Synthesis, Structure, and Electrochemical Studies of Molybdenum and Tungsten Dinitrogen, Diazenido, and Hydrazido Complexes That Contain Aryl-Substituted Triamidoamine Ligands

One-electron reduction of [ArN3N]MoCl complexes (Ar = C6H5, 4-FC6H4, 4-t-BuC6H4, 3,5-Me2C6H3) yields
complexes of the type [ArN3N]Mo−NN−Mo[ArN3N], while two-electron reduction yields {[ArN3N]Mo−NN}- derivatives (Ar = C6H5, 4-FC6H4, 4-t-BuC6H4, 3,5-Me2C6H3, 3,5-Ph2C6H3, and 3,5-(4-t-BuC6H4)2C6H3).
Compounds that were crystallographically characterized include {[t-BuC6H4N3N]Mo}2(N2), Na(THF)6{[PhN3N]Mo−NN}2Na(THF)3, [t-BuC6H4N3N]Mo−NN−Na(15-crown-5), and {[Ph2C6H3N3N]MoNN}2Mg(DME)2. Compounds of the type [ArN3N]Mo−NN−Mo[ArN3N] do not appear to form when Ar = 3,5-Ph2C6H3 or 3,5-(4-t-BuC6H4)2C6H3, presumably for steric reasons. Treatment of diazenido complexes (e.g., [ArN3N]Mo−NN−Na(THF)x) with electrophiles such as Me3SiCl or MeOTf yielded [ArN3N]Mo−NNR complexes (R = SiMe3
or Me). These species react further to yield {[ArN3N]Mo−NNMe2}+ species in the presence of methylating
agents. Addition of anionic methyl reagents to {[ArN3N]Mo−NNMe2}+ species yielded [ArN3N]Mo(NNMe2)(Me) complexes. Reduction of [4-t-BuC6H4N3N]WCl under dinitrogen leads to a rare {[t-BuC6H4N3N]W}2(N2)
species that can be oxidized by two electrons to give a stable dication (as its BPh4- salt). Reduction of hydrazido
species leads to formation of Mo⋮N in low yields, and only dimethylamine could be identified among the many
products. Electrochemical studies revealed expected trends in oxidation and reduction potentials, but also provided
evidence for stable neutral dinitrogen complexes of the type [ArN3N]Mo(N2) when Ar is a relatively bulky terphenyl
substituent.