Reactivity of Hydride Bridges in High-Spin [3M–3(μ-H)] Clusters (M = Fe^II, Co^II)

The designed [3M–3­(μ-H)] clusters (M = Fe^II, Co^II) Fe₃H₃L (1-H) and Co₃H₃L (2-H) [where L^3– is a tris­(β-diketiminate) cyclophane] were synthesized by treating the corresponding M₃Br₃L complexes with KBEt₃H. From single-crystal X-ray analysis, the hydride ligands are sterically protected by the cyclophane ligand, and these complexes selectively react with CO₂ over other unsaturated substrates (e.g., CS₂, Me₃SiCCH, C₂H₂, and CH₃CN). The reaction of 1-H or 2-H with CO₂ at room temperature yielded Fe₃(OCHO)­(H)₂L (1-CO₂) or Co₃(OCHO)­(H)₂L (2-CO₂), respectively, which evidence the differential reactivity of the hydride ligands within these complexes. The analogous reactions at elevated temperatures revealed a distinct difference in the reactivity pattern for 2-H as compared to 1-H; Fe₃(OCHO)₃L (1-3CO₂) was generated from 1-H, while 2-H afforded only 2-CO₂.