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 cyclic phosphazane compounds. The cyclic tetramers and trimer are formed with methyl and ethyl substituents on nitrogen, whereas formation of cyclic dimers (cis-[ClP(μ-NR)]2) have been observed exclusively with more sterically demanding primary amines such as tert-butylamine and aniline.[1]

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.[2]

Chiral cyclodiphosphazanes have found use as ligands in asymmetric catalysis. Gade et al. employed them in enantioselective transition-metal mediated catalysis,[3] while Goldfuss et al. employed di-amino substituted chiral variants in hydrogen bonding catalysis.[4]

Cyclodiphosphazanes have also been found to have a high ability to bind anions via hydrogen bonding - specifically halides - in both their monomeric and macrocyclic forms. They are competitive to or better than comparable bifurcated anion binding structural motifs such as (thio)urea and squaramide.[5][6][7][8][9]

References
  1. Balakrishna, Maravanji S.; Eisler, Dana J.; Chivers, Tristram (2007). "Chemistry of pnictogen(III)–nitrogen ring systems". Chem. Soc. Rev. 36 (4): 650–664. doi:10.1039/b514861h.
  2. Ananthnag, Guddekoppa S.; Kuntavalli, Seema; Mague, Joel T.; Balakrishna, Maravanji S. (2012-05-07). "Resorcinol Based Acyclic Dimeric and Cyclic Di- and Tetrameric Cyclodiphosphazanes: Synthesis, Structural Studies, and Transition Metal Complexes". Inorganic Chemistry. 51 (10): 5919–5930. doi:10.1021/ic300541n.
  3. Roth, Torsten; Wadepohl, Hubert; Wright, Dominic S.; Gade, Lutz H. (2013-08-28). "Chiral Ditopic Cyclophosphazane (CycloP) Ligands: Synthesis, Coordination Chemistry, and Application in Asymmetric Catalysis". Chemistry - A European Journal. 19 (41): 13823–13837. doi:10.1002/chem.201302327.
  4. Klare, Helge; Neudörfl, Jörg M.; Goldfuss, Bernd (2014-01-21). "New hydrogen-bonding organocatalysts: Chiral cyclophosphazanes and phosphorus amides as catalysts for asymmetric Michael additions". Beilstein Journal of Organic Chemistry. 10 (1): 224–236. doi:10.3762/bjoc.10.18. PMC 3944119. PMID 24605142.
  5. Klare, Helge; Hanft, Sebastian; Neudörfl, Jörg M.; Schlörer, Nils E.; Griesbeck, Axel; Goldfuss, Bernd (2014-09-08). "Anion Recognition with Hydrogen-Bonding Cyclodiphosphazanes". Chemistry – A European Journal. 20 (37): 11847–11855. doi:10.1002/chem.201403013. ISSN 0947-6539.
  6. Wolf, Florian F.; Neudörfl, Jörg-M.; Goldfuss, Bernd (2018-03-26). "Hydrogen-bonding cyclodiphosphazanes: superior effects of 3,5-(CF3)2-substitution in anion-recognition and counter-ion catalysis". New Journal of Chemistry. 42 (7): 4854–4870. doi:10.1039/C7NJ04660J. ISSN 1369-9261.
  7. Plajer, Alex J.; Zhu, Jinbo; Proehm, Patrick; Bond, Andrew D.; Keyser, Ulrich F.; Wright, Dominic S. (2019-06-05). "Tailoring the Binding Properties of Phosphazane Anion Receptors and Transporters". Journal of the American Chemical Society. 141 (22): 8807–8815. doi:10.1021/jacs.9b00504. ISSN 0002-7863.
  8. Plajer, Alex J.; Zhu, Jinbo; Pröhm, Patrick; Rizzuto, Felix J.; Keyser, Ulrich F.; Wright, Dominic S. (2020-01-15). "Conformational Control in Main Group Phosphazane Anion Receptors and Transporters". Journal of the American Chemical Society. 142 (2): 1029–1037. doi:10.1021/jacs.9b11347. ISSN 0002-7863.
  9. Shi, Xiaoyan; León, Felix; Sim, Ying; Quek, Shina; Hum, Gavin; Khoo, Yi Xin Joycelyn; Ng, Zi Xuan; Par, Mian Yang; Ong, How Chee; Singh, Varun K.; Ganguly, Rakesh. "N-Bridged Acyclic Trimeric Poly-Cyclodiphosphazanes: Highly Tuneable Cyclodiphosphazane Building Blocks". Angewandte Chemie International Edition. n/a (n/a). doi:10.1002/anie.202008214. ISSN 1521-3773.
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