SYNTHESIS OF RAKIS[(TRI-TERT-BUTYLPHOSPHANE)GOLD(I)]PHOSPHONIUM SALTSAND CRYSTAL-STRUCTURE OF THE TETRAPHENYLBOROXINATE SALT ([(TBU)3PAU]4P)-( [O(PHBO)2BPH2])

The reaction of (Me3Si)3P with {[(tBu)3PAu]3O}+ BF4- in tetrahydrofura n at -78-degrees-C affords the compound {[(tBu)3-PAu]4P}+ BF4- (1a) in high yield. This product is converted into the tetraphenylborate salt (1b) by treatment with Na[BPh4]. The two compounds have been identifi ed on the basis of their analytical and spectroscopic data, but could not be crystallized. In attempts to prepare single crystals of lb, a c rystalline salt {[(tBu)3PAu]4P}+ [O(PhBO)2BPh2]- (1c) has been obtaine d in very small quantities, probably by partial anion hydrolysis. A si ngle crystal X-ray diffraction study of 1c . CH2Cl2 shows the compound to be built up of cations with a strongly distorted tetrahedral (PAu) 4P skeleton and anions with a planar six-membered boroxine ring. Two o f the phenyl groups are attached to two trigonal-planar boron atoms an d the other two phenyl groups to the third (tetrahedral) boron atom of the heterocycle. The origin of the peculiar cation structure is discu ssed in the light of findings with related ammonium- and arsonium-cent ered gold clusters.