Synthesis and structural characterization of the mono- and diphosphine-containing diiron propanedithiolate complexes related to [FeFe]-hydrogenases. Biomimetic H2 evolution catalyzed by (mu-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 (mu-PDT)Fe(2)(CO)(5)[Ph(2)PNH(t-Bu)] (1) was prepared by reaction of parent complex (mu-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 (mu-PDT)Fe(2)(CO)(5)(Ph(2)PH) (2). Further treatment of 2 with 1 equiv of n-BuLi in THF at -78 degrees C followed by 1 equiv of CpFe(CO)(2)I from -78 degrees C to room temperature afforded monophosphine model complex (mu-PDT)Fe(2)(CO)(5)[Ph(2)PFe(CO)(2)Cp] (3), whereas the diphosphine model complexes (mu-PDT)Fe(2)(CO)(4)(Ph(2)PC(2)H(4)PPh(2)) (4), (mu-PDT)Fe(2)(CO)(4)[(Ph(2)P)(2)N(n-Pr)] (5) and (mu-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.