Iron(II) Complexes of the Linear <i>rac-</i>Tetraphos‑1 Ligand as Efficient Homogeneous Catalysts for Sodium Bicarbonate Hydrogenation and Formic Acid Dehydrogenation

The linear tetraphosphine 1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane (tetraphos-1, P4) was used as its rac and meso isomers for the synthesis of both molecularly defined and in situ formed Fe­(II) complexes. These were used as precatalysts for sodium bicarbonate hydrogenation to formate and formic acid dehydrogenation to hydrogen and carbon dioxide with moderate to good activities in comparison to those for literature systems based on Fe. Mechanistic details of the reaction pathways were obtained by NMR and HPNMR experiments, highlighting the role of the Fe­(II) monohydrido complex [FeH­(rac-P4)]+ as a key intermediate. X-ray crystal structures of different complexes bearing rac-P4 were also obtained and are described herein.