Optimisation and mechanistic investigations of visible light photocatalysed decarboxylative Giese reaction using Bi2WO6 semiconductor nanoparticles

Abstract

Heterogenous photocatalysts based on semiconducting metal oxides serve as a sustainable alternative to expensive and toxic transition metal (photo)catalysts in organic transformations including C-C coupling. Upon absorption of a photon, semiconductors can generate excited states and charge carriers (holes and electrons) which at the surface undergo redox reactions with substrates to generate radicals. This project aims to use visible light (405–410 nm) as the energy source to drive an organic transformation (C-C bond formation) via radical chemistry in acetonitrile. Modified Bi2WO6 with Pt nanoparticles was used as a model catalyst in oxidative decarboxylation of phenylacetic acid to yield benzyl radical which underwent a Giese reaction with electron-deficient alkenes. The yield of Giese adduct was 60-70 %. The main byproducts were bibenzyl, benzyl alcohol, and benzaldehyde from GC-MS. In the absence of Pt, no reaction occurred and 0.15wt% Pt was found to be optimum loading amount. Photoluminescence spectroscopy (PL) spectra showed that the platinized catalyst exhibited slightly less recombination compared to the bare catalyst, while time-resolved photoluminescence (TRPL) showed no significant difference in the lifetime of carriers in both catalysts suggesting that the role of Pt is not only to improve charge separation but also to contribute to catalysis.