Study of the Coordination Abilities of Stibine Ligands to Gold(I)

The reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with SbMesnPh3−n (n = 3 (1), 2 (2), 1 (3)) produces the 1:1 adducts [AuCl(SbMesnPh3−n)] (n = 3 (4), 2 (5), 1 (6)), with a Sb−Au−Cl environment, regardless of the molar ratio used (1:1 to 1:4). Addition of the same stibines to [Au(tht)2]ClO4 (molar ratio 1:1 to 1:4) results in isolation of the 1:2 adducts [Au(SbMesnPh3−n)2]ClO4 (n = 3 (7), 2 (10)), containing linear Sb−Au−Sb fragments, or the 1:3 adduct [Au(SbMesPh2)3]ClO4 (11), with a quasi trigonal planar AuSb3 core. The same 1:2 cations are produced when [Au(tht)2]CF3SO3 is reacted with 1 or following a rearrangement process when 4 is treated with AgSbF6, that is, [Au(SbMes3)2]X (X = CF3SO3 (8), SbF6 (9)). The compounds were characterized by spectroscopic methods, and the molecular structures of 2−4, 7, 8·2CDCl3, 9, and 11 were established by single-crystal X-ray diffraction. Theoretical calculations were carried out on model systems of type ER3 and [Au(ER3)n]+ (E = P or Sb; R = Ph or Mes; n = 2, 3, or 4) to gain insight into the bonding nature of SbR3 ligands in homoleptic gold-stibine adducts, in comparison with phosphine-gold(I) compounds. Steric effects govern the coordination of stibines with mesityl substituents. A preference for higher coordination numbers is observed for SbPh3 when compared with PPh3 and experimentally observed C−Sb−C and Sb−C structural distortions of stibines upon coordination are reproduced theoretically.