Structurally Versatile Ligand System for the Ruthenium Catalyzed One-Pot Hydrogenation of CO₂ to Methanol

Abstract

The direct hydrogenation of carbon dioxide to methanol represents a challenging transformation for molecular catalyst, and only a few systems facilitate this reaction. Herein, molecular complexes based on the tridentate tdppcy ligand are described, enabling the variable synthesis of structurally tailored catalytic systems. In combination with selected ruthenium precursors and suitable cocatalysts the direct hydrogenation of carbon dioxide could be demonstrated with unprecedented activity. Moreover, the versatile catalyst allowed the reaction in two-phase systems, paving the way to adapted reaction concepts for the utilization of the renewable carbon source carbon dioxide.

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

“…Very recently the same group also demonstrated a highly active cyclohexyltriphosphine ligand based ruthenium catalyst ( Ru30 , Scheme 53 ) system for the hydrogenation of CO 2 to methanol using aluminum tristriflate (Al(OTf) 3 ) as a Lewis acid additive. 363 Under the optimized conditions of H 2 /CO 2 = 90/30 bar pressure, 120 °C, and 20 h reaction time, a TON of up to 2100 was obtained in ethanol solvent. Moreover, the reduction of CO 2 to methanol was also performed in a biphasic mixture consisting of n -decanol and water with the same system under the optimized reaction condition with maximum TONs up to 1087.…”

Highlights and challenges in the selective reduction of carbon dioxide to methanol

“…The works reporting direct CO2 hydrogenation to methanol using homogeneous metal complexes are not numerous [73][74][75][76][77][78][79][80][81][82] . Typically, a three-step cascade catalysis process is pursued: (i) formic acid formation from CO2 hydrogenation; (ii) functionalization of formate to an activated ester, such as alkyl formate or carbonate or carbamate; and finally (iii) CH3OH formation upon hydrogenation of the previous intermediate.…”

“…species 85 . The nature of ligand plays an important role in the catalytic cycle, through both steric and electronic effects 73 . For example, tuning of the triphos ligand to cis,cis-1,3,5-tris-(diphenylphosphino)cyclohexane (tdppcy) gave high efficiency in direct methanol synthesis (Fig.…”

“…The specific coordination of the triphos ligand is responsible for the remarkable reactivity of these catalysts, as it was already observed with the noble Ru complexes. However, novel versatile ligand structures are necessary for the development of more efficient homogeneous catalysts 73,76 . They should allow adapting the molecular catalyst for the multiphase and multistep reactions as well as permit the catalyst immobilization to facilitate the recovery and recycling.…”

Well‐defined Cp*Co(III)‐catalyzed Hydrogenation of Carbonates and Polycarbonates

“…Very recently, Beller [15] and Prakash [16] reported earth‐abundant cobalt and manganese‐catalysed transformation of CO 2 into methanol by reaching a turn over numbers (TON) up to 78 and 36. While the manuscript was in preparation, Klankermayer and co‐workers reported the unprecedented TON of 2100 for the conversion of CO 2 into MeOH by engineering structurally versatile triphos( t dppcy)/Ru catalytic system [17] …”