HYPERCOORDINATE CARBON IN TRIGOLDBIS(SILYL)METHANIUM CATIONS

The reactions of organolithium compounds of the type (R(3)Si)(2)CHLi ( R(3) = Me(3) or Me(2)Ph) with the gold(I) complex Ph(3)PAuCl afford th e monoaurated bis(silyl)methanes (R(3)Si)(2)- CHAuPPh(3) (1a, b) in hi gh yield. These compounds are converted into complex salts with hyperc oordinate methanium cations {(R(3)Si)(2)C[Au(PPh(3))](3)}(BF4-)-B-+ (3 a, b) by treatment with {[(Ph(3)P)Au]O-3}(BF4-)-B-+. In the reaction m ixtures small amounts of the neutral dinuclear intermediates {(R(3)Si) (2)C[Au(PPh(3))](2)} (2a, b) have been detected and characterized by t heir spectroscopic data. Compounds 1a, b and 3a, b have been studied b y single crystal X-ray diffraction analyses. While the mo-nonuclear mo lecules 1a, b have conventional structures with parameters representin g classical types of bonding, the novel trinuclear complexes 3a, b fea ture cations with a pentacoordinate carbon atom in a distorted trigona l-bipyramidal environment of two silicon atoms and one gold atom in eq uatorial positions and the remaining two gold atoms at the axial verti ces of the polyhedra. The main axis of the bipyramid is strongly bent at the central carbon atoms. This distortion leads to short axial/equa torial Au...Au distances indicating peripheral metal-metal bonding.