Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO2

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique Zn(II)complex of imine-functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO2. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO(2)and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine-POSS is able to chelate metal ions like Zn(II)to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homolepticZn(4)@POSS-1complex. The compound was characterized in solution by NMR (H-1,C-13,Si-29), ESI-MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG-DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross-polarization magic angle spinning (CP MAS) NMR (C-13,Si-29) spectroscopy, and X-ray crystallography.