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

Abstract

Abstract Chloride abstraction from [( R , R )‐( iPr DuPhos)Co(μ‐Cl)] 2 with NaBAr F 4 (BAr F 4 =B[(3,5‐(CF 3 ) 2 )C 6 H 3 ] 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 )‐( iPr DuPhos)Co(η 2 ,η 2 ‐diene)][BAr F 4 ]. 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 )‐( iPr DuPhos)Co(diene)][BAr F 4 ] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt–substrate complex, [( R , R )‐( iPr DuPhos)Co(MAA)][BAr F 4 ] (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.