Molecular Orbital Study of the Mechanism of Platinum(0)-Catalyzed Alkene and Alkyne Diboration Reactions

Abstract

A theoretical study has been carried out for the mechanism of Pt(0)-catalyzed alkyne and alkene diboration reactions with the B3LYP density functional method. Two different paths are studied, path A where the first step is B−B oxidative addition and path B where the first step is alkyne/alkene coordination. Though the coordination energy of acetylene and ethylene to Pt(PH3)2 is larger than the energy gain of oxidative addition of (OH)2B−B(OH)2 to Pt(PH3)2, the trend reverses as the size of substituents on alkynes, alkenes, and (OH)2B−B(OH)2 increases, and for large alkynes path A is expected to be favored over path B. Path A has been shown to proceed via the following steps: (a) coordination of (OH)2B−B(OH)2 to Pt(PH3)2, (b) oxidative addition of the B−B bond to Pt, (c) dissociation of one phosphine ligand, (d) coordination of alkyne/alkene to form a π-complex, (e) migratory insertion of alkyne/alkene into a Pt−B bond, (f) migration of the CHxCHxB(OH)2 (x = 1 or 2) group to become cis to B(OH)2, (g) reco...