- Synthesis and Structural Characterisation of : A Tetrahedral Palladium Cluster with a μ3-Methylidyne Ligand
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The compound has been synthesised from (dba = dibenzylideneacetone), P(t-Bu)3 and CHCl3 and characterised spectroscopically and by single-crystal X-ray analysis; it undergoes substitution reactions with Br(1-) and tertiary phosphines and is a catalyst for the polymerisation of ethyne.
- Burrows, Andrew D.,Mingos, D. Michael P.,Menzer, Stephan,Vilar, Ramon,Williams, David J.
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- Kinetic and computational studies on Pd(I) dimer-mediated halogen exchange of aryl iodides
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Building on our previous discovery and reactivity explorations of the Pd(I) dimer [(PtBu3)PdBr]2-mediated halogen exchange of aryl iodides [ Chem. Sci. 2013, 4, 4434 ], this report presents kinetic studies of this process, giving first-order kinetic dependence in the Pd(I) dimer and aryl iodide. An activation free energy barrier of ΔG? = 24.9 ± 3.3 kcal/mol was experimentally determined. Extensive computational studies on the likely reaction pathway were subsequently carried out. A variety of DFT methods were assessed, ranging from dispersion-free methods to those that better account for dispersion (M06L, ωB97XD, D3-DFT). While significant discrepancies in the quantitative prediction of activation barriers were observed, all computational methods consistently predicted the analogous qualitative reactivity that is in agreement with all spectroscopic and reactivity data collected. Overall, these data provide compelling additional support of the direct reactivity of Pd(I)-Pd(I) with aryl iodides.
- Kalvet, Indrek,Bonney, Karl J.,Schoenebeck, Franziska
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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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- Synthesis of pharmaceutical drugs from cardanol derived from cashew nut shell liquid
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Cardanol from cashew nut shell liquid extracted from cashew nut shells was successfully converted into various useful pharmaceutical drugs, such as norfenefrine, rac-phenylephrine, etilefrine and fenoprofene. 3-Vinylphenol, the key intermediate for the synthesis of these drugs, was synthesised from cardanol by ethenolysis to 3-non-8-enylphenol followed by isomerising ethenolysis. The metathesis reaction worked very well using DCM, but the greener solvent, 2-methyl tetrahydrofuran, also gave very similar results. Hydroxyamination of 3-vinylphenol with an iron porphyrin catalyst afforded norfenefrine in over 70% yield. Methylation and ethylation of norfenefrine afforded rac-phenylephrine and etilefrine respectively. A sequence of C-O coupling, isomerising metathesis and selective methoxycarbonylation afforded fenoprofene in good yield. A comparison of the routes described in this paper with some standard literature syntheses of 3-vinylphenol and of the drug molecules shows significant environmental advantages in terms of precursors, yields, number of steps, conditions and the use of catalysts. The Atom Economy of our processes is generally similar or significantly superior to those of the literature processes mainly because the side products produced during synthesis of 3-vinylphenol (1-octeme, 1,4-cyclohexadiene and propene) are easily separable and of commercial value, especially as they are bio-derived. The E Factor for the production of 2-vinylphenol by our process is also very low compared with those of previously reported syntheses.
- Shi, Yiping,Kamer, Paul C. J.,Cole-Hamilton, David J.
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supporting information
p. 1043 - 1053
(2019/03/12)
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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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- 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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- Ex situ generation of stoichiometric HCN and its application in the Pd-catalysed cyanation of aryl bromides: Evidence for a transmetallation step between two oxidative addition Pd-complexes
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A protocol for the Pd-catalysed cyanation of aryl bromides using near stoichiometric and gaseous hydrogen cyanide is reported for the first time. A two-chamber reactor was adopted for the safe liberation of ex situ generated HCN in a closed environment, which proved highly efficient in the Ni-catalysed hydrocyanation as the test reaction. Subsequently, this setup was exploited for converting a range of aryl and heteroaryl bromides (28 examples) directly into the corresponding benzonitriles in high yields, without the need for cyanide salts. Cyanation was achieved employing the Pd(0) precatalyst, P(tBu)3-Pd-G3 and a weak base, potassium acetate, in a dioxane-water solvent mixture. The methodology was also suitable for the synthesis of 13C-labelled benzonitriles with ex situ generated 13C-hydrogen cyanide. Stoichiometric studies with the metal complexes were undertaken to delineate the mechanism for this catalytic transformation. Treatment of Pd(P(tBu)3)2 with H13CN in THF provided two Pd-hydride complexes, (P(tBu)3)2Pd(H)(13CN), and [(P(tBu)3)Pd(H)]2Pd(13CN)4, both of which were isolated and characterised by NMR spectroscopy and X-ray crystal structure analysis. When the same reaction was performed in a THF : water mixture in the presence of KOAc, only (P(tBu)3)2Pd(H)(13CN) was formed. Subjection of this cyano hydride metal complex with the oxidative addition complex (P(tBu)3)Pd(Ph)(Br) in a 1 : 1 ratio in THF led to a transmetallation step with the formation of (P(tBu)3)2Pd(H)(Br) and 13C-benzonitrile from a reductive elimination step. These experiments suggest the possibility of a catalytic cycle involving initially the formation of two Pd(ii)-species from the oxidative addition of LnPd(0) into HCN and an aryl bromide followed by a transmetallation step to LnPd(Ar)(CN) and LnPd(H)(Br), which both reductively eliminate, the latter in the presence of KOAc, to generate the benzonitrile and LnPd(0).
- Kristensen, Steffan K.,Eikeland, Espen Z.,Taarning, Esben,Lindhardt, Anders T.,Skrydstrup, Troels
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p. 8094 - 8105
(2017/11/27)
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- Dinuclear Pd(i) complexes - Solely precatalysts? Demonstration of direct reactivity of a Pd(i) dimer with an aryl iodide
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This report provides experimental, computational and spectroscopic data in support of the direct reactivity of a Pd(i) dimer with an aryl iodide, resulting in Br/I halogen exchange between the complex and the aryl iodide. The reactivity could not be achieved through analogous Pd(0) conditions, demonstrating the distinct reactivities at such multiple Pd-sites. Computational studies support that the direct oxidative addition to ArI by the dinuclear metal complex is energetically feasible.
- Bonney, Karl J.,Proutiere, Fabien,Schoenebeck, Franziska
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p. 4434 - 4439
(2013/11/19)
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- PROCESS FOR THE PREPARATION OF PALLADIUM (I) TRI-TERT-BUTYLPHOSPHINE BROMIDE DIMER
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The present invention provides a process for the preparation of a complex of formula (I) comprising the steps of: (a) mixing Pd(diolefin)Br2 and tBu3P in a solvent; and (b) adding an alkali hydroxide to form the complex of formula (I).
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Page/Page column 4
(2011/02/24)
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- Reactivity studies of [Pd2(μ-X)2(PBut3)2] (X = Br, I) with CNR (R = 2,6-dimethylphenyl), H2 and alkynes
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Improved syntheses for the dimeric compounds [Pd2(μ-X)2(PBut3)2] (X = Br, I) have been developed and the X-ray crystal structure for the dimer with X = 1 is reported. The reactions of these dimers with CNR (R = 2,6-dimethylphenyl), H2 and a series of terminal and substituted alkynes are also reported. The dimer with X = Br is an initiator for the catalytic polymerisation of phenylacetylene. The product of the dimers with disubstituted alkynes results in the synthesis of trimeric species with formula [Pd3(μ-X){ν2-C4(CO2R) 4}2][PBut3)Me]2 (X = Br, I; R = Me, Et). The X-ray crystal structure of one of these compounds (when R = Et and X = I) is presented, demonstrating that the palladium dimers assist the C-C coupling of the alkynes.
- Durà-Vilà, Víctor,P. Mingos, D. Michael,Vilar, Ramón,White, Andrew J.P.,Williams, David J.
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p. 198 - 205
(2007/10/03)
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