ORGANOMETALLIC HELICOPTERS - STEREOCHEMICAL NONRIGIDITY OF MU-3-ARENE/OLEFIN TRIOSMIUM COMPLEXES IN SOLUTION AND THE SOLID-STATE

The nonrigidity of mu-3-arene/olefin triosmium complexes [Os3(CO)8(eta-2-CH2CHR)(mu-3:eta-2:eta-2:eta-2-C6H6)], R = H, Me, Ph,(t)Bu, has been investigated through a series of one- and two-dimensional NMR experiments in solution, and five independent fluxional processes have been detected. C-13{H-1} two-dimensional exchange spectroscopy clearly defines a 1,2 ring-hopping motion that permutes nuclei in the face-capping benzene ligands, while the ir-bound olefins are fluxional through rotation about their metal-ligand axes and by a trigonal twist pathway that interchanges ligands in the OS(CO)2(olefin) polytopes. These intramolecular rearrangements are designated "helicopter-like' behavior. Localized "turnstile" rotations also operate among the two tricarbonyl ligand sets. C-13{H-1} cross-polarization magic angle spinning (CP/MAS) NMR experiments suggest that analogous processes may occur in the solid state.