C2-Symmetric normal and mesoionic bis-N-heterocyclic carbenes with biphenyl backbone. A comparison of bis(1,2,3-triazol-5-ylidene) and bis(imidazol-2-ylidene) ligands

Abstract

C-2-Symmetric normal and mesoionic bis-N-heterocyclic carbenes (NHCs) derived from 1,1'((1,1'-biphenyl)-2,2'-diylbis(methylene))bis(3-methyl-4-phenyl-1H-1,2,3-triazol-3-ium) diiodide (5) and 3,3'-((1,1'-biphenyl)-2,2'-diyibis(methylene))bis(1-phenyl-1H-imidazol-3-ium) dibromide (6) were used as ligands for the synthesis of the corresponding Pd(II) complexes. 2,2'-Disubstituted 1,1'-biphenyl moiety was used as the C-2-symmetric backbone for the synthesis. 2,2'-Bis(bromomethyl)-1,1'-biphenyl was used as a common precursor for the synthesis of both 5 and 6. These salts were treated with Ag2O for the insitu generation of the corresponding NHC Ag(l) complexes which were transmetallated to the corresponding Pd(II) chloro and acetate complexes. The bis(1,2,3-triazol-5-ylidene) derivative gave structurally well-defined mono nuclear chelate complexes that were characterized by spectroscopic and single crystal XRD data. The bis(imidazol-3-ylidene) derivative gave polymeric complex and not the expected mono nuclear chelate complex. These complexes were compared for their reactivity in Suzuki Miyaura coupling reaction.