Trans-esterification Reaction Catalyzed by Alkoxo(triphenylphosphine)copper(I) Complexes

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Abstract
Alkoxocopper and phenoxocopper complexes ROCu (PPh3)n (PPh3=triphenylphosphine; n=1 for R=n-C3H7 or i-C3H7; n=2 for R=CH3, C2H5, CH2=CHCH2, C6H5CH2, or C6H5) react with esters undergoing exchange of the RO group with carboxylic esters. The alkoxocopper and phenoxocopper complexes are found to be excellent catalysts for the trans-esterification of carboxylic esters, dimethyl carbonate, and trimethyl phosphite with alcohols and phenols. A comparison of the ability of the isopropoxocopper complex as trans-esterification catalyst with that of aluminum isopropoxide and titanium isopropoxide shows the superiority of the isopropoxocopper complex. The rate of trans-esterification between p-nitrophenyl acetate and phenol follows the second-order rate law R=k[p-nitrophenyl acetate][phenol], the activation energy of the reaction being estimated to be 12.4 kcal/mol. A mechanism comprising a nucleophilic attack on the copper-bound carbonyl group of the ester by alcohol is proposed.
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