Scope and Mechanism of the Pt-Catalyzed Enantioselective Diboration of Monosubstituted Alkenes

The
Pt-catalyzed enantioselective diboration of terminal alkenes
can be accomplished in an enantioselective fashion in the presence
of chiral phosphonite ligands. Optimal procedures and the substrate
scope of this transformation are fully investigated. Reaction progress
kinetic analysis and kinetic isotope effects suggest that the stereodefining
step in the catalytic cycle is olefin migratory insertion into a Pt–B
bond. Density functional theory analysis, combined with other experimental
data, suggests that the insertion reaction positions platinum at the
internal carbon of the substrate. A stereochemical model for this
reaction is advanced that is in line both with these features and
with the crystal structure of a Pt–ligand complex.