Oxidative addition of aryl iodides

Phosphine, Amines and Alkenes as Factors Affecting the Rate of the Oxidative Addition. Amatore, Jutand et al. [29] have established that excess PPhs slows down the oxidative addition by formation of the nonreactive Pd°(PPh3)3(OAc) , thereby decreasing the concentration of the reactive Pd°(PPh3)2(OAc) by equilibrium with Pd°(PPh3)3(OAc) . 

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The first detailed study of the individual steps of the cationic pathway of the intramolecular Heck reaction was recently described by Brown (Scheme 8G.21) [46], Oxidative addition of aryl iodide 21.1 to [l,l -bis(diphenylphosphino)ferrocene](cyclooctatetraene)palladium generated 21,2. Complex 21.2 was stable at room temperature and was characterized by X-ray crystallography no interaction between the palladium center and the tethered alkene was observed in this intermediate. Treatment of 21.2 with AgOTf at -78°C removed iodide from the palladium coordination sphere, which facilitated a rapid alkene coordination and subsequent... 

Scheme 2 shows the mechanism generally accepted for the catalytic arylation of olefins with aryl iodides in the presence of a tertiary phosphine-coordinated palladium catalyst and a base (4). Oxidative addition of aryl iodide (Arl) to a Pd(0) species (A), which is most commonly generated from palladium diacetate and a tertiary phosphine ligand, forms an arylpalladium iodide complex (B). Coordination of olefin on B followed by insertion of the coordinated olefin into the Pd-Ar bond forms a a-alkylpalladium species (C), which undergoes p-hydrogen elimination reaction to give the arylation... 

Scheme 4. Oxidative addition of aryl iodides to RuilCOjii.

It is useful to explore this analogy between known alkyne systems and potential benzyne ones. For example, alkynes react with ruthenium carbonyl to form the Ru4( --alkyne)(CO)i2, which form an octahedral RU4C1 arrangement with the metal atoms in a butterfly geometry. Since the synthesis cannot be adapted to arynes, another method is needed. Oxidative addition of aryl iodides to Ru3(CO)i2 gives the aryl complexes described in Sec. 1.14.4.5. Flowever, we have... 

The oxidative addition of an aryl iodide to a zerovalent complex such as [Pd(PPh3)4] gives tra s-[Pd(Ar)I(PPh3)2] having a palladium-aryl and a palladium-iodide bond indeed, this is one of the oldest examples of oxidative addition of aryl iodide to Pd(0) complex (Eq. 1.1) [10]. 

In 2005, Sames and co-workers reported the highly selective (>50 1) C2-arylation of NH-free indoles using a rhodium complex derived from an electron-deficient phosphine as the catalyst, CsOPiv as a base, and iodoar-enes as coupling partners (Scheme 37, 05JA4996). Mechanistic studies revealed that a highly electrophilic Ar-Rh(III) complex was formed in situ through the oxidative addition of aryl iodide to Rh(I) (Scheme 38). Then the displacement of the phosphine ligand by indoles takes place, followed by... 

Although a mechanism has been proposed to rationalize the reaction that contains a several steps for the catalytic cycle, a different mechanism is proposed here. The original mechanism includes the following steps in the catalytic cycle (a) reduction of Pd(OAc)2 to Pd(0) to initiate the catalytic cycle, b) coordination of chloride to palladium, (c) oxidative addition of aryl iodide to Pd(0), d) coordination of alkyne to palladium atom and subsequent regioselective. yyn-insertion into the arylpalladium bond, (e) nitrogen displacement of the halide in the resulting vinylic palldium intermediate to form a palladacycle, and (/) reductive elimination to form indole and the regenerated Pd(0) reenters the catalytic cycle. 

The frani-ArPd(0Ac)L2 complexes are formed in the oxidative addition of aryl iodides to Pd°(PPh3)2(OAc) , generated in situ from Pd(OAc)2 + SPPhs) mixtureJ The oxidative addition proceeds again via a short-lived hve-coordinate anionic arylpalla-dinm(ll) complex in which the acetate ion borne by the palladium(O) remains ligated to the palladinm(ll) center (Scheme... 

Scheme 2.5 Intramolecular oxidative addition of aryl iodide to a Pd(ll) center.

As previously mentioned, oxidative addition of iodonium compounds to Pd(II) or Pt(II) centers provides one of the most effective pathways to M(IV) compounds. Canty [59] applied this method to the synthesis of Pt and Pd(IV) alkynyl derivatives 23 (Eq. (2.6)). To avoid decomposition of the unstable Pd(lV) complex, the reaction of the Pd(ll) complex 6 with the iodonium reagent needs to be carried out at low temperature over a long period (—SC C/l week). Szabo [60] has carried out density functional theory (DFT) calculations to model the addition of alkynyl- and aryliodonium compounds to the Pd pincer complex, and compared these processes with the oxidative addition of aryl iodides (Figure 2.2). Both alkynyl and aryl transfer... 

In 1972, Heck and Nolley [5] improved the reactions by using Pd(OAc)2 as catalyst and /2-BU3N as base (Scheme 1.6). The reactions were performed without any solvent or in A-methylpyrrolidone (NMP) at 100 °C. More importantly, they proposed for the first time a full mechanism for the catalytic reactions. On the basis of what were at that time recent studies by Fitton and coworkers and Coulson on the formation of cr-ArPdXL2 (L = PPhs X = I [6a,c], Br [6c], Cl [6b]) by oxidative addition of aryl halides to Pd L4, Heck and Nolley proposed the formation of [ArPdl] in the oxidative addition of aryl iodide to palladium metal, generated in situ by reduction of Pd(OAc)2 by the alkene. After reaction of [ArPdl] with the alkene as in Scheme 1.4a, the hydridopalladium [HPdl] decomposes to HI (quenched by the base) and palladium(O) available for another catalytic cycle [5]. 

One of the first palladium-catalyzed annulation protocols, in which the involvement of paUadium(IV) intermediates had been proposed, was published by Dyker in the early 1990s. A homocoupling of ort/jo-iodoanisole afforded 6//-dibenzo[ >, flpyran, and a cross-coupling of ort/io-iodoanisole with vinyl bromides provided benzo[6] furans (Scheme 2) [2, 3]. The mechanistic rationale put forward for these processes invoked an initial Csp -H activation induced by the paUadium(II) center, followed by the formation of paUadium(IV) intermediates via oxidative addition of aryl iodide or vinyl halide building blocks. Dyker s reports inspired synthetic chemists... 

Fig. 4 (a) Mono- and bidendate phosphine Au(i) complexes in the oxidative addition of aryl iodides (b) Energy profile of the oxidative addition of phenyl iodide to gold. Reprinted with permission from ref. 102. Copyright 2014 American Chemical Society. 

M. Joost, A. Zeineddine, L. Estevez, S. Mallet - Ladeira, K. Miqueu, A. Amgoune and D. Bourissou, Facile Oxidative Addition of Aryl Iodides to Gold(l) by Ligand Design Bending Turns on Reactivity,/. Am. Chem. Soc., 2014, 136, 14654-14657. 

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