Oxidative Addition Of Phenyl Iodide Research Articles

A New Saddle-Shaped Aza Analog of Tetraphenylene: Atroposelective Synthesis and Application as a Chiral Acylating Reagent

A New Saddle-Shaped Aza Analog of Tetraphenylene: Atroposelective Synthesis and Application as a Chiral Acylating Reagent

Intermolecular Oxidative Addition of Aryl Halides to Platinum(II) Alkyl Complexes

We report a well-defined example of intermolecular aryl halide oxidative addition (OA) to Pt(II). Complexes of the type (IMes)PtMe2(L) and (IMes′)PtMe(L) (L = SMe2, pyridine; IMes = N,N-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; IMes′ = cyclometalated IMes) undergo intermolecular OA of phenyl iodide (PhI) at 60 °C, producing toluene via reductive elimination from a proposed Pt(IV) phenyl species. Isolation of a model Pt(IV) OA product provides evidence for a Pt(II)/Pt(IV) pathway. The OA of PhI is not limited to Pt(II) IMes complexes; analogous reactions also proceed with phosphine-ligated Pt(II) dialkyl complexes, demonstrating that this reaction is feasible for a variety of electron-rich Pt(II) complexes bearing labile ligands.

Autocatalysis for C–H Bond Activation by Ruthenium(II) Complexes in Catalytic Arylation of Functional Arenes

Kinetic data for the C-H bond activation of 2-phenylpyridine by Ru(II)(carboxylate)(2)(p-cymene) I (acetate) and I' (pivalate) are available for the first time. They reveal an irreversible autocatalytic process catalyzed by the coproduct HOAc or HOPiv (acetonitrile, 27 °C). The overall reaction is indeed accelerated by the carboxylic acid coproduct and water. It is retarded by a base, in agreement with an autocatalytic process induced by HOAc or HOPiv that favors the dissociation of one carboxylate ligand from I and I' and consequently the ensuing complexation of 2-phenylpyridine (2-PhPy). The C-H bond activation initially delivers Ru(O(2)CR)(o-C(6)H(4)-Py)(p-cymene) A or A', containing one carboxylate ligand (OAc or OPiv, respectively). The overall reaction is accelerated by added acetates. Consequently, C-H bond activation (faster for acetate I than for pivalate I') proceeds via an intermolecular deprotonation of the C-H bond of the ligated 2-PhPy by the acetate or pivalate anion released from I or I', respectively. The 18e complexes A and A' easily dissociate, by displacement of the carboxylate by the solvent (also favored by the carboxylic acid), to give the same cationic complex B(+) {[Ru(o-C(6)H(4)-Py)(p-cymene)(MeCN)](+)}. Complex B(+) is reactive toward oxidative addition of phenyl iodide, leading to the diphenylated 2-pyridylbenzene.

Mechanism of the oxidative addition of hypervalent iodonium salts to palladium(II) pincer-complexes☆

Oxidative addition of hypervalent iodonium salts to palladium pincer-complexes was studied to rationalize the mechanism of the key-step in related Pd(II)/Pd(IV) based catalytic processes. It was found that this oxidative addition is an exothermic process with a relatively low activation barrier. The activation energy is highly dependent on the organic substituents of the iodoniun salts. For example, an ethynyl group is transferred with a considerably lower activation barrier from iodine to palladium, than a phenyl functionality. We have compared the reaction profiles of the oxidative addition of hypervalent iodonium salts and phenyl iodide. The most important difference between the two processes is that the oxidative addition of phenyl iodide is highly endothermic, as the reductive elimination of phenyl iodide from the Pd(IV) species requires a very low barrier. In contrast, the formation of the Pd(IV) species using hypervalent iodonium salts is an irreversible process, which allows ligand exchange and trasmetallation reactions generating a productive catalytic cycle. The studies indicate that the most important MO's involved in the oxidation is the antibonding σ* orbital of the iodonium salt and a non-bonding Pd(4d) orbital, which is perpendicular to the coordination plane of the palladium atom.

Neutral palladium(0) complexes from Pd(OAc)2 and tri-2-furylphosphine and their reactivity in oxidative addition of phenyl iodide

Neutral palladium(0) complexes from Pd(OAc)2 and tri-2-furylphosphine and their reactivity in oxidative addition of phenyl iodide

Chiral Palladium(0)trans-Stilbene Complexes: Synthesis, Structure, and Oxidative Addition of Phenyl Iodide

The chiral Pd(0) trans-stilbene complexes Pd(diphos*)(trans-stilbene) (diphos* = (R,R)-Me-Duphos, (R,R)-Et-Duphos, (R,R)-i-Pr-Duphos, (R,R)-Me-BPE, (S,S)-Me-FerroLANE, (S,S)-Me-DuXantphos, (S,S)-Et-FerroTANE, (R,S)-CyPF-t-Bu, (R,S)-PPF-t-Bu, (R,S)-BoPhoz) and Ni((R,R)-Me-Duphos)(trans-stilbene) were prepared by NaBH(OMe)3 reduction of the corresponding M(diphos*)Cl2 compounds in the presence of trans-stilbene. The rate of oxidative addition of phenyl iodide to the stilbene complexes, which gave Pd(diphos*)(Ph)(I), depended on the ligand (larger for increased ligand bite angles and reduced steric bulk) and was markedly faster than oxidative addition to mixtures of Pd(dba)2 and diphos*. The complexes Pd(diphos*)(Ph)(I) were prepared independently by treatment of PdL2(Ph)(I) (L2 = TMEDA, (PPh3)2) with diphos*. Oxidative addition of PhI to the complexes M((R,R)-Me-Duphos)(trans-stilbene) occurred in the rate order Pd > Ni ≫ Pt. The complexes Pd(diphos*)Cl2, Pd(diphos*)(trans-stilbene), and Pd(diphos*)(Ph)(I), as well as some analogous Ni compounds, were structurally characterized by X-ray crystallography.

Decelerating Effect of Alkynes in the Oxidative Addition of Phenyl Iodide to Palladium(0) Complexes in Palladium‐Catalyzed Multicomponent Reactions and Sonogashira Reactions

AbstractThe oxidative addition of PhI to [Pd0(PPh3)4] in DMF is slower when performed in the presence of the terminal alkynes (PhC≡CH, EtO2C−C≡CH) that are reagents in palladiumcatalyzed Sonogashira or multicomponent reactions. The concentration of the reactive [Pd0(PPh3)2] complex decreases because of its partial coordination to the alkyne to form [(η2‐RC≡CH)Pd0(PPh3)2] (R = Ph, EtCO2), which is in equilibrium with [Pd0(PPh3)2]. The complex [(η2‐PhC≡CH)Pd0(PPh3)2] was found to be unreactive whereas [(η2‐EtO2C− C≡CH)Pd0(PPh3)2] was found to be the unique reactive complex at high concentrations of EtO2C−C≡CH. As has been reported for alkenes, terminal alkynes play an unexpected role because they interfere in the oxidative addition before their usual reactions in the carbopalladation and transmetallation steps that follow it. Decreasing the rate of the fast oxidative addition with PhI may promote the efficiency of the catalytic cycle by bringing its rate closer to that of the slower carbopalladation or transmetallation steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Decelerating Effect of Alkenes in the Oxidative Addition of Phenyl Iodide to Palladium(0) Complexes in Heck Reactions

In DMF, the oxidative addition of PhI to Pd0(PPh3)4 or to the anionic Pd0(PPh3)3(OAc)- is slower in the presence of an alkene (styrene, methyl acrylate). Indeed, the concentration of the reactive Pd0(PPh3)2 or Pd0(PPh3)2(OAc)- complex decreases because of its coordination to the alkene to form the unreactive (η2-CH2CHR)Pd0(PPh3)2 (R = Ph, CO2Me) or (η2-CH2CHPh)Pd0(PPh3)2(OAc)-, respectively. As already evidenced in palladium-catalyzed Stille reactions, this work establishes that, in palladium-catalyzed Heck reactions as well, the nucleophile plays a role in the kinetics of the oxidative addition (decelerating effect), as soon as it may coordinate Pd0 complexes. This is an essential observation, in view of the general belief that the nucleophile enters the catalytic cycle only at the stage of the attack on the aryl−PdII complex formed in the oxidative addition. Whenever the oxidative addition is not rate determining, the decelerating effect of the alkene on this reaction is in favor of a higher efficiency of the catalytic cycle.

Mechanistic Studies on Oxidative Addition of Aryl Halides and Triflates to Pd(BINAP)2and Structural Characterization of the Product from Aryl Triflate Addition in the Presence of Amine

Kinetic studies of the oxidative addition of phenyl iodide and phenyl triflate to Pd(BINAP)2 (1) are reported. The products of the oxidative addition of phenyl trifluoromethanesulfonate to 1 in the presence of the primary amines n-octylamine and isoamylamine are the cationic aryl palladium(II) complexes [(BINAP)Pd(Ph)(H2NR)]OTf (2a,b), and the product of the oxidative addition of phenyl iodide to 1 is the phenylpalladium iodide {(BINAP)Pd(Ph)I} (3). Structural characterization of the rare, stable σ-aryl Pd(II) triflate complex (2b), in this case coordinated by isoamylamine, is reported. Initial mechanistic studies focused on measuring the rates of reactions containing concentrations of aryl electrophile ranging from 8.94 × 10-7 to 0.2 M. Under these conditions, the oxidative addition of PhOTf and PhI to 1 was inverse first-order in added BINAP ligand when the concentration of ArX was low. The oxidative addition reaction was first-order in ArX when the concentration of ArX was low and was zero order in ArX when the concentration of ArX was high. At these high concentrations, the reaction rate depended solely on the rate for dissociation of BINAP from 1. However, additional experiments using concentrations of aryl iodide and aryl bromide up to 4.0 M led to a measurable increase in observed rate constants and detection of a second concurrent reaction mechanism. This effect was not observed with phenyl triflate. The relevance of this phenomenon to catalytic coupling and oxidative addition of aryl bromides is discussed. Reactions of triflate complex 2a with several bases to form N-octylaniline are also reported.

Rate and mechanism of the oxidative addition of phenyl iodide to Pd0 ligated by triphenylarsine: evidence for the formation of a T-shaped complex.

The oxidative addition of phenyl iodide to the palladium(o) generated from [Pd0(dba)2] and n equivalents of AsPh3 (the most efficient catalytic precursor in Stille reactions) proceeds from [(solv)Pd0(AsPh3)2] (solv= solvent). However, the latter is present only in trace concentrations because it is involved in an equilibrium with the major, but nonreactive, complex [Pd0(dba)(AsPh3)2]. As regards the phosphine ligands, dba has a decelerating effect on the rate of the oxidative addition by decreasing the concentration of the reactive species. Relative to PPh3, the effect of AsPh3 is to increase the rate of the oxidative addition of PhI by a factor ten in DMF and seven in THF, independent of the value of n, provided that n > or = 2. In contrast to PPh3, the addition of more than two equivalents of AsPh3 to [Pd0(dba)2] (dba= trans,trans-dibenzylideneacetone) does not affect the kinetics of the oxidative addition because of the very endergonic displacement of dba from [Pd0(dba)(AsPh3)2] to form [Pd0(AsPh3)3]. The complex trans-[PhPdI(AsPh3)2], formed in the oxidative addition, is involved in a slow equilibrium with the T-shaped complex [PhPdI(AsPh3)] after appreciable decomplexation of one AsPh3. Under catalytic conditions, that is, in the presence of a nucleophile, such as CH2=CH-SnBu3 which is able to coordinate to [Pd0(AsPh3)2], a new Pd0 complex is formed: [Pd0(eta2-CH2=CHSnBu3)(AsPh3)2]; however, this complex does not react with PhI. Consequently, CH2=CH-SnBu3 slows down the oxidative addition by decreasing the concentration of the reactive species [(solv)Pd0(AsPh3)2]. This demonstrates that a nucleophile may be not only involved in the transmetallation step, but may also interfere in the kinetics of the oxidative addition step by decreasing the concentration of reactive Pd0.