- Kinetic studies of the oxidative addition and transmetallation steps involved in the cross-coupling of alkynyl stannanes with aryl iodides catalysed by η2-(dimethyl fumarate)(iminophosphane)palladium(0) complexes
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The complexes [Pd(η2-dmfu)(P-N)] {dmfu = dimethyl fumarate; P-N = 2-(PPh2)C6H4-1-CH=NR, R = C 6H4OMe-4 (1a), CHMe2 (2a), C6H 3Me2-2,6 (3a), C6H3(CHMe 2)2-2,6 (4a)} undergo dynamic processes in solution which consist of a P-N ligand site exchange through initial rupture of the Pd-N bond at lower energy and an olefin dissociation-association at higher energy. According to equilibrium constant values for olefin replacement, the complex [Pd(η2-fn)(P-N)] (fn = fumaronitrile, 1b) has a greater thermodynamic stability than its dmfu analogue 1a. The kinetics of the oxidative addition of ArI (Ar = C6H4CF3-4) to 1a and 2a lead to the products [PdI(Ar)(P-N)] (1c, 2c) and obey the rate law, k obs = k1A k2A[ArI]. The k1A step involves oxidative addition to a reactive species [Pd(solvent)(P-N)] formed from dmfu dissociation. The k2A step is better interpreted in terms of oxidative addition to a species [Pd(η2-dmfu)(solvent) (κ1-P-N)] formed in a pre-equilibrium step from Pd-N bond breaking. The complexes 1c and 2c react with PhC≡CSnBu3 in the presence of an activated olefin (ol = dmfu, fn) to yield the palladium(0) derivatives [Pd(η2-ol)(P-N)] along with ISnBu3 and PhC≡CAr. The kinetics of the transmetallation step, which is rate-determining for the overall reaction, obey the rate law: kobs = k2T[PhC≡CSnBu3]. The k2T values are markedly enhanced in more polar solvents such as CH3CN and DMF. The solvent effect and the activation parameters suggest an associative S E2 mechanism with substantial charge separation in the transition state. The kinetic data of the above reactions in various solvents indicate that, for the cross-coupling of PhC≡CSnBu3 with ArI catalysed by 1a or 2a, the rate-determining step is represented by the oxidative addition and that CH3CN is the solvent in which the highest rates are observed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Crociani, Bruno,Antonaroli, Simonetta,Canovese, Luciano,Uguagliati, Paolo,Visentin, Fabiano
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p. 732 - 742
(2007/10/03)
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- Mechanism of the Stille reaction catalyzed by palladium ligated to arsine ligand: PhPdl(AsPh3)(DMF) is the species reacting with vinylstannane in DMF
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The kinetics of the reaction of PhPdI(AsPh3)2 (formed via the fast oxidative addition of Phl with Pd0(AsPh3)2) with a vinyl stannane CH2=CH-Sn(n-Bu)3 has been investigated in DMF. This reaction (usually called transmetalation step) is the prototype of the rate determining second step of the catalytic cycle of Stille reactions. It is established here that the transmetalation proceeds through PhPdI(AsPh3)(DMF), generated by the dissociation of one ligand AsPh3 from PhPdI(AsPh3)2. PhPdI(AsPh3)(DMF) is the reactive species, which leads to styrene through its reaction with CH2=CH-SnBu3. Consequently, in DMF, the overall nucleophilic attack mainly proceeds via a mechanism involving PhPdI(AsPh3)(DMF) as the central reactive complex and not PhPdI(AsPh3)2. The dimer [Ph2Pd2(μ2-I)2 (AsPh3)2] has been independently synthesized and characterized by its X-ray structure. In DMF, this dimer dissociates quantitatively into PhPdI(AsPh3)(DMF), which reacts with CH2=CH-SnBu3. The rate constant for the reaction of PhPdI-(AsPh3)(DMF) with CH2=CH-SnBu3 has been determined in DMF for each situation and was found to be comparable.
- Amatore, Christian,Bahsoun, Ali A.,Jutand, Anny,Meyer, Gilbert,Ndedi Ntepe, Alexandre,Ricard, Louis
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p. 4212 - 4222
(2007/10/03)
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- Quantitative evaluation of the factors contributing to the copper effect in the stille reaction
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The relative importance of the factors contributing to the accelerating effect of CuI on [PdL4]-catalyzed couplings of R1I and R2SnBu3 (copper effect) has been quantitatively evaluated in THF for R1 = 3,5-C6Cl2F3; R2 = vinyl, C6H4-4-OMe; L = AsPh3, PPh3, using spectroscopic and kinetic methods. The 19F NMR kinetic data show that the rate enhancement produced by addition of CuI is strongly related with the autoretardation effect intrinsic to [PdL4] catalysts and is almost independent of the organotin reagent (vinyl, aryl). The autoretardation is due to the release of 2 equiv of L during the oxidation of [PdL4] to yield trans-[PdR1IL2], which is the species undergoing transmetalation. CuI does not promote the dissociation of L from trans-[PdR1IL2], but it captures part of the free neutral ligand L and therefore mitigates the autoretardation produced by the presence of free L on the rate-determining associative transmetalation. In the conditions studied (Pd:Cu = 1:2; T = 322.6 K; THF as solvent), for L = AsPh3 the CuI added captures about 25% of the free AsPh3 and the copper effect compensates only ca. 1% of the autoretardation, whereas for L = PPh3 the CuI captures about 99% of the free PPh3 and the compensation is about 30%. This remarkable variation is caused by the combined effect of two independent factors: (i) The catalyst [Pd(PPh3)4] is more autoretarded than [Pd(AsPh3)4]; and (ii) CuI is a more effective scavenger for PPh3 than for AsPh3.
- Casado, Arturo L.,Espinet, Pablo
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p. 1305 - 1309
(2008/10/08)
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- Mechanistic study on the cross-coupling of alkynyl stannanes with aryl iodides catalyzed by η2-(dimethyl fumarate)palladium(0) complexes with iminophosphine ligands
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The reactions of [Pd(η2-dmfu)(P-N)] [dmfu = dimethyl fumarate; P-N = 2-(PPh2)C6H4-1-CH=NR, R = C6H4OMe-4 (1a), CHMe2 (2a)] and [Pd(η2-dmfu)(P-N)2] with IC6H 4CF3-4, ISnBu3 and PhC≡SnBu3 have been studied under pseudo-first-order conditions. The oxidative addition of IC6H4CF3-4 yields [PdI(C6H 4CF3-4)(P-N)] (1b or 2b). No reaction takes place with PhC≡CSnBu3 and also with ISnBu3 in the presence of an excess of PhC≡CSnBu3. In the presence of fumaronitrile (fn), 1b and 2b undergo transmetalation by PhC≡CSnBu3 followed by fast reductive elimination to yield [Pd(η2-fn)(P-N)]. The same reaction sequence occurs for the system [PdI(C6H4CF 3-4)(P-N)]/P-N (1: 1 molar ratio) to give [Pd(η2-fn) (P-N)2]. The palladium(0) complexes are active catalysts in the cross-coupling of PhC≡CSnBu3 with aryl iodides ArI (Ar = C 6H4CF3-4, Ph). The catalytic efficiency depends on the complex: [Pd(η2-dmfu)(P-N)2] > [Pd(η2-dmfu)(P-N)], and on the substituent R: C6H 4OMe-4 > CHMe2. The reactivity and spectroscopic data suggest a catalytic cycle involving initial oxidative addition of ArI to a palladium(0) species, followed by transmetalation of the product and by fast reductive elimination to regenerate the starting palladium(0) compound. For [Pd(η2-dmfu)(P-N)] as catalyst, the oxidative addition is the rate-determining step, while for [Pd(η2-dmfu)(P-N)2] the oxidative addition and the transmetalation steps occur at comparable rate. The Royal Society of Chemistry 2003.
- Crociani, Bruno,Antonaroli, Simonetta,Beghetto, Valentina,Matteoli, Ugo,Scrivanti, Alberto
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p. 2194 - 2202
(2007/10/03)
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- Improvement of the extended one-pot (EOP) procedure to form poly(aryleneethynylene)s and investigation of their electrical and optical properties
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A series of π-conjugated homopolymers of type poly(aryleneethynylene) (PAE), [-Ar-C≡C-]n, (Ar = 2,5-bis(butoxy)benzene (7a), 2,5-bis(octyloxy)benzene (7b), 2,5-bis(hexadecyloxy)benzene (7c), 3-butylthiophene (7d), and 3-hexadecylthiophene (7e)) have been prepared by further improvement of the palladium-catalyzed Extended One-Pot (EOP) synthetic protocol. With the use of dioxane as solvent and higher reaction temperature (110°C), much higher polymerization degree, improved catalytic efficiency, and increased material purity were obtained. Numerical simulations have been performed in a series of different conjugated polymers in order to evaluate the role of the connection between aromatic rings in the maintaining of an effective electronic conjugation through the polymer chain. Experimentally, the conjugation properties have been investigated by means of photophysical measurements in liquid solution and in solid-state films. The electric transport properties have been characterized in view of applications to electronic devices.
- Pizzoferrato,Berliocchi,Di Carlo,Lugli,Venanzi,Micozzi,Ricci,Lo Sterzo
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p. 2215 - 2223
(2007/10/03)
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- Mechanism of the Stille reaction. 1. The transmetalation step. Coupling of R1I and R2SnBu3 catalyzed by trans-[PdR1IL2] (R1 = C6Cl2F3; R2 = vinyl, 4-methoxyphenyl; L = AsPh3)
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The so far accepted mechanism of the Stille reaction (palladium- catalyzed cross-coupling of organotin reagents with organic electrophiles) is criticized. Based on kinetic studies on catalytic reactions, and on reactions with isolated intermediates, a corrected mechanism is proposed. The couplings between R1I (1) (R1 = C6-Cl2F3 = 3,5-dichlorotrifluorophenyl) and R2SnBu3 (R2 = CH=CH2, 2a; C6H4-4-OCH3, 2b), catalyzed by trans- [PdR1I(AsPh3)2] (3a), give R1-R2 and obey a first-order law, r(obs) = a[3a][2a]/(b + [AsPh3]), with a = (2.31 ± 0.09) x 10-5 s-1 and b = (6.9 ± 0.3) x 10-4 mol L-1, for [1] = [2a] = 0-0.2 mol L-1, [3a] = 0-0.02 mol L-1, and [AsPh3] = 0-0.07 mol L-1, at 322.6 K in THF. The only organopalladium(II) intermediate detected under catalytic conditions is 3a. The apparent activation parameters found for the coupling of 1 with 2a support an associative transmetalation step (ΔH((±))(obs) = 50 ± 2 kJ mol-1, ΔS((±))(obs) = -155 ± 7 J K-1 mol-1 in THF; and ΔH((±))(obs) = 70.0 ± 1.7 kJ mol-1, ΔS((±))(obs) = -104 ± 6 J K-1 mol-1 in chlorobenzene, with [1]0 = [2]0 = 0.2 mol L-1, [3a] = 0.01 mol L-1). The reactions of 2a with isolated trans-[PdR1X(AsPh3)2 (X = halide) show rates Cl > Br > I. From these observations, the following mechanism is proposed: Oxidative addition of R1X to PdL(n) gives cis- [PdR1XL2], which isomerizes rapidly to trans[PdR1XL2]. This trans complex reacts with the organotin compound following a S(E)2 (cyclic) mechanism, with release of AsPh3 (which explains the retarding effect of the addition of L), to give a bridge intermediate [PdR1L(μ-X)(μ-R2)SnBu3]. In other words, an L-for-R2 substitution on the palladium leads R2 and R1 to mutually cis positions. From there the elimination of XXnBu3 yields a three- coordinate species cis-[PdR1R2L], which readily gives the coupling product R1-R2.
- Casado, Arturo L.,Espinet, Pablo
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p. 8978 - 8985
(2007/10/03)
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- Cleavage of Sn-Sn Bonds in Hexaalkyl(aryl)stannanes under the Action of Yb(II) Derivatives
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Ytterbium(II) derivatives MeYbI, PhYbI, and YbI2 cleave the Sn-Sn bond in distannanes R′3-SnR′3 (R′ = n-Bu, Ph) to give heterobimetallic derivatives R′3SnYbI, which were identified by products of their hydrolysis, exchange with R″3EHlg (R″ = Ph, Me; E = Ge, Si, Sn) and cross coupling with MeI in the presence of NiCl2(Ph3P)2.
- Syutkina,Rybakova,Novgorodova,Petrov
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- Preparation of benzylstannanes by zinc-mediated coupling of benzyl bromides with organotin derivatives. Physicochemical characterization and crystal structures
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Benzyltrialkyl- (1-13) and benzyltriphenylstannanes (16-22) have been easily prepared in a one-pot synthesis via coupling reaction of benzyl bromide derivatives (C6H5CH2Br and XYC6H3CH2Br, X = H, Y = o-, m-, p-CH3, o-, m-, p-F, o-, m-Cl, and p-Br; X = o-F, Y = p-Br) with R3SnCl compounds (R = Et, Pr, Bu, and Ph) in THF/H2O (NH4Cl) medium mediated by zinc powder. Such coupling also occurs with (Bu3Sn)2O. Dibenzyldibutylstannane (15) is prepared by reaction of benzyl bromide with Bu2SnCl2 or (Bu2SnCl)2O, and (2-naphthylmethyl)tributylstannane (14) by reaction of 2-(bromomethyl)naphthalene with Bu3SnCl. 13C-and 119Sn-NMR data are reported for all compounds, and M?ssbauer data for benzyltributylstannanes 10 and 11 and benzyltriphenylstannanes 16-18 and 20-22. The crystal structures of Ph3SnBn, with Bn = o- (17) and m-ClC6H4CH2 (18) and o- (20) and m-FC6H4-CH2 (21) have been determined.
- Marton, Daniele,Russo, Umberto,Stivanello, Diego,Tagliavini, Giuseppe,Ganis, Paolo,Valle, Giovanni Carlo
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p. 1645 - 1650
(2008/10/08)
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- PALLADIUM-CATALYZED REACTION OF ORGANIC HALIDES WITH ORGANOTIN COMPOUNDS INVOLVING OLEFIN INSERTION: SYNTHESIS OF 2,3-DISUBSTITUED NORBORNANES
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2,3-Disubstituted norbornanes were prepared by the palladium-catalyzed reaction of a ternary system composed of organic halide, organotin compound, and norbornene.The scope and limitations of this reaction are described.
- Kosugi, Masanori,Tamura, Hiroyuki,Sano, Hiroshi,Migita, Toshihiko
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p. 961 - 968
(2007/10/02)
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- Substituent effects upon the kinetics of hydrogen transfer from triorganotin hydrides to the 5-hexen-1-yl radical
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Steric and electronic substituent effects were probed for the hydrogen atom transfer reaction of a series of triorganotin hydrides with the 5-hexen-1-yl radical. Rate data were obtained for tributyltin hydride (1), triisopropyltin hydride (2), tri-tert-butyltin hydride (3), trineopentyltin hydride (4), trimesityltin hydride (5), and dibutylethoxytin hydride (6). Arrhenius parameters are reported for the reactions of 1-4 and 6; the reaction of 5 was studied only at 50°C. For compounds 1-4, the activation energy, Ea, decreased monotonically with increasing alkyl size from 3.9 ± 0.1 to 3.1 ± 0.1 kcal mol-1. The preexponential factor, expressed as log A, decreased monotonically from 9.4 ± 0.1 to 8.8 ± 0.1. The effect of the ethoxy substituent, 6, relative to an n-butyl substituent, 1, upon the activation energy was negligible (4.2 ± 0.2 versus 3.9 ± 0.1 kcal mol-1, respectively), but the preexponential factor, log A, increased from 9.4 ± 0.1 to 10.0 ± 0.1. The activation data for 1-4 are interpreted in terms of the steric requirements of the alkyl groups appended to tin. The lack of a significant substituent effect upon Ea by the ethoxy group is reflective of a nonpolarized transition state for the hydrogen atom transfer reaction.
- Pike, Philip W.,Gilliatt, Vernon,Ridenour, Michael,Hershberger, James W.
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p. 2220 - 2223
(2008/10/08)
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- KINETICS AND MECHANISM OF MERCURIDESTANNYLATION OF PHENYLSTANNATRANES AND RELATED DERIVATIVES
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The kinetics and mechanism of mercuridestannylation of phenylstannatrane derivatives, PhSn(OCH2CH2)3N and PhSn(OC6H4)3N have been investigated relative to model systems PhSnBu3, PhSn(OMe)3 in solvent MeOH.For the latter two, the reaction proceeded via the
- Ravenscroft, M. D.,Roberts, R. M. G.
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- SUBSTITUTION AT SATURATED CARBON. PART 25. THE IODODEMETALLATION OF BENZYLTRIALKYLTINS IN METHANOL
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The action of I2/I- in methanol on compounds PhCH2SnR3 leads only to cleavage of the benzyl group (as PhCH2I) when R=Et, Prn or Bun.With PhCH2SnMe3, both benzyl and methyl groups are removed.Rate constants are reported for the iododemetallation of all four PhCH2SnR3 compounds, R=Me, Et, Prn and Bun.The present results and previous literature data show that with a constant SnR3 leaving group, the sequence of alkyl-tin reactivity is Ph>PhCH2>Me>Et>Prn, with the benzyl-tin bond being broken 3-4 times as rapidly as the methyl-tin bond and about 40 times as rapidly as the ethyl-tin bond.The effect of added anions, Cl-, Br-, I- and ClO4- on the rate constants (and products) are reported, and it is shown that both kinetic studies and product analyses lead to the conclusion that foreign anions do not participate in the reaction mechanism.These are, however, specific kinetic salt effects in the order NaBrNaClNaClO4NaI.
- Abraham, Michael H.,Andonian-Haftvan, Jenik
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p. 819 - 830
(2007/10/02)
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- METAL-HALOGEN BONDING STUDIES WITH GROUP IV A TRIALKYLMETAL HALIDES
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Halogen redistribution reactions have been found to take place between benzyl bromide or benzyl iodide and the Group IV A silicon, germanium, tin, and lead containing trialkylmetal chlorides.However, for the reactions of the Si, Ge and Sn compounds, a quaternary ammonium halide catalyst was necessary to enable the equilibria to be established at reasonably rapid rates.The equilibrium constants at 50 deg C have been measured for each of these halogen redistributions.They have been found to increase gradually on going down in Group IV A from silicon to lead, being conside rably less than unity in the case of silicon and somewhat greater than unity in the case of lead for both the R3MCl + BzBr and R3MCl + BzI reactions.The ΔG0 values for these equilibria have been calculated, and it is suggested that their differences may be explained in terms of the relative importance of p?-d? contributions to the halogen-metal bonding in the various Group IV A trialkylmetal halide systems.
- Friedrich, Edwin C.,Abma, Charles B.,Vartanian, Paul F.
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p. 203 - 212
(2007/10/02)
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