Reactions of diiron nonacarbonyl with pyrrolyl-, pyridyl- and thienyl-substituted azines: N{single bond}N bond cleavage, cyclometallation and C{double bond, long}N σ and π-bonding

Polyhedron 25 (2006) 3053–3065

www.elsevier.com/locate/poly

Reactions of diiron nonacarbonyl with pyrrolyl-, pyridyl- and

thienyl-substituted azines: NAN bond cleavage, cyclometallation

and C@N r and p-bonding

*

Chih-Yu Wu, Yi Chen, Shiau-Yi Jing, Chen-Shiang Lee, Joydev Dinda, Wen-Shu Hwang

Department of Chemistry, National Dong Hwa University, 1, Sec. 2, Da-Hsueh Road, Shoufeng, Hualien 974, Taiwan, ROC

Received 10 December 2005; accepted 23 April 2006

Available online 25 May 2006

Abstract

The reactions of 1,4-di-(N-methyl-2⁰-pyrrolyl)-2,3-diaza-1,3-butadiene (1), 1,4-di-(6-methyl-2⁰-pyridyl)-2,3-diaza-1,3-butadiene (2)

and 3,6-di-(2⁰-thienyl)-1,2,4,5-tetrazine (3) with Fe₂(CO)₉in toluene, THF and benzene, respectively, yielded various types of hexa-

carbonyldiiron complexes with ﬁve diﬀerent coordination modes: (1) a complex with two 2-pyrrolylmethylideneamido bridging ligands,

1a, which resulted from NAN bond cleavage of ligand 1, (2) a cyclometallated (l-2,3-g¹:g²-pyrrolyl; g¹:g¹(N)) complex 1b and a cyclo-

metallated (l-2,3-g¹:g²-thienyl; g¹:g¹(N)) complex 3b, (3) a diaza-bridged complex 3a, (4) an imine-bridged (l-r;p-g¹:g²-(C,N); g¹(N_py))

complex 2a and (5) an imine-bridged ðl-p-g¹:g¹-ðC; NÞ; g¹ðN_pyÞ; g¹ðN_p⁰_yÞÞ complex 2b. The molecular structures of the ligands 1 and 3 as

well as of the complexes 1a, 2a and 3a have been determined by single-crystal X-ray crystallography.

Keywords: Iron carbonyl complex; Azine; Cyclometallation; NAN bond activation; Imine r and p-bonding

1. Introduction

Azines, NAN linked diimines, have attracted recent

attention due to their biological properties [5], their poten-

tial applicability in bond formations [6], the design of

liquid crystals [7] as well as non-linear optical materials

[8]. With the possibility of donating from two to eight elec-

trons via the N lone-pairs and the C@N p-electrons, azines

are known to show very versatile coordination properties

to metal centers [9]. Furthermore, NAN bond activation

in various types of organic ligands is important for its rel-

evance especially to catalysis and organic synthesis in gen-

eral. However, there are not so many metal-mediated NAN

bond cleavage reactions [10].

In a previous publication [10g] we have shown that the

thienyl Schiﬀ base 1,4-di-(2-thienyl)-2,3-diaza-1,3-butadi-

ene undergoes NAN bond cleavage, cyclometallation and

double cyclometallation during the course of the reaction

with Fe₂(CO)₉. We report here the preparation and charac-

terization of hexacarbonyldiiron complexes derived from

pyrrolyl, pyridyl and thienyl Schiﬀ bases 1,4-di-(N-methyl-

2-pyrrolyl)-2,3-diaza-1,3-butadiene (1), 1,4-di-(6-methyl-2-

One of the most prominent challenges in organometallic

chemistry in recent decades has been the transition-metal

mediated activation of CAH bonds. Cyclometallation has

been one of the most prevalent methods used in activating

CAH bonds existing in hetero-substituted organic mole-

cules [1]. It is well known that N-donor ligands have a

strong tendency to give ﬁve-membered metallacycles [2]

and Schiﬀ base ligands have traditionally been the com-

pound of choice employed in the study of cyclometallation

reactions due to their strong tendency to give endo cyclo-

metallated derivatives [3]. It has also been shown that Schiﬀ

bases react with Fe₂(CO)₉to produce cyclometallated

hexacarbonyldiiron complexes in which an endo orthomet-

allation accompanies the transformation of the b-proton to

the azomethine carbon to form a methylene group [4].

*

Corresponding author. Tel.: +886 3 863 2001; fax: +886 3 863 2000.

E-mail address: hws@mail.ndhu.edu.tw (W.-S. Hwang).

doi:10.1016/j.poly.2006.04.031

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C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

pyridyl)-2,3-diaza-1,3-butadiene (2) and 3,6-di-(2-thienyl)-

1,2,4,5-tetrazine (3), in which the ligand bridges the diiron

(FeAFe) unit through pyrrolyl, pyridyl and thienyl imine

groups, imine nitrogen groups, imine r and p, and NAN

diaza groups. The original ligand undergoes nitro-

genAnitrogen bond cleavage, endo cyclometallation or

diaza coordination during the course of the reaction with

Fe₂(CO)₉. The choice of this series of ligands stems from

our interest in the synthesis and ﬁnding the reactivity of

new diiron complexes, as well as their biological aspects.

The (l-g¹:g²-pyrrolyl/thienyl; g¹:g¹(N))hexacarbonyl-

diiron complexes, imine-bridged (l-r;p-g¹:g²-(C,N);

g¹(N_py))hexacarbonyldiiron complex and imine-bridged

ðl-p-g¹:g¹-ðC; NÞ; g¹ðN_pyÞ; g¹ðN_p⁰_yÞÞhexacarbonyldiiron com-

plex show unique binding modes to the diiron (FeAFe) unit.

characteristic C@N stretching absorption around

1600 cm^ꢀ1in their IR spectra. The mass spectra of the

ligands all show their own speciﬁc molecular ion peak

(M⁺). The structures of the ligands 1 and 3 were further

conﬁrmed by single crystal X-ray analysis. Crystal and data

collection parameters are shown in Table 1. Their crystal

structures are shown in Figs. 1 and 2, respectively. Selected

bond distances and bond angles are tabulated in Table 2.

The geometries of both 1 and 3 are well planar and all

the p electrons are delocalized through the whole molecule.

2.2. Complex formation and characterization

2.2.1. Complexes derived from ligand 1

The pyrrolyl Schiﬀ base 1 reacts with Fe₂(CO)₉in reﬂux-

ing toluene to give two complexes, which we formulated as

1a and 1b, respectively (Scheme 1). Product 1a is a diiron

hexacarbonyl complex with two new chemically identical

independent ligands, N-methyl-2-pyrrolylmethylideneam-

ido, which were derived from the NAN bond cleavage of

the original ligand 1, and that bridge two Fe(CO)₃units

through azomethine nitrogen atoms. Product 1b is a cyclo-

metallated diiron hexacarbonyl complex, in which the

CAH bond of the b-carbon on one of the pyrrolyl groups

has been activated.

2. Results and discussion

2.1. Synthesis of ligands

The pyrrolyl, pyridyl and thienyl Schiﬀ bases 1,4-di-

(N-methyl-2-pyrrolyl)-2,3-diaza-1,3-butadiene (1), 1,4-di-

(6-methyl-2-pyridyl)-2,3-diaza-1,3-butadiene (2) and 3,6-

di-(2-thienyl)-1,2,4,5-tetrazine (3) were prepared by

condensation of N-methyl-2-formylpyrrol, 6-methyl-2-

formylpyridine and 2-thiophenecarbonitrile with hydrazine

in anhydrous ethanol. These compounds were fully charac-

terized spectrally. Each pyrrolyl, pyridyl or thienyl proton

1

The H NMR spectrum of 1a shows ﬁve sets of signals

with the same pattern as that of ligand 1, indicating that

two pyrrolyl rings as well as two imines in the complex

are in the same chemical environment. Although three sets

of pyrrolyl protons show a little upﬁeld shift, the signal cor-

responding to the imine proton downﬁeld shifts from d

1

in each ligand can be easily assigned from the H NMR

spectra according to its speciﬁc chemical shift and the char-

acteristic coupling constant(s). All the ligands show a

Table 1

Crystal and data collection parameters for compounds 2, 3 and 5

Compound

1

3

1a

2a

3a

3c

Formula

F_w

C

₁₂H₁₄N₄

C₁₀H₆N₄S₂

246.30

monoclinic

P2₁/n

5.227(2)

9.129(1)

10.922(1)

C₁₉H₁₈Fe₂N₄O₇

526.07

triclinic

C₂₀H₁₄Fe₂N₄O₆

518.05

triclinic

C₁₆H₆Fe₂N₄O₆S₂

526.06

triclinic

C₃₃H₂₁Fe₂N₄O₅PS₂

760.34

214.27

orthorhombic

Pbcn

Crystal system

Space group

orthorhombic

P2₁2₁2₁

15.281(3)

18.193(2)

12.444(3)

90

3460(1)

4

ꢀ

P1

˚

a (A)

24.737(4)

6.0359(9)

7.6523(11)

90

7.9882(8)

11.6292(12)

12.9607(13)

99.674(2)

99.752(2)

96.104(2)

1158.4(2)

2

8.351(1)

8.444(1)

15.943(2)

96.46(1)

93.89(1)

96.93(1)

1105.2(3)

2

7.956(2)

15.107(3)

17.61(1)

75.61(1)

78.13(2)

87.25(2)

2032.0(7)

4

˚

b (A)

˚

c (A)

a (ꢁ)

b (ꢁ)

c (ꢁ)

Volume (A )

Z

92.84(2)

3

˚

1142.6(3)

4

520.5(2)

2

D_calc(g/cm³)

Crystal size (mm)

Temperature (K)

h Range (ꢁ)

1.246

1.571

1.494

1.557

0.36 · 0.24 · 0.22

298.2

2.45–26.00

4672

1.719

0.78 · 0.30 · 0.20

298.2

2.05–24.99

7461

1.460

0.96 · 0.42 · 0.40

298.2

2.11–25.99

4124

0.38 · 0.36 · 0.13 0.52 · 0.42 · 0.20 0.37 · 0.14 · 0.10

150(2)

1.65–27.52

6436

298.2

2.23–25.00

1095

150(2)

1.62–27.49

7296

Reﬂections measured

Number of data

1311 (0.0465)

986 (0.011)

5101 (0.0237)

4359 (0.030)

7162 (0.1222)

3820 (0.011)

collected (R_int

Number of reﬂections

Number of parameters 74

)

768 (I > 2.00r(I)) 799 (I > 3.00r(I)) 3523 (I > 2.00r(I)) 3127 (I > 3.00r(I)) 5077 (I > 3.00r(I)) 3314 (I > 3.00r(I))

73

304

289

541

424

F(000)

456

252

526

524

1048

1544

Goodness-of-ﬁt

R₁

wR₂

0.982

0.0453

0.1163

3.275

0.032

0.040

1.055

0.0464

0.1266

1.126

0.0277

0.0396

3.237

0.0476

0.0518

2.519

0.0351

0.0470

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

3055

Fig. 1. ORTEP diagram of 1 at the 30% probability level.

Fig. 2. ORTEP diagram of 3 at the 30% probability level.

appearing at 2061, 2021 and 1972 cm^ꢀ1. The fragmentation

pattern of its mass spectrum shows no evidence of a peak

with a m/z value of 214, corresponding to ligand 1. How-

ever, peaks at m/z 107 and 108 were observed to accom-

pany the presence of a molecular ion peak at m/z 495

and six peaks corresponding to sequential CO loss prod-

ucts, in accordance with the formulated structure.

Table 2

˚

Selected bond lengths (A) and bond angles (ꢁ) for ligands 1 and 3

1

N(2)AN(2A)

C(1)AC(2)

N(2A)AN(2)AC(1)

1.417(3)

1.437(2)

N(2)AC(1)

1.284(2)

111.3(2)

3

N(1)AN(2)

1.317(3)

1.351(3)

N(1)AC(1)

C(1)AC(2)

C(1)AN(1)AN(2)

N(1)AC(1)AC(2)

1.350(3)

1.444(3)

117.8(2)

The ¹H NMR spectrum of 1b shows only one azomethine

proton at d 7.96 ppm, two methylene protons at d 4.53 ppm,

and six methyl protons at d 3.84 ppm, in addition to the ﬁve

sets of pyrrolyl protons in the range of d 7.23–6.08 ppm.

Among the ﬁve sets of pyrrolyl protons, three are doublets

with a coupling constant J_H–H= 2.7 Hz, one is a doublet

with a coupling constant J_H–H= 3.6 Hz, and another set

N(2A)AC(1)

N(1)AN(2)AC(1A)

N(1)AC(1)AN(2A)

117.6(2)

124.5(2)

8.50 ppm (ligand 1) to 9.00 ppm. In its IR spectrum, the

C@N stretching shifts from 1625 cm^ꢀ1in 1 to 1638 cm^ꢀ1

and there are three sharp and intense C@O stretches

,

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C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

H

C

N

Fe₂(CO)₉

Toluene

N

C

H

N

1

(CO)₃

Fe

Fe(CO)₃

H

C

N

H

C

N

C

NN

Fe(CO)₃

+

N

H

C

N

H₂

1a

1b

Scheme 1.

is a doublet of doublets with coupling constants J_H–H= 3.6

and 2.7 Hz, respectively. This result was interpreted as coor-

dination of one of the azomethine nitrogens of the pyrrolyl

azine ligand on one of the iron centers, CAH activation

occurs at the b-carbon of the pyrrolyl ring, which is adjacent

to the coordinated imine, to form a ﬁve-membered endo

metallacycle, and the methine group becomes a methylene

group by adopting the hydrogen originating from the

b-carbon. This transformation follows the sequential route:

coordination, endo cyclometallation and 1,3-hydrogen shift.

The singlet signal of the methylene protons indicates that

the two protons are equivalent. The lack of diastereotopic-

ity of the methylene protons in the azametallacycle of the

complex indicates that a ﬂuxional process, the so-called

‘windscreen-wiper type oscillation’, of the ligand might

occur in the complex [11]. The IR spectrum of the complex

shows a characteristic C@N stretching at 1622 cm^ꢀ1and

three sharp and intense C@O stretches at 2055, 2011 and

1963 cm^ꢀ1. The mass spectrum of 1b shows the molecular

ion peak and the complete loss of six CO ligands in a

sequential manner, in accordance with the formulated

structure.

2.2.2. Complexes derived from ligand 2

The pyridyl Schiﬀ base 2 reacts with Fe₂(CO)₉in reﬂux-

ing THF to yield two hexacarbonyldiiron complexes 2a

and 2b (Scheme 2) in moderate yield. Neither NAN bond

cleavage of the molecule nor cyclometallation, as expected,

was observed in this reaction. In both complexes, one of

the imines of the original ligand is involved in coordination

by using its p-electron system and bridges to two Fe(CO)₃

units. In complex 2a, the azomethine nitrogen acts as the

second bridging atom to the two Fe(CO)₃units and one

pyridyl nitrogen serves as a r-donor atom to complete

H

Fe₂(CO)₉

THF

N

C

N

C

H

N

2

H

C

H

N

HC

N

C

N

C

N

(OC)₃Fe

N

+

H

Fe(CO)₃

N

(OC)₃Fe

e(CO)

F

3

2a

2b

Scheme 2.

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

3057

the 36-electron structure of the iron centers. In complex 2b,

in addition to the bridging imine, both pyridines are

involved and coordinate to the two Fe(CO)₃units, sepa-

rately. When the reaction was conducted at room temper-

ature, complex 2a and a trace amount of 2b were

obtained. If the reaction was allowed to proceed under irra-

diation of UV light, a high yield of complex 2a was

obtained as the sole product.

tains a signal for the molecular ion and six peaks corre-

sponding to sequential CO loss products, in accordance

with the formulated structure.

1

The H NMR spectrum of 2b is very similar in pattern

to that of 2a. Only one azomethine proton appears at d

8.86 ppm. Six diﬀerent pyridyl protons indicate that the

two pyridine rings are in diﬀerent chemical environments.

However, diﬀerent from that in complex 2a, both two

groups of pyridyl protons are found to be upﬁeld shifted,

indicating the coordination of both pyridine rings. The

new singlet signal at d 4.54 ppm is assigned to the proton

on the coordinated azomethine carbon. The IR spectrum

of the 2b shows a characteristic C@N stretching at

1573 cm^ꢀ1and three sharp and intense C@O stretches at

2045, 1992 and 1967 cm^ꢀ1. The mass spectrum of 2b shows

the same result as that of 2a.

1

The H NMR spectrum of 2a shows only one azome-

thine proton at d 8.82 ppm, which is downﬁeld shifted rel-

ative to that in the original ligand 2 (d 8.58 ppm). There

are six sets of signals in the aromatic region corresponding

to two groups of three pyridyl protons indicating that the

two pyridine rings are in diﬀerent environments. One

group of three pyridyl protons (d 7.45(t), 7.21(d) and

6.79(d) ppm) are found to be substantially upﬁeld shifted

relative to that in the free ligand (d 7.98(d), 7.81(t) and

7.37(d) ppm), due to the coordination of the pyridyl nitro-

gen, while another group of three pyridyl protons remain

unchanged in their chemical shifts to that in the free

ligand. There is a new singlet proton, appearing at d

4.82 ppm, that is assigned to be the proton on the coordi-

nated azomethine carbon, which has been turned from sp²

into sp³hybridization causing a drastic upﬁeld shift of the

proton signal from d 8.53 to 4.82 ppm. The IR spectrum of

the complex shows a characteristic C@N stretching at

1583 cm^ꢀ1and three sharp and intense C@O stretches at

2054, 1083 and 1926 cm^ꢀ1. The mass spectrum of 2a con-

2.2.3. Complexes derived from ligand 3

The thienyl ligand 3 reacts with Fe₂(CO)₉in reﬂuxing

benzene to yield two hexacarbonyldiiron complexes 3a

and 3b (Scheme 3). In complex 3a, a diazo group acts

as a 6-electron donor and bridges two Fe(CO)₃units.

Complex 3b is a cyclometallated product, in which the

CAH bond of the b-carbon on one of the thienyl groups

has been activated. We attempted to prepare the doubly

cyclometallated tetrairon complex and the NAN bond

cleaved product under more vigorous reaction conditions

in toluene, but in vain. In the presence of an excess

N

Fe₂(CO)₉

Benzene

S

3

N

(OC)₃Fe

Fe(CO)₃

N

H

+

S

N

S

(OC)₃Fe

Fe(CO)₃

N

3a

3b

PPh₃

N

+

S

N

(OC)₃Fe

Fe(CO)₂(PPh₃)

(Ph₃P)(OC)₂Fe

Fe(CO)₂(PPh₃)

3c

3d

Scheme 3.

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C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

Fig. 3. ORTEP diagram of 1a at the 30% probability level.

Fig. 4. ORTEP diagram of 2a at the 30% probability level.

1

amount of triphenylphosphine, complex 3a was converted

into 3c and 3d in which one or two carbonyls were substi-

tuted by triphenylphosphine.

The H NMR spectrum of 3b shows ﬁve sets of signals

with characteristic coupling constants (J_H–H= 5.1 and

3.6 Hz) corresponding to ﬁve speciﬁc thienyl protons, indi-

cating an asymmetrical geometry of the complex, and a b-

proton on one of the thienyl rings disappeared. There

appears a new broad signal at d 9.01 ppm, which is sub-

jected to shift with diﬀerent concentrations, and is assigned

as an amine proton. In its IR spectrum, other than the

imine (C@N) stretching absorptions at 1637 and

1573 cm^ꢀ1and terminal carbonyl (ACO) stretches at

2072–1952 cm^ꢀ1, there is a secondary amine NAH stretch-

ing absorption at 3352 cm^ꢀ1and a bending absorption at

The ¹H NMR spectrum of 3a shows three sets of thienyl

proton signals similar to that of ligand 3, indicating a sym-

metric geometry of the complex. In its IR spectrum, there is

an imine stretching absorption at 1543 cm^ꢀ1and a number

of terminal carbonyl stretches appearing in the range of

2076–1972 cm^ꢀ1. The mass spectrum of 3a contains a sig-

nal for the molecular ion and six peaks corresponding to

sequential CO loss products, in accordance with the formu-

lated structure.

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

3059

1521 cm^ꢀ1. The mass spectrum of 3b shows the same result

as that of 3a.

761 and 995, respectively, fragments corresponding to the

sequential loss of CO ligands, phosphine and the ligand

ion peak, in accordance with the formulated structures.

Complexes 3c and 3d are derived from 3a through the

substitution of carbonyl ligand(s) with triphenylphosphine.

1

Their H NMR spectra adopt the same pattern as that of

2.3. Molecular structure of complexes 1a, 2a, 3a and 3c

3a except the additional signals of triphenylphosphine.

However, the thienyl protons are upﬁeld shifted from 3a

to 3c to 3d due to the inductive eﬀect of the phosphine

ligand. The inductive eﬀect also drives the lower energy

shift of the IR stretching frequencies of the terminal carbo-

nyls in the same sequence. The mass spectra of 3c and 3d

show their own speciﬁc molecular ion peak (M⁺) at m/z

The molecular structures of 1a, 2a, 3a and 3c, as con-

ﬁrmed by the single crystal X-ray diﬀraction analysis, are

shown in Figs. 3–6, respectively. Their crystal and data col-

lection parameters are tabulated in Table 1 and selected

bond distances and bond angles are summarized in Tables

3 and 4.

Fig. 5. ORTEP diagram of 3a at the 30% probability level.

Fig. 6. ORTEP diagram of 3c at the 30% probability level.

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C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

Table 3

2.3.1. [Fe(CO)₃(MeC₄H₃NCHN)]₂(1a)

˚

Selected bond lengths (A) and bond angles (ꢁ) for complexes 1a and 2a

The structure of 1a, as shown in the Fig. 3, contains two

2-pyrrolylmethylideneamido moieties which bridge two

Fe(CO)₃units through amido nitrogen atoms. It is clear

that the NAN bond in ligand 1 has been cleaved during

the coordination reaction and the non-bonded Nꢁ ꢁ ꢁN dis-

1a

N(2)AC(1)

Fe(1)AN(1)

Fe(2)AN(1)

1.274(6)

1.934(3)

1.935(3)

Fe(1)AFe(2)

Fe(1)AN(2)

Fe(2)AN(2)

2.4084(7)

1.922(3)

Fe(1)AN(1)AFe(2)

Fe(2)AFe(1)AN(1)

N(1)AFe(1)AN(2)

Fe(1)AN(1)AC(1)

N(1)AC(1)AC(2)

77.0(1)

51.52(10)

76.77(13)

136.2(3)

125.1(4)

Fe(1)AN(2)AFe(2)

Fe(1)AFe(2)AN(1)

N(1)AFe(2)AN(2)

Fe(2)AN(1)AC(1)

77.42(11)

51.50(9)

76.93(13)

140.7(3)

˚

tance is 2.399 A. The conﬁguration of the individual mole-

cule has idealized 2-fold symmetry. The tricarbonyl groups

are eclipsed. The amido nitrogen and iron atoms form a tet-

rahedron. The central position of the molecule is thus sim-

ilar in shape to that of Co₂(CO)₈. Plane calculations show

that all pairs of atoms are equidistant from opposite sides

to the C₂axis, which is perpendicular to the mid-point of

the FeAFe bond. Each iron center is coordinated by two

nitrogen atoms and three carbonyls located at the corners

of a distorted octahedron. The FeAFe distance is only

2a

Fe(1)AFe(2)

Fe(1)AC(1)

Fe(2)AN(2)

C(14)AN(3)

2.5698(5)

2.025(3)

2.030(2)

1.268(3)

Fe(1)AN(1)

Fe(2)AN(1)

C(1)AN(1)

N(1)AN(3)

1.930(2)

1.948(2)

1.401(3)

1.419(3)

N(1)AFe(1)AFe(2)

N(1)AFe(1)AC(1)

N(2)AFe(2)AFe(1)

Fe(1)AN(1)AFe(2)

Fe(1)AN(1)AC(1)

Fe(1)AN(1)AN(3)

Fe(2)AN(2)AC(6)

N(1)AC(1)AC(2)

Fe(1)AC(1)AC(2)

48.48(6)

41.40(9)

86.64(6)

82.99(8)

72.9(1)

120.8(1)

130.3(2)

114.8(2)

113.6(2)

C(1)AFe(1)AFe(2)

N(1)AFe(2)AFe(1)

N(1)AFe(2)AN(2)

Fe(2)AN(1)AC(1)

Fe(2)AN(1)AN(3)

N(3)AN(1)AC(1)

Fe(2)AN(2)AC(2)

Fe(1)AC(1)AN(1)

N(1)AN(3)AC(14)

72.19(7)

48.20(6)

83.35(8)

108.8(2)

135.9(2)

113.4(2)

110.3(2)

65.7(1)

˚

2.4084(7) A, which is shorter than usual for diiron com-

˚

plexes (2.5–2.7 A) [4f,4g,12], but can be compared with

the value found in some nitrogen-bridged diiron complexes

[4a,10g,13], and can be attributed to a distinct ‘bent’

ironAiron bond [14]. The bond distances between iron and

˚

bridging nitrogens are Fe(1)AN(1) 1.934(3) A, Fe(1)AN(2)

˚

115.9(2)

1.922(3) A, Fe(2)AN(1) 1.935(2) A and Fe(2)AN(2)

1.922(2) A, which are shorter than those in reported nitro-

gen bridged diiron complexes [4f,4g,10,12e,12f,13]. The sig-

˚

niﬁcantly shorter averaged FeAN bond distance of 1.928 A

in this complex can be ascribed to the structure possessing

two three-coordinated trigonal-like bridging nitrogen

atoms, instead of four-coordinated tetrahedral-like bridg-

ing nitrogen atoms, and the nitrogen atoms of the complex

can be considered as sp²hybridized [15]. The bond distance

Table 4

˚

Selected bond lengths (A) and bond angles (ꢁ) for complexes 3a and 3c

3a

Fe(1)AFe(2)

Fe(1)AN(2)

Fe(2)AN(2)

N(1)AC(1)

C(1)AN(3)

N(4)AN(3)

2.502(1)

1.918(4)

1.921(4)

1.395(6)

1.300(7)

1.396(6)

Fe(1)AN(1)

Fe(2)AN(1)

N(1)AN(2)

N(2)AC(12)

C(12)AN(4)

C(1)AC(2)

1.920(4)

1.923(4)

1.410(6)

1.286(7)

1.444(7)

˚

between C(1) and N(1) (1.273(4) A) is shorter than the

˚

C@N bond distance in ligand 1 (1.284(2) A), and yet is still

in the range of usual bond lengths of imine double bonds. In

the central Fe₂N₂system, the averaged FeANAFe,

NAFeAFe and NAFeAN bond angles are 77.20ꢁ, 51.51ꢁ

and 76.87ꢁ, respectively. The bond angles of Fe(1)AN(1)A

C(1), Fe(2)AN(1)AC(1), Fe(1)AN(2)AC(7) and Fe(2)A

N(2)AC(6) are 136.2(3)ꢁ, 140.7(3)ꢁ, 146.4(3)ꢁ and 134.1(3)ꢁ,

respectively. These large angles are associated with the short

FeAFe bond length and the sp²hybridization of the nitro-

gen atoms.

Fe(2)AFe(1)AN(1)

N(1)AFe(1)AN(2)

Fe(1)AFe(2)AN(2)

Fe(1)AN(1)AFe(2)

Fe(1)AN(1)AN(2)

Fe(2)AN(1)AN(2)

N(2)AN(1)AC(1)

N(1)AC(1)AC(2)

49.4(1)

43.1(2)

49.3(1)

81.3(2)

68.4(3)

116.7(4)

117.3(5)

Fe(2)AFe(1)AN(2)

Fe(1)AFe(2)AN(1)

N(1)AFe(2)AN(2)

Fe(1)AN(2)AFe(2)

Fe(1)AN(2)AN(1)

Fe(2)AN(2)AN(1)

N(1)AC(1)AN(3)

C(1)AN(3)AN(4)

49.4(1)

49.3(1)

43.0(2)

81.4(2)

68.5(2)

68.6(2)

123.1(5)

119.7(5)

3c

The cleavage ofthe NAN bond during the course of ligand

coordination leads to a reduced degree of conjugation of the

ligand and might increase the p-electron density on the imine

group which explains why there is a 0.50 ppm downﬁeld

chemicalshift of theazomethine protonsin its ¹H NMR spec-

trum. On the other hand, relative to the highly conjugated

ligand 1, the bond order of the imine group in the complex

might increase. The IR stretching absorption of the C@N

group is higher energy shifted from 1625 cm^ꢀ1in ligand 1

to 1638 cm^ꢀ1in the iminato-bridged complex and is consis-

tent with the shortening of the C@N bond length in 1a.

Fe(1)AFe(2)

Fe(1)AN(2)

Fe(2)AN(1)

N(1)AN(2)

N(2)AC(29)

C(29)AN(4)

2.512(1)

1.947(4)

1.904(2)

1.419(5)

1.384(7)

1.322(7)

Fe(1)AN(1)

Fe(1)AP(1)

Fe(2)AN(2)

N(1)AC(1)

C(1)AN(3)

N(3)AN(4)

1.910(2)

2.254(2)

1.934(4)

1.417(6)

1.275(6)

1.387(6)

Fe(2)AFe(1)AN(1)

N(1)AFe(1)AN(2)

P(1)AFe(1)AN(2)

Fe(1)AFe(2)AN(1)

N(1)AFe(2)AN(2)

Fe(1)AN(1)AN(2)

Fe(2)AN(1)AN(2)

N(2)AN(1)AC(1)

N(1)AC(1)AN(3)

C(1)AN(3)AN(4)

48.7(1)

43.4(2)

104.5(1)

48.7(1)

43.4(2)

69.8(3)

69.4(2)

116.8(4)

122.5(5)

121.6(5)

Fe(2)AFe(1)AN(2)

P(1)AFe(1)AN(1)

P(1)AFe(1)AFe(2)

Fe(1)AFe(2)AN(2)

Fe(1)AN(1)AFe(2)

Fe(1)AN(2)AFe(2)

Fe(1)AN(2)AN(1)

Fe(2)AN(2)AN(1)

N(1)AC(1)AC(2)

49.4(1)

105.6(1)

151.42(5)

49.4(1)

82.4(2)

69.8(3)

69.4(2)

115.5(5)

2.3.2. Fe₂(CO)₆(MeC₅H₃NCHNNCHC₅H₃NMe) (2a)

The molecular structure of compound 2a, as shown

in Fig. 4, shows that the iron atoms possess a distorted

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

3061

octahedral coordination geometry. The FeAFe inter-metal-

lic distance is 2.5689(5) A (Table 3). The iron atoms are

rings, S(1)AC(2)AC(3)AC(4)AC(5) plane and S(2)AC(13)

AC(14)AC(15)AC(16) plane, are 12.59ꢁ and 9.01ꢁ,

respectively.

˚

bridged by one of the imine fragments, C(1)@N(1), of the

ligand in the g²-C@N bonding mode. The azomethine

N(1) atom and the pyridine N(2) atom, which is next to

the coordinated azomethine, are r-bonded to the Fe(1)

and Fe(2) centers, respectively. Therefore, it can be inferred

that the pyridyl azine is coordinated in the r-N, l²-N⁰, g²-

C@N⁰bonding mode to the iron atoms in which the ligand

forms a 6e bridge between the two Fe(CO)₃moieties. The

Fe(1)AN(1) and Fe(2)AN(1) distances are 1.930(2) and

˚

The FeAFe bond distance is 2.502(1) A (Table 4). The

bond distances Fe(1)AN(1), Fe(1)AN(2), Fe(2)AN(1) and

Fe(2)AN(2) are 1.920(4), 1.918(4), 1.923(4) and 1.921(4)

˚

A, respectively, which are shorter than usual nitrogen

bridged diiron complexes. The Fe(1)AFe(2)AN(1) and

Fe(2)AFe(1)AN(2) bond angles are 49.3(1)ꢁ and the

Fe(2)AFe(1)AN(1) and Fe(2)AFe(1)AN(2) bond angles

are 49.4(1)ꢁ. The bond angles of Fe(1)AN(1)AN(2),

Fe(1)AN(2)AN(1), Fe(2)AN(1)AN(2) and Fe(2)AN(2)

AN(1) are about the same and have an average value of

68.5(3)ꢁ. The N(1)AFe(1)AN(2) and N(1)AFe(2)AN(2)

angles are also about the same (43.1(2)ꢁ versus 43.0(2)ꢁ),

indicating that the Fe(1)Fe(2)N(2)N(1) core is quite sym-

˚

1.948(2) A, respectively; the Fe(1)AC(1) distance is

˚

2.025(3) A, while the Fe(2)AN(2) distance is 2.030(2) A.

These are normal values for such bonds. The C(1)AN(1) dis-

˚

tance of 1.401(3) A is signiﬁcantly elongated compared to

˚

the C(14)AN(3) bond distance (1.268(3) A) in the uncoordi-

nated C@N moiety, as expected for the g²-bonding mode of

metrical. The N(1)AN(2) bond of 1.410(6) A is signiﬁcantly

˚

this fragment [16]. The C(2)AN(2) distance of 1.353(3) A in

elongated compared to the N(1)AN(2) bond distance

˚

the r-N-coordinated pyridine ring is comparable to the

usual r-N-coordinated azomethine group [17], which can

be attributed to eﬀective delocalization of electron density

in the coordinated pyridine ring in the complex.

(1.317(3) A) in the highly conjugated ligand 3, as expected

for the r-N and g²-N@N bonding mode of this fragment.

The elongation of N(3)@N(4), N(1)AC(1) and N(2)

˚

AC(12) bond distances (1.396(6), 1.395(6) and 1.410(6) A)

Around the central core, the N(1)AFe(1)AFe(2),

N(1)AFe(2)AFe(1) and N(1)AFe(1)AC(1) bond angles

are 48.81(6)ꢁ, 48.20(6)ꢁ and 41.40(9)ꢁ, respectively, while

the N(2)AFe(2)AFe(1) and N(2)AFe(2)AN(1) angles are

86.64(6)ꢁ and 83.35(8)ꢁ. The Fe(1)AN(1)AFe(2),

Fe(1)AN(1)AC(1) and Fe(1)AC(1)AN(1) bond angles are

82.99ꢁ, 72.9(1)ꢁ and 65.7(1)ꢁ, respectively. The C(1)AN(1)

AN(3) bond angle is squeezed to a value of 113.4(2)ꢁ.

The Fe(2)AN(1)AC(1)AC(2)AN(2) atoms form a plane

with a torsion angle of 21.44ꢁ between the C(1)AN(1)

and C(2)AN(2) bonds. This implies that the planarity of

the N@CAC@N system in the free ligand is not aﬀected

much by the r-N, l²-N⁰, g²-C@N⁰type coordination

[17b,18] and the dihedral angle deﬁned by the mean plane

of Fe(2)AN(1)AC(1)AC(2)AN(2) and the pyridine plane

is 7.57ꢁ.

and the shortening of C(1)AN(3) and C(12)AN(4) distances

(1.300(7) and 1.286(7) A), relative to that in the uncoordi-

nated ligand 3, indicate that the aromaticity of the tetrazine

ring has been destroyed and the ring has become the combi-

nation of a diaza (NAN) and a diimine (AC@ NAN@CA).

˚

2.3.4. Fe₂(CO)₅PPh₃(C₄H₂SC₂N₄HC₄H₃S) (3c)

The molecular structure and bonding features of 3c, as

shown in Fig. 6 and Table 4, close resemble that of 3a

except one of carbonyl ligands on Fe(1) has been replaced

by a triphenylphosphine ligand. The Fe(1)AP distance is

˚

2.2542(2) A. The P(1)AFe(1)AN(1), P(1)AFe(1)AN(2)

and P(1)AFe(1)AFe(2) bond angles are 105.6(1)ꢁ,

104.5(1)ꢁ and 151.42(5)ꢁ, respectively. A disorder between

S1 and S1a and between S2 and S2a on the two thiophene

rings has been observed. The geometry of the molecule has

ꢂ70% with two thienyl sulfur atoms pointing toward the

iron centers and ꢂ30% with two sulfur atoms pointing

backwards from the iron centers.

2.3.3. Fe₂(CO)₆(C₄H₃SC₂N₄C₄H₃S) (3a)

The molecular structure of complex 3a, as shown in

Fig. 5, shows that the dithienyltetrazine ligand coordinates

to the metal centers through one of its diazo moieties. The

ligand has a r-N, r-N⁰, l²-g²-N@N⁰type of coordination

mode in which the ligand forms a 6e bridge between the

two Fe(CO)₃units. The iron centers possess a distorted

octahedral coordination geometry. The tricarbonyl groups

are eclipsed. There are two geometries in the unit cell of 3a

with a diﬀerence in the orientation of the thienyl rings. The

geometry of ligand 3, as shown in Fig. 2, is planar with a

C_2hsymmetry. However, the two thienyl rings in complex

3a are oriented in the same direction – with both of their

thienyl S atoms pointing towards the iron centers in one

geometry and backwards to the iron centers in the other

geometry. In both cases the FeAFe bond is perpendicular

to the NAN bond of the tertrazine ring. The dihedral

angles between the central tetrazine ring and two thienyl

3. Conclusion

We have demonstrated that using diﬀerent heterocyclic

substituted azines 1, 2 and 3 as ligands, hexacarbonyldiiron

complexes with various coordination modes can be synthe-

sized. In the reaction of iron carbonyls with azines, com-

plexes with diﬀerent coordination modes have been

reported. In the reaction of Fe₃(CO)₁₂with ketazines

(R¹R²C@NAN@CAR¹R², where R¹= R²= Me; R¹=

R²= p-CH₃Ph; R¹= Me, R²= Ph; R¹= H, R²= thienyl),

bis-(l-ketoiminato)hexacarbonyldiiron complexes were

produced, formed by cleavage of the NAN bond

[10a,10f,19]. In contrast, in the similar benzaldazine system

(R¹= H, R²= p-substituted Ph), it led only to the endo

cyclometallation of the phenyl ring [4a,20]. However, in

3062

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

the reaction of N,N⁰-bis-(3-phenyl-allylidene)-hydrazine

(RC@CAC@NAN@CAC@CR) with Fe₂(CO)₉, mono-,

di- and tetrametallic iron carbonyl complexes were synthe-

sized. In this case, no cleavage of the ligand was observed

and only azomethine nitrogen atom(s) and allyl double

bond(s) are bonded to the discrete Fe(CO)₃center(s) [21].

Thus, the type of substituent on the azine system is critical

for the way of complexation.

In this study, in the reaction with Fe₂(CO)₉, both NAN

bond cleavage (g²-N; g²-N⁰mode) and endo cyclometalla-

tion (l-2,3-g¹:g²-pyrrolyl; g¹:g¹(N) mode) are observed

for ligand 1, one pyridyl N and one imine-bridged (l-

r;p-g¹:g²-(C, N); g¹(N_py) mode), and two pyridyl N a₀nd

one imine-bridged (l-p-g¹:g¹-ðC; NÞ; g1ðN_pyÞ; g¹ðN_pyÞ

mode) coordinations are found in the case of ligand 2,

whereas diaza-bridged (l-g²:g²-(N,N⁰) mode) and endo

cyclometallated (l-2,3-g¹:g²-thienyl; g¹:g¹(N) mode) coor-

dinations are involved in the case of ligand 3.

24 h. The solvent was removed by ﬁltration. The precipi-

tate was washed with several portions of ether and dried

in vacuo to give pure yellow product 1 (18.8 mmol, 94%

yield) or 2 (19.6 mmol, 98% yield).

Compound 1: M.p. 114–115 ꢁC. ¹H NMR: d 8.50 (s, 2H),

6.93 (d, J_H–H= 2.6 Hz, 2H), 6.61 (d, J_H–H= 3.8 Hz, 2H),

6.15 (dd, J_H–H= 3.9, 2.7 Hz, 2H), 3.99 (s, 6H). ¹³C

NMR: d 151.8, 128.8, 127.8, 117.0, 108.6, 36.1. IR (KBr

ﬁlm) m_C@N: 1625 cm^ꢀ1. MS (FAB): m/z 214 (M⁺). Anal.

Calc. for C₁₂H₁₄N₄: C, 67.28; H, 6.54; N, 26.16. Found:

C, 67.01; H, 6.64; N, 26.30%.

Compound 2: M.p. 175–176 ꢁC. ¹H NMR (methanol-

d₄): d 8.58 (s, 2H), 7.98 (d, J_H–H= 7.8 Hz, 2H), 7.82

(t, J_H–H= 7.8 Hz, 2H), 7.37 (d, J_H–H= 7.8 Hz, 2H), 2.60

(s, 6H). ¹³C NMR (methanol-d₄): d 161.4, 158.8, 151.8,

137.4, 125.2, 119.4, 22.5. IR (KBr ﬁlm) m_C@N: 1630 cm^ꢀ1

.

MS (FAB): m/z 239 (M⁺). Anal. Calc. for C₁₄H₁₆N₄: C,

70.00; H, 5.87; N, 23.32. Found: C, 70.29; H, 5.79; N,

23.45%.

4. Experimental

4.3. Synthesis of 3,6-bis(2⁰-thienyl)-1,2,4,5-tetrazine (3)

4.1. General

2-Thiophenecarbonitrile (4.36 g, 40.0 mmol) and hydra-

zine monohydrate (8.00 g, 160 mmol) were reﬂuxed in eth-

anol (Merck, 50 ml) for 48 h. After the ﬁltration, the ﬁltrate

was stirred at room temperature under air for 12 h. The red

precipitate was collected and recrystallized using dichloro-

methane as a solvent to give pure product 3 (21.6 mmol,

Diiron nonacarbonyl was prepared through the photol-

ysis of iron pentacarbonyl (Aldrich) in glacial acetic acid

[22]. Solvents were dried (sodium/benzophenone, P₄O₁₀)

and distilled under nitrogen prior to use. N-Methyl-2-pyr-

rolecarboxaldehyde (Acros) and 2-thiophenemethylamine

(Aldrich) were distilled by a Kugelrohr distillation appara-

tus under reduced pressure (0.1 mmHg) prior to use. All

other chemicals were reagent grade and used without fur-

ther puriﬁcation. The NMR spectra were recorded on a

Bruker DX-300 NMR spectrometer (¹H, 299.95 MHz;

¹³C, 75.43 MHz). Chemical shifts were referenced to

TMS and deuterated acetone (Janssen) was used as a sol-

vent and as a secondary reference. Mass spectra were

obtained from a Micromass Platform II spectrometer. IR

spectra were recorded employing a Mattson Genesis FTIR

spectrophotometer. Elemental analyses were performed

using a Perkin–Elmer 2400, 2400II elemental analyzer.

Crystals for X-ray diﬀraction were obtained from ethyl ace-

tate/dichloromethane (1), ethyl acetate/methanol (1a),

ethyl acetate/ether (2a) and dichloromethane (3, 3a and

3c). A single crystal was mounted on a glass ﬁber and the

X-ray diﬀraction intensity data were measured on a Bruker

Smart 1000 CCD XRD (1 and 1a) or a Rigaku AFC7S dif-

fractometer (2a, 3, 3a, and 3c).

1

54% yield). M.p. 191.5–192.5 ꢁC. H NMR: d 8.28 (dd,

J = 3.6, 1.2 Hz, 2H), 7.96 (dd, J = 3.6, 1.2 Hz, 2H), 7.38

(dd, J = 5.1, 3.6, 2H). ¹³C NMR: d 162.6, 137.3, 133.6,

131.6, 130.1. IR (KBr ﬁlm) m_C@N: 1533 cm^ꢀ1. MS (FAB):

m/z 247 (M⁺). Anal. Calc. for C₁₀H₆N₄S₂: C, 48.78; H,

2.44; N, 22.76; S, 26.02. Found: C, 48.84; H, 2.56; N,

22.78; S, 26.62%.

4.4. Reaction of 1 with Fe₂(CO)₉in reﬂuxing toluene to

yield complexes 1a and 1b

1.07 g (5.0 mmol) of compound

1

and 5.46 g

(15.0 mmol) of Fe₂(CO)₉were heated at reﬂux in 60 ml of

toluene in the dark under nitrogen for 12 h. The reaction

mixture was ﬁltered through Celite 545 and the solvent

was removed under reduced pressure. The residue was sep-

arated by a 3.5 cm diameter and 40 cm height column

(230–400 mesh ASTM silica gel (Merck)) with ether/n-hex-

ane (1:3) as eluent. The orange red band produced 0.97 g

(2.0 mmol, 40% yield) of complex 1a. The red band pro-

duced 0.69 g (1.4 mmol, 28% yield) of complex 1b.

4.2. Synthesis of Schiﬀ bases 1,4-di-(N-methyl-2⁰-pyrrolyl)-

2,3-diaza-1,3-butadiene (1) and 1,4-di-(6-methyl-2⁰-

pyridyl)-2,3-diaza-1,3-butadiene (2)

Complex 1a: M.p. 148–149 ꢁC. ¹H NMR: d 9.00 (s, 2H),

6.93 (dd, J_H–H= 2.4, 2.1 Hz, 2H), 6.84 (dd, J_H–H= 3.6,

2.1 Hz, 2H), 6.20 (dd, J_H–H= 3.6, 2.7 Hz, 2H), 3.74 (s,

6H). ¹³C NMR: d 207.1, 155.7, 128.8, 126.1, 117.1, 108.6,

36.1. IR (CH₂Cl₂) m_C@N: 1638 cm^ꢀ1, m_C@O: 2061, 2021,

1972 cm^ꢀ1. MS (FAB): m/z 495 (M⁺), 467 (M⁺ꢀCO),

439 (M⁺ꢀ2CO), 411 (M⁺ꢀ3CO), 383 (M⁺ꢀ4CO), 355

(M⁺ꢀ5CO), 327 (M⁺ꢀ6CO), 271 (M⁺ꢀ6COAFe). Anal.

The synthesis of Schiﬀ bases employed the usual

approach of condensation in alcohol solution [23].

N-Methyl-2-formylpyrrol or 6-methyl-2-formylpyridine

(40.0 mmol) and N₂H₄Æ H₂O (Acros, 20.0 mmol) were

heated at reﬂux in 95% ethanol (E. Merck, 100 mL) for

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

3063

Calc. for C₁₈H₁₄Fe₂N₄O₆: C, 43.76; H, 2.86; N, 11.34.

4.6. Reaction of 3 with Fe₂(CO)₉in benzene to give

complexes 3a and 3b

Found: C, 43.65; H, 2.94; N, 11.24%.

Complex 1b: M.p. 129–130 ꢁC. ¹H NMR: d 7.96 (s, 1H),

7.23 (d, J_H–H= 2.7 Hz, 1H), 6.86 (d, J_H–H= 2.7, 1H), 6.55

(d, J_H–H= 2.7 Hz, 1H), 6.44 (dd, J_H–H= 3.6 Hz, 1H), 6.08

0.75 g (3.0 mmol) of compound

3

and 4.38 g

(12.0 mmol) of Fe₂(CO)₉were heated at reﬂux in 100 ml

of anhydrous benzene in the dark under nitrogen for

24 h. The reaction mixture was ﬁltered through Celite 545

and the solvent was removed under reduced pressure.

The residue was separated by a 3.5 cm diameter and

40 cm height column (230–400 mesh ASTM silica gel

(Merck)) with ethyl acetate/n-hexane (1:30) as eluent. The

red band recovered 0.15 g of unreacted ligand 3 (20%).

The orange red band produced 0.84 g (1.6 mmol, 53%

yield) of complex 3a. The orange yellow band produced

0.16 g (0.3 mmol, 10% yield) of complex 3b.

(dd, J_H–H= 3.6, 2.7 Hz, 1H), 4.53 (s, 2H), 4.21 (s, 6H). ¹³

C

NMR: d 211.9, 151.8, 144.7, 141.0, 131.9, 128.5, 126.7,

116.6, 117.6, 108.2, 61.8, 36.3, 34.7. IR (CH₂Cl₂) m_C@N

:

1638 cm^ꢀ1, m_C@O: 2055, 2011, 1963 cm^ꢀ1. MS (FAB): m/z

495 (M⁺), 466 (M⁺ꢀCO), 438 (M⁺ꢀ2CO), 410

(M⁺ꢀ3CO), 382 (M⁺ꢀ4CO), 354 (M⁺ꢀ5CO), 326

(M⁺ꢀ6CO), 270 (M⁺ꢀ6COAFe), 214 (L⁺). Anal. Calc.

for C₁₈H₁₄Fe₂N₄O₆: C, 43.76; H, 2.86; N, 11.34. Found:

C, 43.85; H, 2.98; N, 11.17%.

1

4.5. Reaction of 2 with Fe₂(CO)₉in THF to yield complexes

2a and 2b

Complex 3a: M.p. 127.8–128.8 ꢁC (decomp.). H NMR:

d 8.00 (d, J = 5.1 Hz, 2H), 7.69 (d, J = 3.6 Hz, 1H), 7.38

(dd, J = 4.8, 3.6 Hz, 2H). IR (KBr ﬁlm) m_CO: 2076, 2035,

2001, 1987, 1972 cm^ꢀ1; m_CN: 1543 cm^ꢀ1. MS(FAB): m/z

527 (M⁺), 499 (M⁺ꢀCO), 471 (M⁺ꢀ2CO), 443 (M⁺ꢀ

3CO), 415 (M⁺ꢀ4CO), 378 (M⁺ꢀ5CO), 359 (M⁺ꢀ6CO),

331 (M⁺ꢀ5COAFe), 247 (L⁺). Anal. Calc. for Fe₂C₁₆H₆-

N₄O₆S₂: C, 36.50; H, 1.14; N, 10.65; S, 12.17. Found: C,

36.55; H, 1.22; N, 10.78; S, 12.45%.

1.50 g (6.20 mmol) of compound

2

and 7.30 g

(20.0 mmol) of Fe₂(CO)₉were heated at reﬂux in 100 ml

of anhydrous THF in the dark under nitrogen for 24 h.

The reaction mixture was ﬁltered through Celite 545

and the solvent was removed under reduced pressure.

The residue was chromatographed on a silica gel column

with ethyl acetate and then with ethanol as eluent to iso-

late dark red product 2a (0.85 g, 1.6 mmol, 26% yield) and

purple complex 2b (1.30 g, 2.45 mmol, 40% yield),

respectively.

If the reaction was carried on at room temperature,

complex 2a (3.3 mmol, 53% yield) and trace amount of

complex 2b were isolated. If the reaction was preceded

under irradiation of UV light, only complex 2b was pro-

duced in 94% yield.

Complex 3b: M.p. 194.7 ꢁC (decomp.). ¹H NMR: d 9.01

(s, 1H), 7.95 (d, J = 5.1 Hz, 1H), 7.65 (d, J = 5.1 Hz, 1H),

7.55 (d, J = 3.6 Hz, 1H), 7.46 (d, J = 5.1 Hz, 1H), 7.11 (dd,

J = 5.1, 3.6 Hz, 1H). IR (KBr ﬁlm) m_NH: 3355, 1521 cm^ꢀ1

;

m

_CO: 2073, 2033, 2012, 1995, 1977, 1952 cm^ꢀ1; m_CN: 1638,

1574 cm^ꢀ1. MS(FAB): m/z 527 (M⁺), 499 (M⁺ꢀCO), 471

(M⁺ꢀ2CO), 443 (M⁺ꢀ3CO), 415 (M⁺ꢀ4CO), 387 (M⁺ꢀ

5CO), 359(M⁺ꢀ6CO), 247 (L⁺). Anal. Calc. for Fe₂C₁₆H₆-

N₄O₆S₂: C, 36.50; H, 1.14; N, 10.65; S, 12.17. Found: C,

36.62; H, 1.19; N, 10.54; S, 12.31%.

Complex 2a: M.p. 126–127 ꢁC. ¹H NMR: d 8.82 (s, 1H),

7.98 (d, J_H–H= 7.8 Hz, 1H), 7.81 (t J_H–H= 7.8 Hz, 1H),

7.45 (t, J_H–H= 7.8 Hz, 1H), 7.37 (d, J_H–H= 7.8 Hz, 1H),

7.21 (d, J_H–H= 7.8 Hz, 1H), 6.79 (d, J_H–H= 7.5 Hz, 1H),

4.82 (s, 1H), 2.64 (s, 3H), 2.62 (s, 3H). ¹³C NMR: d

212.8, 170.3, 160.7, 158.8, 155.7, 151.9, 137.8, 137.1,

124.3, 120.3, 118.6, 115.6, 67.9, 26.0, 23.4. IR (CH₂Cl₂)

4.7. Reaction of complex 3a with triphenylphosphine in

dichloromethane to give 3c and 3d

0.20 g (0.38 mmol) of complex 3a in a 50 ml of anhy-

drous dichloromethane was stirred with 0.20 g (0.76 mmol)

of PPh₃at room temperature under N₂atmosphere for

24 h. After the ﬁltration, the solvent was removed under

reduced pressure and the residue was separated by a

3.5 cm diameter and 40 cm height column (230–400 mesh)

with ethyl acetate/n-hexane (1:5) as eluent to give 0.26 g

(0.34 mmol, 89% yield) of complex 3c and 40 mg

(0.040 mmol, 10% yield) of complex 3d.

m

_C@N: 1562 cm^ꢀ1, m_C@O: 2054, 2000, 1983, 1927 cm^ꢀ1. MS

(FAB): m/z 518 (M⁺), 490 (M⁺ꢀCO), 462 (M⁺ꢀ2CO),

434 (M⁺ꢀ3CO), 406 (M⁺ꢀ4CO), 378 (M⁺ꢀ5CO), 350

(M⁺ꢀ6CO), 294 (M⁺ꢀ6COAFe), 239 (L⁺). Anal. Calc.

for C₂₀H₁₄Fe₂N₄O₆: C, 46.37; H, 2.72; N, 10.81. Found:

C, 46.55; H, 2.78; N, 10.88%.

1

Complex 2b: H NMR: d 8.86 (s, 1H), 7.58 (t, J_H–H

=

7.8 Hz, 1H), 7.52 (t J_H–H= 7.8 Hz, 1H), 7.41 (d, J_H–H

= 7.8 Hz, 1H), 7.32 (d, J_H–H= 7.8 Hz, 1H), 7.02 (t, J_H–H

= 7.8 Hz, 1H), 6.88 (d, J_H–H= 7.8 Hz, 1H), 4.54 (s, 1H),

1

Complex 3c: M.p. 171.4–172.0 ꢁC (decomp.). H NMR:

d 7.89 (d, J = 5.1 Hz, 2H), 7.49 (d, J = 3.6 Hz, 1H), 7.32

(dd, J = 5.1, 3.6 Hz, 2H), 7.27 (m, 15 H). ¹³C NMR: d

211.4, 156.9, 135.3, 134.6, 134.0, 133.7, 133.5, 132.9,

131.5, 129.9, 129.6, 129.4, 129.3. IR (KBr ﬁlm) m_CO: 2046,

1978, 1926 cm^ꢀ1; m_CN: 1541 cm^ꢀ1. MS(FAB): m/z 761

(M⁺), 733 (M⁺ꢀCO), 705 (M⁺ꢀ2CO), 677 (M⁺ꢀ3CO),

649 (M⁺ꢀ4CO), 621 (M⁺ꢀ5CO), 565 (M⁺ꢀ5COAFe),

263 (PPh₃+ 1), 247 (L⁺). Anal. Calc. for Fe₂C₃₃H_21-

2.54 (s, 3H), 2.51 (s, 3H). IR (CH₂Cl₂) m_C@N: 1573 cm^ꢀ1

,

m

_C@O: 2045, 1992, 1967 cm^ꢀ1. MS (FAB): m/z 518 (M⁺),

490 (M⁺ꢀCO), 462 (M⁺ꢀ2CO), 434 (M⁺ꢀ3CO), 406

(M⁺ꢀ4CO), 378 (M⁺ꢀ5CO), 350 (M⁺ꢀ6CO), 294

(M⁺ꢀ6COAFe), 239 (L⁺). Anal. Calc. for C₂₀H₁₄Fe₂N₄O₆:

C, 46.37; H, 2.72; N, 10.81. Found: C, 46.21; H, 2.88; N,

11.10%.

3064

C.-Y. Wu et al. / Polyhedron 25 (2006) 3053–3065

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20 (2001) 353.

N₄O₅PS₂: C, 52.11; H, 2.76; N, 7.37; S, 8.42. Found: C,

52.24; H, 2.73; N, 7.27; S, 8.32%.

Complex 3d: M.p. 217.3–217.8 ꢁC. H NMR: d 7.71 (d,

J = 5.1 Hz, 2H), 7.31 (d, J = 3.6 Hz, 1H), 7.22 (m, 20H),

1

7.27 (m, 12 H). IR (KBr ﬁlm) m_CO

: 1994, 1947,

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1926 cm^ꢀ1; m_CN: 1537 cm^ꢀ1. MS(FAB): m/z 995 (M⁺),

967 (M⁺ꢀCO), 939 (M⁺ꢀ2CO), 911 (M⁺ꢀ3CO), 883

(M⁺ꢀ4CO), 636 (M⁺ꢀ4CO-L), 318 ðFePPh₃^þÞ, 263

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Acknowledgements

Financial support from the National Science Council

(Taiwan, ROC) and National Dong Hwa University are

gratefully acknowledged.

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Appendix A. Supplementary data

Crystallographic data for the structural analysis have

been deposited with the Cambridge Crystallographic Data

Center, CCDC No. 277567 for 1, 277568 for 3, 277569 for

1a, 277570 for 2a, 277571 for 3a and 277572 for 3c. Copies

of this information may be obtained free of charge from

The Director, CCDC, 12 Union Road, Cambridge CB2

1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.

com.ac.uk or http://www.ccde.cam.ac.uk). Supplementary

data associated with this article can be found, in the online

version, at doi:10.1016/j.poly.2006.04.031.

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Article Doi

Reactions of diiron nonacarbonyl with pyrrolyl-, pyridyl- and thienyl-substituted azines: N{single bond}N bond cleavage, cyclometallation and C{double bond, long}N σ and π-bonding

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