Catalytic Reduction of Dinitrogen to Ammonia and Hydrazine Using Iron–Dinitrogen Complexes Bearing Anionic Benzene-Based PCP-Type Pincer Ligands

Abstract

Among synthetic models of nitrogenases, iron-dinitrogen complexes with a Fe-C bond have attracted increasing attention in recent years. Here we report the synthesis of square-planar iron(I)-dinitrogen complexes supported by anionic benzene-based PCP-and POCOP-type pincer ligands as carbon donors. These complexes catalyze the formation of ammonia and hydrazine from the reaction of dinitrogen (1 atm) with a reductant and a proton source at −78 °C, producing up to 252 equiv of ammonia and 68 equiv of hydrazine (388 equiv of fixed N atom) based on the iron atom of the catalyst.Anionic iron(0)-dinitrogen complexes, considered an essential reactive species in the catalytic reaction, are newly isolated from the reduction of the corresponding iron(I)-dinitrogen complexes.This study examines their reactivity using experiments and DFT calculations.

PCP Pincer Complexes of Titanium in the +3 and +4 Oxidation States

“…Others have described forming this in situ, but it can be isolated as a highly reactive white solid in 81% yield. 18,21 Targeting the formation of Ti(IV) PCP complexes, [ tBu PCP] Li was reacted with TiCl 4 (THF) 2 in Et 2 O, resulting in the immediate formation of a red solution. Upon workup the desired product ( tBu PCP)TiCl 3 (1) could be isolated in low yield (30%).…”

PCP Complexes of Titanium in the +3 and +4 Oxidation State

“…Others have described forming this in-situ but it can be isolated as a highly-reactive white solid in 81% yield. 16,19 Targeting the formation of Ti(IV) PCP complexes, [ tBu PCP]Li was reacted with TiCl4(THF)2 in Et2O, resulting in the immediate formation of a red solution. Upon work-up the desired product ( tBu PCP)TiCl3, 1, could be isolated in low yield (30%).…”

Light Alters the NH3 vs N2H4 Product Profile in Iron‐catalyzed Nitrogen Reduction via Dual Reactivity from an Iron Hydrazido (Fe=NNH2) Intermediate

“…Using a related iron compound, P 3 B Fe + , (P 3 B =tris(o‐diisopropylphosphinophenyl)borane), Fe‐mediated N 2 ‐to‐NH 3 catalysis occurs, with only trace N 2 H 4 also observed [21, 22] . Nishibayashi and co‐workers have reported on iron catalysts such as (PNP)Fe(N 2 ) (Figure 1c) and (PCP)Fe(N 2 ) that generate varying amounts of NH 3 and N 2 H 4 depending on the reaction conditions [23–25] . Perhaps most strikingly, Ashley and co‐workers described (depe) 2 Fe(N 2 ) as a catalyst that is highly selective for N 2 ‐to‐N 2 H 4 conversion [26] …”

“…[21,22] Nishibayashi and co-workers have reported on iron catalysts such as (PNP)Fe(N 2 ) (Figure 1c) and (PCP)Fe(N 2 ) that generate varying amounts of NH 3 and N 2 H 4 depending on the reaction conditions. [23][24][25] Perhaps most strikingly, Ashley and co-workers described (depe) 2 Fe-(N 2 ) as a catalyst that is highly selective for N 2 -to-N 2 H 4 conversion. [26] Of ongoing interest is to understand how such iron systems mechanistically discriminate between NH 3 and N 2 H 4 .…”