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

Molybdenum(III) complexes bearing pincer-type ligands are well-known catalysts for N₂-to-NH₃ reduction. We investigated herein the impact of an anionic PNP pincer-type ligand in a Mo(III) complex on the (electro)chemical N₂ splitting ([LMoCl₃]^-, 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 N₂ activation. The catalyst is indeed active in N₂-to-NH₃ conversion utilizing the proton-coupled electron transfer reagent SmI₂/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 N₂ atmosphere. IR- and UV/vis-SEC measurements suggest that N₂ splitting occurs via formation of an "overreduced" but more stable [(L(N₂)₂Mo⁰)₂μ-N₂]^2- dimer. In line with this, the yield in the nitrido complex increases with lower applied potentials.