Cyclodiphosphazane

A cyclodiphosphazane is a type of chemical compound and a saturated four membered P₂N₂ ring and one of the major classes of cyclic phosphazene compounds. Bis(chloro)cyclodiphosphazanes, cis-[ClP(μ-NR)]₂ are important starting compounds for synthesizing a variety of cyclodiphosphazane derivatives by nucleophilic substitution reactions; are prepared by reaction of phosphorus trichloride (PCl₃) with a primary amine (RNH₂) or amine hydrochlorides (RNH₃Cl).

Organic substituents on nitrogen play an important role in formation of cyclicphosphazane compounds. The cyclic tetramers (I) and trimer (II) are formed with organic substituents such as methyl and ethyl on nitrogen, whereas formation of cyclic dimers cis-[ClP(μ-NR)]₂ have been observed exclusively with more sterically demanding primary amines such as ''t''-BuNH₂ and PhNH₂.

Coordination Chemistry

Cyclodiphosphazanes are excellent ligand systems for metallosupramolecular chemistry. The cis-oriented lone pair on phosphorus in cyclodiphosphazane are projected away from each other, so chelation to metal center is not possible. This bridging coordination of cyclodiphosphazane allows formation of metallomacrocycles containing four rhodium and gold centers and metallopolymers CuX, AgX.

Chiral cylcodiphosphazanes have found use as ligands in asymmetric catalysis. Gade et al. employed them in enantioselective transition-metal mediated catalysis(1), while Goldfuss et al. employed di-amino substituted chiral variants in hydrogen bonding catalyis(2).

Literature

(1) T. Roth, H. Wadepohl, D. S. Wright and L. H. Gade, Chemistry, 2013, 19, 13823-13837 (2) H. Klare, J. M. Neudörfl, B. Goldfuss, Beilstein J. Org. Chem., 2014, 10, 224-226