A Kinetics Study of the Oxidative Addition of Bromobenzene to Pd(PCy3)2(Cy = cyclohexyl) in a Nonpolar Medium: The Influence on Rates of Added PCy3and Bromide Ion

Bromobenzene oxidatively adds to the palladium(0) compound Pd(PCy 3 ) 2 to give cleanly the palladium(II) product trans -PdBr(Ph)(PCy 3 ) 2 . Kinetics studies of this reaction under pseudo-first-order conditions (excess PhBr) as well as in the presence of 1 molar equiv of PCy 3 or of added bromide ion (as the toluene-soluble tetraoctylphosphonium salt) have been carried out. We find that oxidative addition is first-order in palladium and that, in the absence of added PCy 3, the reaction involves both the 2:1 species Pd(PCy 3 ) 2 and the 1:1 species Pd(PCy 3 ). Interestingly, added PCy 3 results in inhibition of oxidative addition both by decreasing the relative amount of the reactive 1:1 compound and by converting much of the palladium(0) to the kinetically less active 3:1 compound Pd(PCy 3 ) 3 . Added bromide ion has essentially no effect on the rate, surprising in view of previous literature reports.