Design and Synthesis of a “Starburst”‐Type Nonadiazo Compound and Magnetic Characterization of Its Photoproduct

A “starburst”‐type nonadiazo compound was designed and synthesized by using the cyclotrimerization of 3,5‐dibenzylphenyl ethynyl ketone as a key step. The diazo compound was photolyzed in methyltetrahydrofuran solid solution at cryogenic temperatures and analyzed by means of Faraday magnetometry and EPR spectroscopy. While the m ‐phenylene‐connected nonacarbene was predicted to have a nonadecet ( S = 9) ground state, the magnetic data of the photoproduct was more consistent with a pentadecet ( S = 7) species. The result was interpreted in terms of the intramolecular cross‐linking between the carbene centers by the determination of both the amount and the multiplicity of the spin. In the “starburst”‐type polycarbenes with extended branching, the reactive carbene centers are able to approach one another and thus appear to readily recombine. This study highlights one of the limitations of the extension of the carbene network by way of flexible “starburst”‐type structures.