PLUMBOLES BEARING ORGANOMETALLIC SUBSTITUENTS - THEIR SYNTHESIS AND REACTION-MECHANISM, AS STUDIED BY MULTINUCLEAR MAGNETIC-RESONANCE SPECTROSCOPY

Reaction of bis(trimethylsilylethynyl)dimethyllead (1) with trialkylboranes (2) gives the 3-dialkylboryl-4-alkyl-2,5-bis(trimethylsilyl)-1,1-dimethylplumboles (4). The course of the reactions was monitored by multinuclear NMR (1H, 11B, 13C, 29Si, 207Pb), and various intermediates were identified, including two non-cyclic bis(alkenyl)lead compounds (8, 9) and a zwitterionic species (5) in which a triorganolead cation is stabilized by intramolecular side-on coordination to the CC bond of an alkylnylborate moiety. The presence of at least one trimethylsilylethynyl group is necessary for the formation of plumboles from zwitterionic compounds analogous to 5, as was shown by the synthesis of 3-diethylboryl-4-ethyl-1,1,5-trimethyl-2-trimethylsilylplumbole (11). Positive and negative signs of coupling constants 1J(207Pb13C) in the plumboles have been determined by two-dimensional 13C/1H heteronuclear shift correlations. Features of these data and of the δ207Pb values are compared with 119Sn NMR parameters of comparable tin compounds. © 1990.