Merging Hydrogen Borrowing/Transfer Catalysis with Photochemistry

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This project falls within the EPSRC Synthetic Organic Chemistry research area.Hydrogen borrowing catalysis (HBC) has emerged as a powerful catalytic method for the synthesis of complex molecules. The one-pot oxidation-reduction sequence has an intrinsic high atom economy and alkylation reactions using alcohols (or amines) as feedstock molecules lead to the production of valuable products and water (or ammonia) as the sole by-product. This presents HBC as a green alternative to traditional alkylation chemistry. Unfortunately, HBC typically requires high operating temperatures, leading to poor selectivity with respect to other sensitive parts of the organic molecule of interest (poor functional group tolerance). An alternative way of giving a reaction enough energy to proceed without using such high temperatures is by using high-energy irradiation or from visible light- mediated photocatalysis.Visible light-mediated photocatalysis (PC) has emerged as a powerful and safer alternative to high energy ultra violet light irradiation of organic molecules. Ultra-violet irradiation is extremely harsh and has poor functional group tolerance, meaning it is not suitable as a general method - visible light is significantly safer to operate with and more selective. Although many types of chemistry which can intercept the production of a short-lived oxidised molecules from HBC have been explored, using photochemistry to do so has not. In this project we will aim to combine the two technologies to produce complex organic molecules via tandem hydrogen borrowing/transfer photochemical reactions. Thereby deriving new chemical reactivity and also looking to avert the typically harsh conditions of HBC, creating a more generalised and applicable method which could be used by the pharmaceutical or agrochemical communities.First we will investigate new modes of reactivity, such as the feasibility of creating a short-lived molecule, which is active to PC from a hydrogen-borrowing event (oxidation or reduction). This molecule could be excited by a photocatalyst and undergo a reaction with other organic molecules before a final hydrogen borrowing event (reduction or oxidation) can complete the catalytic cycle. Similarly, we will look to develop catalysts which could in principle perform both the hydrogen borrowing events and photochemical excitation of the organic molecules. To our knowledge, no groups have looked to merge HBC and PC, which in principle could transform the landscape of hydrogen borrowing chemistry in addition to discovering novel chemical reactivity.