Diphosphene
Encyclopedia
In chemistry
, a diphosphene is an organophosphorus compound that has a phosphorus
-phosphorus double bond
, denoted by R-P=P-R'. These compounds are not common but are of theoretical interest. Normally, compounds with the empirical formula RP exist as rings. However, when the organic substituent is very large, the diphosphene becomes stable. The parent compound, called diphosphene (diphosphaethylene), has the formula P2H2, but is not stable near room temperature.
, (PhN=NPh), but it later turned out that their product was the cyclic pentamer with P-P single bonds. Transition metal
complexes formally containing "diphosphene ligands" are known, but such compoounds do not dissociate into and are rarely made from true diphosphenes.
In 1981, Masaaki Yoshifuji and coworkers reported the first stable diphosphene, which is stabilized by very bulky substituents attached to the phosphorus centers. The orange solid is generated by an Wurtz-like coupling reaction
:
Several other diphosphenes have since been characterized, all featuring large organic substituents.
Diphosphenes have trans structures, in which the C-P-P angles deviate from 90° due to steric repulsion between the bulky organic substituents. The P-P distances range from 195.4 to 204.4 pm (1.954 to 2.044 Å), about 10% shorter than typical P-P single bond length of 222 pm.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, a diphosphene is an organophosphorus compound that has a phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
-phosphorus double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
, denoted by R-P=P-R'. These compounds are not common but are of theoretical interest. Normally, compounds with the empirical formula RP exist as rings. However, when the organic substituent is very large, the diphosphene becomes stable. The parent compound, called diphosphene (diphosphaethylene), has the formula P2H2, but is not stable near room temperature.
Synthesis and structure
In 1887, H. Köhler and A. Michaelis reported the isolation of a compound that was thought to be the phosphorus analogue of azobenzeneAzobenzene
Azobenzene is a chemical compound composed of two phenyl rings linked by a N=N double bond. It is the best known example of an azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of molecules that share the core azobenzene structure, with different chemical...
, (PhN=NPh), but it later turned out that their product was the cyclic pentamer with P-P single bonds. Transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
complexes formally containing "diphosphene ligands" are known, but such compoounds do not dissociate into and are rarely made from true diphosphenes.
In 1981, Masaaki Yoshifuji and coworkers reported the first stable diphosphene, which is stabilized by very bulky substituents attached to the phosphorus centers. The orange solid is generated by an Wurtz-like coupling reaction
Wurtz reaction
The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium to form a new carbon-carbon bond:...
:
- 2 (t-Bu)3C6H2PCl2 + 2 Mg → [(t-Bu)3C6H2P]2 + 2 MgCl2 (t-Bu = (CH3)3C)
Several other diphosphenes have since been characterized, all featuring large organic substituents.
Diphosphenes have trans structures, in which the C-P-P angles deviate from 90° due to steric repulsion between the bulky organic substituents. The P-P distances range from 195.4 to 204.4 pm (1.954 to 2.044 Å), about 10% shorter than typical P-P single bond length of 222 pm.