Selectivity of the complexation reactions of four regioisomeric methylcamphorquinoxaline ligands with gold(III): X-ray, NMR and DFT investigations

Reported are the synthesis, spectral and structural characteristics of new quinoxaline-related regioisomeric ligands L1–L4 (1,x,11,11-tetramethyl-1,2,3,4-tetrahydro-1,4-methanophenazine, x = 7, 8, 9 and 6, respectively) and their mononuclear Au(III) complexes (1–4). Fusion of the camphor moiety to the quinoxaline core made two N-atoms of quinoxaline nonequivalent while the introduction of a methyl-substituent at positions 6–9 enabled a tuning of coordination properties of L1–L4. Gold(III) complexes 1–4 and ligands L1–L4 have been studied in detailed by 1D and 2D NMR and the structures of 1–4 have been determined by X-ray crystallography. The results of these analyses revealed a regiospecific coordination of Au(III) to the sterically less hindered N-5 atom (spatially close to the non-substituted bridgehead carbon) of L1–L3, and to N-10 (spatially close to the methyl-substituted bridgehead carbon) of L4. The results of DFT calculations shed light on disparate coordination modes of L1–L4 toward the AuCl3 fragment and explain formation of single coordination products in high yield.

The reactions of novel methyl-substituted camphorquinoxaline ligands with Au(III) ion resulted in the selective formation of gold(III) complexes.Figure optionsDownload as PowerPoint slide