Cationic cobalt(I) catalysts for the asymmetric cyclocarbonylation of 1,6-enynes

Abstract

Cobalt(I) complexes, modified with (R)-(6,6'-dimethoxybiphenyl-2,2'-diyl)bis(diphenylphosphine) [Co((R)-MeO-Biphep)(CO)3]X (X = BF4 [1] or OTf [2]), were synthesized and characterized. The compounds have a trigonal bipyramidal structure and are fluxional. They were tested as catalyst precursors for the enantioselective cyclocarbonylation of 4,4-bis(carboethoxy)hept-5-en-1-yne 3. Enantioselectivities up to 78.5% were attained. However, activity and stereoselectivity are lower compared to catalytic systems based on Co2(CO)8 modified with the same atropisomeric ligand.

Enantioselective Cobalt-Catalyzed Transformations

“…In 2002, Buchwald and Sturla demonstrated that enantioselectivities of up to 75% ee could be achieved in comparable reactions by using chiral aryl bisphosphite ligands . In 2004, enantioselectivities of up to >91% ee combined with high yields of up to 95% were reported by Consiglio et al employing ( R )-MeO-BIPHEP as chiral ligand of Co 2 (CO) 8 in the cyclocarbonylation of 4,4-bis­(carboethoxy)­hex-6-en-1-yne …”