摘要：

Lanthanide trifluoromethanesulfonates, Ln(OTf)(OTf= trifluoromethanesulfonate), serve as effective precatalysts for the rapid, regioselective, intermolecular acylation of activated arenes. This contribution probes mechanism and metal ionic radius effects in the catalytic lanthanide triflate-mediated acylation of anisole with acetic anhydride. Kinetic studies of Ln(OTf) (Ln = La, Eu, Yb, Lu)-mediated anisole acylation with acetic anhydride in nitromethane reveal the rate law ∼ [Ln][acetic anhydride][anisole]. Eyring and Arrhenius analyses yield ΔH= 12.9 (4) kcal mol, ΔS= -44.8 (1.3) e.u., and = 13.1 (4) kcal molfor Ln = Yb, with the negative ΔSimplying a highly organized transition state. The observed primary kinetic isotope effect of /= 2.6 ± 0.15 is consistent with arene C-H bond scission in the turnover-limiting step. The proposed catalytic pathway involves precatalyst formation via interaction of Ln(OTf)with acetic anhydride, followed by Ln-anisole π-complexation, substrate-electrophile σ-complex formation, and turnover-limiting C-H bond scission. Lanthanide size effects on turnover frequencies are consistent with a transition state lacking significant ionic radius-dependent steric constraints. Substrate-Ln interactions using paramagnetic Gdand YbNMR probes, and factors affecting reaction rates such as arene substituent and added LiClOcocatalyst are also explored.

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