Azadiphosphaindane-1,3-diyls: A Class of Resonance-Stabilized Biradicals

Conversion of 1,2-bis(dichlorophosphino)benzene with sterically demanding primary amines led to the formation of 1,3-dichloro-2-aza-1,3-diphosphaindanes of the type C6H4(mu-PCl)(2)N-R. Reduction yielded the corresponding 2-aza-1,3-diphosphaindane-1,3-diyls (1), which can be described as phosphorus-centered singlet biradical(oid)s. Their stability depends on the size of the substituent R: While derivatives with R=Dmp (2,6-dimethylphenyl) or Ter (2,6-dimesitylphenyl) underwent oligomerization, the derivative with very bulky R=(tBu)Bhp (2,6-bis(benzhydryl)-4-tert-butylphenyl) was stable with respect to oligomerization in its monomeric form. Oligomerization involved activation of the fused benzene ring by a second equivalent of the monomeric biradical and can be regarded as formal [2+2] (poly)addition reaction. Calculations indicate that the biradical character in 1 is comparable with literature-known P-centered biradicals. Ring-current calculations show aromaticity within the entire ring system of 1.

Automated summary

The study revealed that the reaction of 1,2-bis(dichlorophosphino)benzene with sterically demanding primary amines resulted in the formation of a series of 1,3-dichloro-2-aza-1,3-diphosphaindanes, with the stability of the products depending on the size of substituent R. These products can be described as phosphorus-centered singlet biradical(oid)s, with oligomerization reactions occurring for some derivatives. Additionally, calculations showed that the biradical character in the products is comparable to known P-centered biradicals, and aromaticity was observed within the entire ring system.