On the stability of early-transition-metal metallacyclobutadiene complexes
On the stability of early-transition-metal metallacyclobutadiene complexes
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DOI：
10.1021/ja00339a025
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发表时间：
1983
影响因子：
15
通讯作者：
B. Bursten
中科院分区：
文献类型：
--
作者：
B. Bursten
几年前，Katz 提出乙炔复分解反应的机理与烯烃复分解反应相似，通过金属环丁二烯中间体进行，可能涉及金属碳炔络合物。 1 该提议得到了 Schrock 观察的大力支持，即某些亚烷基钨 (VI) 络合物是有效的乙炔复分解催化剂。 2 最近，Schrock、Churchill 及其同事分离并表征了向烷叉炔络合物 W (Ct-Bu)(dme) Cl3 加成 1 当量 2-丁炔而得到的产物，发现它是环丁二烯钨络合物 W (CZ-Bu)(MeC= CMe) Cl3，其中有一个基本上为平面的 WC3 环。 3 稳定的金属环丁二烯配合物的存在引发了几个有趣的问题。其中最重要的是为什么这样的系统应该是稳定的，而有机类似物环丁二烯只是暂时稳定的。其次，WC3环3的几何形状有些令人惊讶，因为Ca-C5-Ca角相当大（118.9（8）），而W-Cj键长相当短（2.115（8）μ）。最后，如果要使早期过渡金属亚烷基配合物成为有效的催化剂，则金属环丁二烯配合物的稳定性是不理想的，并且有兴趣确定可以采取什么措施来破坏它们的稳定性。为此，我们对模型化合物 CI3WC3H3 及其金属环丁二烯核 [WC3H3] 3+ 进行了 Fenske-Hall 分子轨道计算4。 5
Several years ago Katz proposed that the mechanism of the acetylene metathesis reaction parallels that of the olefin metathesis reaction by proceeding through a metallacyclobutadiene inter-mediate, presumably involving a metal-carbyne complex. 1 This proposal received strong supportfrom Schrock’s observation that certain tungsten (VI) alkylidyne complexes are effective acetylene metathesis catalysts. 2 More recently, Schrock, Churchill, and co-workers have isolated and structurally characterized the product resulting from the addition of 1 equiv of 2-butyne to the alkylidyne complex W (Ct-Bu)(dme) Cl3 and have found it to be the tungstenacyclobutadiene complex W (CZ-Bu)(MeC= CMe) Cl3, in which there is an essentially planar WC3 ring. 3 The existence of stable metallacyclobutadiene complexes raises several interesting questions. Foremost among these is why such systems should be stable whereas theorganic analogue cyclobutadiene is only transiently so. Secondly, the geometry of the WC3 ring3 is somewhat surprising in that the Ca-C5-Ca angle is quite large (118.9 (8)) and the W-Cj bond length is quite short (2.115 (8) Á). Finally, the stability of metallacyclobutadiene complexes is undesirable if early-transition-metalalkylidyne complexes are to be effective catalysts, and it is of interest to determine what might be done todestabilize them. To theseends, Fenske-Hall molecular orbital calculations4 have been performed on the model compound CI3WC3H3 and its metallacyclobutadienoid core[WC3H3] 3+. 5