Bimetallic catalysis.  A new method for the activation of chloroarenes toward palladium-catalyzed coupling with olefins

Bozell, Joseph J.; Vogt, C. E.

doi:10.1021/ja00216a053

Cited by 84 publications

(30 citation statements)

References 3 publications

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“…This may be due to poor solubility of L F under the conditions used. The yield obtained with the chlorinated derivative is in the range of those reported for similar coupling reactions [27]. The IR spectrum of L G presents an intense CO stretching band at 1636 cm À1 arising from the amide group, a value close to that obtained for the CO groups of L B .…”

supporting

confidence: 79%

Self-Assembled Triple-Stranded Lanthanide Dimetallic Helicates with a Ditopic Ligand Derived from Bis(benzimidazole)pyridine and Featuring an (4-Isothiocyanatophenyl)ethynyl Substituent

Tripier¹,

Hollenstein²,

Elhabiri³

et al. 2002

HCA

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Bis(2-{6-(diethylcarbamoyl)-4-[(4-isothiocyanatophenyl)ethynyl]pyridin-2'-yl}-1-ethylbenzimidazol-5-yl)-methane (L G ) reacts with trivalent lanthanide ions in acetonitrile to yield triple-stranded dimetallic helicates [Ln 2 (L G ) 3 ] 6 . 1 H-NMR Data point to the helicates being the only species formed under stoichiometric conditions and having a time-averaged D 3 symmetry on the NMR time scale. The photophysical properties of L G and its helicates are discussed with respect to the closely related ligands L B , L E , and their complexes, two ligands devoid of the isothiocyanatophenylethynyl substituent. The quantum yield of the ligand fluorescence is three times smaller compared to L E , while that of the Eu III -centered luminescence (1.1%) is three times larger. On the other hand, the luminescence of Tb III is not sensitized by L G . This is explained in terms of energy differences between the singlet and triplet states on one hand, and between the 0-phonon transition of the triplet state and the excited metal ion states on the other. This work demonstrates that bulky substituents in the 4-position of the pyridine ring do not prevent the formation of triple-stranded helicates, opening the way for luminescent probes that can easily be coupled to biological materials.Introduction. ± Supramolecular functional architectures containing lanthanide ions receive a sustained interest, especially in the field of medicine, because the optical and magnetic properties arising from the shielded 4f electronic configurations are easily traceable, therefore, providing suitable diagnostic [1] [2], therapeutic [3] [4], or analytical tools [5] [6]. One challenge associated with the development of such molecular edifices lies in the accurate control of the Ln III inner coordination sphere in order to reach large thermodynamic stability and kinetic inertness without altering the specific properties of the metal ion. In the particular case of photophysical properties, additional features have to be incorporated in the receptor in order to achieve efficient sensitization of the luminescent lanthanide ions [7]. In recent years, we have focused part of our research efforts on the design of segmental ligands featuring aromatic tridentate and/or bidentate coordination units and coded for the self-assembly of 4f-4f [8] or 4f-3d [9] [10] dimetallic helicates. We have shown that the coordination sphere of the Ln III ions can be controlled by semirigid aromatic tridentate ligands such as bis(benzimidazole)pyridines [11] [12]. The covalent connection of two such units leads, for example, to the formation of ditopic ligand L A (Scheme 1), forming stable dimetallic helicates [Ln 2 (L A ) 3 ] 6 in MeCN in which the ligand strands are wrapped around two 9-coordinate Ln III ions with tricapped trigonal prismatic coordination geometry [13] [14]. The self-assembly process results in the formation of protective

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supporting

confidence: 79%

Self-Assembled Triple-Stranded Lanthanide Dimetallic Helicates with a Ditopic Ligand Derived from Bis(benzimidazole)pyridine and Featuring an (4-Isothiocyanatophenyl)ethynyl Substituent

Tripier¹,

Hollenstein²,

Elhabiri³

et al. 2002

HCA

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“…Nickel(ii) dichloride has been reported to catalyze halide exchanges on carbon atoms suggesting the use of a bimetallic catalyst system with palladacycle 1. [18] Despite the promising literature report neither higher yields were observed nor was bromobenzene detected in the reaction with 1/NiCl 2 .…”

Section: Vinylation Of Chlorobenzenementioning

confidence: 93%

“…Chloroarenes can be activated by reaction with hexacarbonylchromium, which reduces the electron density on the aromatic system, [17] or by addition of a nickel(ii ) cocatalyst in the presence of sodium iodide, which was reported to transform the chloroarene into more reactive iodoarenes in situ. [18] We present here a completely different approach to activate chloroarenes. It has long been known that the Heck reaction is performed best in polar solvents such as dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), and 1,4-dioxane.…”

Section: Introductionmentioning

confidence: 99%

Nonaqueous Ionic Liquids: Superior Reaction Media for the Catalytic Heck-Vinylation of Chloroarenes

2000

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Nonaqueous ionic liquids, that is molten salts, constitute an activating and stabilizing noninnocent solvent for the palladium-catalyzed Heck-vinylation of all types of aryl halides. Especially with chloroarenes an improved activity and stability of almost any known catalyst system is observed as compared to conventional, molecular solvents (e.g. dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), or dioxane). Thus, even catalytic amounts of ligand-free PdCl2 yield stilbene from technically interesting chlorobenzene and styrene in high yield (turnover number (TON) = 18) without the need for further promoting salt additives such as tetraphenylphosphonium chloride. The scope of the new reaction medium is outlined for the first time for the vinylation of various aryl halides using different mono- and disubstituted olefins as well as a variety of known palladium(0) and palladium(II) catalyst systems. Furthermore, a novel means of catalyst recycling is presented and its scope is evaluated.

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“…To increase the reaction rates with aryl chlorides, nickel bromide/sodium iodide additives have been employed successfully. [169] Furthermore, the use of basic ligands, which are anticipated to facilitate oxidative addition, has largely been successful. [54], [170] Littke and Fu very recently devised a protocol that allows conversion of electron-rich aryl chlorides in the Heck reaction ( Table 2, entry 13).…”

Section: Bxiii Aryl Chlorides As Starting Materialsmentioning

confidence: 99%

Intermolecular Heck Reaction: Scope, Mechanism, and Other Fundamental Aspects of the Intermolecular Heck Reaction

Larhed

Hallberg

Handbook of Organopalladium Chemistry for Organic Synthesis

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Bimetallic catalysis. A new method for the activation of chloroarenes toward palladium-catalyzed coupling with olefins

Cited by 84 publications

References 3 publications

Self-Assembled Triple-Stranded Lanthanide Dimetallic Helicates with a Ditopic Ligand Derived from Bis(benzimidazole)pyridine and Featuring an (4-Isothiocyanatophenyl)ethynyl Substituent

Self-Assembled Triple-Stranded Lanthanide Dimetallic Helicates with a Ditopic Ligand Derived from Bis(benzimidazole)pyridine and Featuring an (4-Isothiocyanatophenyl)ethynyl Substituent

Nonaqueous Ionic Liquids: Superior Reaction Media for the Catalytic Heck-Vinylation of Chloroarenes

Intermolecular Heck Reaction: Scope, Mechanism, and Other Fundamental Aspects of the Intermolecular Heck Reaction

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