Frustrated Lewis Pairs beyond the Main Group: Synthesis, Reactivity, and Small Molecule Activation with Cationic Zirconocene–Phosphinoaryloxide Complexes

The extension of the frustrated Lewis pair (FLP) concept to the transition series with cationic zirconocene–phosphinoaryloxide complexes is demonstrated. Such complexes mimic the reactivity of main group FLPs in reactions such as heterolytic hydrogen cleavage, CO2 activation, olefin and alkyne addition, and ring-opening of tetrahydrofuran. The interplay between sterics and electronics is shown to have an important role in determining the reactivity of these compounds with hydrogen in particular. The Zr–H species generated from the heterolytic activation of hydrogen is shown to undergo insertion reactions with both CO2 and CO. Crucially, these transition metal FLPs are markedly more reactive than main group systems in many cases, and in addition to the usual array of reactions they demonstrate unprecedented reactivity in the activation of small molecules. This includes SN2 and E2 reactions with alkyl chlorides and fluorides, enolate formation from acetone, and the cleavage of C–O bonds to facilitate SN2 type reactions with noncyclic dialkyl ethers.

本研究证实了将受阻路易斯酸碱对（frustrated Lewis pair, FLP）概念拓展至含阳离子锆茂-膦芳氧基配合物的过渡金属体系的可行性。此类配合物可模拟主族受阻路易斯酸碱对的反应活性，能够参与异裂氢解、二氧化碳活化、烯烃与炔烃加成以及四氢呋喃开环等反应。研究表明，位阻效应与电子效应的相互作用，尤其是在决定此类配合物与氢气的反应活性方面，发挥着关键作用。经氢气异裂活化生成的锆氢（Zr–H）物种，可与二氧化碳及一氧化碳发生插入反应。至关重要的是，此类过渡金属型受阻路易斯酸碱对在多数情况下的反应活性显著优于主族体系；除常规反应类型外，它们在小分子活化领域还展现出前所未有的反应活性，此类反应涵盖了烷基氯与烷基氟参与的双分子亲核取代（SN2）与双分子消除（E2）反应、由丙酮生成烯醇盐的过程，以及通过碳氧键断裂实现非环二烷基醚参与的类SN2反应。