Composition and Chemistry of the Mixed Higher Order Cuprates (PhMe2Si)m(CH3)nCu(CN)Lim+n

Article abstract of DOI:10.1021/jo00011a013

Low-temperature 29Si, 13C, and 1H NMR spectroscopic techniques were used to probe the nature of THF solutions of cuprates derived from PhMe2SiLi, MeLi, and CuCN in the stoichiometric ratios 1:1:1, 2:1:1, and 1:2:1 (Si:Me:Cu).Unlike the corresponding mixed stannyl systems that yield R3Sn(R)2CuLi2 when the ratio of stannyl anion:alkyl anion:cuprous ion is 1:2:1, these mixed silyl systems only form R3Si(R)Cu(CN)Li2.Solutions wherein the ratio of silyl anion and alkyl anion to cuprous ion is greater than 2:1 contain alkyllithium uncoordinated with cuprous ion.The most striking result is the preferential displacement of RLi when R3SiLi is added to solutions of R3Si(R)Cu(CN)Li2 or R2Cu(CN)Li2.These mixed metallocuprate solutions preferentially transfer the PhMe2Si moiety in reactions with α,β-unsaturated enones and other unsaturated organic substrates.However, the mixed alkylsilylcuprate (PhMe2Si)(CH3)Cu(CN)Li2 reacts with 1,2-epoxyoctane to afford up to 31percent of the methylated alcohol.Frontier orbital analysis of both the predominant cuprates species and preferential ligand transfer provides a rationale for the observed behavior.