Influence of pendant amines in phosphine ligands on the formation, structures, and electrochemical properties of diiron aminophosphine complexes related to [FeFe]-hydrogenases

Abstract

Me3NO-assisted substitution reactions of precursor Fe2(μ-adtNPh)(CO)6 (A, adtNPh = SCH2N(Ph)CH2S) and aminodiphosphines (Ph2P)2NR with different N-aryl substituents (R) resulted in the unexpected formation of five new diiron aminophosphine complexes Fe2(μ-adtNPh)(CO)5{κ1-Ph2P(NHR)} (R = C6H5 (1), C6H4Me-p (2), C6H4OMe-p (3), C6H4CO2Me-p (4), and C6H4Cl-p (5)) with adtNPh bridge, which may be regarded as the active site models of [FeFe]-hydrogenases. In order to further observe the influence of the pendant amines of phosphine ligands on the formation, structures, and electrochemical properties of model complexes 1–5 obtained above, two reference analogues Fe2(μ-adtNPh)(CO)5(κ1-dppm) (6, dppm = (Ph2P)2CH2) and Fe2(μ-adtNPh)(CO)5{κ1-Ph2P(CH2Ph)} (7) were prepared from the similar treatment of A with the dppm or Ph2P(CH2Ph) ligands, respectively. Meanwhile, these new complexes 1–5 and 7 have been characterized by elemental analysis, FT-IR and NMR (1H, 31P) spectroscopies, and particularly for 1, 2, 4, 7 by X-ray crystallography, in which the P atoms of the Ph2P(NHR) ligands in 1, 2, 4 reside in an apical position whereas that of the Ph2P(CH2Ph) ligand in 7 occupies at a basal site in the solid state. In addition, the electrochemical and electrocatalytic behaviors of 1–5 and 7 are investigated and compared in the absence and presence of acetic acid (HOAc) as proton source using cyclic voltammetry (CV), indicating they are all found to be active eletrocatalysts for proton reduction to hydrogen (H2).