Krafft M E, Boñaga L V, Hirosawa C
Department of Chemistry, The Florida State University, Tallahassee, Florida 32306-4390, USA.
J Org Chem. 2001 May 4;66(9):3004-20. doi: 10.1021/jo0057708.
In this report we have shown that the commercially available Co(2)(CO)(8) and Co(4)(CO)(12), and enyne--Co(2)(CO)(6) complexes, are sufficiently effective in catalyzing the Pauson--Khand reaction under one atmosphere of CO pressure. It was further demonstrated that the efficiencies of these cyclization protocols could be enhanced by the presence of cyclohexylamine. These procedures have also rendered more practical and highly convenient alternatives for the catalytic Pauson--Khand reaction. Most importantly, we have dispelled the common belief that Co(4)(CO)(12) is inactive in the Pauson--Khand reaction under one atmosphere of carbon monoxide. Of mechanistic importance is that these studies have also shown that the probable formation of Co(4)(CO)(12) is not necessarily a dead end pathway in the Co(2)(CO)(8)-catalyzed Pauson--Khand reaction. It is also of interest that substoichiometric amounts of Co(2)(CO)(8), in DME and in the presence of cyclohexylamine, are sufficient for the cyclocarbonylation of enynes under a nitrogen atmosphere. Our findings have provided more practical protocols for the Pauson-Khand reaction using catalytic amounts of cobalt carbonyl complexes and a better understanding of the influence of Lewis bases on their efficiency. These reports on the activity of Co(4)(CO)(12) are anticipated to develop into a convenient and practical alternative for Co(2)(CO)(8) catalysis.
在本报告中，我们已经表明，市售的Co₂(CO)₈和Co₄(CO)₁₂以及烯炔-Co₂(CO)₆配合物，在CO压力为一个大气压的条件下，对催化Pauson-Khand反应具有足够的有效性。进一步证明，环己胺的存在可以提高这些环化反应的效率。这些方法也为催化Pauson-Khand反应提供了更实用、更方便的替代方案。最重要的是，我们消除了一种普遍的观念，即Co₄(CO)₁₂在一氧化碳一个大气压下的Pauson-Khand反应中是无活性的。从机理重要性来看，这些研究还表明，在Co₂(CO)₈催化的Pauson-Khand反应中，Co₄(CO)₁₂的可能形成不一定是一条死胡同路径。同样有趣的是，在DME中且在环己胺存在下，化学计量以下的Co₂(CO)₈量足以在氮气气氛下使烯炔进行环羰基化反应。我们的研究结果为使用催化量的羰基钴配合物进行Pauson-Khand反应提供了更实用的方法，并更好地理解了路易斯碱对其效率的影响。这些关于Co₄(CO)₁₂活性的报告有望发展成为一种方便实用的Co₂(CO)₈催化替代方法。
