Single crystal structure features of a new Cu (II) coordination polymer as an efficient homogeneous catalyst in the selective conversion of sulfides

Abstract

This study reports the synthesis of a new coordination polymer of Cu (II) formulated as [Cu (Tu)3]n[Cu(Tu)3]·2(pzdc) (1) where tu = thiourea, and (pzdc)2− = 2,3-pyrazinedicarboxylate. Complex 1 was characterized by elemental analysis (CHN), Fourier transformed-infrared (FT-IR) spectroscopy, energy-dispersive X-ray spectroscopy (EDXS or EDS), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The molecular structure of complex 1 has been confirmed by single-crystal X-ray diffraction (SC-XRD). The SC-XRD results show that complex 1 crystallized in a monoclinic crystal system with space group P21/c and metal centers Cu1 and Cu2 adopted slightly distorted tetrahedral and triangular geometry, respectively. The molecular structure of complex 1 is stabilized by a dense network of hydrogen bonds such as NH⋯O, besides electrostatic attraction. Complex 1 was used as a catalyst for the selective oxidation of thioanisole and a number of sulfides to the corresponding sulfoxides or sulfones with high conversion and high selectivity in the presence of hydrogen peroxide as a green oxidant. The results showed that complex 1 accelerates the conversion of sulfides. The influence of varying parameters such as catalyst dosage, temperature, solvent, and H2O2/substrate molar ratio were examined in an attempt to optimize the conversion of thioanisole and, in particular, to improve the selectivity of the desired products (sulfoxides). Then, the optimized conditions were used to investigate the generality of catalytic activity of complex 1 to oxidize several other sulfides to its sulfoxide's analogues, that corresponding sulfoxides were obtained with excellent selectivity in most cases (up to 84 %) through high conversion of sulfides (up to 82 %).