Palladium(II) complexes of pyrazolated thio/selenoethers: syntheses, structures, single source precursors of Pd4Se and PdSe nano-particles and potential for catalyzing Suzuki-Miyaura coupling

Abstract

The reactions of 4-bromo-1-(2-chloroethyl)-1H-pyrazole prepared from 4-bromopyrazole with the in situ generated PhSNa, PhSeNa, Na(2)S and Na(2)Se have resulted in thio/selenoether ligands L1-L4 respectively. The complexes [PdL1/L2Cl(2)](1-2) and [PdL3/L4Cl]BF(4) (3-4) of these ligands have been synthesized by reacting them with [PdCl(2)(CH(3)CN)(2)] in CH(3)CN at 70 °C. The L1-L4 and their complexes (1-4) have been characterized with spectroscopic techniques viz.(1)H, (13)C{(1)H} and (77)Se{(1)H} NMR, IR and HR-MS. Single crystal structures of 1-4 determined by X-ray diffraction reveal nearly square planar geometry around Pd in each case. Thermally stable, moisture/air insensitive complexes 1-4 have been found to be efficient pre-catalysts for Suzuki-Miyaura coupling reactions (yield up to 96% in 2 h). Nano-particles (NPs) (size ~3-19 nm) were formed in the beginning of these reactions. They are composed of Pd and S or Se with more % of Pd. These NPs also catalyze Suzuki coupling and appear to play an important role in catalysis. Single source one pot synthesis of Pd(4)Se and PdSe NPs (size ranges ~8-26 nm), capped with trioctylphosphine (TOP), has been developed by thermolysis of 2 and 4 at 200-250 °C in TOP. HR-TEM, SEM, SEM-EDX and powder XRD have been used to authenticate these nano-particles. The NPs of PdP(2) are formed when attempts were made to prepare nano-sized phases of palladium-sulfide by thermolysis of 1 and 3 in TOP.