Iridium Complexes of the Conformationally Rigid IBioxMe₄ Ligand: Hydride Complexes and Dehydrogenation of Cyclooctene

A method for accessing the formally 14 VE iridium­(III) hydride fragment {Ir­(IBioxMe₄)₂(H)₂}⁺ (2), containing the conformationally rigid NHC ligand IBioxMe₄, is reported. Hydrogenation of trans-[Ir­(IBioxMe₄)₂(COE)­Cl] (1) in the presence of excess Na­[BAr^F₄] leads to the formation of dimeric [{Ir­(IBioxMe₄)₂(H)₂}₂Cl]­[BAr^F₄] (3), which is structurally fluxional in solution and acts as a reservoir of monomeric 2 in the presence of excess halogen ion abstractor. Stable dihydride complexes trans-[Ir­(IBioxMe₄)₂(2,2′-bipyridine)­(H)₂]­[BAr^F₄] (4) and [Ir­(IBioxMe₄)₃(H)₂]­[BAr^F₄] (5) were subsequently isolated through in situ trapping of 2 using 2,2′-bipyridine and IBioxMe₄, respectively, and fully characterized. Using mixtures of 3 and Na­[BAr^F₄] as a latent source of 2, the reactive monomeric fragment’s reactivity was explored with excess ethylene and cyclooctene, and trans-[Ir­(IBioxMe₄)₂(C₂H₄)₂]­[BAr^F₄] (6) and cis-[Ir­(IBioxMe₄)₂(COD)]­[BAr^F₄] (7) were isolated, respectively, through sacrificial hydrogenation of the alkenes. Complex 6 is notable for the adoption of a very unusual orthogonal arrangement of the trans-ethylene ligands in the solid state, which has been analyzed computationally using energy and charge decomposition (EDA-NOCV). The formation of 7 via transfer dehydrogenation of COE highlights the ability to partner IBioxMe₄ with reactive metal centers capable of C–H bond activation, without intramolecular activation. Reaction of 7 with CO slowly formed trans-[Ir­(IBioxMe₄)₂(CO)₂]­[BAr^F₄] (8), but the equivalent reaction with bis-ethylene 6 was an order of magnitude faster, quantifying the strong coordination of COD in 7.