108818-35-5Relevant academic research and scientific papers
Distinguishing between pathways for transmetalation in Suzuki-Miyaura reactions
Carrow, Brad P.,Hartwig, John F.
, p. 2116 - 2119 (2011/04/23)
We report a systematic study of the stoichiometric reactions of isolated arylpalladium hydroxo and halide complexes with arylboronic acids and aryltrihydroxyborates to evaluate the relative rates of the two reaction pathways commonly proposed to account for transmetalation in the Suzuki-Miyaura reaction. On the basis of the relative populations of the palladium and organoboron species generated under conditions common for the catalytic process and the observed rate constants for the stoichiometric reactions between the two classes of reaction components, we conclude that the reaction of a palladium hydroxo complex with boronic acid, not the reaction of a palladium halide complex with trihydroxyborate, accounts for transmetalation in catalytic Suzuki-Miyaura reactions conducted with weak base and aqueous solvent mixtures.
Effect of ligand steric properties and halide identity on the mechanism for oxidative addition of haloarenes to trialkylphosphine Pd(0) complexes
Barrios-Landeros, Fabiola,Carrow, Brad P.,Hartwig, John F.
, p. 8141 - 8154 (2009/12/02)
The oxidative addition of PhX (X ) I, Br, Cl) to the complexes Pd(P tBu3)2 (1), Pd(1-AdPtBu2)2 (2), Pd(CyPtBu2)2 (3), and Pd(PCy3) 2 (4) (1-Ad = 1-adamantyl, Cy = cyclohexyl) was studied todetermine the effect of steric properties on the coordination number of the species that undergoes oxidative addition and to determine whether the type of halide affects the identity of this species. The kinetic dat a imply that the number of phosphines coordinated to the complex that reacts in the irreversible step of the oxidative addition process for complexes 1-4 depends more on the halide than on the steric properties of the ligands. The rate-limiting step of the oxidative addition of PhI occurred with L2Pd(0) in all cases, as determined by the lack of dependence of kobs on [PtBu3], [1-AdPtBu2], or [CyPtBu2] and the inverse dependence of the rate constant on [PCy3] when the reaction was initiated with Pd(PCy3)3. The irreversible step of the oxidative addition of PhCl occurred with a monophosphine species in each case, as signaled by an inverse dependence of the rate constant on the concentration of ligand. The irreversible step of the oxidative addition of PhBr occurred with a bisphosphine species, as signaled by the zeroth-order or small dependence of the rate constant on the concentration of phosphine. Thus, the additions of the less reactive chloroarenes occurthrough lower-coordinate intermediates than additions of the more react ive haloarenes.
Profound steric control of reactivity in aryl halide addition to bisphosphane palladium(0) complexes
Galardon, Erwan,Ramdeehul, Shailesh,Brown, John M.,Cowley, Andrew,Hii, King Kuok,Jutand, Anny
, p. 1760 - 1763 (2007/10/03)
The steric bulk of the phosphane ligand determines the mechanism of the ArX addition to zero-valent [PdL2] complexes. This effect has been studied by variation of ligands (catalyst: [Pd(PCxntBu3-n)2]; n=0-3, Cx = cyclohexyl) in Pd couplings of unsaturated electrophiles, and different reaction pathways (A= associative, B =dissociative) identified, depending on the size of the ligand.
Mechanisms of double and single carbonylation reactions of aryl iodides catalyzed by palladium complexes to give α-keto esters and esters
Ozawa, Fumiyuki,Kawasaki, Nobuo,Okamoto, Hidekazu,Yamamoto, Takakazu,Yamamoto, Akio
, p. 1640 - 1651 (2008/10/08)
Various aryl iodides are converted into α-keto esters and esters on reactions with alcohols and Et3N under CO pressure in the presence of catalytic amounts of palladium complexes. Detailed examination of factors controlling the selectivity for α-keto ester formation revealed the following characteristics of the reactions. (a) Use of palladium catalysts having bulkier tertiary phosphine ligands increases the selectivity for α-keto ester formation. (b) Secondary alcohols of moderate bulkiness and high basicity gave α-keto esters in high selectivity. (c) Addition of less polar solvents such as benzene and dichloromethane to the system improves the selectivity for α-keto ester formation. (d) Higher CO pressure is required to obtain α-keto esters in higher yields. NMR examination of the catalytic system containing PhI, alcohol, Et3N, and PdCl2(PPh3)2 revealed the presence of an aroylpalladium(II) complex as the predominant species. Model studies of the reactions of isolated phenyl- and benzoylpalladium(II) complexes toward alcohols, Et3N, and carbon monoxide indicate that an aroylpalladium(II) intermediate generated by a rapid CO insertion into an arylpalladium(II) complex is responsible for both the ester and α-keto ester formations in the catalytic reactions. Alcohols of higher basicity show higher reactivity in the α-keto ester formation whereas more acidic alcohols give esters at higher reaction rates. A kinetic study on the ester formation indicates that the ester formation proceeds predominantly through a mechanism involving predissociation of a tertiary phosphine ligand. On the basis of the experimental results a mechanism comprising two catalytic cycles to produce α-keto ester and ester is proposed.
