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][BArF4] (BArF4 = B(3,5-(CF3)2C6H3)4) resulted
in isolation of [(depe)2WN][BArF4], 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][BArF4]. 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][BArF4], that was characterized by X-ray diffraction and vibrational
and EPR spectroscopies. The generation of [(dppe)2W(N)][BArF4] was observed in low yield from the in
situ formed mixed N2-bridged compound, [(N2)(depe)2W(μ-N2)W(dppe)2(N2)][BArF4]2, and was
confirmed by independent synthesis using 1-azidoadamantane. Addition
of ammonia or water to [(depe)2WN][BArF4] resulted in formation of the cationic imide and hydroxide
complexes, [(depe)2W(NH)(X)][BArF4] (X = NH2, OH). Irradiation of [(depe)2WN][BArF4] 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][BArF4], 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.