Carbon−Carbon Coupling in Dinuclear Cycloaurated Complexes Containing Bridging 2-(Diphenylphosphino)phenyl or 2-(Diethylphosphino)phenyl. Role of the Axial Ligand and the Fine Balance between Gold(II)−Gold(II) and Gold(I)−Gold(III)

Abstract

Reactions of the homovalent bis(benzoato)digold(II) complexes [AuII2(O2CPh)2(μ-2-C6H4PR2)2] (R = Ph (1a), Et (1b)) with the anions CH3-, C6F5-, and SCN- have been investigated. Dimethylmagnesium gives the stable heterovalent complexes [AuI(μ-2-C6H4PR2)2AuIII(CH3)2] (R = Ph (2a), Et (2b)), whereas (pentafluorophenyl)lithium gives the homovalent complexes [AuII2(C6F5)2(μ-2-C6H4PR2)2] (R = Ph (3a), Et (3b)). On prolonged heating in toluene, the latter rearrange to give predominantly dinuclear bis(pentafluorophenyl)digold(I) complexes of the corresponding (2,2‘-biphenylyl)bis(tertiary phosphines) [AuI2(C6F5)2(μ-2,2‘-R2PC6H4C6H4PR2)] (R = Ph (4a), Et (4b)), resulting from coupling of the C6H4PR2 units. Minor products of these rearrangements are the zwitterionic heterovalent complexes [(C6F5)2AuIII(μ-2-C6H4PR2)2AuI] (R = Ph (5a), Et (5b)). The structure of 5a differs from that of 2a by rotation of one of the bridging 2-C6H4PPh2 groups through 180°. Precursors to 4a/5a and 4b/5b have been detected by 31P NMR spe...