A Bis‐Thiosemicarbazone Pd(II) SiO2 Nanoparticle Conjugate for CC Coupling Catalysis

Abstract

Pd(II) complexes of thiosemicarbazones (TSCs) have previously been used as homogenous precatalysts for constructing CC bonds. Herein, the first SiO2‐supported homogeneous Pd(II)‐TSC catalyst [PdL]–APTES–SiO2 (APTES = (3‐aminopropyl)triethoxysilane) is reported for this purpose. This Pd complex–SiO2 nanoparticle (NP) conjugate is synthesized through covalent binding of the pentadentate bis(N4‐(2‐ethylphenyl)) 2,6‐diacetyl‐pyridine TSC onto monodispersed SiO2, followed by coordination of Pd(II). Characteristic shifts of resonances in the Fourier‐transform infrared spectra allowed confirming the SiO2 functionalization and the Pd‐binding. High‐resolution X‐ray photoelectron spectroscopy (XPS) analysis of N 1s, C 1s, and S 2p shows that the binding energies of the atoms in the CN, CS, CN, NH, pyridine‐N, and imine‐N groups shift to lower values upon Pd coordination. The absence of chloride in the XPS of the H2L–APTES–SiO2 conjugate strongly supports the successful covalent binding of the TSC onto the SiO2 NPs and is in line with the Sthiolate^Nimine^Npyridine^Namide coordination of Pd(II) in the conjugate that is also found in the model complex [Pd(L)]. The [PdL]–APTES–SiO2 NPs are used as precatalyst in Suzuki–Miyaura‐type cross‐coupling reactions with yields ranging from 70% to 83%.