Multi-Nuclear, High-Pressure, Operando Flownmr Spectroscopic Study Of Rh/Pph3 - Catalysed Hydroformylation Of 1-Hexene

The hydroformylation of 1-hexene with 12 bar of 1 : 1 H-2/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 degrees C. Quantitative reaction progress curves that yield rates as well as chemo- and regioselectivities have been obtained with varying P/Rh loadings. Dissolved H-2 can be monitored in solution to ensure true operando conditions without gas limitation. P-31{H-1} and selective excitation H-1 pulse sequences have been periodically interleaved with H-1 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.