A Polystyrene-Supported Tin Trichloride Catalyst with a C11-Spacer. Catalysis Monitoring Using High-Resolution Magic Angle Spinning NMR

The cross-linked polystyrene grafted organotin [P-H]((1-t))[P-(CH2)(11)-SnCl3](t), in which [P-H] represents the monomeric unit of the nonfunctionalized polymer and t is the functionalization degree, has been synthesized and characterized by ID and 2D H-1, C-13, and Sn-119 high-resolution magic angle spinning (HRMAS) NMR spectroscopy, elemental analysis, and IR spectrometry. Its catalytic activity was assessed in the transesterification model reaction between ethyl acetate and n-octanol. The catalyst displays an average conversion degree of 76% after 2 h and can be recycled at least nine times. The experimental concentration profiles were fitted to a mechanistic model, from which a turnover frequency in the range of 10(-2) s(-1) was calculated. Residual tin contents on the order of 5 ppm in the reaction products were assessed by inductively coupled plasma/atomic emission spectroscopy (ICP/AES). The combined use of H-1, C-13, and Sn-119 HRMAS NMR and modulated DSC enables one to assess the chemical integrity of the catalyst upon recycling. Detailed analysis of Sn-119 HRMAS NMR spectra under various chemical conditions mimicking the reaction mixtures allows gaining a better insight into the catalysis mechanism.