- Rationally designed pincer-type heck catalysts bearing aminophosphine substituents: PdIV intermediates and palladium nanoparticles
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The aminophosphine-based pincer complexes [C6H 3-2,6-{XP(piperidinyl)2}2Pd(Cl)] (X = NH 1; X = O 2) are readily prepared from cheap starting materials by sequential addition of 1,1′,1″-phosphinetriyltripiperidine and 1,3-diaminobenzene or resorcinol to solutions of [Pd(cod)(Cl)2] (cod = cyclooctadiene) in toluene under N2 in "one pot". Compounds 1 and 2 proved to be excellent Heck catalysts and allow the quantitative coupling of several electronically deactivated and sterically hindered aryl bromides with various olefins as coupling partners at 140°C within very short reaction times and low catalyst loadings. Increased reaction temperatures also enable the efficient coupling of olefins with electronically deactivated and sterically hindered aryl chlorides in the presence of only 0.01 mol% of catalyst. The mechanistic studies performed rule out that homogeneous Pd0 complexes are the catalytically active forms of 1 and 2. On the other hand, the involvement of palladium nanoparticles in the catalytic cycle received strong experimental support. Even though pincer-type PdIV intermediates derived from 1 (and 2) are not involved in the catalytic cycle of the Heck reaction, their general existence as reactive intermediates (for example, in other reactions) cannot be excluded. On the contrary, they were shown to be thermally accessible. Compounds 1 and 2 show a smooth halide exchange with bromobenzene to yield their bromo derivatives in DMF at 100°C. Experimental observations revealed that the halide exchange most probably proceeded via pincer-type PdIV intermediates. DFT calculations support this hypothesis and indicated that aminophosphine-based pincer-type PdIV intermediates are generally to be considered as reactive intermediates in reactions with aryl halides performed at elevated temperatures.
- Bolliger, Jeanne L.,Blacque, Olivier,Frech, Christian M.
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experimental part
p. 7969 - 7977
(2009/09/08)
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- Oxygen and base-free oxidative heck reactions of arylboronic acids with olefins
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A mild and efficient protocol for palladium-catalyzed oxidative Heck reactions of arylboronic acids with both electron-rich and -deficient olefins is described. In contrast to the normal oxidative Heck coupling, this new method works in the absence of a base, oxygen, or other external oxidants. With a wide variety of substrates tolerated, the method broadens the scope of palladium-catalyzed coupling reactions. Copyright
- Ruan, Jiwu,Li, Xinming,Saidi, Ourida,Xiao, Jianliang
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p. 2424 - 2425
(2008/09/18)
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- Selective terminal heck arylation of vinyl ethers with aryl chlorides: A combined experimental-computational approach including synthesis of betaxolol
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Reaction conditions have been developed for palladium-catalyzed terminal (β-) arylation of acyclic vinyl ethers with high regioselectivity using inexpensive aryl chlorides as starting materials and the P(t-Bu)3 releasing preligand [(t-Bu3)PH]BF4 as the key additive. This swift and straightforward protocol exploits non-inert conditions and controlled microwave heating to minimize handling and processing times and uses aqueous DMF or environmentally friendly PEG-200 as the reaction medium. The selectivity for linear β-product in PEG-200 is slightly higher than in aqueous DMF. DFT calculations support a ligand-driven selectivity rationale, where the electronic and steric influence of bulky P(t-Bu)3 ligand provides improved β-selectivity in the essential insertion step also with electron-rich aryl chlorides. A tentative computational rationalization of the improved selectivity in non-methylated PEG is discussed. Finally the synthetic methodology was used to provide efficient access to linear p-[2- (cyclopropylmethoxy)-ethyl] phenol from p-nitrophenyl chloride, a key intermediate in the synthesis of the β-adrenergic blocking agent Betaxolol.
- Datta, Gopal K.,Von Schenck, Henrik,Hallberg, Anders,Larhed, Mats
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p. 3896 - 3903
(2007/10/03)
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- A new efficient tetraphosphine/palladium catalyst for the Heck reaction of aryl halides with styrene or vinylether derivatives
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cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C 3H5)]2 system efficiently catalyses the Heck reaction of aryl halides with styrene and vinylether derivatives. High turnover numbers can be obtained for the reaction of several aryl halides with styrene and styrene derivatives. Lower turnover numbers have been observed in the presence of vinylethers.
- Feuerstein, Marie,Doucet, Henri,Santelli, Maurice
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p. 2191 - 2194
(2007/10/03)
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- Mild and general cross-coupling of (α-alkoxyvinyl)silanols and -silyl hydrides
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(Matrix presented) (α-Alkoxyvinyl)silanols and (α-alkoxyvinyl)silyl hydrides are efficiently converted to aryl vinyl ethers by a palladium(0)-catalyzed cross-coupling reaction with aryl halides in the presence of tetrabutylammonium fluoride or hydroxide.
- Denmark, Scott E.,Neuville, Luc
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p. 3221 - 3224
(2007/10/03)
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- α-Regioselectivity in Palladium-Catalyzed Arylation of Acyclic Enol Ethers
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Regioselective α-arylation of acyclic enol ethers by aryl trifluoromethanesulfonates, aryl bromide, aryl iodides, and aroyl chlorides is described.The outcome of the reaction proved to be dependent from the relationship between ligand and counterion in the oxidative complex.
- Cabri, Walter,Candiani, Ilaria,Bedeschi, Angelo,Penco, Sergio,Santi, Roberto
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p. 1481 - 1486
(2007/10/02)
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