Tandem Activation and Reduction of N2

最近的研究将小含氧物二氧化碳和一氧化碳的催化还原和利用描述为c1合成子。我们首次报道了将这些商品化学品均相还原为甲醇、甲烷和类似于费托催化生成的同类产品，并表明表面上简单的氢化钙不仅能够合成长期寻求的正烷基衍生物，还促进了前所未有的苯亲核烷基化反应。合成化学中剩余的重大挑战之一是有效利用分子氮来生成复杂的含氮产品。然而，氮素的惰性不仅仅是因为它的三重键很强。最恰当的是，等电子一氧化碳具有更大的键离解热，经历了各种各样的化学反应，包括我们最近报道的以钙为中心的同系化和还原。以第2族为中心的氮气还原的主要挑战部分在于其大的HOMO-LUMO能隙，这既不利于电子转移，也不利于Lewis酸碱反应，但主要是它的非极性和极化性，这排除了必要的高极化过渡态。为了绕过这些限制，该项目将针对在典型的S阻断中心克服氮气激活的动力学障碍的策略。除了更直接的方法外，我们将开发混合系统，其中第2组中心与氮气的协调一起管理到适当的过渡金属中心。长期以来，人们一直知道，自由氮与单个金属中心的结合会导致NN键的强烈极化，从而金属结合的氮中心带正电荷，而未结合的N原子带负电荷。因此，使用先例很好的物种，在不还原的情况下结合氮气，将使得氮气能够以类似于我们所建立的与自由CO和金属羰基络合物的反应的方式，传递到例如氢化钙的还原等价物中。作为说明，方案2显示了使用Ir(I)络合物将脱对称的氮分子传递到氢化钙。红外化合物通常是在还原条件下与硼氢化物合成的，因此应该可以在我的团队已经用于CO和CO2还原的氢硼化条件下使用。在第一个实例中，我们的目标是将氮气依次还原为二叠氮烯、肼，并最终还原为硼胺/氨，并将使用我们的一套可用的第2族氢化物来研究每一类化合物的化学计量反应性。一旦建立，我们将寻求利用这些物种进行进一步的反应，并将这种化学与我们已建立的插入和氢胺化反应结合起来，以生产胺类化合物。

Recent research has described the catalytic reduction and utilisation of the small oxygenates CO2 and CO as C1 synthons. We have reported the first homogeneous reduction of these commodity chemicals to methanol, methane and homologated products reminiscent of those produced by Fischer-Tropsch catalysis and have shown that the superficially simple calcium hydride not only enables the synthesis of long sought n-alkyl derivatives but also facilitates the unprecedented nucleophilic alkylation of benzene. One of the remaining grand challenges in synthetic chemistry is the efficient utilization of molecular dinitrogen in the generation of complex nitrogen-containing products. The inertness of dinitrogen, however, is not just due to its strong triple bond. Most pertinently, the isoelectronic carbon monoxide has an even greater bond dissociation enthalpy undergoes a wide variety of chemical reactions, including our recent report of calcium-centred homologation and reduction cited above. The major challenge of group 2 centred N2 reduction lies partly in its large HOMO-LUMO gap which disfavours both electron transfer and Lewis acid-base reactions, but primarily its non-polarity and polarisability which precludes the requisite highly polarised transition states. To circumvent these limitations this project will target strategies to overcome the kinetic barriers to N2 activation at typical s-block centres. In addition to more direct approaches, we will develop hybrid systems whereby the group 2 centre is administered in conjunction with coordination of N2 to an appropriate transition metal centre. The binding of free N2 to a single metal centre has long been known to induce a strong polarisation of the NN bond whereupon the metal-bound nitrogen centre bears a positive charge and the non-bound N atom a negative charge. The use of well precedented species which bind N2 without reduction will, thus, enable the delivery of N2 to a reducing equivalent of, for example, a calcium hydride in a similar manner our established reactivity with free CO and metal carbonyl complexes. By way of illustration, Scheme 2 shows the use of an iridium(I) complex to deliver the desymmetrised N2 molecule to a calcium hydride. Ir compounds are typically synthesised under reductive condition with borohydrides so should be amenable to use under the hydroboration conditions my group have already used for CO and CO2 reduction. In the first instance we will target sequential N2 reduction to diazenes, hydrazines and ultimately boryl amines/ammonia, and will study the stoichiometric reactivity of each of these classes of compound with our suite of available group 2 hydrides. Once established we will seek to utilise these species in further onward reactivity and to combine this chemistry with our established insertion and hydroamination reactivity to produce amine derivatives.