Selective Hydrosilation of CO₂ to a Bis(silylacetal) Using an Anilido Bipyridyl‐Ligated Organoscandium Catalyst

Abstract

A rigid anilido bipyridyl ligand has been designed for use in an organoscandium-based carbon dioxide hydrosilation catalyst. Ligand attachment by alkane elimination results in metalation of an aryl C-H bond in a 3,5-di-tert-butylphenyl group installed on the pyridyl unit, thus rendering the ligand tetradentate. Insertion of CO2 into the newly formed Sc-C bond leads to a κ(1) carboxylate which, when treated with the borane B(C6F5)3, becomes hemilabile. In addition to activating the catalyst, the k(1) carboxylate effectively sequesters free B(C6F5)3 and the ensemble is able to effectively hydrosilate CO2, in the presence of excess Et3SiH, almost exclusively to R3SiOCH2OSiR3. A maximum turnover number of about 3400 (conversion of silane) is observed. Mechanistic experiments suggest that the sequestration of free B(C6F5)3 by the hemilabile carboxylate contributes to the selectivity observed and prevents over reduction to methane.

Boron-mediated activation of carbon dioxide

“…After this induction period a much faster rate is observed due to the generation of a more active catalyst, which is proposed to be the ion pair 91. M a n u s c r i p t [102]. This system disfavors the formation of methane by limiting the concentration of free B(C 6 F 5 ) 3 due to its interaction with the ligand backbone.…”

“…Scheme 35: CO 2 reduction into bis(silyl)acetal B' bytandem catalysis with 92 and 93[53,102] Garcia et al, instead of using B(C 6 F 5 ) 3 as silane activator used BEt 3 in the hydrosilylation of CO 2 . The nickel complex 94 was employed as co-catalyst to promote the selective formation of the formoxysilane A' (scheme 36)[103].Scheme 36: Tandem catalysis 94 / B(Et)3 [103] …”

Reduction of carbon dioxide and organic carbonyls by hydrosilanes catalysed by the perrhenate anion

“…[1][2][3] A variety of catalysts have been discovered and developed for this reaction, including complexes of Co, 4 Cu, [5][6][7][8] Ir, [9][10][11][12][13][14] Ni, [15][16][17] Pd/Pt, 18 Rh, 19 Ru, [20][21][22][23][24][25] Sc, 26 Zn, [27][28][29] and Zr, 30 frustrated Lewis pairs, [31][32][33][34][35][36] organocatalysts, [37][38][39][40][41][42] alkali metal carbonates, 43 and even polar solvents such as DMF. 38 These reactions result in various reduction products including silyl-formates, -acetals, andethers, CO, and methane.…”

Future perspectives for formaldehyde: pathways for reductive synthesis and energy storage

“…Piers and co-workers reported a Scandium complex for the above described reaction. 20 In general, it should be underlined that the interest for the synthesis of boryl and silyl methylene acetals from CO2 is of fundamental academic nature, and this might stimulates interests for the preparation of inorganic/organic hybrid materials incorporating formaldehyde derived from CO2. Contrary, the above described approaches seems unsuitable for their application to generate organic combustion fuels or liquid organic hydrogen carrier molecules for energy storage, respectively hydrogen storage systems based on CO2-derived formaldehyde.…”