Cobalt- and Iron-Catalyzed Isomerization–Hydroboration of Branched Alkenes: Terminal Hydroboration with Pinacolborane and 1,3,2-Diazaborolanes
作者:Takahiko Ogawa、Adam J. Ruddy、Orson L. Sydora、Mark Stradiotto、Laura Turculet
DOI:10.1021/acs.organomet.6b00823
日期:2017.1.23
The synthesis and characterization of a series of structurally varied N-phosphinoamidinate-ligated cobalt complexes is described, along with the successful application of these and a related iron complex as precatalysts in the isomerization hydroboration of terminal, geminal, and internal alkenes. These reactions proceed under mild conditions (23-65 degrees C), at relatively low base-metal loadings (1-5 mol %), typically without cosolvent, and with high terminal hydroboration selectivity across a broad spectrum of branched alkenes. With some of the alkene substrates examined, the Nphosphinoamidinate-ligated precatalysts employed herein are shown to provide alternative terminal selectivity versus other previously reported precatalyst classes for such transformations. Reports of terminal-selective metal-catalyzed alkene isomerization hydroboration disclosed thus far in the literature employ pinacolborane (HBPin); while effective in the system herein, we also report the first examples of such transformations employing either 1,3-dimethyl-1,3-diaza-2-boracydopentane or benzo-1,3,2-diazaborolane. The application of these 1,3,2-diazaborolanes in place of HBPin in some instances enables novel terminal selectivity in the isomerization hydroboration of branched alkenes.