Halides, aryl, arylation metal catalyzed reaction with

Kappe and Stadler have invented a microwave protocol enabling quick access to triaryl phosphines via coupling of diphenylphosphine with aryl halides and triflates [107]. Because of the value of phosphine ligands in assorted transition metal-catalyzed reactions, convenient routes for their pro-... 

Kappe and Stadler have developed an MW procedure for rapid production of triaryl phosphines by coupling diphenylphospine with aryl halides and triflates [134]. Taking into account the importance of phosphine ligands in a variety of transition metal-catalyzed reactions, convenient procedures for their production is valuable. Both homogeneous Pd-Ni and heterogeneous Pd catalysts were explored and the more unusual substrate phenyl triflate could also be coupled swiftly by use of nickel catalysis (Scheme 15.68). Couplings with other aryl halides proceeded in 26-85% yield after 3-30 min microwave irradiation at 180-200 °C. 

As with other transition metal-catalyzed reactions (Ziegler-Natta polymerization of alkenes, olefin metathesis), the mechanism of the Heck reaction is complicated. In brief, the species that reacts with the aryl halide is I Pd, where L is a ligand such as tiiphenylphosphine. By a process known as oxidative addition, palladium inserts into the carbon-halogen bond of the aryl halide. 

A year later, Blacque and Freeh [24c] performed comprehensive DFT studies on the thermal feasibility of Pd /Pd cycles in pincer-catalyzed Heck reactions and convincingly showed that pincer-type Pd intermediates are indeed thermally accessible with aryl bromides at elevated temperatures and hence are generally to be considered as reactive intermediates in pincer-catalyzed reactions with aryl halides at elevated reaction temperatures (for details, see below). Shortly thereafter, Vicente and coworkers [41] published the first oxidative addition of an aryl iodide on the metal center of a paUadium(II) pincer complex 2-iodobenzoic acid was found to smoothly undergo oxidative addition on the paLladium(II) center of [(ONC)Pd(OAc)]... 

The reaction took place either via the ArSsl or via the AtSn2 mechanism (see Scheme 14.1, paths h,c), and occurred successfully via the first mechanism when using aryl hahdes or esters with electron-donating substituents. Among halides, both aryl chlorides and fluorides underwent photosubstitution when irradiated in an aqueous MeCN solution of KCN (Scheme 14.10, left part) [59]. It should be noted that, in transition metal-catalyzed reactions, the substitution of a chloro- by a cyano-group occurs only under relatively harsh reaction conditions, whereas such a process does not take place at all with aryl fluorides [57]. In the case of aryl esters the photoinduced cyanation occurred conveniently. As esters are easily... 

This section describes selected arylations of phosphorus, sulfur, and halide nucleophiles under metal-free and metal-catalyzed conditions. Arylations of other nucleophiles, e.g., selenium and tellurium, have been reviewed previously [4]. Aryl phosphonates [ArPO(OR)2] can be synthesized by arylation of phosphite anions with diaryliodonium salts and NaH in DMF at 70-80 °C [158]. A copper-catalyzed arylation of various phosphorous nucleophiles, e.g., diarylphosphine oxides and //-phosphonates, was recently reported to proceed at room temperature. The observed chemoselectivity with unsymmetric salts was opposite to the general trend in metal-catalyzed reactions (see Sect. 2.1), which was explained by a radical mechanism [159]. 

The title compound is commonly used as a base in transition metal-catalyzed reactions. Because these reactions involve multiple elementary steps, KOAc may act as a base in many different ways, and the precise mechanism of deprotonation may not always be known. A study on the influence of base on the palladium-black-catalyzed methoxycarbonylation of aryl iodides identified potassium acetate as a suitable base. This method has been widely adopted, and both sodium and potassium acetate are commonly used (e.g., eq 29). Alternatively, the acetate base may directly remove a proton from a metal center. For example, the Heck reaction (e.g., eq 30) generates a palladium(II) complex that bears hydride and halide ligands, and generation of the catalytically active palladium(0) corr5>lex requires deprotonation with stoichiometric base (eq 31). 

Classical synthetic routes to arylsilanes consist of the reaction of aryl Grignard or aryllithium compounds with silicon electrophiles and many of these routes are presented in the various reviews. Recently, metal-catalyzed reactions of aryl halides with silanes have proven to be useful routes to functionalized arylsilanes. Alami reported the first platinum-catalyzed selective silylation of aryl iodides and bromides 9 having electron-withdrawing group to give arylsilanes 10 with triethylsilane and sodium... 

The catalytic activity, however, is generally associated with leaching of the metal into solution, the reaction being most likely catalyzed by soluble active Pd species. Palladium leaching is generally caused by oxidative attack of the aryl halide on the metal nanoparticles, giving catalyt-ically active aryl halide Pd(II) species in solution [30]. 

As noted in Section 11.2.2, nucleophilic substitution of aromatic halides lacking activating substituents is generally difficult. It has been known for a long time that the nucleophilic substitution of aromatic halides can be catalyzed by the presence of copper metal or copper salts.137 Synthetic procedures based on this observation are used to prepare aryl nitriles by reaction of aryl bromides with Cu(I)CN. The reactions are usually carried out at elevated temperature in DMF or a similar solvent. 

There are many other transition-metal catalyzed coupling reactions that are based on organic halides in aqueous media. One example is the coupling of terminal alkyne with aryl halides, the Sonogashira coupling, which has been discussed in detail in the chapter on alkynes (Chapter 4). An example is the condensation of 2-propynyl or allyl halides with simple acetylenes in the presence of copper salts. 

Transition metal-catalyzed transformations are of major importance in synthetic organic chemistry [1], This reflects also the increasing number of domino processes starting with such a reaction. In particular, Pd-catalyzed domino transformations have seen an astounding development over the past years with the Heck reaction [2] - the Pd-catalyzed transformation of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - being used most often. This has been combined with another Heck reaction or a cross-coupling reaction [3] such as Suzuki, Stille, and Sonogashira reactions. Moreover, several examples have been published with a Tsuji-Trost reaction [lb, 4], a carbonylation, a pericyclic or an aldol reaction as the second step. 

Metal-catalyzed cross-coupling reactions of organozinc derivatives with aryl and vinyl halides 408... 

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