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

• Published in: Polyhedron Vol. 105; pp. 137 - 149
• Main Authors: Glišić, Biljana Đ., Hoffmann, Marcin, Warżajtis, Beata, Genčić, Marija S., Blagojević, Polina D., Radulović, Niko S., Rychlewska, Urszula, Djuran, Miloš I.
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 17.02.2016; Elsevier
• Subjects: Camphorquinoxaline; Chemistry; Chemistry, Inorganic & Nuclear; Crystallography; DFT calculations; Gold(III); NMR spectroscopy; Physical Sciences; Science & Technology; X-ray crystallography; Gold(III); X-ray crystallography; Camphorquinoxaline; NMR spectroscopy; DFT calculations; NITROGEN-HETEROCYCLES; CORRELATED MOLECULAR CALCULATIONS; CRYSTAL-STRUCTURE; HYDROLYSIS; POTENTIALS; PYRAZINE; QUINOXALINE; BIOLOGICAL EVALUATION; DERIVATIVES; GAUSSIAN-BASIS SETS
• ISSN: 0277-5387; 1873-3719
• DOI: 10.1016/j.poly.2015.12.009

The reactions of novel methyl-substituted camphorquinoxaline ligands with Au(III) ion resulted in the selective formation of gold(III) complexes. [Display omitted] 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.