Synthesis and Thermally and Light Driven Cleavage of an N-Heterocyclic Diphosphine with Inorganic Backbone

A diphosphine with an unsupported PP bond connecting two carbon-free "inorganic" 1,3,2,4,5-diazaphosphadisilolidine rings was prepared by reductive coupling of a P-chloro-substituted monocyclic precursor molecule. VT-EPR studies revealed that the diphosphine exists in solution, like other compounds of this kind, in dynamic equilibrium with the corresponding phosphinyl radicals. Determination of the radical concentration from the EPR spectra permitted to calculate thermochemical parameters for the homolytic PP bond fission. The results disclose that both the enthalpy and entropy of dissociation are higher than in topologically related bi(diazaphospholidines). The impact of the entropy term allows explaining that, regardless of the presence of an energetically rather stable PP bond, the onset of dissociation is observable even at ambient temperature. Irradiation experiments showed that radical formation cannot only be induced thermally, but also by photolysis.Peer reviewe