title: Selective Reduction of CO2 to CH4 by Tandem Hydrosilylation with Mixed Al/B Catalysts.
abstract: This contribution reports the first example of highly selective reduction of CO2 into CH4 via tandem hydrosilylation with mixed main-group organo-Lewis acid (LA) catalysts [Al(C6F5)3 + B(C6F5)3] {[Al] + [B]}. As shown by this comprehensive experimental and computational study, in this unique tandem catalytic process, [Al] effectively mediates the first step of the overall reduction cycle, namely the fixation of CO2 into HCOOSiEt3 (1) via the LA-mediated C═O activation, while [B] is incapable of promoting the same transformation. On the other hand, [B] is shown to be an excellent catalyst for the subsequent reduction steps 2-4, namely the hydrosilylation of the more basic intermediates [1 to H2C(OSiEt3)2 (2) to H3COSiEt3 (3) and finally to CH4] through the frustrated Lewis pair (FLP)-type Si-H activation. Hence, with the required combination of [Al] and [B], a highly selective hydrosilylative reduction of CO2 system has been developed, achieving high CH4 production yield up to 94%. The remarkably different catalytic behaviors between [Al] and [B] are attributed to the higher overall Lewis acidity of [Al] derived from two conflicting factors (electronic and steric effects), which renders the higher tendency of [Al] to form stable [Al]-substrate (intermediate) adducts with CO2 as well as subsequent intermediates 1, 2, and 3. Overall, the roles of [Al] and [B] are not only complementary but also synergistic in the total reduction of CO2, which render both [Al]-mediated first reduction step and [B]-mediated subsequent steps catalytic.
authors.affiliation: Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523-1872, United States.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Chen
authors.affiliation: Physical Sciences and Engineering Division, Kaust Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia.
authors.forename: Laura
authors.initials: L
authors.lastname: Falivene
authors.affiliation: Dipartimento di Chimica e Biologia, Università di Salerno , Via Papa Paolo Giovanni II, I-84084 Fisciano, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Caporaso
authors.affiliation: Physical Sciences and Engineering Division, Kaust Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia.
authors.forename: Luigi
authors.initials: L
authors.lastname: Cavallo
authors.affiliation: Department of Chemistry, Colorado State University , Fort Collins, Colorado 80523-1872, United States.
authors.forename: Eugene Y-X
authors.initials: EY
authors.lastname: Chen