Gold(I) complexes of 1,2-ditertiary phosphino-o-carborane ligands: two-, three-, and four-co-ordination

Abstract

Ditertiary phosphines (L) of the type R₂P(C₂B₁₀H₁₀)PR′₂(R = R′= Ph; R = R′= NMe₂; R = Ph, R′= NMe₂) react with tetraethylammonium dibromoaurate(I) to form the three-co-ordinate complexes [AuBrL], which have been isolated and characterized by elemental analyses, and i.r. and ³¹P-{¹H} n.m.r. spectroscopy. A dimeric two-co-ordinate complex, [(AuBr)₂{Ph₂P(C₂B₁₀H₁₀)PPh₂}], has also been isolated and characterized. The ³¹P-{¹H} n.m.r. spectra of CD₃COCD₃–CH₂Cl₂(1 : 1) solutions of L and [AuBr₂]^– show evidence for the formation of dimeric two-co-ordinate [(AuBr)₂L], dimeric three-co-ordinate [(AuBr)₂L₂], monomeric three-co-ordinate [AuBrL], and four-co-ordinate [AuL₂]Br complexes. The unusual four-co-ordinate mixed-ligand complex [Au{Ph₂P(C₂B₁₀H₁₀)PPh₂}{(Me₂N)₂P(C₂B₁₀H₁₀)P(NMe₂)₂}] Br is also observed. Phosphorus–phosphorus coupling constants decrease from three-co-ordinate to four-co-ordinate gold(I) complexes, as expected. The tertiary phosphine H(C₂B₁₀H₁₀)PPh₂ also gives [AuBr{H(C₂B₁₀H₁₀)PPh₂}] two-co-ordinate complexes.