Using in situ photochemistry to explore catalysis

Strategy: The aim in this project is to investigate the addition of hydrogen to transition metal centres in conjunction with NMR spectroscopy and photochemistry within an NMR probe. This approach will employ parahydrogen to enable the detection of true reaction intermediates by harnessing the increase in NMR signal strength by factors which approach 30,000 that is available at 9.4 T. This gain will be used to enable the monitoring of reactivity through magnetisation transfer studies in conjunction the observation of new reaction intermediates, and ultimately help to probe the role of the detected reaction intermediates in catalysis.1

Background: We have demonstrated that the generation of a reaction product with an essentially pure spin state is possible using p-H2 (Fig 1). This reaction was initiated by a pulse of UV light from a XeCl excimer laser that was triggered by the NMR spectrometer and featured Ru(CO)2(L2) which forms Ru(H)2(CO)2(L2) with H2. This result, illustrated in Figure 1, shows how we can easily detect photoproducts using the signal gain that is delivered with p-H2.

When a continuous UV irradiation source is employed, it is possible to build up appreciable amounts of a photoproduct at low temperature and then characterise it. However, when this continuous approach is used with p-H2, it also allows the continuous formation of NMR enhancing molecules. We seek to harness this route in conjunction with advanced NMR methods to characterise the reaction intermediates we detect. Furthermore, by varying the temperature, we can control reactivity and thereby their role in catalysis. Catalysis can also be regulated by adding a weakly binding co-ligand which has the potential reduce activity by trapping active species and forming materials that are amenable to characterisation before using photochemistry to reactivate the system.1

Metal dihydrides in catalysis: Our studies on Ru(CO)3L(H)2 and Ru(CO)2(L)2(H)2 have revealed that they can be used to form highly reactive species such as Ru(CO)4, Ru(CO)3 and Ru(CO)2(L) depending on the identity of L. By detecting intermediates such Ru(CO)2(L)(alkyne)(H)2 through trapping with hydrogen and an alkyne we hope to be able to probe their precise role in hydroformylation and hydrogenation. We have already detected related species during thermal studies with the cation Pd(L)2H+; these include vinyl, alkyl and acyl complexes such as Pd(L)2(CPh=CHPh)+ which can be stabilised by adding a passivating two-electron donor such a pyridine to facilitate detection. An array of palladium and ruthenium complexes, in addition to some isoelectronic rhodium spices, will be examined as part of this work.

The student will be based in the centre for hyperpolarisation in magnetic resonance (CHyM, https://www.york.ac.uk/chym/). The student undertaking this project will receive training in synthetic, analytical and catalytic chemistry. The project will involve the preparation of novel ligands and inorganic complexes under inert atmospheres. The characterisation of both inorganic and organic species will be undertaken by NMR and involve some MS. The detailed mechanistic study required will involve advanced NMR methods, including the use of photochemistry. These practical skills will be complemented by group meetings within the centre for hyperpolarisation in magnetic resonance. The student would also have the opportunity to present their work internationally.

All research students follow our innovative Doctoral Training in Chemistry (iDTC): cohort-based training to support the development of scientific, transferable and employability skills. All research students take the core training package which provides both a grounding in the skills required for their research, and transferable skills to enhance employability opportunities following graduation. Core training is progressive and takes place at appropriate points throughout a student’s higher degree programme, with the majority of training taking place in Year 1. In conjunction with the Core training, students, in consultation with their supervisor(s), select training related to the area of their research.

The Department of Chemistry holds an Athena SWAN Gold Award and is committed to supporting equality and diversity for all staff and students. The Department strives to provide a working environment which allows all staff and students to contribute fully, to flourish, and to excel. Chemistry at York was the first academic department in the UK to receive the Athena SWAN Gold award, first attained in 2007 and then renewed in October 2010 and in April 2015.