Synthesis and structural characterization of the mono- and diphosphine-containing diiron propanedithiolate complexes related to [FeFe]-hydrogenases. Biomimetic H2 evolution catalyzed by (μ-PDT)Fe2(CO)4[(Ph2P)2N(n-Pr)]

Abstract As the new H-cluster models, six diiron propanedithiolate (PDT) complexes with mono- and diphosphine ligands have been prepared and structurally characterized. The monophosphine model complex (μ-PDT)Fe 2 (CO) 5 [Ph 2 PNH( t -Bu)] ( 1 ) was prepared by reaction of parent complex (μ-PDT)Fe 2 (CO) 6 ( A ) with 1 equiv of Ph 2 PNH( t -Bu) in refluxing xylene, whereas A reacted with 1 equiv of Me 3 NO · 2H 2 O in MeCN at room temperature followed by 1 equiv of Ph 2 PH to give the corresponding monophosphine model complex (μ-PDT)Fe 2 (CO) 5 (Ph 2 PH) ( 2 ). Further treatment of 2 with 1 equiv of n -BuLi in THF at −78 °C followed by 1 equiv of CpFe(CO) 2 I from −78 °C to room temperature afforded monophosphine model complex (μ-PDT)Fe 2 (CO) 5 [Ph 2 PFe(CO) 2 Cp] ( 3 ), whereas the diphosphine model complexes (μ-PDT)Fe 2 (CO) 4 (Ph 2 PC 2 H 4 PPh 2 ) ( 4 ), (μ-PDT)Fe 2 (CO) 4 [(Ph 2 P) 2 N( n -Pr)] ( 5 ) and (μ-PDT)Fe 2 (CO) 4 [(Ph 2 P) 2 N( n -Bu)] ( 6 ) were obtained by reactions of A with ca.1 equiv of the corresponding diphosphines in refluxing xylene. All the new model complexes were characterized by elemental analysis, spectroscopy and particularly for 1 and 3–6 by X-ray crystallography. On the basis of electrochemical and spectroelectrochemical studies, model 5 was found to be a catalyst for HOAc proton reduction to H 2 , and for this electrocatalytic reaction an ECCE mechanism was proposed.