Ligand structures hydrogenase models

In conclusion, the presented dinuclear iron structure is the first example of a bio-mimetic iron compound, which can be regarded as a first generation model for the class of [Fe]-only hydrogenases. The complex incorporates both relevant carbon monoxide ligands, as well as three bridging thiolato ligands, which could be possibly present in the active site of these enzymes. 

The work on biomimetic models for [NiFe] and [FeFe] hydrogenase has been described in several review articles [15b 158]. In this work, many of the structural features important for proper function found in the native systems have been successfully incorporated for example, the bimetallic Ni-Fe or Fe-Fe core with rather short metal-metal distances and an open coordination site at one metal, the sulfur-rich environment (terminal and bridging thiolate ligands), CO/CN ligation of the iron(s), and the incorporation of a base for acceptance of the proton and, more recently, of hydride bridges. Still-existing problems of many model systems are the O2 sensitivity, the high overpotentials, and lack of activity (low turnover rates). 

Some iron and nickel cyanide and carbonyl complexes have been reported as models of the [FeNi]-hydrogenase enzymes. The preparation and structures of the trigonal bipyramidal nickel and iron complexes with the tetradentate ligands tris(2-phenylthiol)phosphine (PS3) and tris(3-phenyl-2-thiophenyl)phosphine (PS3 ) have been reported [70, 71]. The nickel carbonyl complex [Ni(PS3 )(CO)] exhibits vco at 2029 cm compared with the value of 1940 em" for the iron earbonyl complex [Fe(PS3 )(CO)]. Both of these complexes lose CO upon oxidation. The use of cyanide in place of carbon monoxide allows for the preparation of both [Fe (PS3)(CN)] and [Fe (PS3 )(CN)] eomplexes. The IR properties of... 

A number of generalities can be drawn from the similarities that are observed between the three classes of enzymes, [Fe]-, [FeNi]-, and [FeNiSej-hydrogenases. The similarities in the structure of the active sites are the most pertinent for the purposes of modeling experiments. The three classes of enzymes share a common iron center with two cyanide ligands and one carbon monoxide ligand. This moiety was first proposed from experiments on the enzyme and confirmed by model studies. This [Fe(CN)2(CO)] moiety is connected to a second metal ion which is either... 

The study of model complexes as metalloenzyme mimetics has a long tradition in bioinorganic chemistry (see Chem. Rev. 2004, 104, issue 2 for a complete revision). Several Ni-Fe-based complexes have been prepared, with structural features similar to those found in the FeNi active site.98 Nevertheless, none of them has been tested in its ability to coordinate or decompose H2. Present research is mainly centered in mimicking the thiolate ligands in the Fe-Ni coordination. It has to be mentioned that Fe-only hydrogenase mimics able to electrocatalyze proton reduction have been recently reported.99... 

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