Multi-nuclear, high-pressure, operando FlowNMR spectroscopic study of Rh/PPh3 - catalysed hydroformylation of 1-hexene

Alejandro Bara-Estaún, Catherine L Lyall, John P Lowe, Paul G Pringle, Paul C J Kamer, Robert Franke, Ulrich Hintermair

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Abstract

The hydroformylation of 1-hexene with 12 bar of 1 : 1 H2/CO in the presence of the catalytic system [Rh(acac)(CO)2]/PPh3 was successfully studied by real-time multinuclear high-resolution FlowNMR spectroscopy at 50 °C. Quantitative reaction progress curves that yield rates as well as chemo- and regioselectivities have been obtained with varying P/Rh loadings. Dissolved H2 can be monitored in solution to ensure true operando conditions without gas limitation. 31P{1H} and selective excitation 1H pulse sequences have been periodically interleaved with 1H FlowNMR measurements to detect Rh-phosphine intermediates during the catalysis. Stopped-flow experiments in combination with diffusion measurements and 2D heteronuclear correlation experiments showed the known tris-phosphine complex [RhH(CO)(PPh3)3] to generate rapidly exchanging isomers of the bis-phosphine complex [Rh(CO)2(PPh3)2] under CO pressure that directly enter the catalytic cycle. A new mono-phosphine acyl complex has been identified as an in-cycle reaction intermediate.

Original languageEnglish
Pages (from-to)422-442
Number of pages21
JournalFaraday Discussions
Volume229
Issue number0
DOIs
Publication statusPublished - 1 Jun 2021

Bibliographical note

Funding Information:
This work was supported by the Royal Society (UF160458; fellowship to UH), the EPSRC Dynamic Reaction Monitoring Facility (EP/P001475/1), and the EPSRC Centre for Doctoral Training in Catalysis (EP/L016443; studentship to ABE). The authors thank Dr Christopher Kubis (LIKAT, Germany) for useful discussions and help with pump congurations.

Publisher Copyright:
© 2021 The Royal Society of Chemistry.

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