Syntheses and structural characterization of novel heteroannular cyclopalladated ferrocenylimine

Article abstract of DOI:10.1016/j.jorganchem.2005.08.044

A new heteroannular cyclopalladated ferrocene derivative [PdCl{C ₅H₄FeC₅H₄CH₂NCH-C ₄H₃S}(PPh₃)] (6) was synthesized and characterized by IR, ¹H NMR, ¹³C NMR, high resolution mass spectroscopy, and its molecular structure was further confirmed by X-ray crystal structure determination. According to the crystal structure, the palladium atom is bound to the unsubstituted Cp ring, showing the four-coordinate structure typical of palladium complexes. A preliminary application of these novel cyclopalladated complexes in Mizoroki-Heck reaction is also to be demonstrated in this paper.

Full text of DOI:10.1016/j.jorganchem.2005.08.044

Journal of Organometallic Chemistry 691 (2006) 255–260
www.elsevier.com/locate/jorganchem
Note
Syntheses and structural characterization of novel heteroannular
cyclopalladated ferrocenylimine
*
*
Xue Mei Zhao, Xin Qi Hao, Bin Liu, Mao Lin Zhang, Mao Ping Song , Yang Jie Wu
Department of Chemistry, Zhengzhou University, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Zhengzhou 450052, PR China
Received 26 June 2005; received in revised form 23 August 2005; accepted 29 August 2005
Available online 4 October 2005
Abstract
A new heteroannular cyclopalladated ferrocene derivative [PdCl{C5H4FeC5H4CH2N@CH–C4H3S}(PPh3)] (6) was synthesized and
1
characterized by IR, H NMR, 13C NMR, high resolution mass spectroscopy, and its molecular structure was further confirmed by
X-ray crystal structure determination. According to the crystal structure, the palladium atom is bound to the unsubstituted Cp ring,
showing the four-coordinate structure typical of palladium complexes. A preliminary application of these novel cyclopalladated com-
plexes in Mizoroki–Heck reaction is also to be demonstrated in this paper.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Heteroannular; Ferrocenylimine; Crystal structure; Cyclopalladated
1. Introduction
dated reaction of the Schiff base of ferrocenylmethylamine.
We have found that in this novel cyclopalladation derivative,
the palladium atom is directed into the unsubstituted Cp
ring, forming a new chelated large-membered metallocycle.
In addition, this cyclopalladated reaction is, to the best of
our knowledge, the first example of heteroannular cyclopal-
ladated ferrocene derivative.
Cyclopalladated compounds derived from N-donor li-
gands have attracted great interest in the last decade due
to their wide variety of interesting and novel applications
in the fields of organic synthesis, catalysis, and photochem-
istry [1–4]. However, among all cyclopalladated ferroce-
nylimine derivatives reported so far, the most widely
studied systems are based on the formation of the chelated
five- or six-membered metallocycles depending on some
directing atom that becomes a ligand with the metal.
2. Results and discussion
2.1. Synthesis
´
Lopezꢀs and our laboratory have reported the cyclopallada-
tion of some ferrocenylimines. It is found that the reaction
occurs predominantly at the ortho-position of the substi-
tuted cyclopentadienyl ring to afford the corresponding
cyclopalladated derivatives [5,6].
It is of interest to try to extend the scope of this reaction.
Here, we will describe the synthesis of heteroannular cyclo-
palladated ferrocene derivative via the direct cyclopalla-
Cyclopalldated ferrocene derivative 6 is synthesized as
follows (Scheme 1). We employ formylferrocene (1) as
the starting material to prepare the desired cyclopalladated
compound. Ferrocenecarbaldehyde oxime (2) has been ob-
tained on treatment of the formylferrocene (1) with
hydroxylamine hydrochloride in 80% yield. Ferrocenylm-
ethylamine (3) was prepared by reduction of 2 in 79% yield.
Ferrocenylimine (4) was obtained on treatment of 3 with
thiophenecarboxaldehyde in 55% yield.
*
Corresponding authors. Fax: +86 371 67783012 (M.P. Song); +86 371
67766667 (Y.J. Wu).
Ferrocenylimine (4) underwent palladation readily
when treated with mole equivalents of lithium
E-mail addresses: mpsong9350@zzu.edu.cn (M.P. Song), wyj@zzu.
edu.cn (Y.J. Wu).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.08.044

256
X.M. Zhao et al. / Journal of Organometallic Chemistry 691 (2006) 255–260
Scheme 1. (a) NH2OH Æ HCl, CH3OH, NaHCO3, r.t., 3 h (b) LiAlH4, THF, reflux, 6 h. (c) RCHO, C2H5OH, r.t. (d) Li2PdCl4, CH3OH, r.t., 20 h.
(e) PPh3, CH2Cl2, r.t., 2 h.
tetrachloropalladate (II) in the presence of sodium acetate
in dry methanol for about 20 h at room temperature, and
the resulting precipitates were isolated as a brown-red pow-
der, which is insoluble in all common organic solvents, and
which can be assigned to a binuclear complex of palladium
5. Since the solid readily underwent a bridge-splitting reac-
tion with ligand triphenylphosphine to produce the mono-
meric triphenylphosphine derivative (6 over yield 76%),
which is a typical reaction of a chlorine-bridged binuclear
complex of palladium [7–9]. So the compound 5 was char-
acterised only by IR. The new compounds 4 and 6 were
sufficiently characterized by physical and spectroscopic
data. The solid-state structures were confirmed by X-ray
crystallographic analysis (see Figs. 1 and 2).
2.2. Spectral properties of 4 and 6
The IR spectra of 4 displays two absorption bands at
around 1000 and 1100 cmꢀ1 and this feature is in accor-
dance with the structures of mono-substituted ferrocene
derivatives [10]. But in compound 6, the absorption bands
at 1000 and 1100 cmꢀ1 have not been observed, indicating
no unsubstituted Cp ring in the molecule. In addition, the
C@N absorptions of 6 are shifted to lower wavelengths by
8.73 cmꢀ1 in comparison with 4, indicating that nitrogen is
coordinated to palladium through its lone pair [11]. The
strong absorptions at 740 and 690 cmꢀ1 observed in com-
pound 6, a feature of the mono-substituted benzene ring,
are assigned to the d (CH) of PPh3. These IR features are
in good agreement with the proposed structures for the
compounds 4 and 6.
1
In the H NMR spectra of compound 4, a singlet that
appears at d 4.17 ppm corresponds to the unsubstituted
Cp ring and a downfield singlet at 8.34 ppm is for the pro-
ton of the methine. But in compound 6, these five protons
do not exist, which further confirms that the compound 6 is
Scheme 2. R = COOEt, COOMe, Ph, CN, COOCH2CH(CH2CH3)-
(CH2)4CH3.
Fig. 1. Molecular structure of 4.

X.M. Zhao et al. / Journal of Organometallic Chemistry 691 (2006) 255–260
257
completely consistent with a heteroannular structure. The
proton signals of methine are shifted to high fields. It must
be caused by the existence of intramolecular N ! Pd
coordination.
P1, N1, Cl1 and C1, showing the four-coordinate structure
typical of the palladium complexes. The angles between
adjacent atoms in the coordination sphere lie in the region
of 89.7ꢁ for N1 Pd1C1, and 88.9ꢁ for C1Pd1P1. The phos-
phine molecule and the imino nitrogen adopt a trans
arrangement with P1Pd1N1 angle of 175.5ꢁ. The Pd-ligand
distances are similar to those found in other palladated
2.3. Crystal structures of 4 and 6
˚
The single crystal structures of [C5H5FeC5H4CH2N@
CH–C4H3S] and [PdCl{C5H4FeC5H4CH2N@CH–C4H3S}-
(PPh3)] have been determined. The structures are shown
in Figs. 1 and 2. Crystallographic and data collection
parameters for 4 and 6 are summarized in Table 1. Selected
bond lengths and angles are listed in Tables 2 and 3.
In the solid-state (Fig. 1), 4 displays a trans-configuration
with the N-ferrocenyl-methyl moiety and the thiophene ring
lying on the opposite sides of C@N bond. The thiophene ring
is almost coplanar with the C–N@C–C plane for 4. The car-
bon atom at the 11-position is in the plane of the cyclopenta-
dienyl ring (the C7–C6–C10–C11 and C8–C9–C10–C11
torsion angles are ꢀ178.1(2)ꢁ and 177.9(2)ꢁ, respectively),
while the nitrogen atom is deviated from this plane (the
C6–C10–C11–N1 and C9–C10–C11–N1 torsion angles are
77.3(3)ꢁ and ꢀ99.8(3)ꢁ, respectively) to avoid the ferrocene
compounds. The Pd–N distance of 2.092 A is comparable
with the values found in compounds with a Pd–N bond
˚
(ca. 2.0 A), suggesting the formation of a Pd–N bond in
compound 6. The ferrocene moiety has planar Cp rings
which were not completely parallel, with interplanar angle
˚
2.4ꢁ. The S–Pd distance is 3.086 A, which is slightly shorter
than the sum of the Van der Waals radii of palladium and
˚
sulfur atom (3.540 A), indicating the faint intramolecular
˚
coordination of S ! Pd. The C@N bond length is 1.262 A.
3. Application in Mizoroki–Heck reaction
We use compounds 5 and 6 as a new kind of catalysts in
Mizoroki–Heck reaction for the arylation of olefin deriva-
tives with iodobenzene (see Scheme 2).
As a preliminary study, two solvents (dioxane, DMF)
were used. We find that dixane is a suitable solvent, giving
the fastest reaction and a good yield, and Et3N is a good
base in the process (Table 4).
˚
moiety. The C@N bond length is 1.2523 A.
The solid-state structure of 6 (Fig. 2) is completely con-
sistent with that proposed by the spectral data. The unsub-
stituted cyclopentadienyl ring is palladated, resulting in a
new metallocycle. The palladium atom is coordinated to
It was noteworthy that all of these reactions studied
showed high regioselectivity for trans-coupling, and no
Fig. 2. Molecular structure of 6.

258
X.M. Zhao et al. / Journal of Organometallic Chemistry 691 (2006) 255–260
Table 1
Table 3
˚
Crystallographic and data collection parameters for 4 and 6
Selected bond distances (A) and angles (ꢁ) for 6
4
6
C10–C11
N1–C12
Pd1–N1
Pd1–P1
N1–C11
C12–C13
Pd1–C1
1.479(12)
1.262(11)
2.092(8)
Empirical formula
Formula weight
Temperature (K)
C16H15FeNS
309.20
291(2)
0.71073
Monoclinic
P2(1)/n
C34H29ClFeNPPdS
712.31
291(2)
0.71073
Monoclinic
P2(1)/c
2.263(3)
1.462(11)
1.447(13)
2.016(10)
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
C6–C10–C11
C9–C10–C11
N1–C11– C10
Pd1–N1–C11
N1–C12–C13
N1–Pd1–P1
Pd1–C1–C2
Pd1–C1–Fe1
Fe1–C10–C11
C11–N1–C12
Pd1–N1–C12
N1–Pd1–C1
C1–Pd1–P1
128.7(8)
˚
a (A)
5.8781(12)
12.149(2)
19.752(4)
97.57(3)
1398.2(5)
4
1.469
1.212
640
14.750(3)
22.622(5)
19.306(4)
110.32(3)
6041(2)
4
1.566
1.311
2880
122.6(7)
112.8(8)
118.0(5)
127.6(10)
175.5(2)
125.2(7)
122.7(5)
123.6(6)
115.9(8)
126.0(7)
89.7(3)
˚
b (A)
˚
c (A)
b (ꢁ)
Volume (A )
3
˚
Z
Calculated density (Mg mꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
Crystal size (mm)
h Range for data collection (ꢁ) 1.97–27.49
Index ranges
0.20 · 0.18 · 0.18 0.20 · 0.18 · 0.18
1.44–23.50
0 6 h 6 16,
ꢀ25 6 k 6 25,
ꢀ20 6 l 6 19
12479
0 6 h 6 7,
ꢀ15 6 k 6 15,
ꢀ25 6 l 6 25
5119
88.9(3)
127.7(7)
105.5(4)
Pd1–C1–C5
C1–Fe1–C10
Reflections collected
Independent reflections [Rint
Refinement method
]
2974 [0.0256]
7323 [0.0890]
Full-matrix least- Full-matrix least-
squares on F2
2974/0/173
1.082
squares on F2
7323/0/706
1.090
Table 4
Data/restraints/parameters
Goodness-of-fit on F2
Results of Mizoroki–Heck reactions with catalysts 5 and 6
Entry
R
Cat. (mol%)
T
Time %Yielda
(ꢁC) (h)
Final R indices [I>2r(I)]
R1 = 0.0370,
wR2 = 0.0820
R1 = 0.0507,
wR2 = 0.0866
R1 = 0.0981,
wR2 = 0.1991
R1 = 0.1736,
wR2 = 0.2274
1
2
3
4
5
6
7
Ph
Ph
COOMe
CN
COOEt
COOEt
5 (2.4 · 10ꢀ2
6 (2.4 · 10ꢀ2
5 (2.4 · 10ꢀ2
5 (2.7 · 10ꢀ2
5 (3.2 · 10ꢀ2
6 (3.2 · 10ꢀ2
)
)
)
)
)
)
)
140
140
100
140
100
100
140
22
22
5
12
16
16
18
71
75
85
46
87
92
77
R indices (all data)
Largest differences in
peak and hole (e/A )
0.346 and ꢀ0.372 2.971 and ꢀ0.879
3
˚
Table 2
COOCH2CH(C2H5)- 6 (3.2 · 10ꢀ2
(CH2)4CH3
COOCH2CH(C2H5)- 5 (3.2 · 10ꢀ2
(CH2)4CH3
˚
Selected bond distances (A) and angles (ꢁ) for 4
8
)
140
18
71
C10–C11
N1–C12
C11–N1
C12–C13
1.495(3)
1.2523(3)
1.473(3)
1.460(3)
Reaction conditions: PhI (1 mmol), olefin (1.5 mmol), Et3N (1 mmol),
solvents (3 mL).
a
Isolated yields, based on PhI, average of two runs.
C6–C10–C11
Fe1–C10–C11
C11–N1–C12
C12–C13–C14
C9–C10–C11
C10–C11–N1
N1–C12–C13
C12–C13–S1
126.0(2)
127.85(16)
117.2(2)
127.3(3)
126.4(3)
110.2(2)
123.1(3)
121.7(2)
instrument and are uncorrected. Infrared spectra were ob-
tained with a Bruker VECTOR 22 spectrophotometer. H
1
NMR spectra were recorded on a Bruker DPX 400 instru-
ment using CDCl3 (99.8%) as the solvent and TMS as an
internal standard. Elemental analyses were determined
with a Carlo Erba 1106 Elemental Analyzer. HRMS were
determined on a Waters Q-Tof Micro MS/MS System
ESI spectrometer. Chromatographic work was carried
out using silica gel under reduced pressure. The compounds
1–3 were synthesized according to [12,13]. Their melting
points and IR data were consistent with those of litera-
tures. A lithium tetrachloropalladate (II) solution in meth-
anol (0.1 M) was prepared by stirring two equivalents of
anhydrous lithium chloride and one equivalent of anhy-
drous palladium chloride in methanol until a homogeneous
solution was formed.
cis-product was found. Further studies on the reaction con-
ditions and reaction mechanism are in progress.
4. Experimental
4.1. General
All reagents and solvents were purchased from commer-
cial sources and were further purified by standard methods,
if necessary. Melting points were measured on a WC-1

X.M. Zhao et al. / Journal of Organometallic Chemistry 691 (2006) 255–260
259
4.2. Preparation of the compound 4
1,4-dioxane, undecane as internal standard) or purified by
TLC on silica gel (the purified products were identified by
m.p. and by H NMR, and consistent with those of rele-
1
The compound 4 is prepared in three steps successfully,
according to the published procedure. It is a new ferroce-
nylketimine and characterized as follows: Orange crystals,
yield 55%, m.p. 99–101 ꢁC; IR (KBr): mmax 3094, 2862,
1634, 1102, 1042, 1002 cmꢀ1; 1H NMR (400 MHz. CDCl3):
d 8.33 (s, 1H), 7.39 (d, J = 5.2 Hz, 1H), 7.29 (d, J = 3.6 Hz,
1H), 7.06 (t, J = 3.6, 5.2 Hz, 1H), 4.50 (s, 2H), 4.19 (d,
J = 1.6 Hz, 2H), 4.16 (s, 5H), 4.14 (t, J = 1.6, 3.6 Hz,
2H) ppm; 13C NMR (400 MHz, CDCl3): d 59.2 (CH2),
67.9 (5CH), 68.5 (2CH), 68.6 (2CH), 85.8 (C), 127.3
(CH), 128.8 (CH), 130.3 (CH), 142.7 (C), 154.0 (CH)
ppm; Anal. Calcd. for C16H15FeNS: C, 62.15; H, 4.89; N,
4.53. Found: C, 62.14; H, 4.55; N, 4.80%; HRMS (ESI)
m/z 309.0261 (calcd for C16H15FeNS, m/z 309.0275).
vant literatures).
4.5. Structure determination for 4 and 6
Crystals of 4 and 6 were obtained by recrystallization
from CH2Cl2–petroleum ether solution at r.t., respectively.
A single crystal suitable for X-ray analysis was mounted on
a glass fiber. All measurements were made on a Rigaku-IV
imaging plate area detector with graphite monochromated
˚
Mo Ka radiation (k=0.71073 A). The data were corrected
for Lorentz and polarization factors. The structure was
solved by direct methods [14] and expanded using Fourier
techniques and refined by full-matrix least-squares meth-
ods. The non-hydrogen atoms were refined anisotropically,
and the hydrogen atoms were included but not refined. All
calculations were performed using the TEXSAN [15] crystal-
lographic software package of Molecular Structure
corporation.
4.3. Preparation of the compound 6
A solution of 0.5 mmol lithium tetrachloropalladate (II)
and 0.5 mmol of 4 in 18 mL of methanol was stirred for
about 20 h and then filtered, and the brown-red solid 5
was obtained. The solid was washed many times with meth-
anol and then was treated with PPh3 (0.025 mmol) in
CH2Cl2 at room temperature for 20 min and then filtered.
The filtrate was concentrated in vacuo and the residue
was recrystallized from CH2Cl2–petroleum ether (60–
90 ꢁC) (1:1, v/v), to give the compound 6, 76% overall
yield. It is characterized as follows: Red crystal, m.p.
187–190 ꢁC; IR (KBr): mmax 3081, 1625, 1097, 1024, 740,
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 274548. Copies of this information
may be obtained free of charge from The Director, 12 Un-
ion Road, Cambridge, CB2 1EZ, UK (fax: +44 1223
336033, or e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
688 cmꢀ1
;
1H NMR (400 MHz, CDCl3): d 8.30 (d,
J = 10.8 Hz, 1H), 7.69 (d, J = 3.3 Hz, 1H), 7.57 (d,
J = 4.9 Hz, 1H), 7.15 (t, J = 4.2 Hz, 1H), 7.38 (t,
J = 7.0 Hz, 3H), 7.64 (2d, J = 7.4 Hz, 6H), 7.33–7.29 (m,
6H), 4.85 (d, J = 12.4 Hz, CH2–H), 3.97 (d, J = 12.4 Hz,
CH2–H), 4.36–3.32 (m, 8H) ppm; 13C NMR (400 MHz,
CDCl3): d 60.1 (CH2), 66.2 (CH), 66.6 (CH), 66.0 (CH),
67.4 (C), 69.1 (CH), 69.3 (CH), 72.0 (CH), 74.5 (CH),
73.0 (CH), 83.0 (C), 126.9 (CH), 127.1 (3CH), 127.8
(3CH), 130.2 (C, 3CH), 130.9 (C), 131.5 (C), 132.2 (CH),
134.8 (3CH), 134.9 (3CH), 136.5 (CH), 138.2 (C), 155.0
(CH) ppm; Anal. Calcd. for C34H29ClFeNPPdS: C,
57.33; H, 4.10; N, 1.97. Found: C, 57.42; H, 4.09; N,
1.90%; HRMS calcd for C34H29FeNPPdS (ESI+)
676.0143, Found: 676.0170; calcd for Cl (ESIꢀ) 34.9689,
Found: 34.9690.
Acknowledgements
We are grateful to the China National Science Founda-
tion (20472074), the Natural Science Foundation of Henan
Province (0411020200) and the Specialized Research Fund
for the Doctoral Program of Higher Education (SRFDP)
(20040459008) for their financial support for this work.
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