Palladacycles of Thioethers Catalyzing Suzuki-Miyaura C-C Coupling: Generation and Catalytic Activity of Nanoparticles

Tridentate thioether ligands, 2-HO-4-R-C6H3-(C6H4)CHNH(CH2)(3)SPh [R = H (L1) or -OMe (L2,)] react with Na2PdCl4, giving palladacycles [PdCl(C-,N,S)] (1: (C-,N,S) = L1-H; 2: (C-,N,S) = L2-H). The H-1 and C-13{H-1} NMR spectra of ligands and their palladacycles have been found to be characteristic. Complexes I and 2 have also been characterized with HR-MS. The crystal structure of 2 has been solved. The Pd-S bond length is 2.428(2) angstrom, and palladium has a nearly square planar geometry. During the course of catalysis of Suzuki-Miyaura C-C coupling using 1 and 2 as catalysts, unexpected formation of Pd16S7 nanoparticles (NPs) has been observed with both complexes. This is the first time that such an observation has been made with palladacycles of thioethers used in this coupling reaction. The efficiency of 2 in carrying out the coupling is significantly lower than that of 1. Complex 2 has an additional -OMe group in the ligand structure, and the size of Pd16S7 NPs formed from this complex are larger (6 nm) than those obtained from 1 (2 nm).