Synthesis, Structural Characterization, and Catalytic H₂ Production of Ferrocenyl (Fc) Group Containing Complexes [Ni(P^Fc₂N^Ar₂)₂](BF₄)₂ (Ar = Ph, p‑BrC₆H₄)

Two new ferrocenyl (Fc) group containing 1,5-diaza-3,7-diphosphacyclooctane ligands, P^Fc₂N^Ar₂ (1, Ar = Ph; 2, Ar = p-BrC₆H₄), were prepared by reaction of FcPH₂ with 2 equiv of paraformaldehyde in glycol followed by treatment of the resulting FcP­(CH₂OH)₂ with 1 equiv of aniline or p-bromoaniline in 79% and 67% yields, respectively; however, ligands 1 and 2 could be also prepared by treatment of the isolated and purified FcP­(CH₂OH)₂ with 1 equiv of aniline or p-bromoaniline under similar conditions in 80% and 72% yields, respectively. Further treatment of 1 or 2 with the complex salt [Ni­(MeCN)₆]­(BF₄)₂ in MeCN at room temperature resulted in formation of the first ferrocenyl-containing complexes [Ni­(P^Fc₂N^Ar₂)₂]­(BF₄)₂ (3, Ar = Ph; 4, Ar = p-BrC₆H₄) in 95% and 90% yields, respectively. Compounds 1–4 were structurally characterized by elemental analysis and spectroscopy and particularly for 1, 2, and 4 by X-ray crystallography. When the cyclic voltammetric behavior of 1–4 was investigated, 3 and 4 were found to be electrocatalysts for proton reduction of TFA to give hydrogen under CV conditions.