Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
J Am Chem Soc. 2017 May 24;139(20):6843-6846. doi: 10.1021/jacs.7b03287. Epub 2017 May 16.
With the view of developing self-activating electrophilic catalysts, we are now investigating complexes with a Lewis acidic moiety in the immediate vicinity of the transition metal center. Toward this end, we have synthesized a platinum complex in which the metal is connected to a Lewis acidic bis(triflato)stiboranyl ligand. This complex, ((o-(PhP)CH)SbOTf)PtCl (2), which was obtained by treatment of ((o-(PhP)CH)SbCl)PtCl (1) with 2 equiv of AgOTf, is surprisingly air stable. Yet, it promptly reacts with cyclohexylisocyanide to afford the dicationic chlorostibine complex [((o-(PhP)CH)SbCl)PtCNCy] ([3]) as a bis-triflate salt. Formation of [3] occurs through abstraction of the platinum-bound chloride ligand by the adjacent Lewis acidic antimony center. This halide migration reaction leads to activation of the platinum center. In turn, 2 behaves as a self-activating catalyst in reactions involving alkynes and readily mediates both enyne cyclization and intramolecular hydroarylation reactions, at room temperature, without addition of a chloride abstracting reagent. These results demonstrate that the coordination non-innocence of antimony ligands can be exploited for the purpose of electrophilic catalysis.
为了开发自活化亲电催化剂，我们目前正在研究在过渡金属中心附近具有路易斯酸性部分的配合物。为此，我们合成了一种铂配合物，其中金属与路易斯酸性双（三氟甲磺酸根）-二硼基配体相连。该配合物，((o-(PhP)CH)SbOTf)PtCl（2），通过用 2 当量的 AgOTf 处理((o-(PhP)CH)SbCl)PtCl（1）得到，出人意料地具有空气稳定性。然而，它会迅速与环己基异氰化物反应，以提供二阳离子氯代锑配合物[((o-(PhP)CH)SbCl)PtCNCy]（[3]）作为双三氟甲磺酸盐。[3]的形成是通过相邻路易斯酸性锑中心对与铂键合的氯配体进行抽离实现的。这个卤化物迁移反应导致铂中心的活化。反过来，2 在涉及炔烃的反应中充当自活化催化剂，并在室温下无需添加氯化物抽离试剂的情况下，容易介导烯炔环化和分子内芳基化反应。这些结果表明，锑配体的配位非中性可以被利用来进行亲电催化。
