Cage‐like Fe,Na‐Germsesquioxanes: Structure, Magnetism, and Catalytic Activity

Abstract

As eries of four unprecedented heterometallic metallagermsesquioxanes were synthesized. Their cage-like architectures have au nique type of molecular topology consisting of the hexairon oxo{ Fe 6 O 19 }c ore surrounded in at riangular manner by three cyclic germoxanolates [PhGe-(O)O] 5 .T his structural organization induces antiferromagnetic interactions between the Fe III ions through the oxygen atoms.E valuated for this first time in catalysis,t hese compounds showed ah igh catalytic activity in the oxidation of alkanes and the oxidative formation of benzamides from alcohols.The design of metal-based polycyclicc age-like compounds has attracted ag reat deal of attention from researchers worldwide over several decades owing to their structural diversity and their potential technological applications especially in catalysis. [1] Numerous metal-oxygen clusters, [1b,c,j] metal-organic frameworks [1d,l,m] or metal-organic polyhedrons [1f,n] have been designed by using av ariety of selfassembling or templated reactions.A mong those,awide family of polynuclear cage-like metallasilsesquioxanes (CLMSs) architectures with interesting structural topologies [2] and important catalytic activity (e.g.i ne poxidation, oxidation and polymerization) [3] has been synthesized through ar eaction involving transition-metal ions and silsesquioxane [RSiO 1.5 ] n ligands.S urprisingly,e xamples of cage-like architectures involving another metalloid close to silicon, namely germanium, are scarce despite the great potential of this element in organometallic chemistry.T oour knowledge there is only aseries of compounds obtained from germasesquioxane [RGeO 1.5 ] 2 (R = HOOCCH 2 CH 2 )and various cations. [4] Their hydrothermal synthesis requires relatively hard conditions consisting of several days of reactions at 110 8 8C. It is worth mentioning that to date focus has only been on the synthesis,t hermogravimetric analysis,l uminescence, and sorption properties of these architectures and no investigation of the catalytic activity of metallagermanates has been reported.Herein, we report an alternative and simplified synthetic approach to design aseries of unprecedented individual cagelike metallagermsesquioxanes under mild conditions.I n addition, the catalytic activity and magnetic properties of the metallagermsesquioxanes will be discussed.Thes ingle crystals of Fe,Na-phenylgermsesquioxane [(Ph 5 Ge 5 O 10 ) 3 Fe 6 (OH) 3 (O)Na 2 ]·(EtOH) 2 ·H 2 O 1 (10 %y ield) were obtained by ar eaction between phenyltrimethoxygermane PhGe(OMe) 3 ,N aOH and anhydrous FeCl 3 in ethanol with further crystallization. Thea ddition of N-containing ligands,s uch as phenanthroline,b ipyridine,o rn eocuproine to this reaction allowed us to isolate complexes

High Catalytic Activity of Heterometallic (Fe₆Na₇and Fe₆Na₆) Cage Silsesquioxanes in Oxidations with Peroxides

“…Compound II containing a polynuclear iron complex with chelating oxo-ligands exhibits some features similar to that of binuclear alkane oxygenases, and thus can be considered as an "inorganic alkane oxygenase". In this context, behavior of compound II might be compared to our newest results concerning catalytic activity of Fe(III)-based silsesquioxane [23] and germaniumsesquioxane [58].…”