Stereoselective cyclopalladation of [{(N-methyl-N-aryl)amino}methyl]ferrocenes: Crystal structure of σ-Pd[ClPPh3(η5-C5 H5)Fe(η5-C5H3CH2 N(CH3)C6H4OCH3-4)] · H2O

Article abstract of DOI:10.1016/j.inoche.2006.03.024

Stereoselective cyclopalladation of [(N-methyl-N-aryl)amino]methylferrocenes 1a-f (aryl = 4-CH₃OC₆H₄(a), 4-CH₃C₆H₄(b), C₆H₅(c), 4-ClC₆H₄(d), 3-ClC₆H₄(e), 3-O₂NC₆H₄(f)) with sodium palladium tetrachloride and followed by treatment with triphenylphosphine resulted in the cyclopalladated complexes 3a-f (aryl = same as before) in the form of raceme. The structure of 3a was determined by X-ray single crystal diffraction. Complex 3a crystallizes in triclinic, space group P-1 with a = 10.6685(14), b = 10.7412(14), c = 16.795(2) ?, α = 71.879(2), β = 85.798(2), γ = 64.523(2)°. The possible mechanism for the formation of 3 was discussed.

Full text of DOI:10.1016/j.inoche.2006.03.024

Inorganic Chemistry Communications 9 (2006) 658–661
www.elsevier.com/locate/inoche
Stereoselective cyclopalladation of
[{(N-methyl-N-aryl)amino}methyl]ferrocenes: Crystal structure of
r-Pd[ClPPh3(g5-C5H5)Fe(g5-C5H3CH2N(CH3)C6H4OCH3-4)] Æ H2O
a,
a
a
a
Hong-Xing Wang *, Ying-Jie Li , Ren-Qing Gao , Hong-Fei Wu ,
a
b
Feng-Ying Geng , Rong Jin
a
Department of Chemistry, College of Sciences, Tianjin University, No. 92, Weijin Road, Nankai District, Tianjin 300072, PR China
b
Department of Ultrasound, The First Central Hospital of Tianjin, Tianjin 300192, PR China
Received 26 January 2006; accepted 23 March 2006
Available online 3 April 2006
Abstract
Stereoselective cyclopalladation of [(N-methyl-N-aryl)amino]methylferrocenes 1a–f (aryl = 4-CH3OC6H4(a), 4-CH3C6H4(b), C6H5(c),
4-ClC6H4(d), 3-ClC6H4(e), 3-O2NC6H4(f)) with sodium palladium tetrachloride and followed by treatment with triphenylphosphine
resulted in the cyclopalladated complexes 3a–f (aryl = same as before) in the form of raceme. The structure of 3a was determined by
X-ray single crystal diffraction. Complex 3a crystallizes in triclinic, space group P-1 with a = 10.6685(14), b = 10.7412(14),
˚
c = 16.795(2) A, a = 71.879(2), b = 85.798(2), c = 64.523(2)ꢀ. The possible mechanism for the formation of 3 was discussed.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Ferrocenylamines; Cyclopalladation; Stereoselectivity; Crystal
Cyclopalladation reaction [1] represents one of most
powerful methods for the activation of Csp2–H bonds and
ortho-functionalization in aromatic compounds. The appli-
cation of cyclopalladated compounds especially those bear-
ing nitrogen-chelating atom have been widely used in
organic synthesis such as Heck reaction [2], Suzuki cou-
pling reaction [3], etc. As far as we know, although a lot
of cyclopalladated ferrocenylimines have been described
[1,4], the cyclopalladations of tertiary ferrocenylamines
are still rare mostly because of the lack of suitable sub-
strates. Recently, we reported the synthesis of [{(N-
methyl-N-aryl (or benzyl))amino}methyl]ferrocenes by (i)
methylation of imines with methyl iodide to form iminum
salts and followed by reduction of latter with sodium boro-
hydride [5a] or (ii) direct reductive methylation of ferroce-
nylaldimines (or secondary ferrocenylamines) [5b], [c] in
one step with sodium cyanoborohydride, aqueous formal-
dehyde in the presence of glacial acid. And we observed
that cycloplatination of aliphatic amines, i.e. [{(N-
methyl-N-benzyl)amino}methyl]ferrocenes resulted in
predominately cycloplatinated compounds [6]. These cyclo-
platinated complexes mainly consist of raceme (RNRP and
SNSP). In order to confirm further this stereoselectivity, in
this communication, we wish to report here the first exam-
ple of cyclopalladation of tertiary aromatic ferrocenylam-
ines, i.e. [{(N-methyl-N-aryl)amino}methyl]ferrocenes
1a–f (Scheme 1) and elucidate the relationship between
structures of substrates and their selectivities.
The reactions of 1a–f and sodium palladium tetrachlo-
ride were carried out in methanol at room temperature in
the presence of sodium acetate (Scheme 1). After the reac-
tions completed, triphenylphosphine was added to split
di-l-chloro adducts. Complexes 3a–f were obtained after
*
Corresponding author. Tel.: +86 22 27892355; fax: +86 22 27403475.
E-mail address: Hongxing_wang@hotmail.com (H.-X. Wang).
1387-7003/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.03.024

H.-X. Wang et al. / Inorganic Chemistry Communications 9 (2006) 658–661
659
8
9
6
7
N
N
Cl Pd Cl
L
N
10
5
1
Pd Cl 12
PPh3
11
R
R
R
2
4
Na2PdCl4
(1) NaOAc
(2)PPh3
Fe
1
Fe
2
Fe3
Methanol
rac-3
L =FcCH2N(CH3)C6H4R
Scheme 1. R = 4-MeO(a), 4-Me(b), H(c), 4-Cl(d), 3-Cl(e), 3-NO2(f).
1
column chromatography (silica gel, ethylacetate/hex-
ane = 1:1, v/v). They are very stable in air, and easily sol-
uble in most organic solvents, but poorly soluble in
petroleum ether.
(Cp) [9]. In H NMR spectra of 3a–f, a singlet around d
3.83 ppm corresponds to g-C5H5, two doublet around d
3.75 and 4.20 ppm are assigned to C3-H, C5-H, respec-
tively, a triplet around d 4.12 ppm is attributed to C4-H.
In addition, a typical AB coupling system (around d
3.60 ppm) for C6-H is also observed due to the formation
of a five membered palladocycle.
Direct cyclopalladation of 1a–f with sodium palladium
tetrachloride lead to the low yields of 3a–f (615%), and this
phenomenon is consistence with the literatures reported
[4a,7]. An attempt to prepare 3a–f by transpalladation of
their corresponding ortho-mercurated 1a–f gave the similar
results. Though the yields of 3a–f are low, it seems that
they are related to the characteristics of substituents in sub-
strates. For example, cyclopalladation of 1a gives normally
3a a higher yield (15%). However, the 1d–f provide com-
parative lower yields of 3d–f (<12%).
The N atoms in 1a–f connect three different groups, 1a–f
are undoubtedly chiral amines. However, the determined
optical rotations of 3a–f are 0 under the given conditions
(k = 5893 A, CH2Cl2, 293 K), implying that 3a–f are prob-
ably composed of raceme. The possible mechanism for
their formation is illustrated in Scheme 2.
Coordination of palladium with N atoms of two isomers
1a, b will generate intermediates 2a, b. Our previous results
demonstrated that the orbital occupied by lone-pair elec-
trons in N atom of 1a–f lies above the substituted Cp ring
and points preferably to one of adjacent C–H bonds [10],
˚
The structures of 3a–f were identified by elemental anal-
1
yses, IR and H NMR [8]. The IR spectra of 3a–f display
two absorptions around m 1100 and 1000 cmÀ1, indicating
that they all have an unsubstituted cyclopentadienyl ring
Ar
N
N
Ar
Na2PdCl4
Na2PdCl4
Cl
Ar
L
Pd
Cl
Cl
N
N
2
2
Pd
6
1
1
Ar
6
Cl
Rotate around C1-C6,
then attack at C5
L
Rotate around C1-C6,
then attack at C2
5
5
(RNSp)
(SNRp)
NaOAc
PPh3
NaOAc
attack at C2
attack at C5
PPh3
Cl
Ph3P
Pd
6
1
N
2
5
N
Ar
Pd
Ar
6
1
Cl
Ph3P
(RNRp)
L =FcCH2N(CH3)C6H4R
(SNSp)
Scheme 2. The possible mechanism for the formation of 3.

660
H.-X. Wang et al. / Inorganic Chemistry Communications 9 (2006) 658–661
one can image that after coordination the palladium in 2a,
b will direct preferably to one of the C–H bonds as men-
tioned above. And moreover, the N–Pd moiety in 2a, b
could also rotate in principle around the axis of C1–C6 r
bond. Thus, activation of one of its adjacent C–H bonds
will produce two racemes 3a, b and 3c, d. Mostly impor-
tant, the pair 3a, b are the diastereomers of another pair
3c, d which can be easily separated by column chromatog-
raphy. Indeed, we have isolated a trace product which is
not sufficient to identify. Based on the optical rotations
of 3a–f and in connection with the configuration of 3a
(RNRP) [11] (Fig. 1), it is believed that 3a–f are composed
of the raceme 3a, b in stead of 3c, d and this result is con-
sistence with our previous observation [6]. The preferable
activation of C2-H or C5-H is probably because that the
free rotation of N–Pd moiety in 2 a, b around the axis of
C1–C6 bond (lead to 3c, d) is retarded due to the steric hin-
drance between palladium and hydrogen in Cp.
pentagonal ring of the ferrocenyl fragment and a five-mem-
bered palladocycle with an envelope-like conformation. In
addition, P1 adopts a trans configuration to N1 with a bond
˚
angle N1-Pd1-P1 167.85ꢀ. The N–Pd bond length (2.228 A)
is longer than those of cyclopalladated (N-methyl-N-tert-
˚
butyl)benzylamine (2.097(3) A) [13] and N,N-dimethyl-ami-
˚
nomethylferrocene (2.170(10) A) [14]. The average C–C
˚
bond length of Cp rings (1.419 A) is similar to the values
reported for the other ferrocene derivatives [15]. The Fe-
˚
C(ring) bond distances range from 2.024 to 2.080 A. The
two pentagonal rings of the ferrocenyl fragment are planar
and nearly parallel (interplanar angle 3.3ꢀ).
Supplementary data
Crystallographic data (excluding structure factors) for
the structure of 3a in this paper has been deposited with
the Cambridge Crystallographic Data Centre as supple-
mentary publication numbers CCDC 284688. Copies of
the data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax:
144-(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk].
The structure of 3a was also determined by X-ray single
crystal diffraction. Crystallographic studies [12] demon-
strates that 3a consists of discrete molecule
r-Pd[ClPPh3(g5-C5H5)Fe(g5-C5H3CH2N(CH3)C6H4OCH3-
4)] Æ H2O separated by van der Waals contact in which pal-
ladium is in a slight distorted square-planar environment,
bonded to N1, Cl1, C10 and P1. The deviations of each atom
from the mean plane are Pd1 0.0607, N1-0.1424, Cl1 0.0889,
Acknowledgements
This work was supported by the Natural Scientific
Foundation of Tianjin City, PR China (Project No.
033609011) and the Opening Fund from Ministry of Sci-
ence and Technology, PR China.
˚
C10 0.1240 and P1 À 0.1313 A, respectively. Complex 3a
contains two fused five-membered rings, i.e. the substituted
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Pd1-P1 2.2361(10), Pd1-Cl1 2.3770(12), N1-C13, 1.466(5), O1-C17
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PPd: C 58.21, H 4.34, N 1.89; Found C 58.10, H 4.32, N 1.88. 3e, red
solid, yield 12%, m.p.134–136 ꢀC; 1H NMR (CDCl3, 400 MHz) d:
2.16 (s, 3H, N-CH3), 3.62 (m, 2H, C6–H), 3.75 (d, 1H, C3–H), 3.80 (s,
5H, g-C5H5), 4.11 (m, 1H, C4-H), 4.21 (d, 1H, C5-H), 6.59–7.71 (m,
19H, Ar-H); IR(KBr) m: 3055, 2926, 1597, 1482, 1435, 1097, 999, 745,
692 cmÀ1; Anal. Calcd. for C36H32Cl2FeNPPd: C 58.21, H 4.34, N
1.89; Found C 57.91, H 4.28, N 1.88. 3f, red solid, yield 7%, m.p. 174–
176 ꢀC; 1H NMR (CDCl3, 400 MHz) d: 2.18 (s, 3H, N-CH3), 3.64 (m,
2H, C6-H), 3.77 (d, 1H, C3-H), 3.82 (s, 5H, g-C5H5), 4.15 (m, 1H,
C4-H), 4.27 (d, 1H, C5-H), 6.82–7.89 (m, 19H, Ar-H); IR(KBr) m:
3054, 295, 1595, 1533, 1498, 1435, 1342 1099, 998, 692 cmÀ1; Anal.
Calcd. for C36H32ClFeN2O2PPd: C 57.40, H 4.28, N 3.72; Found C
57.12, H 4.25, N 3.70.
[8] Preparation of 3a–f: To the stirred solution of 1 (2 mmol) [5b] and
sodium acetate (2 mmol) in the mixture of methanol (20 ml) and
dichloromethane (5 ml), was added dropwise a solution of equivalent
sodium palladium tetrachloride in methanol. TLC monitored the
reactions until palladium was consumed up. Without isolation, a
solution of 1.5 equivalents triphenylphosphine in methanol was
added, 1 h later, the mixtures were filtered and the solvent was
removed. The residues were purified by column chromatography
(silica gel, ethyl acetate/hexane = 1:1, v/v), the second band of eluant
was collected, solvent was removed to afford 3 as red-purple powders.
3a, red solid, yield 15%, melting point 156–158 ꢀC; 1H NMR (CDCl3,
400 MHz) d: 2.16 (s, 3H, N-CH3), 2.79 (s, 3H, OCH3), 3.59 (m, 2 H,
C6-H), 3.78 (d, 1H, C3-H), 3.80 (s, 5H, g-C5H5), 4.07 (m, 1H, C4-H),
4.15 (d, 1H, C5-H), 6.87–6.90 (q, 4H, C8-H, C9-H, C11-H, C12-H),
7.36–7.77 (m, 15H, PPh3); IR(KBr) m: 3055, 2911, 1506, 1435, 1248,
1095, 999, 827, 741, 693 cmÀ1; Anal. Calcd. for C37H35ClFeNOPPd:
C 60.19, H 4.78, N 1.90; Found C 59.89, H 4.75, N 1.89. 3b, red solid,
yield 14%, melting point 156–158 ꢀC; 1H NMR (CDCl3, 400 MHz) d:
2.08 (s, 3H, Ar-CH3), 2.24 (s, 3H, N-CH3), 3.55 (m, 2H, C6-H), 3.76
(d, 1H, C3-H), 3.81 (s, 5H, g-C5H5), 4.10 (m, 1H, C4-H), 4.14 (d, 1H,
C5-H), 6.88–6.91 (q, 4H, C8-H, C9-H, C11-H, C12-H), 7.36-7.75 (m,
15H, PPh3); IR(KBr) m: 3059, 2927, 1509, 1434, 1099, 998, 819,
691 cmÀ1; Anal. Calcd. for C37H35ClFeNPPd: C 61.52, H 4.88, N
1.94; Found C 61.23, H 4.86, N 1.94. 3c, red solid, yield 14%, melting
point 130–132 ꢀC; 1H NMR (CDCl3, 400 MHz) d: 2.26 (s, 3H, N-
CH3), 3.58 (m, 2H, C6-H), 3.75 (d, 1H, C3-H), 3.83 (s, 5H, g-C5H5),
4.12 (m, 1H, C4-H), 4.20 (d, 1H, C5-H), 6.89–7.72 (m, 20H, Ar-H);
IR(KBr) m: 3055, 2924, 1595, 1498, 1436, 1098, 999 cmÀ1; Anal.
Calcd. for C36H33ClFeNPPd: C 61.04, H 4.70, N 1.98; Found C
60.79, H 4.66, N 1.97. 3d, red solid, yield 12%, melting point 138–
140 ꢀC; 1H NMR (CDCl3, 400 MHz) d: 2.17 (s, 3H, N-CH3), 3.62 (m,
2H, C6-H), 3.76 (d, 1H, C3-H), 3.83 (s, 5H, g-C5H5), 4.13 (m, 1H,
C4-H), 4.22 (d, 1H, C5-H), 6.91–7.07 (q, 4H, C8-H, C9-H, C11-H,
C12-H), 7.36-7.69 (m, 15H, PPh3); IR(KBr) m: 3055, 2925, 1595, 1499,
1435, 1096, 998, 810, 745, 692 cmÀ1; Anal. Calcd. for C36H32Cl2FeN-
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[12] Intensity data for single crystal of complex 3a were collected on a
Bruker SMART CCD diffractometer with graphite monochromatized
˚
Mo Ka radiation (k = 0.71073 A) at 293 K. The structure was solved
by direct methods and refined by full-matrix least-squares techniques
with anisotropic thermal factors for all non-hydrogen atoms. All
calculations were performed using the SHELX suite of program [16].
Crystal
data:
crystal
dimensions:
0.32 · 0.20 · 0.14 mm3,
˚
FW = 756.35, triclinic, space group P-1, a = 10.6685(14) A,
b = 10.7412(14) A, c = 16.795(2) A, a = 71.879(2)ꢀ, b = 85.798(2)ꢀ,
c = 64.523(2)ꢀ,
˚
˚
3
Dc = 1.525 mg/m3,
˚
V = 1647.1(4) A ,
Z = 2,
F(000) = 772, R = 0.0441.
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