Organometallic Chemistry: Volume 16 (Specialist Periodical Reports - Organometallic Chemistry) - Hardcover

Hardcover

ISBN 10: 0851866417 ISBN 13: 9780851866413

Publisher: CRC Press, 1988

Synopsis

This Specialist Periodical Report aims to reflect the growing interest in the potential of organometallic chemistry.

About this title

About the Author

Professor Abel is an Emeritus Professor at the University of Exeter.

Excerpt. © Reprinted by permission. All rights reserved.

Organometallic Chemistry Volume 16

A Review of the Literature Published During 1986

By E. W. Abel, F. G. A. Stone

The Royal Society of Chemistry

Copyright © 1987 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85186-641-3

Contents

CHAPTER 1 Group I: The Alkali and Coinage Metals By J.L. Wardell, 
CHAPTER 2 Group II: Alkaline Earths and Zinc and its Congeners By J.L. Wardell, 
CHAPTER 3 Boron with the Exception of the Carbaboranes By J.W. Wilson, 
CHAPTER 4 Carbaboranes, including their Metal Complexes By T.R. Spalding, 
CHAPTER 5 Group III: Aluminium, Gallium, Indium and Thallium By P.G. Harrison, 
CHAPTER 6 Group IV: The Silicon Group By D.A. Armitage, 
CHAPTER 7 Group V: Arsenic, Antimony and Bismuth By J.L. Wardell, 
CHAPTER 8 Hetal Carbonyls By B.J. Brisdon, 
CHAPTER 9 Organometallic Compounds Containing Metal – Metal Bonds By W. E. Lindsell, 
CHAPTER 10 Ligand Substitution Reactions of Metal and Organometal Carbonyls with Group V and VI Donor Ligands By D.A. Edwards, 
CHAPTER 11 Complexes Containing Metal – Carbon σ-Bonds of the Groups Scandium to Manganese, Including Carbenes and Carbynes By Mark J. Winter, 
CHAPTER 12 Complexes Containing Metal – Carbon σ-Bonds of the Groups Iron, Cobalt and Nickel By A.K. Smith, 
CHAPTER 13 Metal – Hydrocarbon π-Complexes, Other than π-Cyclopentadienyl and π-Arene Complexes By M. W. Whitley, 
CHAPTER 14 π-Cyclopentadienyl, π-Arene and Related Complexes By A.H. Wright, 
CHAPTER 15 Homogeneous Catalysis by Transition Metal Complexes By M. Bochmann, 
CHAPTER 16 Structures of Organometallic Compounds determined by Diffraction Methods By D.R. Russell, 

CHAPTER 1

Group I: The Alkali and Coinage Metals

BY J. L WARDELL

1 Alkali Metals

1.1 General. Ultrasonic acceleration of the formation of organolithiums using metallic lithium has been further illustrated; o-LiCH2C6H4CH2Br, Anth2-,2Li+, Li2 cyclo-octatetraenide and Li2 acenaphthenide were among the compounds prepared by this route.

1.2 Hydrocarbon dianion compounds. Enthalpies of formation of ArH2-,2Na+ (ArH= Naph, Anth, tetracene, pentacene, pyrene, perylene, etc.) from ArH and Na were calculated to be similar (ca. 40 k cal mol-1). This suggests that entropy effects rather than electron affinities account for the difficulty in forming dianions of the smaller hydrocarbons. N.m.r. spectra have been obtained in THF for K2 acepentalenide (from the hydrocarbon and BuLi,Pet0K), Na2 bifluoran-9-ylide (from metal reduction of the crowded alkene) and Li2 biphenylide (from Li reduction of the hydrocarbon).

1.3 π-Complexes. Co-condensation of Li atoms with C2H4 and N2 in solid argon provides ternary complexes with both C2H4 and N2 co-ordinated to Li. Co-deposition of Li atoms and CO in krypton matrices at 12 K has been reported to produce various products, including Li(CO)n [n=1,2,3,>4] and Lin(CO)m (n=2 or 3, m=1 or 2); SCF and post-SCF-CI calculations have also been carried out. In these complexes, significant electron transfer to the oxygen occurs, leading to large dipole moments for Li-CO and Li-CO-Li.

1.4 Alkyl derivatives. Mass peaks corresponding to [Rn-1Lin]+ (1) and the less stable [HRn-2Lin]+ have been observed in the mass spectra of (RLi)n (2) between 10-70 eV. The ions, (1, n=4 or 6) are formed through a single step fragmentation of [RnLin]+ (n=4 or 6) and these create all the remaining ions in the m.s. by direct and consecutive fragmentations. In the gas phase, it appears that for (2, R=Me, Pri, Bus or But) tetramers are present while for (2, R=Pr, Bu or Bui), tetramers and hexamers occur.

The crystal structures of the following α-silylmethyl-lithiums have been determined: (i) [LiCH2SiMe3]6 (3) {two sets of Li-Li (av. 2.48 and 3.18 Å) and Li-C (av. 2.20 and 2.27 Å) bond lengths; Li.... H (methylene) ca. 2.0 to 2.3 Å}, (ii) [(PMDT)Li(μ-Cl)Li(PMDT) [Li{C(SiMe3)3]2}](4) obtained from PMDT,LiCl and [Li(THF)4][Li{C(SiMe3)3}2] (5) (in (4), cation has a linear LiCLi unit; anion is essentially the same as that in (5)] and (iii) [LiC(SiMe2OMe)3]2 {long Li-C and short C-Si bonds; one OMe group of C(SiMe2OMe)3 in each monomer unit coordinates to the Li in the same monomer and the other two to the other Li in the dimer.}

The structures of other organolithiums containing in-built donor groups have been reported; namely (LiCH2CH2CH2OMe)4 (6)10 and (LiCH2CH2CH2NMe2)4 (7). In the crystal, both (6) and (7) have distorted (CH2)4Li4 cubes with chelating CH2CH2X (X=OMe Or NMe2) groups. Contacts between Li and H (methylene) are 2.12 to 2.16 Å in (6). In hydrocarbon solution, the n.m.r. spectra of (6) indicate the solid state tetramerisinequilibrium with a stereoisomer. Enthalpies of intramolecular co-ordination of various methoxyalkyl-lithiums in PhH have been investigated; included in this study were (6), (MeOCH2CH2CHMeLi)4, 2-Li-7-MeO-norbornane and MeO(CH2)5Li. Klumpp has reviewed the oxygen or nitrogen assisted lithiations and carbolithiations of nonaromatics. Treatment of epoxides, R'CHCHR 0, with ArH-,M+ (2 equiv.) (ArH=PhPh or Naph; M=LiK or 2Mg) in THF at ca. -80 °C provides β-alkoxyethyl derivatives, R'CH(0M)CHRM (e.g. R1=Ph or R2CO2, R1=H; R2=H, R1=alkyl). The syntheses of (LiCH2)3 cyclohexane derivatives (8) have been achieved by cleavage of PhS-C bonds in appropriate compounds by [ButC6H4C6H4But]-·,Li+.

The crystal structure and 13C n.m.r. spectrum of monomeric (Ph2P)2CHLi. TMED have been reported; Li is co-ordinated to bothPatoms (Li-P 2.58(2) Å). In the solid state structure of {[LiCH2PPh2CH2]2(dioxane)3}2 (dioxane), the central features are two 8-membered rings, in the crown conformation; each ring is made up of two (CH2PPh2CH2) ligands bridging two Li atoms. The two rings are linked (via Li) by a bridging dioxane. The effect of α-donor and π-acceptor groups on the stabilization of a series of H3P=CHX, including X=Li, was studied by an ab initio M.O. method.

Lithioalkylsulphoximides, MeN=S(0)PhCR1R2Li (9, R=Li), are obtained on metallation of RH by BuLi.TMED. The crystal structure analysis of [(S)-9 (R1=R2=H)]4.2TMED revealed a tetramer having two pairs of differently coordinated Li atoms and sulphoximide anions; one Li type is co-ordinated to 2 0 (Li-Oav 1.90(5)Å) and to 2 N (Li-Nev 2.10(5) Å), while the other Li's are each bonded to 3 N (of sulphoximide units) (Li-N av 2.09(5) Å) and 2 C (CH2)(Li-C av 2.49(5) Å) with additional contacts Li ... Li (av 2.78(5) Å) and Li ... C (other CH2) (av. 3.24(4) Å). The S-C(H2) bond length indicates significant double bond character. It was calculated from n.m.r. data that (9, R1 ≠ R2) are not configurationally stable in THF solution at the anionic C atom, even at low temperature.

1.5 Enolates and related derivatives. The lithium enolate of CH3CHO (CH2=CHOLi) is tetrameric in THF with a barrier to rotation about the vinyl bond of 6.6 kJ mol-1. The structures of pinacolone enolates [H2C=ButOM]n(THF)m (M=Li, n=m=4; M=Li, n=6, m=0; M=Na, n=4, m=0; m=K, n=m=6) have been investigated. The solid state structures (as well as those in solution) have been determined for the dimeric species (i) lithiated 2-MeO2-cyclohexanone dimethylhydrazone [as the THF solvate; (10)] , (ii) lithiated cyclohexanone phenylimine [as the Pri2NH solvate; (11)] and (iii) lithiated pinacolone phenylimine as the Et2O solvate, [CH2C=ButNPhLi)]2 (Et2O)2, (12). Some dissociation of (10) occurs in hydrocarbon solutions; (11) exists as a rapidly equilibriating mixture of isomers in solution. The structures have been discussed in the light of the selectivity of alkylations and also of the syn effect of lithiated imines.

1.6 Benzyl and related derivatives. Dissociation of XC6H4CH2M (X=H, p-OMe or o-OMe; M=Li, Na, K or Cs) in THF has been investigated using conductometric techniques; Kd, ΔHd and ΔSd values have been obtained. The powerful metallating combination, BuLi-ButOK, has been used to obtain KOC6H4CH2K from cresols, and the tetraanionic species 3-5- (MCH2)2C6H4C6H4(CH2M)2-3,5 (13, M=K), from (13, M=H). In the dilithio species (14), prepared by Li reduction of the hydrocarbon (15), equation 1, n.m.r. data in ethereal solvents clearly indicate two different Li atoms (δ 0.61 and -1.09 ppm) and two distinct carbanionic centres; for (14-6Li) δ C6 59 ppm (t, JC-Li 6.9 Hz (i.e. bonding to 1Li) and δ C8 100 ppm (i.e. no Li-C coupling). It was argued that the structure is effected by intramolecular interaction between the carbanion moiety and the remote π-system as well asby the interactions of the two carbanionic units. The n.m.r. spectra of Li-2-Ph-2,2-Me2-cyclopropane and 8-M-8-Ph-2,3-benzo[3.2.1] octane RM (M=Li, Na or K) (obtained from R-OMe and M) have been compared to those of (14) and the sodio analogue of (14).

Double η3-aza-allyl-1ithium interactions have been found in the solid state structure of 2,6-(Me3SiCHLi)2-pyridine.2TMED in agreement with a MND0 calculation on the derivative, 2,6-(H3SiCHLi)2-pyridine.4THF. Crystal structures have also been determined for (i) [PhS(0)CPhMeLi.TMED]2 (16) (a dimer with a Li2O2 ring) and (ii) (PhCHLiCN.TMED)2.PhH (a dimer with a Li2N2 ring and almost linear C-C-N). Only one diasteromer of (16) was found in the crystal; protonation of (16) in Et2O provides only (RR)/(SS)-PhCHMeSOPh. It has been established that reaction of PhCH2R [R=CN or P(O)(OEt)2] with BuLi (2 equiv.) in THF produces PhCHLiR.LiBu (17) rather than PhCLi2R. Derivatisation of (17) can however provide disubstituted products via a sequence involving metallation and alkylation. The formation and stereochemistry of alkylations of 9-R-10Li-9,10-dihydroanthraoenes have attracted further attention.

Solvent effects on the 13C n.m.r. spectra of indenyl-1ithium have been investigated. The pyrolysis of 9-Li-fluorene at 180 °C provides 9,9-Li2-fluorene. An equilibrium lithium ion-pair indicator scale has been established for a series of fluorene derivatives which form solvent separation ion-pairs in THF; ΔS ° values were found to be small for the indicator equilibria, studied by u.v.-vis spectroscopy.

1.7 Aryl derivatives. Enthalpies of solvation of 2-ROC6H4Li and 8-Li-1-MeO-naphthalene in Bu2O are lower than those of the 4-lithio isomers by ca. 20 and 28 kJ mol-1 respectively.

The closest Li ... H contacts in 2-Li-l-Ph-pyrrole (18) involves H11 in both solution (as found using 6 Li-1H 2D heteronuclear Overhauser NMR spectroscopy) and in the solid state [from a crystal structure determination of (18. TMED)2: Li ... H11 av 2.9 Å with the next shortest Li.... H3 av 3.2 Å]. It is of interest that further metallation of (18) occurs at C11.

Rigid 2-Ph-1,3-dioxanes, having the acetal proton in an axial orientation, are rapidly ortho-1ithiated; such rigid 1,3-dioxanyl groups are stronger ortho-directing groups than is MeO. Lithiation of (FC6H4OMe)Cr(CO)3 occurs ortho to F, in contrast to the situation for uncomplexed FC6H4OMe.

The synthesis and crystal structure of the lithium 1,2-diboratobenzene compound [Li.TMED]2[1,2-C4H4(BNMe2)2] has been reported. It can be considered as a contact ion triple with [Li.TMED] above and below the planar C4B2 ring. (Li-C 2.263(8) to 2.368(7) Å; Li-B 2.471(8) to 2.553(8) Å).

1.8 Alkenyl and other unsaturated derivatives. A 13C n.m.r. study of ButC[equivalent to]13C-6Li in THF revealed 1 dimeric and 3 different tetrameric aggregates; the tetramers probably only differ in number of THF molecules of solvation.

Cyclo-octyne reacts with Li powder at -35 °C in Et2O to give cis-1,2Li2-cyclo-octene (stable at 40 °C but with t½·1 h at RT) and 2,2-Li2-1,1'-bicyclo-octenyl. In contrast, 3-octyne slowly provided the trans-adduct. The mechanism for the isomerisation of trans-1,2-Li2-alkenes has been investigated using an ab-initio method. Configurational instability was also reported (i) for (Z)-PhCLi=CHSiEt3 [obtained from BuLi and (Z)-PhC(SnBu3)=CHSiEt3 at -78 °C], (ii) (Z)-Me3SiCM=CHR (19) [obtained from (E)-Me3SiCI=CHR and ButLi (2 equiv) in pentane/ether at -78 °C], (iii) R1R2C=CLiSD2Ph, at -60 °C and (Z)- EtSCH=CLiS(O)Et at -80 °C (both from MeLi and the appropriate alkene). The most plausible isomerisation-mechanism for (19) involves a synergistic or 'push-pull' interaction of the Li-C σ bond and an empty orbital of Si; the rates of isomerism, investigated by n.m.r., depend on the electropositivity of M and on R (for M=Li, R=p-XC6H4, ρ=-0.1 in Et2O-pentane solution at -20 °C). (E) or (Z)-γ-Alkoxyvinyl-metallic compounds, R2C(OM')CH=CHM (M=Li, M'=MgX; or M'=MgX, M'=Li) have been synthesied, from MeO2CCH=CHCl on successive treatment with RMgX (2 equiv) and Li powder. The compound [(TMED)2NaCBut=C=CMeC=CBut] (20) has been produced from ButC[equivalent to]CCHMeC[equivalent to]CBut, BuNa and TMED in hexane; in the solid, Na co-ordinates to the two chelating TMED units and a terminal carbon of the allene unit [Na-C3 2.595(9), Na ... C4 2.803(8) and Na ... C5 3.45(2) Å].

Bicyclo[3.2.1 ] octa-2,6-dienyl-1ithium (21) has been isolated as the TMED adduct. A crystal structure determination of (21. TMED) indicated that Li is bound to the carbanion by both allylic and olefinic bonding. As TMED is also co-ordinated to Li, Li is 7 co-ordinated; the MNDO structure of (21) shows overall agreement with the X-ray structure of (21.TMED). 13C N.m.r. spectra of (21) and various phenyl derivatives as well as K analogues have also been reported and discussed in terms of the bishomoaromatic character of the anion.

Rates of isomerisation of trans-neopentylallyl-M in THF increases in the sequence Li > Na > K. The crystal and solution structures of [PhSO2CHLiCH=CH2. diglyme]2, from PhSO2CH2CH=CH2 and BuLi in diglyme, have been investigated. In the crystal, there is a Li2O2S2 ring with a penta-co-ordinate Li (to 5 0); the allyl group lies outside the co-ordination sphere of Li. A homonuclear, 6Li, 6Li shift correlation experiment has been performed on Me2C=CLiCLi=CMe2 in THF at -70 °C; two non-equivalent sets of Li were indicated in agreement with the solid state structure (of the tetramer).

An ab initio MO calculation at electron correlated levels has been carried out on C3H3Li. A singlet cyclic structure (CS) was calculated as the most stable.

(Continues...)

Excerpted from Organometallic Chemistry Volume 16 by E. W. Abel, F. G. A. Stone. Copyright © 1987 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: CRC Press
• Publication date: 1988
• Language: English
• ISBN 10: 0851866417
• ISBN 13: 9780851866413
• Binding: Hardcover
• Number of pages: 544
• Editor: E W Abel