Ireneusz Kownacki

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 .

Application of HS-SPME in the determination of potentially toxic organic compounds emitted from resin-based dental materials

Leaching of volatile substances from resin-based dental materials may have a potential impact on the biocompatibility as well as safety of these materials. Information from manufacturers on ingredients in the materials is very often incomplete. Patients and dentists may be in contact with components emitted from cured dental fillings or from substrates applied in their preparation. Therefore, determination of the components of these materials is necessary for better prevention from possible harmful effects caused by dental fillings. The aim of this work was the isolation and identification of organic compounds evolved from four commercial resin-modified glass-ionomer cements (resin-based dental materials applied in dentistry) by using an alternative method of volatile compounds analysis-HS-SPME (headspace-solid phase microextraction). Dental materials were heated in closed vial at various temperatures and volatile substances released into the headspace phase above the sample were isolated on a thin polymeric fibre placed in SPME syringe. Identification was performed by using the GC-MS (gas chromatography-mass spectrometry) technique. Almost 50 RMGIC (resin-modified glass-ionomer cement) components (monomers and additives) were identified. The main identified leachables were: iodobenzene (DPICls-diphenyliodonium chloride degradation product), camphorquinone (photo-initiator), tert-butyl-p-hydroxyanisole (inhibitor), 4-(dimethylamino)ethyl benzoate (co-initiator), ethylene glycol dimethacrylate (monomer).

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.

Synthesis and structure of the first monomeric iridium–siloxide complexes

Abstract The first monomeric iridium–siloxide complexes [Ir(cod)(PCy3)(OSiMe3)] (1), [Ir(cod)(PCy3)(OSiMe2CHCH2)] (2) and [Ir(CO)(PPh3)2(OSiMe3)] (3), whose structures have been successfully determined by the X-ray method, have been synthesised and characterised by 1H, 13C, 31P and 29Si NMR spectroscopy. In all three complexes the coordination of iridium is square planar.

Synthesis and structure of the first cobalt(I)–siloxide complex

Synthesis, spectroscopic ( 1 H NMR, IR) characterisation and X-ray structure of the first cobalt(I)–siloxide complex, [Co(PPh3)3(OSiMe3)] (I), have been presented. Complex I is synthesised by the reaction of [CoCl(PPh3)3] with trimethylsilanolate. The complex occupies a special position of the space group P3 on the three-fold axis passing through the Co, O and Si atoms. The coordination of cobalt is tetrahedral.

Synthesis of new styrylarenes via Suzuki–Miyaura coupling catalysed by highly active, well-defined palladium catalysts

An efficient synthetic route for well-defined palladium(0) complexes [Pd(η(2)-dba)(PPh3)2] (2), [Pd(η(2)-dba)(PCy3)2] (3) and their crystallographic structures is reported. This is the first crystallographic characterization of palladium complexes coordinated with one dibenzylideneacetone and two phosphines. A highly effective, fully controlled method for selective synthesis of mono- (5-9) and distyrylarenes (10-15) via Suzuki-Miyaura coupling is described.

Catalysis of Hydrosilylation by Well-Defined Surface Rhodium Siloxide Phosphine Complexes

Surface rhodium siloxide phosphine complexes have been synthesized directly by condensation of the molecular precursor Rh(cod)(PR3)(OSiMe3) [R=Cy (1), Ph (2), iPr(3); cod=1,5‐cyclooctadiene] with silanol groups on silica (Aerosil 200) and their structures have been characterized by 13C, 29Si, and 31P cross‐polarization magic‐angle spinning (CP/MAS) NMR spectroscopy. Such single‐site complexes have been tested for their activity in hydrosilylation of olefins with heptamethyltrisiloxane and poly(hydromethyl‐co‐dimethyl)siloxane. The immobilized catalysts 1–3 all retained their effectiveness even after recycling up to at least five times and mostly up to ten times. Based on the results of CP/MAS NMR measurements, a mechanism of hydrosilylation catalysis by single‐site rhodium siloxide phosphine complexes is proposed, which involves concurrent pathways of oxidative addition and replacement of phosphine by olefins.

Photochemically induced insertion of an olefin into the Co–Si bond; the key step for silylative coupling with vinylsubstituted organosilicon compounds

Abstract Co(SiEt 3 )(CO) 4 ( I ) as an example of a Co–Si complex is shown to be a catalyst for silylative coupling of olefins (vinylsilanes, styrene) with vinylsilanes and dimerization of divinylsubstituted silicon compounds(although not as effective as previously reported Ru and Rh complexes). The catalytic and stoichiometric study on the insertion of styrene into the Co–Si bond of I confirms that the mechanism involves the first known β -silyl transfer (from β -silylethylcobalt(I)) to the cobalt atom.

Silsesquioxyl rhodium(I) complexes - synthesis, structure and catalytic activity

The first bi- and mononuclear rhodium(I) complexes [{Rh(μ-OSi(8)O(12)(i-Bu)(7))(cod)}(2)] (5), [Rh(cod)(PCy(3))(OSi(8)O(12)(i-Bu)(7))] (6) with a hindered hepta(iso-butyl)silsesquioxyl ligand bonded to the rhodium(I) center through Rh-O-Si bonds have been synthesized and their structures have been solved by spectroscopic methods and X-ray analysis. Their exemplary catalytic properties in silylative coupling of vinylsilanes with styrene are also presented.

New Bis(dialkynyldisiloxane)triplatinum(0) Cluster: Synthesis, Structure, and Catalytic Activity in Olefin‐Hydrosilylation Reactions

A simple route for the synthesis of triplatinum(0) clusters of the general composition [Pt3{O(SiMe2C C R)2}2] is described. These complexes have a unique coordination structure and exhibit excellent reactivity and selectivity towards the addition of Si H bonds to C=C bonds, thereby affording their corresponding hydrosilylation products in high yields. Complexes of d Pt centers are important for a wide variety of homogenous catalytic processes, such as the hydrosilylation of unsaturated compounds. The tris(divinyltetramethyldisiloxane)diplatinum(0) complex, known as Karstedt’s catalyst, which was discovered in 1973 with its X-ray structure reported later in 1991, appears to be the most-active and most-commercially used catalyst for the hydrosilylation of olefins. The structure of the Karstedt catalyst contains both chelatingand bridging 1,3-divinyltetramethyldisiloxane ligands.