28516-49-6Relevant academic research and scientific papers
Reactivity of a Dinuclear PdIComplex [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3: Implications for Cross-Coupling Catalysis Using the Ubiquitous Pd(OAc)2/nPPh3Catalyst System
Scott, Neil W. J.,Ford, Mark J.,Husbands, David R.,Whitwood, Adrian C.,Fairlamb, Ian J. S.
, p. 2995 - 3002 (2021)
[PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] is the reduction product of PdII(OAc)2(PPh3)2, generated by reaction of ‘Pd(OAc)2’ with two equivalents of PPh3. Here, we report that the reaction of [PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3results in a nuanced disproportionation reaction, forming [Pd0(PPh3)3] and a phosphinito-bridged PdI-dinuclear complex, namely [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2]. The latter complex is proposed to form by abstraction of an oxygen atom from an acetate ligand at Pd. A mechanism for the formal reduction of a putative PdIIdisproportionation species to the observed PdIcomplex is postulated. Upon reaction of the mixture of [Pd0(PPh)3] and [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2] with 2-bromopyridine, the former Pd0complex undergoes a fast oxidative addition reaction, while the latter dinuclear PdIcomplex converts slowly to a tripalladium cluster, of the type [Pd3(μ-X)(μ-PPh2)2(PPh3)3]X, with an overall 4/3 oxidation stateperPd. Our findings reveal complexity associated with the precatalyst activation step for the ubiquitous ‘Pd(OAc)2’/nPPh3catalyst system, with implications for cross-coupling catalysis.
Influence of the dba substitution on the reactivity of palladium(0) complexes generated from Pd02(dba-n,n′ -Z) 3 or Pd0(dba-n,n′-Z)2 and PPha 3 in oxidative addition with iodobenzene
Mace, Yohan,Kapdi, Anant R.,Fairlamb, Ian J. S.,Jutand, Anny
, p. 1795 - 1800 (2006)
The reactivity of Pd(0) complexes generated by addition of PPh3 (PPh3/Pd = 2, 4) to either Pd02(dban,n′- Z)3 (n,n′-Z = 4,4′-F, 4,4′-H, 4,4′-MeO, 3,3′,4,4′,5,5′-OMe) or Pd0(dba-n,n′-Z) 2 (n,n′-Z = 4,4′-Br, 4,4′-Cl, 4,4′-H, 4,4′-CH3, 3,3′,5,5′-OMe) in DMF is affected by the electron-donating or -accepting properties of the groups Z substituted on the aromatic rings of dba. Whatever the nature of Z, the unreactive major complexes Pd0(η2-dba-n,n′-Z)(PPh3)2 are formed, which are in equilibrium with the common reactive complex Pd 0(PPh3)2 and dba-n,n′-Z. The latter controls the concentration of the reactive Pd0(PPh3) 2 and, consequently, also controls the rate of the overall oxidative addition with phenyl iodide. The more electron donating the Z group, the lower the affinity of dba-4,4′-Z for Pd0(PPh3) 2. As a result, the overall rate of the oxidative addition with Phi is faster when Z is an electron-donating group. For a given Z, the overall oxidative addition is faster when using Pd02(dba-n,n′-Z) 3 instead of Pd0(dba-n,n′-Z)2. Therefore, the rate of the oxidative addition can be modulated by changing the electronic properties of the dba ligands determined by substituents on its phenyl groups and by changing the structure of the precursors: P02 (dba-n,n′-Z)3 versus Pd0(dba-n,n′-Z) 2.
CRYSTAL STRUCTURE OF TRIS(TRIPHENYLPHOSPHINE) PALLADIUM
Sergienko, V. S.,Porai-Koshits, M. A.
, p. 548 - 552 (1987)
The authors have made an x-ray structural investigation of the reaction product of Pd2(PPh3)2*(μ-CO)(OAc)2 with a tertiary amine, identified in the course of x-ray structural analysis as Pd(PPh3)3.The crystals are triclinic: α=11.659, β=14.803, c=15.843 Angstroem, α=109.31, β=95.17, γ=90.49 deg, ρcalc=1.154 g/cm3, Z=2, space group PI.In the structure the coordination unit PdP3 has the form of a strongly distorted trigonal pyramid.The Pd atom is raised a little above the plane of P3 and is 0.160 Angstroem from it.The spacings of Pd-P are 2.307-2.322 Angstroem, and the values of the angles PPdP are 115.0-126.5 deg.The short intramolecular contacts Pd...H (2.82-2.03 Angstroem) to the ortho atoms of the Ph rings lie above and below the plane P3, blocking the axial positions at the Pd atoms.The results are compared with the literature data on complexes of zero-valent palladium with phosphine ligands.
Kinetic data on the synergetic role of amines and water in the reduction of phosphine-ligated palladium(II) to palladium(0)
Amatore, Christian,El Kaim, Laurent,Grimaud, Laurence,Jutand, Anny,Meignie, Alice,Romanov, Georgy
, p. 4709 - 4713 (2014)
Tertiary amines such as EtN(iPr)2 do not reduce [PdCl 2(PPh3)2] into a Pd0 complex. The latter is formed only after the addition of water (generation of HO -), as was reported by Grushin and Alper for NEt3. The mechanism of the PdII/Pd0 reduction performed in the presence of an excess amount of PPh3 is established quantitatively by means of electrochemical techniques that provide kinetic data (determination of the equilibrium and rate constants) for the disappearance of [PdCl 2(PPh3)2] and the formation of [Pd 0(PPh3)3]. [PdCl(OH)(PPh3) 2] is formed, which allows reductive elimination between OH and the ligated PPh3 (zero-order reaction for PPh3), and this leads to a Pd0 complex. The reducing agent is ligated PPh 3, which ultimately yields (O)PPh3. The rate of the overall reduction process is controlled by the amount of water that imposes the concentration of HO-.
Giant palladium clusters as catalysts of oxidative reactions of olefins and alcohols
Vargaftik,Zagorodnikov,Stolarov,Moiseev,Kochubey,Likholobov,Chuvilin,Zamaraev
, p. 315 - 348 (1989)
Giant cationic palladium clusters approximated as Pd561L60(OAc)180 (L = phen, bipy) and Pd561phen60O60(PF6)60 were synthesized and characterized with high resolution T
A Ketimide-Stabilized Palladium Nanocluster with a Hexagonal Aromatic Pd7 Core
Cook, Andrew W.,Hrobárik, Peter,Damon, Peter L.,Wu, Guang,Hayton, Trevor W.
, p. 1471 - 1480 (2020)
Herein, we report the synthesis and characterization of the mixed-valent, ketimide-stabilized Pd7 nanosheet, [Pd7(N=CtBu2)6] (1), via reaction of PdCl2(PhCN)2 and Li(N=Ct/s
Photophysical Properties of Simple Palladium(0) Complexes Bearing Triphenylphosphine Derivatives
Kakizoe, Daichi,Nishikawa, Michihiro,Ohkubo, Takuma,Sanga, Masashi,Iwamura, Munetaka,Nozaki, Koichi,Tsubomura, Taro
, p. 9516 - 9528 (2021/06/28)
Pd(0) complexes with monodentate phosphine ligands, [Pd(P)n] (n = 3, 4), are well-known catalysts. However, the nature of the Pd(0) complex, especially the basic photophysical properties of the Pd(0) complexes, has not been extensively explored. In this work, we measured the general photophysical properties and crystal structures of Pd(0)-bearing PPh3 derivatives in the solid state and in solution. In the solid state, four-coordinated Pd(0) complexes exhibited blue-yellow emission. On the other hand, three-coordinated Pd(0) complexes displayed yellow-orange emission. In solution, orange emission of three-coordinated complexes was observed, and prompt fluorescence was detected using time-resolved emission spectroscopy, which suggests a thermally activated delayed fluorescence mechanism. Density functional theory (DFT) and time-dependent DFT calculations show that the difference in the transition mechanism between the [Pd(PPh3)4] and [Pd(PPh3)3] complexes explains the different emission colors. The emitting states of both complexes have metal-To-ligand charge-Transfer character, but the metal-centered d → p transition is considerably incorporated for emission of the tris complex.
The ubiquitous cross-coupling catalyst system 'Pd(OAc)2'/2PPh3 forms a unique dinuclear PdI complex: An important entry point into catalytically competent cyclic Pd3 clusters
Scott, Neil W. J.,Ford, Mark J.,Schotes, Christoph,Parker, Rachel R.,Whitwood, Adrian C.,Fairlamb, Ian J. S.
, p. 7898 - 7906 (2019/09/06)
Palladium(ii) acetate 'Pd(OAc)2'/nPPh3 is a ubiquitous precatalyst system for cross-coupling reactions. It is widely accepted that reduction of in situ generated trans-[Pd(OAc)2(PPh3)2] affords [Pd0(PPh3)n] and/or [Pd0(PPh3)2(OAc)]- species which undergo oxidative addition reactions with organohalides-the first committed step in cross-coupling catalytic cycles. In this paper we report for the first time that reaction of Pd3(OAc)6 with 6 equivalents of PPh3 (i.e. a Pd/PPh3 ratio of 1?:?2) affords a novel dinuclear PdI complex [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] as the major product, the elusive species resisting characterization until now. While unstable, the dinuclear PdI complex reacts with CH2Cl2, p-fluoroiodobenzene or 2-bromopyridine to afford Pd3 cluster complexes containing bridging halide ligands, i.e. [Pd3(X)(PPh2)2(PPh3)3]X, carrying an overall 4/3 oxidation state (at Pd). Use of 2-bromopyridine was critical in understanding that a putative 14-electron mononuclear 'PdII(R)(X)(PPh3)' is released on forming [Pd3(X)(PPh2)2(PPh3)3]X clusters from [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2]. Altering the Pd/PPh3 ratio to 1?:?4 forms Pd0(PPh3)3 quantitatively. In an exemplar Suzuki-Miyaura cross-coupling reaction, the importance of the 'Pd(OAc)2'/nPPh3 ratio is demonstrated; catalytic efficacy is significantly enhanced when n = 2. Employing 'Pd(OAc)2'/PPh3 in a 1?:?2 ratio leads to the generation of [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] which upon reaction with organohalides (i.e. substrate) forms a reactive Pd3 cluster species. These higher nuclearity species are the cross-coupling catalyst species, when employing a 'Pd(OAc)2'/PPh3 of 1?:?2, for which there are profound implications for understanding downstream product selectivities and chemo-, regio- and stereoselectivities, particularly when employing PPh3 as the ligand.
On the Triple Role of Fluoride Ions in Palladium-Catalyzed Stille Reactions
Hervé, Marius,Lefèvre, Guillaume,Mitchell, Emily A.,Maes, Bert U. W.,Jutand, Anny
supporting information, p. 18401 - 18406 (2015/12/24)
The mechanism of Stille reactions (cross-coupling of ArX with Ar′SnnBu3) performed in the presence of fluoride ions is established. A triple role for fluoride ions is identified from kinetic data on the rate of the reactions of trans-[ArPdBr(PPh3)2] (Ar=Ph, p-(CN)C6H4) with Ar′SnBu3 (Ar′=2-thiophenyl) in the presence of fluoride ions. Fluoride ions promote the rate-determining transmetallation by formation of trans-[ArPdF(PPh3)2], which reacts with Ar′SnBu3 (Ar′=Ph, 2-thiophenyl) at room temperature, in contrast to trans-[ArPdBr(PPh3)2], which is unreactive. However, the concentration ratio [F-]/[Ar′SnBu3] must not be too high, because of the formation of unreactive anionic stannate [Ar′Sn(F)Bu3]-. This rationalises the two kinetically antagonistic roles exerted by the fluoride ions that are observed experimentally, and is found to be in agreement with the kinetic law. In addition, fluoride ions promote reductive elimination from trans-[ArPdAr′(PPh3)2] generated in the transmetallation step.
Donor-free phosphenium-metal(0)-halides with unsymmetrically bridging phosphenium ligands
Foerster, Daniela,Nickolaus, Jan,Nieger, Martin,Benko, Zoltan,Ehlers, Andreas W.,Gudat, Dietrich
, p. 7699 - 7708 (2013/07/26)
Reactions of (cod)MCl2 (cod = 1,5 cyclooctadiene, M = Pd, Pt) with N-heterocyclic secondary phosphines or diphosphines produced complexes [(NHP)MCl]2 (NHP = N-heterocyclic phosphenium). The Pd complex was also accessible from a chlorophosphine precursor and Pd2(dba) 3. Single-crystal X-ray diffraction studies established the presence of dinuclear complexes that contain μ-bridging NHP ligands in an unsymmetrical binding mode and display a surprising change in metal coordination geometry from distorted trigonal (M = Pd) to T-shaped (M = Pt). DFT calculations on model compounds reproduced these structural features for the Pt complex but predicted an unusual C2v-symmetric molecular structure with two different metal coordination environments for the Pd species. The deviation between this structure and the actual centrosymmetric geometry is accounted for by the prediction of a flat energy hypersurface, which permits large distortions in the orientation of the NHP ligands at very low energetic cost. The DFT results and spectroscopic studies suggest that the title compounds should be described as phosphenium-metal(0)-halides rather than conventional phosphido complexes of divalent metal cations and indicate that the NHP ligands receive net charge donation from the metals but retain a distinct cationic character. The unsymmetric NHP binding mode is associated with an unequal distribution of σ-donor/π-acceptor contributions in the two M-P bonds. Preliminary studies indicate that reactions of the Pd complex with phosphine donors provide a viable source of ligand-stabilized, zerovalent metal atoms and metal(0)-halide fragments.
