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Simple Preparation and Application of TEMPO‐Coated Fe 3 O 4 Superparamagnetic Nanoparticles for Selective Oxidation of Alcohols
Author(s) -
TuckerSchwartz Alexander K.,
Garrell Robin L.
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200903527
Subject(s) - phosphonate , catalysis , oxidizing agent , chemistry , leaching (pedology) , superparamagnetism , adsorption , nanoparticle , alkyne , oxide , inorganic chemistry , alcohol oxidation , metal , magnetic nanoparticles , combinatorial chemistry , organic chemistry , materials science , nanotechnology , physics , environmental science , magnetization , quantum mechanics , magnetic field , soil science , soil water
Abstract The organic oxidant TEMPO (2,2,4,4‐tetramethylpiperdine‐1‐oxyl) was immobilized on iron oxide (Fe 3 O 4 ) superparamagnetic nanoparticles by employing strong metal‐oxide chelating phosphonates and azide/alkyne “click” chemistry. This simple preparation yields recyclable TEMPO‐coated nanoparticles with good TEMPO loadings. They have excellent magnetic response and efficiently catalyze the oxidation of a wide range of primary and secondary alcohols to aldehydes, ketones, and lactones under either aerobic acidic Mn II /Cu II oxidizing Minisci conditions, or basic NaOCl Anelli conditions. The nanoparticles could be recycled more than 20 times under the Minisci conditions and up to eight times under the Anelli conditions with good to excellent substrate conversions and product selectivities. Immobilization of the catalyst through a phosphonate linkage allows the particles to withstand acidic oxidizing environments with minimal catalyst leaching. Clicking TEMPO to the phosphonate prior to phosphonate immobilization, rather than after, ensures the clicked catalyst is the only species on the particle surface. This facilitates quantification of the catalyst loading. The stability of the phosphonate linker and simplicity of this catalyst immobilization method make this an attractive approach for tethering catalysts to oxide supports, creating magnetically separable catalysts that can be used under neutral or acidic conditions.