Catalysts for cross-coupling

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... 

Organylzirconocene derivatives do not show any useful reactivity toward a,[5-unsaturated carbonyl compounds, but the reaction can be promoted by the addition of CuOTf [14], The initial version was stoichiometric in Cu [14], but a Cu-catalyzed version was subsequently developed [112,113]. Adaptation of the Ni salt + DIBAH catalysts for cross-coupling [10] to conjugate addition led to the Ni-catalyzed conjugate addition of alkenylzirconocene chlorides [16,17] (Scheme 1.25). 

Steel PG, Teasdale CWT. Polymer supported palladium A-heterocyclic carbene complexes long lived recyclable catalysts for cross coupling reactions. Tetrahedron Lett 2004 45 8977-8980. 

Kantchev EAB, O Brien CJ, Organ MG (2007) Palladium complexes of A-heterocyclic carbenes as catalysts for cross-coupling reactions - a synthetic chemist s perspective. Angew Chem Int Ed 46 2768-2813 Kerr MS, Rovis T (2004) Enantio selective synthesis of quaternary stereocenters via a catalytic asymmetric Stetter reaction. J Am Chem Soc 126 8876-8877 Kerr MS, Read de Alaniz J, Rovis T (2002) A highly enantio selective catalytic intramolecular Stetter reaction. J Am Chem Soc 124 10298-1029 Kerr MS, Read de Alaniz J, Rovis T (2005) An efficient synthesis of achiral and chiral 1,2,4-triazolium salts bench stable precursors for A-heterocyclic carbenes. J Org Chem 70 5725-5728... 

Hayashi, T., Konishi, M., Kumada, M. Dichloro[1,1 -bis(diphenylphosphino)ferrocene]palladium(ll) an effective catalyst for cross-coupling reaction of a secondary alkyl Grignard reagent with organic halides. Tetrahedron Lett. 1979,1871-1874. 

Ar-heterocycles as ligands in high-turnover palladium catalysts for cross-coupling and Heck chemistry 04MI47. 

Wu J, Zhang L, Gao K (2006) RhCl(PPh3)3/DPPF a useful and efficient catalyst for cross-coupling reactions of activated alkenyl tosylated with arylboronic acids. Eur J Org... 

Iron, cobalt and manganese are effective catalysts for cross coupling and other reactions. They were studied in the very early days of transition-metal catalysis and are now being resurrected." ... 

Upon warming, alkylpalladium complex 4 underwent P-hydride elimination to generate allylbenzene and Pd(P(t-Bu)2Me)2HBr. This process was inhibited by the presence of excess P(t-Bu)2Me, consistent with a pathway that involves initial dissociation of a phosphine [45]. Oxidative-addition adduct 4 reacted with one equivalent of o-tolylboronic acid to generate the coupling product in 94% yield in addition, it served as a competent catalyst for cross-couplings of alkyl bromides and arylboronic acids. 

Pd-N-heterocyclic carbene catalysts for cross-coupling reactions 06AA97. 

Phosphinocarbene or 2 -phosphaacetylene 4, which is in resonance with an ylide form and with a form containing phosphoms carbon triple bond, is a distillable red oil. Electronic and more importantly steric effects make these two compounds so stable. Carbene 4 adds to various electron-deficient olefins such as styrene and substituted styrenes. Bertrand et al. have made excellent use of the push-pull motif to produce the isolable carbenes 5 and 6, which are stable at low temperature in solutions of electron-donor solvents (THF (tetrahydrofuran), diethyl ether, toluene) but dimerizes in pentane solution. Some persistent carbenes are used as ancillary ligands in organometallic chemistry and in catalysis, for example, the ruthenium-based Grubbs catalyst and palladium-based catalysts for cross-coupling reactions. 

Carbon-carbon bond formation plays an essential role in chemical syntheses. In this regard, the development of transition metal-catalysed C-C bond-forming reactions has attracted much interest in recent years and titanium complexes have been found to be highly effective as catalysts for cross-couplings, hydroaminoallq lations, Barbier-type reactions and oligomerisation reactions. 

The polymeric imide could then be reacted with primary amines or ammonia to form ammonium salts for a subsequent reactions with a carboxylic acid in the presence of a coupling reagent. It could then be converted to amides or functionalized as a uranium salt for use as polymer-supported peptide coupling. In addition, the anhydride was also reacted with di(2-pyrldyl)methylamine and formed a recoverable palladium catalyst for cross-coupling reactions that could take place in water. 

Kantchev, E.A.B., O Brien, C.J. and Organ, M.G. (2007) Palladium complexes of N-heterocyclic carbenes as catalysts for cross-coupling reactions - a synthetic chemist s perspective. Angew. Chem. Int. Ed., 46, 2768-813. 

Hayashi, T., Konishi, M., Kobor, Y. et al. (1984) Dichloro[l,l -bis(diphenylphosphino) fer-rocene]paUadium(II) an elfeclive catalyst for cross-coupling of secondary and primary alkyl Grignard and alkylzinc reagents with organic halides. J. Am. Chem. Soc., 106,158 3. 

Gaertner reported an interesting recyclable iron catalyst system using imidazo-lium-derived ionic liquid 16 as the reaction medium. This liquid possesses a ferrate counteranion, which serves as a catalyst for cross-couplings between alkyl bromides and arylmagnesium bromides. As shown in Equation 5.32, the arylation of dodecyl bromide can be performed in this recyclable catalyst system, without losing significant activity even at a fifth cycle [39]. 

Hillier, A.C., Nolan, S.P. Palladium/nucleophilic carbene catalysts for cross-coupling reactions.Plat. Met. Rev. 46, 50 (2002)... 

Because analogous platinum complexes are less reactive catalysts for cross-coupling chemistry, the oxidative addition of aryl halides to platinum(O) has received less scrutiny than the oxidative addition of aryl halides to paUadium(O). Faster rates for the oxidative addition of aryl haHdes to (PPhjjjPt in the presence of AIBN under photolysis suggested that the reaction occurs, at least in part, by a radical-chain mechanism. However, the small difference between the rates in the presence and absence of this additive in the dark does not make a compelling case for a radical path. 

Examples of the various classes of ligands used with copper precursors to generate catalysts for cross coupling. Adapted from Figure 1 of reference 502. 

Many palladacycles have also been described as useful catalysts for cross-coupling and the related reactions [184-192]. However, strong evidence has been accumulated indicating that the palladacycles merely act as a reservoir of Pd(ll), which requires reduction to Pd(0) to enter into the catalytic cycle [189,190,193]. Thus, in a... 

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