Trapping Highly Reactive Metal(H)2(η2-H2) species to form Trihydride Complexes and Clusters

Metal dihydride dihydrogen-derived intermediates can be short-lived and difficult to detect despite their ubiquitous role in chemical transformations such as hydrogenation. Here, highly reactive [Ir(H)3(η2-η2-COD)(IMes)] forms by trapping [Ir(H)2(η2-H2)(η2-η2-COD)(IMes)]X [X = Cl or MeO], resulting from reaction of the Ir(I) precatalyst [IrCl(η2-η2-COD)(IMes)] with a base and H2. This trihydride allows access to the unusual [Ir2(H)4(OMe)(IMes)2(pyridine)3]X, [Ir2(H)2(µ2-H)2(η2-η2-COD)(IMes)2], [Ir3(H)9(IMes)3], [Ir4(H)12(IMes)4] and [Ir2(H)4(µ2-H)2(IMes)2(pyridine)2]. A combination of 2D NMR, parahydrogen hyperpolarized NMR, MS, and XRD are used to characterise these reaction products and rationalise their formation via the moiety {Ir(H)3(IMes)}. Consequently, the results of these studies have implications for iridium-catalyzed polarization transfer from parahydrogen via the well-known precursor [IrCl(η2-η2-COD)(IMes)].