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Organometallic Chemistry by E W Abel, Royal Society of Chemistry

Organometallic chemistry is an interdisciplinary science which continues to grow at a rapid pace. Although there is continued interest in synthetic and structural studies the last decade has seen a growing interest in the potential of organometallic chemistry to provide answers to problems in catalysis synthetic organic chemistry and also in the development of new materials. This Specialist Periodical Report aims to reflect these current interests reviewing progress in theoretical organometallic chemistry, main group chemistry, the lanthanides and all aspects of transition metal chemistry. Specialist Periodical Reports provide systematic and detailed review coverage of progress in the major areas of chemical research. Written by experts in their specialist fields the series creates a unique service for the active research chemist, supplying regular critical in-depth accounts of progress in particular areas of chemistry. For over 80 years the Royal Society of Chemistry and its predecessor, the Chemical Society, have been publishing reports charting developments in chemistry, which originally took the form of Annual Reports. However, by 1967 the whole spectrum of chemistry could no longer be contained within one volume and the series Specialist Periodical Reports was born. The Annual Reports themselves still existed but were divided into two, and subsequently three, volumes covering Inorganic, Organic and Physical Chemistry. For more general coverage of the highlights in chemistry they remain a 'must'. Since that time the SPR series has altered according to the fluctuating degree of activity in various fields of chemistry. Some titles have remained unchanged, while others have altered their emphasis along with their titles; some have been combined under a new name whereas others have had to be discontinued. The current list of Specialist Periodical Reports can be seen on the inside flap of this volume.

Product Details

ISBN-13: 9780851867014
Publisher: Royal Society of Chemistry, The
Publication date: 12/31/1993
Series: Specialist Periodical Reports Series , #22
Pages: 524
Product dimensions: 5.43(w) x 8.50(h) x (d)

About the Author

Professor Abel is an Emeritus Professor of the University of Exeter, UK.

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Organometallic Chemistry Volume 25

A Review of the Literature Published During 1995


By E. W. Abel

The Royal Society of Chemistry

Copyright © 1996 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85404-308-8



CHAPTER 1

Group I: The Alkali and Coinage Metals

BY J. L. WARDELL


1. Alkali Metals

1.1. General

A review has been published on the bonding in, structures and energies of organolithium compounds; the review includes updated higher-level calculations. Density functional calculations on several classes of organolithiums have been reported and the results compared to those using MNDO, PM3 and ab initio methods as well as with experimental findings.

Reviews have also been published on (i) the properties and applications of RLi species, (ii) the application of 1H-6Li heteronuclear Overhauser effect spectroscopy (HOESY) in the study of organolithiums, (iii) the preparations and reactions of polylithiated organic compounds and (iv) the use of [p-ButC6H4C6H4But-p]- ·Li+ (LDBB) as a lithiating agent.


1.2 Alkyl compounds

The synthesis of alkyl-lithium compounds from alkyl aryl selenides and ArH-·Li+ has attracted lurther attention. Alkyl-lithiums have been generated and used in situ in reactions of alkyl aryl sulphones with Li / catalytic naphthalene (Naph-H) in the presence of an organic electrophile. Ab initio calculations have been carried out on the NMR coupling constants in methyl-lithium and tert-butyl-lithium using self-consistant pertubation theory. Crystal structures have been reported for (i) ionic [CsC(SiMe3)3.3PhH].0.5PhH: each Cs+ is coordinated to the central C of the neighbouring anion and η6 to each of 3 PhH units, and (ii) RbC(SiMe3)3: a one-dimensional ionic solid with chains of alternating Rb+ and planar anions; the MC(SiMe3)3 compounds were obtained by reaction of HC(SiMe3)3 with MeM, produced from MeLi and MO(CH2)2CEtPr.

Reviews have been published on the theory, structures and reactions of the carbenoid-like compounds, RRlC(X)Li (X = NR2 or OR). The Li-N chelate bond energies decrease in the order [LiCH2SiMe2CH2NMe2]4 > [LiCH2SiMe2CH2N(CH2CH2NMe2)Me]2 > [LiCH2SiMe2CH2N(CH2CH2NMe2)2], Ring cleavage of thiochromane and benzohydrothiophene by LDBB provides arylthiolato-substituted alkyl-lithiums. A mechanistic study has been carried out on the enantiomerisation of α-thio-, α-seleno-and α-telluro-alkyl-lithiums.

Ab initio calculations of the molecular structure and NMR C-Li coupling constants of Cl3CLi and (Cl2CHLi)n (n = 1 or 2) have been reported. A crystal structure determination of [4-But-thiazolato-C,N)(glyme)lithium], a formyl anion equivalent, revealed it to be dimeric with a carbenoid character: each Li atom has a stronger interaction with N than with C of a monomeric unit and is additionally bonded to C of another monomer and to 2 O of a glyme unit. Examples have been obtained of compounds having reduced configurational stabilty as a result of chelation, eg., [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], as well as those having greater stability, e.g. PhSCHLiSiMe2CH2R [R = H, OMe, OCH2CH2OMe or N(CH2)4]

NMR spectroscopy, including 1H- 6Li HOESY, 1H- 1H HOESY and 6Li- 6Li NOESY techniques, has been used to study the structure of [{(R)-MeOCH2CHPh}{(S)-MeCHPh)NLi.BuLi]2. Catalytic amounts of (-)-sparteine act as a promoter for the enantiomeric carbolithiation of, cinnamyl derivatives. The efficacies of BusLi / chiral ligand complexes as reagents for the asymmetric deprotonation of Boc-pyrrolidine have been evaluated. Complexation between [(-)-sparteine.PriLi] and Boc-pyrrolidine was detected prior to the deprotonations.

Facile cleavage of Et2O occurs with (Me3Si)3CLi in the presence of BX3. Irradiation of CdS powder, suspended in ethereal solutions of RLi, produce elemental Cd and R-R. Protonation of RCOLi by CH2Cl2, ArCHCl2 or MeCN has been used in synthesis, e.g. reaction of PhCHCl2 with BuLi in the presence of CO in THF / Et2O / pentane at -110 °C, followed by hydrolysis with NH4C1 provides PhCCl2CHOHBu.


1.3 Alkenyl compounds

Retention of configuration occurs in the Li/I exchange reactions of alkenyl or allenyl iodides and BuLi in hydrocarbon solvents at 25 °C. The formation of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], from [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and BuLi or ButLi, has been reported. The lithiated cyclopropyl carbons in dimeric, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], as shown by X-ray crystallography, have near planar geometries: the compound has a puckered ladder structure with Li(l) bridging the carbanion of one monomer and the O atom of another, while Li(2) is chelated by a dianion. Unsolvated H2C=CLi(OEt), (1), obtained by tin/lithium exchange, has a polymeric chain structure, involving tetrameric subunits linked by C=C -Li interactions. The mean C-O bond length, 1.428(7) ?, in 1 indicates some carbenoid character. There are two distinct types of lithium atoms present: Li(l) is coordinated to 2 O and 3 C (within a tetrameric unit) while Li(2) is coordinated to 3 C (within a tetrameric unit) and by a π-bond to C=C of an adjacent tetramer. Low-temperature 13C NMR spectra, as well as calculations on H2C=CLi(OMe), were also reported. Reaction of Cl2C=P(Ar)=CR2 (Ar = 2,4,6-But3C6H2, R = SiMe3) with BuLi in THF at -80 °C provides stereoisomers of the carbenoid, (THF)3LiCCl=P(Ar)=CR2, which have been characterised by NMR, and, in the case of the endo-isomer, also by X-ray crystallography; the C-Li bond length is 2.193(12) ?. Ab initio calculations (of valence double-zeta quality) have been reported on the effect of solvation on the structure of H2C=CLi(Cl). The solution structure and aggregation of o- LiC6H4CPh=CLiR [2; R = (E)-Pr or (Z)-H] have been investigated by 1-D and 2-D 1H, 13C and 6Li NMR spectroscopy; dimers of 2 exist in Et2O solution, while in THF and on addition of TMED a monomer-dimer equilibrium is set up. NMR spectral studies, including 1H-6Li HOESY experiments, have shown that H2C=CHCMe2(CH2)2C(SPh)Li, obtained by Sn/Li exchange, exists in THF at -80 °C partially as an internally π-complexed species. A crystal structure determination of the solvent separated ion paired, [Li(glyme)3]+[Ph2C-CH-CH- CPh2]-·, indicated a C-C bond order in the radical anion reversed to that in the neutral molecule.


1.4 Allylic compounds

The relative rates of allylic metallation of α- and β-pinene and various endo- and exo- cycloalkenes by BuLi.TMED or BuLi/KOBut have indicated a very high reactivity for β-pinene. (Z)-1,4- Dilithio-1,4-bis(trimethylsilyl)but-2-ene (3) has been prepared as the bis-THF adduct, via metallation of (E)-Me3SiCH2CH=CHCH2SiMe3, by BuLi in THF or by reduction of (E,E)-Me3SiCH=CH-CH=CHSiMe3 with Li in THF; 3 is dimeric in the solid state with two Li atoms bridging the organic dianion, while the other two Li atoms are external to the dianionic unit and are solvated by two THF, forming an inverted double-decker sandwich structure. Deprotonation of 1-Y-indene (Y = Me or Bu) by Li / (-)-sparteine in Et2O / hexane occurs stereospecically, as shown by the determination of the crystal structure of [{1-(R)-1-Bu-indenyl-Li}.(-)-sparteine]; in contrast, reaction in THF / hexane at -70 °C is completely non-stereospecific, as indicated by the structure determination of [{(±)-l-Me-indenyl-Li}.(THF)3], A synthetic, structural, mechanistic and theoretical MO study of 1,3-Ph2-2-azaallyl-M compounds (M = Li, Na or K), obtained from (PhCH2)2NM and TMED, has been reported. Ab initio and semi-empirical PM3 calculations have been performed on azaallyl-lithium systems, related to the growing poly(2-vinylpyridine) chain end, e.g. -[CH2--CH--C5H4N-o]Li. Dilithiation of N,Nl,Nl-triphenylguanidine with BuLi in THF provided the dimeric, triazatrimethylenemethane dianionic compound, {Li4[C-(- NPh)3]2. (THF)6); the X-ray crystal structure indicated that the two dianionic units are bridged by two Li atoms, each coordinated to 3 N and 1 O, while the other two Li atoms are coordinated to the third N of each unit, to an Cipso- Cortho bond of the adjacent phenyl and to two THF molecules.


1.5 Allenyl / propargylic compounds

Crystal structure determinations have revealed that [η3-lithio-1,3,3- triphenylpropyne.(Et2O)2] has a propargylic structure, while that of [1-lithio-1-(o-MeOC6H4)-3,3-Ph2- allene.Et2O]2 is of the allenyl type. An NMR spectroscopic study has been reported on the solution structures of allenyl- / propargyl-lithium species: the initial results indicate that such reagents have an inherent bias towards allenyl-lithium structures. Neither alkyl groups on the allenyl nor ether groups on the propargylic precursors favour the propargyl isomer sufficiently for it to be detected. Three types of reagents were shown to favour a propargylic structure (i) those with two substituents at the propargylic carbon forming a cyclopropyl ring, (ii) those with such groups as Ph, PhS or PhSe and (iii) those in which a powerful chelating group, such as carbamoyl, stabilises the propargylic structure. The stable product of Li/Sn exchange of either H2C=C=C(SnMe3)Pri or PriC[equivalent to]CCH2SnMe3 was shown by NMR to be H2C=C=C(Li)Pri; the role of ate-complexes, solvent-separated and contact-ion-pairs in the exchange reactions was also studied. The same dianionic species, PhCHLi-C[equivalent to]CLi, was obtained by lithiation of PhC[equivalent to]CMe, PhCH=C=CH2 or PhCH2C[equivalent to]CH by BuLi; however at low temperature in THF, distinct monoanions, PhCH2C[equivalent to]CLi, PhC[equivalent to]CCH2Li and PhCH=C=CHLi, were also detected. The reaction of excess LiNPri2 with Ph2C=CMe(OSiButMe2) and PhCH=C(CH2R)(OSiButMe2) (R = Ph or Me) provides the allenes, Ph2C=C=CLi2 and PhLiC=C=CLiR, respectively.


1.6 Alkynyl compounds

The intermediacy of organolithium species was indicated in the Barbier-type reactions of CIC[equivalent to]CCH2CH2Cl (and also H2C=CClCH2Cl) with Li powder and a catalytic amount of (p-ButC6H4)2 (DBB) in the presence of an organic electrophile. Propynyl-lithium can be readily generated in high yield from (ZIE)-MeCH=CHBr and BuLi in THF at -78 °C.

The structural, electronic and dynamic properties of C2H2Li2 have been investigated by ab initio molecular dynamics simulations based on the Car-Parrinello method; dynamic simulated annealing techniques suggested the low-energy structure to be the complex, HC[equivalent to]CLi.LiH. The synthesis and solid-state structures of MC[equivalent to]CMe (M = Rb or Cs) have been reported; comparisons were made with the structures of the analogues of the other alkali metal compounds.


1.7 Cyclopentadienyl compounds

Mutinuclear NMR studies (1H, 13C and 6Li) have shown that the cyclopentadienyl species, lithium tricyclo[5.2.1.0]deca-3,5,8-trienide, exists as a monomer at RT and as a dimer-monomer pair at -108 °C ; Li+ is located at the endo face in the monomer and at the two endo faces in the dimer. A η1 - η5 dilithium structure was determined for [(THF)5Li2.tetraphenylsilole] in the solid state; one Li is η5 - bonded to the silole ring and to 2 THF molecules, while the other is η1 - bonded to Si and to 3 THF units.


1.8 Benzyl compounds

Benzyl-lithiums, previously considered to be ion-paired species in solution, have been found to exhibit 13C-6Li spin couplings under conditions in which bimolecular C-Li bond exchanges are too slow to average the coupling constant. These conditions involve the use of species in which Li is internally solvated or of dilute solutions at low T. The C-Li bonds in benzyl-lithiums are concluded to lie in a continuum of C-Li covalency between the monomeric forms in which 1J(13C- 6Li), is 16 ± 1 Hz and separated ion pairs. Reactions between 2,4,6-Me3-1,3- (Me2NCH2)2C6H (ArH) and BuLi produce Ar2Li4Bu2 (4) and [ArLi]n; the latter compound reacts with RLi (R = Bu, p-tolyl or 1) to give the mixed aggregate, Ar2Li4R2. NMR spectra and the crystal structure of 4 were reported. Each of the Li3-faces of the Li4 tetrahedron in solid 4 is bonded to a benzylic C via 4c-2e interactions; the butyl groups are also 4c-2e bonded and the coordination of each Li is saturated by N atoms. The crystal structure of [{2,6- (LiCH2)2C6H3OLi.TMED}4.(PhH)15] consists of a tub-shaped Li4O4 core and 3 distinct Li sites: Li(1) is coordinated to 2 O [mean Li-O = 1.92 (Å) and to the benzylic C [mean C-Li = 2.31 Å], Li(2) is chelated by TMED and bridges a benzylic C [C-Li = 2.29 Å] and an O [O-Li = 1.94 Å], while Li(3) bridges a benzylic C [C-Li = 2.09 Å] and the π system of another aryl ring [C-Li 2.22 - 2.42 Å], The solvation and type of ion-pairing of PhCH(SPh)Li and of the crown-ether derivatives, [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3; X = H or SPh) in THF have been investigated by NMR; 1H-6Li HOESY experiments showed that Li is attached to the anionic centre and is held in place mainly by the remote O of the crown ether ring. The barriers to racemisation of PhCHLiXCH2Ph (X = S or Se) and PhCHLiNPriMe have been determined using NMR spectroscopy; the rate determining step was considered to be the transformation of the contact-ion-pair to the solvent separated ion pair. The formation of o-LiO(CH2)nC6H4CH2Li from [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (n = 1 or 2)/Li powder/cat. DBB has been described. Equilibrium lithium ion-pair acidities of 2-(p-RC6H4)-1,3-dithiane have been reported. Crystal structures have been determined for (i) molecular [KCPh3.PMDET], (ii) polymeric [KCPh3.diglyme] , which has a zig-zag structure, (iii) and polymeric [KCPh3.THF], which possesses a sheet structure. X-Ray diffraction studies indicated that in [o-LiRRlCC5H4N.Li(TMED)]n, obtained by lithiation of o-RRlCH-pyridine (n = 1; R = Me3Si, Rl = Ph: n = 2, R = H, Rl = Ph or ButMe2Si), the organic ligand is bonded more strongly to Li via N.


(Continues...)

Excerpted from Organometallic Chemistry Volume 25 by E. W. Abel. Copyright © 1996 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

Contents

Chapter 1 Group I: The Alkali and Coinage Metals By J. L. Wardell, 1,
Chapter 2 Group II: The Alkaline Earths and Zinc and its Congeners By J. L. Wardell, 12,
Chapter 3 Boron with the Exception of the Carbaboranes By J. W. Wilson, 24,
Chapter 4 Carbaboranes, including their Metal Complexes By T. R. Spalding, 38,
Chapter 5 Group III: Aluminium, Gallium, Indium, and Thallium By P. G. Harrison, 56,
Chapter 6 Group IV: The Silicon Group By D. A. Armitage, 83,
Chapter 7 Group V: Arsenic, Antimony, and Bismuth By J. L. Wardell, 133,
Chapter 8 Metal Carbonyls By B. J. Brisdon, 140,
Chapter 9 Organometallic Compounds containing Metal–Metal Bonds By W. E. Lindsell, 150,
Chapter 10 Substitution Reactions of Metal and Organometal Carbonyls with Group V and VI Ligands By D. A. Edwards, 187,
Chapter 11 Complexes containing Metal–Carbon σ-Bonds of the Groups Scandium to Manganese By K. J. Karel and P. L. Watson, 214,
Chapter 12 Complexes containing Metal–Carbon σ-Bonds of the Groups Iron, Cobalt and Nickel By A. K. Smith, 236,
Chapter 13 Metal–Hydrocarbon π-Complexes, other than π-Cyclopentadieny1 and π-Arene Complexes By J. A. S. Howell, 271,
Chapter 14 π-Cyclopentadienyl, π-Arene, and Related Complexes By W. E. Watts, 317,
Chapter 15 Homogeneous Catalysis by Transition–Metal Complexes By M. E. Fakley, 345,
Chapter 16 Organometallic Compounds in Biological Chemistry By B. Ridge, 381,
Chapter 17 Structures of Organometallic Compounds determined by Diffraction Methods By D. R. Russell, 407,

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