- Heterogeneous Rates of Electron Transfer. Application of Cyclic Voltammetric Techniques to Irreversible Electrochemical Processes
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The anodic peak potentials in the irreversible cyclic voltammograms of various homoleptic alkylmetals in acetonitrile show a striking linear correlation with their ionization potentials ID determined in the gas phase.Application of various transient electrochemical techniques proves that the electrode process arises from a totally irreversible ECE sequence in which the peak potential is determined solely by the kinetics of heterogeneous electron transfer and diffusion-uncomplicated by any follow-up chemical reaction.As a result, the anodic peak potential Ep can be directly related to the activation free energy for electron transfer, and the correlation of EP and ID represents a linear free-energy relationship.The mechanism of heterogeneous electron transfer is described as an outer-sphere process, dependent only on the driving force for one-electron oxidation and independent of steric effects of the alkylmetal.The close relationship between the activated compexes for heterogeneous and homogeneous electron transfer is emphasized in a direct comparison of the electrochemical process with the oxidation of the same alkylmetals by a series of poly(pyridine)iron(III) complexes in solution.
- Klingler, R. J.,Kochi, J. K.
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Read Online
- Ruthenium-Catalyzed Coupling Reactions of CO2 with C2H4 and Hydrosilanes towards Silyl Esters
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A series of in situ-prepared catalytic systems incorporating RuII precursors and bidentate phosphine ligands has been probed in the reductive carboxylation of ethylene in the presence of triethylsilane as reductant. The catalytic production of propionate and acrylate silyl esters was evidenced by high-throughput screening (HTS) and implemented in batch reactor techniques. The most promising catalyst systems identified were made of Ru(H)(Cl)(CO)(PPh3)3 and 1,4-bis(dicyclohexylphosphino)butane (DCPB) or 1,1’-ferrocene-diyl-bis(cyclohexylphosphine) (DCPF). A marked influence of water on the acrylate/propionate selectivity was noted. Turnover numbers [mol mol(Ru)?1] up to 16 for acrylate and up to 68 for propionate were reached under relatively mild conditions (20 bar, 100 °C, 0.5 mol % Ru, 40 mol % H2O vs. HSiEt3). Possible mechanisms are discussed.
- Kunihiro, Kana,Heyte, Svetlana,Paul, Sébastien,Roisnel, Thierry,Carpentier, Jean-Fran?ois,Kirillov, Evgueni
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supporting information
p. 3997 - 4003
(2021/02/01)
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- Towards Naked Zinc(II) in the Condensed Phase: A Highly Lewis Acidic ZnII Dication Stabilized by Weakly Coordinating Carborate Anions
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The employment of the hexyl-substituted anion [HexCB11Cl11]? allowed the synthesis of a ZnII species, Zn[HexCB11Cl11]2, 3, in which the Zn2+ cation is only weakly coordinated to two carborate counterions and that is soluble in low polarity organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of at least one of the counterions, and this near nakedness of the cation results in high catalytic activity in the hydrosilylation of 1-hexene and 1-methyl-1cyclohexene. Fluoride ion affinity (FIA) calculations reveal a solution Lewis acidity of 3 (FIA=262.1 kJ mol?1) that is higher than that of the landmark Lewis acid B(C6F5)3 (FIA=220.5 kJ mol?1). This high Lewis acidity leads to a high activity in catalytic CO2 and Ph2CO reduction by Et3SiH and hydrogenation of 1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, and DFT studies.
- Adet, Nicolas,Specklin, David,Gourlaouen, Christophe,Damiens, Thibault,Jacques, Béatrice,Wehmschulte, Rudolf J.,Dagorne, Samuel
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supporting information
p. 2084 - 2088
(2020/11/30)
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- Additive-free Semihydrogenation of an Alkynyl Group to an Alkenyl Group over Pd?TiO2 Photocatalyst Utilizing Temporary In-situ Deactivation
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Lindlar's catalyst, i. e., calcium carbonate-supported palladium (Pd) modified with lead, has been used for semihydrogenation of an alkynyl group in the presence of hydrogen gas (H2). We examined hydrogenation of an alkynyl group in organosilane and hydrocarbon in methanolic suspensions of a Pd-loaded titanium(IV) oxide (Pd?TiO2) photocatalyst without the use of additives and H2. In the photocatalytic reaction, Pd particles worked as co-catalysts for hydrogenation and alkyne hydrogenation had priority to alkene hydrogenation. Since the Pd co-catalyst was temporarily deactivated during the reaction owing to accumulation of the oxidized product(s) of methanol, the capacity of hydrogenation of the unsaturated C?C bond was limited. By optimizing the capacity and amount of alkynes, almost complete semihydrogenation of alkynes was achieved under a poison-free condition. Pd?TiO2 can be regenerated by very simple treatments, i. e., washing and drying at room temperature.
- Kojima, Yasumi,Fukui, Makoto,Tanaka, Atsuhiro,Hashimoto, Keiji,Kominami, Hiroshi
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p. 3605 - 3611
(2018/08/01)
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- MONONUCLEAR IRON COMPLEX AND ORGANIC SYNTHESIS REACTION USING SAME
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Provided is a mononuclear iron complex that comprises an iron-silicon bond that is represented by formula (1) and that exhibits excellent catalyst activity in each of a hydrosilylation reaction, a hydrogenation reaction, and reduction of a carbonyl compound. In formula (1), R 1 -R 6 either independently represent an alkyl group, an aryl group, an aralkyl group or the like that may be substituted with a hydrogen atom or X, or represent a crosslinking substituent in which at least one pair comprising one of R 1 -R 3 and one of R 4 -R 6 is combined. X represents a halogen atom, an organoxy group, or the like. L represents a two-electron ligand other than CO. When a plurality of L are present, the plurality of L may be the same as or different from each other. When two L are present, the two L may be bonded to each other. n and m independently represent an integer of 1 to 3 with the stipulation that n+m equals 3 or 4.
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Paragraph 0218-0220
(2016/12/01)
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- Synthesis of the first persilylated ammonium ion, [(Me3Si) 3NSi(H)Me2]+, by silylium-catalyzed methyl/hydrogen exchange reactions
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This work describes the unexpected synthesis and characterization of the first persilylated ammonium ion, [(Me3Si)3NSi(H)Me 2]+, in the reaction of (Me3Si)3N with [Me3Si-H-SiMe3][B(C6F5) 4]. NMR and Raman studies revealed a transition-metal-free silylium ion catalyzed substituent redistribution process when [Me3Si-H- SiMe3]+ was used as the silylating reagent. These observations were affirmed in the reaction with [Et3Si-H-SiEt 3][B(C6F5)4]. A Lewis acid catalyzed scrambling process always occurs if an excess of silanes is present in the formation of silylium cations while employing the standard Bartlett-Schneider- Condon type reaction. Additionally, the thermodynamics of this process was accessed by DFT computations at the pbe1pbe/aug-cc-pVDZ level, indicating alkyl substituent exchange equilibria at the silane and preference of the formation of [(Me3Si)3NSi(H)Me2]+ over [(Me 3Si)4N]+.
- Labbow, Rene,Reiss, Fabian,Schulz, Axel,Villinger, Alexander
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supporting information
p. 3223 - 3226
(2014/08/05)
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- Catalytic study of heterobimetallic rhodium complexes derived from partially alkylated s-indacene in dehydrogenative silylation of olefins
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This work describes the catalytic study of heterobimetallic rhodium compounds derived from partially alkylated s-indacene in dehydrogenative silylation of olefins in order to elucidate as much as possible the effects of: solvent, temperature, chemical substrates, olefin effect, silane effect, and secondary metallic fragment. The rhodium complexes, anti-[Cp*Fe-s- Ic′-Rh(COD)] 1, anti-[Cp*Ru-s-Ic′-Rh(COD)] 2, and syn-[Cp*Ru-s-Ic′-Rh(COD)] 2′ (with s-Ic′: 2,6-diethyl-4,8-dimethyl-s-indaceneiide) were previously synthesized and characterized, and were compared with the catalytic activity of the complexes previously reported; monometallic [(COD)Rh-s-Ic′H] 3, and homobimetallic anti-[{(COD)Rh}2-s-Ic′] 4, and syn-[{(COD)Rh} 2-s-Ic′] 4′. The heterobimetallic complexes show a high activity and selectivity for the dehydrogenative silylation of styrene and these complexes show also the presence of a cooperative effect between both metallic centers, which is evidenced when compared with monometallic complex.
- Adams,Riviere,Riviere-Baudet,Morales-Verdejo,Dahrouch,Morales,Castel,Delpech,Manríquez,Chávez
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p. 266 - 274
(2013/11/19)
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- Catalyst design for iron-promoted reductions: An iron disilyl-dicarbonyl complex bearing weakly coordinating η2-(H-Si) moieties
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Iron disilyl dicarbonyl complex 1, in which two H-Si moieties of the 1,2-bis(dimethylsilyl)benzene ligand were coordinated to the iron center in an η2-(H-Si) fashion, was synthesized by the reaction of (η4-C6H8)Fe(CO)3 with 2 equiv. of 1,2-bis(dimethylsilyl)benzene under photo-irradiation. Complex 1 demonstrated high catalytic activity toward the hydrogenation of alkenes, the hydrosilylation of alkenes and the reduction of carbonyl compounds.
- Sunada, Yusuke,Tsutsumi, Hironori,Shigeta, Keisuke,Yoshida, Ryota,Hashimoto, Toru,Nagashima, Hideo
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supporting information
p. 16687 - 16692
(2013/12/04)
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- Deoxygenative reduction of carbon dioxide to methane, toluene, and diphenylmethane with [Et2Al]+ as catalyst
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The strong Lewis acid [Et2Al]+ catalyzes the reduction of carbon dioxide with hydrosilanes under mild conditions to methane. In benzene solution, the side products toluene and diphenylmethane are also obtained through Lewis acid catalyzed benzene alkylation by reaction intermediates. Copyright
- Khandelwal, Manish,Wehmschulte, Rudolf J.
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supporting information; experimental part
p. 7323 - 7326
(2012/09/08)
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- Probing the catalytic potential of chloro nitrosyl rhenium(i) complexes
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The reduction of the mononitrosyl Re(ii) salt [NMe4] 2[ReCl5(NO)] (1) with zinc in acetonitrile afforded the Re(i) dichloride complex [ReCl2(NO)(CH3CN)3] (2). Subsequent ligand substitution reactions with PCy3, PiPr 3 and P(p-tolyl)3 afforded the bisphosphine Re(i) complexes [ReCl2(NO)(PR3)2(CH3CN)] (3, R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement with H2 (1 bar) to afford the dihydrogen Re(i) complexes [ReCl2(NO)(PR3) 2(η2-H2)] (4, R = Cy a, iPr b). The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of Me2NH·BH3, dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of Me2NH·BH3, the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy3 ligands exhibit high catalytic activities. Monochloro Re(i) hydrides [Re(Cl)(H)(NO)(PR3)2(CH3CN)] (5, R = Cy a, iPr b) were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to ensure high catalytic activity.
- Jiang, Yanfeng,Blacque, Olivier,Berke, Heinz
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experimental part
p. 2578 - 2587
(2011/05/03)
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- Facile synthetic access to rhenium(II) complexes: Activation of carbonbromine bonds by single-electron transfer
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The five-coordinated Re1 hydride complexes [Re(Br)(H)(NO) (PR3)2] (R = Cy la, iPr lb) were reacted with benzylbromide, thereby affording the 17-electron mononuclear ReII hydride complexes [Re(Br)2(H)(NO)(PR3)2] (R = Cy 3a, iPr 3b), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded ReII hydrides 3 in addition to Re1 carbene hydrides [Re(= CHR1)(Br)(H)(NO)(PR3)2,] (R 1 = H 4, Br 5; R = Cy a, iPr b) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen Re 1 dibromide complexes [Re(Br)2(NO)(PR3MIf- H2)] (R = Cy 2 a, iPr 2 b) were reacted with allyl- or benzylbromide, thereby affording the monophosphine ReII complex salts [R 3PCH2R'][Re(Br)4(NO)(PR3)] (R' = -CH=CH2 6, Ph 7). The reduction of ReII complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford la or lb in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3a 150, 3b 134 h-1) or allylbromide (TOF: 3a 150, 3b 562 h-1). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine Re 1 complexes [Re(Br)2(NO)(MeCN)2(PR 3)] (R = Cy 8a, iPr 8b), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h-1). Single-electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a, 6 a, 6 b, 7 a, 7 b, and 8 a were established by single-crystal X-ray diffraction studies.
- Jiang, Yanfeng,Blacque, Olivier,Fox, Thomas,Freeh, Christian M.,Berke, Heinz
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scheme or table
p. 2240 - 2249
(2010/07/05)
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- Highly selective dehydrogenative silylation of alkenes catalyzed by rhenium complexes
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Rhenium(I) complexes of type [ReBr2(L)(NO)(PR3) 2] (L = H2 (1), CH3CN (2), and ethylene (3); R = iPr (a) and cyclohexyl (Cy; b)) catalyze dehydrogenative silylation of alkenes in a highly selective ma
- Jiang, Yanfeng,Blacque, Olivier,Fox, Thomas,Freeh, Christian M.,Berke, Heinz
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experimental part
p. 2121 - 2128
(2009/09/30)
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- Process for the preparation of vinyl- or allyl-containing compounds
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A vinyl- or allyl-containing compound represented by following Formula (3): wherein R2, R3, R4, R5, and R6 each represent hydrogen atom or a nonmetallic atom-containing group; R7 represents a nonmetallic atom-containing group; Y represents a group selected from the group consisting of —Si(R8) (R9) —, —Si(R10) (R11)—O—, the left hand of which is combined with R7, and —NR12—, wherein R8, R9, R10, R11, and R12 each represent hydrogen atom or a nonmetallic atom-containing group; and “n” represents 0 or 1, is prepared by reacting a vinyl or allyl ester compound represented by following Formula (1): wherein R1 represents hydrogen atom or a nonmetallic atom-containing group; R2, R3, R4, R5, R6, and “n” are as defined above, with a compound represented by following Formula (2): [in-line-formulae]R7—Y—H ??(2)[/in-line-formulae] wherein R7 and Y are as defined above, in the presence of a transition element compound.
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Page/Page column 6
(2008/06/13)
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- Stepwise organomagnesium synthesis of mixtures of ethyletoxysilanes and ethylchlorosilanes
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Mixture of ethylethoxy- and ethylchlorosilanes was prepared in a toluene solution by successive reaction of magnesium with a mixture of ethyl chloride and tetraethoxysilane and then with a mixture of ethyl chloride and tetrachlorosilane.
- Klokov
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p. 1863 - 1865
(2007/10/03)
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- Mechanistic studies of palladium(II)-catalyzed hydrosilation and dehydrogenative silation reactions
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The cationic Pd(II) complexes, [(phen)Pd(CH3)(L)]+[BAr'4]- phen = 1,10-phenanthroline; L = Et2O, Me3SiC≡CSiMe3; Ar' = 3,5-(CF3)2C6H3) catalyze the hydrosilation and dehydrogenative silation of olefins. Hydrosilation of ethylene, tert-butylethylene, 1-hexene, and cyclohexene by HSiR3 (R = CH2CH3, C6H5) occurs in the presence of 1 mol% [(phen)Pd(CH3)(L)]+[BAr'4]-. The reaction of tert-butylethylene with HSi(i-Pr)3 in the presence of [(phen)Pd(CH3)(L)]+[BAr'4]- yields neohexane and t-BuCH=CHSi(i-Pr)3. Low-temperature NMR experiments revealed that the catalyst resting state for the silations of ethylene and alkyl-substituted olefins is [(phen)Pd(SiR3)(η2-H2C=CHR')]+[BAr'4]-. Evidence for rapid, reversible silyl migration at -70°C was observed by 1H NMR spectroscopy. Deuterium labeling studies show that the intermediate Pd(II) alkyl complexes can isomerize via a series of β-hydride eliminations followed by reinsertions of olefin prior to reaction with DSiEt3. Styrene undergoes both hydrosilation and dehydrogenative silation in the presence of [(phen)Pd(CH3)(L)]+[BAr'4]- or [(phen)Pd(η3-CH(CH3)C6H5)]+[BAr'4]- yielding ethylbenzene, R3SiCH2CH2C6H5 and trans-R3SiCH=CHPh (R = CH2CH3, CH(CH3)2). 1H NMR spectroscopy revealed that the π-benzyl complexes [(phen)Pd(η3-CH(CH2SiR3)C6H5)]+[BAr'4]- and [(phen)Pd(η3-CH(CH3)C6H5)]+[BAr'4]- are the catalyst resting states for the silation reactions of styrene.
- LaPointe, Anne M.,Rix, Francis C.,Brookhart, Maurice
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p. 906 - 917
(2007/10/03)
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- Electrosynthesis of tetraethylsilane from elemental silicon
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Electrolysis of alkylation reagents at silicon-containing electrodes results in alkylsilanes in both cathodic and anodic processes.A mechanism for the reaction is proposed. - Key words: electrosynthesis; silicon-containing electrodes; alkylsilanes.
- Zhuikov, V. V.,Kargin, Yu. M.
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p. 379 - 381
(2007/10/02)
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- Competitive-consecutive reaction of vinyltrimethylsilane with triethylsilane catalyzed by ruthenium complexes
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A complex reaction of vinyltrimethylsilane with triethylsilane catalyzed by ruthenium carbonyl and ruthenium phosphine complexes and performed at 80-130 degC in air or oxygen-free conditions was followed by GC-MS.Catalytic examinations and identification of the products (I-X) allowed us to propose a general scheme for the competitive-consecutive reaction in which the complexes containing Ru-H and Ru-Si bonds play the role of key intermediates. ruthenium complex / dehydrogenative silylation / metathesis / vinyltrimethylsilane / triethylsilane
- Gulinski, Jacek,Pietraszuk, Cezary,Marciniec, Bogdan,Maciejewski, Hieronim
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p. 609 - 614
(2007/10/02)
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- The Regioselectivite Hydroformylation of Vinylsilanes. A Remarkable Difference in the Selectivity and Reactivity of Cobalt, Rhodium, and Iridium Catalysts
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The zwitterionic rhodium complex, Rh(COD)BPh4, produces 2-(trimethylsilyl)propanal selectively in the hydroformylation of trimethylvinylsilane under quite mild conditions .Excess hydrogen is crucial for obtaining the branched aldehyde as the major product (B:L = 70:30).This is the first reported example of an α-selective hydroformylation of vinylsilanes.The potentially useful α-silyl aldehydes are difficult to prepare and isolate by other means, but using this procedure they can be obtained in one step from commercially available vinyltrimethylsilane, albeit in low isolated yields (20-30percent).The addition of as little as 2 equiv of PPh3 causes a complete shift in the selectivity yielding the linear isomer as the major product in the hydroformylation of vinyltriethylsilane (B:L = 7:93).The isolated yield increases from 30percent to 91percent after only 1.5 h.Iridium catalysts yielded the linear aldehydes (3-(trialkylsilyl)propanal) with excellent regioselectivities (90-100percent) without the addition of any phosphine.A competing reaction is hydrogenation of the starting material.This can be suppressed by increasing the amount of CO in the gas mixture (CO:H2 = 7:1).Of those complexes examined, hydrated IrCl3 (after preactivation at 160 deg C) gave the best selectivity for the linear isomer (98-100percent).The cationic complex, (+)BF4, also gave the linear aldehyde predominantly (95-97percent) in 75-80percent yields.Although most of the cobalt complexes tested were unreactive, the cationic cobalt cluster 6-C6H6)3(μ3-CO)2>BPh4 was the most active catalyst for the hydroformylation of vinyltriethylsilane.At 100 deg C, this complex completed six turnovers per minute, yielding the linear silyl aldehyde as the major product (B:L = 24:76).
- Crudden, Cathleen M.,Alper, Howard
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p. 3091 - 3097
(2007/10/02)
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- Single-Operation Synthesis of Vinylsilanes from Alkenes and Hydrosilanes with the Aid of Ru3(CO)12
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Alkenes (RCH=CH2, where R = C6H5, p-CH3C6H4, p-CH3OC6H4, p-ClC6H4, 2-naphthyl, (CH3)3C, Me3SiO(CH3)2C, n-C4H9O, and Et3Si) with HSiEt3 with Ru3(CO)12 as a catalyst gave corresponding vinylsilanes (1, 6-13) without formation of simple addition products.Hydrosilanes such as HSiMe3, HSiEt2Me, HSiPhMe2, and HSi(OEt)3 also yielded vinylsilanes.Alkenes having a hydrogen atom at the allylic position (1-hexene, allylbenzene, 3-phenoxyprop-1-ene, vinylcyclohexane, β-methylstyrene, α-methylstyrene, 2-hexene) formed mixtures of vinylsilanes and allylsilanes.The ratio of vinylsilane 16 to allylsilane 17 decreased with an increase in temperature and with time.Substituted styrenes with a hydrosilane in the presence of 1-hexene gave vinylsilanes 1 and 6-8 in good yields based on the styrenes along with n-hexane.
- Seki, Yoshio,Takeshita, Kenji,Kawamoto, Kazuaki,Murai, Shinji,Sonoda, Noboru
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p. 3890 - 3895
(2007/10/02)
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