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

Oxidation of the Chatt-type tungsten dinitrogen compound, -(depe)W-(N) (depe = EtPCHCHPEt), with [(η-CH)Fe]-[BAr ] (BAr = B-(3,5-(CF)CH)) resulted in isolation of [(depe)WN]-[BAr ], a rare example of a tungsten-(IV) nitride prepared from N cleavage. A bimetallic μ-N ditungsten intermediate supported by terminal N ligands was identified, and irradiation with visible light promoted dinitrogen cleavage and formation of [(depe)WN]-[BAr ]. Performing the analogous one-electron oxidation of the related tungsten dinitrogen compound, -(dppe)W-(N) (dppe = PhPCHCHPPh), furnished the corresponding cationic, 17-electron tungsten dinitrogen complex, [(dppe)W-(N)]-[BAr ], that was characterized by X-ray diffraction and vibrational and EPR spectroscopies. The generation of [(dppe)W-(N)]-[BAr ] was observed in low yield from the formed mixed N-bridged compound, [(N)-(depe)W-(μ-N)-W-(dppe)(N)]-[BAr ], and was confirmed by independent synthesis using 1-azidoadamantane. Addition of ammonia or water to [(depe)WN]-[BAr ] resulted in formation of the cationic imide and hydroxide complexes, [(depe)W-(NH)-(X)]-[BAr ] (X = NH, OH). Irradiation of [(depe)WN]-[BAr ] with 440 nm visible light in the presence of Ir-(ppy) (ppy = 2-phenylpyridine) under 4 atm of dihydrogen resulted in hydrogenation of the tungsten nitride to the cationic tungsten pentahydride, [(depe)WH]-[BAr ], 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.