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

摘要

(eta(5)-C5H5)(2)Mo-2(CO)(5)(CNMe)] has been re-examined by H-1 and C-13 NMR spectroscopy in (CD3)(2)NCDO and all five isomers have been identified. Activation energies have been determined for their interconversion and ligand scrambling. The lowest energy dynamic process is intramolecular ligand exchange via [(eta(5)-C5H5)(2)Mo-2(mu-CO)(mu-CNMe)(CO)(4)] which is more facile 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 exchange via [(eta(5)-C5H5)(2)Mo-2(mu-CO)(2)(CO)(3)(CNMe)] which is more facile 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 to the Mo-Mo bond where Delta G double dagger = 14.4 +/- 0.2 and 14.7 +/- 0.2 kcal mol(-1). [References: 18