Green Chemistry for Catalytic C-C Coupling of Renewable Feedstocks

• Applicant: Professor Dr. Bernhard Breit
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 181737472

The majority of chemical commodities (plastics, foams, pharmaceuticals, agrochemicals) are made from rapidly depleting petroleum feedstocks. Consequently, there is a growing need to develop catalytic processes that enable byproduct-free manufacture of chemical products from abundant, renewable resources. Progress in this area will depend on the discovery of new patterns in chemical reactivity, as well as new strategies for controlling catalyst selectivity and activity. Hence, the primary goal of the proposed collaborative research is to develop selective, byproduct-free catalytic C-C couplings applicable to abundant, renewable alcohols (methanol, ethanol and glycerol) and carbon dioxide. The proposed research will merge new concepts catalyst selectivity-activity control pioneered by the Breit Group together with novel C-C bond forming hydrogenations established by the Krische Group (Scheme 1). Scheme 1. Developing catalysts for C-C coupling of abundant renewable feedstocks. The Breit Group has developed novel supramolecular catalysts that possess phosphine ligands incorporating acylguanidine substructures. In the proposed funding period, these ligands will be used to activate carbon dioxide as an electrophile in byproduct-free hydrogen-mediated C-C bond formations developed by the Krische Group. By stabilizing the transition state for carbonyl addition through hydrogen-bond donor-acceptor interactions, we hope to develop the first byproduct-free catalytic hydrocarboxylations employing carbon dioxide as a C1-building block (Scheme 2). Scheme 2. Development of byproduct-free catalytic hydrocarboxylations employing carbon dioxide as a C1- building block. (b) Byproduct-Free C-C Coupling of Abundant Renewable Alcohols (C.4.2): Research from the Krische Group demonstrates that ruthenium and iridium complexes catalyze the direct C-C coupling of alcohols to various π-unsaturated compounds. Here, it is our objective to (a) extend these processes to renewable alcohols (methanol, ethanol and glycerol) and (b) enable use of α-olefins as coupling partners. In these processes, the nucleophile-electrophile pairs generated via hydrogen exchange are present in only catalytic amounts, which raises the entropy of activation (ΔS*) for C-C coupling. For this reason, attempted couplings of α-olefins provide only trace amounts of products. Using hydrogen-bond donor ligands developed in the Breit Group, the entropy of activation such processes will be lowered. Efficient catalysts alcohol-α-olefin C-C coupling would avail chemical processes of enormous impact, e.g. the direct conversion of methanol or ethanol to less abundant higher alcohols (Scheme 3). Scheme 3. Direct byproduct-free conversion of lower alcohols to higher alcohols.

• DFG Programme: Research Grants
• International Connection: USA
• Participating Person: Professor Dr. Michael J. Kirsche