Acetylene-insertion reactions into Pt(II)–H and Pt(II)–SiH3 bonds. An ab initio MO study and analysis based on the vibronic coupling model

Acetylene insertion into Pt(II)–H and Pt(II)SiH₃ bonds of PtH(SiH₃)(PH₃) was investigated using ab initio molecular orbital and M?ller-Plesset perturbation theory methods. The insertion into PtH was predicted to proceed with a smaller activation energy (E _a =12.8 kcal/mol) than that into PtSiH₃ (E _a =20.9 kcal/mol). The reaction energy (ΔE) of the insertion into PtH is 10 kcal/mol smaller than that for the insertion into PtSiH₃, which reflects differences in bond energies between CH and CSi and between PtH and PtSiH₃. A comparison with ethylene insertion revealed that the acetylene insertion occurs more easily, and the latter reaction is more exothermic. A simple vibronic coupling model combined with Toyozawa's interaction mode analysis was used to examine interesting differences in E _a and ΔE between insertions into PtH and PtSiH₃, and between acetylene and ethylene insertions. This analysis suggests that the factors determining E _a are the stiffness of the PtH and PtSiH₃ bonds and the vibronic coupling strength of acetylene and ethylene. Received: 13 August 1998 / Accepted: 2 September 1998 / Published online: 15 February 1999     

Experimental viscosities and viscosity predictions of a ternary mixture comprising silicone oils and 1-octene from 293.15 K to 353.15 K

Viscosities of the ternary and binary mixtures of 1-octene, Rhodorsil H68, Rhodorsil 308V750 have been measured at different temperatures between 293.15 and 353.15 K and at atmospheric pressure. Two correlations were established to predict the viscosity of all mixtures. The first is a statistical expression deduced from an experimental design. The second is based on an additivity law and the temperature effect on binary mixtures.     

Dopant passivation and work function tuning through attachment of heterogeneous organic monolayers on silicon in ultrahigh vacuum

Electronic structures of silicon-organic interfaces were studied by the scanning Kelvin probe technique. These surfaces were fabricated by covalent bonding of a range of phenylacetylene-based molecules (p-X-C₆H₄CCH, where X = CF₃, OCH₃, and H) onto a hydrogen-terminated silicon surface. Organic molecules were bound to the surface under high vacuum conditions by ultraviolet light-induced hydrosilylation. Changes in the electronic structure due to electron-donating ability and dipole moment were analyzed under dark and illuminated conditions. The origin of the silicon band bending was tested to separate the effects of molecular monolayers and unintended dopant passivation. In addition, heterogeneous monolayers were grown by controllably diluting the incoming vapor stream with acetylene during growth. The measured work functions follow a trend linked to dipole moment that can be further tuned by molecular dilution. These results suggest a way to use heterogeneous organic monolayers to tune the electron affinity of silicon and directly alter channel modulation in small semiconductor devices.     

Synthesis of bi- and tetracatenar highly fluorinated compounds for grafting on silicone materials

A series of highly fluorinated compounds bearing two or four perfluoroalkyl (R_F) chains, with a flexible or rigid core have been synthesized. Radical additions, nucleophilic addition or condensation reactions were implemented for these synthesis, using perfluoroalkylated iodides and alcohols and various type of substrates: bis(allylic) derivatives, epichlorhydrin, diacid derivatives. All compounds contain an unsaturated moiety (vinyl, allyl or internal double bond) to be grafted on silicone materials by a catalyzed hydrosilylation reaction.     

Platina-β-diketones as catalysts for hydrosilylation and their reactivity towards hydrosilanes

The platina-β-diketones [Pt₂{(COMe)₂H}₂(μ-Cl)₂] (1), [PPh₄][Pt{(COMe)₂H}Cl₂] (2) and [Pt{(COMe)₂H}-(acac)] (3) were found to catalyze the hydrosilylation of alkynes (hex-1-yne, hex-2-yne, hex-3-yne) and alkenes (hex-1-ene, styrene, trimethylvinylsilane) with methyldiphenylsilane (n_silane:n_substrate:n_Pt = 3000:3000:1, T = 27 °C, in C₆D₆). The comparison with the well-established catalysts from Speier (4) and Karstedt (5) exhibited up to twice as high activities for catalyst 1 and comparable regioselectivities. To get insight into the mechanism of the hydrosilylation, Si-H oxidative addition reactions towards the dinuclear platina-β-diketone 1 have been explored. Reactions of 1 with 2-picolyl substituted hydrosilanes of the type NSiMe₂H and NSiMeHN resulted in decomposition with the formation of platinum black, only. On the other hand, the analogous reaction with the 8-quinolyl substituted silane of the type NSiMeHN was found to proceed under loss of H₂ with the formation of a diacetyl(silyl)platinum(IV) complex [Pt(COMe)₂Cl(NSiMeN-κ²N,N′,κSi)] (23). DFT calculations gave insight into the reason for this different reactivity and into the course of reaction. For comparison, the reaction of 1 with bis(2-picolyl)amine was performed resulting under proton shift in the sense of an oxidative addition reaction in the formation of the diacetyl(hydrido)platinum(IV) complex [Pt(COMe)₂Cl(NNHN-κ³N,N′,N′′)] (25). The complexes 23 and 25 were fully characterized spectroscopically (¹H, ¹³C, ¹⁹⁵Pt, ²⁹Si NMR, IR) and by single-crystal X-ray structure determinations.     

New organocatalysts for the asymmetric reduction of imines with trichlorosilane

Asymmetric reduction of prochiral ketimines 1a-f with trichlorosilane can be catalyzed by the Lewis-basic formamides (S)-4a,b, derived from N-methyl valine, with ≤91% enantioselectivity and low catalyst loading (≤5 mol %) at room temperature in toluene.     

Funktionalisierung von Silicium‐Nanopartikeln mit Fluorwasserstoff und Olefinen

Functionalization of Silicon Nanoparticles with Hydrogen Fluoride and Olefins Silicon nanoparticles (Si‐NPs) from a hot wall reactor (size: 50–300 nm) were freed of surface‐bound SiO_x with anhydrous HF, leaving H‐terminated Si‐NPs. Thermally induced hydrosilylation with 1‐octene lead to the formation of surface bound octyl layers. Using anhydrous HF instead of 40 % hydrofluoric acid leads more efficiently to alkylated Si‐NPs.     

Mechanistic investigation on hydrogenation and hydrosilylation of ethylene catalyzed by rhenium nitrosyl complex

The mechanistic study for hydrogenation and hydrosilylation of ethylene catalyzed by a rhenium nitrosyl complex is carried out with the aid of density functional theory computations. The hydrogenation of ethylene is found to be available kinetically in which the oxidative addition of H₂ plays a role in decreasing the reaction barrier. For the case of hydrosilylation of ethylene, it is found the oxidative addition of HSiMe₃ cannot occur due to steric reasons, instead, a σ-bond metathesis process for reductive elimination of C₂H₅SiMe₃ is proposed. The major reason for the inaccessibility for the hydrosilylation is resulted from the fact that the oxidative addition of HSiMe₃ cannot give a more stable intermediate.     

3－氯丙基三甲氧基硅烷的合成

采用氯铂酸／异丙醇和三苯基膦／环己酮为催化剂，在室温下能够使三氯硅烷与３－氯丙烯迅速发生硅氢加成反应，高产率地生成３－氯丙基三氯硅烷，继而将３－氯丙基三氯硅烷与无水甲醇同时滴加到沸腾的石油醚中进行醇解，合成了３－氯丙基三甲氧基硅烷     

Kronenether-funktionalisierte Carbosilandendrimere

The synthesis of the allyloxymethyl-functionalized crown ethers of type CH₂CHCH₂OCH₂[15-crown-5] (3a) and CH₂CHCH₂OCH₂[18-crown-6] (3b) can be achieved by treatment of HOCH₂[15-crown-5] (1a) and HOCH₂[18-crown-6] (1b) with CH₂CHCH₂Br (2) in presence of KOH. The hydrosilylation of 3a and 3b with Si(CH₂CH₂CH₂SiMe₂H)₄ (4) and Si(CH₂CH₂CH₂SiMe(CH₂CH₂CH₂SiMe₂H)₂)₄ (6) in presence of the Karstedt catalyst affords the respective crown ether end-capped carbosilane dendrimers Si(CH₂CH₂CH₂SiMe₂CH₂CH₂CH₂OCH₂[15-crown-5])₄ (5a), Si(CH₂CH₂CH₂SiMe₂CH₂CH₂CH₂OCH₂[18-crown-6])₄ (5b), Si(CH₂CH₂CH₂SiMe(CH₂CH₂CH₂SiMe₂CH₂CH₂CH₂OCH₂[15-crown-5])₂)₄ (7a) and Si(CH₂CH₂CH₂SiMe(CH₂CH₂CH₂SiMe₂CH₂CH₂CH₂OCH₂[18-crown-6])₂)₄ (7b). The latter dendrimers are obtained in almost quantitative yield. The complexation behaviour of 5 and 7 towards different alkali metal cations is discussed.