Synthesis and structural characterisation of [Pd2(µ-Br)2(PBut3)2], an example of a palladium(<scp>I</scp>)–palladium(<scp>I</scp>) dimer

Vilar, Ramón; Mingos, D. Michael P.; Cardin, Christine J.

doi:10.1039/dt9960004313

Cited by 108 publications

(72 citation statements)

References 13 publications

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“…Nevertheless, the peak at + 0.88 Vr apidly decreased when adding 10 equivalent of para-fluorophenylboronic acida long with 1equivalent of nBu 4 NF ( Figure S12 in the Supporting Information). This behavior is consistent with the presence of aP d I -Pd I dimer, [26] as was reported for hindered monophosphines [27][28][29] (see below for further evidence of its formation by 31 PNMR studies). This oxidation peak is similart ot hat observed fort he commercially available [Pd(PtBu) 3 m-I] 2 at + 0.95 V( see Supporting information,FigureS10).…”

Section: And Xphosinthfsupporting

confidence: 89%

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Wagschal

Perego

Simon

et al. 2019

Chemistry A European J

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Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross‐coupling reactions. Even though the XPhos/Pd(OAc)2 catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd0 complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc)2 initially associates with the ligand to form a complex in solution, which has been characterized as PdII(OAc)2(XPhos). This PdII center is then reduced to the Pd0(XPhos)2 species by an intramolecular process. This study also sheds light on the formation of PdI–PdI dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd0(XPhos) as the reactive species in equilibrium with the unreactive Pd0(XPhos)2. Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides.

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Section: And Xphosinthfsupporting

confidence: 89%

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Wagschal

Perego

Simon

et al. 2019

Chemistry A European J

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“…The reactions catalyzed by the single-component catalyst precursor {[P( t -Bu) 3 ]PdBr} 2 41-43 or the combination of Pd(dba) 2 and P( t -Bu) 3 or Q-phos formed the coupled product quantitatively (entries 1, 2, and 7). The coupled product was formed in lower yield with less sterically demanding trialkyl phosphine ligands (entries 3–6).…”

Section: Introductionmentioning

confidence: 99%

Palladium-Catalyzed α-Arylation of Zinc Enolates of Esters: Reaction Conditions and Substrate Scope

Hama

Hartwig

2013

J. Org. Chem.

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The intermolecular α-arylation of esters by palladium-catalyzed coupling of aryl bromides with zinc enolates of esters is reported. Reactions of three different types of zinc enolates have been developed. α-Arylation of esters occurs in high yields with isolated Reformatsky reagents, with Reformatsky reagents generated from α-bromo esters and activated zinc, and with zinc enolates generated by quenching lithium enolates of esters with zinc chloride. The use of zinc enolates, instead of alkali metal enolates, greatly expands the scope of the arylation of esters. The reactions occur at room temperature or at 70 °C with bromoarenes containing cyano, nitro, ester, keto, fluoro, enolizable hydrogen, hydroxyl or amino functionality and with bromopyridines. The scope of esters encompasses acyclic acetates, propionates, and isobutyrates, α-alkoxyesters, and lactones. The arylation of zinc enolates of esters was conducted with catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) or the highly reactive dimeric Pd(I) complex {[P(t-Bu)3]PdBr}2.

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“…Proto-nated phosphine [HPtBu3] + (6) (12%) was also detected by 31 P NMR spectroscopy; the anion in this salt lacks an NMR active nucleus and is likely to be bromide. Each of the side products [3][4][5] was identified by independent synthesis and comparison of 31 P NMR chemical shifts to those of the reaction mixture.…”

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confidence: 99%

Autocatalytic Oxidative Addition of PhBr to Pd(P^tBu₃)₂via Pd(P^tBu₃)₂(H)(Br)

2008

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The oxidative addition of aryl halides or sulfonates to Pd(0) complexes is the first step in classic and recently developed cross-coupling reactions. Among the most active catalysts for many coupling reactions are complexes of P t Bu 3 . 1 Recently, we reported the isolation of unusual three-coordinate products from oxidative addition of bromoarenes to Pd(0) complexes of P t Bu 3 . 2 We have now studied the mechanism of the oxidative addition of bromoarenes to Pd (P t Bu 3 ) 2 , and this mechanism is equally unusual. The reaction in the absence of a strong base is autocatalytic, and a side product, Pd(P t Bu 3 ) 2 (H)(Br), is capable of acting as the catalyst. In contrast to the typically higher reactivity of haloarenes with Pd(0) species than with Pd(II), the reaction of bromobenzene with Pd(P t Bu 3 ) 2 (H)(Br) occurs faster than with Pd(P t Bu 3 ) 2 to form Pd(P t Bu 3 )(Ph)(Br). Studies that support these conclusions are reported here.(1)The oxidative addition of PhBr to Pd(P t Bu 3 ) 2 (1) produces the three-coordinate (P t Bu 3 )Pd(Ph) (Br) (2). 2 The yields of 2 and side products in polar and nonpolar solvents are shown in eq 1. The reaction in polar solvents, such as methyl ethyl ketone (MEK), formed 2 in high yield. Reactions in toluene were slower, and this slower rate allowed decomposition of the product (vide infra) to occur in parallel with the oxidative addition. Thus, a typical product distribution in toluene was 2 (60%), (P t Bu 3 ) 2 Pd(H)(Br) 3 (3) (10%), [(P t Bu 3 )Pd(μ-Br)] 2 4 (4) (13%), and [Pd(P t Bu 2 C(CH 3 ) 2 CH 2 )(μ-Br)] 2 5 (5) (16%). Proto-nated phosphine [HPtBu3] + (6) (12%) was also detected by 31 P NMR spectroscopy; the anion in this salt lacks an NMR active nucleus and is likely to be bromide. Each of the side products 3-5 was identified by independent synthesis and comparison of 31 P NMR chemical shifts to those of the reaction mixture.The rate of reaction of the Pd(0) complex 1 with bromoben-zene was measured by 31 P NMR spectroscopy with [1] = 0.040 M and [PhBr] = 1.9 M in toluene, THF, and 2-butanone solvent at 70 °C. The reaction of 1 in toluene in the absence of any additive (open squares, Figure 1) was clearly not exponential and was characteristic of an autocatalytic reaction. To determine the origin of this kinetic behavior, the rate of the reaction of PhBr with 1 was conducted with jhartwig@uiuc.edu. Supporting Information Available: Experimental procedures and characterization of reaction products. This material is available free of charge via the Internet at http://pubs.acs.org. Because several of the compounds that affected the oxidative addition contained HBr, we sought to determine if the accelerating effect of these additives resulted from H + , Br − , or a combination of the two. The oxidative addition of PhBr to 1 in the presence of 5 mol % NBu 4 Br 6 (0.020 M) occurred much faster than in the absence of an additive and was complete in about 30 min (Figure 2). The reaction in the presence of only 5 mol % NEt 3 · HBr occurred faster than in the absence of an...

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Synthesis and structural characterisation of [Pd₂(µ-Br)₂(PBu^t₃)₂], an example of a palladium(I)–palladium(I) dimer

Cited by 108 publications

References 13 publications

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Palladium-Catalyzed α-Arylation of Zinc Enolates of Esters: Reaction Conditions and Substrate Scope

Autocatalytic Oxidative Addition of PhBr to Pd(P^tBu₃)₂via Pd(P^tBu₃)₂(H)(Br)

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Synthesis and structural characterisation of [Pd2(µ-Br)2(PBut3)2], an example of a palladium(I)–palladium(I) dimer

Cited by 108 publications

References 13 publications

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Palladium-Catalyzed α-Arylation of Zinc Enolates of Esters: Reaction Conditions and Substrate Scope

Autocatalytic Oxidative Addition of PhBr to Pd(PtBu3)2via Pd(PtBu3)2(H)(Br)

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Synthesis and structural characterisation of [Pd₂(µ-Br)₂(PBu^t₃)₂], an example of a palladium(I)–palladium(I) dimer

Autocatalytic Oxidative Addition of PhBr to Pd(P^tBu₃)₂via Pd(P^tBu₃)₂(H)(Br)