Nickel(II)-PPh3 Complexes of S,N-Substituted Thiosemicarbazones - Structure, DFT Study, and Catalytic Efficiency

Abstract

Five 2-hydroxyacetophenone thiosemicarbazones with [-(NH)-H-4-R-(SH)J (where R is ethyl or phenyl) and [-(NH)-H-4-R- (SR1)] (where R/R-1 denote methyl/methyl, methyl/propyl, or phenyl/methyl) substituents on the thioamide group were synthesized. The ligands have an ONS or ONN donor set, and the reaction of the dibasic ligands with [Ni(PPh3)(2)Cl-2] yields chelate complexes with general formula [Ni(L)(PPh3)]. The stable solid complexes were characterized by IR and H-1 NMR spectroscopy and elemental analysis. The crystallographic structures of two complexes, one with an S-methyl-N-4-phenyl- and the other with an S-propyl-N-4-methyl-substituted thiosemicarbazidato ligand, are reported. The complexes crystallize in the monoclinic space group P2(1)/n, and the nickel centers have a distorted square planar environment. The coupling reaction of phenylmagnesium bromide with bromobenzene was used to determine the catalytic activities of the nickel(11) complexes prepared, and the results show that the ONN complexes provide higher yields relative to those with ONS donors. The catalytic efficiency of the nickel complexes was modeled by using density functional theory (DFT).