Reactivity and Regioselectivity of Insertion of Unsaturated Molecules into M−C (M = Ir, Rh) Bonds of Cyclometalated Complexes

The reactivity of four different cyclometalated iridium and rhodium complexes (1, Ir−N−Me; 2, Rh−N−Me; 3, Ir−N−Py; 4, Rh−N−Py) with ancillary ligands with different electronic and steric properties has been investigated by reactions of ethylene (a), propylene (b), carbon monoxide (c), tert-butylisocyanide (d), acetylene (e), and phenylacetylene (f). Only coordination products were obtained for the reactions of ethylene and propylene with 1 and 3, while inserted and rearranged products were achieved for the reactions with 2 and 4. Insertion of a single equivalent of acetylene was observed for the reactions with 2, 3, and 4, whereas reaction with 1 produces a product in which 4 equiv of acetylene has undergone insertion. The reactions with carbon monoxide showed clean M−C bond insertion products, while tert-butylisocyanide formed only terminal adducts. Two equivalents of phenylacetylene were observed to insert for all of the cyclometalated complexes. The regioselectivity was also investigated for each cyclometalated complex by using a series of internal unsymmetrical alkynes, and the results revealed that the regioselectivity was controlled by both steric and electronic factors. The insertion compounds were fully characterized by ¹H NMR spectroscopy, ¹³C NMR spectroscopy, elemental analysis, and X-ray determinations for selected cases.