Application of Hetero-Triphos Ligands in the Selective Ruthenium-Catalyzed Transformation of Carbon Dioxide to the Formaldehyde Oxidation State

Challenges and Prospects in the Catalytic Conversion of Carbon Dioxide to Formaldehyde

Formaldehyde (HCHO) is a crucial C₁ building block for daily-life commodities in a wide range of industrial processes. Industrial production of HCHO today is based on energy- and cost-intensive gas-phase catalytic oxidation of methanol, which calls for exploring other and more sustainable ways of carrying out this process. Utilization of carbon dioxide (CO₂ ) as precursor presents a promising strategy to simultaneously mitigate the carbon footprint and alleviate environmental issues. This Minireview summarizes recent progress in CO₂ -to-HCHO conversion using hydrogenation, hydroboration/hydrosilylation as well as photochemical, electrochemical, photoelectrochemical, and enzymatic approaches. The active species, reaction intermediates, and mechanistic pathways are discussed to deepen the understanding of HCHO selectivity issues. Finally, shortcomings and prospects of the various strategies for sustainable reduction of CO₂ to HCHO are discussed.

Mechanistic exploration of CO2 conversion to dimethoxymethane (DMM) using transition metal (Co, Ru) catalysts: an energy span model

The conversion of CO₂ to DMM is an important transformation for various reasons. Co and Ru-based triphos catalysts have been investigated using density functional theory (DFT) calculations to understand the mechanistic pathways of the CO₂ to DMM conversion and the role of noble/non-noble metal-based catalysts. The reaction has been investigated sequentially through methylformate (MF) and methoxymethane (MM) intermediates as they are found to be important intermediates. For the hydrogenation of CO₂ and MF, the hydrogen sources such as H₂ and methanol have been investigated. The calculated reaction free energy barriers for all the possible pathways suggest that both hydrogen sources are important for the Co-triphos catalyst. However, in the case of the Ru-triphos catalyst, molecular H₂ is calculated to be the only hydrogen source. Various esterification and acetalization possibilities have also been explored to find the most favorable pathway for the conversion of CO₂ to DMM. We find that the hydride transfer to the CO₂ is the rate determining step (RDS) for the overall reaction. Our mechanistic investigation reveals that the metal center is the active part for the catalysis rather than the Brønsted acid and the redox triphos ligand plays an important role through the push-pull mechanism. The implemented microkinetic study shows that the reaction is also quite dependent on the concentration of the gaseous reactants and the rate constant increases exponentially above 363 K.

Catalytic Reductive Alcohol Etherifications with Carbonyl-Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

Ether derivatives have myriad applications in several areas of chemical industry and academia. Hence, the development of more effective and sustainable protocols for their production is highly desired. Among the different methodologies reported for ether synthesis, catalytic reductive alcohol etherifications with carbonyl-based moieties (aldehydes/ketones and carboxylic acid derivatives) have emerged in the last years as a potential tool. These processes constitute appealing routes for the selective production of both symmetrical and asymmetrical ethers (including O-heterocycles) with an increased molecular complexity. Likewise, ester-to-ether catalytic reductions and hydrogenative alcohol etherifications with CO2 to dialkoxymethanes and other acetals, albeit in less extent, have undergone important advances, too. In this Review, an update of the recent progresses in the area of catalytic reductive alcohol etherifications using carbonyl-based compounds and CO2 have been described with a special focus on organic synthetic applications and catalyst design. Complementarily, recent progress made in catalytic acetal/ketal-to-ether or ester-to-ether reductions and other related transformations have been also summarized.

Synthesis and CO2 photoreduction of two 3d–4f heterometal–organic frameworks

Two 3d–4f heterometal–organic frameworks with similar structures were synthesized by a steam-assisted conversion method and exhibited high activity and selectivity for the photoreduction of CO2.

Identifying high-performance catalytic conditions for carbon dioxide reduction to dimethoxymethane by multivariate modelling

In times of a warming climate due to excessive carbon dioxide production, catalytic conversion of carbon dioxide to formaldehyde is not only a process of great industrial interest, but it could also serve as a means for meeting our climate goals. Currently, formaldehyde is produced in an energetically unfavourable and atom-inefficient process. A much needed solution remains academically challenging. Here we present an algorithmic workflow to improve the ruthenium-catalysed transformation of carbon dioxide to the formaldehyde derivative dimethoxymethane. Catalytic processes are typically optimised by comprehensive screening of catalysts, substrates, reaction parameters and additives to enhance activity and selectivity. The common problem of the multidimensionality of the parameter space, leading to only incremental improvement in laborious physical investigations, was overcome by combining elements from machine learning, optimisation and experimental design, tripling the turnover number of 786 to 2761. The optimised conditions were then used in a new reaction setup tailored to the process parameters leading to a turnover number of 3874, exceeding by far those of known processes.