18077-26-4Relevant academic research and scientific papers
Conventional lithium bases as unconventional sources of methyl anion: Facile Me-Si and Me-C bond cleavage in RLi, R2NLi, and BR4- by an electrophilic osmium dihydride
Yandulov, Dmitry V.,Huffman, John C.,Caulton, Kenneth G.
, p. 4030 - 4049 (2008/10/08)
cis,trans-Os(H)2(OTf)(NO)(PiPr3)2 (1-OTf) and several other precursors (1-X) to Os(H)2- (NO)(PiPr3)2+ (1+) react with (Me3Si)2NLi, (Me3Si)2CHLi, lithium 2,2,6,6-tetramethylpiperidide (TMPLi), Me3SiCH2Li, and B(CH2SiMe3)4- by a highly unusual, facile β-Me- transfer, the exclusive reaction pathway for the first two in nonpolar solvents. A series of lithium alkyls and alkylamides and organoborate reagents have been examined to reveal widespread occurrence of the direct β-R′- transfer (R′ = H, Me) to the Os electrophile, being completely selective for β-H- over β-Me-, with the sole (surprising) exception of NpLi. The β-R′ elimination was ruled out as the mechanism of the net β-R′- transfer for two representative RLi cases with R′ = H, Me, and a single-electron-transfer mechanism was shown to be inoperative for tetraalkylborates. The mechanistic studies also uncovered the important role of Li in RLi and R2NLi, which acts as a potent Lewis acid to abstract the halide/pseudohalide X from 1-X in generating the unsaturated Os species. The proposed intimate mechanism of Me-C and Me-Si bond cleavage is a direct SE2 substitution at carbon with inversion of the Me group, supported by DFT calculations. While the imines formed in the process of C-H and C-Me cleavage are lithiated by, and compete for the Os with, the original base, the unsaturated silicon species formed by Si-Me cleavage react with the remaining base by 1,2-addition of (N,C)-Li, forming intermediates that are also reactive by β-Me- transfer. A complex mixture of Os-free coproducts is obtained in both cases. The structural features of 1+ responsible for its unusual reactivity are discussed.
Chemistry of boron. 130. The reaction of organolithium compounds with borane donors. Preparation and isolation of lithium monoorganotrihydroborates
Biffar, Werner,N?th, Heinrich,Sedlak, Dieter
, p. 579 - 585 (2008/10/08)
The reactions of a series of organolithium compounds with the borane donors BH3·THF, BH3·SMe2, and BH3·NMe3 have been studied in order to develop a general synthesis of lithium organotrihydroborates, LiRBH3. Starting from RLi and BH3 in THF, all members of the series LiR4-nBHn, are formed irrespective of reaction conditions. Bulky substituents R prevent the formation of LiBR4, with BR3 being produced instead. Much higher proportions of LiRBH3 result from the interaction of RLi and BH3·SMe2, with low temperature favoring their formation. Crystalline LiMe2CHBH3 and LiMe3CBH3 can be obtained by this method in good yield. However, LiBH4 is an inevitable byproduct. Other compounds are also formed in minor quantities. Temperatures of >80°C are required for the reaction of RLi with BH3·NMe3, and LiPhBH3·TMEDA and LiPhCH2BH3·TMEDA were isolated in 35 and 90% yield, respectively. Increasing the bulkiness of R (e.g., CMe3) favors deprotonation of BH3·NMe3 over amine displacement. Either LiMe2NCH2BH3 or [Me2NCH2BH2]2 is formed depending on the reaction conditions.
Rearrangement in borane adducts of trimethylsilylmethylenedimethylsulfurane
McMullen,Miller
, p. 2291 - 2295 (2008/10/08)
Boron halide, borane, and trimethylboron adducts of the silyl-substituted sulfonium ylide (CH3)3SiCHS(CH3)2 are readily formed. The borane and alkylboron adducts rearrange at low temperature with simultaneous loss of dimethyl sulfide to give sym-bis(trimethylsilylmethyl)diborane and 1-(trimethylsilylmethyl)ethyldimethylborane, respectively. These rearranged products were isolated and characterized. A trimethylamine adduct with the dialkyldiborane could be converted into the asymmetrical borane cations (CH3)3SiCH2BHN(CH3) 3py+ and (CH3)3SiCH2BHN(CH3) 3P(CH3)3+.
