Monodentate, didentate chelating, and bridging 1,8-naphthyridine complexes of pentamethylcyclopentadienyliridium(III): Syntheses and structures in the solid states and in solution

A series of new iridium(III) complexes containing pentamethylcyclopentadienyl (Cp∗ = η5-C5Me5) and 1,8-naphthyridine (napy) have been prepared. X-ray crystallography revealed that napy acted as a monodentate, a didentate chelating, and a bridging ligand in complexes of [Cp∗IrCl2(napy)] (1), [Cp∗IrCl(napy)]PF6 (2), and [(Cp∗IrCl)2(H)(napy)]PF6 (4), respectively. The crystal structure of [Cp∗Ir(napy)2](PF6)2 (3) has also been determined; the dicationic complex bore both monodentate and chelating napy ligands. Dinuclear Cp∗IrIII complex bridged by napy was only isolable if two IrIII centers were supported by a hydride (H−) bridge. In complexes 2 and 3, the four-membered chelate rings formed by napy exhibited a large steric strain; in the rings the Nsingle bondIrsingle bondN bond angles were only 60.5(2)–61.0(4)° and the Irsingle bondNsingle bondC angles were 94.7(8)–96.7(8)°. The bridging coordination of napy in complex 4 also afforded a large strain, i.e., the IrIII centers were displaced by 0.84(3) Å from the napy plane, due to the steric interaction between two Cp∗IrCl moieties. The monodentate napy complex 1 in CDCl3 or CD2Cl2 at ambient temperature showed a rapid coordination-site exchange reaction, which gave two N sites of napy equivalent; at temperatures below −40 °C, the 1H NMR spectra corresponded to the molecular structure of [Cp∗IrCl2(napy-κN)]. The analogous diazido complex of [Cp∗Ir(N3)2(napy)] (5) has also been prepared, and the crystal structure has been determined. In contrast to the dichloro complex 1, the diazido complex 5 exhibited a dissociation equilibrium of coordinated napy in solution.