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Lookup NU author(s): Dr Simon DohertyORCiD, Dr Julian Knight, Reece Paterson, Dr Corinne Wills, Dr Casey Dixon
Impregnation of phosphine decorated polymer immobilized ionic liquid with the tetrachloroaurate anion results in reduction of the gold(III) to gold(I) with concomitant oxidation of the phosphine to its oxide. In situ reduction of the resulting precursor, AuCl@O=PPh2-PEG-PIILS, generated the corresponding O=PPh2-PEGPIIL-stabilised AuNPs, AuNP@O=PPh2-PEGPIILS, which is a highly active and selective catalysts for the solvent dependent partial reduction of nitrobenzene to N-arylhydroxylamine in water and azoxybenzene in ethanol. The initial TOFs of 2,280 mole nitrobenzene converted Au-1 h-1 in water and 1,680 mole nitrobenzene converted mol Au-1 h-1 in ethanol are comparable to those of 1,980 mole nitrobenzene converted mol Au-1 h-1 and 2,220 mole nitrobenzene converted mol Au-1 h-1 obtained with gold nanoparticles generated by reduction of tetrachloroaurate impregnated phosphine oxide decorated polymer immobilised ionic liquid AuCl4@O=PPh2-PEGPIILS i.e. the activity and selectivity do not appear to depend on whether the AuNPs are generated from Au(III) or in situ generated Au(I). In stark contrast, gold nanoparticles prepared by NaBH4 reduction of AuCl@PPh2-PEGPIILS based on gold(I) confined in phosphine modified polymer immobilised ionic liquid gave markedly lower initial TOFs of 460 mole nitrobenzene converted mol Au-1 h-1 in water and 240 mole nitrobenzene converted mol Au-1 h-1 in ethanol; however, the selectivity profiles in each solvent were comparable to those obtained with its phosphine oxide counterpart. A survey of the hydrogen donor revealed that the use of dimethylamine borane (DMAB) resulted in a substantial and dramatic enhancement in activity for reductions conducted in water compared with NaBH4 and the initial TOF of 20,400 mole nitrobenzene converted mol Au-1 h-1 obtained with AuNPs generated in situ from AuCl4@O=PPh2-PEGPIILS is among the highest to be reported for the metal nanoparticle catalysed selective reduction of nitrobenzene to N-phenylhydroxylamine; this is a significant improvement on existing protocols and should enable the partial selective reduction of nitroarenes to be conducted in water with a low catalyst loading under extremely mild conditions. TEM micrographs of 4a-c revealed that the AuNP were near monodisperse and that those generated by reduction of Au(I) supported on phosphine decorated PIIL were slightly smaller (1.7 nm) than their phosphine oxide counterparts 4a-b (2.1 and 2.9 nm). The redox reaction that occurs during the impregnation of PPh2-PEGPIILS with [AuCl4]- has been monitored using [AuCl4]- and PPh3 as model substrates and a significant build-up of PPh3PCl2 was identified prior to formation of the triphenylphosphine oxide and as such several possible mechanisms have been discussed.
Author(s): Doherty S, Knight JC, Alharbi HY, Paterson R, Wills C, Dixon C, Chamberlain TW, Yan HM, Griffiths A, Daly H, Chansai S, Hardacre C
Publication type: Article
Publication status: Published
Journal: ChemCatChem
Year: 2024
Pages: epub ahead of print
Online publication date: 09/12/2024
Acceptance date: 09/12/2024
Date deposited: 09/12/2024
ISSN (print): 1867-3880
ISSN (electronic): 1867-3899
Publisher: Wiley-VCH Verlag GmbH & Co. KGaA
URL: https://doi.org/10.1002/cctc.202401702
Data Access Statement: The data that support the findings of this study are available in the supplementary material of this article.
