[(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 η(5)-C5Me5, and the polycyclic aromatic hydrocarbons (PAHs) pyrene, acenaphthylene and fluoranthene afforded the known [Cp*Ru(η(6)-pyrene)][PF6] (1) and the new mixed sandwiches [Cp*Ru(η(6)-acenaphthylene)][PF6] (2) and [Cp*Ru(η(6)-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, (1)H and (13)C 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 η(6)-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.

DFT study of inter-ring haptotropic rearrangement in CpRu+ complexes of polycyclic aromatic ligands

“…This was already proven for tricarbonyls of group 6 metals (M= Cr, Mo, W)with large coronene and kekulene[22], as well as graphene[23] and nanotubes[24]. This trend was supported by Sato et al[25] with the result of some decrease of activation barrier for (η 6coronene)RuCp + (∆G # = 31-33 kcal/mol) in comparison with the data on IRHR for small PAH (∆G # = 36-41 kcal/mol)[21]. In this paper, we further increase the size of the PAH model by two additional layers around the central coronene molecule, thus modeling already non-synthesized RuCp + complexes of graphene with the (C 96 H 24 )RuCp + complex I and we show by DFT calculations that the computed IRHR energy barriers are much lower than with complexes of smaller PAHs.…”

“…In contrast, recent experimental investigations of η 6 η 6 -IRHRs in synthesized Cp*Ru + complexes of a number of common PAH showed the absence of any rearrangement, in polar solvents [21]. This was supported by DFT calculations which led to very high activation barriers (∆G # = 36-41 kcal/mol), precluding observation of such rearrangements at reasonable temperatures.…”

Two Discrete RuCp* (Cp*=Pentamethylcyclopentadienyl) Binding Modes of N‐Confused Porphyrins: Peripheral π Complex and Sitting Atop Ruthenocenophane Complex by Skeletal Transformation

“…The distance between the ruthenium metal and the Cp* ring is relatively longer (1.819 Å) compared to the corresponding value (ca. 1.801–1.805 Å) of RuCp*–polyarene complexes due to the mutual repulsion between the methyl groups of Cp* ring and the NCP core framework …”

“…1.801-1.805 )o fR uCp*-polyarene complexes due to the mutual repulsion between the methyl groups of Cp* ring andt he NCP core framework. [17] In addition, the characteristicc orrelation between ap eripheral b-CH of the confusedr ing and methyl CHs of the Cp* ring of the non-metalatedr eference, 7-RuCp* was observed in the rotatingf rame nuclear Overhauser effect (ROESY) spectrum (Figures S2 and S3 in the Supporting Information). This site-selective p-coordination of RuCp* moiety could be attributed to the thermodynamic stabilization of the putative intermediate depicted in Scheme 1.…”

DFT Investigation of the η6 ⇌ η6-Inter-ring Haptotropic Rearrangement of the Group 8 Metals Complexes [(graphene)MCp]+ (M = Fe, Ru, Os)

“…42 In fact, all attempts to detect IRHRs in the (RuCp) + complexes of planar PAHs such as pyrene, acenaphthylene and f luoranthene in polar solvents were unsuccessful, which was proved both by the lack of NMR signal broadening in CH 3 NO 2 even at the complex decomposition temperature (90 °C) and by DFT calculations. 43 However, it has been shown by DFT calculations additionally to the experimental data that nonpolar solvents can facilitate IRHRs of [(PAH)MCp] + complexes, because they favor the formation of contact ion pairs (CIPs) with the counter-anions. In such CIPs, anions tend to stabilize the IRHR unsaturated intermediates and transition states.…”