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.

The selective hydrosilylation of carbon dioxide (CO 2 ) to either the formic acid, formaldehyde, or methanol level using a molecular cobalt(II) triazine complex can be controlled based on reaction parameters such as temperature, CO 2 pressure, and concentration. Here, we rationalize the catalytic mechanism that enables the selective arrival at each product platform. Key reactive intermediates were prepared and spectroscopically characterized, while the catalytic mechanism and the energy profile were analyzed with density functional theory (DFT) methods and microkinetic modeling. It transpired that the stepwise reduction of CO 2 involves three consecutive catalytic cycles, including the same cobalt(I) triazine hydride complex as the active species. The increasing kinetic barriers associated with each reduction step and the competing hydride transfer steps in the three cycles corroborate the strong influence of the catalyst environment on the product selectivity. The fundamental mechanistic insights provide a consistent description of the catalytic system and rationalize, in particular, the experimentally verified opportunity to steer the reaction toward the formaldehyde product as the chemically most challenging reduction level.

The Lewis acid−base reaction between a nucleophilic hafnocene-based germylene and tris-pentafluorophenylborane (B-(C 6 F 5 ) 3 ) to give the conventional B−Ge bonded species in almost quantitative yield is reported. This reaction is surprisingly slow, and during its course, radical intermediates are detected by EPR and UV− vis spectroscopy. This suggests that the reaction is initiated by a single electron-transfer step. The hereby-involved germanium radical cation was independently synthesized by oxidation of the germylene by the trityl cation or strong silyl-Lewis acids. A perfluorinated tetraarylborate salt of the radical cation was fully characterized including an XRD analysis. Its structural features and the results of DFT calculations indicate that the radical cation is a hafnium(III)-centered radical that is formed by a redox-induced electron transfer (RIET) from the ligand to the hafnium atom. This valence isomerization slows down the coupling of the radicals to form the polar Lewis acid−base product. The implications of this observation are briefly discussed in light of the recent finding that radical pairs are formed in frustrated Lewis pairs. Article pubs.acs.org/JACS