Reduction of CO2 by Hydrosilanes in the Presence of Formamidinates of Group 13 and 12 Elements
journal contribution
posted on 2020-02-24, 20:15 authored by Weiheng Huang, Thierry Roisnel, Vincent Dorcet, Clement Orione, Evgueni KirillovHomoleptic complexes 1-M of group 13 and 12 elements
(M = B–In and M = Zn, respectively) incorporating electron-withdrawing
formamidinate ligands {(C6F5)NCHN(C6F5)}− ({NCN}−) were synthesized and isolated in high yields. The compounds were
characterized by X-ray crystallography, NMR spectroscopy, and elemental
analysis. While the single-component 1-M appeared to
be sluggishly active or inactive in the reduction of CO2 with hydrosilanes, a good catalytic performance was achieved with
the two-component systems derived from combinations of 1-M and E(C6F5)3 (E = B, Al). In particular,
the binary combination 1-Al/B(C6F5)3 showed the best performance within the whole series,
thus providing quantitative hydrosilane (Et3SiH) conversions
under a range of conditions (PCO2, temperature, benzene or bromobenzene solvent) and affording
mainly CH2(OSiEt3)2 and CH4 as products. Kinetic and mechanistic studies revealed that at the
initiation step the binary catalytic systems undergo a complex transformation
in the presence of CO2/Et3SiH, affording the
products of 1-Al decomposition: namely, (C6F5)N(H)SiEt3, (C6F5)N(Me)SiEt3, {NCN}SiEt3, and also some unidentified aluminum
species. Thus, the overall process of the reduction of CO2 with hydrosilanes is presumed to be catalyzed by complex multisite
systems, evolved from the formamidinate precursor 1-Al, implicating different tandem combinations of N-base/B(C6F5)3 with putative Al-containing species.
