Counterintuitive kinetics in Tsuji-Trost allylation: ion-pair partitioning and implications for asymmetric catalysis

The kinetics of Pd-catalyzed Tsuji-Trost allylation employing simple phosphine ligands (L = Ar3P, etc.) are consistent with turnover-limiting nucleophilic attack of an electrophilic L2Pd(allyl)]+ catalytic intermediate. Counter-intuitively, when L is made more electron donating, which renders L2Pd(allyl)]+ less electrophilic (by up to an order of magnitude), higher rates of turnover are observed. In the presence of catalytic NaBAr'F, large rate differentials arise by attenuation of ion-pair return (via generation of L2Pd(allyl)]+ BAr'F]-) a process that also increases the asymmetric induction from 28 to 78% ee in an archetypal asymmetric allylation employing BINAP (L*) as ligand. There is substantial potential for analogous application of M]n+(BAr'F]-)n cocatalysis in other transition metal catalyzed processes involving an ionic reactant or reagent and an ionogenic catalytic cycle.