Catalysis coupling reactions

Ni(0)-Ni(I)-Ni(II) Catalysis Coupling Reactions of Alkyl Halides with... 

Keywords Catalysis Coupling reactions Polycyclic aromatic hydrocarbons... 

To date a number of reactions have been carried out in ionic liquids [for examples, see Dell Anna et al. J Chem Soc, Chem Commun 434 2002 Nara, Harjani and Salunkhe Tetrahedron Lett 43 1127 2002 Semeril et al. J Chem Soc Chem Commun 146 2002 Buijsman, van Vuuren and Sterrenburg Org Lett 3 3785 2007]. These include Diels-Alder reactions, transition-metal mediated catalysis, e.g. Heck and Suzuki coupling reactions, and olefin metathesis reactions. An example of ionic liquid acceleration of reactions carried out on solid phase is given by Revell and Ganesan [Org Lett 4 3071 2002]. 

The first unequivocal evidence for the AE + DE mechanism came in three papers by Zollinger (1955 a-c) dealing with general base catalysis and primary kinetic hydrogen isotope effects in azo coupling reactions of various types. Three classes of reactions were identified i) reactions with no isotope effects (ArH/A D - 1.0) and no general base catalysis, ii) others with large isotope effects (k /k — 6.5) and (practically) linear base catalysis, and iii) intermediate cases with isotope effects of around 3.0 and less-than-linear base catalysis. 

The original investigations on the general base catalysis of azo coupling reactions were made with nucleophilic substrates in which the reacting carbon atom was... 

Kishimoto et al. (1974, 1981) found a general acid catalysis by protonated pyridines in coupling reactions of the 1-naphthoxide ion if weakly electrophilic diazonium ions were used. In this case it is likely that the general acid protonates the carbonyl oxygen of the o-complex, with a concerted or stepwise deprotonation at the 4-position (transition stage 12.150). 

A true intramolecular proton transfer in the second step of an azo coupling reaction was found by Snyckers and Zollinger (1970a, 1970b) in the reaction of the 8-(2 -pyridyl)-2-naphthoxide ion (with the transition state 12.151). This compound shows neither a kinetic deuterium isotope effect nor general base catalysis, in contrast to the sterically similar 8-phenyl-2-naphthoxide ion. Obviously the heterocyclic nitrogen atom is the proton acceptor. 

There are two cases in which the general base catalysis observed for an azo coupling reaction is due not to a rate-limiting proton transfer from the o-complex (Scheme 12-66) but to deprotonation of the coupling component when the species involved in the substitution is formed. These reactions are shown in Schemes 12-71 H I... 

Micellar catalysis of azo coupling reactions was first studied by Poindexter and McKay (1972). They investigated the reaction of a 4-nitrobenzenediazonium salt with 2-naphthol-6-sulfonic and 2-naphthol-3,6-disulfonic acid in the presence of sodium dodecylsulfate or hexadecyltrimethylammonium bromide. With both the anionic and cationic additives an inhibition (up to 15-fold) was observed. This result was to be expected on the basis of the principles of micellar catalysis, since the charges of the two reacting species are opposite. This is due to the fact that either of the reagents will, for electrostatic reasons, be excluded from the micelle. 

Experience in PTC with cationic catalysts showed that, in general, the most suitable compounds have symmetrical structures, are lipophilic, and have the active cationic charge centrally located or sterically shielded by substituents. For anionic catalysis sodium tetraphenylborate fulfills these conditions, but it is not stable under acidic conditions. However, certain derivatives of this compound, namely sodium tetra-kis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB, 12.162) and sodium tetrakis[3,5-bis-(l,l,l,3,3,3-hexafluoro-2-methoxy-2-propyl)phenyl]borate (HFPB) are sufficiently stable to be used as PTC catalysts for azo coupling reactions (Iwamoto et al., 1983b 1984 Nishida et al., 1984). These fluorinated tetraphenylborates were found to catalyze strongly azo coupling reactions, some of which were carried out with the corresponding diazotization in situ. 

Telomers, in Meerwein reactions 248 Tetrahydropyridazines 129 Tetraphenylborates, in phase transfer catalysis of azo coupling reactions 378 f. 

Tamao K, Miyaura N (2002) Introduction to Cross-Coupling Reactions. 219 1-9 Tanaka M (2003) Homogeneous Catalysis for H-P Bond Addition Reactions. 232 25-54 Tanner PA (2004) Spectra, Energy Levels and Energy Transfer in High Symmetry Lanthanide Compounds. 241 167-278 ten Cate MGJ, see Crego-Calama M (2005) 249 in press ten Holte P,see Zwanenburg B (2001) 216 93-124 Thiem J,see Werschkun B (2001) 215 293-325... 

From the above it is obvious that merely the magnitude of the numerical value of Fj and the shape of the plot of Fj versus ([Ac]/[I])o do not make it possible to classify induced reactions correctly. It is necessary to learn more about the mechanism of induced reactions. The schemes presented show clearly that a genuine coupled reaction can be regarded as an open-chain, and an induced catalysis as a closed-chain reaction. However, these limiting types of reactions occur only rarely. 

Transition metal-catalysed reactions have emerged as powerful tools for carbon-carbon (C-C) bond formation [1], Cross-coupling reactions (Suzuki-Miyaura, Mizoroki-Heck, Stille, etc.) are recognised to be extremely reliable, robust and versatile. However, some other catalysed arylation reactions have been studied and have been reported to be very efficient [2]. In recent years, A -heterocyclic carbenes (NHC) have been extensively studied and their use as ligands for transition-metal catalysis has allowed for the significant improvement of many reactions [3]. This chapter highlights the use of NHC-bearing complexes in those arylation reactions. 

During the past decade, NHCs have been coordinated to virtually all transition metals (TM) and studied in numerous catalytic transformations, pushing back the frontiers of catalysis. In this regard, the most salient examples are found in olefin metathesis and cross coupling reactions, and more recently in organocatalysis. 

The ratio ARH/ARj (monoalkylation/dialkylation) should depend principally on the electrophilic capability of RX. Thus it has been shown that in the case of t-butyl halides (due to the chemical and electrochemical stability of t-butyl free radical) the yield of mono alkylation is often good. Naturally, aryl sulphones may also be employed in the role of RX-type compounds. Indeed, the t-butylation of pyrene can be performed when reduced cathodically in the presence of CgHjSOjBu-t. Other alkylation reactions are also possible with sulphones possessing an ArS02 moiety bound to a tertiary carbon. In contrast, coupling reactions via redox catalysis do not occur in a good yield with primary and secondary sulphones. This is probably due to the disappearance of the mediator anion radical due to proton transfer from the acidic sulphone. 

Under all the conditions studied, addition of bare Si02-SH to Heck or Suzuki coupling reactions using a variety of bases, aryl halides and solvents resulted in complete cessation of the catalytic activity (35). These results suggest that catalysis with this precatalyst is also associated with labile palladium species that... 

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