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)3SPh [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 1H and 13C­{1H} NMR spectra of ligands and their palladacycles
have been found to be characteristic. Complexes 1 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) Å, 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).