Abstract
Chloride abstraction from [(R,R)-(iPr DuPhos)Co(μ-Cl)]2 with NaBArF 4 (BArF 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)][BArF 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)][BArF 4 ] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt-substrate complex, [(R,R)-(iPr DuPhos)Co(MAA)][BArF 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.
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