Novel diphosphine-modified palladium catalysts for oxidative carbonylationof styrene to methyl cinnamate

The oxidative carbonylation of styrene has been achieved in MeOH with known and new palladium(II) catalysts of general formulae [Pd(P-P)(MeCN)(2)][PF6 ](2), [Pd(P-P)(bipy)][PF6](2), Pd(P-P)(OAc)(2), [Pd-2(cyclo-tetraphos)(MeCN )(4)][PF6](4), [Pd-2(cyclo-tetraphos)(bipy)(2)][PF6](4), Pd-2(cyclo-tetraph os)(OAc)(4) (P-P=1,2-bis(diphenylphosphino)ethane), meso-2,3-bis(diphenylph osphino)butane or rac-2,3-bis(diphenylphosphino)butane; cyclo-tetraphos=cis ,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane; bipy=2,2'-bipyri dine; OAc=acetate). The influence of various catalytic parameters on the ov erall conversion of styrene into carbonylated products and on the product s electivity has been studied by systematically varying the type of palladium initiator, the concentrations of organic oxidant (1,4-benzoquinone) and pr otic acid (p-toluenesulfonic acid), and the CO pressure. This investigation has allowed a partial optimization of the process so as to obtain the larg ely predominant formation of either methyl cinnamate (highest selectivity 9 9%) or dimethyl phenylsuccinate (highest selectivity 88%).