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

Chloride abstraction from [(R,R)-((iPr)DuPhos) Co(mu-Cl)](2) with NaBAr4F (BAr4F= 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)((iPr)DuPhos) Co(eta(2), eta(2)-diene)][BAr4F]. 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)][BAr4F] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt-substrate complex, [(R,R)-((iPr)DuPhos)Co(MAA)][BAr4F] (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.