Influence of aromatic ring substituents and co-ligand on the binding mode of a phosphine-borane-stabilized carbanion; crystal structures of [[(Me3Si)2{Ph2P(BH3)}C]KLn]2[Ln = (OEt2)2, pmdeta; pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine]

Metalation of (Me3Si)2CHPPh2(BH3) (1) with MeK in diethyl ether gives the dimeric complex [[(Me3Si)2{Ph2P(BH3)}C]K(OEt2)2]2 (2b), in which there are BH3⋯K and Ph⋯K contacts, but no contact between K and the carbanion center. In the presence of pmdeta the adduct [[(Me3Si)2{Ph2P(BH3)}C]K(pmdeta)]2 (2a) is isolated, in which the Ph⋯K contacts are absent.