Catalytic Carboxylation of Terminal Alkynes with Copper(I) Azothioformamide Complexes

Abstract

Redox-active azothioformamide (ATF) ligands produce coordination complexes with Cu(I) salts. A series of monosubstituted ligands were used to synthesize Cu(I) complexes and investigated for the catalytic insertion of carbon dioxide into terminal alkynes. The optimal catalytic conditions were found using phenylacetylene with 4 mol % of a halogen-bridged (μ-I)-para-substituted [(p-MeOATF-Cu(I)I)]2 dimer with 3 equiv of Cs2CO3 as the base in dimethyl sulfoxide under 1 atm of CO2 at 40 °C for 24 h, followed by treatment with HCl. A variety of aryl and alkyl substrates were evaluated giving yields from 47 to 99%. The reaction was computationally deconstructed, and a series of likely intermediates and associated energies are provided along with a proposed mechanism. Additionally, it was found that the conditions were suitable for one-pot esterification.