An electrochemical investigation of intermediates and processes involved in the catalytic reduction of dinitrogen by [HIPTN_3N]Mo (HIPTN _3N = (3,5-(2,4,6-i-Pr_3C_6H_2) _2C_6H_3NCH_2CH_2) _3N)

摘要

The redox properties of [HIPTN3N]Mo complexes (where HIPTN _3N = (3,5-(2,4,6-i-Pr_3C_6H_2) _2C_6H_3NCH_2CH_2) _3N) involved in the catalytic dinitrogen reduction cycle were studied using cyclic voltammetry in fluorobenzene with Bu_4NPF_6 as the electrolyte. MoN_2 (Mo = [HIPTN_3N]Mo, E_(1/2) = -1.96 V vs. Fc~+/Fc at a Pt electrode), Mo≡N (E_(1/2) = -2.68 V vs. Fc~+/Fc (Pt)), and [Mo(NH_3)] BAr′_4 (Ar′ = 3,5-(CF_3)_2C _6H_3, E_(1/2) = -1.53 V vs. Fc~+/Fc (Pt)) each undergo a chemically reversible one-electron reduction, while [MoNNH _2]BAr′_4 (E_(1/2) = -1.50 V vs. Fc ~+/Fc (Pt)) and [MoNH]BAr′_4 (E_(1/2) = -1.26 V vs. Fc~+/Fc (Pt)) each undergo a one-electron reduction with partial chemical reversibility. The acid employed in the catalytic reduction, [2,4,6-collidinium]BAr′_4, reduces irreversibly at -1.11 V vs. Fc~+/Fc at Pt and at -2.10 V vs. Fc~+/Fc at a glassy carbon electrode. The reduction peak potentials of the Mo complexes shift in the presence of acids. For example, the reduction peak for MoN_2 in the presence of [2,4,6-collidinium]BAr′_4 at a glassy carbon electrode shifts positively by 130 mV. The shift in reduction potential is explained in terms of reversible hydrogen bonding and/or protonation at a nitrogen site in Mo complexes. The significance of productive and unproductive proton-coupled electron transfer reactions in the catalytic dinitrogen reduction cycle is discussed. This journal is