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Multi-nuclear, high-pressure, operando FlowNMR spectroscopic study of Rh/PPh3 - catalysed hydroformylation of
Alejandro Bara-Estaún1, Catherine L Lyall1, John P Lowe1
1Department of Chemistry, University of Bath, Claverton Down, BA2 7AY Bath, UK. u.hintermair@bath.ac.uk and Dynamic Reaction Monitoring Facility, University of Bath, Claverton Down, BA2 7AY Bath, UK.
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.
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