[(η5-C5Me5)Ru]+ fragments ligated to polyaromatic hydrocarbons: an experimental and computational approach to pathways for haptotropic migration

Abstract

Ligand exchange reactions between [Cp*Ru(NCMe)₃][PF₆], where Cp* represents η⁵-C₅Me₅, and the polycyclic aromatic hydrocarbons (PAHs) pyrene, acenaphthylene and fluoranthene afforded the known [Cp*Ru(η⁶-pyrene)][PF₆] (1) and the new mixed sandwiches [Cp*Ru(η⁶-acenaphthylene)][PF₆] (2) and [Cp*Ru(η⁶-fluoranthene)][PF₆] (3), respectively, isolated in quantitative yields (94–100%). Complex 3 is formed as a mixture of two isomers: 3A as the major product where the [Cp*Ru⁺] moiety is coordinated to the naphthalene fragment of fluoranthene, and 3B with the coordination of the arenophile to the peripheral benzene ring, in a 90/10 spectroscopic ratio. The composition and identity of the complexes were deduced by elemental analysis, ¹H and ¹³C multidimensional NMR spectroscopy, and mass spectrometry. Compounds 1A, 3A and 2A have been characterized using X-ray structural investigations. That showed that the [Cp*Ru⁺] unit is η⁶-attached to one of the two naphthalene rings in each complex. Heating 1 and 3 at 90 °C in CD₃NO₂ solutions or heating 3 at 120 °C in the solid phase did not provide any evidence for thermally induced intramolecular inter-ring haptotropic rearrangements. These rearrangements were modelled by DFT calculations which indicated rather high activation energies.