The Synthesis and Reactivity of Zirconium and Hafnium Hydrazides

点击翻译按钮获取中文摘要

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.