- Reactivity of a Dinuclear PdIComplex [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3: Implications for Cross-Coupling Catalysis Using the Ubiquitous Pd(OAc)2/nPPh3Catalyst System
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[PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] is the reduction product of PdII(OAc)2(PPh3)2, generated by reaction of ‘Pd(OAc)2’ with two equivalents of PPh3. Here, we report that the reaction of [PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3results in a nuanced disproportionation reaction, forming [Pd0(PPh3)3] and a phosphinito-bridged PdI-dinuclear complex, namely [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2]. The latter complex is proposed to form by abstraction of an oxygen atom from an acetate ligand at Pd. A mechanism for the formal reduction of a putative PdIIdisproportionation species to the observed PdIcomplex is postulated. Upon reaction of the mixture of [Pd0(PPh)3] and [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2] with 2-bromopyridine, the former Pd0complex undergoes a fast oxidative addition reaction, while the latter dinuclear PdIcomplex converts slowly to a tripalladium cluster, of the type [Pd3(μ-X)(μ-PPh2)2(PPh3)3]X, with an overall 4/3 oxidation stateperPd. Our findings reveal complexity associated with the precatalyst activation step for the ubiquitous ‘Pd(OAc)2’/nPPh3catalyst system, with implications for cross-coupling catalysis.
- Scott, Neil W. J.,Ford, Mark J.,Husbands, David R.,Whitwood, Adrian C.,Fairlamb, Ian J. S.
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- Influence of the dba substitution on the reactivity of palladium(0) complexes generated from Pd02(dba-n,n′ -Z) 3 or Pd0(dba-n,n′-Z)2 and PPha 3 in oxidative addition with iodobenzene
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The reactivity of Pd(0) complexes generated by addition of PPh3 (PPh3/Pd = 2, 4) to either Pd02(dban,n′- Z)3 (n,n′-Z = 4,4′-F, 4,4′-H, 4,4′-MeO, 3,3′,4,4′,5,5′-OMe) or Pd0(dba-n,n′-Z) 2 (n,n′-Z = 4,4′-Br, 4,4′-Cl, 4,4′-H, 4,4′-CH3, 3,3′,5,5′-OMe) in DMF is affected by the electron-donating or -accepting properties of the groups Z substituted on the aromatic rings of dba. Whatever the nature of Z, the unreactive major complexes Pd0(η2-dba-n,n′-Z)(PPh3)2 are formed, which are in equilibrium with the common reactive complex Pd 0(PPh3)2 and dba-n,n′-Z. The latter controls the concentration of the reactive Pd0(PPh3) 2 and, consequently, also controls the rate of the overall oxidative addition with phenyl iodide. The more electron donating the Z group, the lower the affinity of dba-4,4′-Z for Pd0(PPh3) 2. As a result, the overall rate of the oxidative addition with Phi is faster when Z is an electron-donating group. For a given Z, the overall oxidative addition is faster when using Pd02(dba-n,n′-Z) 3 instead of Pd0(dba-n,n′-Z)2. Therefore, the rate of the oxidative addition can be modulated by changing the electronic properties of the dba ligands determined by substituents on its phenyl groups and by changing the structure of the precursors: P02 (dba-n,n′-Z)3 versus Pd0(dba-n,n′-Z) 2.
- Mace, Yohan,Kapdi, Anant R.,Fairlamb, Ian J. S.,Jutand, Anny
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- CRYSTAL STRUCTURE OF TRIS(TRIPHENYLPHOSPHINE) PALLADIUM
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The authors have made an x-ray structural investigation of the reaction product of Pd2(PPh3)2*(μ-CO)(OAc)2 with a tertiary amine, identified in the course of x-ray structural analysis as Pd(PPh3)3.The crystals are triclinic: α=11.659, β=14.803, c=15.843 Angstroem, α=109.31, β=95.17, γ=90.49 deg, ρcalc=1.154 g/cm3, Z=2, space group PI.In the structure the coordination unit PdP3 has the form of a strongly distorted trigonal pyramid.The Pd atom is raised a little above the plane of P3 and is 0.160 Angstroem from it.The spacings of Pd-P are 2.307-2.322 Angstroem, and the values of the angles PPdP are 115.0-126.5 deg.The short intramolecular contacts Pd...H (2.82-2.03 Angstroem) to the ortho atoms of the Ph rings lie above and below the plane P3, blocking the axial positions at the Pd atoms.The results are compared with the literature data on complexes of zero-valent palladium with phosphine ligands.
- Sergienko, V. S.,Porai-Koshits, M. A.
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- Kinetic data on the synergetic role of amines and water in the reduction of phosphine-ligated palladium(II) to palladium(0)
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Tertiary amines such as EtN(iPr)2 do not reduce [PdCl 2(PPh3)2] into a Pd0 complex. The latter is formed only after the addition of water (generation of HO -), as was reported by Grushin and Alper for NEt3. The mechanism of the PdII/Pd0 reduction performed in the presence of an excess amount of PPh3 is established quantitatively by means of electrochemical techniques that provide kinetic data (determination of the equilibrium and rate constants) for the disappearance of [PdCl 2(PPh3)2] and the formation of [Pd 0(PPh3)3]. [PdCl(OH)(PPh3) 2] is formed, which allows reductive elimination between OH and the ligated PPh3 (zero-order reaction for PPh3), and this leads to a Pd0 complex. The reducing agent is ligated PPh 3, which ultimately yields (O)PPh3. The rate of the overall reduction process is controlled by the amount of water that imposes the concentration of HO-.
- Amatore, Christian,El Kaim, Laurent,Grimaud, Laurence,Jutand, Anny,Meignie, Alice,Romanov, Georgy
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- Giant palladium clusters as catalysts of oxidative reactions of olefins and alcohols
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Giant cationic palladium clusters approximated as Pd561L60(OAc)180 (L = phen, bipy) and Pd561phen60O60(PF6)60 were synthesized and characterized with high resolution T
- Vargaftik,Zagorodnikov,Stolarov,Moiseev,Kochubey,Likholobov,Chuvilin,Zamaraev
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- A Ketimide-Stabilized Palladium Nanocluster with a Hexagonal Aromatic Pd7 Core
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Herein, we report the synthesis and characterization of the mixed-valent, ketimide-stabilized Pd7 nanosheet, [Pd7(N=CtBu2)6] (1), via reaction of PdCl2(PhCN)2 and Li(N=Ct/s
- Cook, Andrew W.,Hrobárik, Peter,Damon, Peter L.,Wu, Guang,Hayton, Trevor W.
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- Photophysical Properties of Simple Palladium(0) Complexes Bearing Triphenylphosphine Derivatives
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Pd(0) complexes with monodentate phosphine ligands, [Pd(P)n] (n = 3, 4), are well-known catalysts. However, the nature of the Pd(0) complex, especially the basic photophysical properties of the Pd(0) complexes, has not been extensively explored. In this work, we measured the general photophysical properties and crystal structures of Pd(0)-bearing PPh3 derivatives in the solid state and in solution. In the solid state, four-coordinated Pd(0) complexes exhibited blue-yellow emission. On the other hand, three-coordinated Pd(0) complexes displayed yellow-orange emission. In solution, orange emission of three-coordinated complexes was observed, and prompt fluorescence was detected using time-resolved emission spectroscopy, which suggests a thermally activated delayed fluorescence mechanism. Density functional theory (DFT) and time-dependent DFT calculations show that the difference in the transition mechanism between the [Pd(PPh3)4] and [Pd(PPh3)3] complexes explains the different emission colors. The emitting states of both complexes have metal-To-ligand charge-Transfer character, but the metal-centered d → p transition is considerably incorporated for emission of the tris complex.
- Kakizoe, Daichi,Nishikawa, Michihiro,Ohkubo, Takuma,Sanga, Masashi,Iwamura, Munetaka,Nozaki, Koichi,Tsubomura, Taro
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p. 9516 - 9528
(2021/06/28)
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- The ubiquitous cross-coupling catalyst system 'Pd(OAc)2'/2PPh3 forms a unique dinuclear PdI complex: An important entry point into catalytically competent cyclic Pd3 clusters
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Palladium(ii) acetate 'Pd(OAc)2'/nPPh3 is a ubiquitous precatalyst system for cross-coupling reactions. It is widely accepted that reduction of in situ generated trans-[Pd(OAc)2(PPh3)2] affords [Pd0(PPh3)n] and/or [Pd0(PPh3)2(OAc)]- species which undergo oxidative addition reactions with organohalides-the first committed step in cross-coupling catalytic cycles. In this paper we report for the first time that reaction of Pd3(OAc)6 with 6 equivalents of PPh3 (i.e. a Pd/PPh3 ratio of 1?:?2) affords a novel dinuclear PdI complex [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] as the major product, the elusive species resisting characterization until now. While unstable, the dinuclear PdI complex reacts with CH2Cl2, p-fluoroiodobenzene or 2-bromopyridine to afford Pd3 cluster complexes containing bridging halide ligands, i.e. [Pd3(X)(PPh2)2(PPh3)3]X, carrying an overall 4/3 oxidation state (at Pd). Use of 2-bromopyridine was critical in understanding that a putative 14-electron mononuclear 'PdII(R)(X)(PPh3)' is released on forming [Pd3(X)(PPh2)2(PPh3)3]X clusters from [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2]. Altering the Pd/PPh3 ratio to 1?:?4 forms Pd0(PPh3)3 quantitatively. In an exemplar Suzuki-Miyaura cross-coupling reaction, the importance of the 'Pd(OAc)2'/nPPh3 ratio is demonstrated; catalytic efficacy is significantly enhanced when n = 2. Employing 'Pd(OAc)2'/PPh3 in a 1?:?2 ratio leads to the generation of [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] which upon reaction with organohalides (i.e. substrate) forms a reactive Pd3 cluster species. These higher nuclearity species are the cross-coupling catalyst species, when employing a 'Pd(OAc)2'/PPh3 of 1?:?2, for which there are profound implications for understanding downstream product selectivities and chemo-, regio- and stereoselectivities, particularly when employing PPh3 as the ligand.
- Scott, Neil W. J.,Ford, Mark J.,Schotes, Christoph,Parker, Rachel R.,Whitwood, Adrian C.,Fairlamb, Ian J. S.
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p. 7898 - 7906
(2019/09/06)
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- On the Triple Role of Fluoride Ions in Palladium-Catalyzed Stille Reactions
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The mechanism of Stille reactions (cross-coupling of ArX with Ar′SnnBu3) performed in the presence of fluoride ions is established. A triple role for fluoride ions is identified from kinetic data on the rate of the reactions of trans-[ArPdBr(PPh3)2] (Ar=Ph, p-(CN)C6H4) with Ar′SnBu3 (Ar′=2-thiophenyl) in the presence of fluoride ions. Fluoride ions promote the rate-determining transmetallation by formation of trans-[ArPdF(PPh3)2], which reacts with Ar′SnBu3 (Ar′=Ph, 2-thiophenyl) at room temperature, in contrast to trans-[ArPdBr(PPh3)2], which is unreactive. However, the concentration ratio [F-]/[Ar′SnBu3] must not be too high, because of the formation of unreactive anionic stannate [Ar′Sn(F)Bu3]-. This rationalises the two kinetically antagonistic roles exerted by the fluoride ions that are observed experimentally, and is found to be in agreement with the kinetic law. In addition, fluoride ions promote reductive elimination from trans-[ArPdAr′(PPh3)2] generated in the transmetallation step.
- Hervé, Marius,Lefèvre, Guillaume,Mitchell, Emily A.,Maes, Bert U. W.,Jutand, Anny
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supporting information
p. 18401 - 18406
(2015/12/24)
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- Donor-free phosphenium-metal(0)-halides with unsymmetrically bridging phosphenium ligands
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Reactions of (cod)MCl2 (cod = 1,5 cyclooctadiene, M = Pd, Pt) with N-heterocyclic secondary phosphines or diphosphines produced complexes [(NHP)MCl]2 (NHP = N-heterocyclic phosphenium). The Pd complex was also accessible from a chlorophosphine precursor and Pd2(dba) 3. Single-crystal X-ray diffraction studies established the presence of dinuclear complexes that contain μ-bridging NHP ligands in an unsymmetrical binding mode and display a surprising change in metal coordination geometry from distorted trigonal (M = Pd) to T-shaped (M = Pt). DFT calculations on model compounds reproduced these structural features for the Pt complex but predicted an unusual C2v-symmetric molecular structure with two different metal coordination environments for the Pd species. The deviation between this structure and the actual centrosymmetric geometry is accounted for by the prediction of a flat energy hypersurface, which permits large distortions in the orientation of the NHP ligands at very low energetic cost. The DFT results and spectroscopic studies suggest that the title compounds should be described as phosphenium-metal(0)-halides rather than conventional phosphido complexes of divalent metal cations and indicate that the NHP ligands receive net charge donation from the metals but retain a distinct cationic character. The unsymmetric NHP binding mode is associated with an unequal distribution of σ-donor/π-acceptor contributions in the two M-P bonds. Preliminary studies indicate that reactions of the Pd complex with phosphine donors provide a viable source of ligand-stabilized, zerovalent metal atoms and metal(0)-halide fragments.
- Foerster, Daniela,Nickolaus, Jan,Nieger, Martin,Benko, Zoltan,Ehlers, Andreas W.,Gudat, Dietrich
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p. 7699 - 7708
(2013/07/26)
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- The triple role of fluoride ions in palladium-catalyzed Suzuki-Miyaura reactions: Unprecedented transmetalation from [ArPdFL2] complexes
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Fluoride ions play three roles in the Suzuki-Miyaura reaction. They favor the reaction by formation of trans-[ArPdF(PPh3)2], which reacts with Ar B(OH)2 in an unprecedented rate-determining transmetalation, and by promoting the reductive elimination from the trans-[ArPdAr (PPh3)2] intermediate. Conversely, F - disfavors the reaction by formation of unreactive anionic Ar B(OH)n-3Fn- (n=1-3), leading to two antagonistic effects of F- in the transmetalation. Copyright
- Amatore, Christian,Jutand, Anny,Leduc, Gaatan
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p. 1379 - 1382
(2012/03/27)
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- Developing synthetic approaches with non-innocent metalloligands: Easy access to IrI/Pd0 and IrI/Pd 0/IrI cores
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Guilty as charged is the verdict for anionic Ir complex [Ir(bpa-2 H)(cod)]- in its reactions with PdII compounds. The net transfer of two electrons from the Ir complex to Pd allows easy preparation of di- and trinuclear π-imine-coordinated Pd0 compounds such as [{Ir(PyCH2NCHPy)(cod)}2Pd] (see picture; C white, Ir red, N blue, Pd yellow). bpa-2 H: doubly deprotonated form of N,N-bis(2-picolyl)amine (bpa); cod: 1,5-cyclooctadiene.
- Tejel, Cristina,Asensio, Laura,Del Rio, M. Pilar,De Bruin, Bas,Lopez, Jose A.,Ciriano, Miguel A.
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p. 8839 - 8843
(2011/10/19)
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- Organometallic complexes of palladium (II) derived from 2,6-diacetylpyridine dimethylketal
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PdCl2 reacts with 2,6-diacetylpyridine(dap) (1:1) in refluxing MeOH to give the pincer complex [Pd(O1,N1,C 1-L)Cl](1) and (QH)2[{PdCl2(μ-Cl)}]2 (2), where L is the monoanionic ligand resulting from deprotonation of the acetyl methyl group of the monoketal of dap and QH is C5H 3NH{C-(OMe)Me}2-2,6, the diketal of Hdap+. Reaction of 2 with NEt3 (1:2) in MeOH affords Q = C5H 3N{C(OMe)2Me}2-2,6(3). Complex 1 reacts with 2 equiv of RNC at 0 °C to give trans-[Pd(C1-L)Cl(CNR) 2](R = Xy = 2,6-dimethylphenyl(4a), tBu (4b)) but at room temperature affords [Pd(O2, C2-LR)Cl(CNR)](R = Xy (5a), tBu(5b)). The ligand LR results from the insertion of one isocyanide into the Pd-C bond plus a tautomerization process from η-ketoimine to β-ketoenamine and coordinates in 5 through the carbonyl oxygen atom (O2) and the inserted isocyanide carbon atom (C2). The reaction of 1 with 1 equiv of RNC at 0 °C leads to a mixture of [Pd (N1,C1-L)Cl(CNR)] (R = Xy (6a), tBu (6b); 85-90%), 1, and 4, but at room temperature gives the pincer complex [Pd (O1,N1,C2-LR)Cl] (R = Xy (7a), tBu (7b)), resulting from insertion/tautomerization processes similar to that leading to 5. Complex 7 reacts at 0 °C (1) with 2 equiv of RNC to give trans-[Pd (C2-LR)Cl (CNXy) 2] (R = Xy (8a), tBu (8b)) or (2) with 1 equiv of tBuNC to afford 5b. The reaction of 1 (1) with [Tl(acac)] gives [Pd(N1,C1-L)(acac)] (9); (2) with chelating ligands N ∧N affords [Pd(C1-L)Cl(N∧N)](N ∧N = 2,2'-bipyridine = bpy (10), 4,4'-di-tert-butyl-2,2'- bipyridine = dbbpy (11)); (3) with 1 equiv of PPh3 gives, in the same way as with isocyanides, an equilibrium mixture of [Pd(N1,C 1-L)Cl(PPh3)] (12), 1, and trans-[Pd(C1-L)Cl (PPh3)2](13), which is the only product when 2 equiv of PPh3 is added to the reaction mixture; and(4) with excess PPh 3 affords the monoketal of dap, C5H3N{C(O)Me-2} {C(OMe)2Me-6}(14), and [Pd(PPh3)4]. The crystal structures of complexes 1, 2, 5b, 6a, and 7a have been determined.
- Vicente, Jose,Arcas, Aurelia,Julia-Hernandez, Francisco,Bautista, Delia,Jones, Peter G.
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p. 3066 - 3076
(2010/10/04)
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- Rate and mechanism of the oxidative addition of aryl halides to palladium(0) complexes generated in situ from a Pd(0)-triolefinic macrocyclic complex and phosphines
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The rate and mechanism of the oxidative addition of aryl halides (PhI, PhBr) to Pd(O) complexes generated in situ upon addition of phosphines (PPh 3, PnBu3, dppf) to the macrocyclic triolefinic complex Pd0(1a) have been investigated in THF or DMF. The macrocyclic ligand la is known to allow a good recycling of the catalyst in catalytic reactions. It is established that the ligand la affects the kinetics of oxidative addition, as monitored by electrochemical techniques. As far as PPh3 is concerned, a reactivity order with PhI has been established in THF, Pd0(PPh 3)4 > {Pd0(1a) + 4 PPh3), as a consequence of an equilibrium between Pd0(1a) and Pd 0(PPh3)3 which decreases the concentration of Pd0(PPh3)3 and consequently that of the reactive Pd0(PPh3)2. As expected, (Pd 0(1a) + 2 PPh3} is more reactive than {Pd0(1a) + 4 PPh3). In contrast to PPh3, the addition of n equivalents of PnBu3 to Pd0(1a) in DMF leads to the formation of Pd0(η2-1a)(PnBu3)2 and Pd0(PnBu3)3 (n > 2), characterized by 31P NMR. At equal phosphine/Pd loading, the Pd(0) complex ligated by PnBu3 is more reactive than that ligated by PPh3 and allows activation of PhBr at 25°C in DMF. When n = 2, Pd 0(PnBu3)2 is the unique species, which reacts with PhBr, but its concentration is controlled by the concentration of la, which favors the formation of the unreactive Pd0(η2-1a) (PnBu3)2 in a reversible reaction. The rate of the oxidative addition is limited by the dissociation of Pd0(η 2-1a)(PnBu3)2 to the reactive Pd 0(PnBu3)2 at high PhBr concentrations (>0.04 M). The reaction with PhI involves both Pd0(PnBu3) 2 and Pd0(η2-1a)(PnBu3) 2 as reactive species. The addition of 1 equiv of dppf to Pd 0(1a) leads to a complex mixture of Pd(0) complexes in THF. A reactivity order with PhI has been established, {Pd0(1a) + 2 PPh 3) > {Pd0(1a) + 1 dppf), in THF at 25°C.
- Serra-Muns, Anna,Jutand, Anny,Moreno-Manas, Marcial,Pleixats, Roser
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p. 2421 - 2427
(2009/02/03)
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- Carbon-carbon bond-forming reductive elimination from arylpalladium complexes containing functionalized alkyl groups. Influence of ligand steric and electronic properties on structure, stability, and reactivity
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A series of arylpalladium alkyl complexes of the formula [(DPPBz)Pd(Ar)(R)] (DPPBz = 1,2-bis(diphenylphosphino)benzene; R = methyl, benzyl, enolate, cyanoalkyl, trifluoroalkyl, or malonate) has been prepared to reveal the influence of steric and electronic parameters on structure, stability, and reactivity. Arylpalladium enolate and cyanoalkyl complexes ligated by EtPh 22P, 1,1-bis(diisopropylphosphino)ferrocene (D iPrPF), and BINAP were prepared to evaluate the effect of the ancillary ligand. The coordination modes of the enolate and cyanoalkyl complexes were determined by spectroscopic methods, in combination with X-ray crystallography. In the absence of steric effects, the C-bound isomer was favored electronically if the enolate or cyanoalkyl group was located trans to a phosphine, and the O-bound isomer was favored if the enolate was located trans to an aryl group. The thermodynamic stability of the enolate and cyanoalkyl complexes was controlled by the steric properties of the enolate or cyanoalkyl group, and complexes with more substitution at the α-carbon were less stable. Arylpalladium methyl, benzyl, enolate, cyanoalkyl, and trifluoroethyl complexes underwent carbon-carbon bond-forming reductive elimination upon heating. Reductive elimination was faster from complexes with electron-withdrawing substituents on the palladium-bound aryl group and with sterically hindered alkyl groups. The electronic properties of the alkyl group had the largest impact on the rate of reductive elimination: electron-withdrawing groups on the α-carbon retarded the rate of reductive elimination. The rates of reductive elimination correlated with the Taft polar substituent constants of the groups on the carbon alpha to the metal.
- Culkin, Darcy A.,Hartwig, John F.
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p. 3398 - 3416
(2008/10/09)
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- Rate and mechanism of the oxidative addition of vinyl triflates and halides to palladium(0) complexes in DMF
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In a coordinating solvent such as DMF, the fast oxidative addition of vinyl triflates to Pd0(PPh3)4 performed under stoichiometric conditions gives the cationic complexes [(η1-vinyl)- Pd(PPh3)2(DMF)]+TfO-, which have been characterized by conductivity measurements, electrospray mass spectrometry, and NMR spectroscopy, before their decomposition to vinyl-phosphonium salts [vinyl-PPh3]+TfO- and Pd0 complexes. [(η1-vinyl)Pd(PPh3)2(DMF)]+ TfO- complexes are less stable than [(aryl)Pd(PPh3)2(DMF)]+TfO- formed in the oxidative addition of aryl triflates to Pd0(PPh3)4. The rate constant of the oxidative addition of vinyl triflates and bromides to Pd0(PPh3)4 has been determined and compared to that of aryl triflates and halides. The following reactivity orders are established in DMF: vinyl-OTf ? vinyl-Br > PhBr and vinyl-OTf ? PhOTf.
- Jutand, Anny,Negri, Serge
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p. 4229 - 4237
(2008/10/08)
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- Mechanistic features of boron-iodine bond activation of B-iodocarboranes
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Oxidative addition of the B-I bond of 9-iodo-m-carborane to [(Ph3P)nPd] (n = 3, 4) is reversible, the equilibrium being shifted to the Pd(0) and the iodocarborane. In the presence of [(Ph3P)4Pd] and [Bu4N]Br in THF, 9-iodo-m-carborane undergoes halide exchange to produce 9-bromo-m-carborane. Coordinatively unsaturated Pd(0) and hydrido Pd(II) species generated upon thermal decomposition of [(Ph3P)2Pd(Ph)(O2CH)] and [(Ph3P)2Pd2(Ph)2 (μ-O2CH)2] reduce 9-iodo-m-carborane to m-carborane with 100% selectivity. The thermal decomposition of [(Ph3P)2Pd2(Ph)2 (μ-O2CH)2] in the presence of excess 9-iodo-m-carborane and PhI (1:1) results in the formation of m-carborane (3%) and [(Ph3P)2Pd2(Ph)2 (μ-I)2] (97%), whose structure was confirmed by single-crystal X-ray diffraction. X-ray analysis of 9-iodo-m-carborane and m-carboran-9-yl(phenyl)iodonium tetrafluoroborate shows that in the iodonium salt the B-I bond is longer by ca. 0.03 A? than in the iodocarborane. In contrast, the C-I bond distances in carboran-9-yl(phenyl)iodonium tetrafluoroborate (2.111(2) A?) and in iodobenzene (2.098(4) A?) are only marginally different. The elongation of the B-I bond, not the C-I bond, likely contributes to (i) the enhanced reactivity of B-carboranyl(phenyl)-iodonium cations toward nucleophiles and (ii) the remarkably high selectivity of these SN reactions that occur exclusively at the boron atom. A new crystallographic form of 9,10-diiodo-m-carborane is reported.
- Marshall, William J.,Young Jr., Robert J.,Grushin, Vladimir V.
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p. 523 - 533
(2008/10/08)
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- Thermal stability, decomposition paths, and Ph/Ph exchange reactions of [(Ph3P)2Pd(Ph)X] (X = I, Br, Cl, F, and HF2)
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Complexes of the type [(Ph3P)2Pd(Ph)X], where X = I (1), Br (2), Cl (3), F (4), and HF2 (5), possess different thermal stability and reactivity toward the Pd-Ph/P-Ph exchange reactions. While 1 decomposed (16 h) in toluene at 110 °C to [Ph4P]I, Pd metal, and Ph3P, complexes 2 and 3 exhibited no sign of decomposition under these conditions. Kinetic studies of the aryl-aryl exchange reactions of [(Ph3P)2Pd(C6D5)X] in benzene-de demonstrated that the rate of exchange decreases in the order 1 > 2 > 3, the observed rate constant ratio, kI:kBr:kCl, in benzene at 75 °C being ca. 100:4:1 for 1-d5, 2-d5, and 3-d5. The exchange was facilitated by a decrease in the concentration of the complex, polar media, and a Lewis acid, e.g., Et2O·BF3. Unlike [Bu4N]PF6, which speeded up the exchange reaction of 2-d5, [Bu4N]-Br inhibited it due to the formation of anionic four-coordinate [(Ph3P)Pd(C6D5)Br2]-. The latter and its iodo analogue were generated in dichloromethane and benzene upon addition of [Bu4N]X or PPN Cl to [(Ph3P)2Pd2(Ph)2(μ-X) 2] (X = I, Br, or Cl) and characterized in solution by 1H and 31P NMR spectral data. The mechanism of the aryl-aryl exchange reactions of [(Ph3P)2Pd(C6D5)X] in noncoordinating solvents of low polarity may not require Pd-X ionization but rather involves phosphine dissociation, the ease of which decreases in the order X = I > Br > Cl, as suggested by crystallographic data. Two mechanisms govern the thermal reactions of [(Ph3P)2Pd(Ph)F], 4. One of them is similar to the aryl-aryl exchange and decomposition path for 1-3, involving a tight ion pair intermediate, [Ph4P][(Ph3P)PdF], within which two processes were shown to occur. At 75 °C, the C-P oxidative addition restores the original neutral complex (4). At 90 °C, reversible fluoride transfer from Pd to the phosphonium cation resulted in the formation of covalent [Ph4PF] and [(Ph3P)Pd], which was trapped by PhI to produce [(Ph3P)2Pd2(Ph)2(μ-I) 2]. The other decomposition path of 4 leads to the formation of [(Ph3P)3Pd], Pd, Ph2 , Ph3PF2, and Ph2P-PPh2 as main products. Unlike the aryl-aryl exchange, this decomposition reaction is not inhibited by free phosphine. The formation of biphenyl was shown to occur due to PdPh/PPh coupling on the metal center. Mechanisms accounting for the formation of these products are proposed and discussed. The facile (4 h at 75 °C) thermal decomposition of [(Ph3P)2Pd(Ph)(FHF)] (5) in benzene resulted in the clean formation of PhH, Ph3PF2, Pd metal, and [(Ph3P)3Pd].
- Grushin, Vladimir V.
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p. 1888 - 1900
(2008/10/08)
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- Preparation and reactions of bis(triphenylphosphine)palladium(0)
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The two-coordinate palladium complex, (Ph3P)2Pd, is succesfully prepared by the reaction of 3-allyl)Pd(PPh3)2>+ PF6- with Ph2MeSiLi.The complex has been characterized by Ir, 1H NMR, 13C NMR, 31P NMR, and UV spectroscopy
- Urata, Hisao,Suzuki, Hiroharu,Moro-oka, Yoshihiko,Ikawa, Tsuneo
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p. 235 - 244
(2007/10/02)
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- η3-Allylmetal-Sulfur Complexes, V. Mono- and Bimetallic, Polynuclear η3-Allylmetal-Sulfur Complexes of Nickel, Palladium and Platinum
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η3-Allylhydrogensulfidopalladium (6) reacts with bis-(η3-allyl)- (4) or η5-cyclopentadienyl-η3-allyl-palladium (11) with elimination of propene to give the known η3-allyl-palladium-sulfur-cluster (2).The same method was used to prepare the first bimetallic η3-allyl-Ni-Pd-, Ni-Pt- and Pd-Pt-sulfur complexes 12-14 (IR-spectra); their structures are still unknown.The polynuclear η3-metallylpalladium- and -platinum-sulfur complexes 2a and 3a, soluble in benzene and toluene, have been prepared from the corresponding bis(η3-methallyl)metal compounds and H2S.In benzene, 2a may have a structure in which the four palladium atoms adopt a square planar (2a') or tetrahedral (2a'') geometry. - Keywords: η3-Allylnickel- and -palladium-sulfur Complexes, η3-Methallylpalladium- and -platinum-sulfur Complexes, Bimetallic η3-Allylmetal-sulfur Complexes of Nickel, Palladium and Platinum, IR Spectra
- Bogdanovic, Borislav,Goettsch, Peter,Rubach, Martin
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p. 599 - 603
(2007/10/02)
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