dissolved in CH2C12, the solution was filtered, and the solvent was removed in vacuo, giving crystals which were orange-brown and visibly different frorn the red pipN(H)BiNDip]2. Unfortunately, the crystds turned to powder upon exposure to X- rays and a crystal structure could not be obtained. A melting point could also not be obtained because the crystals decomposed when heated up to 150°C. An Il3 spectrum was obtained and dthough it looked similar to the spectrum of DipN(H)BiNDip]2, there were several differences (see Section 2.1).
No reactions between BiCls and 'BuNoLi had previously been reported. The
1:3 reaction was performed twice, with crystals being obtained in both trials. In the first trial, only orange crystals were obtained. These were mounted in gIass capillary tubes for
X-ray crystalIography, but were found not to contain any bismuth. When the reaction was repeated, a mixture of orange and a few red crystals was obtained. The red crystals 39 were very smail and oily. They were mounted in capillary tubes but a crystal structure could not be obtained.
3.3 Reaction of SbCIJ + 3 'BuNHLi
The reaction of SbC13 with 3 equivalents of 'BuN(l3)Li was also carried out. The addition step was performed at -78OC with immediate formation of a white precipitate and a beige colour. Filtration gave a yeliow solution from which yellow crystals were obtained upon slow removd of solvent. It was expected that the product would either be the tris-arnino stibine [s~(NH'Bu)~]or the diazastibetidine ['BB~NOF)S~N$U]~.However, the IR did not show any N-H stretches and there was no hydropn corresponding to an
NH group present in the NMR. The NMR did show a large 'Bu peak at 1.47 ppm, indicating its presence in the crystals. Several crystals were mounted in capillary tubes for crystallography, and they diffracted, but the structure could not be determined.
3.4 Improved synthetic route to mipN(H)ENDip]2 (E = Sb, Bi)
Preliminary res~lts~~showed that pipN(H)SbNDip]~could be synthesized by reacting 3 equivalents of LiN(H)Dip with one equivalent of SbCl, in EtrO at room temperature. Yellow cube-shaped crystals were obtained by filtering out the LiCl and slowly removing the solvent. However, the crystals were very oily and needed to be washed repeatedly (more than 10 times) for a yield of only 4%. The bismuth analogue was prepared by adding a solution of one equivalent of BiC13 in THF to a solution of 3 equivalents of LiNODip in EtzO at room ~ern~erature.'~After stirring for 16 hours, the solvents were removed in vacuo. Hexane was added to isolate the precipitating crude 40
product and a Soxhlet apparatus was used to extract the solid. Removal of the hexane
gave red crystds of LDipN(H)BiNDipI2 in 57% yield. While this is a rnuch better yield
than for the Sb analogue, the procedure is more complicated and time consuming. One of
the reasons for the low yield of the Sb analogue, and one of the reasons a Soxhlet
apparatus was used to make the Bi analogue is because two equivdents of DipNH2 are
produced in the reaction. This is a viscous oil that is not very volatile and is therefore
hard to rernove, making isolation of crystdline material difficult. By using two
equivalents of LiN(H)Dip followed by the introduction of one equivalent of LiN(H)'Bu at
-78"C,the byproduct that is produced is the relatively volatile 'BUNH~(equation 14),
which is much easier to rernove than the viscous DipNH2. Using this procedure, the
isolated yield of [PipN(H)SbNDipI2was 54% and the yield of the bismuth analogue was
49%.
PipN(H)SbNDipl2 is isostmctural with the bismuth analogue." Cyclic Sb-N
bond lengths are 2.032(6) and 2.064(6) A and acyclic bond lenaes are 2.032(6) A.
Cyclic N-Sb-N and Sb-N-Sb bond angles are 77.7(3) and 102.3(3)" respectively while
acyclic N-Sb-N angles are 97.3(3) and 99.0(3)". These lengths and angles are very
sirnilar to those reported for Pb(yNR)(NHR)]2 (R = 2,6-~e&&))'~ which has cyclic
Sb4bond lengths of 2.034(4) and 2.057(4) A and acyclic Sb-N bond lengths of 2.042(4)
and 2.057(4) A. As for DipN(H)SbNDip]l, the N-Sb-N bond angle is much smdler
(77 S(2)O) than the Sb-N-Sb angle (102.5(2)"). 4 1
3.5 Reactions using [DipN(H)ENDipI2 as starüng matenal
The reaction of [DipN(H)BiNDipl2 with excess p yridine gave an adduct with the formula i2(p-NDip)2(NHDip)2(pyr)] where one p yridine rno lecule is CO ordinated to O ne of the bismuth centres (Figure 13). This result is prelirninary in nature as there are currently two peaks of electron density in the Fourier map that cannot be accounted for. mi2(p-NDip)2(NHDip)2(pyr)] crystallizes as a CH2C12 solvate (not shown in the crysta1 structure) .
Tables 7 and 8 contain selected bond lengths and angles. The coordinative bond length of Bi(l) to N(5) is approxirnately 2.86 which is within the sum of the van der
Waals radii. Cyclic Bi-N bond lengths (average 2.18 A) are ve.ry similar to those in
@lipN(H)BNDip]2 (average 2.16 A). However, the presence of the p yridine molecule does change some of the bond angles. The Bi(1)-N(1)-C(1) angle changes from 125.7(3) to 138(1)" and the Bi(2)-N(1)-C(I) angle becomes more acute, changing from 125.4(3) to
110(l)O. The N(1)-Bi(1)-N(3) angle is sirnilas in the two compounds (97.4(2) in
@3ipN(H)B Wipl2compared to 94.3(8) in [Bi2(p-NDip)2(NHDip)2(pyr)]).
Table 7: Selected bond lengths (A) for [Ei2(p-NDip)2(MIDip)2(pyr)]
Table 8: Selected bond angles (O) for Bi2(p-mip)2(NHDip)2(pyr)]
(1- (1 - (2 lOO(2) N(2) - Bi(1) - N(3) 92.0(6)
Bi(2)-(2)-(1 102(2) (2- (1 - (1 1lO(1)
N(1) - B i(2) - N(2) 79(2) Bi(l ) - N(3) - C(25) 120(2)
(2Bi) - (1 79(2) Bi(2)-N(2)-C(13) 131(2)
(1- (1 - (3 94.3 (8) (1-(2-Bi) 120(2)
N(2) - Bi(2) - N(4) 92.0(9)
Contrary to expectations, the addition of a base (pyridine) does not lead to the dissociation of the intermonomer bond in [DipN(H)BïNDipl2. What this reaction does show, however, is that it is possible to coordinate ligands ont0 the bismuth centres. In other words, the sterïc bulk of the Dip groups is not so great that they offer cornplete protection of the bismuth centres-
The other reactions that were performed using PipN(H)BiNDipl2as a starting material did not gïve products that could be isolated. The observations are listed in Table
6 (Section 2.2).
3.6 Reactions of EC13 with [.N(H)Li] and F9NOR)Li]
The reaction of BiC13 with one equivalent of DipN(H)Li followed by one equivalent of Mes*NoLi at -78OC gave as an isolable product a six-membered ring containing alternating bismuth and nitrogen atoms. The crystal structure is shown in
Figure 14. Tables 9 and 10 contain selected bond lengths and angles.
45 Table 9: Selected bond lengths (A) for cyclo-[1 ,3-C12-5-@ipNH)-2,4,6-(Dip)3(E3ml3]
From the crystal structure it can be seen that the product co-crystallizes with a molecule of DipNH2. It comprises a unique bismuth atom @i(l)J bonded to a primary amido group and two bridging imido groups, each of the latter being further bonded to a second bismuth centre [Bi(2) and Bi(3)J. Bi(2) and Bi(3) are each further bonded to a chlorine atom and are bndged together by another irnido group. A connectivity diagram of cyc10-[1,3-C1~-5-(DipNH)-2,4,6-(Dip)~(BiN)]is shown in Figure 15. It can clearly be seen from this drawing that there is a tris-aminobismuthine fragment (BiN3)and two bis- aminobismuth chloride fragments (BïN2C1).
Figure 15: connectivity diagram of cyclo-[1 ,3-Clz-5-@ipMI)-2,4,6-oip)3(BiN>3] 46
Cyclic Bi - N bond distances are equivalent (2.12 - 2.14 A) except for the bond
between Bi(1) and N(l) which is slightly longer (2.25 A). These bond lengths are similar
to those in pi3{ p-N(2,6-Me&&) }4 {NH(2,6-Me2Ca3))] ,12 whic h range fro m 2.15(2)
to 2.23(2) & and those in ~ip~(H)~NDip]~which range from 2.158(4) to 2. IW(5) A
The geometry at each of the bismuth centres is approximately trigonal pyramidal [sum of
angles: Bi(1) 279.1, Bi(2) 272.2, Bi(3) 29 1,7"]. The geometry at nitrogen centres N(2)
and N(3) is approximately trigona1 planar [sum of angles: N(2) 360, N(3) 358"] while the
geometry at N(1) deviates from this somewhat [sum of angles: 337.7"].
Table 10: Selected bond angles (O) for cyclo-[l ,3-C12-5-@ipNH)-2,4,6-@ip)3(B m3]
(3- (1 - (1 83.6(7) (4- (1 - 1 97.1(7)
N(2)-Bi(2)-N(1) 84.6(7) N(3) - Bi(3) - Cl(2) 94.5(5)
N(3) - Bi(3) - N(2) 105.9(8) N(2) - Bi(3) - C1(2) 9 1-3 (7)
(2- (1) - (1 1 15.9(7) (2-(2-Cl) 99.5(6)
Bi(2) - N(2) - Bi(3) 114.8(9) (1-Bi-1 93.1(4)
(3- (3 - Bi) 116.3(10) N(3)-Bi(1)-N(4) 98.4(9)
- -- -
Six-membered rings normally adopt either a chair or a boat conformation- Figure
16 clearly shows that cycl0-[1,3-C1~-5-(DipNH)-2,4,6-@ip)~(BiN)~]is in a boat conformation. There is a coordinative bond between N(l) and Bi(3) (2.841 A) that helps stabilize this arrangement. With the exception of Cl(1) which is axial, the substituents are all in equatorial positions (the Dip group that is bonded to N(1) is in between an axial
and an equatoristl position). The only other 6-membered ring containing altemating Bi and N atoms that has been stnicturally characterized is [Bi3@-N(2,6-
~e2C&)}4 ~(2,6-~e&H3)]] ,12 which is bicyclic and involves both conformations. As in cyclo-[1,3 -C1~-5-@ipMH)-2,4,6-@ip)3(E3 w3],however, the substituents are
mostly in equatonal positions.
Figure 16: Core of cyc10-[1,3-C1~-5-@ipNH)-2,4,6-fDip)~@~~]
it is curious that the reaction gave cyclo-(1 ,3-C12-5-@ipNH)-2,4,6-@ip)3@~3] as a product because it contains no Mes*. It was expected that the reaction would lead to the formation of any of the three compounds shown in Figure 17.
Mes' Dip CI I I H-N, Dip Mes* I / H-N, / Bi Bi-N Bi-N H, H, N/ \N/H II II /N-Bi \ \ 1 1 Dip N-H 'Mes /N-Bi N-H Dip Mes* I 1 Mes* ~ip
Figure 17: P~ssibleproducts of the reaction BiC13 + DipN(H)Li + Mes*N(HJLi 48 There are currently no reported examples of an amînobismuthine where the bismuth is bonded to two or more different amine groups. If any of the products depicted in Figure
17 were formed in tbe reaction, they were not isolated. However, it should be emphasized that the reaction was not quantitative and there must be more than one product. It was reported by ~oesk~"that the reaction of BiC13 with DipN(H)Li always gives the dimeric species [DipN(H)BiNDipI2,regardless of stoichiornetry or reaction conditions, However, it seems that the addition of Mes*N(H)Li to the reaction mixture
(containing BiC13 and DipN(H)Li) somehow quenched the arnination of BiCI3. The cornpound (M~~s~(N~BU)~B~C~)~~also contains a bismuth-chlorine bond and can be used for comparisons. The Bi-Cl bond lengths in cyclo-[1,3-C12-5(DipNH)-2,4,6-
(Dip)@iN),] are shorter (2.563(8) and 2.501(8) A) than that in Me2Si(N$u)z~i~l
(2.748(4)A). However, the bonding environments are different in the two compounds.
In Me2Si(~t~u)z~iC1,the chlonne atoms interact with neighbouring molecules, creating an infinite Bi-CI-Bi-Cl chah whereas in cycIo-[l ,3-C12-S-(DipNH)-2,4,6-(Dip)3(13iN)3] the Cl atoms do not interact with neighbouring molecuIes.
Reactions of ECb with RNOI)Li should be carried out at -78°C to prevent the reaction mixtures from becoming contarninated with decomposition products. Even using this optirnized addition procedure, it is very difficult to isoIate pure materials. It is probable that in many cases there is more than one species formed. Separating and characterizing these multiple products is very challenging. 49 It was proposed that the addition of an acid or base could lead to the dissociation of the intermonomer bond in pipNoENDip]2. Only one of the attempted reactions gave a product that could be isolated and charactenzed. This was the reaction of
DipN(H)BWipI2with excess pyridine, which gave a pyridine adduct as a product. The significance of this observation is that it is possible to get a base to coordinate onto the bismuth centres in pipN(H)BiNDip]2.
Although it was reported that reactions of BiCb with DipN(H)Li always give the product DipN(K)BiNDip]z regardless of stoichiometry and reaction conditions,' l the reaction of BiC13 with one equivalent of DipNOLi and one equivalent of Mes*N(H)Li somehow prevented thïs dimer fiom forming. Tt gave a six-membered ring containing altemating bismuth and nitrogen atoms with the formula cyclo-[I ,3-Cl2-5-@ipNH)-2,4,6-
@i~)~(BiN)~l.This is probably just one of rnany products that forms dong the way to obtaining the dimer and gives us an idea about how complicated the chemistry can be. (1) Greenwood, N. N.; Eamshaw, A. Chemistry of the Elernenfs; Pergamon: Oxford, 1984.
(2) Emsley, J. The Elements; 2"d edltion; Clarendon Press: Oxford, 1991.
(3) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5" edition; John Wiley & Sons: Toronto, 1988.
(4) Sharpe, A. G. Inorganic Cherni- 3d edition; John Wiley & Sons: New York, 1992.
(5) CRC Handbook of Chemistry and Physics, 79" edition; CRC Press: New York, 1998.
(6) Moedritzer, K. Inorg. Chem 1964,3,609-610.
(7) Kiennemann, A.; Levy, G.; Schuté, F.; TaniéLian, C. J. Organomet Chem. 1972, 35, 143-148.
(8) Ando, F.; Hayashi, T.; Ohashi, K.; Koketsu, J. J. Inorg. Nucl. Chem. 1975,37, 201 1-2013.
(9) Clegg, W.; Compton, N. A.; ErrËngton, R. J.; Norman, N. C.; Wishart, N. Polyhedron. 1989,8, 1579- 198%
(10) Clegg, W.; Compton, N. A.; Emngton, R. J.; Fisher, G. A.; Green, M. E.; Hockless, D. C. R.; Norman, N. C. Inorg. Chem. 1991,30,4680-4682.
(1 1) Wirringa, U.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Inorg. Chem. 1994,33,4607-4608.
(12) James, S. C.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Weckenmann, U. J. Chem. Soc., Dalton Trans. 1996,4159416 1.
(13) Norman, N. C. Personnal commmication.
(14) Burford, N.; Macdonald, C. L. B.; Robertson, K. N.; Carneron, T. S. Inorg. Chem. 1996,35,4013-4016.
(15) Veith, M.; Bertsch, B. 2. Anorg. A&. Chern. 1988,557, 7-22.
(16) Fauré, J.-L.; Gomitzka, H.; Réau, R.; Stalke, D.; Bertrand, G. Eur. J. Inorg. Chem. 1999,2295-2299.
(17) Kuhn, N.; Scherer, O. J. 2. Naturforsch., Teil B. 1979,34 , 888-889. 50 (18) Ross, B.; Belz, J.; Nieger, M. Chern. Ber. 1990, 123,975-978.
(19) Edwards, A. J.; Leadbeater, N. E,; Paver, M. A.; Raithby, P. R,; Russell, C. A.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1994, 1479-1482.
(20) Edwards, A. J.; Paver, M. A.; Rennie, M.-A.; Raithby, P. R.; RusseLi, C- A.; Wright, D. S. J. Cham. Soc., Dalton Trans. 1994,2963-2966.
(2 1) Beswick, M. A.; Harmer, C. N.; Hopkins, A. D.; Paver, M. A-; Raithby, P. R.; Wright, D. S. Polyhedron. 1998,17,745-748.
(22) Scherer, O. J.; Hornig, P.; Schmidt, M. Organornef. Chern, 1966,6,259-264.
(23) Meinema, H. A.; Noltes, J, G. Inorg, Nucl. Chern. Letiers. 1970,6,241-243.
(24) Dasent, W. E. Nonexistent Cornpounds, Cornpounds of Low Stabiliry; MarceI Dekker, Inc.: New York, 1965.
(25) Power, P. P. Chern. Rev. 1999,99,3463-3503.
(26) Norman, N. C. Polyhedron 1993, 12,2431-2446.
(27) Burford, N.; Clyburne, J. A. C.; Chan, M. S. W.Inorg. Chem. 1997,36, 3204- 3206.
(28) Niecke, E.; Gudat, D. Angew. Chem. Int. Ed. Engl. 1991,30,217-237.
(29) Ahlemann, JI-T.; Künzel, A.; Roesky, H. W.; Noltemeyer, M.; Markovskii, L.; Schmidt, H.-G. Inorg. Chern. 1996,35,6644-6645.
(30) Hitchcock, P. B.; Lappert, M. F.; Rai, A. K.; Williams, H. D. J. Chem. Soc., Chem, Commun. 1986, 1633-1 634.
(3 1) Kruppa, C.; Nieger, M.; Ross, B.; Vath, 1. Eur. J. Inorg. Chern, 2000, 1 65- 168.
(32) Burford, N.; Muller, J.; Parks, T. M. J. Chem. Educ, 1994, 71, 807-809-
(33) Macdonald, C. L. B. Steric and Electronic Control of Low-Coordinate Pnictogen Bonding. 1998. Dalhousie University. Ref Type: Thesis/Dissertation