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

Oxidation of the Chatt-type tungsten dinitrogen compound, <i>trans</i>-(depe)₂W-(N₂)₂ (depe = Et₂PCH₂CH₂PEt₂), with [(η⁵-C₅H₅)₂Fe]-[BAr^F ₄] (BAr^F ₄ = B-(3,5-(CF₃)₂C₆H₃)₄) resulted in isolation of [(depe)₂WN]-[BAr^F ₄], a rare example of a tungsten-(IV) nitride prepared from N₂ cleavage. A bimetallic μ-N₂ ditungsten intermediate supported by terminal N₂ ligands was identified, and irradiation with visible light promoted dinitrogen cleavage and formation of [(depe)₂WN]-[BAr^F ₄]. Performing the analogous one-electron oxidation of the related tungsten dinitrogen compound, <i>trans</i>-(dppe)₂W-(N₂)₂ (dppe = Ph₂PCH₂CH₂PPh₂), furnished the corresponding cationic, 17-electron tungsten dinitrogen complex, [(dppe)₂W-(N₂)₂]-[BAr^F ₄], that was characterized by X-ray diffraction and vibrational and EPR spectroscopies. The generation of [(dppe)₂W-(N)]-[BAr^F ₄] was observed in low yield from the <i>in situ</i> formed mixed N₂-bridged compound, [(N₂)-(depe)₂W-(μ-N₂)-W-(dppe)₂(N₂)]-[BAr^F ₄]₂, and was confirmed by independent synthesis using 1-azidoadamantane. Addition of ammonia or water to [(depe)₂WN]-[BAr^F ₄] resulted in formation of the cationic imide and hydroxide complexes, [(depe)₂W-(NH)-(X)]-[BAr^F ₄] (X = NH₂, OH). Irradiation of [(depe)₂WN]-[BAr^F ₄] 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^F ₄], 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.