2,5‐Norbornadiene C–C Coupling Reactions Mediated by Iridium Complexes

Abstract

The treatment of [{Ir(µ‐Cl)(cod)}2] (cod = 1,5‐cyclooctadiene) with 2,5‐norbornadiene (nbd) in the presence of triethylphosphane under an atmosphere of ammonia afforded the cation complex [Ir(κC,κC‐C21H24)(NH3)3(PEt3)]Cl (1a) and complex [Ir(κC,κC‐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 metallacycle has been found to occur through several steps. First, the nbd displaces the cod in [{Ir(µ‐Cl)(cod)}2] to give the IrIII chloro‐bridged complex [{Ir(κC,κC‐C14H16)(µ‐Cl)(η4‐C7H8)}2] (2), which bears a η4‐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(κC,κC‐C21H24)(µ‐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(κC,κC‐C14H16)Cl(η4‐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.