Synthesis of Pd(ii)–NHC complexes via C–H oxidative addition of triazolium salts to Pd(0)

Abstract

We report the first example of direct C–H oxidative addition of 1,2,4-triazolium salts to Pd₂(dba)₃, providing a new route to palladium N-heterocyclic carbene (NHC) complexes. Three triazolium ligands, 4-benzyl-1-butyl-1,2,4-triazolium bromide, 4-benzyl-1-methyl-1,2,4-triazolium bromide and 1,4-dibutyl-1,2,4-triazolium bromide were synthesized and reacted with Pd₂(dba)₃. This reaction occurs in air and proceeds efficiently in 1–3 hours to afford air stable, mostly trans, [Pd(NHC)₂Br₂] complexes. The complexes are isolated in good yield and fully characterized. All complexes exhibit NMR evidence of rotamers (anti and syn). The structures of three complexes were confirmed by single-crystal X-ray diffraction.