Synthesis, structure and reactivity of homobimetallic Rh(I) and Ir(I) complexes of s- and as-indacene-diide

The Rh(COD) and Ir(COD) homobimetallic complexes of s-indacene-diide. 2,6-dimethyl-s-indacene-diide, as-indacene-diide, and 2,7-dimethyl-as-indacene-diide have been synthesized from the di-lithium salts of the dianions and metal dimers [M(mu-Cl)L-2](2) (M = Rh, Ir; L-2 = COD, NBD, (ethylene)(2), (CO)(2)) as mixtures of syn and anti isomers. The syn/anti ratio depends on the nature of the ancillary ligands at the metal and on the s or as geometry of the bridging ligand. In the reaction of the 2,7-dimethyl-as-indacene-diide-[M(COD)](2) species with CO, the higher reactivity of the syn isomers has been justified on the basis of a greater instability of the ground state due to steric interactions between the COD groups. Bis-eta(1) metal-bonded intermediates have been identified in the carbonylation of iridium derivatives; on the other hand, the formation of the bis-eta(5) mixed complexes syn and anti-(2,7-dimethyl-as-indacene-diide-[Rh and their reactivity strongly support the existence of metal-metal interaction in the rhodium derivatives. (C) 2000 Elsevier Science S.A. All rights reserved.