Hieronim Maciejewski

Transition metal-siloxide complexes; synthesis, structure and application to catalysis

Abstract Synthesis and structural characterization of molecular transition-metal (TM)-siloxide (TMOSi) complexes by X-ray spectroscopic and other physico-chemical methods reported since 1982 are reviewed. TM siloxides include terminal and/or bridging siloxy ancillary ligands. Stereoselective properties of the two forms of siloxide ligand have been employed as advanced models (e.g. incompletely condensed silsesquioxanes) of catalytically active centers of early-TM complexes (mainly terminal structures) in such reactions as polymerization and metathesis of olefins and/or as precursors for catalysis by low-coordinate and low-oxidation state late-TM-complex catalysts (in the form of bridging structures).

Metathesis of silicon containing olefins: II. Synthesis of 1,2-bis(silyl)ethenes by metathesis of vinylsilanes

Highly effective metathesis of vinyl-trisubstituted silanes containing two or three alkoxy groups at silicon, has permitted the synthesis of 1,2-bis(silyl)ethenes consisting either, two isomers viz., trans-(E) and cis-(Z) in a near 1/1 ratio, or favouring the E isomer. In consequence bis(silyl)ethenes of general formula (RO)nMe3-n SiCHCHSiMe3-n(OR)n (where n = 2, 3; R = CH3, C2H5, C3H7, iso-C3H7) were prepared, isolated, and identified by predominantly spectroscopic methods.

Chitin-Lignin Material as a Novel Matrix for Enzyme Immobilization

Innovative materials were made via the combination of chitin and lignin, and the immobilization of lipase from Aspergillus niger. Analysis by techniques including FTIR, XPS and 13C CP MAS NMR confirmed the effective immobilization of the enzyme on the surface of the composite support. The electrokinetic properties of the resulting systems were also determined. Results obtained from elemental analysis and by the Bradford method enabled the determination of optimum parameters for the immobilization process. Based on the hydrolysis reaction of para-nitrophenyl palmitate, a determination was made of the catalytic activity, thermal and pH stability, and reusability. The systems with immobilized enzymes were found to have a hydrolytic activity of 5.72 mU, and increased thermal and pH stability compared with the native lipase. The products were also shown to retain approximately 80% of their initial catalytic activity, even after 20 reaction cycles. The immobilization process, using a cheap, non-toxic matrix of natural origin, leads to systems with potential applications in wastewater remediation processes and in biosensors.

Catalysis of hydrosilylation: Part XXXIV. High catalytic efficiency of the nickel equivalent of Karstedt catalyst [{Ni(η-CH2CHSiMe2)2O}2{μ-(η-CH2CHSiMe2)2O}]

Abstract The nickel equivalent of Karstedt catalyst [{Ni(η-CH 2 CHSiMe 2 ) 2 O} 2 {μ-(η-CH 2 CHSiMe 2 ) 2 O}] ( 1 ) appeared to be a very efficient catalyst for dehydrogenative coupling of vinyl derivatives (styrene, vinylsilanes, vinylsiloxanes) with trisubstituted silanes HSi(OEt) 3 , HSiMe 2 Ph. The reaction occurs via three pathways of dehydrogenative coupling, involving formation of an unsaturated compound as the main product as well as a hydrogenated olefin (DS-1) pathway, hydrogenated dimeric olefin (DS-2) and dihydrogen (DC), respectively. The reaction is accompanied by side hydrosilylation. Stoichiometric reactions of 1 with styrene and triethoxysilane, in particular synthesis of the bis(triethoxysilyl) (divinyltetramethyldisiloxane) nickel complex 3 and the first documented insertion of olefin (styrene) into NiSi bond of complex 3 , as well as all catalytic data have allowed us to propose a scheme of catalysis of this complex reaction by 1 .

Hydrosilylation of functionalised olefins catalysed by rhodium siloxide complexes in ionic liquids

The use of ionic liquids for the immobilization of rhodium siloxide complexes has permitted development of highly effective catalysts for the hydrosilylation processes. Herein, we report the synthesis of organosilicon compounds in a biphasic reaction setup, allowing separation of the product, recovery and reuse of the catalyst, which is fundamental from the point of view of “green chemistry”.

Catalysis of hydrosilylation: Part XXXI. Functionalization of poly(methylhydro)siloxanes via hydrosilylation of allyl derivatives†

The synthesis of functional poly(methylhydro)siloxanes has been successfully performed by effective quantitative hydrosilylation of allyl derivatives (allyl phenyl ether, allyl glycidyl ether, allyl methacrylate, allyl chloride, allylamine) and 1-octene with poly(methylhydro)siloxanes catalyzed by platinum [Pt(PPh3)2(CH2=CH2), PtCl2(PPh3)2, H2PtCl6–cyclohexanone] and ruthenium (Ru3(CO)12) complexes. The products were isolated and characterized by 1H NMR, FT IR and GPC methods and can be regarded as examples of well-defined functionalized polysiloxanes with various practical applications.

Metathesis of vinylsubstituted silanes in the presence of ruthenium complexes

Abstract Novel synthetic application of the versatile reaction, the metathesis of vinyltrisubstituted silanes and their co-metathesis with alkenes, dienes and allylsilanes, has been reported. Metathesis of vinyltrimethylsilane is efficiently catalysed by many ruthenium complexes yielding E-bis(silyl)ethene and, unexpectedly 1,1-bis(silyl)ethene (only in the presence of phenylphosphine ligand at ruthenium) as main products accompanied by products of dimerization and co-dimerization. A sequence of five pathways initiating two essential mechanisms — by metal carbene species and the insertion of vinylsilane into RuSi (RuH) and β-H (β-Si) elimination of products was proposed.

Catalysis of hydrosilylation: XXIII. Effect of substituents at silicon on unusual hydrosilylation of vinylsilanes catalysed by nickel acetylacetonate

Abstract Nickel acetylacetonate catalyses a competitive-consecutive reaction of trisubstituted silanes ((EtO) 3 SiH and Et 3 SiH) with a variety of vinyl-tr

Effect of the type of fluorofunctional organosilicon compounds and the method of their application onto the surface on its hydrophobic properties

Fluorofunctional silanes, polysiloxanes and silsesquioxanes were used for the modification of glass surfaces and their influence on hydrophobic properties were determined. To increase hydrophobicity of the surface, the modification was performed in two stages: (i) by a pretreatment using a silica sol (a rise in the surface roughness), and (ii) modification with the above silicon compounds. The hydrophobicity was determined by measuring the contact angle by drop profile tensiometry. The fluorocarbofunctional organosilicon derivatives examined were found to be good precursors for the synthesis of highly hydrophobic materials and coatings. In some cases the contact angles measured after surface modification exceeded 150°, i.e. they fell in the range characteristic of superhydrophobic surfaces.

Dehydrogenative coupling of styrene with trisubstituted silanes catalyzed by nickel complexes

Abstract Trisubstituted silanes, e.g., Me n (EtO) 3− n SiH (where n =0–2) and Me 2 PhSiH in the presence of nickel complexes, e.g., [Ni(acac) 2 ] and [Ni(cod) 2 ], undergo two reactions of dehydrogenative silylation of styrene to yield in both cases an unsaturated product— E -1-phenyl-2-silyl-ethene as well as products of styrene hydrogenation—ethylbenzene DS-1 and of hydrogenative dimerization of styrene—1,3-diphenylbutane—DS-2. The two reactions are accompanied by the hydrosilylation products H as well as redistribution of the silanes containing at least one ethoxy substituent. The catalytic examinations and identification of nickel square planar complexes suggest that the intermediates containing Ni–Si (I), Ni–H (II) and Ni–C (III) bonds are responsible for the catalysis.