DFT studies on the mechanism of Ag₂CO₃‐catalyzed hydroazidation of unactivated terminal alkynes with TMS‐N₃: An insight into the silver(I) activation mode

Abstract

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-N participated hydroazidation proceed through HN formation, deprotonation and silver acetylides formation, nucleophilic addition, and protonation of terminal carbon by AgHCO . It is also found that water molecules and activation modes of Ag (I) have a significant influence on the title reaction mechanism. Initially, catalyst Ag CO coordinates preferentially with internal N atom of TMS-N to assist water as hydrogen source and proton-shuttle in facilitating HN formation. Then, the regioselective anti-addition of HN 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, Ag CO is the critical catalyst, acting as activator, base, and stabilizer to promote the HN and vinyl azide formation. Water molecule plays an important role as proton shuttle to promote HN and key active silver acetylides formation, thus improving the yield of product. © 2017 Wiley Periodicals, Inc.

Distinct Roles of Ag(I) and Cu(II) as Cocatalysts in Achieving Positional-Selective C–H Alkenylation of Isoxazoles: A Theoretical Investigation

“…Possible heterodimetallic Pd­(OAc) 2 –Ag 2 CO 3 ( Pd-Ag-cat1 ) and Pd­(OAc) 2 –AgOAc ( Pd-Ag-cat2 ) catalysts could be generated in situ using the palladium acetate and silver salt additives (Scheme ). A salient feature of these bimetallic systems is the short Pd–Ag contact (2.91 and 2.90 Å), which is shorter than the sum of the van der Waals radii of Pd and Ag (3.35 Å), thereby suggesting a significant heterodimetallic d 8 –d 10 interaction . The Gibbs energy of Pd-Ag-cat1 is 18.2 kcal/mol lower than that of trimeric Pd­(OAc) 2 and can be considered as the genuine active catalyst in reaction B.…”

α-Substituted vinyl azides: an emerging functionalized alkene

“…A silver acetylide species is then thought to be generated, which undergoes nucleophilic addition by HN 3 , with protodemetallation yielding the vinyl azide. 28 The 2-azidoallyl alcohol products were further converted into useful synthons including α-carbonyl vinyl azides, and N-H aziridines, on treatment with pyridinium chlorochromate and K 3 PO 4 respectively. Furthermore, by adding a stoichiometric amount of H 2 O, the reaction was extended to simple terminal alkynes 17d (nitriles were produced in anhydrous solvents).…”

AgN3-Catalyzed Hydroazidation of Terminal Alkynes and Mechanistic Studies

“…However, the hydroazidation of alkynes is primarily dependent on the Michael addition of azide anions to the activated alkynes . In terms of more general unactivated alkynes, no efficient method was available until we reported a Ag 2 CO 3 -catalyzed hydroazidation reaction of terminal alkynes in 2014 (Figure a) . Since then, our group and others have further demonstrated the power of this method by developing a wide variety of tandem reactions involving such a silver-catalyzed reaction as a critical step. ,, However, this fundamental reaction has not yet been well-developed because of the following significant issues: (1) the reaction mechanism is unclear; (2) the loading of silver salt is high (equal to 20 mol % Ag), which has seriously limited the practicality of this method.…”