Tandem Activation and Reduction of N2

最近的研究描述了催化还原和利用小氧合物CO2和CO作为C1合子。我们已经报道了这些商品化学品首次均相还原为甲醇、甲烷和类似于费托催化产生的同质产物，并表明表面简单的氢化钙不仅能够合成长期寻找的正烷基衍生物，而且还促进了苯的前所未有的亲核烷基化。合成化学中仍然存在的重大挑战之一是在生成复杂含氮产品时有效利用分子二氮。然而，二氮的惰性不仅仅是由于它的强三键。最重要的是，等电子一氧化碳具有更大的键解离焓，可以经历各种各样的化学反应，包括我们最近提到的以钙为中心的同源性和还原。以2族为中心的N2还原的主要挑战部分在于其较大的HOMO-LUMO间隙，这不利于电子转移和刘易斯酸碱反应，但主要是它的非极性和极化性，这排除了必要的高度极化过渡态。为了规避这些限制，该项目将针对克服典型s区块中心N2活化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，使第二组中心与N2协调到适当的过渡金属中心一起管理。人们早就知道，自由氮原子与单个金属中心的结合会引起神经网络键的强烈极化，因此金属结合的氮原子中心带正电荷，而非结合的氮原子带负电荷。因此，使用已有的结合N2而不还原的物质将使N2能够以类似于我们与游离CO和金属羰基配合物建立的反应性的方式传递到还原等价物，例如氢化钙。作为说明，方案2显示了使用铱(I)配合物将不对称的N2分子传递给氢化钙。Ir化合物通常是在硼氢化物的还原条件下合成的，所以应该可以在硼氢化条件下使用，我的小组已经用于CO和CO2的还原。在第一个例子中，我们的目标是将氮气顺序还原为二氮、肼和最终的硼胺/氨，并将研究这类化合物与我们可用的2族氢化物的化学计量反应性。一旦确定，我们将寻求进一步利用这些物种的反应性，并将这种化学与我们已建立的插入和氢胺化反应性相结合，以生产胺衍生物。

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.