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  • Title: Counterintuitive kinetics in Tsuji-Trost allylation: ion-pair partitioning and implications for asymmetric catalysis.
    Author: Evans LA, Fey N, Harvey JN, Hose D, Lloyd-Jones GC, Murray P, Orpen AG, Osborne R, Owen-Smith GJ, Purdie M.
    Journal: J Am Chem Soc; 2008 Nov 05; 130(44):14471-3. PubMed ID: 18839958.
    Abstract:
    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.
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