DFT studies on the mechanism of Ag₂ CO₃ -catalyzed hydroazidation of unactivated terminal alkynes with TMS-N₃ : An insight into the silver(I) activation mode

Silver-mediated hydroazidation of unactivated alkynes has been developed as a new method for the synthesis of vinyl azides. Density functional theory calculations toward this reaction reveal that terminal alkynes with TMS-N₃ participated hydroazidation proceed through HN₃ formation, deprotonation and silver acetylides formation, nucleophilic addition, and protonation of terminal carbon by AgHCO₃ . It is also found that water molecules and activation modes of Ag (I) have a significant influence on the title reaction mechanism. Initially, catalyst Ag₂ CO₃ coordinates preferentially with internal N atom of TMS-N₃ to assist water as hydrogen source and proton-shuttle in facilitating HN₃ formation. Then, the regioselective anti-addition of HN₃ to triple bond of active silver-acetylide or ethynyl carbinols affords product vinyl azide via Ag-C σ-bond activation or Ag…C π-coordination activation modes, and the former one is more favorable. The origin of the difference regioselectivity is ascribed to the electronic and orbital effects of the reactive sites. Moreover, Ag₂ CO₃ is the critical catalyst, acting as activator, base, and stabilizer to promote the HN₃ and vinyl azide formation. Water molecule plays an important role as proton shuttle to promote HN₃ and key active silver acetylides formation, thus improving the yield of product. © 2017 Wiley Periodicals, Inc.