Gold(I) clustering at the triphenylphosphinimine nitrogen atom
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abstract
The nitrogen atoms of phosphinimines R3P=NH can function as clustering centers for (ligand)gold(I) units to give di- and trinuclear complex cations. Salts containing these novel cations are best prepared from the reactions of silylated phosphinimines R3P=NSiR3 (R = Ph, R = Me) with the corresponding aliquots of tris[(phosphine)gold]oxonium tetrafluoroborates [(Ph3P)Au]3O+BF-4 or (phosphine)gold tetrafluoroborates [(Ph3P)Au]+BF-4. Attempts to use a Staudinger reaction of a -azido-bis[(phosphine)gold] tetrafluoroborate [(Ph3P)Au]2N+3BF-4 with triphenylphosphine as an alternative preparative pathway were unsuccessful and afforded only [(Ph3P)2Au]BF4. All products have been characterized by analytical and spectroscopic data. The crystal structures of: (1) {Ph3PN[Au(PPh3)]2}+BF -4 THF; (2) {Ph3PN[Au(PPh3)]2}2+3BF-4. THF2CH2Cl2; and (3) [(Ph3P)Au]2N+3BF-4 have been determined. In all three compounds the gold atoms are in close intramolecular contacts indicating significant metal-metal interactions (auriophilicity). Accordingly, the angles at nitrogen are found to be smaller than expected for trigonal planar (1), (3) or tetrahedral (2) coordination. The dication of (2) is isoelectronic and isostructural with the triply aurated phosphonium cation {Ph3PC[Au(PPh3)]3}+. The isolobality concept relates the cation of compound (1) with standard aminophosphonium cations like Ph3PNH+2 (H+/LAu+). There is no isolobal analogue for the dication in (2), however, and this result suggests that the cluster formation of gold contributes significantly to the stability of polyaurated species.
