Iridaoxacyclohexadiene-Bridged Mixed-Valence Iridium Cyclooctadiene Complex: Oxidative Addition and Hydrogen-Transfer to Coordinated Cyclooctadiene

The systematic exploration of the synthesis of heteropentadienyl metal complexes leads us to study the metathesis reaction of [(η4-COD)­Ir­(μ2-Cl)]2 with lithium 2,4-dimethyl­oxopentadienide, which affords the dinuclear Ir0–IrII compound (η4-COD)­Ir­[η1:1-μ2-η4-CHC­(Me)­CHC­(Me)­O)]­Ir­(η4-COD) (1) with a metal–metal bond. The COD ligands are coordinated η4 to each Ir center, whereas the oxopentadienyl ligand is bridging both Ir atoms, allowing the formation of a novel iridapyran complex with IrII and bonding η4 with Ir0. The addition of CO, PMe3, and PMe2Ph to the coordinatively unsaturated complex 1 has led, under mild conditions, to the corresponding dinuclear coordinatively saturated compounds (η4-COD)­Ir­[η1:1-μ2-η3-CHC­(Me)­CHC­(Me)­O)]­Ir­(η4-COD)­(μ2-CO) (2) and (η4-COD)­Ir­[η1:1-μ2-η4-CHC­(Me)­CHC­(Me)­O)]­Ir­(η4-COD)­(PR3) (R = Me, 3; PR3 = PMe2Ph, 4). Compound 3 showed a reversible reaction by dissociation of PMe3, recovering compound 1. The reaction of 1 with H2 and PMe3, PMe2Ph, and P­(n-Bu)3 allows the isolation of cyclooctenyl derivatives (η4-COD)­Ir­[η1:1-μ2-η3-CHC­(Me)­CHC­(Me)­O)]­Ir­(μ2-H)­(η1:η2-C8H13)­(PR3) (R = Me, 5; R3 = Me2Ph, 6; R = n-Bu, 7), where the hydrogen promotes the formation of a metal-hydride, as well as hydrogen-transfer to one of the coordinated cyclooctadiene ligands. In the presence of molecular hydrogen, 4 leads also to the formation of 6 in better yield. The iridaoxacycle bridging ligand stabilizes these dinuclear iridium complexes, which easily undergo intermolecular insertion into activated C–H bonds. When the more sterically demanding phosphine P­(i-Pr)3 is added in the presence of H2, a different reaction takes place, with the displacement of one COD ligand and the formation of (η4-COD)­Ir­(μ2-H)­[η1:1-μ2-η3-CHC­(Me)­CHC­(Me)­O)]­Ir­(H)­(Pi-Pr3)2 (8). The novel complexes 1–8 have been fully characterized, where 1 shows dynamic behavior in one of the COD ligands in solution and gives evidence of two different isomers present in the crystalline structure. Molecular structures of 1–3 and 5–8 have been determined by single-crystal X-ray diffraction studies.