- A dinuclear palladium(I) ethynyl complex: Synthesis, structure, and dynamics
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The reaction of Pd(η3-C3H5)2 with PiPr3 at -30°C affords yellow crystals of the PdII complex (iPr3P)Pd(η3-C3H5) (η1-C3H5) (1). At 20°C 1 transforms into the dinuclear PdI complex {(iPr3P)Pd}2 (μ-C3H5)2 (2) due to oxidative C-C coupling of two allyl groups with elimination of 1,5-hexadiene. Heating 1 or 2 in 1,6-heptadiene to 80°C produces the Pd0 complex (iPr3P)Pd(η2,η2- C7H12) (3) {(η3-C3H5)PdCl}2 reacts with iPr3P to give (iPr3P)Pd(η3-C3H5)Cl (4b), from which further derivatives (iPr3P)Pd(η3-C3H5)X (X = OSO2CF3 (4a), C≡CH (5a), CH3 (5b)) are obtained by replacement reactions. The mononuclear PdII-acetylide 5a and complex 3 combine to give the dinuclear PdI derivative {(iPr3P)Pd}2(μ-C3H5) (μ2-η2-C2H) (6). The Pd-Pd bond in 6 is unsymmetrically bridged by a π-allyl and a σ-π-ethynyl group, as determined by X-ray structure analysis. The structures of 1, 4a,b, and 6 are dynamic in solution, with 1 undergoing an exchange of the binding modes of the π- and σ-coordinated allyl groups and 4a,b displaying a π/σ-allyl group rearrangement, and in 6 the C≡CH substituent oscillates in its π-coordination from one PdI atom to the other.
- Krause, Jochen,Goddard, Richard,Mynott, Richard,P?rschke, Klaus-Richard
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- A cluster model for the catalytic hydrogenation of CFCs and the synthesis and structural characterisation (when X = Br) of [Pd4(μ3-CF)(μ-X)3(PBut 3)4] (X = Cl, Br)
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The syntheses, characterisation and crystal structure (when X = Br) of [Pd4(μ3-CF)(μ-X)3(PBut 3)4] (X = Cl, Br) are reported; the μ3-CF moiety is hydrogenated to CFH3 under mild conditions and serves as a model for the heterogeneous hydrogenation of CFCs to HCFCs.
- Vilar, Ramon,Lawrence, Simon E.,Mingos, D. Michael P.,Williams, David J.
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- NMR Studies of the Species Present in Cross-Coupling Catalysis Systems Involving Pd(η3-1-Ph-C3H4) (η5-C5H5).
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The compounds Pd(η3-1-Ph-C3H4) (η5-C5H5) (I), Pd2(dba) 3 (II), Pd(OAc)2 (III), and [Pd(η3-1-Ph- C3H4)Cl]2 (IV) are frequently utilized as catalyst precursors for a variety of cross-coupling processes, including Suzuki-Miyaura, Heck-Mizoroki, Sonogashira, and Buchwald-Hartwig reactions. In the preceding paper in this issue, we assess and compare catalyst systems based on I-IV activated with PBut3, XPhos, and/or Mor-Dalphos for the prototypical Buchwald-Hartwig amination reactions of 4-bromo- and 4-chloroanisole with morpholine, noting several apparent incongruities which seem to indicate mechanistic dissimilarities for various reactant/precatalyst combinations. In this paper we investigate by NMR spectroscopy the solution chemistry of I and IV with PBut3, XPhos, and Mor-Dalphos, noting similarities and differences in the respective abilities of these precursor-ligand combinations to generate palladium(0) catalyst systems. We find inter alia that steric requirements prevent Xphos and Mor-Dalphos from forming 2:1 palladium(0) complexes and, surprisingly, that 1:1 palladium(0) complexes of Xphos and Mor-Dalphos are unstable with respect to dissociation to free ligand and palladium metal. In other words, these two ligands and, by implication, other sterically demanding phosphine ligands do not form palladium(0) compounds.
- Borjian, Sogol,Baird, Michael C.
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- Oxidative ring expansion of a low-coordinate palladacycle: Synthesis of a robust T-shaped alkylpalladium(II) complex
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The synthesis of an unusual T-shaped alkylpalladium(II) complex featuring a cyclometalated tri-tert-butylphosphineoxide ligand by oxidation of the corresponding cyclometalated tri-tert-butylphosphine complex with PhIO is reported. We speculate that this reaction proceeds by formation of a transient palladium oxo intermediate and there are structural similarities with a late transition metal exemplar: Milstein's seminal pincer ligated Pt(IV) oxo (Nature 2008, 455, 1093–1096).
- Sinclair, Matthew J.G.,Chaplin, Adrian B.
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- Ligand effects on decarbonylation of palladium-acyl complexes
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The influences of perturbations of supporting phosphine ligands on the dehydrative decarbonylation of (Ln)PdII(Cl)-hydrocinnamoyl complexes (L = PtBu3, n = 1; L = PPh3, n = 2; L = dppe, n = 1) to yield styrene were studied through combined experiment and theory. Abstraction of chloride from the complexes by silver and zinc salts, as well as sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, enhanced the efficiency of styrene formation, according to the following trend in L: PtBu3 > dppe > PPh3. DFT calculations corroborated the experimental findings and provided insights into the ligand influences on reaction step barriers and transition state structures. Key findings include the following: a stable intermediate forms after chloride abstraction, from which β-hydride elimination is most affected by ligand choice, the low coordination number for the PtBu3 case lowers reaction barriers for all steps, and the trans disposition of two ligands for L = PPh3 contributes to the low efficiency for styrene production in that case.
- Wiessner, Tedd C.,Fosu, Samuel Asiedu,Parveen, Riffat,Rath, Nigam P.,Vlaisavljevich, Bess,Tolman, William B.
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supporting information
p. 3992 - 3998
(2020/11/30)
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- PROCESS
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The present invention provides a process for the preparation of a complex of formula (I): comprising the step of reacting Pd(diolefin)X2 or PdX2 and PR1 R2R3 in a solvent to form the complex of formula (I), wherein the process is carried out in the absence of a base, the molar ratio of Pd(diolefin)X2 : PR1 R2R3 or PdX2 : PR1 R2R3 is greater than 1 : 1.1, up to about 1 :2.5; each X is independently a halide; and R1, R2 and R3 are independently selected from the group consisting of tert-butyl and isopropyl.
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Page/Page column 16
(2018/05/16)
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- General C-H Arylation Strategy for the Synthesis of Tunable Visible Light-Emitting Benzo[a]imidazo[2,1,5-c,d]indolizine Fluorophores
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Herein we report the discovery of the benzo[a]imidazo[2,1,5-c,d]indolizine motif displaying tunable emission covering most of the visible spectrum. The polycyclic core is obtained from readily available amides via a chemoselective process involving Tf2O-mediated amide cyclodehydration, followed by intramolecular C-H arylation. Additionally, these fluorescent heterocycles are easily functionalized using electrophilic reagents, enabling divergent access to varied substitution. The effects of said substitution on the compounds' photophysical properties were rationalized by density functional theory calculations. For some compounds, emission wavelengths are directly correlated to the substituent's Hammett constants. Easily introduced nonconjugated reactive functional groups allow the labeling of biomolecules without modification of emissive properties. This work provides a straightforward platform for the synthesis of new moderately bright fluorescent dyes remarkable for their chemical stability, predictability, and unusually high excitation-emission differential.
- Lévesque, éric,Bechara, William S.,Constantineau-Forget, Léa,Pelletier, Guillaume,Rachel, Natalie M.,Pelletier, Joelle N.,Charette, André B.
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supporting information
p. 5046 - 5067
(2017/05/24)
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- Understanding the Unusual Reduction Mechanism of Pd(II) to Pd(I): Uncovering Hidden Species and Implications in Catalytic Cross-Coupling Reactions
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The reduction of Pd(II) intermediates to Pd(0) is a key elementary step in a vast number of Pd-catalyzed processes, ranging from cross-coupling, C-H activation, to Wacker chemistry. For one of the most powerful new generation phosphine ligands, PtBu3, oxidation state Pd(I), and not Pd(0), is generated upon reduction from Pd(II). The mechanism of the reduction of Pd(II) to Pd(I) has been investigated by means of experimental and computational studies for the formation of the highly active precatalyst {Pd(μ-Br)(PtBu3)}2. The formation of dinuclear Pd(I), as opposed to the Pd(0) complex, (tBu3P)2Pd was shown to depend on the stoichiometry of Pd to phosphine ligand, the order of addition of the reagents, and, most importantly, the nature of the palladium precursor and the choice of the phosphine ligand utilized. In addition, through experiments on gram scale in palladium, mechanistically important additional Pd- and phosphine-containing species were detected. An ionic Pd(II)Br3 dimer side product was isolated, characterized, and identified as the crucial driving force in the mechanism of formation of the Pd(I) bromide dimer. The potential impact of the presence of these side species for in situ formed Pd complexes in catalysis was investigated in Buchwald-Hartwig, α-arylation, and Suzuki-Miyaura reactions. The use of preformed and isolated Pd(I) bromide dimer as a precatalyst provided superior results, in terms of catalytic activity, in comparison to catalysts generated in situ.
- Johansson Seechurn, Carin C. C.,Sperger, Theresa,Scrase, Thomas G.,Schoenebeck, Franziska,Colacot, Thomas J.
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supporting information
p. 5194 - 5200
(2017/05/04)
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- Synthetic method used for preparing bis(tri-tert-butylphosphine) palladium (O)
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The invention provides a synthetic method used for preparing bis(tri-tert-butylphosphine) palladium (O). The synthetic method is high in yield and low in cost. According to the synthetic method, tri-tert-butylphosphonium tetrafluoroborate is reacted with two bivalent palladium compounds, tris(dibenzylideneacetone)dipalladium-chloroform adduct and dibromo(1,5-cyclooctadiene) palladium so as to obtain bis(tri-tert-butylphosphine) palladium (O) in an alkaline environment. The synthetic method is used for solving problems of the prior art that raw materials are expensive, yield is low, and reaction conditions are strict; and yield of the synthetic method is higher than 50%. The synthetic method possesses excellent popularization potential, and a promising application prospect.
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Paragraph 0014-0015
(2017/03/08)
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- Acid Chloride Synthesis by the Palladium-Catalyzed Chlorocarbonylation of Aryl Bromides
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We report a palladium-catalyzed method to synthesize acid chlorides by the chlorocarbonylation of aryl bromides. Mechanistic studies suggest the combination of sterically encumbered PtBu3 and CO coordination to palladium can rapidly equilibrate the oxidative addition/reductive elimination of carbon-halogen bonds. This provides a useful method to assemble highly reactive acid chlorides from stable and available reagents, and can be coupled with subsequent nucleophilic reactions to generate new classes of carbonylated products. The Good, the Bad and the Bulky! By employing a sterically encumbered phosphine ligand, tri-tert-butyl phosphine, under palladium catalysis inert aryl bromides are chlorocarbonylated to create reactive acid chlorides by reversible carbon-halogen bond reductive elimination. This general platform allows for an expanded scope of the Heck carbonylation reaction to include previously incompatible nucleophiles.
- Quesnel, Jeffrey S.,Kayser, Laure V.,Fabrikant, Alexander,Arndtsen, Bruce A.
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supporting information
p. 9550 - 9555
(2015/06/30)
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- Highly Efficient C-SeCF3 Coupling of Aryl Iodides Enabled by an Air-Stable Dinuclear PdI Catalyst
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Building on our recent disclosure of catalysis at dinuclear PdI sites, we herein report the application of this concept to the realization of the first catalytic method to convert aryl iodides into the corresponding ArSeCF3 compounds. Highly efficient C-SeCF3 coupling of a range of aryl iodides was achieved, enabled by an air-, moisture-, and thermally stable dinuclear PdI catalyst. The novel SeCF3-bridged dinuclear PdI complex 3 was isolated, studied for its catalytic competence and shown to be recoverable. Experimental and computational data are presented in support of dinuclear PdI catalysis.
- Aufiero, Marialuisa,Sperger, Theresa,Tsang, Althea S.-K.,Schoenebeck, Franziska
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supporting information
p. 10322 - 10326
(2015/09/01)
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- Pd(η3-1-PhC3H4)(η5- C5H5) as a catalyst precursor for Buchwald-Hartwig amination reactions
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The compound Pd(η3-1-Ph-C3H4) (η5-C5H5) (I) reacts cleanly with many tertiary phosphines L to undergo reductive elimination of PhC3H 4-C5H5 and form palladium(0) species of the types PdLn (n = 2, 3), long believed to be exemplary catalysts for Suzuki-Miyaura, Heck-Mizoroki, and Sonogashira cross-coupling reactions. I has accordingly been shown to be generally much more effective for these catalytic processes than are conventional catalyst precursors such as Pd(PPh 3)4, Pd2(dba)3, PdCl2, and Pd(OAc)2, in large part because I stands alone in this series for its ability to generate specifically and efficiently the desired species PdL2 in many cases. We have now investigated I as a precursor for prototypical Buchwald-Hartwig amination reactions of 4-bromo- and 4-chloroanisole with morpholine, making comparisons with Pd2(dba) 3, Pd(OAc)2, and [Pd(η3-1-Ph-C 3H4)Cl]2 (IV). In this work we have utilized PBut3 because of its general effectiveness, and we have also assessed XPhos and Mor-Dalphos, representatives of important classes of phosphines utilized elsewhere for amination reactions.
- Borjian, Sogol,Tom, David M. E.,Baird, Michael C.
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p. 3928 - 3935
(2014/12/10)
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- The impact of palladium(II) Reduction pathways on the structure and activity of palladium(0) catalysts
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Two roads diverged: The mechanism of insitu PdII catalyst activation to generate an active {LnPd0} catalyst from an air-stable PdII precursor was examined using the standard conditions of a Miyaura borylation reaction. Two pathways for catalyst activation exist under these conditions, producing two structurally and chemically distinct {LnPd0} complexes (see scheme). Copyright
- Wei, Carolyn S.,Davies, Geraint H. M.,Soltani, Omid,Albrecht, Jacob,Gao, Qi,Pathirana, Charles,Hsiao, Yi,Tummala, Srinivas,Eastgate, Martin D.
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supporting information
p. 5822 - 5826
(2013/07/11)
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- Pd(η3-1-PhC3H4)(η5- C5H5), an unusually effective catalyst precursor for heck-mizoroki and sonogashira cross-coupling reactions catalyzed by bis-phosphine palladium(0) compounds
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The compound Pd(η3-1-PhC3H4) (η5-C5H5) reacts essentially quantitatively with a variety of phosphines L to form cross-coupling catalysts of the type PdL2 and has recently been shown to be a much more effective catalyst precursor for Suzuki-Miyaura cross-coupling reactions in comparison to more commonly utilized precursors such as Pd(PPh3)4, Pd 2(dba)3, and Pd(OAc)2, which do not effectively generate two-coordinate species PdL2. This advantage is expected to apply also to e.g. Heck-Mizoroki and Sonogashira cross-coupling reactions, both of which are generally believed to be catalyzed by species of the type PdL 2. Therefore, comparisons of the efficacies of catalyst systems based on Pd(η3-1-PhC3H4)(η5- C5H5), Pd(PPh3)4, Pd 2(dba)3, and Pd(OAc)2 are made utilizing the conventional coupling reactions of aryl halides with methyl acrylate and styrene for Heck-Mizoroki coupling and with phenylacetylene for Sonogashira coupling. As anticipated, catalyst systems based on Pd(η3-1-PhC 3H4)(η5-C5H5) are found to be significantly more active.
- Fraser, Andrew W.,Jaksic, Bryan E.,Batcup, Rhys,Sarsons, Christopher D.,Woolman, Michael,Baird, Michael C.
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supporting information
p. 9 - 11
(2013/03/13)
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- Characterization, reactivity, and potential catalytic intermediacy of a cyclometalated tri-tert -butylphosphine palladium acetate complex
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Palladium acetate and tri-tert-butylphosphine react at room temperature via C-H activation of a tert-butyl group to form the novel palladium(II) complex [(PtBu3)Pd(CH2C(CH3) 2PtBu2)(OAc). This cyclometalated complex can be reduced to Pd(PtBu3)2 by either heat or hydrogen, but is resistant to reduction by alkoxide bases and amines. As a result of the existence of this cyclometalated complex, the production of catalytically active palladium(0) species generated in situ from Pd(OAc) 2 and tri-tert-butylphosphine is diminished, as evident by the catalytic inactivity of this complex. Additionally, datively bound tri-tert-butylphosphine is easily displaced by amines and less basic phosphines to form a series of novel cyclometalated palladium(II) complexes.
- Henderson, William H.,Alvarez, Jimmy M.,Eichman, Chad C.,Stambuli, James P.
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p. 5038 - 5044
(2011/11/05)
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- Palladium-catalyzed formylation of aryl bromides: Elucidation of the catalytic cycle of an industrially applied coupling reaction
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The first comprehensive study of the catalytic cycle of the palladium-catalyzed formylation of aryl bromides with synthesis gas (CO/H 2, 1:1) is presented. The formylation in the presence of efficient (Pd/PR2nBu, R = 1-Ad, tBu) and nonefficient (Pd/PtBu3) catalysts was investigated. The main organometallic complexes involved in the catalytic cycle were synthesized and characterized, and their solution chemistry was studied in detail. Comparison of stoichiometric and catalytic reactions using P(1-Ad)2nBu, the most efficient ligand known for the formylation of aryl halides, led to two pivotal results: (1) The corresponding carbonylpalladium(O) complex [Pd n(CO)mLn] and the respective hydrobromide complex [Pd(Br)(H)L2] are resting states of the active catalyst, and they are not directly involved in the catalytic cycle. These complexes maintain the concentration of most active [PdL] species at a low level throughout the reaction, making oxidative addition the rate-determining step, and provide high catalyst longevity. (2) The product-forming step proceeds via base-mediated hydrogenolysis of the corresponding acyl complex, e.g., [Pd(Br)(p-CF 3C6H4CO){P(1-Ad)2 nBu}]2 (8), under mild conditions (25-50°C, 5 bar). Stoichiometric studies using the less efficient Pd/PtBu3 catalyst resulted in the isolation and characterization of the first stable three-coordinated neutral acylpalladium complex, [Pd(Br)(p-CF3C 6H4CO)(PtBu3)] (10). Hydrogenolysis of 10 needed significantly more drastic conditions compared to that of dimeric 8. In the presence of amine base, complex 10 gave a catalytically inactive diamino acyl complex, which explains the low activity of the Pd/P tBu3 catalyst formylation of aryl bromides.
- Sergeev, Alexey G.,Spannenberg, Anke,Beller, Matthias
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p. 15549 - 15563
(2009/03/12)
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- Aryl-fluoride reductive elimination from Pd(II): Feasibility assessment from theory and experiment
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DFT methods were used to elucidate features of coordination environment of Pd(II) that could enable Ar - F reductive elimination as an elementary C-F bond-forming reaction potentially amenable to integration into catalytic cycles for synthesis of organofluorine compounds with benign stoichiometric sources of F-. Three-coordinate T-shaped geometry of PdIIAr(F)L (L = NHC, PR3) was shown to offer kinetics and thermodynamics of Ar - F elimination largely compatible with synthetic applications, whereas coordination of strong fourth ligands to Pd or association of hydrogen bond donors with F each caused pronounced stabilization of Pd(II) reactant and increased activation barrier beyond the practical range. Decreasing donor ability of L promotes elimination kinetics via increasing driving force and para-substituents on Ar exert a sizable SNAr-type TS effect. Synthesis and characterization of the novel [Pd(C6H4-NO2)ArL(μ-F)] 2 (L = P(o-Tolyl)3, 17; P(t-Bu)3, 18) revealed stability of the fluoride-bridged dimer forms of the requisite Pd IIAr-(F)L as the key remaining obstacle to Ar - F reductive elimination in practice. Interligand steric repulsion with P(t-Bu)3 served to destabilize dimer 18 by 20 kcal/mol, estimated with DFT relative to PMe3 analog, yet was insufficient to enable formation of greater than trace quantities of Ar - F; C - H activation of P(t-Bu)3 followed by isobutylene elimination was the major degradation pathway of 18 while Ar/F - scrambling and Ar - Ar reductive elimination dominated thermal decomposition of 17. However, use of Buchwald's L = P(C6H 4-2-Trip)(t-Bu)2 provided the additional steric pressure on the [PdArL(μ-F)]2 core needed to enable formation of aryl-fluoride net reductive elimination product in quantifiable yields (10%) in reactions with both 17 and 18 at 60° over 22 h.
- Yandulov, Dmitry V.,Tran, Ngon T.
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p. 1342 - 1358
(2007/10/03)
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- Reductive elimination of ether from T-shaped, monomeric arylpalladium alkoxides
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(Chemical Equation Presented) Isolated truth: The synthesis, structures, and reductive elimination chemistry of arylpalladium(II) phenoxide and alkoxide complexes with a single bulky phosphine ligand are reported. These complexes are true intermediates in palladium-catalyzed etherification of aryl halides. They undergo reductive elimination of the alkyl aryl ether directly from the isolated complex (see scheme), and the rates of these reductive eliminations are slower than those from related arylpalladium amido complexes. Ad = adamantyl.
- Stambuli, James P.,Weng, Zhiqiang,Incarvito, Christopher D.,Hartwig, John F.
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p. 7674 - 7677
(2008/09/18)
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- Reductive elimination of aryl halides upon addition of hindered alkylphosphines to dimeric arylpalladium(II) halide complexes
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We report the reductive elimination of haloarene from {Pd[P(o-tol)3](Ar)(μ-X)}2 (X = Cl, Br, I) upon addition of the strongly electron-donating, but sterically hindered, phosphine P(t-Bu)3and related ligands. Reductive elimination of aryl chlorides, bromides, and iodides from these dimeric arylpalladium(II) halide complexes was observed upon the addition of P(t-Bu)3. Conditions to observe the elimination and addition equilibria were established for all three halides, and values for these equilibrium constants were measured. Reductive elimination of aryl chlorides was most favored thermodynamically, and elimination of aryl iodide was the least favored. However, reactions of the aryl chloride complexes were the slowest. Detailed mechanistic data revealed that cleavage of the starting dimer, accompanied by ligand substitution either before or after cleavage, led to the formation of a three-coordinate arylpalladium(II) halide monomer that reductively eliminated haloarene.
- Roy, Amy H.,Hartwig, John F.
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p. 1533 - 1541
(2008/10/09)
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- Synthesis, Structure, Theoretical Studies, and Ligand Exchange Reactions of Monomeric, T-Shaped Arylpalladium(II) Halide Complexes with an Additional, Weak Agostic Interaction
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A series of monomeric arylpalladium(II) complexes LPd(Ph)X (L = 1-AdP tBu2, PtBu3, or Ph 5FcPtBu2 (Q-phos); X = Br, I, OTf) containing a single phosphine ligand have been prepared. Oxidative addition of aryl bromide or aryl iodide to bis-ligated palladium(0) complexes of bulky, trialkylphosphines or to Pd(dba)2 (dba = dibenzylidene acetone) in the presence of 1 equiv of phosphine produced the corresponding arylpalladium(II) complexes in good yields. In contrast, oxidative addition of phenyl chloride to the bis-ligated palladium(0) complexes did not produce arylpalladium(II) complexes. The oxidative addition of phenyl triflate to PdL2 (L = 1-AdPtBu2, PtBu 3, or Q-phos) also did not form arylpalladium(II) complexes. The reaction of silver triflate with (1-AdPtBu2)Pd(Ph)Br furnished the corresponding arylpalladium(II) triflate in good yield. The oxidative addition of phenyl bromide and iodide to Pd(Q-phos)2 was faster than oxidative addition to Pd(1-AdPtBu2)2 or Pd(PtBu3)2. Several of the arylpalladium complexes were characterized by X-ray diffraction. All of the arylpalladium(II) complexes are T-shaped monomers. The phenyl ligand, which has the largest trans influence, is located trans to the open coordination site. The complexes appear to be stabilized by a weak agostic interaction of the metal with a ligand C-H bond positioned at the fourth-coordination site of the palladium center. The strength of the Pd...H bond, as assessed by tools of density functional theory, depended upon the donating properties of the ancillary ligands on palladium.
- Stambuli, James P.,Incarvito, Christopher D.,Buehl, Michael,Hartwig, John F.
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p. 1184 - 1194
(2007/10/03)
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- Synthesis, Structure, and Reductive Elimination Chemistry of Three-Coordinate Arylpalladium Amido Complexes
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Four three-coordinate arylpalladium amido complexes with a single hindered phosphine were isolated and structurally characterized. Each possessed a T-shaped geometry. Several of these complexes possessed true three-coordinate structures that lacked any additional coordination by ligand C-H bonds. All of the three-coordinate complexes underwent reductive elimination to form the corresponding triarylamine. A comparison of the rate of reaction of the three-coordinate compounds demonstrated that the rate of elimination from the pentaphenylferrocenyl di-tert-butylphosphine complex were the fastest. A comparison of the rates of reactions between three-coordinate and four-coordinate complexes showed that the rates were much faster from the three-coordinate complexes. Copyright
- Yamashita, Makoto,Hartwig, John F.
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p. 5344 - 5345
(2007/10/03)
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- Directly Observed Reductive Elimination of Aryl Halides from Monomeric Arylpalladium(II) Halide Complexes
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Monomeric, three-coordinate arylpalladium(II) halide complexes undergo reductive elimination of aryl halide to form free haloarene and Pd(0). Reductive elimination of aryl chlorides, bromides, and iodides were observed upon the addition of P(t-Bu)3/
- Roy, Amy H.,Hartwig, John F.
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p. 13944 - 13945
(2007/10/03)
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- The first general method for palladium-catalyzed Negishi cross-coupling of aryl and vinyl chlorides: Use of commercially available Pd(P(t-Bu)3)2 as a catalyst
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With a single protocol, commercially available Pd(P(t-Bu)3)2 can effect the Negishi cross-coupling of a wide range of aryl and vinyl chlorides with aryl- and alkylzinc reagents. The process tolerates nitro groups, and it efficiently generates sterically hindered biaryls. In addition, a high turnover number (>3000) can be achieved.
- Dai,Fu
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p. 2719 - 2724
(2007/10/03)
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- 1,6-Diene complexes of palladium(0) and platinum(0): Highly reactive sources for the naked metals and [L-M0] fragments
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The complexes (cod)MCl2 (M = Pd, Pt; cod = cis,cis-1,5-cyclooctadiene) react with Li2(cot) (cot = cyclooctatetraene) in a 1,6-diene/diethyl ether mixture (1,6-diene = hepta-1,6-diene, diallyl ether, dvds (1,3-divinyl- 1,1,3,3-tetramethyldisiloxane)) to afford the isolated homoleptic dinuclear Pd0 and Pt0 compounds Pd2(C7H12)3 (1), Pd2(C6H10O)3·C6H10O (2'; 2: Pd2(C6H10O)3), Pd2(dvds)3 (3), and Pt2(C7H12)3 (4). When 1-4 are treated with additional 1,6-diene the equally homoleptic but mononuclear derivatives of type M(1,6-diene)2 (5-8) and with ethene the mixed alkene complexes (C2H4)M(1,6-diene) (9-12) are obtained in solution. Complexes 1-12 react with donor ligands such as phosphanes, phosphites, or (t)BuNC to give isolated complexes of types L-M(1,6-diene) (13-41), which have also been prepared by other routes. In all complexes the metal centers are TP-3 coordinated: complexes 1-4 contain chelating and bridging 1,6-diene ligands, whereas the other complexes contain a chelating 1,6-diene ligand and an η2-alkene (5-12) or η1-donor ligand (13-41). Of the studied 1,6-diene complexes the hepta-1,6-diene derivatives are most reactive, while the diallyl ether complexes are often more convenient to handle. The readily isolable dinuclear hepta-1,6-diene and diallyl ether complexes 1, 2', and 4, and their mononuclear pure olefin derivatives are among the most reactive sources for naked Pd0 and Pt0. The corresponding L-M(1,6-diene) complexes are equally reactive precursor compounds for the generation of [L-M0] fragments in solution, which for M =Pd are available otherwise only with difficulty. The results are significant for the operation of naked Pd0 and L-Pd0 catalysts in homogeneous catalysis.
- Krause, Jochen,Cestaric, Günter,Haack, Karl-Josef,Seevogel, Klaus,Storm, Werner,P?rschke, Klaus-Richard
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p. 9807 - 9823
(2007/10/03)
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- Hepta-1,6-diene and diallyl ether complexes of palladium(0) and platinum(0): A route to L-M(alkene)2 complexes containing non-activated alkenes
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With hepta-1,6-diene and diallyl ether, Pd0 and Pt0 form highly reactive homoleptic dinuclear M2(1,6-diene)3 complexes, which are cleaved by donors L (e.g. C2H4, phosphanes, phosphites, isonitriles) to afford mononuclear derivatives L-M(1,6-diene); the X-ray structure of (Me3P)Pd{(η2-CH2=CHCH2) 2O} has been determined.
- Krause, Jochen,Haack, Karl-Josef,Cestaric, Guenter,Goddard, Richard,Poerschke, Klaus-Richard
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p. 1291 - 1292
(2007/10/03)
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- Synthesis and structural characterisation of [Pd2(μ-Br)2(PBut3)2], an example of a palladium(I)-palladium(I) dimer
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The syntheses, spectroscopic characterisation and in one case (X = Br) the single-crystal structure of the novel PdI-PdI dimers [Pd2(μ-X)2(PBut3)2] (X = Br or I) have been determined; preliminary results on their reactions with CO, H2, CNC6H3Me2 and C2H2 have also been obtained.
- Vilar, Ramon,Mingos, D. Michael P.,Cardin, Christine J.
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p. 4313 - 4314
(2007/10/03)
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- Structural characterization and simple synthesis of {Pd[P(o-Tol)3]2}, dimeric palladium(II) complexes obtained by oxidative addition of aryl bromides, and corresponding monometallic amine complexes
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The palladium(0) complex {Pd[P(o-Tol)3]2} was prepared by addition of P(o-Tol)3 to crude "[Pd(DBA)2]", which is an approximately equimolar mixture of Pd2(DBA)3 and Pd(DBA)3, followed by crystallization from the reaction medium by addition of ether. The formation of {Pd[P(o-Tol)3]2} appeared to be driven by its insolubility in the benzene/ether solvent mixture. Benzene solutions of "[Pd(DBA)2]" and P(o-Tol)3 did not contain amounts of the L2Pd compound that could be detected by 31P NMR spectroscopy. {Pd[P(o-Tol)3]2} was characterized crystallographically and showed an exactly linear geometry. Similar Pd(O) compounds {Pd[P(2,4-dimethylphenyl)3]2}, {Pd[P(2-methyl-4-fluorophenyl)3]2}, and the low-coordinate trialkylphosphine complex {Pd[P(t-Bu)a]2} were also prepared by this method, but [Pd(PCy3)2-(DBA)] was produced from reactions involving PCy3 and "[Pd(DBA)2]", and [Pd(TMPP)(DBA)2] was isolated after addition of tris(1,3,5-trimethoxyphenyl)phosphine (TMPP) to "[Pd(DBA)2]". The oxidative addition of aryl halides to {Pd[P(o-Tol)3]2} at room temperature led to dimeric products {Pd[P(o-Tol)3](Ar)(Br)}2. An example of these compounds was characterized crystallographically as well as by solution molecular weight analysis. This aryl halide complex was shown to be dimeric in the solid state as well as in solution. The NMR spectra of the large triarylphosphine complexes showed temperature dependent behavior, presumably due to isomerizations and ligand rotations that occurred on the NMR time scale. The aryl halide compounds did not form four-coordinate monometallic species in the presence of excess P(o-Tol)3, but they did undergo cleavage to four-coordinate monometallic complexes upon addition of primary and secondary amines.
- Paul, Frédéric,Patt, Joe,Hartwig, John F.
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p. 3030 - 3039
(2008/10/09)
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