Controlling the Product Platform of Carbon Dioxide Reduction: Adaptive Catalytic Hydrosilylation of CO₂ Using a Molecular Cobalt(II) Triazine Complex

Abstract

The catalytic reduction of carbon dioxide (CO2) is considered a major pillar of future sustainable energy systems and chemical industries based on renewable energy and raw materials. Typically, catalysts and catalytic systems are transforming CO2 preferentially or even exclusively to one of the possible reduction levels and are then optimized for this specific product. Here, we report a cobalt‐based catalytic system that enables the adaptive and highly selective transformation of carbon dioxide individually to either the formic acid, the formaldehyde, or the methanol level, demonstrating the possibility of molecular control over the desired product platform.

Partnering a Three‐Coordinate Gallium Cation with a Hydroborate Counter‐Ion for the Catalytic Hydrosilylation of CO2

“…[88,93] As imilar effect is observed in the cationic aluminium complex [( Dipp L)Al(Me)] [B(C 6 F 5 ) 4 ], and presumably reflects (at least in part) the effect of coordination number on bond lengths. [94,95] The 1 HNMR spectrumo f2-H features two doubletsa nd one septetf or the iPr CH 3 and CH groups of the Dipp substituents, respectively,c onsistentw ith C 2v symmetry on the NMR timescale, and suggestst hat the cationic component of 2-H retains its three-coordinate nature in solution (or is rapidly fluxional/ labile).M oreover,t he resonances associated with the g-CH unit in the 1 Ha nd 13 4 ] À salt) using the modified version of the Gutmann method reported by Adamcyk-Wozniake tal. [96] Using Et 3 PO as the Lewis basic probe,ana cceptor number (AN) of 69.8 can be determined.…”

“…While the hydrogenation of CO 2 can afford a variety of products and is a desirable process in terms of atom economy, the use of silane reductants allows for the use of significantly milder reaction conditions (T<100 °C, P CO2 <3 atm), and benefits thermodynamically from the stability of the generated products featuring Si−O bonds [7–9] . In addition, the use of silanes has allowed for the development of catalytic systems which exercise greater control over selectivity for products with different carbon oxidation levels, including silyl formates, silyl acetals, methoxysilanes and methane (which is formed in conjunction with bis(silyl)ethers) [8–13] …”

“…Thus, a variety of homogenous catalytic systems based on metals (Pd/Pt, [14–17] Rh, [18] Re, [19, 20] Ru, [21–26] Ir, [8, 27–30] Co, [13, 31] Mn, [12] Zr, [32, 33] Cu, [34–38] Ni, [39–42] Sc, [43–46] Zn, [47–57] Mg [57, 58] and Sr [59] ), Lewis acids, [60–66] frustrated Lewis pairs (FLPs), [67, 68] organo‐catalysts, [69–75] alkali metal carbonates, [76, 77] and metal borohydrides [78] have been investigated for this process. Many of these catalytic systems feature reactive metal hydride or alkyl groups, which effect the initial activation of CO 2 via insertion.…”

“…[7][8][9] In addition, the use of silanesh as allowed for the development of catalytic systemsw hich exercise greaterc ontrolo ver selectivity for products with different carbon oxidationl evels,i ncluding silyl formates,s ilyl acetals, methoxysilanes and methane (which is formed in conjunction with bis(silyl)ethers). [8][9][10][11][12][13] Thus, av arietyo fh omogenousc atalytic systemsb ased on metals (Pd/Pt, [14][15][16][17] Rh, [18] Re, [19,20] Ru, [21][22][23][24][25][26] Ir, [8,[27][28][29][30] Co, [13,31] Mn, [12] Zr, [32,33] Cu, [34][35][36][37][38] Ni, [39][40][41][42] Sc, [43][44][45][46] Zn, [47][48][49]…”

“…In particular, selectiver eduction to yield bis(silyl)acetal products is important,a si th as been demonstrated that they can act as formaldehyde surrogates. [58] Mechanismsf or controlling the reductivep rocesst o selectively yield products representingd ifferent carbon oxidation levels are dependent on the catalytic system and also on the nature of the silane, [13,31,32,57] reaction temperature, [12,21] and amount/nature of Lewis acid co-catalyst used. [14,42,65] Thus, while it has been demonstrated that the use of B(C 6 F 5 ) 3 as a co-catalyst commonly leads to enhancement of catalytic activity,t he presenceo fB (C 6 F 5 ) 3 -activated silane often leads to undesirable over-reduction of the formic acid, formaldehyde and methanol derivatives to methane.…”