NHC-mediated synthesis of an asymmetric, cationic phosphoranide, a phosphanide, and coinage-metal phosphanido complexes.
NHC-mediated synthesis of an asymmetric, cationic phosphoranide, a phosphanide, and coinage-metal phosphanido complexes.
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DOI：
10.1002/anie.201308309
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发表时间：
2013-12
影响因子：
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通讯作者：
K. Schwedtmann;Michael H. Holthausen;Kai‐Oliver Feldmann;J. Weigand
中科院分区：
文献类型：
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作者：
K. Schwedtmann;Michael H. Holthausen;Kai‐Oliver Feldmann;J. Weigand
在磷化学中使用咪唑基N-杂环卡宾（NHC）作为试剂，产生了一系列有趣的化合物（图1）。MacDonald及其同事描述了通过使PCl 3与作为还原剂的卡宾反应获得的阳离子1a+。[1a]同样从PCl 3开始，罗宾逊及其同事报道了磷酰胺衍生物1b，其中P原子是超配位的。[1b]1b还原后得到2，3-二磷杂双环戊二烯基2，其中P原子为二配位。[1c]该化合物被Bertrand氧化为32+[2]，说明咪唑基取代基不仅可以很好地稳定低配位和超配位的P原子，而且还可以制备阳离子。我们以前证明，相关的有机磷阳离子显示出显着的稳定性，例如，通过分离的叠氮基PIII阳离子4+。[3]此外，某些膦基取代的咪唑鎓离子的有趣的反应性进行了讨论。例如，用KHMDS处理5 [Cl]导致膦基取代基迁移到咪唑鎓环的4位，得到6a（方案1）。[4]此外，我们最近报道了阳离子7+还原为化合物8+，其中双阳离子二膦作为螯合刘易斯酸作用于氯阴离子（方案1）。[5]上述实例被描述为NHC配体和相应的P-中心部分的供体-受体络合物，或者被描述为在咪唑基取代基上带有正电荷的咪唑基取代的P化合物。Haaland [6]提供了一个通用的概念基础来描述这种成键环境，因此，后一种模型对我们来说似乎更现实，并在本文中使用。然而，独立于任何此类争议，上述化合物中的咪唑基取代基至少可用于三个目的。首先，它们有助于稳定低配位和超配位的Patoms。[7]其次，它们有利于通过正电荷的离域来稳定阳离子。[7]第三，它们用于降低直接键合的PIII原子的亲核性，从而限制分解途径并使分子成为用于过渡金属催化的有趣的贫电子配体。[7，8]在这种情况下，我们对阳离子7+的反应性感兴趣。在这里，我们报告的反应的盐7+与NHC，形成一个非常稳定的，罕见的例子的阳离子衍生物的磷酰胺，和调查其后续的化学，包括制备的磷酰胺阳离子和阳离子膦配合物的钴金属。
The use of imidazole-based N-heterocyclic carbenes (NHCs) as reagents in phosphorus chemistry resulted in an array of intriguing compounds (Figure 1). MacDonald and co-workers described cation 1a+ obtained by reacting PCl3 with a carbene as a reducing reagent.[1a] Also starting from PCl3, Robinson and co-workers reported the phosphoranide derivative 1b, in which the P atom is hypercoordinated.[1b] Upon reduction of 1b, 2, 3-diphosphabutadiene 2 is obtained in which the P atoms are two-coordinate.[1c] This compound was oxidized to 32+ by Bertrand [2] illustrating that imidazoliumyl substituents not only serve well for the stabilization of low-and hypercoordinated P atoms but also for the preparation of cations. We previously demonstrated that related organophosphorus cations show remarkable stability, for example, through the isolation of diazido PIII cation 4+.[3] Additionally, the intriguing reactivity of certain phosphanyl-substituted imidazolium ions has been discussed. For example, treatment of 5 [Cl] with KHMDS results in the migration of the phosphanyl substituent to the 4 position of the imidazolium ring to give 6a (Scheme 1).[4] Furthermore, we recently reported on the reduction of cation 7+ to compound 8+ in which a dicationic diphosphane acts as a chelating Lewis acid toward a chloride anion (Scheme 1).[5] The above-mentioned examples are either described as donor–acceptor complexes of NHC ligands and the respective P-centered moiety or as imidazoliumyl-substituted Pcompounds that bear a positive charge on the imidazoliumyl substituent. Haaland [6] provides a general conceptual basis to describe such bonding environments, and thus, the latter model appears to be more realistic for us and is used throughout this paper. Independent of any such controversy, however, the imidazoliumyl substituents in the above compounds serve well for at least three purposes. First, they help to stabilize low-as well as hypercoordinated Patoms.[7] Second, they are advantageous for the stabilization of cations through delocalization of the positive charge.[7] Third, they serve to reduce the nucleophilicity of a directly bonded PIII atom, thus limiting decomposition pathways and rendering the molecules interesting electron-poor ligands for transitionmetal catalysis.[7, 8]In this context, we were interested in the reactivity of cation 7+. Herein, we report on the reaction of salts of 7+ with an NHC, the formation of a remarkably stable, rare example of a cationic derivative of a phosphoranide, and investigations of its follow-up chemistry, including the preparation of a phosphanide cation and cationic phosphanido complexes of coinage metals.