Hydrophosphination Catalysis Using Low-Coordinate Iron Complexes

Organophosphorus compounds are one of the most important species in chemistry, driving critical advances in areas such as medicine, metal extraction, nuclear fuel processing, lubricants, agrochemicals, materials and supramolecular chemistry. Their wide use as ligands to transition metals underpins many modern homogeneous catalytic processes, for example in metal-catalysed cross-coupling, alkene metathesis and C-H activation reactions. Classic synthetic routes to phosphines often display poor functional group tolerance, side product formation, and use a significant number of steps including stoichiometric amounts of additives, toxic metal reagents and protecting groups. These limitations lead to copious waste, representing a problem for atom economy.
Hydrophosphination reactions involve the addition of a P-H moiety across an unsaturated bond, and offer the potential for 100% atom efficiency with the opportunity to generate significant complexity in the organophosphorus products using relatively simple starting materials. In particular, the hydrophosphination of C=X (X = O, N, S) bonds is a powerful way to introduce heteroatom functionality into products, but remains poorly explored due to the paucity of suitable catalytic complexes, competing side reactions and catalyst poisoning. Thus, the use of this reaction as a convenient strategy to heterofunctionalised phosphorus compounds has not been exploited. Driven by major global efforts towards chemical synthesis using earth-abundant and non-toxic metals, we propose to deliver a new approach for the syntheses of organophosphorus compounds using iron complexes as pre-catalysts for the hydrophosphination of heterocumulene compounds. Significantly, our complexes can catalyse novel diinsertion pathways for this reaction, which are very rare and usually difficult to control. These new reaction pathways have the power to unlock new reactions and synthetic methodologies.
We will explore this hydrophosphination chemistry and use unexplored substrates to deliver new families of organophosphorus compounds and develop a rational approach to control reactivity and regioselectivity through the manipulation of the structure of the catalyst and the reaction conditions. This chemistry will be used to synthesise specific organophosphorus targets and the elucidation of the mechanisms for this catalysis will provide experimental and theoretical data to inform new reaction strategies that may be developed in new catalytic reactions. This research programme will thus deliver a wealth of fundamental knowledge in addition to a bank of new organophosphorus compounds, which will be made available to researchers in academia and industry.
This research programme has the potential to have significant impact for a broad range of academic and industrial applications due to the extensive properties and potential uses of a range of very different organophosphorus species. We envisage that our approach to the catalysis of hydrophosphination will impact a range of hydroelementation reactions and may impact other methodologies such as homologation, polymerisation and selective oligomerisation reactions.

Organophosphorus compounds are one of the most important species in chemistry, underpinning critical advances in many areas such as catalysis, medicine, metal extraction, nuclear fuel processing, agrochemicals and lubricants. While the current methodologies to phosphines are effective, synthetic routes often display poor functional group tolerance, use a number of steps, protecting groups and coupling reactions, which gives rise to copious waste which is a problem for atom economy. This research programme will deliver a new approach using iron complexes to catalyse the hydrophosphination of heterocumulenes accessing novel reaction pathways to deliver new families of organophosphorus compounds of significant impact in the above applications. The beneficiaries will be the Commercial Sector, the Public Sector, and Society, as detailed below.
Commercial Sector: In the short term, industrial organisations will benefit from new samples of organophosphorus compounds with uses in areas such as catalysis, medicine, metal extraction, nuclear fuel processing, agrochemicals and lubricants. In the long term, this research, although fundamental in nature, has the potential to inform new, more efficient catalytic methodologies using abundant and environmentally benign metals, which has the capability to reduce waste and improve sustainability. R&D is crucial to the UK chemicals industry, and its growth and competitiveness in the world market can only be sustained by exploiting new catalysts and processes from fundamental research. Industry will also benefit from the inspiration of workers for its labour force (see below).
Public Sector/Knowledge Base: This research will feed into the EPSRC Prosperity Outcome Productive Nation (Delivery Plan 2016-20), addressing the EPSRC Catalysis and Sustainable Chemistry Priority Areas, and EPSRC Theme Manufacturing the Future, benefitting policy makers, funding bodies and academic institutions in the short through to long term by providing clear evidence of the value of fundamental, internationally leading research in the UK which aligns with the EPSRC ideals. This research will be of immediate benefit to academics interested in synthesis, structure, reaction catalysis and methodology, theory, green chemistry and new phosphines for myriad uses. In the long term this project will provide a platform for future technological exploitation, both in academia and industry. The EPSRC/RSC report "The Economic Benefits of Chemistry Research to the UK" highlights the contribution that cutting-edge chemistry research makes to the UK science base. The academic investigators will see significant personal career development through this collaborative research programme, broadening their knowledge, particularly through exposure to Industrial Stakeholders and their research. This project will provide a wealth of scientific and training and transferrable skills, benefitting the PDRA.
Society: In the short term society will benefit from an increased awareness of chemistry through outreach activities. If the UK is to be competitive in the global market, public support for scientific research is essential. Furthermore, a general public with a good understanding of science and technology will be better equipped to provide an adaptable labour force with the skills and flexibility to deal with technological change. The Social Market Foundation's "In the Balance: the STEM Human Capital Crunch" report states that by 2020 "a 49% increase in STEM graduates would be required if employment requirements are to be met from domestic supply." Thus, in the long term the next generation of STEM students will help to secure future prosperity, from the inspiration of people to take an interest in science. In the long term, the public will benefit from the generation of new chemicals and new industrial processes resulting from this research programme. These benefits may involve new products, reduced costs, or from improved sustainability.