Effects of bases, ligands, and additives

the regioselectivity of the Heck reactions with unsymmetrical aikenes can favorably be manipulated by appropriate variations of the catalyst cocktail [123] for example, the best conditions for the couphng of bromobenzene with t-butyl acrylate in the presence of Pd[(o-Tol)3P]2Cl2 (Tol, tolyl) were found to be with potassium carbonate in ethanol at 80 °C. This is unusual for this kind of catalyst system. The active catalyst is actually believed to be nanodispersed palladium metal generated by reduction of the catalyst precursor by ethanol under basic conditions (Table 8.5). 

3) Carried out by researchers at Cynora GmbH, Eggenstein-Leopoldshafen, Germany. 

Acid-sensitive alkenyl triflates Anti elimination Spirocyclization 

Excellent base, increase in enantiomeric excess and/or yields [94a] [174[ 

increase in enantiomeric excess with Ag3P04 [177] 

the regioselectivity of Heck reactions with unsymmetrical alkenes can be manipulated favorably by appropriate variations of the catalyst cocktail . The impact of silver(I) and thallium(I) salts [97] on Pd-catalyzed reactions extends beyond just increasing 

Nitrile SiR3 Sn P [17b] (13), [73] (HIZp) 182] (I), [120] (ip) (elimination of SiR3 possible) Stille coupling occurs (see Chapter 4)  

A major achievement was the discovery that Heck reactions are greatly accelerated in the presence of phase-transfer catalysts using quaternary ammonium salts and solid bases [ Jeffery conditions Pd(OAc)2, MHCO, (M = K, Na), nBu4NX (X = Br, Cl), DMSO or DMF] [100]. Under these conditions, iodoarenes and iodoalkenes can be coupled to alkenes 

The effects of various reagents, additives, and other conditions on the Heck reaction are summarized in Table 3-5. 

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More recent approaches to the effects of the ligands on the redox activity of metal complexes are based upon the assumption that the electrode potential of a redox change involving a metal complex is determined by the additivity of the electronic contribution of all the ligands linked to the metal centre, or to the overall balance between the c-donor and the 7r-acceptor capability of each ligand.3 In particular two ligand electrochemical parameters have gained popularity ... 

As the follow up to our studies in connection to the development of Ti-cat-alyzed cyanide additions to meso epoxides [4], we developed the corresponding catalytic enantioselective additions to imines [5]. A representative example is shown in Scheme 1 chiral non-racemic products maybe readily converted to the derived cx-amino acids (not available through catalytic asymmetric hydrogenation methods). In these studies, we further developed and utilized the positional optimization approach effected by examination of parallel libraries of amino acid-based chiral ligands (e.g., 1 and 2). Thus, the facile modularity of these ligands and their ease of synthesis were further exploited towards the development of a new catalytic enantioselective method that delivers various ar-... 

The reaction which is accelerated by the presence of water can be carried out in water when a 2/3-cyclodextrin-[Rh(OH)(cod)]2,943,944 [Rh(cod)Cl]2/TPPTS,945 or amphiphilic resin-supported rhodium(i) complex was used.946 It was also reported that potassium alkenyl and aryltrifluoroborates [RBF3]K undergo similar addition to enones in the presence of an Rh(i) catalyst.935,947,948 The cationic rhodium(i) complexes such as [Rh(cod)]BF4, [Rh(cod)(CH3CN)2]BF4, or its combination with a diphosphine ligand (dppp or dppb) efficiently catalyzed the reaction. The neutral complexes, generated in situ from Rh(acac)(GH2=GH2)2, or Rh(acac)(coe)2, and dppp or dppb, were also effective. The effects of catalysts, solvents, and bases,949 and the mechanism of catalytic cycle950 have been studied in detail. 

Nature of Cooperative Effects in Mixed-Ligand Thiocyanate Complexes Various explanations have been put forward to account for the effects of neutral ligands on the nature of the metal-thiocyanate bond TT-bonding, symbiosis, and antisymbiosis of hard and soft acids and bases as well as steric effects have all been discussed. In addition, directional... 

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