[(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).

Inter-metal carbonyl exchange in [(eta(5)-C5H5)(2)Mo-2(CO)(6)] and [(eta(5)-C5H5)(2)MoW(CO)(6)], via [(eta(5)C(5)H(5))(2)Mo-2(mu-CO)(2)(CO)(4)] and [(eta(5)-C5H5)(2)MoW(mu-CO)(2)(CO)(4)], has been observed by C-13 NMR spectroscopy. The Delta G(double dagger) for the exchange is 13.9 +/- 0.2 kcal mol(-1) for the gauche isomer of[(eta(5)-C5H5)(2)Mo-2(CO)(6)] and 14.9 +/- 0.2 kcal mol(-1) for the trans isomer.

Inter-metal carbonyl exchange in [(η5-C5H5)2Mo2(CO)6] and [(η5-C5H5)2MoW(CO)6], via [(η5-C5H5)2Mo2(μ-CO)2(CO)4] and [(η5-C5H5)2MoW(μ-CO)2(CO)4], has been observed by 13C NMR spectroscopy. The ΔG⧧ for the exchange is 13.9 ± 0.2 kcal mol-1 for the gauche isomer of [(η5-C5H5)2Mo2(CO)6] and 14.9 ± 0.2 kcal mol-1 for the trans isomer.

The structures of [Fe3(CO)9{P(OR)3}3](R = Me or Pri) that were assigned previously on the basis of NMR investigations have been questioned. The crystal structures of these compounds have now been determined and shown to be in complete agreement with the predicted structures. The crystal structure of [Fe3(CO)9{P(OPri)3}3] is the first structure determination of a derivative of [Fe3(CO)12] with pseudo D3 symmetry and is similar to that commonly found for the ruthenium and osmium analogues.