1,5-Diaza-3,7-diphosphacyclooctanes are

organophosphorus compound 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 hydrocarbo ...

s with the formula 'NCHP(R)CH often abbreviated PN. They are air-sensitive white solids that are soluble in organic solvents. The ligands exist as meso and d,l-

diastereomer In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have di ...

s, but only the meso forms function as

bidentate ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ...

s. Some metal-PN complexes catalyze the

hydrogen evolution reaction Hydrogen evolution reaction (HER) is a chemical reaction that yields H2. The conversion of protons to H2 requires reducing equivalents and usually a catalyst. In nature, HER is catalyzed by hydrogenase enzymes which rely on iron- and nickel-based c ...

as well as the oxidation of

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

(H). The catalytic mechanism involves the interaction of substrate with the amines in the

second coordination sphere In coordination chemistry, the first coordination sphere refers to the array of molecules and ions (the ligands) directly attached to the central metal atom. The second coordination sphere consists of molecules and ions that attached in various ...

Synthesis and reactions

The ligands are prepared by the condensation of a primary phosphine,

formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

, and a primary amine: : Diazadiphosphacyclooctanes function as chelating

diphosphine Diphosphane, or diphosphine, is an inorganic compound with the chemical formula . This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air. Properties, ...

ligands. Typical nickel complexes contain two such ligands are give the formula i(PN) Cationic complexes of these and related ligands often exhibit enhanced reactivity toward H₂. These complexes serve as electrocatalysts for H₂ evolution.

Related ligands

Azadiphosphacycloheptanes are a related family of

s, but containing only one amine. They are prepared by condensation of 1,2-bis(phenylphosphino)ethane, formaldehyde, and a primary amine. From the meso-isomer, typical nickel complexes contain two such ligands, i.e. i(PNR') When bound to metals, these ligands adopt a conformation similar to that of 1,4-diazacycloheptanes. Acyclic phosphine-amine ligands have the formula (RPCH)NR'.

References

{{DEFAULTSORT:Diaza-3, 7-diphosphacyclooctanes, 1, 5- Chelating agents Diphosphines Phosphorus heterocycles