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Rhenium complexes bearing tridentate and bidentate phosphinoamine ligands in the production of biofuel alcohols via the Guerbet reaction

King, Ashley M., Wingad, Richard L., Pridmore, Natalie E., Pringle, Paul G. and Wass, Duncan F. 2021. Rhenium complexes bearing tridentate and bidentate phosphinoamine ligands in the production of biofuel alcohols via the Guerbet reaction. Organometallics 40 (16) , pp. 2844-2851. 10.1021/acs.organomet.1c00313

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Abstract

We report a variety of rhenium complexes supported by bidentate and tridentate phosphinoamine ligands and their use in the formation of the advanced biofuel isobutanol from methanol and ethanol. Rhenium pincer complexes 1–3 are effective catalysts for this process, with 2 giving isobutanol in 35% yields, with 97% selectivity in the liquid fraction, over 16 h with catalyst loadings as low as 0.07 mol %. However, these catalysts show poorer overall selectivity, with the formation of a significant amount of carboxylate salt solid byproduct also being observed. Production of the active catalyst 1d has been followed by 31P NMR spectroscopy, and the importance of the presence of base and elevated temperatures to catalyst activation has been established. Complexes supported by diphosphine ligands are inactive for Guerbet chemistry; however, complexes supported by bidentate phosphinoamine ligands show greater selectivity for isobutanol formation over carboxylate salts. The novel complex 7 was able to produce isobutanol in 28% yield over 17 h. The importance of the N–H moiety to the catalytic performance has also been established, giving further weight to the hypothesis that these catalysts operate via a cooperative mechanism.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Publisher: American Chemical Society
ISSN: 0276-7333
Funders: EPSRC and BP
Date of First Compliant Deposit: 9 August 2021
Date of Acceptance: 16 July 2021
Last Modified: 24 Nov 2021 15:31
URI: http://orca.cardiff.ac.uk/id/eprint/143257

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