Palladium forms a variety of ionic, coordination, and organopalladium compounds, typically with oxidation state Pd0 or Pd2+. Palladium(III) compounds have also been reported. Palladium compounds are frequently used as catalysts in cross-coupling reactions such as the Sonogashira coupling and Suzuki reaction.
Most ionic compounds of palladium involve the Pd2+ oxidation state. Palladium(II) chloride is a starting point in the synthesis of other palladium compounds and complexes. [1] Palladium(II) acetate plus triphenylphosphine is used as a catalyst in organic synthesis. [2]
Coordination compounds of palladium contain ligands coordinated to a central Pd0 or Pd2+ center. They are typically synthesized by adding ligands to an ionic palladium compound. For example, acetonitrile, benzonitrile, or triphenylphosphine may be coordinated to palladium(II) chloride (PdCl2) to form bis(acetonitrile)palladium dichloride (PdCl2(NCC6H5)2), bis(benzonitrile)palladium dichloride (PdCl2(PPh3)2), or bis(triphenylphosphine)palladium chloride (PdCl2(PPh3)2), [1] respectively. Many other more exotic ligands form a large variety of palladium-phosphine catalysts, such as 1,1'-bis(diphenylphosphino)ferrocene (dppf) to form [1,1'-bis(diphenylphosphino)ferrocene]palladium(II) dichloride (PdCl2(dppf)).
Another precursor to coordination compounds of palladium is sodium tetrachloropalladate, to which dibenzylideneacetone (dba) and acetylacetonate may be coordinated to form tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) [3] and palladium(II) bis(acetylacetonate), respectively.
Bis(triphenylphosphine)palladium chloride, which contains palladium as Pd2+, may be reduced using hydrazine in the presence of triphenylphosphine to form tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4), which contains Pd0. [4]
Both ionic and coordination palladium compounds are frequently used to catalyze cross-coupling reactions. The catalytic ability is due to palladium's ability to switch between the Pd0 and Pd2+ oxidation states. An organic compound adds across Pd0 to form an organic Pd2+ complex (oxidative addition). After transmetalation with an organometallic compound, two organic ligands to Pd2+ may exit the palladium complex and combine, forming a coupling product and regenerating Pd0 (reductive elimination). [2]
For the Suzuki reaction, commonly used catalysts include Pd(PPh3)4, PdCl2(PPh3)2, [1] PdCl2(dppf), as well as Pd(OAc)2 plus triphenylphosphine (PPh3). [2] A large variety of phosphine-based ligands may be used in palladium-phosphine catalysts. Bulky, electron-rich ligands such as tris(2,4,6-trimethoxyphenyl)phosphine result in catalysts that are more reactive in the oxidative addition step [2] and can catalyze the coupling of aryl chlorides, which are typically unreactive. [5]
The Heck reaction is the chemical reaction of an unsaturated halide with an alkene in the presence of a base and a palladium catalyst to form a substituted alkene. It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry, which he shared with Ei-ichi Negishi and Akira Suzuki, for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed cross-coupling reactions. The Heck reaction is a way to substitute alkenes.
The Suzuki reaction or Suzuki coupling is an organic reaction that uses a palladium complex catalyst to cross-couple a boronic acid to an organohalide. It was first published in 1979 by Akira Suzuki, and he shared the 2010 Nobel Prize in Chemistry with Richard F. Heck and Ei-ichi Negishi for their contribution to the discovery and development of noble metal catalysis in organic synthesis. This reaction is sometimes telescoped with the related Miyaura borylation; the combination is the Suzuki–Miyaura reaction. It is widely used to synthesize polyolefins, styrenes, and substituted biphenyls.
The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst as well as copper co-catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vinyl halide.
In chemistry, a transition metal pincer complex is a type of coordination complex with a pincer ligand. Pincer ligands are chelating agents that binds tightly to three adjacent coplanar sites in a meridional configuration. The inflexibility of the pincer-metal interaction confers high thermal stability to the resulting complexes. This stability is in part ascribed to the constrained geometry of the pincer, which inhibits cyclometallation of the organic substituents on the donor sites at each end. In the absence of this effect, cyclometallation is often a significant deactivation process for complexes, in particular limiting their ability to effect C-H bond activation. The organic substituents also define a hydrophobic pocket around the reactive coordination site. Stoichiometric and catalytic applications of pincer complexes have been studied at an accelerating pace since the mid-1970s. Most pincer ligands contain phosphines. Reactions of metal-pincer complexes are localized at three sites perpendicular to the plane of the pincer ligand, although in some cases one arm is hemi-labile and an additional coordination site is generated transiently. Early examples of pincer ligands were anionic with a carbanion as the central donor site and flanking phosphine donors; these compounds are referred to as PCP pincers.
Organopalladium chemistry is a branch of organometallic chemistry that deals with organic palladium compounds and their reactions. Palladium is often used as a catalyst in the reduction of alkenes and alkynes with hydrogen. This process involves the formation of a palladium-carbon covalent bond. Palladium is also prominent in carbon-carbon coupling reactions, as demonstrated in tandem reactions.
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to PPh3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a ligand for transition metal complexes, including ones that serve as catalysts in organometallic chemistry. PPh3 exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.
Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value in organic synthesis. It is prepared by the reaction of chlorine with palladium metal at high temperatures.
Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine palladium) is the chemical compound [Pd(P(C6H5)3)4], often abbreviated Pd(PPh3)4, or rarely PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air.
Tris(dibenzylideneacetone)dipalladium(0) or [Pd2(dba)3] is an organopalladium compound. The compound is a complex of palladium(0) with dibenzylideneacetone (dba). It is a dark-purple/brown solid, which is modestly soluble in organic solvents. Because the dba ligands are easily displaced, the complex is used as a homogeneous catalyst in organic synthesis.
1,1′-Bis(diphenylphosphino)ferrocene, commonly abbreviated dppf, is an organophosphorus compound commonly used as a ligand in homogeneous catalysis. It contains a ferrocene moiety in its backbone, and is related to other bridged diphosphines such as 1,2-bis(diphenylphosphino)ethane (dppe).
Bis(triphenylphosphine)palladium chloride is a coordination compound of palladium containing two triphenylphosphine and two chloride ligands. It is a yellow solid that is soluble in some organic solvents. It is used for palladium-catalyzed coupling reactions, e.g. the Sonogashira–Hagihara reaction. The complex is square planar. Many analogous complexes are known with different phosphine ligands.
Dichlorotris(triphenylphosphine)ruthenium(II) is a coordination complex of ruthenium. It is a chocolate brown solid that is soluble in organic solvents such as benzene. The compound is used as a precursor to other complexes including those used in homogeneous catalysis.
Dichloro[1,3-bis(diphenylphosphino)propane]nickel a coordination complex with the formula NiCl2(dppp); where dppp is the diphosphine 1,3-bis(diphenylphosphino)propane. It is used as a catalyst in organic synthesis. The compound is a bright orange-red crystalline powder.
[1,1'‑Bis(diphenylphosphino)ferrocene]palladium(II) dichloride is a palladium complex containing the bidentate ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf), abbreviated as [(dppf)PdCl2]. This commercially available material can be prepared by reacting dppf with a suitable nitrile complex of palladium dichloride:
Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric structures, such as palladium chloride.
A metal-phosphine complex is a coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).
Dichlorobis(triphenylphosphine)nickel(II) refers to a pair of metal phosphine complexes with the formula NiCl2[P(C6H5)3]2. The compound exists as two isomers, a paramagnetic dark blue solid and a diamagnetic red solid. These complexes function as catalysts for organic synthesis.
In organometallic chemistry, palladium-NHC complexes are a family of organopalladium compounds in which palladium forms a coordination complex with N-heterocyclic carbenes (NHCs). They have been investigated for applications in homogeneous catalysis, particularly cross-coupling reactions.
Dialkylbiaryl phosphine ligands are phosphine ligands that are used in homogeneous catalysis. They have proved useful in Buchwald-Hartwig amination and etherification reactions as well as Negishi cross-coupling, Suzuki-Miyaura cross-coupling, and related reactions. In addition to these Pd-based processes, their use has also been extended to transformations catalyzed by nickel, gold, silver, copper, rhodium, and ruthenium, among other transition metals.
Miyaura borylation, also known as the Miyaura borylation reaction, is a named reaction in organic chemistry that allows for the generation of boronates from vinyl or aryl halides with the cross-coupling of bis(pinacolato)diboron in basic conditions with a catalyst such as PdCl2(dppf). The resulting borylated products can be used as coupling partners for the Suzuki reaction.