from first principles PP-I-1

PP-III-88A DFT Study of Electronic and Steric Effects of Alkoxy Ligandsfor Dialkyl Carbonate Formation from CO 2 and n-Bu 2 Sn(OR) 2Poor Kalhor M. 1 , Chermette H. 1 , Ballivet-Tkatchenko D. 21 Institut de Sciences Analytiques, UMR 5180 CNRS, University of Lyon1, Lyon, France2 Institut de Chimie Moléculaire, UMR 6302 CNRS, University of Burgundy, Dijon, Franceballivet@u-bourgogne.frThe current interest in the catalytic coupling of CO 2 and alcohols to dialkyl carbonates arisesfrom CO 2 conversion to entering the chemical value chain. It is a challenging reaction and themechanism is poorly understood. Here, we report on a DFT study of electronic and stericeffects for CO 2 insertion into the Sn-OR bonds of tin (IV) complexes, (R') 2 Sn(OR) 2 (R = Me,Et, iPr; R' = Me, n-Bu) [1,2]. DFT calculations were performed with ADF software, a TZPbasis set, and PBE as GGA exchange-correlation functional.The reaction pathways are exothermic and the driving force for CO 2 insertion is assigned to acharge-transfer between the HOMO of the tin complex, mainly localized on the oxygen atomof the alkoxy ligands, and the LUMO of CO 2 . Results nicely point out that the steric effect ofthe R group does increase the concentration of mono-hemicarbonato species, which furtherreacts with CO 2 to the bis-hemicarbonato species (Scheme 1). Unexpectedly, the energybarrier of the second CO 2 insertion step is much lower than the first one. The steric effect isevidenced for the rotation step of the hemicarbonato group leading to a kinetically andthermodynamically stabilization vs extrusion of CO 2 , as found experimentally [3].CO 2 COR' R' 2 Sn(OR)(OCO 2 R) 22 Sn(OR) 2 R' 2 Sn(OCO 2 R) 2E 0R= R'= CH 3R= CH 3 ,R'= n-BuR = CH(CH 3 ) 2 , R’=n-BuScheme 1. Energy profile of CO 2 insertion into Sn-OR bond.References:[1] M. Poor Kalhor, H. Chermette, S. Chambrey, D. Ballivet-Tkatchenko, Phys. Chem. Chem. Phys.13 (2011) 2401.[2] M. Poor Kalhor, H. Chermette, D. Ballivet-Tkatchenko, Polyhedron, 32 (2012) 73.[3] D. Ballivet-Tkatchenko, O. Douteau, S. Stutzmann, Organometallics, 19 (2000) 4563.245