A Novel Wilkinson’s Type Silica Supported Polymer Catalyst: Insights from Solid-State NMR and Hyperpolarization Techniques

Abstract

The synthesis of a novel immobilized Wilkinson’s catalyst [SiO2∼PvPy-Wilk] is presented. The support material of this catalyst consists of silica particles that are modified with polymer brushes carrying pyridyl moieties that enable the coordination of Wilkinson’s catalyst. The synthesis of this catalyst is monitored by 1D and 2D multinuclear solid-state NMR techniques to confirm the success of the immobilization. The [SiO2∼PvPy-Wilk] catalyst is then tested in the hydrogenation of styrene, and its reusability is inspected showing that significant structural changes after several reaction cycles yield an activation of the catalyst. Finally, the catalyst is tested in PHIP experiments giving rise to about 200-fold enhancement of the signals of the hydrogenation product ethylbenzene.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

“…110 It is interesting that in some instances structural or electronic changes in the tethered catalysts may be required for their activation; in those cases, an increase (rather than a decrease) in activity is seen in reusability tests. 145,320 However, these are the exception rather than the rule. At the other extreme, namely, if the interaction between the support and the tethered functionality is strong, as in cases involving covalent bonding, the catalysts are hard to regenerate once the molecular functionality decomposes.…”

“…This may be a particularly acute problem with immobilized catalysts based on Rh, − Pd, − and other transition metals. − Alternative mechanisms for the loss of activity with tethered catalysts include clustering of the metal ions into metal NPs , and the hydrolysis of silane bonds . It is interesting that in some instances structural or electronic changes in the tethered catalysts may be required for their activation; in those cases, an increase (rather than a decrease) in activity is seen in reusability tests. , However, these are the exception rather than the rule. At the other extreme, namely, if the interaction between the support and the tethered functionality is strong, as in cases involving covalent bonding, the catalysts are hard to regenerate once the molecular functionality decomposes.…”

Recent advances in the application of parahydrogen in catalysis and biochemistry

“…Currently there are three possible solutions to this problem, namely (i) the immobilization of an homogeneous catalyst via tethering to e.g. a silica surface, [57][58][59][60][61][62] (ii) employing supported MNPs and (iii) physical separation via solubility properties, 63 which is discussed in more detail in the application chapter. However, with all these methods great care has to be taken that no metal centers or other potentially harmful fragments leach into the solution.…”

The Journal of Physical Chemistry C Virtual Special Issue on Advanced Characterization by Solid-State NMR and In Situ Technology and in Recognition of Michael Hunger’s 65th Birthday

“…Estes and coworkers probed the interactions of immobilized Ru complexes with metal oxide supports by 31 P­{ 1 H}­HETCOR for CO 2 hydrogenation . The Buntkowsky group used 1D and 2D multinuclear magic-angle spinning (MAS) NMR to monitor the synthesis of the novel Wilkinson’s type silica supported polymer catalysts . The guest localization in mesoporous silica particles was mapped by 1 H and 19 F MAS NMR by the Potrzebowski group .…”

“…11 The Buntkowsky group used 1D and 2D multinuclear magic-angle spinning (MAS) NMR to monitor the synthesis of the novel Wilkinson's type silica supported polymer catalysts. 12 The guest localization in mesoporous silica particles was mapped by 1 H and 19 F MAS NMR by the Potrzebowski group. 13 The Sun group investigated the structure−property relationship of chitosanbased biopolymers.…”