화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.141, No.8, 3710-3716, 2019
Heterobimetallic Control of Regioselectivity in Alkyne Hydrostannylation: Divergent Syntheses of alpha- and (E)-beta-Vinylstannanes via Cooperative Sn-H Bond Activation
Cooperative Sn-H bond activation of hydrostannanes (Bu3SnH) by tunable heterobimetallic (NHC)Cu-[M-CO] catalysts ([M-CO] = FeCp(CO)(2) or Mn(CO)(5)) enables the catalytic hydrostannylation of terminal alkynes under mild conditions, with Markovnikov/anti-Markovnikov selectivity controlled by the Cu/M pairing. By using the (Me)IMesCu-FeCp(CO)(2) catalyst, a variety of alpha-vinylstannanes were produced from simple alkyl-substituted alkynes and Bu3SnH in high yield and good regioselectivity; these products are challenging to access under mononuclear metal-catalyzed hydrostannylation conditions. In addition, reversed regioselectivity was observed for aryl-substituted alkynes under the Cu/Fe-catalyzed conditions, affording the (E)-beta-vinylstannanes as major products. On the other hand, by using the IMesCu-Mn(CO)(5) catalyst, a variety of (E)-beta-vinylstannanes were produced from primary, secondary, and tertiary alkyl-substituted alkynes, thus demonstrating divergent regioselectivity for alkyne hydrostannylation controlled by Cu/Fe vs Cu/Mn pairing. Both methods are amenable to gram-scale vinylstannane synthesis as well as late-stage hydrostannylation in a natural-product setting. Mechanistic experiments indicate the syn addition of Bu3SnH to the alkynes and imply the involvement of Sn-H bond activation in the rate-determining step. Two distinct catalytic cycles were proposed for the Cu/Fe and Cu/Mn catalysis based on stoichiometric reactivity experiments.