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

Abstract

Two types of heterometallic (Fe(III),Na) silsesquioxanes [Ph5Si5O10]2[Ph10Si10O21]Fe6(O2‒)2Na7(H3O+)(MeOH)2(MeCN)4.5.1.25(MeCN), I, and [Ph5Si5O10]2[Ph4Si4O8]2Fe6Na6(O2‒)3(MeCN)8.5(H2O)8.44, II, were obtained and characterized. X-Ray studies established distinctive structures of both products, with pair of Fe(III)-O-based triangles surrounded by siloxanolate ligands, giving fascinating cage architectures. Complex II proved to be catalytically active in the formation of amides from alcohols and amines, thus becoming a rare example of metallasilsesquioxanes performing homogeneous catalysis. Benzene, cyclohexane and other alkanes, as well as alcohols, can be oxidized in acetonitrile solution to phenol, the corresponding alkyl hydroperoxides and ketones, respectively, by hydrogen peroxide in air in the presence of catalytic amounts of complex II and trifluoroacetic acid. Thus, the cyclohexane oxidation at 20 °C gave oxygenates in very high for alkanes yield (48% based on alkane). The kinetic behaviour of the system indicates that the mechanism includes the formation of hydroxyl radicals generated from hydrogen peroxide in its interaction with diiron species. The latter are formed via monomerization of starting hexairon complex with further dimerization of the monomers.

Cage-like manganesesilsesquioxanes: features of their synthesis, unique structure, and catalytic activity in oxidative amidations

“…In the next stage, further increase of phenanthroline loading allowed for the isolation of another intriguing example of CLMS, namely complex 5. In this case, one could identify a cyclic four-membered silsesquioxane ligand, earlier observed for various (Ti(IV)-, 79 Fe(III)-, 80 Co(II)-, 19 Zn(II)-, 25 Cu(II)-, 66 Ln(III)-, 24,32,81 and Mn(II)- 35 ) based CLMS complexes. Despite this, the structural type of 5 is unprecedented because complex 5 represents a cardinally different "open cage" molecular topology (Fig.…”

High-Throughput Small-Molecule Crystallography at the ‘Belok’ Beamline of the Kurchatov Synchrotron Radiation Source: Transition Metal Complexes with Azomethine Ligands as a Case Study

“…The mean productivity of the beamline in the small-molecule crystallography mode is 25-30 new crystal structures per week and roughly 500 per year. Examples of recently published challenging crystal structures include cage polynuclear metal-containing organosiloxanolates [52][53][54], synthetic analogs of naturally occurring alkaloids [55] and other biologically active substances [56], unstable catalysis-related intermediates [57,58], products of photoinitiated single crystal-single crystal solid-state reactions [59], etc.…”