Synthesis of N,O-heterocyclic carbene and coordination to rhodium(I) and copper(I)

5,7-Di-tert-butyl-3-phenyl benzoxazolium tetra fluoroborate 1 could be prepared by simple reaction of the corresponding aminophenol with triethyl orthoformate under acidic conditions. Both rhodium(I) and copper(I) complexes with benzoxazol-2-ylidene ligand were then efficiently synthesised in a straightforward and smooth manner involving the reaction of benzoxazolium salt 1 with metal precursor and an external base. The complexes have been fully characterised and used in metal-catalysed hydrosilylation of ketones, where they showed poor catalytic activity, presumably due to low stability of the complexes under those conditions. (C) 2009 Elsevier Ltd. All rights reserved.