Chiral tricyclic triazolooxazine derived mesoionic carbene (MIC)-Pd(II) complexes of cyclohexene oxide scaffold: Synthesis, structure, and characterizations

Abstract

We herein report the well-defined two novel chiral palladium(II) complexes 1(b−c), of the chiral N-fused tricyclic triazolooxazine derived mesoionic carbene (tz-MIC) ligand 1a. The chiral tricyclic PEPPSI type complex (pyridine enhanced pre-catalyst preparation stabilization and initiation) namely, trans-[tz-MIC)-PdI2(pyridine)] (1b), and the chiral tricyclic bis(tz-MIC)-palladium complex namely, cis-[tz-MIC)2-PdCl2] (1c). The chiral tricyclic trans-[tz-MIC)-PdI2(pyridine)] PEPPSI type complex (pyridine enhanced pre-catalyst preparation stabilization and initiation) (1b) was directly obtained from their respective chiral tricyclic triazolooxazinium iodide salt (1a), by treatment with PdCl2 and K2CO3 in pyridine in 77% yield. The chiral tricyclic triazolooxazinium iodide salt (1a), was first 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) in 84% yield. 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.