A tungsten complex containing a highly delocalized metal–ligand system

Nucleophilic attack of (triphenylphosphonio)cyclopentadienide on the dichlorodiazomethane–tungsten complex trans‐BrW(dppe)₂(N₂CCl₂)]PF₆ dppe is 1,2‐bis(diphenylphosphino)ethane] results in C—C bond formation and affords the title compound, trans‐W(C₂₄H₁₈ClN₂P)Br(C₂₆H₂₄P₂)₂]PF₆·0.6CH₂Cl₂. This complex, bis1,2‐bis(diphenylphosphino)ethane]bromido{chloro3‐(triphenylphosphonio)cyclopentadienylidene]diazomethanediido}tungsten hexafluorophosphate dichloromethane 0.6‐solvate, contains the previously unknown ligand chloro3‐(triphenylphosphonio)cyclopentadienylidene]diazomethane. Evidence from bond lengths and torsion angles indicates significant through‐ligand delocalization of electron density from tungsten to the nominally cationic phosphorus(V) centre. This structural analysis clearly demonstrates that the tungsten–dinitrogen unit is a powerful π‐electron donor with the ability to transfer electron density from the metal to a distant acceptor centre through an extended conjugated ligand system. As a consequence, complexes of this type could have potential applications as nonlinear optical materials and molecular semiconductors.