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 (η 2 ‐η 2 ‐COD)(IMes)] forms by trapping [Ir(H) 2 (η 2 ‐H 2 )(η 2 ‐η 2 ‐COD)(IMes)]X [X=Cl or MeO], resulting from reaction of the Ir(I) precatalyst [IrCl(η 2 ‐η 2 ‐COD)(IMes)] with a base and H 2 . This trihydride allows access to the unusual [Ir 2 (H) 4 (OMe)(IMes) 2 (pyridine) 3 ]X, [Ir 2 (H) 2 (μ 2 ‐H) 2 (η 2 ‐η 2 ‐COD)(IMes) 2 ], [Ir 3 (H) 9 (IMes) 3 ], [Ir 4 (H) 12 (IMes) 4 ] and [Ir 2 (H) 4 (μ 2 ‐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(η 2 ‐η 2 ‐COD)(IMes)].