Diphosphine ligands

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Skeletal formula of a generic diphosphine ligand. R represents a side chain. The phosphine donors are connected by a backbone linker. Generic-diphoshine-ligand-2D-skeletal.png
Skeletal formula of a generic diphosphine ligand. R represents a side chain. The phosphine donors are connected by a backbone linker.

Diphosphines, sometimes called bisphosphanes, are organophosphorus compounds most commonly used as bidentate phosphine ligands in inorganic and organometallic chemistry. They are identified by the presence of two phosphino groups linked by a backbone, and are usually chelating. [1] A wide variety of diphosphines have been synthesized with different linkers and R-groups. Alteration of the linker and R-groups alters the electronic and steric properties of the ligands which can result in different coordination geometries and catalytic behavior in homogeneous catalysts.

Contents

Synthesis

Chlorodiisopropylphosphine is a popular building block for the preparation of diphosphines. IPr2PCl.png
Chlorodiisopropylphosphine is a popular building block for the preparation of diphosphines.

From phosphide building blocks

(2-Bromophenyl)diphenylphosphine is a precursor to unsymmetrical diphosphines. BrC6H4PPh2.png
(2-Bromophenyl)diphenylphosphine is a precursor to unsymmetrical diphosphines.

Many widely used diphosphine ligands have the general formula Ar2P(CH2)nPAr2. These compounds can be prepared from the reaction of X(CH2)nX (X=halogen) and MPPh2 (M = alkali metal): [2]

Cl(CH2)nCl + 2 NaPPh2 → Ph2P(CH2)nPPh2 + 2 NaCl

Diphosphine ligands can also be prepared from dilithiated reagents and chlorophosphines: [3]

XLi2 + 2 ClPAr2 → X(PAr2)2 + 2 LiCl (X = hydrocarbon backbone)

This approach is suitable for installing two dialkylphosphino groups, using reagents such as chlorodiisopropylphosphine.

Another popular method, suitable for preparing unsymmetrical diphosphines, involves the addition of secondary phosphines to vinylphosphines:

Ph2PH + 2 CH2=CHPAr2 → Ph2PCH2-CH2PAr2

(2-Lithiophenyl)diphenylphosphine can be used also to give unsymmetrical diphosphines. The lithiated reagent is available from (2-bromophenyl)diphenylphosphine:

Ph2P(C6H4Br) + BuLi → Ph2P(C6H4Li) + BuBr
Ph2P(C6H4Li) + R2PCli → Ph2P(C6H4PR2) + LiCl

From bis(dichlorophosphine) precursors

Many diphosphines are prepared from compounds of the type X(PCl2)2 where X = (CH2)n or C6H4. The key reagents are 1,2-bis(dichlorophosphino)ethane and 1,2-bis(dichlorophosphino)benzene.

1,2-Bis(dichlorophosphino)ethane is a key intermediate in the synthesis of 1,2-bis(dimethylphosphino)ethane. C2H4(PCl2)2.svg
1,2-Bis(dichlorophosphino)ethane is a key intermediate in the synthesis of 1,2-bis(dimethylphosphino)ethane.

Chain length and coordinating properties

The short-chain diphosphine dppm tends to promote metal-metal interactions as illustrated by A-frame complexes. When the two phosphine substituents are linked by two to four carbon centres, the resulting ligands often chelate rings with a single metal. A common diphosphine ligand is dppe, which forms a five-membered chelate ring with most metals.

Some diphosphines, such as the extraordinary case of tBu2P(CH2)10PtBu2, give macrocyclic complexes with as many as 72 atoms in a ring. [6]

To position phosphine donor groups trans on a coordination sphere, several atoms are required to link the donor centres and long-chain diphosphines are typically floppy and do not chelate well. This challenge has been resolved by the long but rigid diphosphine SPANphos. [7] The bite angle of the diphosphine influences the reactivity of the metal center. [8]

Some examples of non-chelating diphosphine also exist. Due to steric effect, these phosphorus atoms can not react with anything except a proton. [9] It can be changed from non-chelating to chelating diphosphine by tuning the length of the linking arm. [10]

Representative ligands

Particularly common diphosphine ligands are shown in the table below: [11]

AbbreviationCommon name
(from which abbreviation derived)
StructureBite angle
dppm 1,1-Bis(diphenylphosphino)methane Dppm-2D-skeletal.png 73
dmpe 1,2-Bis(dimethylphosphino)ethane Dmpe-2D-skeletal-B.png
dippe 1,2-Bis(diisopropylphosphino)ethane 1,2-Bis(diisopropylphosphino)ethane-2D-by-AHRLS-2012.png
dppbz 1,2-Bis(diphenylphosphino)benzene Dppbz.svg
dppe 1,2-Bis(diphenylphosphino)ethane DPPE structure.svg 86
DIPAMP derivative of phenylanisylmethylphosphine DIPAMP.png
dcpe Bis(dicyclohexylphosphino)ethane Dcpe.svg
dppp 1,3-Bis(diphenylphosphino)propane Dppp.svg 91
dppb 1,4-Bis(diphenylphosphino)butane Dppb.svg 94
DIOP (S,S)-DIOP (O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) (S,S)-DIOP.svg
Chiraphos 2,3-Bis(diphenylphosphino)butane Chiraphos.svg
BINAP 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl BINAP Enantiomers Structural Formulae V.1.svg 93
Xantphos 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene Xantphos.svg 108
DPEphos Bis[(2-diphenylphosphino)phenyl] ether DPEphos.svg 104
SPANphos 4,4,4',4',6,6'-Hexamethyl-2,2'-spirobichromane-8,8'-diylbis(diphenylphosphane) SPANphos.svg
SEGPHOS 4,4'-Bi-1,3-benzodioxole-5,5'-diylbis(diphenylphosphane) R-SEGPHOS.svg
dppf 1,1'-Bis(diphenylphosphino)ferrocene Dppfnew.png 99
Me-DuPhos 1,2-Bis(2,5-dimethylphospholano)benzene DuPhos ligands.svg
Josiphos (Diphenylphosphino)ferrocenyl-ethyldicyclohexylphosphine1,5-Diaza-3,7-diphosphacyclooctanes Josiphos.png
P2N2 1,5-Diaza-3,7-diphosphacyclooctanes P2N2ligand.png

See also

Dialkylbiaryl phosphine ligands

Related Research Articles

<span class="mw-page-title-main">Triphenylphosphine</span> Chemical compound

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.

Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective insecticides, although some are extremely toxic to humans, including sarin and VX nerve agents.

<span class="mw-page-title-main">1,2-Bis(diphenylphosphino)ethane</span> Chemical compound

1,2-Bis(diphenylphosphino)ethane (dppe) is an organophosphorus compound with the formula (Ph2PCH2)2 (Ph = phenyl). It is a commonly used bidentate ligand in coordination chemistry. It is a white solid that is soluble in organic solvents.

<span class="mw-page-title-main">Hapticity</span> Number of contiguous atoms in a ligand that bond to the central atom in a coordination complex

In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated. In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity, and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.

Organophosphines are organophosphorus compounds with the formula PRnH3−n, where R is an organic substituent. These compounds can be classified according to the value of n: primary phosphines (n = 1), secondary phosphines (n = 2), tertiary phosphines (n = 3). All adopt pyramidal structures. Organophosphines are generally colorless, lipophilic liquids or solids. The parent of the organophosphines is phosphine (PH3).

<span class="mw-page-title-main">1,1'-Bis(diphenylphosphino)ferrocene</span> Chemical compound

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).

<span class="mw-page-title-main">1,2-Bis(dimethylarsino)benzene</span> Chemical compound

1,2-Bis(dimethylarsino)benzene (diars) is the organoarsenic compound with the formula C6H4(As(CH3)2)2. The molecule consists of two dimethylarsino groups attached to adjacent carbon centers of a benzene ring. It is a chelating ligand in coordination chemistry. This colourless oil is commonly abbreviated "diars."

<span class="mw-page-title-main">Bite angle</span>

In coordination chemistry, the bite angle is the angle on a central atom between two bonds to a bidentate ligand. This ligand–metal–ligand geometric parameter is used to classify chelating ligands, including those in organometallic complexes. It is most often discussed in terms of catalysis, as changes in bite angle can affect not just the activity and selectivity of a catalytic reaction but even allow alternative reaction pathways to become accessible.

<span class="mw-page-title-main">Diphenylphosphine</span> Chemical compound

Diphenylphosphine, also known as diphenylphosphane, is an organophosphorus compound with the formula (C6H5)2PH. This foul-smelling, colorless liquid is easily oxidized in air. It is a precursor to organophosphorus ligands for use as catalysts.

<span class="mw-page-title-main">Bis(diphenylphosphino)methane</span> Chemical compound

1,1-Bis(diphenylphosphino)methane (dppm), is an organophosphorus compound with the formula CH2(PPh2)2. Dppm, a white, crystalline powder, is used in inorganic and organometallic chemistry as a ligand. It is more specifically a chelating ligand because it is a ligand that can bond to metals with two phosphorus donor atoms. The natural bite angle is 73°.

<span class="mw-page-title-main">1,3-Bis(diphenylphosphino)propane</span> Chemical compound

1,3-Bis(diphenylphosphino)propane (dppp) is an organophosphorus compound with the formula Ph2P(CH2)3PPh2. The compound is a white solid that is soluble in organic solvents. It is slightly air-sensitive, degrading in air to the phosphine oxide. It is classified as a diphosphine ligand in coordination chemistry and homogeneous catalysis.

<span class="mw-page-title-main">Metal-phosphine complex</span>

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).

<span class="mw-page-title-main">Spectator ligand</span>

In coordination chemistry, a spectator ligand is a ligand that does not participate in chemical reactions of the complex. Instead, spectator ligands occupy coordination sites. Spectator ligands tend to be of polydentate, such that the M-spectator ensemble is inert kinetically. Although they do not participate in reactions of the metal, spectator ligands influence the reactivity of the metal center to which they are bound. These ligands are sometimes referred to as ancillary ligands.

<span class="mw-page-title-main">Transition-metal allyl complex</span>

Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2, which is usually described as two equivalent resonance structures.

<span class="mw-page-title-main">1,5-Diaza-3,7-diphosphacyclooctanes</span>

1,5-Diaza-3,7-diphosphacyclooctanes are organophosphorus compounds with the formula [R'NCH2P(R)CH2]2, often abbreviated PR2NR'2. They are air-sensitive white solids that are soluble in organic solvents. The ligands exist as meso and d,l-diastereomers, but only the meso forms function as bidentate ligands.

In organophosphorus chemistry, an aminophosphine is a compound with the formula R3−nP(NR2)n where R = H or an organic substituent, and n = 0, 1, 2. At one extreme, the parent H2PNH2 is lightly studied and fragile, but at the other extreme tris(dimethylamino)phosphine (P(NMe2)3) is commonly available. Intermediate members are known, such as Ph2PN(H)Ph. These compounds are typically colorless and reactive toward oxygen. They have pyramidal geometry at phosphorus.

<span class="mw-page-title-main">1,4-Bis(diphenylphosphino)butane</span> Chemical compound

1,4-Bis(diphenylphosphino)butane (dppb) is an organophosphorus compound with the formula (Ph2PCH2CH2)2. It is less commonly used in coordination chemistry than other diphosphine ligands such as dppe. It is a white solid that is soluble in organic solvents.

1,2-Bis(dichlorophosphino)ethane is an organophosphorus compound with the formula (CH2PCl2)2. A colorless liquid, it is a precursor to chelating diphosphines.

1,2-Bis(diphenylphosphino)benzene (dppbz) is an organophosphorus compound with the formula C6H4(PPh2)2 (Ph = C6H5). Classified as a diphosphine ligand, it is a common bidentate ligand in coordination chemistry. It is a white, air-stable solid. As a chelating ligand, dppbz is very similar to 1,2-bis(diphenylphosphino)ethylene.

cis-1,2-Bis(diphenylphosphino)ethylene (dppv) is an organophosphorus compound with the formula C2H2(PPh2)2 (Ph = C6H5). Both the cis and trans isomers are known, but the cis isomer is of primary interest. Classified as a diphosphine ligand, it is a bidentate ligand in coordination chemistry. For example it gives rise to the complex Ni(dppv)2 and the coordination polymer [Ni(dppv)]n. As a chelating ligand, dppv is very similar to 1,2-bis(diphenylphosphino)benzene.

References

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