From recovered metal waste to effective catalysts for C-C and C-N bond formation

Palladium-mediated reactions are among the most widely used transformations in organic chemistry yet this metal is found in low abundance in only a few places on earth. The high price of palladium is driven by its technological use, such as in automotive catalytic converters, yet these end-of-life products are frequently not recycled in many countries due to the energy-intensive processes required. A new, low-energy route to selectively extract palladium from mixed-metal waste has progressed to pilot plant stage. The Pd recovery product generated from this process is [Pd2I6]2-. Rather than the energy-intensive (and costly) process of returning the palladium content of this compound to metallic form, it is proposed to use the molecular species directly as a (pre)catalyst. Preliminary results indicate very encouraging reactivity in Suzuki coupling reactions, matching the performance of the commonly used [PdCl2(PPh3)2] and [Pd(PPh3)4]. Through ligand exchange reactions, analogous compounds, such as [PdI2(PPh3)2] and [PdI2(dppf)], are also readily accessible from [Pd2I6]2-. In order for these recovery compounds to be embraced widely by the synthetic community, their reactivity profile and substrate scope needs to be investigated. The project aims to do this using a thorough, systematic approach, aided by the kinetic and multivariable analysis provided by the ROAR facility. The investigation will then be extended to other important transformations based around Pd(0) active species, such as Sonogashira, Heck and the challenging coupling of sp3 hybridised moieties, as well as Buchwald-Hartwig amination reactions. The overarching goal is thus to provide well-understood recovered-metal catalyst options for the key Pd-mediated C-C and C-N bond forming reactions used across industry and academia. The overall process represents the recovery of end-of-life heterogeneous catalysts for use as new homogeneous catalysts.

Keywords: Palladium, catalysis, recovery and re-use, sustainability

Academic impact:
Recent advances in data science and digital technology have a disruptive effect on the way synthetic chemistry is practiced. Competence in computing and data analysis has become increasingly important in preparing chemistry students for careers in industry and academic research.

The CDT cohort will receive interdisciplinary training in an excellent research environment, supported by state-of-the-art bespoke facilities, in areas that are currently under-represented in UK Chemistry graduate programmes. The CDT assembles a team of 74 Academics across several disciplines (Chemistry, Chemical Engineering, Bioengineering, Maths and Computing, and pharmaceutical manufacturing sciences), further supported by 16 industrial stakeholders, to deliver the interdisciplinary training necessary to transform synthetic chemistry into a data-centric science, including: the latest developments in lab automation, the use of new reaction platforms, greater incorporation of in-situ analytics to build an understanding of the fundamental reaction pathways, as well as scaling-up for manufacturing.

All of the research data generated by the CDT will be captured (by the use of a common Electronic Lab Notebook) and made openly accessible after an embargo period. Over time, this will provide a valuable resource for the future development of synthetic chemistry.

Industrial and Economic Impact:
Synthetic chemistry is a critical scientific discipline that underpins the UK's manufacturing industry. The Chemicals and Pharmaceutical industries are projected to generate a demand for up to 77,000 graduate recruits between 2015-2025. As the manufacturing industry becomes more digitised (Industry 4.0), training needs to evolve to deliver a new generation of highly-skilled workers to protect the manufacturing sector in the UK. By expanding the traditional skill sets of a synthetic chemist, we will produce highly-qualified personnel who are more resilient to future challenges. This CDT will produce synthetic chemists with skills in automation and data-management skills that are highly prized by employers, which will maintain the UK's world-leading expertise and competitiveness and encourage inward investment.

This CDT will improve the job-readiness of our graduate students, by embedding industrial partners in our training programme, including the delivery of training material, lecture courses, case studies, and offers of industrial placements. Students will be able to exercise their broadened fundamental knowledge to a wide range of applied and industrial problems and enhance their job prospects.

Societal:
The World's population was estimated to be 7.4 billion in August 2016; the UN estimated that it will further increase to 11.2 billion in the year 2100. This population growth will inevitably place pressure on the world's finite natural resources. Novel molecules with improved effectiveness and safety will supersede current pharmaceuticals, agrochemicals, and fine chemicals used in the fabrication of new materials.

Recent news highlights the need for certain materials (such as plastics) to be manufactured and recycled in a sustainable manner, and yet their commercial viability of next-generation manufacturing processes will depend on their cost-effectiveness and the speed which they can be developed. The CDT graduates will act as ambassadors of the chemical science, engaging directly with the Learned Societies, local council, general public (including educational activities), as well as politicians and policymakers, to champion the importance of the chemical science in solving global challenges.