- Kinetic selection of Pd4L2metallocyclic and Pd6L3trigonal prismatic assemblies
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The self-assembly of Pd4L2metallocylcic and Pd6L3trigonal prismatic assemblies are described. The selection of one species over the other has been achieved by careful choice of ancilliary ligands, which switch the dynamics of the Pd-pyridine bonds such that a highly unusual and distorted smaller assembly can be kinetically trappeden routeto the more energetically favourable larger species. Both assemblies provide promise as easy to access multicavity reaction vessels.
- O’Connor, Helen M.,Coletta, Marco,Etcheverry-Berríos, Alvaro,Nichol, Gary S.,Brechin, Euan K.,Lusby, Paul J.
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- Combining the reactivity properties of pcy3 and P t Bu3 into a single ligand, P(i Pr)(t Bu)2. reaction via mono- or bisphosphine palladium(0) centers and palladium(i) dimer formation
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Trialkylphosphine ligands are ubiquitous in catalysis. Via modulation of the steric bulk of these ligands, two central aspects that dictate reactivity and selectivity in catalysis can be controlled: i.e., the coordination sphere and favored oxidation stat
- Proutiere, Fabien,Lyngvi, Eirik,Aufiero, Marialuisa,Sanhueza, Italo A.,Schoenebeck, Franziska
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- Preparation of (Chloromethyl)palladium(II) Derivatives from Complexes of Palladium Dichloride by Reaction with Diazomethane or Bis(chloromethyl)-mercury
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Treatment, with diazomethane, of a range of palladium dichloride and dibromide complexes containing chelaing ligands has been examined.With all but one, the formation of a mono(halogenomethyl) product was observed.The methylene insertion products from complexes of palladium dichloride are relatively stable if at least one olefin or phosphine ligand is present, but with bis-amine or -sulphide ligands the insertion products could not be isolated.However, all of the insertion products showed at least some tendency to revert to the starting dichloro complexes by loss of the methylene moiety.Products of insertion into a Pd-Br bond are less readily formed than those of the corresponding chloride and the resulting bromomethyl derivatives are less stable than their chloromethyl analogues.Chloromethyl derivatives were also prepared from the dichloride by treatment with bis(chloromethyl)mercury (only one of the two chloromethyl groups is transfered) or from a performed chloromethyl complex by ligand exchange.
- McCrindle, Robert,Arsenault, Gilles J.,Farwaha, Rajeev,McAlees, Alan J.,Sneddon, David W.
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- Synthesis of (MeCN)2Pd(CF3)OTs, a general precursor to palladium(II) trifluoromethyl complexes LPd(CF3)X
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In palladium-catalyzed aryl-trifluoromethyl cross-coupling reactions, reductive elimination is often the rate-limiting step. Stoichiometric studies of reductive elimination have proved effective in evaluating the ability of various ligands to facilitate t
- King, Ryan P.,Buchwald, Stephen L.
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- Double-Decker Coordination Cages
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Bis(pyridin-3-ylmethyl) pyridine-3,5-dicarboxylate (L) possessing one internal and two terminal pyridine moieties displayed differential coordination ability when combined with suitable PdIIcomponents. The compound L acted as a bidentate chelating ligand to form mononuclear complexes when combined with cis-[Pd(tmeda)(NO3)2] or Pd(NO3)2in calculated ratios. The combination of Pd(NO3)2with L in a ratio of 3:4, however, afforded the trinuclear “double-decker” cage [(NO3)2?Pd3(L)4](NO3)4, in which L acts as a nonchelating tridentate ligand and the counter anion (i.e., NO3–) acts as template. The encapsulated NO3–can be replaced by F–, Cl–, or Br–but not by I–. The F–-encapsulated cage could not be isolated due to its reactivity, whereas the Cl–or Br–encapsulated cages could be isolated. Although anionic guests such as NO3–, Cl–, or Br–stabilized the cages, the presence of excess Cl–or Br–(not NO3–) facilitated decomplexation reactions releasing the ligand. The complexation of Pd(Y)2(Y = BF4–, PF6–, CF3SO3–, or ClO4–) with L afforded the corresponding mononuclear complexes under appropriate conditions. However, these counter anions could not act as templates for the construction of double-decker cages.
- Bandi, Sreenivasulu,Samantray, Sagarika,Chakravarthy, Rajan Deepan,Pal, Amlan K.,Hanan, Garry S.,Chand, Dillip Kumar
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- Selective hydrolysis of the unactivated peptide bond in N-acetylated L-histidylglycine catalyzed by various palladium(II) complexes: Dependence of the hydrolysis rate on the steric bulk of the catalyst
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Hydrolytic reactions between various palladium(II) complexes of the type cis-[Pd(L)(H2O)2]2+ in which L is a chelating diamine (ethylenediamine, en; 1,2-propylenediamine, 1,2-pn; N-methylethylenediamine, Meen; isobutylenediamine, ibn and N,N,N',N'-tetramethylethylenediamine, Me4en) or S,N-coordinated amino acid (S-methyl L-cysteine, MeS-L-HCys and L-methionine, L-HMet) and N-acetylated L-histidylglycine (MeCO-His-Gly), were studied by 1H NMR spectroscopy. The reactions were carried out in the pH range 2.0-2.5 and at 60°C. In all these reactions, a palladium(II) complex bound to a histidine residue effects the regioselective cleavage of the amide bond involving the carboxylic group of histidine. We found that the rate of hydrolysis decreases as the steric bulk of the palladium(II) complex increases (en > 1,2-pn > Meen > MeS-L-HCys > ibn > L-HMet > Me4en). The observed rates of hydrolytic reaction are discussed in terms of steric hindrance of the chelating diamine or sulfur-containing amino acid on the palladium(II) complexes. This study is an important step in the development of new palladium(II) complexes as artificial metallopeptidases. (C) 2000 Elsevier Science Ltd.
- Djuran, Milo? I,Milinkovi?, Sne?ana U
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- Metal-binding sites of N-acetylneuraminic acid
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Sialic acid represents a group of thirty derivates of neuraminic acid with various substituents at the amino residue and the alcoholic hydroxy groups. We analysed the behaviour of the tetracoordinated metal ions palladium(II) and silicon(IV) against the most important derivative N-acetylneuraminic acid (NANA). The molecular structures were assigned by a combined 1H, 13C and 29Si NMR-spectroscopic approach. Despite the presence of many different functional groups, the coordination chemistry of NANA with PdII follows established rules. Coordination via the N-acetyl-group - sterically impossible with PdII - was realised with SiIV. Copyright
- Illi, Sarah,Schulten, Johanna,Kluefers, Peter
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- Selective Co-Encapsulation Inside an M6L4Cage
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There is broad interest in molecular encapsulation as such systems can be utilized to stabilize guests, facilitate reactions inside a cavity, or give rise to energy-transfer processes in a confined space. Detailed understanding of encapsulation events is required to facilitate functional molecular encapsulation. In this contribution, it is demonstrated that Ir and Rh-Cp-type metal complexes can be encapsulated inside a self-assembled M6L4metallocage only in the presence of an aromatic compound as a second guest. The individual guests are not encapsulated, suggesting that only the pair of guests can fill the void of the cage. Hence, selective co-encapsulation is observed. This principle is demonstrated by co-encapsulation of a variety of combinations of metal complexes and aromatic guests, leading to several ternary complexes. These experiments demonstrate that the efficiency of formation of the ternary complexes depends on the individual components. Moreover, selective exchange of the components is possible, leading to formation of the most favorable complex. Besides the obvious size effect, a charge-transfer interaction may also contribute to this effect. Charge-transfer bands are clearly observed by UV/Vis spectrophotometry. A change in the oxidation potential of the encapsulated electron donor also leads to a shift in the charge-transfer energy bands. As expected, metal complexes with a higher oxidation potential give rise to a higher charge-transfer energy and a larger hypsochromic shift in the UV/Vis spectrum. These subtle energy differences may potentially be used to control the binding and reactivity of the complexes bound in a confined space.
- Leenders, Stefan H. A. M.,Becker, René,Kumpulainen, Tatu,de Bruin, Bas,Sawada, Tomohisa,Kato, Taito,Fujita, Makoto,Reek, Joost N. H.
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supporting information
p. 15468 - 15474
(2016/10/13)
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- An efficient method for sterically demanding Suzuki-Miyaura coupling reactions
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An efficient method for sterically demanding Suzuki-Miyaura coupling reactions has been developed with two catalysts, Pd/BI-DIME (see scheme) and Pd/phenanthrene-based ligand. The Pd/BI-DIME catalyst facilitates the syntheses of extremely hindered biaryls
- Zhao, Qing,Li, Chengxi,Senanayake, Chris H.,Tang, Wenjun
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supporting information
p. 2261 - 2265
(2013/03/28)
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- Pd complexes with trans-chelating ligands composed of two pyridyl groups and rigid π-conjugated backbone
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1,2-Bis(2-pyridylethynyl)benzene derivatives, having two pyridyl groups and π-conjugated backbone, were prepared from the 1:2 Sonogashira reaction of 1,2-diiodobenzene with 2-alkynyl pyridines. The obtained ligands react with the palladium(II) complexes such as [PdCl2(cod)] and [PdCl 2(MeCN)2] to form the complexes with the ligands coordinated in a trans-chelating bidentate mode. The ligand obtained from 1,3-diiodobenzene and 2-alkynyl pyridine bridges two Pd(II) centers, yielding a dipalladium complex. A dichloropalladium complex with the trans-chelating ligand, containing two methoxy groups in the central arylene group, promotes coupling of phenyl lithium and of phenyl acetylene to yield the respective homo-coupling products. The ligand displacement reactions of {bis(2-pyridylethynyl)benzene}palladium(II) complex with phosphine and dinitrogen ligands, such as PPh3, dppe, dppb, en, tmeda, bpy and phen, takes place smoothly to release the trans-chelating ligand.
- Jung, Miso,Suzaki, Yuji,Saito, Takashi,Shimada, Kyoichi,Osakada, Kohtaro
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p. 168 - 174
(2012/08/28)
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- Synthesis and characterization of sterically hindered thiolate Pd(II) complexes of the type [Pd(SR)2(TMEDA)]: Examination of their catalytic properties in phosphane-free Suzuki-Miyaura cross couplings
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The sterically hindered thiolate complexes [Pd(SR)2(TMEDA)] SR = SC6F5 (2), SC6F4-4-H (3), SC6H4-2-SiPh3 (4) were easily synthesized by metathetical reactions of the corresponding palladium chloro compound [Pd(Cl)2(TMEDA)] (1) and the lead salt of the corresponding thiol. The identity of the three species being unequivocally determined by single crystal X-ray diffraction techniques. The catalytic activity of the palladium species [Pd(SR)2(TMEDA)] was explored in the Suzuki-Miyaura cross coupling reactions of different p-substituted bromobenzenes.
- Basauri-Molina, Manuel,Hernández-Ortega, Simón,Toscano, Rubén A.,Valdés-Martínez, Jesús,Morales-Morales, David
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p. 1222 - 1229
(2010/08/04)
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- A new class of easily activated palladium precatalysts for facile C-N cross-coupling reactions and the low temperature oxidative addition of aryl chlorides
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A new class of one-component Pd precatalysts bearing biarylphosphine ligands is described. These precatalysts are air- and thermally stable, are easily activated under normal reaction conditions at or below room temperature, and ensure the formation of the highly active monoligated Pd(0) complex necessary for oxidative addition. The use of these precatalysts as a convenient source of LPd(0) in C-N cross-coupling reactions is explored. The reactivity that is demonstrated in this study is unprecedented in palladium chemistry. Copyright
- Biscoe, Mark R.,Fors, Brett P.,Buchwald, Stephen L.
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p. 6686 - 6687
(2008/12/22)
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- Supramolecular assemblies of cis-palladium complexes dominated by C{single bond}H?Cl interactions
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Two cis-related palladium(II) complexes [PdCl2(PPh3)(tu)] (1) and [PdCl2(tmen)] (2) {PPh3 = triphenylphosphine, tu = thiourea, tmen = N,N,N′,N′-tetramethylethylenediamine} have been synthesized and characterized by elemental analysis, IR and NMR spectroscopies, and single crystal X-ray diffraction. In 1, N{single bond}H?Cl hydrogen bonds are responsible for the formation of a dimer which connects to an adjacent one through weak C{single bond}H?Cl interactions, yielding 1D tapes. The crystal packing of compound 2 consists of zigzag ribbons of [PdCl2(tmen)] self-assembled by C{single bond}H?Cl hydrogen bonds which also holds the chains together, giving rise to a 2D layered structure.
- Moro,Watanabe,Ananias,Mauro,Netto,Lima,Ferreira,Santos
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p. 493 - 496
(2008/10/09)
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- Synthesis of new ketonyl palladium(II) and platinum(II) complexes with nitrogen-donor ligands. Crystal structure of [Pt{CH2C(O)Me}2(bpy)]
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Complexes [MCl2L2] (M = Pd, Pt; L2 = 2,2′-bipyridine (bpy) or Me2N(CH2)2NMe2 (tmeda)) react with ketones MeC(O)R (R = Me, Et) in the presence of bases (Ag2O or M′OH (M′ = Na, K)) to give the new types of ketonyl palladium(II) and platinum(II) complexes [M{CH2C-(O)R}ClL2] (M = Pd, L2 = N,N,N′,N′-tetramethylethylenediamine = tmeda; M = Pt, L2 = 2,2′-bipyridine = bpy) and [Pt{CH2C(O)R}2L2] (R = Me, Et, L2 = bpy). Oxidative addition of chloroacetone on [Pt(dba)2] in the presence of bpy also yields [Pt{CH2C(O)R}ClL2]. [Pd-{CH2C(O)Me}Cl(tmeda)] reacts with PhNHNH2 in the presence of TlOTf(OTf = CF3SO3) to give the cyclometalated complex [Pd{CH2C(Me)=NNH(Ph)}(tmeda)]OTf. The crystal structure of [Pt{CH2C(O)Me}2(bpy)] has been determined. The platinum atom is in a distorted square-planar environment. The strong trans influence of the acetonyl ligand promotes the lengthening of both Pt-N bonds (2.082(3) and 2.091(3) ?) with concomitant narrowing of the NPtN bond angle (78.89(13)°).
- Vicente, José,Abad, José Antonio,Chicote, María-Teresa,Abrisqueta, Maria-Dolores,Lorca, José-Angel,Ramírez De Arellano, M. Carmen
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p. 1564 - 1568
(2008/10/08)
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- Kinetic study of the interaction of aquated palladium (II) complexes with purine 5′-nucleoside monophosphates and ribose 5′-monophosphate in aqueous solution. Effects of steric hindrance and phosphate-induced reactivity
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The complex formation reactions of a series of complexes of the type Pd(R4en)(H2O)22+ (R4en = N-substituted ethylenediamine, R = H, Me, Et) with ribose, adenosine, inosine, and guanosine 5′-monophosphate were investigated as a function of monophosphate concentration and temperature in the pH range 4-5. In all cases the complex formation with 5′-XMP (X = R, A, I, G) occurs in two consecutive steps for which the pseudo-first-order rate constants fit the equation kobs = ka + kb[XMP]. The experiments with ribose monophosphate revealed complex formation rate constants significantly smaller than those reported before for inosine, but larger than those found for adenosine. This trend is also observed for the nucleoside monophosphates for which the rate constants follow the sequence AMP a significant transition state stabilization effect by the monophosphate group during the complex formation reactions. The systematic variation of the substituents on the en ligand decreases the formation rate constant by as much as 3 orders of magnitude in going from the unsubstituted (R = H) to the most sterically hindered species (R = Et). The complex formation reactions all proceed according to an associative substitution mechanism and are accompanied by significantly negative ΔS? values. The results are discussed in reference to data available for the corresponding nucleosides and structural information on the final reaction products reported in the literature.
- Hohmann, Heribert,Hellquist, Bj?rn,Van Eldik, Rudi
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p. 1090 - 1095
(2008/10/08)
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- Dimethyl(N,N,N′,N′-tetramethylethanediamine)palladium(II) and dimethyl[1,2-bis(dimethylphosphino)ethane]palladium(II): Syntheses, X-ray crystal structures, and thermolysis, oxidative-addition, and ligand-exchange reactions
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PdMe2(tmeda) (2a) (tmeda = N,N,N′,N′-tetramethylethanediamine) has been prepared and characterized by means of NMR spectroscopy and X-ray crystallography. Crystals of PdMe2(tmeda) are monoclinic, space group P21/n, with un
- De Graaf, Wim,Boersma, Jaap,Smeets, Wilberth J. J.,Spek, Anthony L.,Van Koten, Gerard
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p. 2907 - 2917
(2008/10/08)
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