N-heterocyclic carbenes on metal surfaces - towards applications in corrosion inhibition and catalysis

This proposal aims to examine the utility of N-heterocyclic carbenes (NHCs) in a number of technologically important areas including corrosion inhibition, etching of metal surfaces and enantioselective heterogeneous catalysis. This is a collaborative project between a catalytic surface scientist (Prof. Chris Baddeley, St Andrews) and experts in organometallic chemistry and materials science (Prof. Cathy Crudden, Queen's University, Ontario) and surface and materials chemistry (Prof. Hugh Horton, Queen's University, Ontario).

NHCs are an exciting class of molecules that have been successfully and extensively employed in homogeneous catalysis since the 1990s. There has recently been a rapid increase in interest in the use of NHCs for the stabilisation of transition metal nanoparticles and extended metal surfaces.
A very attractive feature of NHCs is their highly flexible synthesis. This makes it relatively straightforward to introduce functionality into the molecular structure of NHCs in order to tailor their properties.

A key advance in this area was the development by Crudden's group of synthetic methods to produce bench stable NHCs in the carbonate form. Our work showed that NHCs of this type could be vapour deposited in ultrahigh vacuum onto metal surfaces (Baddeley) as well as being deposited from solution (Horton). Since the 1980s the creation of self-assembled monolayers (SAMs) on metal surfaces has led to many important applications. Commonly, SAMs consist of thiolate modified Au surfaces. Crudden and Horton showed that NHCs on Au outperform their thiolate analogues in terms of chemical and thermal stability. Baddeley was able to measure the strength of the Au-carbene bond and show that it is significantly stronger than the Au-S bond in thiolate SAMs.

This project aims to exploit the chemical and thermal stability of NHC modified metals in a number of ways. Baddeley will use the complementary techniques of scanning tunnelling microscopy, high resolution electron energy loss spectroscopy and temperature programmed desorption to quantify the adsorption energy of NHCs on metal surfaces, to characterise the orientation, packing and thermal stability of adsorbed NHC molecules. The ability of NHCs to etch oxide surfaces and to passivate metal surfaces will be investigated with the objective of applying NHCs in the field of corrosion inhibition. The adsorption of chiral NHCs onto metal surfaces will be investigated with the aim of developing enantioselective heterogeneous catalysts - i.e. catalysts capable of producing one mirror image form of an organic molecule and not the other. Enantioselective catalysis is extremely important in the pharmaceutical and agrochemicals industries, but, to date, heterogeneous catalysts have made little impact on an industrial scale.

This proposal seeks to functionalise metallic surfaces with N-heterocyclic carbenes in order to create systems that can be exploited in a range of technological applications including enantioselective heterogeneous catalysis, corrosion inhibition and development of new functional materials for application in Surface Plasmon Resonance (SPR).

Economy, Society and Environment:
Tackling corrosion is important in many areas. The development of corrosion inhibitors for Cu based microelectronic devices will impact in the electronics industry and a greater understanding of the mechanism of corrosion inhibition could impact in other areas where Cu corrosion is a significant problem (e.g. industrial cooling systems).

Producing highly stable NHC coated Ag surfaces will facilitate the development of more robust instrumentation for the technique of SPR which currently has a number of biotechnological applications including the development of new pharmaceuticals and in characterising protein function and disease mechanisms. The ability to use NHCs to etch oxide surfaces to create high quality metallic surfaces would benefit companies interested in growing low defect graphene films.

The delivery of highly selective catalytic processes will have enormous impact across the UK chemical industry in a 10-50 year time-frame. The commercial sector face economic pressures including escalating disposal charges and increasing raw material/energy costs, which can be addressed by improved process selectivity. The production of enantiomerically pure compounds via enantioselective catalysis is increasingly important in the pharmaceutical industry. In addition, there is a growing demand for chiral products in the agrochemicals, flavours and fragrances sectors. Heterogeneous enantioselective catalysts are essentially unused in these sectors despite the many potential advantages of heterogeneous systems over their homogeneous counterparts including ease of separation of products from the catalyst. Therefore, the development of new enantioselective heterogeneous catalysts would be of considerable benefit in these industries.
This project will strengthen UK leadership in this field, providing significant employment and wealth creation.

Scientist Training:
The PhD student associated with this project will gain expertise in a range of analytical techniques. The project will develop the leadership skills of the PDRA. Industry and/or academia will benefit via the provision of highly skilled individuals with unique technical and commercial skills that can contribute directly to the chemical sector as effective sustainability practitioners. The sharing of ideas between the groups based in Canada and Baddeley's group in St Andrews will enhance the activities of each research group.