Synthesis and Catalytic Properties of Two Trinuclear Complexes of Rhodium and Iridium with the N-Heterocyclic Tris-carbene Ligand TIMEN<SUP>iPr</SUP>

Two trinuclear complexes of rhodium and iridium have been obtained by reaction of the tris-N-heterocyclic carbene ligand TIMEN^iPr and [(COD)MCl]<INF>2</INF> or [(COD)<INF>2</INF>M](BF<INF>4</INF>) (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.