The Synthesis and Reactivity of Zirconium and Hafnium Hydrazides

酰肼锆铪的合成及反应活性

• 批准号: 1811529
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1811529
• 关键词: Synthesis; Reactivity; Zirconium; Hafnium; Hydrazides

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.

特别是在过去的十年中，已经证明了(L)M=NNR2类型的第四族肼可以与不饱和底物进行各种Ti=N-α多键的加成或插入反应。第4族肼的一个独特方面是N-α-α-N-β键的典型容易还原断裂，这也可以与CO、异氰化物和炔烃等可氧化底物发生，以形成新的N元素官能团和/或有机产品。这些肼类化合物的化学性质与一系列优雅的氮素活化和早期过渡金属的加成反应密切相关。最近，Monttford小组的工作从实验和计算两个方面研究了氮化钛(E=C(Sp1)，B和Si)的E-H键活化反应以及其他小分子活化反应。然而，这一化学过程中的许多元素仍然没有被发现，因为使用了这些元素可以改变化学反应的活性，从而形成了一套截然不同的配位体(L在(L)M=nNR2中)。这使得能够捕获反应路径上的中间体，并将不同的反应产物从类似的反应中分离出来。这个项目将研究这种反应，以及金属中心上的一系列配位体。本月进行的初步反应已经分离出了DFT研究预测的第4族肼与硅烷反应的中间体--为计算研究提供了实验证据。除了对锆和肼的反应性研究外，还将探索以前无法获得的肼的合成。以前只合成和研究了(L)型(NNPh2)Zr和Hf的酰肼化合物。然而，(L)型的Zr和Hf酰肼在反应和催化方面很有价值，因为类似的二甲基钛酰肼对二苯基钛的酰肼表现出更高的反应活性和更有利的催化作用。此前，人们曾尝试过合成二甲基肼和氢化锆，尽管该络合物已二聚化成一种与小分子没有反应活性的络合物。然而，人们认为配体组的改变可能不利于二聚化，并允许分离所需的产物。这一点将在这个项目中进行研究，如果成功，新的二甲基肼和锆肼可以测试许多小分子的反应性和催化剂。这项拟议的研究项目涉及新的反应性研究，以及一条新的合成路线，这将允许一系列未知的反应性和催化测试。这些研究将通过实验和计算(在小组内和我们的合作者Eric Clot博士)进行，以充分了解其中的化学作用。