摘要:
Various tetrametallamethanes, (Me3Si)4C (1), (Me3Sn)4C (2), (Me3Pb)4C (3a), (Me3Si)3CSnMe3 (4a), (Me3Si)3CPbMe3 (4b), (Me3Pb)3CSiMe3 (5a) and (Me3Pb)3CSnMe3 (5b), were studied by C-13 NMR, using the INEPT pulse sequence, based on long range coupling constants 3J((CMCH))-C-13-H-1. This allowed the convenient measurement of the C-13 NMR signals for the quaternary carbon atoms, the fast determination of coupling constants 1J((MC))-C-13 (M = Si-29, Sn-119, Pb-207), and it formed the basis for the determination of the sign of these coupling constants via two-dimensional (2D)C-13/H-1 heteronuclear shift correlations. A number of other organometallic substituted methanes, such as (Me3Pb)3CH (3b), (Me3Pb)2CH2 (3c), Me4-nPb(CH2SiMe)n (n = 1, 2, 3, 4; 6a-d), Et4-nPb(CH2SiMe3)n (n = 1, 2, 3; 7a-c), Me4-nM[CH(SiMe3)2]n (n = 1, 2; M = Sn, Pb; 8a, b, 9a, b), have been included in this study, and, in addition, the signs of 2J((PbSi))-Pb-207-Si-29 (> 0) and of 2J((SnSi))-Sn-119-Si-29 (< 0) were determined by 2D Si-29/H-1, Pb-207/H-1 and Sn-119/H-1 heteronuclear shift correlations. All coupling constants 1J((SiC))-Si-29-C-13 and 1J((SnC))-Sn-119-C-13 have a sign (reduced coupling constants 1K > 0!), in contrast with 1J((PbC))-Pb-207-C-13 values for which sign inversion has been observed for the first time for tetraalkyl lead compounds. In the same way it was shown that the sign of 1J((SiSi))-Si-29-Si-29) for tetrakis(trimethylsilyl)silane (10) is positive.