Silver complexes of 1,2,4-triazole derived N-heterocyclic carbenes: Synthesis, structure and reactivity studies

Two silver(I) complexes {[1-R-4-(N-t-butylacetamido)-1,2,4-triazol-5-ylidene](2)Ag}(+) Cl- [R = Et (1b), i-Pr (2b)] of N/O-functionalized N-heterocyclic carbenes derived from 1,2,4-triazoles are reported. The silver complexes, 1b and 2b, have been synthesized from the reaction of the N/O-functionalized triazolium chloride salts namely, 1-R-4-(N-t-butylacetamido)-1,2,4-triazolium chloride [R = Et (1a), i-Pr (2a)] by treatment with Ag2O in 53-56% yield. The 1,2,4-triazolium chloride salts 1a and 2a were prepared by the allcylation reaction of 1-R-1,2,4-triazole (R = Et, i-Pr) with N-t-butyl-2-chloro acetamide in 47-63% yield. The molecular structures of the silver(I) complexes, 1b and 2b, have been determined by X-ray diffraction studies. The density functional theory studies on the silver 1b and 2b complexes suggest that the 1,2,4-triazole derived N-heterocyclic carbenes to be strong sigma-donating ligands similar to the now much recognized imidazole-based N-heterocyclic carbenes. The reactivity studies with (SMe2)AuCl and (SMe2)CuBr indicated the silver complexes, 1b and 2b, to be good transmetallating agents.