Pyridyl-Functionalized 1-Phosphabarrelene: Synthesis, Coordination Chemistry and Photochemical di-pi-Methane Rearrangement

The [4+2] cycloaddition of 2‐(2′‐pyridyl)‐4,6‐diphenyl‐λ³‐phosphinine with the highly reactive dienophile hexafluoro‐2‐butyne has been studied and the first pyridyl‐functionalized 1‐phosphabarrelene was obtained and structurally characterized. Although monodentate CF₃‐1‐phosphabarrelenes show only a poor coordination ability, the chelating nature of the novel P,N‐hybrid ligand gives access to various transition‐metal complexes. Upon irradiation with UV light, the pyridyl‐functionalized 1‐phosphabarrelene undergoes a rather selective di‐π‐methane rearrangement in the coordination sphere of the metal center, leading to the formation of a complex based on a hitherto unknown pyridyl‐functionalized 5‐phosphasemibullvalene derivative. DFT calculations provide first insights into the mechanism of this reaction.