(CO)-C-13 exchange studies of racemization catalyst (eta(5)-Ph5C5)Ru(CO)(2)Cl and (eta(5)-Ph5C5)Ru(CO)(2)(Ot-Bu) by C-13 NMR spectroscopy are reported. CO exchange for the active catalyst form, (eta(5)-Ph5C5)Ru(CO)(2)(Ot-Bu) is approximately 20 times faster than that for the precatalyst (eta(5)-Ph5C5)Ru(CO)(2)Cl. An inhibition on the rate of racemization of (S)-1-phenylethanol was observed on addition of CO. These results support the hypothesis that CO dissociation is a key step in the racemization of sec-alcohols by (eta(5)-Ph5C5)Ru(CO)(2)Cl, as also predicted by DFT calculations.