(Electro)chemical N 2 Splitting by a Molybdenum Complex with an Anionic PNP Pincer-Type Ligand.

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 ([ L MoCl 3 ] - , 1 - , L H = 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. IR- and 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.