A Ni(II) PNP pincer complex immobilized on SBA-15 as catalyst for the 4-nitrophenol hydrogenation

The Ni(II) complex [NiCl(bda)]+ containing the aliphatic PNP pincer ligand bis((2-diphenylphosphino)ethyl)amine (bda) was covalently immobilized on the mesoporous silica SBA-15. SBA-15 was functionalized with (3-chloropropyl)triethoxysilane as an anchoring agent, which was further reacted with the amine group of the Ni-coordinated bda ligand, forming the hybrid material SBA-15@PTES@Ni. The material was characterized using Fourier-transform infrared spectroscopy, UV-visible-diffuse reflectance spectroscopy, thermogravimetric analysis, low-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and inductively coupled plasma. SBA-15@PTES@Ni was used as a catalyst for the hydrogenation of 4-nitrophenol to 4-aminophenol using NaBH4 in aqueous solution. With catalyst loadings of 1 to 3 mg, complete conversions were achieved in 6 to 10 min, with rate constants up to 6.92 × 10–3 s–1.