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 Fe 2 ( μ ‐Me 2 pdt)(CO) 6 ( A , Me 2 pdt = (SCH 2 ) 2 CMe 2 ) with monophosphines or small bite‐angle diphosphines are studied as follows. Firstly, the monodentate complexes Fe 2 ( μ ‐Me 2 pdt)(CO) 5 { κ 1 ‐P(C 6 H 4 R‐ p ) 3 } [R = Me ( 1a ) and Cl ( 1b )] and Fe 2 ( μ ‐Me 2 pdt)(CO) 5 { κ 1 ‐Ph 2 PX'} [X' = NHPh ( 2a ) and CH 2 PPh 2 ( 2b )] are readily afforded through the Me 3 NO‐assisted reactions of A with monophosphines P(C 6 H 4 R‐ p ) 3 (R = Me, Cl) and diphosphines (Ph 2 P) 2 X (X = NPh, CH 2 (dppm)) in MeCN at room temperature, respectively. Secondly, the chelate complexes Fe 2 ( μ ‐Me 2 pdt)(CO) 4 ( κ 2 ‐(Ph 2 P) 2 X) [X = NPh ( 3a ) and NBu n ( 3b )] can be efficiently prepared by the UV‐irradiated reactions of A with small bite‐angle diphosphines (Ph 2 P) 2 X (X = NPh, NBu n ) in toluene. Thirdly, the bridge complexes Fe 2 ( μ ‐Me 2 pdt)(CO) 4 ( μ ‐(Ph 2 P) 2 X) [X = NPh ( 4a ) and CH 2 ( 4b )] are well obtained from the refluxing solutions of A and diphosphines (Ph 2 P) 2 X (X = NPh, CH 2 ) 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 ( 1 H, 31 P) 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 (H 2 ).