Synthesis of N-heterocyclic nitrenium (NHN) ions and related donor systems: Coordination with d10-metal ions

Abstract

The synthesis of three new NNN- and CNC type N-heterocyclic nitrenium (NHN) ion based pincer ligands is reported from 1,3-di-(2′-bromoethyl)-triazolium bromide (5). The reaction of 5 with ammonium hexafluorophosphate followed by two equivalent of pyrrolidine/diethylamine afforded NHN ions (10a and 10b). The reaction of 5 with N-butylbenzimidazole (6) afforded nitrenium ion 7, where the chelating arms have benzimidazole based carbene carbons. In an attempt to synthesize hybrid NHN ligand containing soft tellurium donor in the chelating arm, 1-(2′-bromoethyl)-benzotriazole was first reacted with in situ generated NaTePh to afford tellurated benzotriazol (13). However, when compound 13 was treated with methyl iodide, an unexpected methylation underwent at tellurium center to afford compound 14. Reaction of 7 with Hg(OAc)2 and 10a with CuI afforded complexes 8 and 11 respectively. Both these complexes are characterized by NMR (1H, 13C), HRMS and CHN analysis. The Natural Bond Order (NBO) calculations and Atoms in Molecules (AIM) analyses sufficiently substantiate the presence of interaction between triazolium N atom with metal centre. The reaction of N,N′-disubstituted benzimidazoles, 17a–17b with in situ generated Na2Se2 in the presence of potassium tert-butoxide at room temperature afforded two novel benzimidazoline-2-chalcogenones (18a and 18b). Nitrenium ion (10a–10b), tellurated benzotriazole (13 and 14) and selone 18a are authenticated by single crystal X-ray diffraction studies.