Synthesis and structural characterization of the mono- and diphosphine-containing diiron propanedithiolate complexes related to [FeFe]-hydrogenases. Biomimetic H 2 evolution catalyzed by (μ-PDT)Fe 2(CO) 4[(Ph 2P) 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 2PNH( t-Bu)] ( 1) was prepared by reaction of parent complex (μ-PDT)Fe 2(CO) 6 ( A) with 1 equiv of Ph 2PNH( t-Bu) in refluxing xylene, whereas A reacted with 1 equiv of Me 3NO · 2H 2O in MeCN at room temperature followed by 1 equiv of Ph 2PH to give the corresponding monophosphine model complex (μ-PDT)Fe 2(CO) 5(Ph 2PH) ( 2). Further treatment of 2 with 1 equiv of n-BuLi in THF at −78 °C followed by 1 equiv of CpFe(CO) 2I from −78 °C to room temperature afforded monophosphine model complex (μ-PDT)Fe 2(CO) 5[Ph 2PFe(CO) 2Cp] ( 3), whereas the diphosphine model complexes (μ-PDT)Fe 2(CO) 4(Ph 2PC 2H 4PPh 2) ( 4), (μ-PDT)Fe 2(CO) 4[(Ph 2P) 2N( n-Pr)] ( 5) and (μ-PDT)Fe 2(CO) 4[(Ph 2P) 2N( 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.