Osmium fluxionality

Co-condensation of osmium atoms with benzene gives moderate yields of [Os (T -CgHg) (TiG-CgHg) ] (2iL). The molecule is fluxional as demonstrated by variable temperature n.m.r experiments.1H... 

Both the 1 1 and the 1 2 bonded alkenes should show structural isomers, with, for the ethylene adduct, nonequivalence of the two protons bonded to the carbon. For substituted olefins, it is often possible to detect the presence of both isomeric forms, especially with the osmium derivatives. However, all these molecules are fluxional and the flux-... 

These differences have been attributed to the "benzyne group behaving as a four- or two-electron donor system. The fluxionality in these molecules has been investigated by NMR studies over a temperature range. These have established that the benzyne ring rotates about the osmium triangle (see Section IH,D). 

An interesting case of fluxional behaviour of a benzene ligand on the surface of a trimetallic osmium cluster has been observed for [Os3(CO)8(ti -C2H4)(p3,t), ti, ti -C6H6)] [51]. The motion is described as a ring jumping between discrete nuclear sites with minimum potential rather than as a hindered rotation when intermediate orientations might be populated for... 

At -100 °C, at least four environments aroimd the osmium atoms coexist, three of them are rigid, while the fourth one is fluxional even at -100 °C. 

The fluxional behavior of the osmium equivalents of the ruthenium(II) complexes mentioned in the final citation of the previous section has been described/ Time scales have been established for proton exchange at sulfur and at phosphorus in (26), R = Me or Et, and for deprotonation of (27) by the base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene)/ ... 

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