Catalytic Reduction of Carbon Dioxide Using Cationic Organoaluminum and -Gallium Compounds.

Ethide abstraction from Et3M (M = Al and Ga), (2,6-Ph2C6H3)AlEt2, 1, and (2,6-Dipp2C6H3)GaEt2, 2 (Dipp = 2,6-iPr2C6H3), using the silylium ion [Et3Si][CHB11Cl11] afforded crystalline ion-like compounds [Et2M][CHB11Cl11] (M = Al, 3; Ga, 5) and [(2,6-Ph2C6H3)AlEt][CHB11Cl11], 4, and the likely solvent-separated ion pair [(2,6-Dipp2C6H3)GaEt][CHB11Cl11], 6. Crystalline compounds 3-5feature cation•••anion contacts in the solid state, and their solubility in low polarity benzene indicates that these contacts are maintained in solution. All compounds catalyze the reduction of CO2 with Et3SiH, but the activity of the gallium compound 5 is significantly lower due to its polymeric structure and the lower Lewis acidity of gallium. Whereas the reduction products from the reactions catalyzed by compounds 3-5 are mostly methane and toluene (from Friedel-Crafts alkylation of the benzene solvent), catalysis by 6 led mostly to Et3SiOCH3. [ABSTRACT FROM AUTHOR]