Primary Silanes Research Articles

Catalytic hydrosilylation of alkenes by a ruthenium silylene complex. Evidence for a new hydrosilylation mechanism.

Novel ruthenium and osmium silylene species containing Si-H bonds have been synthesized and characterized by NMR spectroscopy. The ruthenium complex [Cp*(iPr3P)(H)2Ru=Si(H)Ph.Et2O][B(C6F5)4] catalyzes the hydrosilyation of alkenes with excellent substrate selectivity for primary silanes and exclusive anti-Markovnikov regiochemistry. Evidence for a novel mechanism involving direct addition of an alkene to the silylene Si-H bond is presented.

Dehydrogenative coupling of primary alkyl silanes using Wilkinson's catalyst

Primary alkyl silanes (RSiH 3, where R= n-C 12H 25 or n-C 8H 17) undergo dehydrogenative coupling in the presence of (Ph 3P) 3RhCl ( 1) to give oligomeric products. 29Si{ 1H}-NMR and gel permeation chromatography suggest that chains of up to 5–6 silicons are forming in these reactions. Variations in product distributions observed for these two substrates, of supposedly comparable SiH reactivity, may be correlated with the relative rates of departure of hydrogen gas from the reaction mixtures. The sensitivity of this system to H 2(g) concentrations may ultimately allow control over specific chain lengths formed.

Activations of Silanes with [PhB(CH2PPh2)3]Ir(H)(η3-C8H13). Formation of Iridium Silylene Complexes via the Extrusion of Silylenes from Secondary Silanes R2SiH2

The abstraction of methide from (Me_3P)_3Ir(SiHMes_2)(Me)(H) (1) with B(C_6F_5)_3 gave the silylene complex [fac-(Me_3P)_3(H)_2Ir(SiMes_2)][MeB(C_6F_5)_3] (2) via 1,2-hydrogen migration. Secondary silanes (H_2SiR_2) reacted with [PhBP_3]Ir(H)(η^3-C_8H^(13)) (3) (where [PhBP_3] = PhB(CH_2PPh_2)_3^-) to give silylene complexes of the type [PhBP_3](H)_2Ir═SiR_2 (R = 2,4,6-trimethylphenyl (Mes), 4a; R = Ph, 4b; R = Et, 4c; R = Me, 4d), with loss of cyclooctene. Analogously, the germylene complex [PhBP_3](H)2Ir═GeMes_2 was obtained via the reaction of 3 with Mes_2GeH_2. Primary silanes (H_3SiR) reacted with 3 to give [PhBP_3](H)_2Ir═Si(R)(c-C_8H_(15)) (R = Mes, 8a; R = 2,4,6-triisopropylphenyl (Trip), 8b) via an intermediate silylene complex with an Si−H bond, [PhBP_3](H)_2Ir═Si(R)(H). With tertiary silanes (R_3SiH), silyl-capped trihydride complexes of the type [PhBP_3]IrH_3(SiR_3) (R = Et, 7a; R = Me, 7b) and 1,3-cyclooctadiene were produced. The mechanisms of these processes are discussed.

Dehydrocoupling reactions of amines with silanes catalyzed by [(Et 2N) 3U][BPh 4

Dehydrocoupling reactions of primary amines RNH 2 with PhSiH 3 were catalyzed by [(Et 2N) 3U][BPh 4] to give the corresponding aminosilanes PhSiH 3− n (NHR) n ( n=1–3), the relative yields of the products were found to be dependent on the experimental conditions and on the nature of R. For a primary silane (PhSiH 3), the reactivity of RNH 2 follows the order primary>secondary>tertiary. Similar dehydrocoupling reactions using secondary amines with secondary silanes were found to be less reactive. Homodehydrocoupling of the silane was found not to be a competing reaction at room temperature. The hydride [(RNH) 2UH][BPh 4], which is plausibly formed in the reaction of [(RNH) 3U][BPh 4] with PhSiH 3 is a likely intermediate in the catalytic cycle.

Synthesis and Characterization of Atactic Poly(p-tolylsilane) via the Catalytic Dehydrocoupling of p-Tolylsilane1

The primary silane p-TolSiH3 (p-Tol = p-CH3C6H5) can be polymerized to poly(p-tolylsilane) with 1.0 mol % of both the chiral and achiral zirconocenes Cp2ZrCl2, Cp(CpSi*)ZrCl2, and (CpSi*)2ZrCl2 (Cp = C5H5, CpSi* = C5H4Si(CH3)2-(1R)-endo-(+)-OC10H17) in combination with 2.0 mol % of n-BuLi. Generally, higher molecular weight linear polymers were obtained when using the substituted zirconocenes in comparison to the parent zirconocene, which in turn produced larger quantities of low-molecular-weight cyclic products. Each polysilane sample was analyzed by 29Si{1H} DEPT and 1H and 13C{1H} NMR spectroscopy. Deconvolution of selected regions of the 29Si{1H} DEPT and the 1H NMR spectra for higher molecular weight linear polymers indicated that these catenates were predominantly atactic, on the basis of a triad level Bernoullian statistical model. The data suggested that, in this case, chiral substitution of the zirconocene rings had no effect on the stereogrowth of the polysilane chain.

Hydrosilylation Catalysis by C2-Symmetric Bis(silylamido) Complexes of Yttrium

The yttrium hydride {[DADMB]YH(THF)}2 (2; DADMB = 2,2‘-bis(tert-butyldimethylsilylamido)-6,6‘-dimethylbiphenyl), conveniently generated in situ from [DADMB]YMe(THF)2 (1), is an active olefin hydrosilylation catalyst. This system represents the first use of a d0 metal complex with non-Cp ligands in the catalytic hydrosilylation of olefins. Studies of the reactivity and regio- and enantioselectivity for various olefins and silanes are presented. High preference for terminal addition in the case of aliphatic olefins is observed, while aromatic olefins exhibit preference for 2,1-addition. Both primary and secondary silanes have been employed. Preliminary studies of the enantioselectivity of the chiral catalyst show that 90% ee can be achieved in the hydrosilylation of norbornene with PhSiH3. Kinetic studies support a mechanism consistent with the generally accepted one for hydrosilylation catalyzed by early transition metal species, involving rapid olefin insertion into a Y−H bond followed by a Si−C bond-form...

Synthesis and characterization of sterically hindered arylsilanes containing the 2,4,6-trimethoxyphenyl ligand (TMP): X-ray structures of (TMP)SiH 3, (TMP) 2SiH 2, and (TMP) 3SiH

The homologous series of primary, secondary and tertiary silanes containing the sterically demanding 2,4,6-trimethoxyphenyl (TMP) group have been prepared in yields ranging from 22 to 45%. The arylsilanes were characterized by multinuclear NMR, IR, GC–MS, elemental analyses, and X-ray crystallography. Relatively short intramolecular distances are observed between Si and the O atoms in the ortho-methoxy groups of the aryl ligand and are shorter than the sum of the van der Waal’s radii in the solid state for all three arylsilanes.

Silicon-Modified Ziegler−Natta Polymerization. Catalytic Approaches to Silyl-Capped and Silyl-Linked Polyolefins Using “Single-Site” Cationic Ziegler−Natta Catalysts

This contribution reports efficient and selective organotitanium-mediated silanolytic (PhSiH3, PhMeSiH2, Me2SiH2, Et2SiH2) chain transfer in the homogeneous polymerization and copolymerization of a variety of α-olefins. The result is several broad classes of silyl-capped and silyl-linked polyolefins which have been characterized by 1H/13C/29Si NMR and IR spectroscopy as well as by GPC. “Single-site” Ziegler−Natta catalysts effect this chain transfer with significant efficiency and scope. For [Me2Si(Me4C5)tBuN]TiMe+B(C6F5)4--mediated propylene polymerization, the mechanism of chain transfer is supported by the observation that Mn of the capped atactic polypropylenes produced at constant [catalyst], [PhSiH3], and [propylene] is inversely proportional to [PhSiH3]. Using the same catalyst, this process also efficiently produces silyl endcapped poly(1-hexene), ethylene + 1-hexene copolymers, ethylene + styrene copolymers (both with high degrees of comonomer incorporation), and (at low temperatures) polyethylene. In the case of rac-C2H4(Ind)2TiMe+B(C6F5)4- + propylene and (Me5C5)TiMe2+B(C6F5)4- + styrene, PhH2Si-functionalized isotatic polypropylene and syndiotactic polystyrene, respectively, are produced. Using 1,4-disilabenzene and 1,3,5-trisilabenzene as chain-transfer agents in the presence of [Me2Si(Me4C5)tBuN]TiMe+B(C6F5)4- + propylene, linear diblock and starlike atactic polypropylene structures, respectively, are produced. In addition to primary silanes, secondary silanes (PhMeSiH2, Me2SiH2, Et2SiH2) are efficient and selective chain-transfer agents in this organotitanium-mediated polymerization. In the presence of [Me2Si(Me4C5)tBuN]TiMe+B(C6F5)4- + propylene, (Me5C5)TiMe2+B(C6F5)4- + propylene, and (Me5C5)TiMe2+B(C6F5)4- + styrene, PhMeHSi- or Me2HSi-capped atactic polypropylene and PhMeHSi-, Me2HSi-, or Et2HSi-capped syndiotactic polystyrene are produced, respectively. Using PhH2Si-capped polypropylene as a chain-transfer agent, an atactic polypropylene−syndiotactic polystyrene AB block copolymer is produced in the presence of (Me5C5)TiMe2+B(C6F5)4- + styrene.

The Syntheses and Characterization of the Bulky Terphenyl Silanes and Chlorosilanes 2,6-Mes2C6H3SiCl3, 2,6-Trip2C6H3SiCl3, 2,6-Mes2C6H3SiHCl2, 2,6-Trip2C6H3SiHCl2, 2,6-Mes2C6H3SiH3, 2,6-Trip2C6H3SiH3and 2,6-Mes2C6H3SiCl2SiCl3

The synthesis and characterization of the primary terphenyl silanes and chlorosilanes 2,6-Mes2C6H3SiCl3 (1a), 2,6-Trip2C6H3SiCl3 (1b), 2,6-Mes2C6H3SiHCl2 (2a), 2,6-Trip2C6H3SiHCl2(2b) 2,6-Mes2C6H3SiH3(3a), 2,6-Trip2C6H3SiH3 (3b) and 2,6-Mes2C6H3SiCl2SiCl3(4), (where Mes = 2,4,6-Me3C6H2 and Trip = 2,4,6-i-Pr3C6H2) are described. Compounds (1a, 1b), (2a, 2b) and (4) were prepared by the reaction between SiCl4, SiHCl3 or Si2Cl6, respectively, and the appropriate aryl lithium reagent (2,6-Mes2C6H3Li or 2,6-Trip2C6H3Li·OEt2). Compounds (3a) and (3b) were prepared by reduction of (1a) and (1b) with LiAlH4, respectively. The derivatives (1a) - (3a) were characterized by 1H, 13C, 29Si NMR and IR spectroscopy. The structures of (1a), (1b) and (4) have been determined. Crystal data with CuKα (λ = 1.54178 A) at 130 K: (1a), a = 9.074(2) A, b = 16.681(3) A, c = 15.842(3) A, β = 105.20(3)°, V = 2313.9(8) A3, Z = 4, space group P21/c, 2772 (I > 2σ(I)) data, R = 0.042; (1b), a = 12.197(2) A, b = 25.602(5) A, c = 11.098(...

Investigation of the Regioselectivity of Alkene Hydrosilylation Catalyzed by Organolanthanide and Group 3 Metallocene Complexes

The regioselectivity of monosubstituted alkene hydrosilylation catalyzed by organolanthanide and group 3 organometallic complexes has been studied as a function of catalyst structure. A wide variety of catalyst variations were shown to be compatible with the hydrosilylation process. Several novel complexes were synthesized to widen the scope of this investigation. The results show complexes containing larger lanthanide metal ions and reduced substitution on the cyclopentadienyl ligands produce increased yields of the secondary silane product. Several complexes were identified that are highly selective for primary silane generation.

Transformation of Coordinated Dinitrogen by Reaction with Dihydrogen and Primary Silanes

The reaction of dihydrogen with a side-on bound dinitrogen complex of zirconium was investigated. Instead of a displacement of the dinitrogen moiety, which is the common mode of reactivity, a complex containing both a bridging hydride and a bridging hydrazido unit with a nitrogen-hydrogen bond was observed. This reaction was extended to primary silanes to produce a species that contained a nitrogen-silicon bond. In addition, an intermediate in the dihydrogen addition has been structurally characterized as having a bridging dihydrogen unit.

An Efficient Catalyst for the Conversion of Hydrosilanes to Alkoxysilanes

AbstractThe copper(I) hydride [Ph3PCuH]6 is an efficient catalyst for the alcoholysis of primary and secondary silanes. The reactions proceed at room temperature within a few hours and give the alkoxysilanes in high yields. Only with bulky alcohols or silanes are longer reaction times and/or increased temperatures required. The presence of air accelerates the reactions and gives rise to higher yields of alkoxysilanes, particularly with bulky alcohols. Diols react with PhRSiH2 (R = Me, Ph) to afford 1,3‐dioxo‐2‐silacycloalkanes and with tertiary silanes to furnish the bissilylated diols. When unsaturated alcohols (2‐propen‐1‐ol or 2‐propyn‐1‐ol) are employed, the double or triple bond is retained.

Reaction of primary silanes with dinuclear rhodium hydride complexes: silane coupling reactions

The reaction of the dinuclear rhodium hydride dimer [(dippe)Rh] 2(μ-H) 2 (dippe=l,2-bis(diisopropylphosphino)ethane) with primary silanes is described. In the presence of two equivalents of RSiH 3 (R=Bu n and Tol P), dinuclear bis(μ-silylene) complexes of the formula [(dippe)Rh] 2(μ-SiHR) 2 result. Attempts to generate silylhydride complexes of the formula [(dippe)Rh] 2(μ-H)(μ-H-SiHR) by the addition of one equiv. of RSiH 3 failed. The bis(μ-silylene) complexes react with hydrogen to form adducts wherein two equivalents of H 2 per dimer unit have been activated; on the basis of NMR spectral studies these complexes are proposed to have the following formula: [(dippe)RhH] 2(μ-H-SiHR) 2. These molecules are extremely fluxional and lose H 2 rather readily. Addition of more than three equivalents of primary silane to 1 generated dinuclear rhodium derivatives with three silicon-containing ligands, having the formula [(dippe)Rh] 2(μ-SiHR)(μ-H-SiHR) 2. In the presence of excess primary silane, the dinuclear rhodium hydride 1 acts as a catalyst precursor for the dehydrogenative coupling of silanes. With the p-tolylsilane, dimerization does occur but the process is complicated by dispro- portionation reactions to generate (Tol P) 2SiH 2 and (Tol P) 3SiH; with butylsilane, SiSi chains with up to five silicons have been produced with no evidence of disproportionation. Crystals of [(dippe)Rh] 2(μ-SiHBu n) 2 ( 2a) are monoclinic, a=10.889(1), b=13.105(2), c=16.676(2) Å,β=104.06(1)°, Z=2, space group P2 1/n.; and those of [(dippe)Rh] 2(μ-η 2-H-SiHTol P) 2(μ-SiHTol P) ( 4b) are monoctinic, a=25.839(4), b=13.084(3), c=17.133(3) Å, β=107.10(1)°, Z=4, space group P21/ a. The structures were solved by Patterson ( 2a) and direct ( 4b) methods and were refined by full-matrix least-squares procedures to R=0.035 and 0.047 ( R w=0.030 and 0.060) for 3184 and 5997 reflections with 1⩾3η( I), respectively.

ChemInform Abstract: Condensation of Primary Silanes in the Presence of Cp2MCl2/nBuLi (M: Ti, Zr, Hf).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Condensation of primary silanes in the presence of Cp 2MCl 2/ nBuLi (M  Ti, Zr, Hf)

The condensation of RSiH 3 (R  Ph, nBu, nHex) to silicon oligomers in the presence of the catalyst precursor combination Cp 2MCl 2/2 nBuLi (M  Ti, Zr, Hf) has been monitored by gas chromatography and the intermediate oligomers characterized by GC-MS. The average molecular weights of the isolated products from PhSiH 3 depend on the catalyst and increase through the sequence, Hf < Ti < Zr, to a maximum of about 1800 for reactions conducted at room temperature. In the condensation of alkylsilanes linear oligomers are produced in the initial stages of the reaction and as the reaction continues cyclic polysilanes are formed with increasing numbers of isomers as the number of silicon atoms increases. A large rate difference is observed in the formation of the diastereomers of the tetrasilane produced from PhSiH 3 for all three catalysts. For reactions conducted at 50°C both diastereomers of H( nBuSiH) 4H are produced in equal amounts throughout the reaction period for M  Ti but at different rates for M  Zr and only one diastereomer is observed for M  Hf. The observations are discussed in terms of chain growth through sigma-bond metathesis processes.

Conversion of hydrosilanes to alkoxysilanes catalyzed by Cp2TiCl2/nBuLi

Abstract The combination of Cp 2 TiCl 2 and n BuLi provides an effective catalyst for alcoholysis of the model silanes n-HexSiH 3 , PhMeSiH 2 , Ph 2 SiH 2 and PhMe 2 SiH by ethanol, isopropanol, t-butyl alcohol and phenol. Increasing the steric bulk of the substituents on either the alcohol or the silane generally requires longer reaction periods and/or increasing temperature. All SiH bonds are converted to SiOEt groups by ethanol and a single SiH bond in secondary silanes and two SiH bonds in tertiary silanes are replaced by t-butyl alcohol. Diols including pinacol, 2,4-pentanediol and 2,5-hexanediol react with PhRSiH 2 (R  Me, Ph) to give 1,3-dioxa-2-silacyclopentanes, -hexanes and -heptanes, respectively. Attempts to form caged structures by condensation of primary silanes and triols was unsuccessful. Hydrolysis of PhRSiH 2 is promoted by Cp 2 TiCl 2 / n BuLi and the siloxane is produced in quantitative yield when R  Ph and a mixture of linear disiloxanes and trisiloxanes in addition to cyclopolysilanes are produced when R  Me. Other protic reagents including acids, mercaptans, amines and enolizable ketones did not react. The effects of reaction parameters such as temperature, silane to catalyst ratio, solvent, transition metal and replacements for n BuLi were also determined.

Exchange reactions of primary and secondary silanes with binuclear rhodium complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExchange reactions of primary and secondary silanes with binuclear rhodium complexesWei Dong Wang and Richard EisenbergCite this: Organometallics 1992, 11, 2, 908–912Publication Date (Print):February 1, 1992Publication History Published online1 May 2002Published inissue 1 February 1992https://doi.org/10.1021/om00038a061RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (613 KB) Get e-Alerts Get e-Alerts

Synthesis and characterization of mono- and bis(silyl)iridium bis(phosphine) complexes

The trihydride complex IrH 3 (CO)(dppe) (dppe=1,2-bis(diphenylphosphino) ethane) reacts with primary, secondary, and tertiary silanes to yield mono- and bis(silyl) hybride complexes of the formulas IrH 2 (SiRR' 2 )(CO)(dppe) (1) and IrH(SiRR' 2 ) 2 (CO)(dppe) (2). The different silanes used include Ph 3 SiH, Et 3 SiH, Me 3 SiH, Me 2 ClSiH, MeCl 2 SiH, Ph 2 SiH 2 , Me 2 SiH 2 , PhSiH 3 , and EtSiH 3 . The reactions were monitored by 1 H NMR and 31 P NMR spectroscopies, which allow unambiguous assignment of the coordination geometries of the products

Reactions of silanes with bis(cyclopentadienyl)dialkylzirconium complexes

A systematic comparison between the dimethylzirconocene (DMZ) and dimethyltitanocene (DMT) catalyzed dehydrocoupling of organosilanes is reported. The polymerization rates of primary silanes are about ten times faster for DMZ than for DMT, but the characteristics of the polymers produced are essentially identical. Variations of molecular weight and molecular weight distribution with varying monomer and reaction time, and the relative amounts of linear and cyclic polymer are also essentially the same for the two catalysts.Oligomerizations of phenylmethylsilane, diphenylsilane, and 1,2-diphenyldisilane are described. The compound Cp2Zr(SiPhMeH)(μ-H)2(SiPhMe2)ZrCp2 (1b) is isolated from the reaction of phenylmethylsilane with DMZ and its structure confirmed by crystallography and 1H-NMR spectroscopy. The compound Cp2Zr(Me)(μ-H)2(SiPh2H)ZrCp2 (1d) is isolated from the reaction of diphenylsilane with DMZ and its structure assigned by NMR spectroscopy. A number of other hydride bridged species are observed by 1H-NMR in the reactions of DMZ with phenylmethyl-, diphenyl-, and n-butylmethylsilanes and their structures are tentatively assigned. The implications of these observations on the mechanism of transformation of DMZ into active catalyst and our current views of the polymerisation mechanism are also discussed. Key words: silanes, dehydrocoupling, titanocene, zirconocene, polysilanes.

Copper(I) chloride catalyzed cross-dehydrocoupling reactions between silanes and ethynyl compounds. A new method for the copolymerization of silanes and alkynes

In the presence of an amine, copper(I) chloride is an effective catalyst for the cross-dehycrocoupling of silanes with alkynes. The reactions proceed at useful rates above 100 °C, but rates drop dramatically on going from 1° to 2° to 3° organosilanes. Primary silanes, RSiH3 (R = Ph,n-hexyl), react in a stepwise fashion with phenylacetylene to give the products RSiH3−x (CCPh)x (x = 1–3), each of which has been isolated and characterized. The secondary silanes RR′SiH2 (R = R′ = Ph; R = Ph, R′ = Me; R = n-Bu, R′ = Me) also give mono- and diphenylethynyl products. The dehydrocoupling reaction has been applied to the synthesis of new polymers containing both acetylene units and silicon atoms in the backbone. 1,3-Diethynylbenzene gives polymers of relatively high molecular weight [Formula: see text] with phenylsilane and phenylmethylsilane, but reactions of phenylmethyldiethynylsilane are too slow to give anything beyond low molecular weight oligomers. Keywords: organosilanes, alkynes, dehydrocoupling, copper(I) chloride, polymers, catalysis.