ABinuclearIsocyanideIronAzadithiolateRelevanttotheActiveSiteofFe-OnlyHydrogenases:Synthesis,StructureandElectrochemicalProperties资源-CSDN文库

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http://www.paper.edu.cn

-1-

A Binuclear Isocyanide Iron Azadithiolate Relevant to the

Active Site of Fe-Only Hydrogenases: Synthesis, Structure

and Electrochemical Properties

Hou Jun

, Peng Xiaojun

*, Liu Jifeng

, Gao Yunling

, Zhao Xing

, Gao Shang

, Han

Keli

State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, P. R. China

(116012)

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

, is highly

efficient catalyzed by Fe-only hydrogenases ([Fe]H

ases), with rates in the range of 6000-9000

turnover per second.

[1]

Because of the significant efficiency, [Fe]H

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

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

. Theoretic studies support assignment of the bridging ligand has the structure of –SCH

NCH

S–

(ADT),

[5]

since the nitrogen heteroatom likely plays an important role in H

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

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

from sodium/benzophenone. Acetonitrile was distilled once from

Support by Specialized Research Fund for the Doctoral Program of Higher Education (No. 20030141024).

http://www.paper.edu.cn

-2-

CaH

and once from P

and freshly distilled from CaH

prior to use. Dichloromethane was distillated

over P

under N

. The following materials were commercially available reagents and used without

further purification: paraformaldehyde, 4-methylaniline, p-iodoaniline. The reagent of LiEt

BH was

purchased from Aldrich and used as received. Compounds N, N-bis(chloromethyl)-4-methylaniline (2),

[(μ-S)

(CO)

], [(μ-LiS)

(CO)

] (1) and 4-iodophenylisocyanide (4) were synthesized according

to the literature procedures.

[12, 15-17]

Infrared spectra were recorded on a FT-IR spectrophotometer.

H and

C NMR were collected on

a Varian INOVA 400 NMR spectrometer. Mass spectra were recorded on a HP 100 MSD. HR-MS

spectra determinations were made on a Q-TOF mass spectrometry and GC-TOF instrument

(Micromass).

Synthesis of [{(μ-SCH2)2N(4-CH3C6H4)}Fe2(CO)6] (3)

LiEt

BH solution (1 M solution in THF, 2.9 mL, 2.9 mmol) was added to a solution of

[(μ-S)

(CO)

] (500 mg, 1.45 mmol) in THF (30 mL) by syringe at –78 over 30 minutes. The ℃

solution of N, N-bis(chloromethyl)-4-methylaniline (2) in THF (20 mL) was added to the resulting

green solution, causing an immediate change of color to dark red. After stirring for 2 h at –78 and ℃

for 1 h at room temperature, the solvent was removed in vacuo and the resulting dark red solid was

purified by column chromatography on silica gel using CH

/hexane (10/100) as eluant to afford the

dark red solid. Yield: 57% (recrystallized from CH

/hexane).

H NMR (400 MHz; CDCl

): δ = 7.12

(s, 2H), 6.66 (s, 2H), 4.31(s, 4H), 2.28 (s, 3H);

C NMR (100 Mz; CDCl

): δ = 209.0, 207.2, 142.8,

130.6, 130.2, 116.3, 53.6, 50.2, 19.5; IR (CH

): ν(CO) =2071, 2030, 1999 cm

–1

; MS (API-ES):

(m/z): 478 ([M+H]

); HR-MS (ESI): (m/z) calcd for: 477.8805 ([M+H]

); found: 477.8793.

Synthesis of [{(μ-SCH2)2N(4-CH3C6H4)}Fe2(CO)4(4-IC6H4NC)2] (5)

Method A: A solution of complex 3 (1 g, 2.09 mmol) in CH

CN (30 mL) was treated with a

solution of 4-IC

NC (0.96 g, 4.19 mmol) in CH

(30 mL) at room temperature, followed by the

addition of Me

NO·H

O (0.465 g, 4.19 mmol) in CH

CN (20 mL). The solution immediately turned

into dark purple, and after 5 h, the color was changed to dark red. The mixture was stirred at room

temperature for 48 h and TLC showed the reaction was completed. The solvent was removed in vacuo

and the dark red residue was purified by column chromatography on silica gel eluting with

hexane-dichloromethane 5:1. Two main bands were observed: the first red band

[{(μ-SCH

)

N(4-CH

)}Fe

(CO)

(4-IC

NC)], IR (CH

): ν

= 2124 cm

–1

, ν

=2040, 2000,

1975 cm

–1

, was collected with ~ 600 mL eluant, and the second red band (5) with ~1000 mL eluant was

collected to give the red product 5. Yield: 640 mg, 34% (recrystallized from CH

/hexane).

NMR (400 MHz; acetone-d

): δ = 7.77 (d, J = 8.4 Hz, 2H), 7.11(d, J = 8.4 Hz, 2H), 7.03 (d, J = 8.0 Hz,

2H), 6.77 (d, J = 8.0 Hz, 2H); 4.38 (s, 4H), 2.14 (s, 3H)

C NMR (100 MHz; CDCl

): δ

= 211.5,

= 205.5, 202.5, 147.0, 143.5, 138.6, 130.2, 128.7, 127.5, 115.8, 93.3, 49.8, 20.5; IR (CH

ν(CN) = 2122, 2094 cm

–1

, ν(CO)= 1996, 1980, 1950 cm

–1

; HR-MS (EI): (m/z): calcd for: 878.7605

); found: 878.7601.

Method B: A 100 mL Schlenk flask was charged with [{(μ-SCH

)

N(4-CH

)}Fe

(CO)

] (3)

(500 mg, 1.04 mmol) and 4-IC

NC (479 mg, 2.09 mmol). 50 mL of CH

were added to this flask

and the solution was stirred 48 h at room temperature. The solvent was removed in vacuo and the

residue was purified by column chromatography on silica gel eluting with hexane-dichloromethane 5:1.

The first band for monoisocyanide-substituted product with large quantity was collected with ~ 800 mL

eluant, and the second red band for 5 with ~ 200 mL. Yield for 5: 92 mg, 10% (recrystallized from

/hexane).

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