S. I. Pomogailo

Polymer-matrix nanocomposite gas-sensing materials

A new approach has been proposed for producing nanocomposite gas-sensing materials: in situ preparation of a polymer matrix and metal sulfide or oxide nanoparticles through the frontal polymerization of Co(II), Cd(II), Zn(II) and Pb(II) acrylamide complexes. The composition and structure of the nanocomposites thus obtained have been determined using X-ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopy. The nanocomposites have been tested as room-temperature liquefied petroleum gas sensors.

Hybrid polymer-immobilized palladium nanoparticles: Preparation and catalytic properties

A new approach to the synthesis of mixed-type immobilized catalysts was developed: the frontal polymerization of a metal-containing monomer in the presence of a highly dispersed mineral support. The synthesis of an acrylamide complex of Pd(II) nitrate on the surface of SiO2, Al2O3, or C and its subsequent polymerization and reduction resulted in the formation of an organic-inorganic composite that included nanosized Pd particles stabilized by a polymer matrix and an inorganic support. The resulting hybrid nanocomposites are efficient and selective catalysts for the hydrogenation reactions of cyclohexene and alkene and acetylene alcohols.

Preparation of nanostructured materials through thermolysis of metal chelate complexes

We demonstrate that nanocomposites (metals and metal carbides and sulfides) can be produced by thermolysis (370 and 600°C) in a self-generated atmosphere using Cu(II), Co(II), and Ni(II) 2-hydroxy- and 2-N-tosylaminobenzaldehyde azomethine bis-chelates as precursors.

Synthesis and properties of Rh6- and Os3-cluster-containing monomers and their copolymers with styrene

Cluster metal-containing monomers were obtained and characterized. Mono- and disubstituted products were obtained under mild conditions via the interaction of Rh 6 (CO) 16 with 4-vinylpyridine (4-VPy) in the presence of trimethylamin-N-oxide. Substitution of labile acetonitrile ligand in Rh 6 (CO) 15 NCMe by allyldiphenylphosphine (AlPPh 2 ) yields Rh 6 (CO) 14 (μ,η 2 -PPh 2 CH 2 CH=CH 2 ) with formation of π-complex. The structures of Rh 6 (CO) 15 (4-VPy), Rh 6 (CO) 14 (μ,η 2 -PPh 2 CH 2 CH=CH 2 ) and (μ-H)Os 3 (μ-OCNM 2 )(CO) 9 PPH 2 CH 2 CH=CH 2 have been determined by single-crystal X-ray diffraction studies, as well as by IR-, 1 H NMR spectroscopies. The Rh - Rh bond lengths are within 2.72÷2.80 A. The copolymerization of cluster-containing monomers synthesized with traditional monomers has been studied. It was found that Rh 6 - and Os 3 -containing monomers did not change either the ligand surroundings or the structure of cluster monomer framework during polymerization reaction.

SYNTHESIS AND REACTIVITY OF METAL-CONTAINING MONOMERS. 51. SYNTHESIS AND MOLECULAR STRUCTURE OF THE CLUSTER-CONTAINING COMPLEX RH6(CO)14(MU , ETA 2-PP H2CH2CH=CH2)

The reaction of Rh6(CO)15MeCN with allyldiphenylphosphine under mild conditions afforded the cluster-containing complex [Rh6(CO)14(μ,η2-PPh2Ch2CH=CH2)]. Its molecular structure was characterized. The resulting complex is an octahedral Rh cluster with ten terminal and four μ3-bridging CO ligands. The average Rh−Rh distance is 2.762(2) Å. The unsaturated ligand is additionally coordinated to the metal center (Rh(4)–C(232), 2.37(1) Å; and Rh(4)–C(233), 2.32(2) Å) to form a π-bond.

Synthesis, structure, and catalytic properties of polymer-immobilized rhodium clusters

Immobilized Rh6 clusters (cyclohexene hydrogenation catalysts) were prepared by the polymer-analogous transformations or copolymerization of cluster-containing monomers and characterized. Intermediates formed in the course of a catalytic reaction were studied using IR spectroscopy, XPS, and atomic force microscopy. It was found that the relative intensity of a low-energy line in the Rh3d5/2 spectrum of the initial polymer-immobilized cluster in the XPS spectrum of Rh6 increased in the course of hydrogenation. The catalytic activity of the immobilized complex changed symbatically with both the number of Rh atoms bound to the H(CO) group and the number of Rh atoms, the charge on which was greater than that in the parent cluster. Some experimental evidence was obtained in favor of the hypothesis of cluster fragmentation in the course of hydrogenation with the formation of highly active, most likely, nanosized particles, which are true catalysts, in low concentrations. The surface of macrocomplex particles after hydrogenation became more homogeneous and hydrophilic; this fact is also indicative of an increase in the concentration of polar functional groups in surface layers. This was likely due to Rh-Rh bond cleavage in the polymer-immobilized cluster.

Synthesis and reactivity of metal-containing monomers 76. Nanostructured materials obtained by controlled thermolysis of Ni, Co, and Cu chelate complexes with azomethine ligands

The controlled thermolysis of mono(NiII, CuII, and CoII) and dinuclear (NiII, CuII, and FeII) chelate complexes with azomethine ligands, containing oxygen, nitrogen, and sulfur atoms in the chelate rings, was studied. The effect of the ligand environment on the thermal stability and composition of the resulting nanocomposites was examined. Comparative thermal analysis (DSC, DTA, and TGA) of the metal chelate complexes was performed. Their thermolysis products were characterized using elemental analysis, X-ray powder diffraction, scanning electron microscopy, and gel permeation chromatography. The magnetic properties of the nanocomposites obtained were analyzed.

Hafnium-containing nanocomposites

New types of hafnium-containing nanocomposites are prepared by combining polymer synthesis and controlled thermolysis. This approach involves the preparation and subsequent thermolysis of hafnium-containing polymers or concurrent solid-state polymerization of hafnium-containing monomers and thermal decomposition of the forming metal-containing polymer at different temperatures. The composition and structure of the synthesized hafnium-containing precursors and thermolysis products are determined by elemental analysis, IR spectroscopy, mass spectrometry, optical microscopy, and x-ray diffraction. Thermodynamic analysis is used to assess the equilibrium composition of the Hf-C-H-O system and establish the conditions under which HfC and HfO2 are formed.

Preparation and reactivity of metal-containing monomers 53. Synthesis and stability of a cluster monomer (μ-H)Os3(μ-OCNMe2)(CO)9PPh2CH2CH=CH2 in solution

The stability of the complex (μ-H)Os3(μ-OCNMe2)(CO)9PPh2CH2CH=CH2 (1), which contains a free unsaturated functional group in the terminal ligand PPh2CH2CH=CH2, with respect to isomerization, chelation of the ligand, and other transformations in solutions was examined. No transformations of complex1 were observed in the course of synthesis from (μ-H)Os3(μ-OCNMe2)(CO)9NMe3 or upon heating in solution. Complex1 as well as complexes (μ-H)Os3(μ-OCNMe2)(CO)9PHPh2 and (μ-H)Os3(μ-OCNMe2)(CO)9PPh3, which were formed as admixtures, were isolated in the solid state and identified by1H,1H-{31P}, and1H-{1H} NMR, IR, and Raman spectroscopy and mass spectrometry.

Polymer-immobilized rhodium complexes forming in situ: preparation and catalytic properties

We elaborated a method for frontal polymerization of a Rh-containing monomer in the presence of a conventional support to obtain polymer-immobilized hydrogenation catalysts. A hybrid nanocomposite forms during the propagation of a narrow molten zone (first-order phase transition) and is characterized by stable front propagation throughout the reaction volume. The products were characterized by various physicochemical methods and were tested as catalysts in the hydrogenation of cyclohexene, allyl alcohol, and nitrobenzene. The transformation of the X-ray photoelectron spectrum (XPS) on passing from the starting rhodium nitrate complex to its metal monomer (acrylamide complex), polymer, and supported catalyst is described. Native intermediate products were isolated and characterized by XPS.