Fürstner A, Ackermann L, Beck K, Hori H, Koch D, Langemann K, Liebl M, Six C, Leitner W
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim/Ruhr, Germany.
J Am Chem Soc. 2001 Sep 19;123(37):9000-6. doi: 10.1021/ja010952k.
Liquid or supercritical carbon dioxide (scCO(2)) is a versatile reaction medium for ring-opening metathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-defined metal catalysts. The molybdenum alkylidene complex 1 and ruthenium carbenes 2 and 3 bearing PCy(3) or N-heterocyclic carbene ligands, respectively, can be used and are found to exhibit efficiency similar to that in chlorinated organic solvents. While compound 1 is readily soluble in scCO(2), complexes 2 and 3 behave like heterogeneous catalysts in this reaction medium. Importantly, however, the unique properties of scCO(2) provide significant advantages beyond simple solvent replacement. This pertains to highly convenient workup procedures both for polymeric and low molecular weight products, to catalyst immobilization, to reaction tuning by density control (RCM versus acyclic diene metathesis polymerization), and to applications of scCO(2) as a protective medium for basic amine functions. The latter phenomenon is explained by the reversible formation of the corresponding carbamic acid as evidenced by (1)H NMR data obtained in compressed CO(2). Together with its environmentally and toxicologically benign character, these unique physicochemical features sum up to a very attractive solvent profile of carbon dioxide for sustainable synthesis and production.
液态或超临界二氧化碳（scCO₂）是一种通用的反应介质，适用于使用特定金属催化剂的开环易位聚合（ROMP）和闭环烯烃易位（RCM）反应。分别带有PCy₃或N-杂环卡宾配体的钼亚烷基络合物1以及钌卡宾2和3均可使用，并且发现它们的效率与在氯化有机溶剂中的效率相似。虽然化合物1易溶于scCO₂，但络合物2和3在该反应介质中表现得像多相催化剂。然而，重要的是，scCO₂的独特性质提供了超越简单溶剂替代的显著优势。这涉及到聚合物和低分子量产物的非常方便的后处理程序、催化剂固定化、通过密度控制进行反应调节（RCM与无环二烯易位聚合）以及scCO₂作为碱性胺官能团保护介质的应用。后一种现象可通过在压缩CO₂中获得的¹H NMR数据证明的相应氨基甲酸的可逆形成来解释。连同其环境和毒理学上的良性特性，这些独特的物理化学特征总结出二氧化碳对于可持续合成和生产而言极具吸引力的溶剂特性。
