Our research encompasses the synthesis and application of molecules and materials.
Photocatalysts are a class of material that mediate chemical reactions using photons as a source of energy. There are many potential uses including the degradation of chemicals detrimental to the environment, chemical synthesis, and the conversion of solar into chemical energy. We are interested in the later two applications and particularly the production of dihydrogen and dioxygen from water (which although technically not a catalytic reaction because it is endoenergetic), could potentially provide the basis for a clean fuel source with very low carbon emissions.
The concept is simple: to generate reducing (electrons) and oxidizing (holes) from excitation across a bandgap (Figure 1), which can subsequently be used for REDOX chemistry (e.g. water to dihydrogen and dioxygen). However, it is unlikely a single compound will be able to perform all the required steps efficiently (absorption across the visible spectrum, electron/hole migration to the surface, and catalysis of the chosen reaction, whilst remaining stable for a long time). Therefore 'engineered' materials composites are the more likely solution where more than one material can be used to perform one or two of the functions. We have recently built photocatalytic testing facilities and a microwave plasma reactor to help discover new materials for photocatalytic applications. The use of microwave-induced plasmas (MIP) builds on some of our earlier work exploring the synthesis of materials using microwave methods.
We have recently built a testing facility and microwave plasma reactor (Figure 2) to discover new materials for photocatalytic applications. The use of microwave-induced plasmas (MIP) builds on some of our earlier work exploring the synthesis of materials using microwave methods.
Microwave heating is a well established technique for solution based synthetic chemistry and most modern molecular laboratories now contain a microwave reactor. Commonly, rapid reaction rates can be achieved because of superheating that is a result of coupling between the solvent (or reactants) and microwave radiation. Similarly in the solid state one of the components of a reaction must couple with the microwaves, generating heat via dielectric or conduction losses to drive a reaction. Solids can heat at enormous rates (100 K/s), however many of interest do not couple with microwaves at room temperature limiting the application of this technique to preparative materials chemistry.
We have designed and constructed a reactor capable of initiating and sustaining microwave-induced plasmas of various gases including Ar, N2, H2/N2, NH3 and O2. The plasma can be used as a source of heat to drive bulk solid state reactions and also as a source of reactive species for gas-solid reactions for surface or bulk modification.
Nitrogen based compounds are amongst the most versatile and interesting ligands in transition metal and main group chemistry supporting a wide range of reactive species and promoting stoichiometric and catalytic reactivity. Examples include proteins and porphyrins in biological metalloenzymes, amido ligands in C-H and multiple bond activation, and imines and amines in polymerization, oxidation and Lewis acid catalysis.
We have been interested in developing a new simple class of N-donor compounds that can be simplistically characterised as neutral amido ligands. Initial work has focused on 1H-pyridin-(2E)-ylidenes (PYEs) that are very easy to synthesize in one step. PYE type ligands appear to be strong donors and their structure renders the N-substituent (R1, Figure 3) close to the metal, which can control reactivity.
This project is supported by DFT studies to probe metal-ligand bonding and electron distribution across the ligand.
Our interest in this class of compound has been to prepare new achiral and chiral compounds and investigate their application as ancillary ligands for metal-mediated catalysis. We have recently prepared a new class of enamine that results from formal addition of a NHC to an imine (Figure 4). The organic and organometallic chemistry of this very reactive molecule should be of interest for the preparation of new classes of N-heterocycles and also potentially chelating NHC-acyclic carbene complexes via insertion of a metal into the C=C double bond.
In addition to their growing popularity over the last 10 years for catalytic applications NHC are also of interest because of their unusual electronic properties and structure. In common with many other groups we are also interested in preparing complexes that may exhibit new stoichiometric reactions that may have future application to new catalytic processes.
The Department of Chemistry has modern analytical facilities including NMR spectrometers (700, 600, 500, 400, 300, 270 MHz), IR, UV and ESR spectrometers; a CCD diffractometer and mass (ESI, FAB) spectrometers; powder diffraction, XRF, TGA, DSC, and BET surface area measurements. Since the foundation of the York Jeol Nanocentre the group has access to an array of electron microscopy facilities including SEM and TEM.
In addition to standard laboratory equipment the group also has its own fibre optic UV-Vis and diffuse reflectance spectrometer, semi-prep HPLC, GC-MS, autoclaves, carousel reactors and drybox.