2,5-Norbornadiene C–C coupling reactions mediated by Iridium complexes

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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.
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