From CO2 to dimethyl carbonate with dialkyldimethoxystannanes: the key role of monomeric speciesElectronic supplementary information (ESI) available: Geometrical parameters for 7, 8, and 11; energy profiles of the reaction of CO2 with 1-6, and 9; HOMOs and LUMOs of CO2 and 2 to 9; PW91 functional energy diagrams for the reaction of CO2 with 1; Gibbs energy diagrams for the reaction of CO2 with 1 at 298 and 423 K. See DOI: 10.1039/c0cp02089c

The formation of dimethyl carbonate (DMC) from CO 2 and methanol with the dimer [ n -Bu 2 Sn(OCH 3 ) 2 ] 2 was investigated by experimental kinetics in support of DFT calculations. Under the reaction conditions (357-423 K, 10-20 MPa), identical initial rates are observed with three different reacting mixtures, CO 2 /toluene, supercritical CO 2 , and CO 2 /methanol, and are consistent with the formation of monomeric di- n -butyltin( iv ) species. An intramolecular mechanism is, therefore, proposed with an Arrhenius activation energy amounting to 104 ± 10 kJ mol −1 for DMC synthesis. DFT calculations on the [(CH 3 ) 2 Sn(OCH 3 ) 2 ] 2 /CO 2 system show that the exothermic insertion of CO 2 into the Sn-OCH 3 bond occurs by a concerted Lewis acid-base interaction involving the tin center and the oxygen atom of the methoxy ligand. The Gibbs energy diagrams highlight that, under the reaction conditions, the dimer-monomer equilibrium is significantly shifted towards monomeric species, in agreement with the experimental kinetics. Importantly, the two Sn-OCH 3 bonds are prompt to insert CO 2 . These results provide new insight into the reaction mechanism and catalyst design to enhance the turnover numbers. Experimental kinetics and density functional theory calculations demonstrate the ability of dialkyltin( iv ) monomers to convert CO 2 , that opens up a novel route to catalyst optimization.