Remarkable transformations of thiophene ligands in their pentamethylcyclopentadienyl iridium (Cp*Ir) complexes

The cationic eta(5)-2,5-dimethylthiophene complex Cp*Ir(eta(5)-2,5-Me2T)(2+) (1) is the entry point for the synthesis of a variety of complexes resulting from nucleophilic attack on or reduction of 1. Reduction gives Cp*Ir(eta(4)-2,5-Me2T) (4), in which the thiophene ligand is coordinated through only the four carbon atoms, and its isomer Cp*Ir(C,S-2,5-Me2T) (5) in which there is a six-membered aromatic ring incorporating the original thiophene and iridium. These isomers undergo a range of reactions with Lewis acids, bases, and mono- and polynuclear transition metal complexes. Analogous studies of benzo[b]thiophene and dibenzothiophene complexes are also reviewed. (C) 2000 Elsevier Science S.A. All rights reserved.