In Situ High-Pressure 31P{1H} NMR Studies of the Hydroformylation of 1-Hexene by RhH(CO)(PPh3)3

The hydroformylation of 1-hexene with syngas (40 bar of 1:1 CO/H2) in the presence of the catalyst precursor RhH(CO)(PPh3)3 has been studied by high-pressure NMR spectroscopy in a 10 mm sapphire tube equipped with a Ti-alloy valve. Except for RhH(CO)2(PPh3)2, no direct observation of labile intermediates involved in the catalytic cycle has been detected; however as many as four rhodium resting states have been seen, and some factors controlling their formation/interconversion/inhibition have been identified. The information gathered from this in situ investigation is particularly relevant to a better understanding of the inhibiting action of the CO pressure as well as the positive action of PPh3 addition.