Synergetic Catalysis for One-pot Bis-alkoxycarbonylation of Terminal Alkynes over Pd/Xantphos−Al(OTf)₃ Bi-functional Catalytic System

Tandem bis-alkoxycarbonylation of alkynes allows for the preparation of 2-substituted succinates from alkynes and nucleophile alcohol via two successive alkoxycarbonylation with advantages of 100 % atomic economy and simplified one-pot operation. Herein, the one-pot tandem bis-alkoxycarbonylation of alkynes was accomplished over the bi-functional catalytic system containing Xantphos-modified Pd-complex and Lewis super-acid of Al(OTf)₃. It was found that, via the synergetic catalysis, the involved Xantphos-modified Pd-complex was responsible for the activation of CO and the alkynes through coordination to Pd-center while Al(OTf)₃ was in charge of the activation of the alcohol to facilitate the formation of [Pd−H]⁺ active species. The in situ high-pressure FT-IR analysis, coupled with ¹H/¹³C NMR spectral characterizations, confirmed that the introduced Al(OTf)₃ with intensive oxophilicity (via acid-base pair interaction) was able to activate nucleophilic MeOH to be a reliable proton-donor (i. e. hydride-source) to warrant the formation and stability of [Pd−H]⁺ species upon the oxidation of Pd⁰ by H⁺ (Pd⁰+H⁺→[Pd^II−H]⁺). Over the developed bi-functional catalytic system, the yields of the target diesters were obtained in the range of 36∼86 % in this sequence with the wide substrate scope.