Ligand Exchange at a Gold(I) Carbene Complex

Dedicated to Professor Heinrich Nöth on the occasion of his 85th birthday Gold complex [AuCl(NHC)] (NHC = N,N′-dipropylbenzimidazolin-2-ylidene) 1 undergoes facile substitution reactions at the gold(I) center. Treatment of 1 with anionic phenylacetylide or thiophenolate led to the neutral gold complexes 2 and 3, respectively. The cationic gold complexes [Au(NHC)(pyridine)](BF4) [4]BF4 and [Au2(NHC)2(4,4-bipyridine)](BF4)2 [5](BF4)2 were obtained via abstraction of the chloro ligand from 1 and reaction with the appropriate amine. Reaction of 1 with AgBF4 in the presence of PPh3 instead of an amine led to an inseparable product mixture of the mixed NHC/PPh3 complex [6]BF4, the dicarbene complex [Au(NHC)2]BF4, [7]BF4, and [Au(PPh3)2]BF4, [8]BF4. Crystals of 2 and [6]BF4 were obtained, and X-ray diffraction structure analyses revealed that the gold(I) atoms are coordinated in a linear fashion by the NHC and the co-ligand.