Iridium Complexes of the Conformationally Rigid IBioxMe<sub>4</sub> Ligand: Hydride Complexes and Dehydrogenation of Cyclooctene

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