Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

Chloride abstraction from [(R,R)‐(^iPrDuPhos)Co(μ‐Cl)]₂ with NaBAr^F₄ (BAr^F₄=B[(3,5‐(CF₃)₂)C₆H₃]₄) in the presence of dienes, such as 1,5‐cyclooctadiene (COD) or norbornadiene (NBD), yielded long sought‐after cationic bis(phosphine) cobalt complexes, [(R,R)‐(^iPrDuPhos)Co(η²,η²‐diene)][BAr^F₄]. The COD complex proved substitutionally labile undergoing diene substitution with tetrahydrofuran, NBD, or arenes. The resulting 18‐electron, cationic cobalt(I) arene complexes, as well as the [(R,R)‐(^iPrDuPhos)Co(diene)][BAr^F₄] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt–substrate complex, [(R,R)‐(^iPrDuPhos)Co(MAA)][BAr^F₄] (MAA=methyl 2‐acetamidoacrylate) was crystallographically characterized as the opposite diastereomer to that expected for productive hydrogenation demonstrating a Curtin–Hammett kinetic regime similar to rhodium catalysis.