Electrochemical Evaluation of Titanocenes in Ionic Liquids with Non‐coordinating and Coordinating Anions and Application for NH 3 Synthesis

Redox behaviors of monomeric and dimeric titanocenes, [Cp 2 TiCl 2 ] ( 1 ) and [(Cp 2 TiCl) 2 ] ( 2 ), were investigated in two different types of ionic liquid (IL) with non‐coordinating and coordinating anions, 1‐butyl‐1‐methylpyrrolidinium tris(pentafluoroethyl)‐ trifluorophosphate (Pyr 4 FAP) and 1‐butyl‐1‐methylpyrrolidinium triflate (Pyr 4 OTf), respectively. UV‐vis/NIR spectra obtained during the electrochemical reduction of 1 revealed that it was converted to 2 in the ILs through the formation of [Cp 2 TiCl] ( 3 ). In Pyr 4 OTf, 3 was coordinated with the OTf anion in the η 1 ‐O mode, during the electrochemical reductions of Ti(IV/III) process, whereas 3 was not coordinated by the FAP anion in Pyr 4 FAP. Additionally, electrochemical NH 3 synthesis was carried out in a solid polymer electrolyte cell by using a gas diffusion electrode coated with Pyr 4 FAP or Pyr 4 OTf containing titanocenes. The electrochemical reduction using 2 in Pyr 4 FAP at −1.5 V (vs. Ag/AgCl) gave a high yield (34 % at 29.9 C) of NH 3 per Ti ion. The electrochemical reduction using 1 in Pyr 4 OTf gave a 6.8 % yield of NH 3 per Ti ion at 20 °C. These findings indicate that the use of an IL with a non‐coordinating anion such as FAP contributes to the coordination and reduction of N 2 to titanocenes.