The 1,1-Carboboration of Bis(alkynyl)phosphanes as a Route to Phosphole Compounds
The 1,1-Carboboration of Bis(alkynyl)phosphanes as a Route to Phosphole Compounds
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DOI：
10.1002/anie.201107398
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Erker, Gerhard
中科院分区：
文献类型：
--
作者：
Moebus, Juri;Bonnin, Quentin;Erker, Gerhard
磷杂环戊二烯作为一类化合物受到越来越多的关注。他们拥有一个平面的五元杂环框架，具有重15族元素纳入一个显着的非平面的协调几何结构。因此，与其他第一排五元杂芳烃相比，磷杂环戊烯仅具有弱芳香性。[1]与它们的第一行元素亲属相比，磷杂环戊烯的合成途径要少得多。Mathey et al. [2]已经通过一些第4族金属茂炔偶联/磷酸化途径和相关的合成得到增强。[3]尽管如此，磷杂环戊二烯框架越来越多地被用于材料科学，[4]特别是与硼基受体取代基结合，与P供体共轭。[5]最近还研究了刚性共辄两性离子鳞/硼酸盐框架，并发现了相当大的兴趣。[6]我们现在已经发现了一种新的非常简单的合成方法，该方法在一锅反应中直接从合适的双-（炔基）膦得到3-硼基取代的磷杂环戊烯。本文描述和表征了几个代表性的实施例，并探索了它们的合成利用。我们最近已经表明，在用强刘易斯酸三（五氟苯基）硼烷（2）处理时，双（炔基）硅烷1在非常温和的反应条件下经历“Schiackmeyer 1，1-碳硼化反应”序列[7]的特殊变体，得到相应的硼基硅杂环戊烯3。[8，9]该反应可能涉及如方案1中所描绘的序列，涉及活化炔的一系列典型的1，1-碳硼化反应。[10]芳基双（炔基）膦5a-c是通过用相应的炔基锂试剂LiC CR（R= SiMe 3（a），nC 3 H 7（B），Ph（c））处理（tipp）PX 2化合物4（X= Cl，Br; tipp= 2，4，6-三异丙基苯基）制备的。类似地制备均三甲苯基P（C1 C-SiMe 3）2起始材料6a。将双（炔基）膦5a用1当量的B（C6 F5）3的甲苯溶液在70 ℃下处理（2小时），得到磷杂环戊烯7a，产率为79%（方案2）。化合物7a在d= 63 ppm处显示了三价RB（C6 F5）2硼刘易斯酸的典型宽11B NMR共振，在d= 59.1 ppm处显示了31 P NMR信号，在d= 107处显示了一对29 Si NMR共振。8和108。2ppm。7a的X射线晶体结构分析（图1）显示了平面中心五元环。典型地，弱芳香杂环内部的磷-碳距离P1 C1和P1 C4明显短于环外P1 C（芳基）键（表1），但是磷的配位几何结构明显是非平面的。三角平面硼部分的配位平面从中心环平面显著旋转（二面角C1-C2-B1-C51：π 52。0（6）8）。
Phospholes have been receiving increasing interest as a class of compounds. They possess a planar five-membered heterocyclic framework that has the heavy Group15 element incorporated in a markedly nonplanar coordination geometry. Consequently, in contrast to the other first-row five-membered heteroarenes, the phospholes are only weakly aromatic.[1] There are far fewer established synthetic pathways to phospholes compared to their first-row-element relatives. The classical elimination pathway described by Mathey et al.[2] has been augmented by some Group4 metallocene alkyne coupling/phosphorylation pathways and related syntheses.[3] Nevertheless, the phosphole framework is increasingly being used, for example, in materials science,[4] especially in conjunction with boron-based acceptor substituents in conjugation with the P donor.[5] Also rigid conjugated zwitterionic phosphonium/borate frameworks have recently been studied and found considerable interest.[6] We have now found a new very simple synthesis that directly makes 3-boryl substituted phospholes available from suitable bis-(alkynyl) phosphanes in a one-pot reaction. Several representative examples are described and characterized herein and their synthetic utilization explored. We have recently shown that bis (alkynyl) silanes 1 undergo a special variant of the “Wrackmeyer 1, 1-carboboration reaction” sequence [7] under very mild reaction conditions upon treatment with the strong Lewis acid tris (pentafluorophenyl) borane (2) to give the respective borylsiloles 3.[8, 9] The reaction probably involves a sequence as depicted in Scheme1, involving a typical series of 1, 1-carboboration reactions of activated alkynes.[10] The arylbis (alkynyl) phosphanes 5a–c were prepared by treatment of the (tipp) PX2 compounds 4 (X= Cl, Br; tipp= 2, 4, 6-triisopropylphenyl) with the respective alkynyl lithium reagents LiC CR (R= SiMe3 (a), nC 3H7 (b), Ph (c)). The mesitylP (C C-SiMe3) 2 starting material 6a was prepared analogously. The bis (alkynyl) phosphane 5a was treated with one equivalent of B (C6F5) 3 in toluene solution at 708C (2 h) to give the phosphole 7a in 79% yield (Scheme 2). Compound7a shows the typical broad 11B NMR resonance of a trivalent RB (C6F5) 2 boron Lewis acid at d= 63 ppm, a 31P NMR signal at d= 59.1 ppm and a pair of 29Si NMR resonances at d= À7. 8 and À8. 2ppm. The X-ray crystal-structure analysis of 7a (Figure1) shows the planar central five-membered ring. Typically, the phosphorus–carbon distances P1ÀC1 and P1À C4 inside the weakly aromatic heterocycle are markedly shorter than the exocyclic PÀC (aryl) bond (Table 1), but the coordination geometry at phosphorus is markedly nonplanar. The coordination plane of the trigonal-planar boron moiety is rotated markedly from the central ring plane (dihedral angle C1-C2-B1-C51: À52. 0 (6) 8).