29Si NMR investigations on oligosilane dendrimers

Starting with the high functionalized trisilane SiClMe(SiCl₂Me)₂ and tetrasilane SiMe(SiCl₂Me)₃ several octa- and decasilane dendrimers containing directly neighboured branchings were prepared. In these compounds the ²⁹Si NMR chemical shifts of the different silyl groups are shifted towards lower field compared with those of analogous groups in tetra- or hexasilanes. This observation is a helpful tool for the characterization of further dendritic oligomers by ²⁹Si NMR. Received: 3 June 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996     

Silylphosphane mit Adamantan-Struktur durch Umsetzung von P4 und Na/K mit Dichlorsilanen sowie deren 31P-NMR-Spektren

Silylphosphanes with an Admantane Skeleton Formed in Reactions of P₄ and Na/K with Dichlorsilanes, and their ³¹P NMR Spectra The reactions of P₄ and Na/K (molar ratio 1:3) with EtMeSiCl₂, Et₂SiCl₂, and PhMeSiCl₂ give access to the silylphosphanes with adamantane structure (EtMeSi)₆P₄ 1 , (Et₂Si)₆P₄ 2 , and (PhMeSi)₆P₄ 3 . Likewise, the Si-functional adamantanes [Vinyl(Me)Si]₆P₄ 4 , (MeHSi)₆P₄ 5 , and (MeHSi)(Et₂Si)₆P₄ 6 can be obtained by the reaction of alkali phosphides with Vinyl(Me)SiCl₂, MeHSiCl₂, or Et₂SiCl₂/MeHSiCl₂ (molar ratio 5:1), respectively. The compounds form colorless crystals ( 3 crystallies reluctantly). The reactions of the alkali phosphides with t-Bu₂SiCl₂ and Ph₂SiCl₂ do not lead to the corresponding adamantanes; t-Bu₂SiCl₂ doesn't react product mixture of the more reactive Ph₂SiCl₂ traces of (Ph₂Si)₆P₄ could not be detected. The ³¹P-NMR-spectra of the compounds 1–6 are interpreted.     

Bisphosphinodihalogensilane-vorstufen zum 1,3-diphospha-2-silaallen

The syntheses and NMR spectra of the phosphinosilanes (ArHP)₂SiCl₂, (ArHP)₂SiBr₂ and ArHPSiCl₃ are described (Ar = 2,4,6-t-Bu₃C₆H₂). Treatment of (ArHP)₂SiCl₂ with t-BuLi results in the formation of a 1,3-diphospha-2-silaallyl anion, which has been identified by ³¹P and ²⁹Si NMR spectroscopy.     

Spirocyclische Titanamide mit der Diphenylsila-titanadiazacyclobutan- Baueinheit. Kristall- und Molekülstruktur von Ti[(NSiMe3)2SiPh2]2 [1]

Durch Umsetzung der N-lithiierten Silylamine Ph₂Si(NHR)₂ mit SiCl₄ bzw. TiBr₄ wurden die spirocyclischen Amide B (R = Me, Et, i-Pr) und C (R = i-Pr, Me₃Si) dargestellt und ihre Konstitution durch Analysen, ¹H- und ²⁹Si-NMR-Spektren gesichert. Von C, R = Me₃Si, wurde an einem Einkristall eine Röntgenstrukturanalyse durchgeführt. Wichtige Strukturdaten sind: TiN 1,918(2) Å, SiN endocycl. 1,750(2) Å, exocycl. 1,738(2) Å, ? SiNTi 90,3(1)°. Spirocyclic Titanium Amides Containing the Diphenylsila-titana-diazacyclobutane Fragment. Crystal and Molecular Structure of Ti[(NSiMe₃)₂SiPh₂]₂ By reaction of the N-lithiated silylamines Ph₂Si(NHR)₂ with SiCl₄ and TiBr₄, the spirocyclic amides B (R = Me, Et, i-Pr) and C (R = i-Pr, Me₃Si) respectively have been prepared. Their constitutions have been confirmed by elemental analyses and by ¹H and ²⁹Si nmr spectroscopy. C, R = Me₃Si, has been investigated by a single crystal x-ray structure analysis. Important structural parameters are: TiN 1.918(2) Å, SiN endocycl. 1.750(2) Å, exocycl. 1.738(2) Å, ? SiNTi 90.3(1)°.     

1,3,2-Diazasiloles derived from 1,2-bis(trimethylsilylimino)acenaphthene

The reduction of 1,2-bis(trimethylsilylimino)acenaphthene (tms-BIAN, 1) with metallic lithium in toluene affords the dilithium salt (tms-BIAN)Li_2· 1,3,2-Diazasiloles (tms-BIAN)SiCl₂ (2) and (tms-BIAN)SiMe₂ (3) were prepared by the reactions of (tms-BIAN)Li₂ with SiCl₄ and Me₂SiCl₂, respectively. The reaction of (tms-BIAN)Li₂ with an excess of Me₂SiCl₂ produces (Cldms-BIAN)SiMe₂ (4), where Cldms-BIAN is 1,2-bis(chlorodimethylsilylimino)-acenaphthene. The compound (tms-BIAN)(SiCl₃)₂ (5) containing two different silyl substituents (Me₃Si and Cl₃Si) at each nitrogen atom was synthesized by the reaction of compound 1 with Cl₃SiSiCl₃. The elimination of SiCl₄ from compound 5 is accompanied by cyclization to give derivative 2. Compounds 2-5 were characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy. The crystal structures of 2-5 were established by X-ray diffraction.     

The Insertion of EII and EIV Chlorides (E=Si,Ge) into the Si−Si Bond of Disilylene

Reactions of silicon and germanium dichlorides L ⋅ ECl₂ (E=Si, L=IPr; E=Ge, L=dioxane) with the phosphinoamidinato-supported disilylene ({κ²(N,P)-NNP}Si)₂ resulted in formal tetrylene insertions into the Si−Si bond. In the case of the reaction with silylene, two products were isolated. The first product ({κ²(N,P)-NNP}Si)₂SiCl₂, is the formal product of direct SiCl₂ insertion into the Si−Si bond of ({κ²(N,P)-NNP}Si)₂ and thus features two separated silylamido silylene centers. Over time, migration of the SiCl₂ group to a lateral position afforded the second product, the disilylene {κ²(Si,P)−SiCl₂NNP}Si−Si{κ²(N,P)-NNP}. In contrast, insertion of GeCl₂ resulted only in the isolation of the germanium analogue of {κ²(Si,P)−SiCl₂NNP}Si−Si{κ²(N,P)-NNP}, containing a Ge atom in the central position namely, compound {κ²(Si,P)−SiCl₂NNP}Ge−Si{κ²(N,P)-NNP}, which is a rare example of a silylene-germylene. Finally, reaction of disilylene ({κ²(N,P)−NNP}Si)₂ with SiCl₄ and SiHCl₃ led to the formation of the new bis(silyl)silylene, ({NNP}SiCl₂)₂Si:. All four new products from these insertion reactions have been characterized by multinuclear NMR and single-crystal X-ray diffraction studies.     

New hyperbranched carbosiloxane–carbosilane polymers with aromatic units in the backbone

New hyperbranched polymers based on a carbosiloxane–carbosilane skeleton with aromatic units in the backbone have been prepared via one-pot hydrosilylation reaction using HSi(Me)₂–O–CH₂–C₆H₄–OSiMe–(CH₂)₄(C₃H₅)₂ as a novel AB₂ monomer. These polymers are easy to prepare, have narrow polydispersity values and present allyl groups on the surface which can be used as synthetic platforms for the introduction of different terminal groups like amine groups through hydrosilylation reactions, opening the door to functionalized polymers. The polymerization process was monitored using real-time ¹H NMR spectroscopy and the resulting hyperbranched polymers were characterized using ¹H NMR, ¹³C NMR, ²⁹Si NMR and SEC/MALLS. The degree of branching in these polymers was determined by quantitative ²⁹Si NMR spectroscopy and found to be very close to the theoretical value of 0.50 for AB₂ systems. The hydrolytic degradation of these polymers in protic solvents has been studied by ²⁹Si NMR.     

Bildung siliciumorganischer Verbindungen. LXII. Teilbromierte Carbosilane

Formation of Organosilicon Compounds. LXII. Partial Brominated Carbosilanes The photobromination of 1 leads to compound 2 as well as to C-chlorinated derivatives if the time of reaction is prolonged. Compound 2 is also formed from (Br₂Si–CH₂)₃; Gl. (1) see ?Inhaltsübersicht”?. In a corresponding reaction (Cl₃Si–CH₂)₂SiCl₂ gives successively Cl₃Si–CHBr–SiCl₂–CH₂–SiCl₃, Cl₃Si–CBr₂–SiCl₂–CH₂–SiCl₃ and Cl₃Si–CCl₂–SiCl₂–CH₂–SiCl₃. (Cl₃Si)₂CBr₂ is accessible through the photobromination of (Cl₃Si)₂CH₂. The reactivity of the CBr₂-group is quite obvious in the reaction of Cl₂Si–CBr₂–SiCl₂–CH₂–SiCl₃ with LiAlH₄ yielding (H₃Si–CH₂)₂SiCl₂ as well as in the reaction of compound 2 with CH₃MgCl yielding [(CH₃)₂Si–CH₂]₃. By treatment of the SiH groups with bromine the preparation of compounds with the general formulas CH₃SiH_nBr_3?n; (H_3?nSiBr_n)₂CH₂; (H_3?nSiBr_n? CH₂)₂SiH_2?nBr_n; (H_2?nBr_nSi? CH₂)₃ and (H_3?nSiBr_n)₂CCl₂ is possible. Analysis of the nmr spectra shows that 1,3-Dibromo-1,3,5-trisilacyclohexane is formed to 67% in the trans and to 33% in the cis configuration; 1,3,5-Tribromo-1,3,5-trisilacyclohexane is formed to 80–90% in teh cis-trans configuration. The results of ¹H and ²⁹Si NMR investigations are reported.     

Synthesen,Einkristall-Röntgenstrukturanalysen und 29Si-Festkörper-NMR-Untersuchungen eines zwitterionischen λ5-Spirosilicats und eines käfigartigen Octa(silasesquioxans)

Syntheses, Single-Crystal X-Ray Analyses and Solid-State ²⁹Si NMR Studies of a Zwitterionic λ⁵-Spirosilicate and a Cage-like Octa(silasesquioxane) The zwitterionic λ⁵-spirosilicate bis[2,3-naphthalenediolato(2 ?)][2-(dimethylammonio)phenyl]silicate ( 1 ; isolated as 1 · 1/2 CH₃CN) was synthesized by reaction of the [2-(dimethylamino)phenyl]dimethoxyorganosilanes 5, 6 and 7 [2-(Me₂N)C₆H₄Si(OMe)₂R: R = Ph ( 5 ), cyclo? C₆H₁₁ ( 6 ), Me ( 7 )] with 2,3-dihydroxynaphthalene in acetonitrile at room temperature. Reaction of 1 · 1/2 CH₃CN or [2-(dimethylamino)phenyl]trimethoxysilane ( 3 ) with water in acetonitrile yielded the cage-like octa{[2-(dimethylamino)phenyl]silasesquioxane} ( 2 ). The crystal structures of 1 · 1/2 CH₃CN and 2 were studied by X-ray diffraction. In addition, 1 · 1/2 CH₃CN and 2 were characterized by solid-state (²⁹Si CP/MAS) and solution NMR studies (¹H, ¹³C, ²⁹Si).     

Formation of borosilicate glasses from silicon alkoxides and metaborate esters in dry non-aqueous solvents

The reaction of metaborate esters (RO)₃B₃O₃ [R = Me, Et, ClCH₂CH₂–, Cl₃CCH₂–, ClCH₂CH₂CH₂–, (ClCH₂)₂CH–] with Si(OR)₄ (R = Me, Et), either neat or in dry propan-2-one or dry THF at room temperature, led to gels which when dried and heated in air for 20 mins at 600°C afforded borosilicate glasses in high ceramic yields. The dried gels and glasses were characterized by elemental analysis, TGA, IR, and powder XRD, and solid-state MAS ²⁹Si and ¹¹B NMR. The gelling reaction was investigated by solution ¹¹B and ²⁹Si NMR. These NMR studies indicated B–O–Si reaction intermediates and a mechanism involving alkoxy exchange and various condensation/elimination reactions of the borosilicate esters have been proposed.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

Bildung siliciumorganischer Verbindungen. 110. Reaktionen von (Cl3Si)2CCl2, seiner Si-methylierten Derivate,von (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me und Me2CCl2 mit Silicium (Cu-Kat.)

Formation of Organosilicon Compounds. 110. Reactions of (Cl₃Si)₂CCl₂ and its Si-methylated Derivatives as well as of (Cl₃Si)₂CHCl, (Cl₃Si)₂C(Cl)Me and Me₂CCl₂ with Silicon (Cu cat.) The reactions of (Cl₃Si)₂CCl₂ 1 , its Si-methylated derivatives (Me₃Si)₂CCl₂ 8 , Me₃Si? CCl₂? SiMe₂Cl 9 , (ClMe₂Si)₂CCl₂ 10 , Me₃Si? CCl₂? SiMeCl₂ 11 , Cl₂MeSi? CCl₂? SiCl₃ 12 as well as of (Cl₃Si)₂CHCl 38 , (Cl₃Si)₂CClMe 39 and of Me₂CCl₂ with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl₃Si)₂CCl₂ 1 yields C(SiCl₃)₄ 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si₆C₂Cl₁₆ 3 and the related C-spiro linked disilacyclobutanes Si₈C₃Cl₂₀ 4 , Si₁₀C₄Cl₂₄ 5 , Si₁₂C₅Cl₂₈ 6 , Si₁₄C₆Cl₃₂ 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl₂MeSi? CCl₂? SiCl₃ 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si₆C₂Cl₁₅Me 34 and cis- and trans Si₆C₂Cl₁₄Me₂ 35 as well as the spiro-linked disilacyclobutanes Si₈C₃Cl₁₉Me 36 , Si₈C₃Cl₁₈Me₂ 37 . (Cl₃Si)₂CHCl 38 mainly yields HC(SiCl₃)₃ 31 and also the disilacyclobutanes cis- and trans-(Cl₃Si)HC(SiCl₂)₂CH(SiCl₃) 41 and (Cl₃Si)₂C(SiCl₂)₂CH(SiCl₃) 45 the 1,3,5-trisilacyclohexane [Cl₃Si(H)C? SiCl₂]₃ 44 as well as [(Cl₃Si)₂CH]₂SiCl₂, and (Cl₃Si)₂CClMe 39 mainly yields (Cl₃Si)₂C?CH₂and (Cl₃Si)₂besides of HC(SiCl₃)₃, MeC(SiCl₃)₃and (Cl₃Si)₃C? SiCl₂Me.,. Me₂CCl₂ 59 mainly yields Me(Cl)C?CH₂, Me₂CHCl and HCl₂Si? CMe₂? SiCl₃, besides of Me₂C(SiCl₃)₂ and Me₂C(SiCl₂H)₂ Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: α_Si = 94,2°> 85,8° = α_C.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: α_Si = 93,9°> 84,4° = α_C are comparable to those of compound 3.     

Synthese der Silatetraphospholane (tBuP)4SiMe2, (tBuP)4SiCl2 und (tBuP)4Si(Cl)SiCl3 Molekül- und Kristallstruktur von (tBuP)4SiCl2

Synthesis of the Silatetraphospholanes (tBuP)₄SiMe₂, (tBuP)₄SiCl₂, and (tBuP)₄Si(Cl)SiCl₃ Molecular and Crystal Structure of (tBuP)₄SiCl₂ The reaction of the diphosphide K₂[(tBuP)₄] 7 with the halogenosilanes Me₂SiCl₂, SiCl₄ or Si₂Cl₆ in a molar ratio of 1:1 leads via a [4 + 1]-cyclocondensation reaction to the silatetraphospholanes (tBuP)₄SiMe₂ 1,1-dimethyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 1 , (tBuP)₄SiCl₂, 1,1-dichloro-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 2 , and (tBuP)₄Si(Cl)SiCl₃, 1-chloro-1-trichlorsilyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 3 , respectively, with the 5-membered P₄Si ring system. The reaction leading to 1 is accompanied with the formation of the by-product Me₂(Cl)-Si–(tBuP)₄–Si(Cl)Me₂ 1a (5:1), which has a chain structure. On warming to 100°C 1a decomposes to 1 and Me₂SiCl₂. The compounds 2 and 3 do not react further with an excess of 7 due to strong steric shielding of the ring Si atoms by the t-butyl groups. 1, 2 and 3 could be obtained in a pure form and characterized NMR spectroscopically; 2 was also characterized by a single crystal structure analysis. 1a was identified by NMR spectroscopy only.     

1,3,2-Diazasilols based on 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene

Reduction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (1, dpp-bian) in the presence of SiCl₄ with two equivalents of potassium graphite (KC₈) in tetrahydrofuran leads to the formation of compound (dpp-bian)SiCl₂ (2), which was also synthesized by the exchange reaction of SiCl₄ with the magnesium complex (dpp-bian)Mg(THF)₃. An analog of compound 2, the bromo derivative (dpp-bian)SiBr₂ (3), was obtained by the reaction of SiBr4 with one equivalent of Na2(dpp-bian) (in situ from Na and dpp-bian) in toluene. The silylene (dpp-bian)Si (4) was synthesized by the reduction of a mixture of dpp-bian and SiCl₄ (1: 1) with four equivalents of potassium graphite in tetrahydrofuran. Treatment of compound 4 with diimine 1 gives the derivative (dpp-bian)₂Si (5). Compounds 2–5 were characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy, as well as by elemental analysis, their molecular structure was established by X-ray diffraction studies.     

Ionic Dissociation of SiCl4: Formation of [SiL6]Cl4 with L=Dimethylphosphinic Acid

Reactions of SiCl₄ with R₂PO(OH) (R=Me, Cl) yield compounds with six-fold coordinated silicon atoms. Whereas R=Me afforded the hexacoordinated tetra-cationic silicon complex [Si(Me₂PO(OH))₆]⁴⁺ with chloride counter-ions, R=Cl caused release of HCl with formation of a cyclic dimeric silicon complex [Si(Cl₂PO(OH))(Cl₂PO₂)₃(μ-Cl₂PO₂)]₂ with bridging bidentate dichlorophosphates.     

An Electrophilic Carbene‐Anchored Silylene–Phosphinidene

The cyclic alkyl(amino) carbene‐anchored silylene–phosphinidene was isolated as L−Si−P(:cAAC−Me) (L=benzamidinate) at room temperature, synthesized from the reduction of L−Si(Cl₂)−P(:cAAC−Me) ( 1 ) using two equivalents of KC₈. Compound 1 was prepared by the oxidative addition of a chlorophosphinidene to the benzamidinate substituted silylene center. This is the first molecular example of a silylene–phosphinidene characterized by single‐crystal X‐ray structural analysis. Moreover, ¹H, ³¹P, and also ²⁹Si NMR spectroscopic data supported the formulation of the products. The theoretical calculations of compound 2 are in good agreement with the experimental results.     

A Novel Synthesis of AlCl[(NPh)2P(O)H] and SiCl2[(NPh)2P(O)H]: Two New Phosph(V)azane Derivatives

Reactions of phosph(V)azane derivatives of bis(anilino)phosphine oxide (PhNH)₂P(O)H (1) with AlCl₃ and SiCl₄ produce two new phosph(V)azane complexes, AlCl[(NPh)₂P(O)H] (2) and SiCl₂[(NPh)₂P(O)H] (3). In these reactions, an HCl elimination occurs and M─N bonds (M = Si, Al) form directly between a bis(anilino)phosphine oxide ligand with aluminum and silicon halides. The reactions do not require any base to deprotonate the phosphazane ligand. The final products have been fully characterized by means of elemental analysis and IR, MS, and multinuclear NMR (¹H, ¹³C, ³¹P, ²⁷Al, and ²⁹Si) spectroscopy.     

Pentacoordinate Silicon Complexes with N‐(2‐pyridylmethyl)­salicylamide as a Dianionic (ONN′) Tridentate Chelator

The title compound, N‐(2‐pyridylmethyl)salicylamide ( 1 ), was synthesized by ester aminolysis of methyl salicylate and 2‐picolylamine. In the presence of triethylamine as a supporting base, the salicylamide moiety reacts with the organodichlorosilanes RR′SiCl₂ to form the desired six‐membered heterocycles of the type RR′Si–O–(o‐C₆H₄)–C(=O)N(pic), with pic being the 2‐pyridylmethyl (i.e., 2‐picolyl) moiety and RR′ = Me, Me ( 2a ); Me, Ph ( 2b ); Ph, Ph ( 2c ); Bn, Bn ( 2d ); All, Ph ( 2e ) and Ph, H ( 2f ). Despite the absence of notable ring strain release Lewis acidity (i.e., only a six‐membered chelate is formed by the dianion, and smaller rings are not present in the compound), the poor electron withdrawal from silicon by its C– or H– substituents and the flexible methylene bridge between the salicylamide and the pyridine moiety, the pyridine N donor atom furnishes pentacoordinate silicon coordination spheres in all of these compounds 2a – 2f . The coordination number of the silicon atom was confirmed by single‐crystal X‐ray diffraction analysis for the solid state and by ²⁹Si NMR spectroscopy for the solution state.     

Nonhydrolytic synthesis and structural study of methoxyl-terminated polysiloxane D/Q resins

Low-viscosity, methoxylated polysiloxane resins incorporating Me₂SiO_2/2 (D) and SiO_4/2 (Q) units were prepared using nonhydrolytic condensation between Si—Cl and Si—OMe groups with the formation of MeCl, catalyzed by a Lewis acid. With the commonly used catalysts, condensation between two Si—OMe groups, with formation of Me₂O, also took place to a large extent, hindering the control of the degree of condensation of the resins. Several catalysts were tested by monitoring the formation of MeCl and Me₂O using sealed NMR tubes and ¹H-NMR spectroscopy. The best compromise between reactivity and selectivity was obtained with ZrCl₄. Resins with various compositions were prepared in the absence of solvent by condensation between Me₂SiCl₂ and Si(OMe)₄ at 130°C, catalyzed by 1 mol % ZrCl₄. They were characterized using viscosimetry, gas chromatography coupled with mass-spectrometry (GC-MS), and quantitative ²⁹Si-NMR spectroscopy. The resins consisted of a complicated mixture of oligomers, linear or branched (n > 1) and cyclic (n > 3), with a high degree of D/Q bonding. The distribution of Si—OMe and Si—OSi bonds and the bonding between D and Q units were found to be nearly random. This was ascribed to the occurrence of Si—OSi/Si—OMe and Si—OSi/Si—OSi redistribution reactions that reached equilibrium during the synthesis. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2415–2425, 1998     

1‐Silacyclopent‐2‐enes and 1‐silacyclohex‐2‐enes bearing functionally substituted silyl groups in 2‐positions. Novel electron‐deficient Si?H?B bridges

The reactions of alkyn‐1‐yl(vinyl)silanes R₂Si[C?C‐Si(H)Me₂]CH?CH₂ [R = Me (1a), Ph (1b)], Me₂Si[C?C‐Si(Br)Me₂]CH?CH₂ (2a), and of alkyn‐1‐yl(allyl)silanes R₂Si[C?C‐Si(H)Me₂]CH₂CH?CH₂ (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo[3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (¹H, ¹¹B, ¹³C and ²⁹Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd.