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

摘要

One-electron reduction of [ArN_3N]MoCl complexes (Ar = C_6H_5, 4-FC_6H_4, 4-t-BuC_6H_4, 3,5-Me_2C_6H_3) yields complexes of the type [ArN_3N]Mo-N=N-Mo[ArN_3N], while two-electron reduction yields {[ArN_3N]Mo-N=N}~- derivatives (Ar = C_6H_5, 4-FC_6H_4, 4-t-BuC_6H_4, 3,5-Me_2C_6H_3, 3,5-Ph_2C_6H_3, and 3,5-4-t-BuC_6H_4)_2C_6H_3). Compounds that were crystallographically characterized include {[t-BuC_6H_4N]Mo}_2(N_2), Na(THF)_6{[PhN_3N]Mo}-N=N}_2(THF)_3, [t-BuC_6H_4N_3N]Mo-N=Na(15-crown-5), and {[Ph_2C_6H_3N_3N]MoNN}_2Mg(DME)_2. Compounds of the type [ArN_3N]Mo-N=N-Mo[ArN_3N] do not appear to form when Ar = 3,5-Ph_2C_6H_3, or 3,5-(4-t-BuC_6H_4)_2C_6H_3, presumably for steric reasons. Treatment of diazenido complexes (e.g., [ArN_3N]Mo-N=N-Na(THF)_x) with electrophiles such as Me_3SiCl or MeOTf yielded [ArN_3N]Mo-N=NR complexes (R = SiMe_3 or Me). These species react further to yield {[ArN_3N]Mo-N=NMe_2}~+ species in the presence of methylating agents. Addition of anionic methyl reagents to {[ArN_3N]Mo-N=NMe_2}~+ species yielded [ArN_3N]Mo(N=NMe_2}(Me) complexes. Reduction of [4-t-BuC_6H_4N_3N]WCl under dinitrogen leads to a rare {[t-BuC_6H_4N_3N]W}_2(N_2) species that can be oxidized by two electrons to give a stable dication (as its BPh_4~- 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 [ArN_3N]Mo(N_2) when Ar is a relatively bulky terphenyl substituent.