Synthesis and catalytic properties of two trinuclear complexes of rhodium and iridium with the N-heterocyclic tris-carbene ligand TIMENiPr

Two trinuclear complexes of rhodium and iridium have been obtained by reaction of the tris-N-heterocyclic carbene ligand TIMENiPr and [(COD)MCl](2) or [(COD)(2)M](BF4) (M = Rh and Ir). The new complexes have been fully characterized by means of NMR spectroscopy and single-crystal X-ray diffraction studies. The trinuclear rhodium complex shows efficient activity in cyclization of acetylenic carboxylic acids, ranking among the highest known for this type of reaction.