Stable Au(III) Complexes Bearing Hemilabile P∧N and C∧N Ligands: Coordination of the Pendant Nitrogen upon Oxidation of Gold

The oxidation of Au(I) complexes featuring two hemilabile ligands was investigated. The phosphine-amine (P<^>N) and mesoionic N-heterocyclic carbene-pyridine (C<^>N) ligands were shown to stabilize the ensuing Au(III) complexes by chelation. Oxidation of (MeDalphos)AuCl with PhICl2 directly affords the corresponding P<^>N-chelated cationic Au(III) complex without requiring a chloride abstractor. The C<^>N hemilabile ligand is shown to efficiently chelate Au(III), but not Au(I). Cationization of the (C<^>N)AuCl complex 3 affords the dinuclear complex 4 with the C<^>N ligand bridging two Au centers. Oxidation of 3 with PhICl2 does not spontaneously enforce coordination of the pyridine side arm, as with the P<^>N ligand. However, cationization of the resulting AuCl3 complex 5 with a chloride abstractor successfully promoted pyridine chelation. The structures of all complexes have been ascertained by NMR spectroscopy and X-ray diffraction analyses.