High-energy, early transition metal hydrazides for N atom transfer reactions in synthesis and catalysis: scope, mechanism and applications.

6族过渡金属酰肼，(L)M=NH_2，在氮气生物转化和工业转化为氨的反应中占有举足轻重的地位。在自然界和几个重要的模型系统中，这是通过一系列电子转移和质子化步骤进行的。在尝试使用中间过渡金属肼络合物作为合成增值有机氮产品的试剂方面，国际上也付出了相当大的努力。这种直接使用大气中的氮气作为商业原料的圣杯概念将绕过高能的哈伯-博世(NH3合成)过程。然而，中间金属M=NNR2官能团的反应性很低。它的特征只是涉及NR2的变换(涉及N-H基团的质子化或插入/缩合)。结构数据和计算研究解释了这一点：对于中后期的金属，NNR2最好被视为中性异二氮烯：N=NR2。M-NNR2键的更具配位性和N=N的多键特性降低了这两个位置的本征反应性。相反，我们对第4族NNR2系统的X射线和密度泛函结果发现它们是还原的酰肼，[NNR2]2-。具体地说，当N-N pi*mos被占据时，N-N键被延长和减弱；M=N多键是不饱和的，并且非常活跃，被β-NR2孤对进一步破坏稳定。虽然有一个简单的式NNR2，但中金属异二氮烯和早期金属肼配体与费休卡宾和施罗克亚烷基一样是根本不同的。正如早期金属M=Cr2比晚期金属M=Cr2具有更高的活性一样，M=NNR2也是如此。我们最近开发了三种方法来在非常不同的环境中制备这些迄今尚未开发的具有Ti=NNR2官能团的早期过渡金属肼。对一系列有机底物(末端和内部的炔烃、腈、异腈、膦炔、二氧化碳、异氰酸酯)的初步结果表明了丰富的环加成化学。值得注意的是，某些炔和腈通过独特的单N原子转移步骤插入到N-N键中。我们还发现，这可以是催化的，因此在室温下，1，2-二氨基烯由肼和跨越C-C三键的炔烃：N-N加成生成。如果二胺化反应可以延长，它最终可以提供一种方法，在任何不饱和的C元素键上加成任何一般的N-X(X=N，O，P)。这有可能改变1，2-二胺和相关化合物的合成模式。因此，在这个项目中，我们将开发几乎未被探索的早期过渡金属肼化学领域，能够以100%有效的方式将高能、高度还原的N-NR2和相关官能团输送到一系列底物上。我们最新的合成方法学突破和初步反应性研究提供了一个完美和及时的平台，可以启动快速进展。与领先的DFT计算项目合作伙伴合作，我们将提供一个基本工具箱，以了解和利用这一独特的反应范围、机制和在C-N、C-C和一般C-杂元素键形成方面的应用。

Group 6 transition metal hydrazides, (L)M=NNH2, occupy a pivotal position on the pathway for the biological and industrial conversion of N2 to NH3. In nature and in several important model systems this proceeds through a series of electron transfer and protonation steps. Considerable international effort has also been spent on trying to use mid-transition metal hydrazide complexes as reagents for the synthesis of value-added organo-nitrogen products. This holy grail concept of directly using atmospheric N2 as a commercial feedstock would by-pass the high-energy Haber-Bosch (NH3 synthesis) process. However, mid-metal M=NNR2 functional group reactivity is minimal. It is characterised only by transformations involving the NR2 (protonation or insertion/condensation involving N-H groups). No M=N bond reactivity is seen and N-N bond cleavage occurs only under highly forcing conditions using external reductants.Structural data and computational studies explain this: for mid-later metals NNR2 is best viewed as a neutral isodiazene :N=NR2. The more dative nature of the M--NNR2 bond and multiple bond character of N=N reduces the intrinsic reactivity at these two sites. In contrast, our X-ray and DFT results for Group 4 NNR2 systems find them to be reduced hydrazides, [NNR2]2-. Specifically, the N-N bonds are lengthened and weakened as the N-N pi* MOs are occupied; the M=N multiple bond is unsaturated and very reactive, further destabilised by the beta-NR2 lone pair. While sharing a simple formula NNR2 , mid-metal isodiazene and early metal hydrazide ligands are as fundamentally different as Fischer carbenes and Schrock alkylidenes. Just as early metal M=CR2 groups are intrinsically more reactive than later metal M=CR2, so it is for M=NNR2.We have recently developed three methods for making these hitherto undeveloped early transition metal hydrazides with Ti=NNR2 functional groups in very different environments. Preliminary results with a range of organic substrates (terminal and internal alkynes, nitriles, isonitriles, phospha-alkynes, CO2, isocyanates) indicate a wealth of cycloaddition chemistry. Remarkably certain alkynes and nitriles insertion into the N-N bond via a unique single N atom transfer step. We have also found this can be made catalytic so that a 1,2-diaminoalkene is formed catalytically at room temperature from a hydrazine and an alkyne: N-N addition across a C-C triple bond. If the diamination reaction can be extended it could ultimately provide a means of adding any general N-X (X = N, O, P) across any unsaturated C-element bond. This has the potential for a paradigm shift in the synthesis of 1,2-diamine and related compounds.In this project we will therefore develop the virtually unexplored area of early transition metal hydrazide chemistry, capable of delivering high-energy, highly reduced N-NR2 and related functional groups to a range of substrates in a 100% efficient, atom by atom manner. Our very recent synthetic methodology breakthroughs and preliminary reactivity studies provide a perfect and timely platform from which rapid progress can be launched. Working with a leading DFT computational Project Partner, we will deliver a fundamental toolbox for understanding and exploiting this unique reactivity in terms of scope, mechanism and applications in C-N, C-C and general C-heteroelement bond formation.