FLUXIONAL REARRANGEMENTS IN MOLYBDENUM(O), TUNGSTEN(O) AND RHENIUM(I)CARBONYL-COMPLEXES OF 2,6-BIS[(4S)-ISOPROPYLOXAZOLIN-2-YL]-PYRIDINE (L) - CRYSTAL-STRUCTURE OF [MO(CO)(4)L]

Treatment of the [ReX(CO)(5)] (X = Cl, Pr or I) and [M(CO)(4)(pip)(2)] (M = Mo or W, pip = piperidine) compounds with the C-2-symmetric liga nd 2,6-bis[(4S)-isopropyloxazolin-2-yl]pyridine (L) yielded complexes of general formulae fac-[ReX(CO)(3)L] and cis-[M(CO)(4)L], in which th e ligand is co-ordinated in a bidentate fashion. In solution these com plexes undergo a fluxional process that exchanges the co-ordinated and pendant oxazoline rings. In the case of the M(CO)(4) complexes all pe rmutational isomers are equivalent. However, in the rhenium(I) complex es the lower symmetry of the metal moiety leads to the formation of ch emically distinct species. The different exchange pathways between the se species gives rise to different magnetisation transfers, providing a spectroscopic handle on the mechanism of the ligand rearrangement. T he activation parameters have been evaluated by standard one-dimension al band shape analysis and by two-dimensional exchange spectroscopy; D elta G double dagger (298 K) approximate to 52.0 and 62.6 kJ mol(-1), respectively for the complexes of Mo-0 and W-0 and is in the range 78. 5-80.5 kJ mol(-1) for the rhenium(I) complexes.