(Electro)chemical N₂ Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand

Abstract

Molybdenum(III) complexes bearing pincer-type ligands are well-known catalysts for N 2 -to-NH 3 reduction. We investigated herein the impact of an anionic PNP pincer-type ligand in a Mo(III) complex on the (electro)chemical N 2 splitting ([LMoCl 3 ] − , 1 − , LH = 2,6-bis((di-tert-butylphosphaneyl)methyl)pyridin-4-one). The increased electron-donating properties of the anionic ligand should lead to a stronger degree of N 2 activation. The catalyst is indeed active in N 2 -to-NH 3 conversion utilizing the proton-coupled electron transfer reagent SmI 2 /ethylene glycol. The corresponding Mo(V) nitrido complex 2H exhibits similar catalytic activity as 1H and thus could represent a viable intermediate. The Mo(IV) nitrido complex 3 − is also accessible by electrochemical reduction of 1 − under a N 2 atmosphere. IRand UV/vis-SEC measurements suggest that N 2 splitting occurs via formation of an "overreduced" but more stable [(L(N 2 ) 2 Mo 0 ) 2 μ-N 2 ] 2− dimer. In line with this, the yield in the nitrido complex increases with lower applied potentials.

Mechanistic Insights into Key Steps of Dinitrogen Reduction to Ammonia with Pincer ligated Mo Complexes: Case Study of Easily Reduced PSP Mo Complexes

“…Other Mo-pincer complexes have also been found to effectively catalyze ammonia formation or, in some cases, to effect the key N2 cleavage step though not as part of an catalytic cycle for ammonia formation. 12,16,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] Figure 1. (a) Schrock's (triamidoamine)Mo catalyst.…”