Four separate fluxional processes in (η⁶-cyclo-octatetraene)(η⁴-cyclo-octa-1,5-diene)osmium. A novel example of a metal [1,5] shift on a π-co-ordinated polyene ligand

Complexes of Ruthenium and Osmium Containing η2–η6 Hydrocarbon Ligands: (iii) Complexes Containing Six-, Seven- and Eight-membered Rings

“…291 As in [Fe(cot) 2 ], the rings are equivalent on the NMR ('H, I3 C) timescale at room temperature; on cooling to 223 K, the motion o f the r| 6 -ring freezes out but that of the r| 4 There are also two lower energy processes in [OS(1-6T|-cot)(r|-cod)]: a 'twitch' motion of the cod and cot ligands resulting in an apparent plane of symmetry (AG* = 37.2 kJ mol~l) and, at higher temperature, a complete rotation of the cod and cot ligands with respect to each other (AG* =48 kJ mol" 1 ). 292 ' 293 The r| 5 -2,5-dimethylpentadienyl complex [RUH(T| 5 -C 7 H 11 ) 2 ]BF 4 (see Section 7.10, Chapter 7, this volume) reacts with chpt and cot to give [Ru(rj 5 -C 7 H n )(r| 6 -chpt)] + and [Ru(T| 5 -C 7 H 1 ,)(l-6r|-cot)] + , respectively. Migration of the metal atom round the cot ligand in the latter does not occur rapidly on the NMR timescale, even at 353 K, like [Ru(r|-C 5 H 5 )(l-6T|-cot)] + (see Section 8.2.6.2 in Chapter 8, this volume), but in contrast with the zero-valent metal complexes discussed earlier.…”