Green Chemistry for Catalytic C-C Coupling of Renewable Feedstocks

大多数化学商品(塑料、泡沫、药品、农用化学品)都是由迅速耗尽的石油原料制成的。因此，人们越来越需要开发催化工艺，使之能够从丰富的可再生资源中生产无副产品的化学产品。这一领域的进展将取决于化学反应性的新模式的发现，以及控制催化剂选择性和活性的新策略。因此，拟议的合作研究的主要目标是开发适用于丰富的可再生醇(甲醇、乙醇和甘油)和二氧化碳的选择性、无副产物的催化C-C偶联。这项拟议的研究将把Breit Group开创的催化剂选择性-活性控制新概念与Krische Group建立的新的C-C键形成氢化(方案1)结合起来。方案1.开发丰富的可再生原料的C-C偶联催化剂。Breit Group开发了新型超分子催化剂，该催化剂具有含有酰基胍亚结构的膦配体。在拟议的资助期内，这些配体将被用来激活二氧化碳，作为Krische Group开发的无副产物氢介导的C-C键形成中的电泳剂。通过氢键给体-受体相互作用稳定了羰基加成反应的过渡态，我们希望开发出第一个以二氧化碳为构筑基团的无副产物催化氢羧化反应(方案2)。方案2.开发无副产物的催化氢羧化反应，使用二氧化碳作为c1构筑基团。(B)丰富的可再生醇的无副产物C-C偶联(C.4.2)：Krische Group的研究表明，Ru和Ir的络合物催化醇与各种π不饱和化合物直接C-C偶联。在这里，我们的目标是(A)将这些过程扩展到可再生醇(甲醇、乙醇和甘油)和(B)能够使用α-烯烃作为偶联伙伴。在这些过程中，通过氢交换产生的亲核-亲核对只存在于催化量中，这提高了C-C偶联的活化熵(ΔS*)。出于这个原因，α-烯烃的尝试偶联只能提供微量的产品。使用Breit Group开发的氢键给体配体，此类过程的激活熵将会降低。高效的催化剂醇-α-烯烃C-C偶联将有助于影响巨大的化学过程，例如将甲醇或乙醇直接转化为含量较低的高级醇(方案3)。方案3.低级醇直接无副产物转化为高级醇。

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.