Metallocenes, such as ferrocene (Cp2Fe) and nickelocene (Cp2Ni), can be adsorbed on high surface area materials by dry grinding of the components in the absence of a solvent. Favorable supports include mesoporous silica, alumina, carbon nanotubes and activated carbon. The adsorption progresses quickly on these supports, within minutes, although the melting points of the metallocenes are high. The underlying translational mobilities of the colorful metallocenes can be visualized, monitored, and quantified on a macroscopic scale when they migrate into large silica gel specimens. The mobilities of the metallocene molecules on a surface lead to interesting solid-state NMR phenomena. The isotropic spiraling movement across the curved walls of the support eliminate line-broadening anisotropic interactions in the solid state. For example, quadrupolar effects in the 2H solid-state NMR spectra of adsorbed deuterated ferrocene vanish, and a narrow line is obtained for the highly mobile adsorbed molecules. Importantly, all metallocenes form well-defined monolayers on the surface when they are adsorbed by dry grinding. Analyzing an equimolar amount of ferrocene and nickelocene, adsorbed on the same silica surface, by paramagnetic solid-state NMR shows that the metallocenes mix on the molecular level. Nickelocene adsorbed in a sub-monolayer on silica can be reduced with hydrogen to form a Ni(0) single atom catalyst. The latter catalyzes the cyclotrimerization of acetylenes, while nickelocene is not catalytically active. In the presentation, it will be demonstrated that this easy, straightforward path to generating single atom catalysts is of a general nature.

Metallocenes adsorbed on surfaces in well-defined monolayers: Easily accessible precursors for single atom catalysts

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

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