om500254w_si_001.cif (964.48 kB)

Adsorption of Ruthenium and Iron Metallocenes on Silica: A Solid-State NMR Study

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posted on 09.06.2014 by Kyle J. Cluff, Nattamai Bhuvanesh, Janet Blümel
Ruthenocene, bis­(indenyl)­ruthenium, bis­(tetrahydroindenyl)­ruthenium, cyclododecane, ferrocene, and ferrocene-d2 have been adsorbed on silica surfaces by grinding the polycrystalline materials with silica. The adsorption process proceeds without solvent and is practically complete within 2 h. Its progress is monitored by 1H, 13C, and 2H solid-state NMR spectroscopy. The transition from the crystal lattice to the surface species that are highly mobile is proven by strongly reduced chemical shift anisotropies and diminished dipolar interactions. Furthermore, the residual line widths are reduced. All solid-state NMR spectra indicate that the transition from a monolayer to the crystalline state is abrupt, and no multiple layers form on the surfaces. A correlation between surface coverage and 2H residual line widths has been established. Besides a hydrophobic dry silica surface, wet and TMS-capped silica have been used as supports. The adsorption leads to the highest surface coverages and most mobile species for the surface of rigorously dried silica. The 2H MAS spectra of surface-adsorbed ferrocene-d2 prove that the motion of the metallocenes on the surfaces is fast and nearly isotropic, as in solution. Consequently, it is demonstrated that 1H and 13C NMR spectra of adsorbed ferrocene can be recorded using a conventional liquids NMR instrument.