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

Abstract

A series of new iridium(III) complexes containing pentamethylcyclopentadienyl (Cp ∗ = η 5-C 5Me 5) 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 ∗IrCl 2(napy)] ( 1), [Cp ∗IrCl(napy)]PF 6 ( 2), and [(Cp ∗IrCl) 2(H)(napy)]PF 6 ( 4), respectively. The crystal structure of [Cp ∗Ir(napy) 2](PF 6) 2 ( 3) has also been determined; the dicationic complex bore both monodentate and chelating napy ligands. Dinuclear Cp ∗Ir III complex bridged by napy was only isolable if two Ir III 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 N Ir N bond angles were only 60.5(2)–61.0(4)° and the Ir N C angles were 94.7(8)–96.7(8)°. The bridging coordination of napy in complex 4 also afforded a large strain, i.e., the Ir III 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 CDCl 3 or CD 2Cl 2 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 ∗IrCl 2(napy-κ N)]. The analogous diazido complex of [Cp ∗Ir(N 3) 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.