Mechanism of C-P Reductive Elimination from trans-[Pd(CH=CHPh)Br(PMePh2)2]

The (E)- and (Z)-styryl isomers of trans-[Pd(CH=CHPh)Br(PMePh2)(2)] (1a) and [Pd(eta(2)-PhCH= CHPMePh2)Br(PMePh2)] (2a) were prepared, and their C-P reductive elimination (1a -> 2a) and C-P oxidative addition (2a -> 1a) behaviors examined. Kinetics and thermodynamics of the reactions are strongly affected by E/Z configurations of the styryl group and solvent polarity. Complex (E)-1a readily undergoes C-P reductive elimination in CD2Cl2 as a polar solvent in high selectivity. On the other hand, while the (Z)-isomer of la is unreactive toward reductive elimination, (Z)-2a undergoes C-P oxidative addition favorably in nonpolar benzene. X-ray diffraction analysis and DFT calculations for 1a and 2a provided reasonable accounts for these reaction features. Kinetic examinations revealed two types of C-P reductive elimination processes, which involve predissociation and association of the PMePh2 ligand, respectively.