Final Report Summary - MAINGROUPACT (Low-valent main-group systems for reversible small molecule activation) Catalysis is a pivotal technology in today’s society, enabling efficient access to complex molecular architectures. Metal-catalysed processes such as Pd-catalysed cross couplings or olefin metathesis are fundamental in synthetic and industrial chemistry. Many of these processes use the scarce (and correspondingly expensive) platinum-group metals. The scarcity of these metals - and the potential for geopolitical instabilities in their supply - has prompted the EU and national governments to call for efforts to find alternative technologies that decrease our reliance on these rare resources. In the search for replacements for metal catalysts, low-valent compounds of the heavier p-block elements present a potential solution. This project targets the systematic synthesis of unsaturated main group compounds that can mimic the reactivity of transition metals. In this project we have developed the synthesis of aluminium compounds and investigated their reactivity, particularly towards reduction. We have studied the effect of coordinated Lewis bases on reductive elimination from the prototypical aluminium(III) system Cp*2AlH, and gained a detailed pictures of how reductive elimination proceeds from this compound. In parallel studies, we have shown how aluminium(I) compounds can first activate unsaturated organic molecules such as alkynes, and how the resulting products can be treated with another class of unsaturated organic compound – isonitriles – to generate complex molecular structures in a single step.We have prepared low-valent mixed phosphorus/boron systems and investigated their reactivity. We developed a new, robust route to the synthesis of base-stabilised P=B bonded systems, via the elimination of a chlorosilane. We were able to intercept an intermediate formed along the pathway of silane elimination, gaining insight into mechanisms operative in chemical vapour deposition of mixed group 13/15 systems. We have also developed methods to chemically trap thermally generated phosphinidene boranes, RP=BR, using Lewis bases and alkynes, and are developing the onward chemistry of these compounds for the development of materials with extended π-conjugated systems containing main-group elements. Notably, these compounds can also activate small molecules such as CO or isonitriles.These results will help chemists understand how abundant main-group elements can contribute to reducing the demand for scarce elements by achieving similar chemical transformations to make useful, complex molecules from simple precursors.
