CO fluxionality in Rh4(CO)12 and Rh6(CO)16

Both Rh4(CO)12 and Rh6(CO)16 exhibit CO-fluxionality and modern, variable temperature, NMR methods allow the unambiguous assignment of the three terminal CO resonances and, for Rh4(CO)12, show that the mechanism of CO-fluxionality, which has been controversial for a long time, unambiguously involves the merry-go-round process; Rh6(CO)16, which was previously thought to be static, is also shown to be fluxional, although the rate of CO-exchange is much less than found for substituted derivatives, and possible pathways for this CO-exchange are discussed.