NHC-manganese(i) complexes as carbene transfer agents.

Tautomerization of coordinated azoles to their corresponding N-heterocyclic carbenes (NHCs) has been carried out by reaction of complexes fac-Mn(L)(CO)(3)(dppe) (L = N-phenylimidazole) and fac-Mn(L)(CO)(3)(bipy) (L = N-methylbenzimidazole, benzoxazole, benzothiazole) with KO(t)Bu and subsequent protonation of the azolyl intermediates with NH(4)PF(6). Several NHC-manganese(i) complexes bearing an N-H residue of general formula fac-Mn(NHC)(CO)(3)(dppe) and fac-Mn(NHC)(CO)(3)(bipy) have been tested as carbene transfer agents to the gold fragments Au(L) (L = PPh(3), CNPh, CNXylyl), allowing isolation or spectroscopic detection of various Mn(i)/Au(i) heterometallic intermediates containing azolyl bridging ligands, which liberate the gold(i) carbene complexes Au(NHC)(L) by means of acid hydrolysis. By contrast, when using the silver(i) fragment Ag(PPh(3)) as carbene acceptor no transmetallation process occurred but instead inverse tautomerization of the NHC to the corresponding imidazole ligand was observed.