The identification of all five isomers of [(eta(5)-C5H5)(2)Mo-2(CO)(5)(CNMe)] and the mechanisms of fluxionality

[(eta(5)-C5H5)(2)Mo-2(CO)(5)(CNMe)] has been re-examined by H-1 and C-13 NM R spectroscopy in (CD3)(2)NCDO and all five isomers have been identified. A ctivation energies have been determined for their interconversion and ligan d scrambling. The lowest energy dynamic process is intramolecular ligand ex change via [(eta(5)-C5H5)(2)Mo-2(mu-CO)(mu-CNMe)(CO)(4)] which is more faci le in the gauche-isomer with Delta G double dagger = 11.7 +/- 0.2 kcal mol( -1) than in the trans-isomer with Delta G double dagger = 12.2 +/- 0.2 kcal mol(-1). The next lowest energy dynamic process is intramolecular ligand e xchange via [(eta(5)-C5H5)(2)Mo-2(mu-CO)(2)(CO)(3)(CNMe)] which is more fac ile in the gauche-isomer with Delta G double dagger = 12.4 +/- 0.2 and 12.6 +/- 0.2 kcal mol(-1) than in the trans-isomer with Delta G double dagger = 14.5 +/- 0.2 kcal mol(-1). The highest energy dynamic process is rotation about the Mo-Mo bond which was only detected in the isomers with CNMe cis t o the Mo-Mo bond where Delta G double dagger = 14.4 +/- 0.2 and 14.7 +/- 0. 2 kcal mol(-1).