Cross aryl chlorides

Similarly, Kappe and Walla showed that (2-pyridinyl)zinc chloride can be quickly cross-coupled with electron-deficient aryl chlorides using Pd2(dba)3/ t-Bu3P.HBp4 as a precatalyst in THF at 175 °C for 10 min (Scheme 2) [21]. hi a reverse approach, 4-chloropyridine rapidly reacted with (4-methoxyphenyl) zinc chloride (Scheme 2). 

FuNn iONAL Group Tolerance of PdildbrO VIMes.HCI Catalyzed Suzuki Cross-Coupling Reactions of Aryl Chlorides with Phenyi.boronic Acid Derivatives... 

In summary, these results demonstrate that air-stable POPd, POPdl and POPd2 complexes can be directly employed to mediate the rate-limiting oxidative addition of unactivated aryl chlorides in the presence of bases, and that such processes can be incorporated into efficient catalytic cycles for a variety of cross-coupling reactions. Noteworthy are the efficiency for unactivated aryl chlorides simplicity of use, low cost, air- and moisture-stability, and ready accessibility of these complexes. Additional applications of these air-stable palladium complexes for catalysis are currently under investigation. 

The low catalytic reactivity of aryl chlorides in cross-coupling reactions is usually attributed to their reluctance towards oxidative addition to Pd(0). For a discussion, see V. V. Grushin and H. Alper, Chem. Rev., 94, 1047-1062 (1994), and reference therein. 

Various PX-ligands showed high efficiency in catalyzing cross-coupling reactions of aryl chlorides. The PO-ligand (L5) is used in the system (1% Pd(dba)2-3L, CsF, toluene, reflux).391... 

The cross-coupling of organotin compounds with aryl chlorides can be realized with either PCy3 (Pd(OAc)2/PCy3, K3P04, dioxane, reflux)402 or P Bu3 (Pd2dba3/P/Bu3, Pd L=l 2, CsF,... 

Commercially available Pd(PtBu3)2 is a unique, air-stable 14e Pd° complex, an excellent catalyst for cross-coupling reactions of aryl chlorides. The ability of P Bu3 to stabilize such a coordin-atively unsaturated, extremely reactive, and yet easily manageable form of Pd° is one of the most amazing and fruitful recent findings in Pd-based catalysis. The cross-coupling of arylzinc reagents with aryl or vinyl chlorides can be readily accomplished with as little as 0.03% of this catalyst. Both electron-rich and sterically hindered substrates are welcome in this protocol.404... 

The cross-coupling of aryl or alkenylsilanes with aryl chlorides bearing electron-withdrawing substituents has been reported to require trialkylphosphine (P Pr3) ligands.407... 

A similarly high performance has been reported for oxime-derived (125) and benzylsulfide-derived (126) palladacycles.438 These precatalysts are effective in the cross-coupling of arylboronic acids,438,439 organotin compounds,440 and terminal acetylenes441 with aryl iodides and bromides, and of activated aryl chlorides. SC-palladacycles can effect the Suzuki-Miyaura reaction even at room temperature. 

Simple Pd salts and complexes which contain neither phosphines nor any other deliberately added ligands are well known to provide catalytic activity in cross-coupling reactions. Such catalytic systems (often referred to as ligand-free catalysts ) often require the use of water as a component of the reaction medium.17 In the majority of cases such systems are applicable to electrophiles easily undergoing the oxidative addition (aryl iodides and activated bromides), although there are examples of effective reactions with unactivated substrates (electron-rich aiyl bromides, and some aryl chlorides).18,470... 

Besides the advantage of recyclability, reactions in ionic liquids are generally faster and are run under milder conditions than reactions with conventional solvents. Further activation may come from ultrasonic agitation.520 Since the majority of ionic liquids used are imidazolium salts, the effect of these solvents can be at least partly attributed to the in situ formation of carbene complexes (Section 9.6.3.4.10).521 Cross-coupling of ArB(OH)2 can also be efficiently performed in ionic liquids based on long-chain tetraalkylphosphonium salts, in which case aryl bromides and some aryl chlorides can be processed in the presence of the trivial ligand PPh3.522... 

Activated aryl chlorides, which are close in reactivity to unactivated aryl bromides, underwent reaction with the original P(o-tol)3-ligated catalyst.58 Nickel complexes, which catalyze classic C—C bond-forming cross-couplings of aryl chlorides, 9-64 also catalyzed aminations of aryl chlorides under mild conditions.65,66 However, the nickel-catalyzed chemistry generally occurred with lower turnover numbers and with a narrower substrate scope than the most efficient palladium-catalyzed reactions. 

Scheme 35 Cross-coupling reaction of azabismocines with aryl chlorides...

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