Oxidizing Ability of a Dioxygen-Activating Nonheme Iron(II)-Benzilate Complex Immobilized on Gold Nanoparticles

Abstract

An iron­(II)-benzilate complex [(TPASH)­FeII­(benzilate)]­ClO4@­C8Au (2) (TPASH = 11-((6-((bis­(pyridin-2-yl­methyl)­amino)­methyl)­pyridin-2-yl)­meth­oxy)­undecane-1-thiol) immobilized on octanethiol stabilized gold nanoparticles (C8Au) of core diameter less than 5 nm has been prepared to evaluate its reactivity toward O2-dependent oxidations compared to a nonimmobilized complex [(TPA-O-Allyl)­FeII­(benzilate)]­ClO4 (1a) (TPA-O-Allyl = N-((6-(allyl­oxy­methyl)­pyridin-2-yl)­methyl)­(pyridin-2-yl)-N-(pyridin-2-ylmeth­yl)­methan­amine). X-ray crystal structure of the nonimmobilized complex 1a reveals a six-coordinate iron­(II) center in which the TPA-O-Allyl acts as a pentadentate ligand and the benzilate anion binds in monodentate fashion. Both the complexes (1a and 2) react with dioxygen under ambient conditions to form benzophenone as the sole product through decarboxylation of the coordinated benzilate. Interception studies reveal that a nucleophilic iron-oxygen intermediate is formed in the decarboxylation reaction. The oxidants from both the complexes are able to carry out oxo atom transfer reactions. The immobilized complex 2 not only performs faster decarboxylation but also exhibits enhanced reactivity in oxo atom transfer to sulfides. Importantly, the immobilized complex 2, unlike 1a, displays catalytic turnovers in sulfide oxidation. However, the complexes are not efficient to carry out cis-dihydroxylation of alkenes. Although the immobilized complex yields a slightly higher amount of cis-diol from 1-octene, restricted access of dioxygen and substrates at the coordinatively saturated metal centers of the complexes likely makes the resulting iron-oxygen species less active in oxygen atom transfer to alkenes. The results implicate that surface immobilized nonheme iron complexes containing accessible coordination sites would exhibit better reactivity in O2-dependent oxygenation reactions.

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

“…Recently, an iron(II)‐benzilate complex on alkane–thiolate AuNPs has shown cis ‐dihydroxylation reaction of olefins, along with sulfide oxidations. However, the catalyst could not be reused due to leaching problems arising from the oxidation of alkane–thiolate chains . An iron(II)‐BPMEN [BPMEN= N 1, N 2‐dimethyl‐ N 1, N 2‐bis(pyridin‐2‐ylmethyl)‐ethane‐1,2‐diamine] complex was immobilized on silica and polymer resin supports.…”

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

“…Many charged ligands complexes have also been aplied to coat Au NPs in a singlelayer organo-metallic complex shell [150]. Therefore, the coordination of metal ions can be understood by the carboxylate functional group.…”

Functionalization of Gold Nanoparticles by Inorganic Entities

“…Complexes with various charged ligands have also been used to encase gold nanoparticles in monolayer organometallic metal-complex shells [187]. Hence, chelation of metal ions can be realized by carboxylate groups.…”

“…Due to the unique Scheme 26. Illustration of the oxidizing ability of a dioxygen-activating from nonheme Iron(II)-Benzilate complex immobilized on Au-NPs, reproduced with permission from [187]. ACS 2019.…”