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 the monoaurated bis(silyl)methanes (R(3)Si)(2)- CHAuPPh(3) (1a, b) in high yield. These compounds are converted into complex salts with hypercoordinate methanium cations {(R(3)Si)(2)C[Au(PPh(3))](3)}(BF4-)-B-+ (3a, b) by treatment with {[(Ph(3)P)Au]O-3}(BF4-)-B-+. In the reaction mixtures small amounts of the neutral dinuclear intermediates {(R(3)Si)(2)C[Au(PPh(3))](2)} (2a, b) have been detected and characterized by their spectroscopic data. Compounds 1a, b and 3a, b have been studied by single crystal X-ray diffraction analyses. While the mo-nonuclear molecules 1a, b have conventional structures with parameters representing classical types of bonding, the novel trinuclear complexes 3a, b feature cations with a pentacoordinate carbon atom in a distorted trigonal-bipyramidal environment of two silicon atoms and one gold atom in equatorial positions and the remaining two gold atoms at the axial vertices of the polyhedra. The main axis of the bipyramid is strongly bent at the central carbon atoms. This distortion leads to short axial/equatorial Au...Au distances indicating peripheral metal-metal bonding.