The Synthesis and Reactivity of Zirconium and Hafnium Hydrazides

特别是在过去的十年中，已经证明(L)M=NNR2型的4族酰肼可以与不饱和底物发生多种Ti= n - α多键的加成或插入反应。第4族肼的一个独特之处是n - α - α - n - β键的典型易还原裂解，这种裂解也可以与可氧化底物如CO、异氰酸酯和炔发生，形成新的n元素官能团和/或有机产物。这些肼类化合物的化学性质与早期过渡金属的优雅的二氮活化和加成反应有密切的联系。Mountford小组最近的工作，通过实验和计算，研究了钛肼（E = C(sp1)， B和Si）的E- h键激活反应以及其他小分子激活反应。然而，这种与锆和铪肼的化学反应仍未被探索。锆和铪的使用可以改变反应性，并允许研究一个完全不同的配体集（L in (L)M=NNR2）。这使得反应途径上的中间体可以被捕获，不同的反应产物可以从类似的反应中分离出来。这个项目将研究这些反应，以及金属中心的一系列配体。本月进行的初步反应已经分离出了DFT研究预测的4族肼与硅烷反应的中间产物——为计算研究提供了实验证据。除了锆和铪酰肼的反应性研究外，还将探索以前无法实现的酰肼的合成。目前只合成和研究了(L)Zr=NNPh2型锆和铪酰肼。然而，(L)Zr=NNMe2型的Zr和Hf肼在反应性和催化作用方面更有意义，因为类似的二甲基钛肼比二苯基钛肼表现出更高的反应性和更有利的催化作用。在此之前，人们曾尝试合成二甲基锆和铪肼，但这种配合物已经二聚成一种对小分子没有反应性的配合物。然而，人们认为配体设置的变化可能不利于二聚化，并允许所需的产物被分离。这将在本项目中进行研究，如果成功，新的二甲基锆和铪肼就可以用许多小分子进行反应性和催化性测试。这个拟议的研究项目涉及新的反应性研究，以及以前无法获得的一类锆和铪肼的新合成路线，这将允许进行一系列未开发的反应性和催化试验。这些研究将进行实验和计算（在小组内和我们的合作者埃里克·克洛特博士），以充分了解化学的作用。

It has been shown over the last decade in particular that Group 4 hydrazides of the type (L)M=NNR2 can undergo a variety of addition or insertion reactions of the Ti=N-alpha multiple bond with unsaturated substrates. A distinctive aspect of Group 4 hydrazido is the typically facile reductive cleavage of the N-alpha-alpha-N-beta bond that can also occur with oxidizable substrates such as CO, isocyanides and alkynes to form new N-element functional groups and/or organic products. The chemistry of these hydrazides is tangentially connected with an established body of elegant dinitrogen activation and addition reactions of the early transition metals. Recent work in the Mountford group has investigated, both experimentally and computationally, E-H bond activation reactions of titanium hydrazides (E = C(sp1), B and Si) as well as other small molecule activation reactions. However, much of this chemistry with zirconium and hafnium hydrazides remains unexplored.The use of zirconium and hafnium can alter reactivity, and allow for a drastically different ligand set (L in (L)M=NNR2) to be investigated. This enables intermediates on reaction pathways to be trapped and different reaction products to be isolated from analogous reactions. This project will investigate such reactions, as well as a range of ligand sets on the metal centre. Initial reactions carried out this month have already isolated an intermediate predicted by DFT studies for the reaction of Group 4 hydrazides with silanes - providing experimental proof of computational studies.In addition to the reactivity studies of zirconium and hafnium hydrazides, the synthesis of previously unattainable hydrazides will be explored. Only zirconium and hafnium hydrazides of the type (L)Zr=NNPh2 have been synthesised and studied before. However, Zr and Hf hydrazides of the type (L)Zr=NNMe2 would be of much interest in reactivity and catalysis, as analogous dimethyl titanium hydrazides have shown increased reactivity and more favourable catalysis to diphenyl titanium hydrazides. Previously the synthesis of dimethyl zirconium and hafnium hydrazides has been attempted before, though the complex has dimerized to a complex that shows no reactivity to small molecules. However, it is thought that a change in ligand set may disfavour dimerization and allow the desired product to be isolated. This will be investigated in this project and, if successful, the novel dimethyl zirconium and hafnium hydrazides can then be tested with many small molecules for reactivity as well as for catalysis.This proposed research project involves novel reactivity studies, as well as a novel synthesis route to a previously unattainable class of zirconium and hafnium hydrazides, which would allow for a series of unexplored reactivity and catalysis tests. These studies will be carried out both experimentally and computationally (within the group and with our collaborator Dr Eric Clot) to allow for a full understanding of the chemistry at play.