Selective C-C bond cleavage under ambient conditions is challenging but it can be valuable for organic syntheses and biomass valorization. In this poster, we show that base-metal vanadium photocatalysts can harvest visible light to effect the photoredox C-C bond cleavage of benzylic alcohols that represent lignin, under ambient conditions. Lignin, predominant found in non-food biomass, is an inexpensive, accessible source of aromatic fine chemical feedstocks, such as phenols and aryl ethers. However, current lignin depolymerization technologies are harsh and indiscriminately degrade valuable functional groups to produce intractable mixtures. In the course of our studies on lignin model compounds, we have discovered a new photoredox C-C activation reaction, which occurs under exceptionally mild conditions with high conversions using visible light as the energy source. Selective C-C bond cleavage leads to value-added and versatile fine chemicals such as substituted aryl aldehydes and formates. We have conducted isotope labeling experiments, product analyses, and intermediate radical trapping, together with density functional theory (DFT) studies. We present an expanded substrate beyond lignin model compounds. In addition, femtosecond time-resolved photophysical measurements have been utilized to understand the mechanistic details after photoexcitation. Our photophysical measurements and DFT calculations suggest a unique pathway that involves a photogenerated T1 state during the C-C bond cleavage reactions. Our study demonstrates a sustainable approach to use photoredox C-C activation reactions as an approach for biomass valorization.[1],[2] [1] Gazi, S.; Ng, W. K. H.; Ganguly, R.; Moeljadi, A. M. P.; Hirao, H.; Soo, H. S.* Chem. Science 2015, 6, Advance Article (DOI: 10.1039/c5sc02923f). [2] Soo, H. S.*; Gazi, S. “Selective carbon-carbon bond cleavage by earth abundant vanadium compound under visible light photocatalysis,” Singapore provisional patent 10201500823Q, filed 3 February 2015.

Selective photocatalytic C-C bond cleavage under ambient conditions with earth abundant vanadium complexes

251st National Meeting (2016)

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