Amine‐containing tertiary phosphine‐substituted diiron ethanedithioate (edt) complexes Fe 2 ( μ ‐edt)(CO) 6‐n L n ( n = 1, 2): Synthesis, protonation, and electrochemical properties

As diiron subsite models of [FeFe]‐hydrogenases for catalytic proton reduction to hydrogen (H 2 ), a new series of the phosphine‐substituted diiron ethanedithiolate complexes Fe 2 ( μ ‐edt)(CO) 6‐n L n ( n = 1, 2) were prepared from the variable substitutions of all‐CO precursor Fe 2 ( μ ‐edt)(CO) 6 ( A ) and tertiary phosphines (L1‐L4) under different reaction conditions. While the Me 3 NO‐assisted substitutions of A and one equiv. ligands L1‐L4 [L = Ph 2 P(CH 2 NHBu t ), Ph 2 P(CH 2 CH 2 NH 2 ), Ph 2 P(NHBu t ), and Ph 2 P(C 6 H 4 Me‐ p )] produced the monosubstituted complexes Fe 2 ( μ ‐edt)(CO) 5 L ( 1 – 4 ) in good yields, the refluxing xylene solution of A and two equiv. ligand L1 prepared complex Fe 2 ( μ ‐edt)(CO) 5 { κ 1 ‐Ph 2 P(CH 2 NHBu t )} ( 1 ) in low yield. Meanwhile, the UV‐irradiated toluene solution of A and two equiv. ligand L3 resulted in the rare formation of the disubstituted complex Fe 2 ( μ ‐edt)(CO) 4 { κ 1 , κ 1 ‐(Ph 2 PNHBu t ) 2 } ( 5 ) in low yield, whereas the Me 3 NO‐assisted substitution of A and two equiv. ligand L4 afforded the disubstituted complex Fe 2 ( μ ‐edt)(CO) 4 { κ 1 , κ 1 ‐(Ph 2 PC 6 H 4 Me‐ p ) 2 } ( 6 ) in good yield. All the model complexes 1 – 6 have been characterized by elemental analysis, FT‐IR, NMR spectroscopy, and particularly for 1 , 3 , 5 by X‐ray crystallography. Further, the protonations of complexes 1 – 4 are studied and compared with excess acetic acid (HOAc) and trifluoroacetic acid (TFA) by using FT‐IR and NMR techniques. Additionally, the electrochemical and electrocatalytic properties of model complexes 1 – 6 are investigated and compared by cyclic voltammetry (CV), suggesting that they are electrocatalytically active for proton reduction to H 2 in the presence of HOAc.