Mining the air for amines

点击翻译按钮获取中文摘要

Dinitrogen is plentiful and the source of ammonia (used in fertilizers on mega-tonne scales) and organoamines (for speciality, fine, and pharmaceutical chemicals) via Haber Bosch industrial processes, but ironically it is one of the most challenging bonds to activate and thus incorporate into added-value molecules in a sustainable way. Fortunately, however, various transition metals are quite effective at binding and activating dinitrogen, so the challenge for us is to harness that and develop it to include functionalization. Producing ammonia is still fundamentally interesting from a mechanistic perspective, but a major step-change will be to activate dinitrogen and incorporate it directly into organic molecules containing NR3 and R2N-NR2 units, that have extensive added-value, thus by-passing the need for several post-ammonia reaction steps. Elucidating the mechanism of these transformations is also critical to achieve, because this thermodynamic and kinetic information at a fundamental level is badly needed to feedback into designing new dinitrogen to organoamine catalytic cycles.After decades of research, there are still only 7 metals from the entire Periodic Table that in molecular species can catalytically reduce and fix dinitrogen into ammonia and 5 were added in the past 4 years: Ti, V, Mo, Fe, Ru, Os, Co. Ti is our work introduced only recently (Scheme 1 left, Angew. Chem. Int. Ed., 2018, 57, 6314-6318), which is appealing as Ti is 9th in crustal abundance and 2nd only to Fe for metals that can activate dinitrogen. Now we have established that a molecular Ti-Tren complex can catalytically fix dinitrogen to ammonia, and also shown that FLPs can split dihydrogen and introduce those H-atoms to produce ammonia (Scheme 1 right, Angew. Chem. Int. Ed., 2019, 58, 6674-6677). We seek to develop this science.Our aim is to make major advances in our understanding of dinitrogen reduction chemistry and its fixation by way of functionalization into ammonia and organoamines directly. We seek to achieve this aim by securing the following objectives: extend this catalysis to Zr and Hf; develop this to include direct formation of NR3 and R2N-NR2 compounds via C-N bond formation reactions without having to go via ammonia; unravel the reaction mechanisms to feedback, via structure-reactivity correlations, to reaction optimisation and generation of new catalytic cycles; develop the FLP aspect to deliver catalytic ammonia synthesis using dihydrogen.This project will thus involve: significant synthetic studies; catalysis; mechanistic analysis; computational modelling.The project is firmly rooted in chemocatalysis. It seeks to exploit the inorganic and N2 reduction expertise of STL with the amine synthesis and mechanistic expertise of DW to derive new chemical reactivity and atom-efficient routes to amines which could have biological relevance. It is therefore by definition a problem-solving, inter-disciplinary integrated catalysis project that seeks to make transformative step-changes in our understanding of catalysis that links to real-world challenges involving ammonia and organoamine syntheses. At this point in time with two preliminary papers published, this project is very much as TRL0, but we believe this project will be the perfect vehicle to develop the science and links to industry, via iCAT andthe UK Catalysis Hub, in order to make the fundamental-applied transition and raise the TRL rating of this research to exploitable outcomes.