An electrochemical investigation of intermediates and processes involved in the catalytic reduction of dinitrogen by [HIPTN sub(3)N]Mo (HIPTN sub(3)N = (3,5-(2,4,6-i-Pr sub(3)C sub(6)H sub(2)) sub(2)C sub(6)H sub(3)NCH sub(2)CH sub(2)) sub(3)N)

The redox properties of [HIPTN sub(3)N]Mo complexes (where HIPTN sub(3)N = (3,5-(2,4,6-i-Pr sub(3)C sub(6)H sub(2)) sub(2)C sub(6)H sub(3)NCH sub(2)CH sub(2)) sub(3)N) involved in the catalytic dinitrogen reduction cycle were studied using cyclic voltammetry in fluorobenzene with Bu sub(4)NPF sub(6) as the electrolyte. MoN sub(2) (Mo = [HIPTN sub(3)N]Mo, E sub(1/2) = -1.96 V vs. Fc super(+)/Fc at a Pt electrode), Mo identical with N (E sub(1/2) = -2.68 V vs. Fc super(+)/Fc (Pt)), and [Mo(NH sub(3))]BAr' sub( 4) (Ar' = 3,5-(CF sub(3)) sub(2)C sub(6)H sub(3), E sub(1/2) = -1.53 V vs. Fc super(+)/Fc (Pt)) each undergo a chemically reversible one-electron reduction, while [Mo&z.dbd; NNH sub(2)]BAr' sub(4) (E sub(1/2) = -1.50 V vs. Fc super(+)/Fc (Pt)) and [Mo&z.dbd; NH]BAr' sub(4) (E sub(1/2) = -1.26 V vs. Fc super(+)/Fc (Pt)) each undergo a one-electron reduction with partial chemical reversibility. The acid employed in the catalytic reduction, [2,4,6-collidinium]BAr' sub(4), reduces irreversibly at -1.11 V vs. Fc super(+)/Fc at Pt and at -2.10 V vs. Fc super(+)/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 sub(2) in the presence of [2,4,6-collidinium]BAr' sub(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.