Chiral Tricyclic 1,2,3-Triazol-3-Ylidene–Pd(II) Complexes of Cyclohexene Oxide Scaffold: Synthesis, Structure, and Characterizations

Abstract

We herein report the two novel well-defined palladium(II) complexes 1(b−c), of the chiral N-fused tricyclic 1,2,3-triazolium-derived mesoionic carbenes (MIC) ligand 1a. The chiral tricyclic PEPPSI type complex namely, trans-{2-methyl-(5aS,9aS)-5a,6,7,8,9,9a-hexahydro-4H-benzo[b][1,2,3]triazolo[1,5-d][1,4]oxazin-3-ylidene}PdI2(pyridine)} (1b), and the chiral tricyclic bis(tz-MIC)-palladium complex namely, {2-methyl-(5aS,9aS)-5a,6,7,8,9,9a-hexahydro-4H-benzo[b][1,2,3]triazolo[1,5-d][1,4]oxazinium-3-ylidene}2PdCl2} (1c). The chiral tricyclic (tz-MIC)PdI2(pyridine) type PEPPSI complex (1b) was obtained by direct reaction of the corresponding chiral tricyclic 1,2,3-triazolium-derived mesoionic carbenes (MIC) ligand 1a, by treatment with PdCl2 in the presence of K2CO3 as a base in pyridine in 87% yield. (Scheme 1). The chiral tricyclic 1,2,3-triazolium iodide salt (1a) was converted to its in-situ silver analogue by reaction with Ag2O and then subsequently upon treatment with (COD)PdCl2 to produce the chiral tricyclic (tz-MIC)2PdCl2 type palladium complex (1c). All these palladium complexes were isolated for the first time and structurally characterized by 1H NMR and 13C{1H}-NMR spectroscopy, FT-IR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray crystallography.