Synergetic Catalysis for One-pot Bis-alkoxycarbonylation of Terminal Alkynes over Pd/Xantphos−Al(OTf)3 Bi-functional Catalytic System
Graphical Synergetic catalysis : 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 . 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. 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 1 H/ 13 C 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 Pd 0 by H + (Pd 0 +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.
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