2,5-Norbornadiene C-C Coupling Reactions Mediated by Iridium Complexes

The treatment of [{Ir(mu-Cl)(cod)}(2)] (cod = 1,5-cyclooctadiene) with 2,5-norbornadiene (nbd) in the presence of tri-ethylphosphane under an atmosphere of ammonia afforded the cation complex [Ir(kappa C,kappa C-C21H24)(NH3)(3)(PEt3)] Cl (1a) and complex [Ir(kappa C,kappa C-C21H24) Cl(NH3)(2)(PEt3)] (1b), the structures of which include a novel seven-membered iridacycle formed by three half-coupled nbd molecules. The formation of the metal-lacycle has been found to occur through several steps. First, the nbd displaces the cod in [{Ir(kappa-Cl)(cod)}(2)] to give the Ir-III chloro-bridged complex [{Ir(kappa C,kappa C-C14H16)(kappa-Cl)(eta(4)-C7H8)}(2)] (2), which bears a eta(4)-C= C-coordinated nbd and a five-membered iridacycle formed by two half-coupled nbd moieties. Further reaction with PEt3 induces the C-C coupling between the iridacycle and the coordinated nbd to give the chloro-bridged complex [{Ir(kappa C,kappa C-C21H24)(mu-Cl)(PEt3)} 2] (4). Finally, 4 reacts with gaseous ammonia to split the chloro bridges and form species 1a and 1b. Also, complex 2 was found to react with several donor ligands to afford the corresponding mononuclear adducts [Ir(kappa C,kappa C-C14H16) Cl(eta(4)-C7H8)(L)] [L = py (5), NH3 (6), PMe2Ph (7), tBuNC (8)]. The X-ray molecular structures of 5, 7 and 8 show the presence of a five-membered iridacycle, but their stereochemistries differ by virtue of the relative locations of the respective added ligand.