Abstract
Density functional theory calculations have been performed to investigate the mechanism of the reactions of amines with primary alcohols to produce amides, catalyzed by the pincer complex Ru(II)-PNN (PNN = 2-(di-tert-butylphosphinomethyl)-6-diethylaminomethyl)pyridine). The results lead us to propose a catalytic cycle that includes four stages: (stage I) alcohol dehydrogenation to aldehyde, (stage II) coupling of aldehyde with amine to form hemiaminal, (stage III) hemiaminal dehydrogenation to amide, and (stage IV) catalyst regeneration via H2 elimination of the trans Ru dihydride complex produced in the two dehydrogenation stages. Both of the dehydrogenation reactions proceed via the bifunctional double hydrogen transfer mechanism rather than the β-H elimination mechanism. The selectivity of amide over ester is determined by the coupling stage in which the aldehyde∧amine coupling to give hemiaminal is more favorable than aldehyde∧alcohol coupling to give hemiacetal. The competition between dehydrogenatio...
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