Research
Photoredox catalysis (PRC) is a new methodology that over the past decade has begun to transform the field of organic synthetic chemistry. PRC uses light to drive chemical reactions, easily achieving normally challenging transformations under very mild conditions. More precisely, PRC exploits the fact that a photocatalyst (PC) can become a much more powerful oxidant or reductant upon photoexcitation, allowing it to mediate challenging redox processes without stoichiometric use of strong redox reagents.
Unfortunately, despite the rapid development of this field, an emphasis on (semi-)empirical reaction development means that the detailed mechanisms of most PRC reactions remain poorly understood. In response, we are pioneering the preparative synthesis and isolation of key PRC intermediate radical anions (PC•−) and cations (PC•+), to allow for their detailed and unambiguous characterisation and study. By deepening our fundamental understating of the elementary steps involved in PRC it is anticipated that improved and entirely new transformations can be devised, including methods for inorganic synthetic chemistry.
The N2 molecule is notoriously unreactive, yet its transformation into the chemically accessible “fixed” nitrogen source NH3 is among the most important chemical reactions in the modern world. Currently achieved using the well-known Haber-Bosch process, industrial N2 fixation is estimated to consume around 2% of the world’s entire energy supply, and to be responsible for a similar fraction of its CO2 emissions.
Recently, there has been much interest in the use of well-defined molecular complexes to mediate the reduction of N2 to NH3 and related products. However, despite several seminal proof-of-concept reports, the number of reported reactions remains extremely limited, as does typically their selectivity and thermodynamic efficiency. By incorporating photoredox steps into these reactions, we are able to target new and improved methods for N2 functionalisation, with improved selectivity and broader product scope.
P4 is the common precursor from which all synthetic phosphorus containing compounds are made, but state-of-the-art methods for its transformation rely on inefficient, wasteful, and indirect strategies. In ongoing work, we have developed several practical new methods by which P4 (and its bench-stable allotrope red phosphorus) can be turned directly into useful and industrially relevant phosphorus products, using simple p-block compounds as mediators or catalysts. Most of this research is carried out in close collaboration with the Wolf group of the University of Regensburg.
Since the turn of the millennium there has been a renaissance in the field of p-block chemistry, leading to the isolation of a plethora of low-valent complexes that show remarkable stoichiometric reactivity. In many cases this reactivity is reminiscent of that displayed by transition metals. However, despite much effort, there have been few examples of p-block complexes successfully mimicking transition metals’ versatile and valuable catalytic reactivity. Indeed, while oxidative reactions at low-valent p-block species are often facile, subsequent reductive regeneration of these species is highly challenging. To allow the closure of transition metal-like catalytic redox cycles, we are therefore developing photochemical strategies to induce reductive elimination at p-block centres.
