The Heck reaction: mechanistic insights and novel ligands (original) (raw)
Related papers
ChemInform, 2002
A simple and efficient experimental protocol has been developed for the catalytic arylation of alkenes by the air and water stable, and phosphine-free compound PdCl 2 (SEt 2 ) 2 associated with tetrabutyl ammonium bromide. Using this catalytic protocol, aryl iodides and bromides, and electron-poor aryl chlorides are coupled with n-butylacrylate and styrene under relatively mild reaction conditions with high catalytic activity. Reaction vessel ultra-trace amounts (ppt) of this Pd precursor promotes the coupling of iodo benzene with n-butylacrylate with turnover numbers (mol product/mol Pd) up to 10 9 .
On the use of phosphine-free PdCl 2(SEt 2) 2 complex as catalyst precursor for the Heck reaction
Tetrahedron Letters, 2001
A simple and efficient experimental protocol has been developed for the catalytic arylation of alkenes by the air and water stable, and phosphine-free compound PdCl2(SEt2)2 associated with tetrabutyl ammonium bromide. Using this catalytic protocol, aryl iodides and bromides, and electron-poor aryl chlorides are coupled with n-butylacrylate and styrene under relatively mild reaction conditions with high catalytic activity. Reaction vessel ultra-trace
Recent Developments and New Perspectives in the Heck Reaction
Accounts of Chemical Research, 1995
More than two decades ago, Mizorokil and Heck2 independently discovered the palladium-catalyzed arylation and vinylation of olefins. This methodology, known worldwide as the Heck reaction (Scheme 1),3 is attractive from a synthetic point of view because high chemoselectivity and mild reaction conditions are associated with low toxicity and cost of the reagent^.^ During the past few years, the experience obtained in several palladium-based reactions helped in understanding the rules which govern the coordinationinsertion of unsaturated systems on palladium(I1) complexes. In fact, this process has a central role in determining the reaction rate, stereoselectivity, and regioselectivity of intra-and intermolecular Heck reactions, hydrosilylations, oligomerizations of olefins, and olefin-CO copolymerization^.^ The purpose of this account is to review and critically evaluate the results on the Heck reaction recently obtained by several research groups. These results can be explained on the basis of a common mechanistic hypothesis for the coordination-insertion process of unsaturated systems on palladium(I1) complexes (Scheme 2, step b). Heck Reaction Mechanism Oxidative Addition (Scheme 2, Step a). Except for the case of aryl iodides, the presence of ligands is necessary in order to effect oxidative addition of RX to the palladium(0) complex at a reasonable temperature (Scheme 2, step a).6 The catalytically active species is a 14-electron complex, LzP~(O),~ and effective ligands in the Heck reaction are monodentate3 and bidentate phosphines8 and 1 ,lo-phenanthroline de-rivative~.~ Coordination-Insertion (Scheme 2, Step b). The geometry of the complex is a central point, and
Examination of Ligand Effects in the Heck Arylation Reaction
Tetrahedron, 2000
AbstractÐThe Heck arylation reaction between aryl bromide and iodide with methyl acrylate was evaluated. A new class of ligands, R±N(CH 2 CH 2 PPh 2 ) 2 , is compared with conventional monodentate and bidentate ligands, and was found to confer greater catalyst stability. The nitrogen substituent (R) has a noticeable effect on the rate of the turnover. We believe this is the ®rst report of the application of such hemilabile ligands in Heck arylation chemistry. q
Heck reaction with heteroaryl halides in the presence of a palladium-tetraphosphine catalyst
Tetrahedron Letters, 2002
cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/ 1 2 [PdCl(C 3 H 5 )] 2 system catalyses efficiently the Heck reaction of heteroaryl halides with n-butyl acrylate, styrene, vinylpyridine and vinyl ether derivatives. High turnover numbers can be obtained for the reactions with halo pyridines, quinolines, furans or thiophenes.
Tetrahedron Letters, 2003
cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C 3 H 5 )] 2 system catalyses efficiently the Heck reaction of aryl halides with linear alkenes such as pent-1-ene, oct-1-ene or dec-1-ene. Selectivities up to 70% in favour of E-1-arylalk-1-ene isomers can be obtained. In the presence of cyclic alkenes the selectivities of the reactions strongly depends on the ring size. Addition to cyclohexene or cycloheptene led mainly to 1-arylcycloalk-3-ene derivatives. On the other hand, addition to cyclooctene led to 1-arylcycloalk-1-ene adducts.
Application of 3-aroyl-4(5)-arylimidazols as efficient ligands in Pd-catalyzed Heck reactions
TURKISH JOURNAL OF CHEMISTRY, 2014
The Heck coupling of haloarenes with various alkenes was successfully performed in the presence of 0.25 mol% PdCl 2 and 0.5 mol% biphenyl-4-yl-[4(5)-(biphenyl-4-yl)-1 H-imidazol-2-yl]ketone 2f as a ligand with Na 2 CO 3 as optimal base, in a 1:1 mixture of H 2 O/DMF as the reaction solvent at 80 • C for 8 h. Imidazole 2f was found to be an inexpensive, air-stable, easily available, and efficient ligand in the palladium-catalyzed Heck reactions of aryl iodides (76%-94%), bromides (52%-79%), and chlorides (40%-70%).
Advanced Synthesis & Catalysis
This study identifies new phosphite-oxazoline ligands that have been successfully applied in the palladiumcatalyzed intermolecular asymmetric Heck reaction. The design of the new phosphite-oxazoline ligands derives from a previous successful generation of phosphine-oxazoline ligands, by replacing the phosphine group with several πacceptor biaryl phosphite moieties. With these simple modifications, the new phosphite-based ligands, unlike previous phosphine-oxazoline, not only present a modular design with numerous potential phosphite groups available, but they are also air-stable solids, which can be made in the same number of synthetic steps as the phosphine analogues. The substitution of the phosphine by a biaryl phosphite group extended the range of substrates and triflates sources that can be coupled with regio-, enantioselectivities and activities comparable to the few best ones reported. In addition, the ligands that provided the best selectivities contained an isopropyl oxazoline moiety instead of the tert-butyl group found in the related phosphine-oxazoline ligands, which is made from a much more expensive precursor. In this paper we have also carried out kinetic studies and a Hammett plot analysis to determine the rate determining step of this system in the regime of interest. We suggest a likely explanation for the fast Heck reaction of the phosphite-oxazoline catalysts.
Inorganica Chimica Acta, 2009
Novel as well as known C,N-palladacyclic neutral complexes were tested as precatalyst in the Heck reaction between bromobenzene and styrene under aerobic conditions. The catalytic system Pd(II) complex/ K 2 CO 3 /EGME-H 2 O (EGME = ethylene glycol monomethyl ether) showed to be highly efficient. Best performances of the catalysts were achieved by controlling the amount of water: generally a H 2 O content within the 25-50% v/v range resulted in the highest conversion of the substrates into trans-stilbene. As a matter of fact, bromobenzene and styrene can be converted quantitatively using only 0.01 mol% of precatalyst with very high regioselectivity for the trans product and with a TOF of 10 000 h À1 . In the absence of water, all complexes were less efficient and differences in their activity were found, while such a differentiation disappeared when water was added.