1,2-Bisethane (dppe) is a commonly used bidentate ligand

Ligand

In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

 in coordination chemistry. Dppe is almost invariably chelated

Chelation

Chelation is the formation or presence of two or more separate coordinate bonds between apolydentate ligand and a single central atom....

, although there are examples of unidentate (e.g., W(CO)₅(dppe)) and of bridging behavior.

Preparation

The preparation of dppe is conducted via the alkylation

Alkylation

Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...

 of NaPPh₂ which is typically prepared from triphenylphosphine

Triphenylphosphine

Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

 (P(C₆H₅)₃) as follows:

1. P(C₆H₅)₃ + 2 Na → NaP(C₆H₅)₂ + NaC₆H₅

NaP(C₆H₅)₂, which is readily air-oxidized, is treated with 1,2-dichloroethane

1,2-Dichloroethane

The chemical compound 1,2-dichloroethane, commonly known by its old name of ethylene dichloride , is a chlorinated hydrocarbon, mainly used to produce vinyl chloride monomer , the major precursor for PVC production. It is a colourless liquid with a chloroform-like odour...

 (ClCH₂CH₂Cl) to give dppe:

2. 2 NaP(C₆H₅)₂ + ClCH₂CH₂Cl → (C₆H₅)₂PCH₂CH₂P(C₆H₅)₂ + 2 NaCl

Reduction

The reduction of dppe by lithium

Lithium

Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 to give PhHP(CH₂)₂PHPh has been reported.

1. Ph₂P(CH₂)₂PPh₂ + 4 Li → PhLiP(CH₂)₂PLiPh + 2 PhLi

Hydrolysis by water gives:

2. PhLiP(CH₂)₂PLiPh + 2 PhLi + 4H₂O → PhHP(CH₂)₂PHPh + 4 LiOH + 2C₆H₆

Oxidation

Treatment of dppe with conventional oxidants such as hydrogen peroxide

Hydrogen peroxide

Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 (H₂O₂), aqueous bromine

Bromine

Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

(Br₂), etc., always produces dppeO in low yield (e.g., 13%) as a result of non-selective oxidation leading to mixtures of the starting material, the monoxide, and dioxide. Selective mono-oxidation of dppe can be achieved by reaction with PhCH₂Br to give dppeO.

3. Ph₂P(CH₂)₂PPh₂ + PhCH₂Br → Ph₂P(CH₂)₂PPh₂(CH₂Ph)⁺Br^-

This is followed by purification and alkaline catalyzed hydrolysis of the mono-phosphonium salt.

4. Ph₂P(CH₂)₂PPh₂(CH₂Ph)⁺Br^- + NaOH + H₂O → Ph₂P(CH₂)₂P(O)Ph₂

Coordination chemistry

Coordination complexes of dppe, and diphosphine ligands in general, are almost entirely used as homogeneous catalysts for a wide range of reactions. Two simple coordination complexes of dppe include Pd(dppe)₂ and Ir(dppe)₂. Pd(dppe)₂ can be prepared by reduction of Pd(II) with NaBH₄. It is most conveniently prepared, however, in situ from Pd(OAc)₂.