Synthesis, Structures and Electrochemical Properties of Nitro‐ and Amino‐Functionalized Diiron Azadithiolates as Active Site Models of Fe‐Only Hydrogenases

Abstract

Complex [[(mu-SCH2)2N(4-NO2C6H4)]Fe2(CO)6] (4) was prepared by the reaction of the dianionic intermediate [(mu-S)2Fe2(CO)6](2-) and N,N-bis(chloromethyl)-4-nitroaniline as a biomimetic model of the active site of Fe-only hydrogenase. The reduction of 4 by Pd-C/H2 under a neutral condition afforded complex [[(mu-SCH2)2N(4-NH2C6H4)]Fe2(CO)6] (5) in 67 % yield. Both complexes were characterized by IR, 1H and 13C NMR spectroscopy and MS spectrometry. The molecular structure of 4, as determined by X-ray analysis, has a butterfly 2Fe2S core and the aryl group on the bridged-N atom slants to the Fe(2) site. Cyclic voltammograms of 4 and 5 were studied to evaluate their redox properties. It was found that complex 4 catalyzed electrochemical proton reduction in the presence of acetic acid. A plausible mechanism of the electrocatalytic proton reduction is discussed.

Synthesis and Characterization of Hydroxy‐Functionalized Models for the Active Site in Fe‐Only‐Hydrogenases

“…5), the potentials of which are listed in Two cathodic redox processes have been observed, one of which is quasi-reversible and the second is an irreversible reduction wave. In comparison to compounds B and C (Table 4), as reported by Sun and co-workers [12], the redox potential of the cathodic process is shifted to more negative potentials at À 1.53 V. This is ascribed to a oneelectron process [ (3) 184.9 C(1)ÀC (2) 152.9 O(1)ÀH (1) 98.4 C(2)ÀC (3) 152.9 C(2)ÀO (1) 142.5…”

“…-The present study shows that disulfanyl alkohols and diols react with Fe 3 (CO) 12 by oxidative addition to provided complexes, which can be seen as models for Fe-only hydrogenases. Whereas 1,3-disulfanylpropan-2-ol reacts with Fe 3 (CO) 12 in the usual way to form a dinuclear complex 1, 1,4-disulfanylbutane-2,3-diol leads, under (2) C (1)ÀC (2) C (3)ÀC (2) O (1)ÀC (2) s similar reaction conditions, to a tetranuclear complex 2. Here, the dithiolato ligands are coordinated to two different Fe 2 (CO) 6 moieties.…”

“…was separated from the insoluble precipitate. After removing the solvent, the crude product was purified by flash chromatography (FC; THF/hexane 1 : 1), and the remaining red solid was dissolved in CH 2 12 were dissolved in 20 ml of THF, and the resulting soln. was heated at reflux under Ar for 2 h. Within 2 h, the color of the soln.…”

Electrochemical Insights into the Mechanisms of Proton Reduction by [Fe2(CO)6{μ‐SCH2N(R)CH2S}] Complexes Related to the [2Fe]H Subsite of [FeFe]Hydrogenase

“…It is therefore likely that, in acetonitrile, [Fe 2 (CO) 6 A C H T U N G T R E N N U N G {m-SCH 2 N(R)CH 2 S}] complexes cannot be protonated at the N atom by acetic acid (pK a = 22.3 in MeCN). [41] As a consequence, for [Fe 2 (CO) 6 A C H T U N G T R E N N U N G {m-SCH 2 N(R)CH 2 S}] complexes in which the R substituent carries a NO 2 group, [52,53] the enhanced current observed in the presence of CH 3 CO 2 H at a potential substantially less negative than the reduction of the complex most probably arises from a proton-dependent reduction of the nitro group rather than from an initial N-protonation of the complex.…”

Influence of the Introduction of Cyanido and Phosphane Ligands in Multifunctionalized (Mercaptomethyl)silane [FeFe] Hydrogenase Model Systems

“…The presence of these basic sites led to an increased susceptibility to protonation prior to reduction of the complex, which is indicated by a positive shift in the reduction potential of the least negative cathodic process. [30] Upon addition of 1 mmol of HOAc, the reduction potential of this process shifted by approximately 200 mV in the negative direction, and an increase in the height of the peak was observed. The intensity of the current continued to increase with each increment of acid added thereafter, which is indicative of an electrocatalytic current.…”