Hydrofunctionalisation of an Aromatic Triphosphabenzene

The aromatic heterocycle 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene reacts with a series of silanes, germanes and stannanes, with weaker E−H bonds reacting in an increasingly facile manner. All react by 1,4-addition to give bicyclic products with diastereomeric ratios varying with the substrate. Density functional theory (DFT) calculations show that activation of the E−H bond occurs across the 1,4-C/P axis of the triphosphabenzene, with the small energetic differences with respect to the stereochemistry of the addition offering insight into the experimentally observed diastereomeric ratios.     

Regioselective Hydrosilylation of Olefins Catalyzed by a Molecular Calcium Hydride Cation

Chemo‐ and regioselectivity are often difficult to control during olefin hydrosilylation catalyzed by d‐ and f‐block metal complexes. The cationic hydride of calcium [CaH]⁺ stabilized by an NNNN macrocycle was found to catalyze the regioselective hydrosilylation of aliphatic olefins to give anti‐Markovnikov products, while aryl‐substituted olefins were hydrosilyated with Markovnikov regioselectivity. Ethylene was efficiently hydrosilylated by primary and secondary hydrosilanes to give di‐ and monoethylated silanes. Aliphatic hydrosilanes were preferred over other commonly employed hydrosilanes: Arylsilanes such as PhSiH₃ underwent scrambling reactions promoted by the nucleophilic hydride, while alkoxy‐ and siloxy‐substituted hydrosilanes gave isolable alkoxy and siloxy calcium derivatives.     

Structural Elucidation of Silver(I) Amides and Their Application as Catalysts in the Hydrosilylation and Hydroboration of Carbonyls

This study details the isolation and characterisation of three novel silver(I) amides in solution and solid-state, [Ag(Cy₃P)(HMDS)] 2 , [Ag(Cy₃P){N(TMS)(Dipp)}] 3 and [Ag(Cy₃P)₂(NPh₂)] 4 . Their catalytic abilities have proved successful in hydroboration and hydrosilylation reactions with a full investigation performed with complex 2 . Both protocols proceed under mild conditions, displaying exceptional functional-group tolerance and chemoselectivity, in excellent conversions at competitive reaction times. This work reveals the first catalytic hydroboration of aldehydes and ketones performed by a silver(I) catalyst.     

Electrophilic Organobismuth Dication Catalyzes Carbonyl Hydrosilylation

Bismuth compounds are gaining importance as potential alternatives to transition-metal complexes and electron deficient lighter p-block compounds in homogeneous catalysis. Computational analysis on the two-coordinate [(Me₂NC₆H₄)Bi]²⁺ possessing three electrophilic sites is experimentally evidenced by the isolation of [{Me₂NC₆H₄}Bi{OP(NMe₂)₃}₃][B(3,5-C₆H₃Cl₂)₄]₂. These observations led us to generate dicationic organobismuth catalyst, [(Me₂NC₆H₄)Bi(L)₃]²⁺ (L=aldehyde/ketone), evidenced by NMR spectroscopy in solution and by single-crystal X-ray diffraction in the solid state. It efficiently catalyzes hydrosilylation of aldehydes and ketones resulting in silyl ethers as the only products in high yields. Our investigations support a carbonyl activation mechanism at the bismuth center followed by Si−H addition.     

Rare earth alkyl and hydride complexes bearing silylene-linked cyclopentadienyl-phosphido ligands. Synthesis, structures, and catalysis in olefin hydrosilylation and ethylene polymerization

A series of silylene-linked cyclopentadienyl-phosphido rare earth alkyl and hydride complexes of type Me₂Si(C₅Me₄)(PR′)LnR (Ln=Y, Yb, Lu; R′=Ph, Cy, C₆H₂^tBu₃-2,4,6; R=CH₂SiMe₃, H) have been synthesized and structurally characterized, and their activity in ethylene polymerization and olefin hydrosilylation has been studied. These complexes represent the first examples of rare earth alkyl and hydride complexes bearing cyclopentadienyl-phosphido ligands, which are in sharp contrast both structurally and chemically with the analogous cyclopentadienyl-amido and metallocene complexes.     

Problems of synthesis of tetrahedral organosilsesquioxanes. Hydrolytic condensation of hexafunctional branched organotetrasiloxanes

The hydrolytic condensation of methyltris(methyldichlorosiloxy)silane (1b), methyl(1a), and vinyltris(methyldiethoxysiloxy)silanes (1c) in dilute homogeneous solutions was studied. It was found by X-ray diffraction and¹H NMR methods that, irrespective of reaction conditions, only octaorganooctasilsesquioxanes (T ₈), namely, octamethyloctasilsesquioxane and 1,4-divinylhexamethyloctasilsesquioxane, were obtained instead of the expected tetraorganotetrasilsesquioxanes (T ₄). These data suggest that the condensation processes involved in the hydrolysis of1a–c are predominantly intermolecular, and the molecules of the starting oligomers do not undergo rearrangements. Probably, the formation ofT ₄, whose molecules are built of four strained six-membered organosiloxane cycles, is less favorable thermodynamically than the formation of their homologs (T ₈) built of eightmembered organosiloxane cycles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1332–1339, July, 1995.     

Polyhedral oligomeric silsesquioxane bound fulleropyrrolidines

The first reported examples of polyhedral oligomeric silsesquioxane (POSS) cages containing a fulleropyrrolidine species are reported herein. Monosubstituted POSS‐dioxalane species were synthesized through the hydrosilylation of a silyl‐dioxalane with mono‐vinyl substituted POSS. Subsequent deprotection yielded the desired aldehyde functionality. An alternative synthetic pathway, involving the nucleophilic substitution of mono‐benzyl chloride POSS with 4‐hydroxybenzaldehyde yielded the desired aldehyde functionality. Each mono‐aldehyde POSS was then reacted with N‐methylglycine and C₆₀ to yield the desired POSS fulleropyrrolidines. The prepared compounds were characterized by multinuclear NMR, electrospray mass spectrometry, elemental analysis, UV–vis, fluorescence and optical power limiting measurements. Copyright © 2008 John Wiley & Sons, Ltd.     

The influence of additives to the Speier catalyst on hydrosilylation of functionalized alkenes

Hydrosilylation of several unsaturated compounds with triethoxysilane in the presence of the Speier catalyst with various additives influencing the reaction rate and selectivity was studied. The mechanism of hydrosilylation is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1413–1417, July, 1998.     

Synthesis and properties of blue light‐emitting,silicon‐containing,regio‐ and stereoregular conjugated polymers

This article concerns the hydrosilylation polyaddition of 1,4‐bis(dimethylsilyl)benzene ( 1 ) with 4,4′‐diethynylbiphenyl, 2,7‐diethynylfluorene ( 2b ), and 2,6‐diethynylnaphthalene with RhI(PPh₃)₃ catalyst. Trans‐rich polymers with weight‐average molecular weights (M_w's) ranging from 19,000 to 25,000 were obtained by polyaddition in o‐Cl₂C₆H₄ at 150–180 °C, whereas cis‐rich polymers with M_w's from 4300 to 34,000 were obtained in toluene at 0 °C–r.t. These polymers emitted blue light in 4–81% quantum yields. The cis polymers isomerized into trans polymers upon UV irradiation, whereas the trans polymers did not. The device having a layer of polymer trans‐ 3b obtained from 1 and 2b demonstrated electroluminescence without any dopant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2774–2783, 2004