L→S Coordination Complexes Containing Benzothiazol-2-ylidene Ligand: Quantum Chemical Analysis and Synthesis

Abstract

(NHC)→E coordination interactions were known where NHC is an N-heterocyclic carbene, and E is a main group element (B, C, N, Si, P). Recently, it was suggested that compounds with (NHC)→S coordination chemistry are also possible. This work reports quantum chemical analysis and synthesis of (NHC)→S-R⁽⁺⁾ complexes in which benzothiazol-2-ylidene acts as a ligand. A Density functional study established that (NHC)→S interaction can best be described as a coordination interaction. Synthetic efforts were made, initially, to generate divalent sulfur compounds containing benzothiazole substituents. N-alkylation of the heterocyclic ring in these sulfides using methyl triflate led to the generation of the desired products with (NHC)→S coordination chemistry, which involves the in situ generation of NHC ring ligands. The observed changes in the ¹³C NMR spectra, before and after methylation, confirmed the change in the electronic character of the C-S bond from a covalent character to a coordination character.

Keywords: (NHC)→S Coordination bond; Benzothiazol-2-ylidene; DFT (Density Functional Theory) study; N-heterocyclic carbenes; Sulfide.