Exploiting hemi-labile ligands in Main Group catalysis

点击翻译按钮获取中文摘要

A catalyst is a substance which speeds up the rate of a chemical reaction without being consumed itself. They do this by offering an alternative, lower-energy mechanism by which the reaction happens, at the end of which the original catalyst is reformed. They are crucial for energy efficiency, as using them allows for reactions to be carried out quicker and at lower temperatures. As such, the use of catalysts is ubiquitous in industry for chemical processes of all types.The transition metals (the block of elements in the centre of the periodic table) make excellent catalysts, as their outermost electron shells are partially filled, allowing easy access to both electrons and empty binding sites around each metal atom. However, the metals which are important to catalysis, such as palladium and rhodium in catalytic converters for cars, tend to be toxic to life, expensive, and rare. As reserves in the Earth's crust dwindle, social and environmental difficulties have arisen with their supply and extracting them from their ores. It is vital, therefore, for replacements to be found.Elements belonging to the main group (on the right side of the periodic table, such as aluminium and silicon) tend to be much more benign environmentally and economically. Historically, these elements were thought to invariably form compounds with completed shells of electrons, making them poor catalysts. A series of more recent discoveries around this has challenged this view, and these elements are now known to undergo similar types of reaction to transition metals with a wide variety of molecules. Because of this, they are now currently being explored for use as catalysts.A ligand is a molecule which binds (or coordinates) to a central metal atom to form a coordination complex. A hemi-labile ligand is one which contains two or more sites which can coordinate, where at least one of them can reversibly dissociate, while the rest stay(s) firmlybound. This vacated space allows for other molecules to bind, which now allows a chemical reaction to easily occur.Hemi-labile ligands are now known to promote 'transition-metal' like behaviour in the main group elements where otherwise it would not be seen. A few promising potential catalysts have already been found by exploiting this behaviour. As such, this project aims expand upon this work and to develop efficient catalysts for a wider scope of important reactions.The ultimate objective is for the eventual replacement of transition metals with main group elements in catalysis. The potential impact is a more sustainable future, where chemical manufacturing is achieved solely using abundant, inexpensive, and environmentally benign elements.This project falls within the EPSRC 'Manufacturing the Future' research area.