Synthesis, structures, and electrocatalytic properties of phosphine‐monodentate, −chelate, and ‐bridge diiron 2,2‐dimethylpropanedithiolate complexes related to [FeFe]‐hydrogenases

Abstract

To further extend diiron subsite models of [FeFe]‐hydrogenases, the various substitutions of all‐carbonyl diiron complex Fe2(μ‐Me2pdt)(CO)6 (A, Me2pdt = (SCH2)2CMe2) with monophosphines or small bite‐angle diphosphines are studied as follows. Firstly, the monodentate complexes Fe2(μ‐Me2pdt)(CO)5{κ1‐P(C6H4R‐p)3} [R = Me (1a) and Cl (1b)] and Fe2(μ‐Me2pdt)(CO)5{κ1‐Ph2PX'} [X' = NHPh (2a) and CH2PPh2 (2b)] are readily afforded through the Me3NO‐assisted reactions of A with monophosphines P(C6H4R‐p)3 (R = Me, Cl) and diphosphines (Ph2P)2X (X = NPh, CH2 (dppm)) in MeCN at room temperature, respectively. Secondly, the chelate complexes Fe2(μ‐Me2pdt)(CO)4(κ2‐(Ph2P)2X) [X = NPh (3a) and NBun (3b)] can be efficiently prepared by the UV‐irradiated reactions of A with small bite‐angle diphosphines (Ph2P)2X (X = NPh, NBun) in toluene. Thirdly, the bridge complexes Fe2(μ‐Me2pdt)(CO)4(μ‐(Ph2P)2X) [X = NPh (4a) and CH2 (4b)] are well obtained from the refluxing solutions of A and diphosphines (Ph2P)2X (X = NPh, CH2) in xylene. Rarely, the diphosphine‐bridge complex 4b may be produced in low yield via the UV‐irradiated solutions of A and the dppm ligand in toluene emitting at 365 nm. Eight new complexes obtained above have been well characterized by using element analysis, FT‐IR, NMR (1H, 31P) spectroscopies, and particularly for 1a, 1b, 2a, 3b, 4a, 4b by X‐ray crystallography. Meanwhile, the electrochemical and electrocatalytic properties of three representative complexes 2a, 3a, and 4a with pendant N‐phenyl groups are investigated and compared by using cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (TFA) as a proton source, indicating that they are all found to be active for electrocatalytic proton reduction to hydrogen (H2).