Abstract
Density functional theory (DFT) calculations with the B3LYP functionals elucidated the reactivity, selectivity, and mechanisms of a rhodium-catalyzed intermolecular [2 + 2] cycloaddition of terminal alkynes with electron-deficient alkenes. The most plausible reaction pathway was discussed as three distinct processes in full catalytic cycles, including (1) substrate exchange, (2) nucleophilic addition and cyclization, and (3) separation of product and recycling of catalyst; the formal [2 + 2] cycloaddition indeed proceeded through a rate-determining and stepwise addition–cyclization process. We then compared the outer-sphere and inner-sphere mechanisms for the formation of cyclobutene intermediates and reported that the former pathway is more accessible kinetically and thus more competitive, being contrary to the proposed mechanism for some nickel-catalyzed cycloaddition reactions in the literature. Furthermore, the substituent effect has been investigated using various alkenes CH2═CHR (R = COOMe, CN, H, C...
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