Synthesis and Photodriven Hydrogenation of Tungsten Nitride Complexes Prepared from Dinitrogen Cleavage

Oxidation of the Chatt-type tungsten dinitrogen compound, trans-(depe)₂W(N₂)₂(depe = Et₂PCH₂CH₂PEt₂), with [(η⁵-C₅H₅)₂Fe][BAr^F₄] (BAr^F₄= B(3,5-(CF₃)₂C₆H₃)₄) resulted in isolation of [(depe)₂WN][BAr^F₄], a rare example of a tungsten(IV) nitride prepared from N₂cleavage. A bimetallic μ-N₂ditungsten intermediate supported by terminal N₂ligands was identified, and irradiation with visible light promoted dinitrogen cleavage and formation of [(depe)₂WN][BAr^F₄]. Performing the analogous one-electron oxidation of the related tungsten dinitrogen compound, trans-(dppe)₂W(N₂)₂(dppe = Ph₂PCH₂CH₂PPh₂), furnished the corresponding cationic, 17-electron tungsten dinitrogen complex, [(dppe)₂W(N₂)₂][BAr^F₄], that was characterized by X-ray diffraction and vibrational and EPR spectroscopies. The generation of [(dppe)₂W(N)][BAr^F₄] was observed in low yield from the in situ formed mixed N₂-bridged compound, [(N₂)(depe)₂W(μ-N₂)W(dppe)₂(N₂)][BAr^F₄]₂, and was confirmed by independent synthesis using 1-azidoadamantane. Addition of ammonia or water to [(depe)₂WN][BAr^F₄] resulted in formation of the cationic imide and hydroxide complexes, [(depe)₂W(NH)(X)][BAr^F₄] (X = NH₂, OH). Irradiation of [(depe)₂WN][BAr^F₄] with 440 nm visible light in the presence of Ir(ppy)₃(ppy = 2-phenylpyridine) under 4 atm of dihydrogen resulted in hydrogenation of the tungsten nitride to the cationic tungsten pentahydride, [(depe)₂WH₅][BAr^F₄], with the release of free ammonia in 21% yield, a rare example of ammonia generation from dinitrogen and dihydrogen from a well-defined tungsten nitride.