The extraordinary fluxionality of Ru6(μ6-C)(μ-CO)(CO)16

The 13C NMR spectrum of Ru6(μ6-C)(μ-CO)(CO)16 (1) in solution at − 125 °C indicates that the CO ligands of the equatorial Ru4(μ6-CO)(CO)10 unit are undergoing ultra-fast exchange estimated to be ≳ 3 × 107 s− 1. The variable temperature solution IR spectra of 1 shows bands that are attributed to the Ru4(μ6-CO)(CO)10 unit at − 58 °C that broaden and collapse almost to the baseline in the spectrum at + 70 °C. On the other hand, two of the three strong CO stretches of the Ru(CO)3 units of 1 observed in the low temperature spectra coalesce to a sharp signal typical of a C3v fac-L3M(CO)3 grouping. These results are interpreted in terms of the carbonyls of the equatorial Ru4(μ-CO)(CO)10 unit undergoing exchange on the IR timescale (~ 1012 s− 1) at room temperature, consistent with DFT calculations.