Divergent Reactivity of [OsCl 2 (PPh 3 ) 3 ]: Formation of a Cyclometalated Osmium(II) Acetate Complex and an Osmium Hydride Species

Osmium phosphine complexes remain considerably less explored than their ruthenium analogs, although their hydride chemistry and propensity for cyclometalation are relevant to understanding their reactivity under homogeneous catalytic conditions. Mononuclear osmium(II) acetate phosphine complexes are comparatively underexplored, particularly with regard to their formation pathways, structural diversity, and subsequent reactivity. Here, we investigate whether the established NaOAc‐mediated acetate chemistry of [RuCl 2 (PPh 3 ) 3 ] can be transferred to [OsCl 2 (PPh 3 ) 3 ] or whether divergent reactivity occurs. Treatment of [OsCl 2 (PPh 3 ) 3 ] with NaOAc in tBuOH does not afford the expected bis(acetato) analog but instead gives the cyclometalated osmium(II) acetate complex [Os(OAc)(PPh 3 ) 2 ( κ 2 ‐C,P‐C 6 H 4 PPh 2 )] ( 1 ). Multinuclear NMR spectroscopy, ESI‐ and LIFDI‐MS, and single‐crystal X‐ray diffraction confirm a κ 2 ‐O,O‐bound acetate ligand and a κ 2 ‐C,P‐cyclometalated phosphine. Complex 1 and [OsCl 2 (PPh 3 ) 3 ] show only low activity in the transfer hydrogenation of acetophenone using iPrOH and NaOiPr. Upon treatment with excess NaOiPr in iPrOH, both precursors afford spectroscopically similar white phosphine‐supported osmium hydride material. The 1 H and 31 P{ 1 H} NMR data closely match reported values for [OsH 4 (PPh 3 ) 3 ], while LIFDI‐MS data are consistent with hydrogen‐loss fragments derived from an Os(PPh 3 ) 3 ‐based species. Overall, the osmium system does not simply mirror the corresponding ruthenium chemistry but instead follows distinct pathways involving cyclometalation and hydride formation.