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

Abstract

Chloride abstraction from [(R,R)-(^iPr DuPhos)Co(μ-Cl)]₂ with NaBAr^F ₄ (BAr^F ₄ =B[(3,5-(CF₃ )₂ )C₆ H₃ ]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(η² ,η² -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.

Keywords: alkene hydrogenation; asymmetric catalysis; catalyst-substrate complex; cobalt.