Copper‐Containing SiCN Precursor Ceramics (Cu@SiCN) as Selective Hydrocarbon Oxidation Catalysts Using Air as an Oxidant

Abstract

A molecular approach to metal-containing ceramics and their application as selective heterogeneous oxidation catalysts is presented. The aminopyridinato copper complex [Cu(2)(Ap(TMS))(2)] (Ap(TMS)H=(4-methylpyridin-2-yl)trimethylsilanylamine) reacts with poly(organosilazanes) via aminopyridine elimination, as shown for the commercially available ceramic precursor HTT 1800. The reaction was studied by (1)H and (13)C NMR spectroscopy. The liberation of the free, protonated ligand Ap(TMS)H is indicative of the copper polycarbosilazane binding. Crosslinking of the copper-modified poly(organosilazane) and subsequent pyrolysis lead to the copper-containing ceramics. The copper is reduced to copper metal during the pyrolysis step up to 1000 degrees C, as observed by solid-state (65)Cu NMR spectroscopy, SEM images, and energy-dispersive spectroscopy (EDS). Powder diffraction experiments verified the presence of crystalline copper. All Cu@SiCN ceramics show catalytic activity towards the oxidation of cycloalkanes using air as oxidant. The selectivity of the reaction increases with increasing copper content. The catalysts are recyclable. This study proves the feasibility of this molecular approach to metal-containing SiCN precursor ceramics by using silylaminopyridinato complexes. Furthermore, the catalytic results confirm the applicability of this new class of metal-containing ceramics as catalysts.

Aerobic Copper-Catalyzed Organic Reactions

“…For example, Kempe and coworkers recently reported the reaction of cycloalkanes under air with copper-modified SiCN ceramics (Cu@SiCN). 54 Oxidation afforded the ketone as the major product, and larger cycloalkanes afforded greater conversions, with cyclohexane affording almost no conversion at all (Scheme 19). The catalysts were formed through the cross-linking of cupper-coordinated poly(oraganosilazanes), and were able to be recycled with only a small loss of activity.…”

Single-catalyst high-weight% hydrogen storage in an N-heterocycle synthesized from lignin hydrogenolysis products and ammonia

“…Synergistic effects of Pd catalysts, when combined with other transition metals, have been reported for hydrogenation reactions28 and can be rationalized by assuming a lower hydride-binding energy in a metal alloy29. Recently, the silicon carbonitride (SiCN) matrix has been introduced as an attractive support for metal catalysts3031. Amorphous SiCN is very robust thermally and chemically inert32.…”

Title Pages

“…The translation of lab-scale aqueous procedures ('in water' 'on water' or 'by water' 81 ) to the industrial level can be seen in the same 'green' light, courtesy in part to the design of water-soluble reagents: note, for example, the application of copper sulfonatosalen complexes for amination of aryl halides in water 82 and copper 2-pyridylaldoxime complexes for the the aqueous conversion of aryl halides to phenols 83 . Looking more abstractly at the current highlights, mention might be given to developments in alkane oxidation: note the angular hydroxylation of bicyclic hydrocarbons with Ce(IV) and a catalytic amount of Ir(III) 84 , and the aerobic oxidation of cycloalkanes with robust copper-containing ceramic material (Cu@SiCN), in which the copper content can be simply varied to adjust selectivity 85 . An interesting terminal functionalization of alkanes in one pot is also at hand via iridium-catalyzed dehydrogenation to the terminal alkene and subsequent regiospecific hydrozirconation prior to electrophilic substitution 86 .…”