Phosphinine

Phosphinine (aka phosphorine, phosphorin, and phosphabenzene¹) is a heteroaromatic compound that is the phosphorus analogue of pyridine. It was first described in 1961 by H. Depoorter, J. Nys, and A. Van Dormael at Gevaert Photo-Producten N.V. (Mortsel, Belgium) in an article on new classes of phosphorus-containing dyes, although none of the dyes contained the phosphinine structure.

In 1968, Karl Dimroth and co-workers at Philipps University of Marburg (Germany) wrote about the oxidation products of phosphorin, but the work pertained only to phosphinine derivatives. But 3 years later, Arthur A. Ashe III at the University of Michigan (Ann Arbor) reported the synthesis and properties of phosphabenzene and the related heteroarene arsabenzene². Ashe and Paul Shu treated the previously prepared molecule 1,4-dihydro-1,1-dibutylstannabenzene³ with phosphorus tribromide⁴ to form the hydrobromide salt of phosphinine, then added base to give the unsubstituted compound. They found that phosphinine/phosphabenzene is an air-sensitive but otherwise stable colorless, volatile liquid. Arsabenzene was similarly prepared by using arsenic trichloride⁵ in place of phosphorus tribromide. In 2016, Ashe wrote an essay about the background of his syntheses of phosphabenzene and its analogues.

Although phosphinine derivatives have been studied since the 1970s, few reports involve the base compound. In one from 2020, Jan Řezáč  at the Czech Academy of Science (Prague) included phosphinine (as phosphorine) in a dataset of the Non-Covalent Interactions Atlas of Benchmark Data Sets of hydrogen bonding in an extended chemical space. And in 2024, Slavko Radenković at the University of Kragujevac (Serbia), Miquel Solà at the University of Girona (Spain), Henrik Ottosson at Uppsala University (Sweden), and co-workers included the molecule in their study of the lowest excited n,π* states of heteroaromatic compounds. Among other findings, they concluded that the ³n,π* state of phosphinine is antiaromatic.

Phosphinine is not an article of commerce; thus, no hazard information is available.

1. These terms are used interchangeably in this article.
2. CAS Reg. No. 289-31-6.
3. CAS Reg. No. 31732-31-7.
4. CAS Reg. No. 7789-60-8.
5. CAS Reg. No. 7784-34-1.