Carbon‐Nanotube‐Appended PAMAM Dendrimers Bearing Iron(II) α‐Keto Acid Complexes: Catalytic Non‐Heme Oxygenase Models

Abstract

Poly(amidoamine) dendrimers grafted on carbon nanotubes have been appended with iron(II)‐α‐keto acid (benzoylformate) complex of polypyridyl ligand to design artificial non‐heme oxygenase model. This nano‐enzyme was applied for selective catalytic oxidation of organic molecules. Although the carbon nanotubes serve as a robust heterogeneous platform, the amine terminals of dendrimers provide catalysts binding sites and the amide bonds provide a necessary second coordination sphere similar to the enzymatic polypeptide chains. Such a hybrid design prevented the deactivation of the primary active sites leading to 8 times faster oxidative decarboxylation rates than those of its homogeneous analogue. An electrophilic iron(IV)‐oxo intermediate has been intercepted, which catalyzes the selective oxidation of alcohols to aldehydes and incorporates single oxygen atoms into sulfides and olefins by using aerial oxygen with multiple turnover numbers. The catalyst was consecutively regenerated three times by mild chemical treatment and showed negligible loss of activity.

Iron(ii)-α-keto acid complexes of tridentate ligands on gold nanoparticles: the effect of ligand geometry and immobilization on their dioxygen-dependent reactivity

“…In contrast, the iron( ii )–BF complex supported by a nitrogen donor tetradentate ligand covalently linked to polyamidoamine (PAMAM) dendrimers on carbon nanotubes has been reported to display catalytic oxidation of sulfides with up to TON 6. 32 Furthermore, the covalently linked relatively robust catalyst could be recycled for further use as a catalyst. All these information together point to the requirements of oxidatively stable facial ligands and covalent anchoring of the resulting complexes on a robust solid support with a protein-like shield in developing efficient catalytic models of dioxygen-activating oxygenases.…”

“…Heterogenization of metal complexes has been sought to overcome these problems to attain better systems. [29][30][31][32] Literature reports disclose the use of functionalized gold nanoparticles that provide a scaffold for anchoring specific functional groups for developing functional molecular systems. [33][34][35][36][37] Alkanethiolate-protected gold nanoparticles (AuNP) are highly soluble in organic solvents, are easy to synthesize and are used as building blocks for further functionalization.…”

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

“…The architecture in this case turned out to be somewhat complex, with the roles of the cavitand scaffold being the prevention of the catalytic Fe ions from interacting directly with the silica surface and the provision of a controlled environment for reversible redox catalysis. In another example, a catalyst with multiple metal centers was prepared by first grafting poly­(amidoamine) dendrimers on carbon nanotubes and then appending those with polypyridyl ligands to functionalize with iron­(II)-benzoylformate complexes; this design was aimed at mimicking artificial non-heme oxygenase for the selective catalytic oxidation of organic molecules . Tethered calixarenes have also been used to create new surface sites with controlled accessibility, − and even to control stereoselectivity …”