η6-Cyclooctatetraene-metal complexes revisited: A study of two-dimensional NMR exchange spectroscopy of tricarbonyl(η6-cyclooctatetraene)-chromium and -tungsten

The rates and associated activation energies for metal migration in [M(CO)3(η6-C8H8)] (M = Cr or W) have been precisely determined by variable temperature 1H two dimensional NMR exchange spectroscopy. For M = W the 1,2 and 1,3 shifts are almost equally favoured, whereas for M = Cr the 1,3-migration pathway is slightly preferred. Planar monocyclooctatriene(η4-C8H8) and/or bicyclo[4.20]octatriene are considered to be probable intermediates for this fluxionality.