Stability and Reactivity of Grafted Cr(CO)₃Species on MOF Linkers: A Computational Study

Abstract

The possibility to modulate Cr(CO)(3) properties by grafting it onto metal-organic framework (MOF) linkers of different natures has been investigated using density functional methods. MOF linkers were modeled using clusters constituted by benzene rings doubly substituted in the para position. The effect of the electron-donor or electron-acceptor nature of benzene substituents on the stability of the (eta(6)-arene)Cr(CO)(3) adduct and on the shift of the CO bands has been considered. Different electron-donor (-NH(2), -CH(3), -OH, -COONa) and electron-acceptor (-F, -COOH, -CN, -CF(3)) substituents have been used and the results compared with the bare benzene. C(6)H(4)(COOZnOH)(2) and C(6)H(4)(Zn(4)O(13)C(6)H(5))(2) clusters have also been adopted as models of the MOF-5 benzene rings. The possibility of modulating the stability and the reactivity of Cr(CO)(3) species by grafting them to MOFs with different organic linkers was verified. In particular, this study indicates that electron-acceptor (e.g., C(6)H(4)(COOH)(2)) substituted MOF linkers facilitate the substitution of CO by incoming molecules, whereas the use of electron-donor ones (e.g., C(6)H(4)(OH)(2)) would improve the stability of the Cr(CO)(3) adduct and the ring acidity. Furthermore, an almost linear dependence of the Cr(CO)(3) binding energies on the calculated structural and vibrational features of the tricarbonyl was found, suggesting that the stability of the Cr(CO)(3) adduct can be inferred experimentally from vibrational and diffraction data. In the end, on the basis of the results obtained, it was possible to successfully explain the experimental shift of the CO IR stretching features of grafted Cr(CO)(3) on the UiO-66, CPO-27-Ni, and MOF-5 aromatic linkers and on the benzene rings of poly(ethylstyrene-co-divinylbenzene). The sign of the Delta nu(CO) shift with respect to C(6)H(6)Cr(CO)(3) has been found to be strongly dependent on higher/lower electron density on the ring.

Influence of functionalization of terephthalate linker on the catalytic activity of UiO-66 for epoxide ring opening

“…In particular, the electron donating or withdrawing ability of the functional groups on the aromatic linkers can modulate the electron density of the complexing groups (e.g. carboxylates) coordinated to the cations and, consequently, influence the catalytic activity of the MOF through controlling the electron density of the active metal site [12], [14], [15]. As previously shown, the ligand functionalization of the microporous UiO-66, a cubic close packed structure based on Zr6O4(OH)4 oxoclusters linked together by terephthalate linkers, strongly affects its Lewis acid catalytic activity [15].…”

Grafting of Molecularly Ordered Mesoporous Phenylene‐Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of Olefins

“…[24] Such materials are potentially interesting as (pre)catalysts for a variety of organic transformations. [25] In particular, cyclopentadienylmolybdenum tricarbonyl complexes of the type Cp'Mo(CO) 3 X (X = Cl, alkyl) have been immobilized in ordered mesoporous silicas by either direct grafting or tethering via ligands, and examined as precursors to heterogeneous catalysts for the epoxidation of olefins with TBHP as the oxidant. [26] The tricarbonyl complexes undergo oxidative decarbonylation in situ with TBHP to give supported oxomolybdenum(VI) species such as Cp'MoO 2 X and/or Cp'MoO(O 2 )X.…”

Delineating similarities and dissimilarities in the use of metal organic frameworks and zeolites as heterogeneous catalysts for organic reactions

“…In contrast to this, there are several transition-metal MOFs that have shown to be stable under liquid-phase reaction conditions. 54, 55 Thus, these MOFs combine high surface area and porosity together with a high density of single site metal ions or metal ion clusters that can be stable under some reaction conditions.…”