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

Abstract

Due to the increasing demand for formaldehyde as a building block in the chemical industry as well as its emerging potential as feedstock for biofuels in the form of dimethoxymethane and the oxymethylene ethers produced therefrom, the catalytic transformation of carbon dioxide to the formaldehyde oxidation state has become a focus of interest. In this work, we present novel ruthenium complexes with hetero-triphos ligands, which show high activity in the selective transformation of carbon dioxide to dimethoxymethane. We substituted the apical carbon atom in the backbone of the triphos ligand platform with silicon or phosphorus and optimized the reaction conditions to achieve turnover numbers as high as 685 for dimethoxymethane. The catalytic systems could also be tuned to preferably yield methyl formate with turnover numbers of up to 1370, which in turn can be converted into dimethoxymethane under moderate conditions.

Reaction Network Analysis of the Ruthenium‐Catalyzed Reduction of Carbon Dioxide to Dimethoxymethane

“…At elevated temperatures, the differences become more pronounced and the reductive transformation of MM to MeOH has its lowest activation barrier, resulting in greater MeOH yields. The observed trends for the activation parameters match very well with experimental data, where synthesis of MF is carried out at lower temperatures, [24] while DMM is synthesized at higher temperatures [9,11] and for MeOH synthesis the highest temperatures [14,20] are applied. Nevertheless, it has to be noted that the determined absolute values for Δ G ≠ of the hydrogenation steps seem to disfavor DMM formation.…”

“…Previous studies focused on structural and electronic modifications of the catalyst, like interchanging the transition metal center, [10] varying the coordinating phosphorus moiety, [9] or introducing different hetero‐atoms in the apex position of the triphos ligand [11] . Furthermore, it was reported that formic acid can be employed as starting compound for the synthesis of DMM under the same catalytic conditions [12] .…”

“…[9] Previous studies focused on structural and electronic modifications of the catalyst, like interchanging the transition metal center, [10] varying the coordinating phosphorus moiety, [9] or introducing different hetero-atoms in the apex position of the triphos ligand. [11] Furthermore, it was reported that formic acid can be employed as starting compound for the synthesis of DMM under the same catalytic conditions. [12] In addition, the ruthenium triphos formate complex has been identified as an active catalytic species and catalyst deactivation pathways can be suppressed by addition of formic acid and monodentate phosphine ligands, thus contributing to catalyst recycling.…”

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

“…As a result of this study, a well‐defined Ru(N‐Triphos Ph )(tmm) complex in the presence of Al(OTf) 3 (Scheme 35E) was reported as the most active system for DMM production from CO 2 /H 2 , reaching a TON of 786 at 90 °C [204] . These excellent results encouraged the authors to further extend their study to related backbone‐modified tripodal ligands bearing a silicon (F and G, where R=Si−Ph and Si−Me, respectively) or phosphorous (H, where R=P) as apidal constituents [205] . Among the different systems, Ru( Me Si‐Triphos Ph )(tmm), in combination with Al(OTf) 3 , (Scheme 35G) afforded the best results for DMM (TON=685), albeit without surpassing the more active system (Scheme 35E) [205] .…”

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

“…25,26 Recently, we applied a univariate optimisation approach including several hundred catalytic reactions to improve the selective ruthenium-catalysed transformation of carbon dioxide to dimethoxymethane (DMM) reaching a turnover number (TON) of 786 (Scheme 1). 27,28 The product DMM itself is a high value feedstock for biofuels, but can also be hydrolysed yielding formaldehyde and methanol or directly employed as a formaldehyde synthon. 29,30 Beside the desired product, only methyl formate (MF) was formed with TONs of up to 1290 (Scheme 1).…”