We initially examined the hydroformylation of ethyl acrylate catalysed by [Rh(acac)(CO) 2 ]–1 under various conditions. Table 1 summarises the results obtained. Intriguingly, the average turnover frequency (TOF) for the formation of ethyl 2-formylpropionate varies with the pressure of CO 2 . Thus, the TOF was found to be 1255 h −1 at 200 bar, but rose to a higher value of 2066 upon lowering the pressure to 150 bar. The change in rate with CO 2 pressure could be ...