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-1-
A Binuclear Isocyanide Iron Azadithiolate Relevant to the
Active Site of Fe-Only Hydrogenases: Synthesis, Structure
and Electrochemical Properties
1
Hou Jun
1
, Peng Xiaojun
1,
*, Liu Jifeng
2
, Gao Yunling
2
, Zhao Xing
1
, Gao Shang
1
, Han
Keli
2
1
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, P. R. China
(116012)
2
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical
Physics, Chinese Academy of Science, Dalian, P. R. China (116022)
E-mail：pengxj@dlut.edu.cn
Abstract
Diiron complexes 3 and 5 as mimics for the active site of the Fe-only hydrogenases have been
synthesized. The structures were fully characterized by X-ray crystallography. The
4-iodophenylisocyanide ligands in 5 are in basal positions and are nearly parallel to each other,
showing the π-π stacking interactions. The electrochemical properties of complexes 3 and 5 were
investigated by cyclic voltammetry.
Keywords: Fe-only hydrogenase, Bioinorganic chemistry, Diiron carbonyl, Isocyanide
Introduction
Proton reduction to hydrogen in protein, according the reaction 2H+ + 2e
-
H
2
, is highly
efficient catalyzed by Fe-only hydrogenases ([Fe]H
2
ases), with rates in the range of 6000-9000
turnover per second.
[1]
Because of the significant efficiency, [Fe]H
2
ases have drawn considerable
attention of chemists in the past years.
As revealed by a combination of X-ray crystallography
[2, 3]
and IR spectroscopy,
[4]
the active site of
[Fe]H
2
ases is comprised of a 2Fe2S subunit linked to a 4Fe4S cluster via a cysteinyl-S bridge. The
4Fe4S unit is probably responsible for electron transfer while 2Fe2S subsite is utilized as a catalytic
center of hydrogen formation and activation. In the 2Fe2S subunit, the two iron atoms are bridged by
the sulfur atoms of a propanedithiolate (PDT) ligand and bear biologically unusual ligands, CO and
CN
-
. Theoretic studies support assignment of the bridging ligand has the structure of –SCH
2
NCH
2
S–
(ADT),
[5]
since the nitrogen heteroatom likely plays an important role in H
2
production in the natural
system.
The unique structure of the active site has inspired bioinorganic chemists to synthesize the
structural and functional models.
[6-8]
Although ADT-bridged diiron complexes have been extensively
studied,
[9-12]
to the best of our knowledge, there is no report on the electrocatalytic reduction of protons
catalyzed by the functionally substituted diiron azadithiolate derivatives in literature to date. With these
considerations, we present a binuclear isocyanide iron azadithiolate complex 5 in which isocyanide
ligand was chosen because it can be used as a surrogate for the relevant CN
-
without complicating
reactivity of the cyanide nitrogen in catalytic reaction.
[13, 14]
We herein describe the preparation,
structural characterization and electrochemical properties of complexes 3 and 5.
Experimental
Reagents and instrument
All reactions and operations were carried out under N
2
atmosphere using standard Schlenk
techniques. All solvents were dried and distilled prior to use according to the standard methods. THF
was purified by distillation under N
2
from sodium/benzophenone. Acetonitrile was distilled once from
1
Support by Specialized Research Fund for the Doctoral Program of Higher Education (No. 20030141024).
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