Mechanistic action of ferric oxide in the hydrosilylation of 1,6-divinyl(perfluorohexane) with trichlorosilane

In the hydrosilylation of 1,6-divinyl(perfluorohexane) (FDV) with trichlorosilane (TCS) in the presence of catalytic chloroplatinic acid (Pt-Cat) under an air atmosphere (0.99 MPa), a runaway reaction accompanied by a severe pressure release occurred when Fe₂O₃ was present as an impurity in the system. In this study, we investigated the mechanism of action of Fe₂O₃ on this hydrosilylation by monitoring the thermal behavior of TCS/FDV/Pt-Cat/Fe₂O₃ mixtures with various compositions, using an accelerating rate calorimeter (ARC). In the case of TSC/FDV/Pt-Cat, a typical hydrosilylation composition in the industrial process, heat release, possibly due to hydrosilylation, began at 90 °C. On the other hand, for TCS/FDV/Pt-Cat/Fe₂O, the heat release due to hydrosilylation was hardly observed, but abrupt heat and pressure releases occurred at higher temperatures (>170 °C). Like TCS/FDV/Pt-Cat/Fe₂O₃, TCS/FDV, which contain neither Pt-Cat nor Fe₂O₃, released heat and pressure at high temperatures (>210 °C), while the heat and pressure release rates were comparatively low. From these results, the runaway reaction may occur when hydrosilylation is prevented, and Fe₂O₃ behaves as a negative catalyst for hydrosilylation. In the FT-IR spectrum of TCS/FDV/Pt-Cat/Fe₂O₃ after heating, an absorption peak at approximately 1,710 cm^?1, which may be attributed to a carbonyl group, was observed. Thus, it is considered that the runaway reaction observed during the hydrosilylation results from the action of Fe₂O₃ as a negative catalyst for hydrosilylation as well as as an oxidation catalyst for the by-product generated from the reaction between TCS and FDV.     

Efficient electrophilic and nucleophilic epoxidations utilizing a sulfonylperoxy radical and peroxysulfate species

Reaction of superoxide anion radical (O₂^−·) with o‐nitrobenzenesulfonyl chloride yields a o‐nitrobenzenesulfonyl peroxy radical with strong oxidizing ability, which is capable of oxidizing aryl methylene moieties to aryl ketones and relatively electron‐rich alkenes regioselectively to epoxides. The oxidizing species is tentatively attributed to the o‐nitrobenzenesulfonyl peroxy radical of structure 1 . Tetrabutylammonium peroxydisulfate ((TBA)₂S₂O₈, 2 ) was prepared by the reaction of tetrabutylammonium hydrogen sulfate with potassium peroxydisulfate. The epoxidation of enals and enones, such as α,β‐unsaturated aldehydes or ketones, was efficiently achieved with 2 in the presence of hydrogen peroxide and base in acetonitrile or in methanol at 25°C. A base‐sensitive substrate, such as cinnamaldehyde, could be successfully epoxidized under mild reaction conditions and in short reaction time. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:431–436, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10078     

Hydrogen transfer reduction of different ketones in ionic liquids

Ionic liquids were tested as the reaction media for hydrogen transfer reduction of substituted acetophenones and some other ketones with the [RuCl(TsDPEN)]₂ complex as the catalyst. Reactions were going well and faster than in common solvents. Corresponding alcohols had high ees in the case of aryl alkyl ketones, but just medium ees were reached in the case of dialkyl or unsaturated ketones. An interesting phenomenon was observed, namely that rise of the reaction temperature did not have negative influence on the ee of the reaction product.     

Organic peroxide assisted transition metal hydrosilylation catalysis

Summary The catalytic activity of rhodium complexes for the hydrosilylation of substrates such as alkenes, 1,3-dienes, 1-alkynes, or ketones, is enhanced by the addition of organic oxidizing agents, such ast-butyl hydroperoxide, hydrogen peroxide, orm-chloroperbenzoic acid. Similar enhancement is found for the Group VIA hexacarbonyls in the hydrosilylation of 1,3-dienes.     

Mesoionic Carbene Cobalt Complexes as Multipurpose Catalyst Precursors for Hydrosilylation and Dihydropyrimidinone Synthesis

Metalation of CH₂OH-substituted triazolium salts with CoCl₂ under basic conditions affords C,O-bidentate chelating carbene Co(III) complexes ( 3a , 3b ), while analogous phenyl-substituted triazolium salts produce monodentate carbene Co(II) complexes ( 3c , 3d ). The distinct substituent-induced properties of the metal centers were demonstrated by electrochemical measurements and catalytic activities in two specific processes. The complexes showed appreciable activity in the reduction of C=O bonds through hydrosilylation, with methoxybenzene-functionalized triazolylidene Co(III) complex 3a achieving a high selectivity towards aldehydes vs. ketones with turnover frequencies (TOFs) up to 200 h⁻¹. The C,O-chelate systems were also active catalysts in the Biginelli process, a one-step three-component reaction for efficient dihydropyrimidinone synthesis. Optimization of reaction conditions provides high activity with complex 3a , reaching TOFs of 800 h⁻¹, the highest activity known for cobalt NHC complexes to date.     

Hydrogen transfer reduction of different ketones in ionic liquids

Ionic liquids were tested as the reaction media for hydrogen transfer reduction of substituted acetophenones and some other ketones with the [RuCl(TsDPEN)]₂ complex as the catalyst. Reactions were going well and faster than in common solvents. Corresponding alcohols had high ees in the case of aryl alkyl ketones, but just medium ees were reached in the case of dialkyl or unsaturated ketones. An interesting phenomenon was observed, namely that rise of the reaction temperature did not have negative influence on the ee of the reaction product. Correspondence: Štefan Toma, Faculty of Natural Science, Comenius University Bratislava, SK-84215 Bratislava, Slovakia.     

Catalyse heterogene en presence de sels et sans solvant : II. Hydrosilylation d'aldehydes et de cetones satures et α,β ethyleniques

Hydrosilylation of saturated and α,β-unsaturated carbonyl compounds by heterogeneous catalysis without solvent and in the presence of salts (HCO2K, o-Ph(CO₂K)₂, FK, FCs) was carried out with good yields. FCs is a very efficient salt for hydrosilylation of aldehydes and ketones: for instance α-NpSiH₃ reacts quantitatively at room temperature with PhCOPh giving α-NpSi(OCHPh₂)₃. With α,β-unsaturated ketones FCs leads to 1,2-addition. It allows the isomerization of allysilyl ethers in silyl enol ethers, providing that the transferring hydrogen is benzylic.     

Transition metal–carbene complexes XCVII. π-cyclopentadienyldicarbonylmethylphenylcarbenerhenium

Addition of P(OMe)₃ to [Rh(η³?C₃H₅) (CO)₂] gives [Rh(η³?C₃H₅){P(OMe)₃}₃]; this reacts with hydrogen or silanes to form a species which is an effective hydrogenation catalyst for olefins and a hydrosilylation catalyst for terminal olefins, aldehydes and ketones.     

Cobalt Complexes Supported by Phosphinoquinoline Ligands for the Catalyzed Hydrosilylation of Carbonyl Compounds

P,N phosphinoquinoline based ligands differing by the nature of the phosphorus substituent (ⁱPr, Ph) were employed to synthesize a series of cobalt(II) complexes ( [LCoBr₂] , [L₂CoBr](PF₆) and [L’₂CoBr](PF₆) ). The latter were obtained in high yield and characterized among others by X-ray analysis and elemental analysis. Complex [L₂CoBr](PF₆) showed a very good catalytic activity for the hydrosilylation of various ketones. The catalysis proceeds at a low catalytic loading (1 mol %) with only 1 equivalent of Ph₂SiH₂ in mild conditions and was efficient with aliphatic or aromatic ketones giving moderate to excellent yields of the corresponding silylated ether.     

Chemoselective Reduction of Tertiary Amides to Amines Catalyzed by Triphenylborane

Triphenylborane (BPh₃) was found to catalyze the reduction of tertiary amides with hydrosilanes to give amines under mild condition with high chemoselectivity in the presence of ketones, esters, and imines. N,N‐Dimethylacrylamide was reduced to provide the α‐silyl amide. Preliminary studies indicate that the hydrosilylation catalyzed by BPh₃ may be mechanistically different from that catalyzed by the more electrophilic B(C₆F₅)₃.     

Synthesis of fluorosilicone having highly fluorinated alkyl side chains based on the hydrosilylation of fluorinated olefins with polyhydromethylsiloxane

Hydrosilylation of fluorinated olefins with polyhydromethylsiloxane (PHMS) in the presence of a platinum catalyst was investigated to synthesize fluorosilicone having highly fluorinated alkyl side chains (R_f; C_nF_2n+1? ). The hydrosilylation of 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10‐heptadecafluoro‐1‐decene (C₈F₁₇CH?CH₂) ( 1 ) with poly(dimethylsiloxane‐co‐hydromethylsiloxane) {(CH₃)₃SiO[? (H)CH₃SiO? ]₈[? (CH₃)₂ SiO? ]₁₈Si(CH₃)₃} ( 4 ) converted the hydrogen bonded to silicons into the 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10‐heptadecafluorodecyl group or fluorine bonded to silicons in the ratio of about 52:48, and the formation of the byproduct C₇F₁₅CF?CHCH₃ ( 8 ) was observed. The hydrosilylation of 7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14‐heptadecafluoro‐4‐oxa‐1‐tetradecene (C₈F₁₇CH₂CH₂OCH₂CH?CH₂) ( 2 ) with 4 converted the hydrogen bonded to silicons into the 7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14‐heptadecafluoro‐4‐oxa‐tetradocyl group bonded to silicons, but an excess amount of 2 was required to complete the reaction because the isomerization of 2 occurred in part to form C₈F₁₇CH₂CH₂OCH?CHCH₃ ( 9 ). The hydrosilylation of 4,4,5,5,6,6,7,7,8,8,9,9, 10,10,11,11,11‐heptadecafluoro‐1‐undecene (C₈F₁₇CH₂CH?CH₂) ( 3 ) with 4 converted the hydrogen bonded to silicons into the 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11‐heptadecafluoroundecyl group bonded to silicons. This type of fluorinated olefin was successfully applied to the hydrosilylation with other PHMS's that involved a homopolymer of PHMS and a cyclic PHMS. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3120–3128, 2002     

Hydrosilylation in Aryliminopyrrolide‐Substituted Silanes

A range of silanes was synthesized by the reaction of HSiCl₃ with iminopyrrole derivatives in the presence of NEt₃. In certain cases, intramolecular hydrosilylation converts the imine ligand into an amino substituent. This reaction is inhibited by factors such as electron‐donating substitution on Si and steric bulk. The monosubstituted (^DippIMP)SiHMeCl (^DippIMP=2‐[N‐(2,6‐diisopropylphenyl)iminomethyl]pyrrolide), is stable towards hydrosilylation, but slow hydrosilylation is observed for (^DippIMP)SiHCl₂. Reaction of two equivalents of ^DippIMPH with HSiCl₃ results in the hydrosilylation product (^DippAMP)(^DippIMP)SiCl (^DippAMP=2‐[N‐(2,6‐diisopropylphenyl)aminomethylene]pyrrolide), but the trisubsitituted (^DippIMP)₃SiH is stable. Monitoring the hydrosilylation reaction of (^DippIMP)SiHCl₂ reveals a reactive pathway involving ligand redistribution reactions to form the disubstituted (^DippAMP)(^DippIMP)SiCl as an intermediate. The reaction is strongly accelerated in the presence of chloride anions.     

Synthesis of new iron–NHC complexes as catalysts for hydrosilylation reactions

A series of new piano‐stool iron(II) complexes comprising N‐heterocyclic carbene ligands [Fe(Cp)(CO)₂(NHC)]I (NHC = 1,3‐disubstituted imidazolidin‐2‐ylidene) have been synthesized and analyzed by ¹H NMR, ¹³C NMR, IR, elemental analysis and mass spectrometric techniques. These compounds were easily prepared from the reaction of disubstituted imidazolidin‐2‐ylidene with [FeI(Cp)(CO)₂] in toluene at room temperature. These complexes were tested in the catalytic hydrosilylation reaction of aldehydes and ketones with phenylsilane in solvent‐free conditions. After a basic hydrolysis step, the corresponding alcohols were obtained in good yields. Copyright © 2013 John Wiley & Sons, Ltd.     

1-Butyl-3-methylimidazolium Hydrogen Sulfate ([bmim]-HSO4)–Mediated Synthesis of Polysubstituted Quinolines

In this research, polysubstituted quinolines are prepared from the reaction of 2-aminobenzophenones and ethylacetoacetate or ketones in the presence of 1-butyl-3-methylimidazolium hydrogen sulfate [bmim]HSO₄ as an acidic ionic liquid in good to high yields at 70 °C under solvent-free conditions.     

Catalytic Transfer Hydrogenation with a Methandiide‐Based Carbene Complex: An Experimental and Computational Study

The transfer hydrogenation (TH) reaction of ketones with catalytic systems based on a methandiide‐derived ruthenium carbene complex was investigated and optimised. The complex itself makes use of the noninnocent behaviour of the carbene ligand (M?CR₂→MH?C(H)R₂), but showed only moderate activity, thus requiring long reaction times to achieve sufficient conversion. DFT studies on the reaction mechanism revealed high reaction barriers for both the dehydrogenation of iPrOH and the hydrogen transfer. A considerable improvement of the catalytic activity could be achieved by employing triphenylphosphine as additive. Mechanistic studies on the role of PPh₃ in the catalytic cycle revealed the formation of a cyclometalated complex upon phosphine coordination. This ruthenacycle was revealed to be the active species under the reaction conditions. The use of the isolated complex resulted in high catalytic activities in the TH of aromatic as well as aliphatic ketones. The complex was also found to be active under base‐free conditions, suggesting that the cyclometalation is crucial for the enhanced activity.     

Effect of catalysts on the reaction of allyl esters with hydrosilanes

The reaction of hydrosilylation of allyl esters XOCH₂CH=CH₂ (X = MeCO, CF₃CO, C₃F₇CO) and PhOCH₂CH=CH₂ with hydrosilanes HSiY₃ (Y = Cl, OEt) in the presence of the Speier catalyst, the Speier catalyst with additives, and of various nickel complexes was studied. The catalytic hydrosilylation reaction in the presence of the Speier catalyst is accompanied by the reduction. Additives to the Speier catalyst (vinyltriethoxysilane and some ethers) allow to suppress considerably the reduction reaction. In the presence of the studied nickel complexes mainly reduction and isomerization reactions occurred. The best nickel catalysts of hydrosilylation were the mixtures of NiCl₂ or Ni(acac)₂ with phosphine oxides. In contrast to allyl esters, the hydrosilylation of simple olefins proceeds easier, the content of the product of hydrosilylation in the reaction mixture reaches 94.3%.     

RuCl3·xH2O: A Novel and Efficient Catalyst for the Facile Synthesis of 1,5-Benzodiazepines Under Solvent-Free Conditions

1,5-Benzodizepines are synthesized in excellent yields via condensation of o-phenylenediamine with ketones having a hydrogen at the α-position. The reaction is performed in solvent-free conditions and 5 mol% of RuCl₃·xH₂O is enough to direct the reaction to completion.     

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.     

Investigation of N‐Heterocyclic Carbene‐Supported Group 12 Triflates as Pre‐catalysts for Hydrosilylation/Borylation

N‐Heterocyclic carbene (NHC) complexes of Cd and Hg triflates (OTf) were prepared and their attempted conversion into rare cadmium and mercury hydrides was explored. In contrast to zinc, which forms stable [ZnH]⁺ complexes with NHCs, the heavier Cd and Hg congeners could not be formed; the increased instability of Cd‐H and Hg‐H units was rationalized with the aid of computations. It was also discovered that the dimeric adduct [IPr?Cd(μ‐OTf)₂]₂ (IPr=[(HCNDipp)₂C:]; Dipp=2,6‐iPr₂C₆H₃) is an active precatalyst for the hydrosilylation and hydroborylation of hindered aldehydes and ketones. The related zinc congener was inactive as a catalyst highlighting a distinct advantage of using heavy Group 12 metals to promote catalytic hydrosilylation/borylation.     

Chiral Frustrated Lewis Pairs Catalyzed Highly Enantioselective Hydrosilylations of Ketones

A highly enantioselective Piers‐type hydrosilylation of simple ketones was successfully realized using a chiral frustrated Lewis pair of tri‐tert‐butylphosphine and chiral diene‐derived borane as catalyst. A wide range of optically active secondary alcohols were furnished in 80%—99% yields with 81%—97% ee's under mild reaction conditions.