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

Pd(II) complexes of thiosemicarbazones (TSCs) have previously been used as homogenous precatalysts for constructing CC bonds. Herein, the first SiO 2 ‐supported homogeneous Pd(II)‐TSC catalyst [PdL]–APTES–SiO 2 (APTES = (3‐aminopropyl)triethoxysilane) is reported for this purpose. This Pd complex–SiO 2 nanoparticle (NP) conjugate is synthesized through covalent binding of the pentadentate bis( N 4‐(2‐ethylphenyl)) 2,6‐diacetyl‐pyridine TSC onto monodispersed SiO 2 , followed by coordination of Pd(II). Characteristic shifts of resonances in the Fourier‐transform infrared spectra allowed confirming the SiO 2 functionalization and the Pd‐binding. High‐resolution X‐ray photoelectron spectroscopy (XPS) analysis of N 1 s , C 1 s , and S 2 p 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 H 2 L–APTES–SiO 2 conjugate strongly supports the successful covalent binding of the TSC onto the SiO 2 NPs and is in line with the S thiolate ^N imine ^N pyridine ^N amide coordination of Pd(II) in the conjugate that is also found in the model complex [Pd(L)]. The [PdL]–APTES–SiO 2 NPs are used as precatalyst in Suzuki–Miyaura‐type cross‐coupling reactions with yields ranging from 70% to 83%.