31989-49-8Relevant academic research and scientific papers
The synergistic copper/ppm Pd-catalyzed hydrocarboxylation of alkynes with formic acid as a CO surrogate as well as a hydrogen source: An alternative indirect utilization of CO2
Chen, Kai-Hong,He, Liang-Nian,Qiu, Li-Qi,Xia, Shu-Mei,Yang, Zhi-Wen,Yao, Xiang-Yang
supporting information, p. 8089 - 8095 (2021/11/01)
An unprecedented strategy has been developed involving the earth-abundant Cu-catalyzed hydrocarboxylation of alkynes with HCOOH to (E)-acrylic derivatives with high regio- and stereoselectivity via synergistic effects with ppm levels of a Pd catalyst. Both symmetrical and unsymmetrical alkynes bearing various functional groups were successfully hydrocarboxylated with HCOOH, and the modification of a pharmaceutical molecule exemplified the practicability of this process. This protocol employs HCOOH as both a CO surrogate and hydrogen donor with 100% atom economy and it can be viewed as an alternative approach for indirect CO2 utilization. Mechanistic investigations indicate a Cu/ppm Pd cooperative catalysis mechanism via alkenylcopper species as potential intermediates formed from Cu-hydride active catalytic species with HCOOH as a hydrogen source. This bimetallic system involving inexpensive Cu and trace Pd provides a reliable and efficient hydrocarboxylation method to access industrially useful acrylic derivatives with HCOOH as a hydrogen source, and it provides novel clues for optimizing other Cu-H-related co-catalytic systems.
Pd-catalyzed carbonylative α-arylation of aryl bromides: Scope and mechanistic studies
Nielsen, Dennis U.,Lescot, Camille,Gogsig, Thomas M.,Lindhardt, Anders T.,Skrydstrup, Troels
supporting information, p. 17926 - 17938 (2014/01/17)
Reaction conditions for the three-component synthesis of aryl 1,3-diketones are reported applying the palladium-catalyzed carbonylative α-arylation of ketones with aryl bromides. The optimal conditions were found by using a catalytic system derived from [Pd(dba)2] (dba=dibenzylideneacetone) as the palladium source and 1,3-bis(diphenylphosphino)propane (DPPP) as the bidentate ligand. These transformations were run in the two-chamber reactor, COware, applying only 1.5 equivalents of carbon monoxide generated from the CO-releasing compound, 9-methylfluorene-9-carbonyl chloride (COgen). The methodology proved adaptable to a wide variety of aryl and heteroaryl bromides leading to a diverse range of aryl 1,3-diketones. A mechanistic investigation of this transformation relying on 31P and 13C NMR spectroscopy was undertaken to determine the possible catalytic pathway. Our results revealed that the combination of [Pd(dba)2] and DPPP was only reactive towards 4-bromoanisole in the presence of the sodium enolate of propiophenone suggesting that a [Pd(dppp)(enolate)] anion was initially generated before the oxidative-addition step. Subsequent CO insertion into an [Pd(Ar)(dppp)(enolate)] species provided the 1,3-diketone. These results indicate that a catalytic cycle, different from the classical carbonylation mechanism proposed by Heck, is operating. To investigate the effect of the dba ligand, the Pd0 precursor, [Pd(η3-1-PhC 3H4)(η5-C5H5)], was examined. In the presence of DPPP, and in contrast to [Pd(dba)2], its oxidative addition with 4-bromoanisole occurred smoothly providing the [PdBr(Ar)(dppp)] complex. After treatment with CO, the acyl complex [Pd(CO)Br(Ar)(dppp)] was generated, however, its treatment with the sodium enolate led exclusively to the acylated enol in high yield. Nevertheless, the carbonylative α-arylation of 4-bromoanisole with either catalytic or stoichiometric [Pd(η3-1-PhC3H4) (η5-C5H5)] over a short reaction time, led to the 1,3-diketone product. Because none of the acylated enol was detected, this implied that a similar mechanistic pathway is operating as that observed for the same transformation with [Pd(dba)2] as the Pd source. CO-operation is the key! The first palladium-catalyzed carbonylative α-arylation of aryl bromides is described. A wide array of different aryl 1,3-diketones can be isolated in good-to-excellent yields using only stoichiometric amounts of CO (see scheme). A mechanistic study is presented that suggests the need for enolate coordination prior to oxidative addition when [Pd(dba)2] is employed as the precatalyst. Copyright
Reductive elimination from metal phosphonate complexes: Circumvention of competing protonolysis reactions
Stockland Jr., Robert A.,Levine, Adam M.,Giovine, Matthew T.,Guzei, Ilia A.,Cannistra, Joseph C.
, p. 647 - 656 (2008/10/09)
The formation of MeP(O)(OPh)2 by reductive elimination from L2PdMe(P(O)(OPh)2) species has been investigated. The electronic and steric effects of the supporting ligands were investigated by studying reductive elimination reactions from a series of discrete complexes containing nitrogen- and phosphorus-based ligands. The P(O)-C(sp3) bond-forming reaction is slow when the intermediate species contains bidentate nitrogen ligands or small basic monodentate phosphines. Analogous complexes bearing large bite angle diphosphines such as dppf and Xantphos undergo reductive elimination at ambient temperature. The rate of MeP(O)(OPh)2 formation by reductive elimination from (dppf)PdMe(P(O)(OPh)2) is not affected by the identity or concentration of added ligand (excess dppf or PPh3), suggesting that the reductive elimination occurs from a four- or three-coordinate intermediate. When the rate of reductive elimination is slow, protonolysis reactions between L2PdMe(P(O)(OPh)2) intermediates and HP(O)(OPh)2 leads to the formation of bis-phosphonate complexes. The protonolysis reaction can be circumvented by the use of large bite angle phosphines such as dppf and Xantphos, which lead to rapid rates of P(O)-C(sp3) bond formation. These results demonstrate that the formation of P(O)-C(sp3) bonds by reductive elimination from L2PdRP(O)(OR)2 complexes is quite sensitive to the steric bulk of the supporting ligand and the presence of excess hydrogen phosphonate.
Formation of palladium(0) complexes from Pd(OAc)2 and a bidentate phosphine ligand (dppp) and their reactivity in oxidative addition
Amatore, Christian,Jutand, Anny,Thuilliez, Audrey
, p. 3241 - 3249 (2008/10/08)
A Pd0 complex is spontaneously generated from Pd(OAc)2 and a bidentate phosphine such as dppp (1,3-bis(diphenylphosphino)propane). dppp is the reducing agent and is oxidized to the hemioxide dppp(O). The intramolecular reduction step is reversible. A stable Pd0 complex is quantitatively formed in the presence of 2 equiv of dppp, water, and a base (NEt3). The oxidative addition of PhI gives a cationic complex, PhPd(dppp)(dppp(O))+, in which dppp(O) behaves as a monodentate ligand. PhPd(OAc)(dppp) is formed in the presence of added AcO-. The oxidative addition of PhI is an intricate reaction whose kinetics has been investigated only in the presence of added AcO-. It involves reactive dimeric or/and monomeric Pd0 complexes ligated by AcO- whose relative reactivity is a function of the PhI concentration.
Lewis acids accelerate reductive elimination of RCN from P2Pd(R)(CN)
Huang, Jinkun,Haar, Christopher M.,Nolan, Steven P.,Marcone, John E.,Moloy, Kenneth G.
, p. 297 - 299 (2008/10/08)
The rate of reductive elimination of the complexes dpppPd(CH2TMS)(CNER3) (E = B, Al) is accelerated up to 60-fold over dpppPd(CH2TMS)(CN). Based on kinetic considerations and the isoelectronic relationship of CN- and CO, a migration-type mechanism for reductive elimination is proposed. The rate acceleration correlates directly with Lewis acid strength, the latter determined by solution calorimetric analyses of the Lewis acid adduct forming reaction Pd-CN + ER3 → Pd-CN-ER3.
Carbon-sulfur bond-forming reductive elimination involving sp-, sp2-, and sp3-hybridized carbon. Mechanism, steric effects, and electronic effects on sulfide formation
Mann, Grace,Baranano, David,Hartwig, John F.,Rheingold, Arnold L.,Guzei, Ilia A.
, p. 9205 - 9219 (2007/10/03)
Palladium thiolato complexes [(L)Pd(R)(SR')], within which L is a chelating ligand such as DPPE, DPPP, DPPBz, DPPF, or TRANSPHOS, R is a methyl, alkenyl, aryl, or alkynyl ligand, and R' is an aryl or alkyl group, were synthesized by substitution or proton-transfer reactions. All of these thiolato complexes were found to undergo carbon-sulfur bond-forming inductive elimination in high yields to form dialkyl sulfides, diaryl sulfides, alkyl aryl sulfides, alkyl alkenyl sulfides, and alkyl alkynyl sulfides. Reductive eliminations forming alkenyl alkyl sulfides and aryl alkyl sulfides were the fastest. Eliminations of alkynyl alkyl sulfides were slower, and elimination of dialkyl sulfide was the slowest. Thus the relative rates for sulfide elimination as a function of the hybridization of the palladium-bound carbon follow the trend sp2 > sp >> sp3. Rates of reductive elimination were faster for cis-chelating phosphine ligands with larger bite angles. Kinetic studies, along with results from radical trapping reactions, analysis of solvent effects; and analysis of complexes with chelating phosphines of varying rigidity, were conducted with [Pd(L)(S-tert-butyl)(Ar)] and [Pd(L)(S- tert-butyl)(Me)]. Carbon-sulfur bond-forming reductive eliminations involving both saturated and unsaturated hydrocarbyl groups proceed by an intramolecular, concerted mechanism. Systematic changes in the electronic properties of the thiolate and aryl groups showed that reductive elimination is the fastest for electron deficient aryl groups and electron rich arenethiolates, suggesting that the reaction follows a mechanism in which the thiolate acts as a nucleophile and the aryl group an electrophile. Studies with thiolate ligands and hydrocarbyl ligands of varying steric demands favor a migration mechanism involving coordination of the hydrocarbyl ligand in the transition state.
Chelate effect on the structure and reactivity of electron-rich palladium complexes and its relevance to catalysis
Portnoy, Moshe,Milstein, David
, p. 1655 - 1664 (2008/10/08)
In order to clarify the origin of the "chelate effect" in catalysis by palladium, complexes of Pr2P(CH2)niPr2P (n = 2, dippe; n = 3, dippp; n = 4, dippb), Ph2P(CH2)3PPh2 (dppp), and PiPr2nBu were prepared and their structures, dynamic properties, and reactivities were compared. Pd(dippe)2 1d is a coordinatively saturated complex, both in solution and in the solid state. X-ray characterization exhibits a distorted tetrahedral geometry. The dippe bite angle is 87.05°. The compound crystallizes in the orthorhombic space group Pnna with a = 16.713(3) A?, b = 17.561(3) A?, c = 11.116(2) A?, V = 3277(1) A?3, Z = 4. Pd(dippp)2 (1a) and Pd(dippb)2 (1e) are coordinatively unsaturated, trigonal complexes and are in equilibrium with the binuclear complexes LPd(η2-L)PdL, 1b and 1f, respectively. Whereas 1d does not exhibit dynamic behavior, 1a and 1e undergo fast, intramolecular phosphine exchange, a process which is not observed with 1b and 1f. The trigonal complexes (dippp)PdPiPr2Bu (1c) and (PiPr2nBu)3Pd were also prepared for comparison. The dippp complexes 1a-1c react with aryl chlorides to produce cis-(dippp)Pd(C6H4X)Cl as the major product and trans-(η1-dippp)2Pd(C6H4X)Cl as the minor one (X = 4-OMe, 4-Me, H, 3-OMe, 4-COMe, 4-CHO, 4-NO2). In contrast, the dippb complex 1e oxidatively adds chlorobenzene to yield only the trans complex (η1-dippb)2Pd(Ph)Cl. Reaction monitoring reveals that the cis and trans complexes are formed in parallel pathways. Cis/trans equilibrium is on the cis side for dippp and on the trans side for dippb. Reactivity toward chlorobenzene follows the trend Pd(dippp)2 > Pd(PiPr2nBu)3 ? Pd(dippe)2 ? Pd(dppp)2. These results are interpreted in terms of chelate stability, ligand basicity, concentration of the active 14e species and effect of the P-Pd-P angle on its reactivity. The dippp ligand is unique in that it is the only one of those studied which results in Pd(0) complexes which (a) exhibit high reactivity in oxidative addition and (b) form cis complexes preferentially.
Fluoride-induced reduction of palladium(II) and platinum(II) phosphine complexes
Mason,Verkade
, p. 2212 - 2220 (2008/10/08)
A novel redox reaction involving fluoride and phosphine complexes of palladium(II) is reported. The scope of this reaction has been investigated using the ligands PPh3, Ph2P(CH2)nPPh2 (n = 1-4), Ph2PCH2C(CH3)2CH2PPh 2, Ph2PCH3, and P(CH2CH2CN)3; several solvents including DMSO, pyridine, acetonitrile, and THF; and either n-Bu4NF·3H2O or KF/18-crown-6 as the fluoride source. The reduction products are palladium(0) phosphine complexes for which this reaction offers a convenient synthetic route. 31P and 19F NMR spectra permitted identification of the initial oxidation products as difluorophosphoranes (R3PF2), which subsequently hydrolyzed, forming phosphine oxides if a hydrated fluoride source is used. Results implicating a fluoride-induced redox reaction in the thermal decomposition of [(Ph3P)3PdCl]BF4 to yield [Pd3Cl(PPh2)2(PPh3) 3]BF4 are also presented. Preliminary results indicate that platinum complexes also undergo this reaction, but nickel complexes yield NiF2. The X-ray parameters for Pd(dppp)2 (dppp = 1,3-bis(diphenyphosphino)propane) are: monoclinic, space group C2/c (No. 15), a = 18.396 (2) A?, b = 13.290 (1) A?, c = 20.186 (2) A?, β = 109.383 (5)°, and Z = 4.
Fluoride-assisted reduction of palladium(II) phosphine complexes
Mason, Mark R.,Verkade, John G.
, p. 864 - 865 (2008/10/08)
PdCl2 in the presence of chelating or monodentate arylphosphines reduces in high yields to give Pd(O) phosphine complexes when the reaction is carried out in the presence of n-Bu4NF·3H2O.
