Synthesis, characterization and crystal structures of a novel 1,1′-bisferrocenylimine and its monocyclopalladated derivative

Article abstract of DOI:10.1016/j.inoche.2006.02.008

The synthesis and characterization of a new 1,1′-bisferrocenylimine [{(η⁵-C₅H₄)-CH{double bond, long}NCy}₂Fe] 4 and its monocyclopalladated derivative 6 are reported. The compound 6 was found to be [PdCl{[(η⁵-C₅H₄)-CHO]Fe[(η ⁵-C₅H₃)-CH{double bond, long}NCy]}(PCy₃)], which was obtained from the reaction of 4 with two mole equivalents of Li₂PdCl₄/NaOAc in methanol at room temperature and subsequent treatment of the resulting product with tricyclohexylphosphine (PCy₃). The X-ray single-crystal structures of the two new compounds are also described.

Full text of DOI:10.1016/j.inoche.2006.02.008

Inorganic Chemistry Communications 9 (2006) 456–459
www.elsevier.com/locate/inoche
Synthesis, characterization and crystal structures of a novel
1,10-bisferrocenylimine and its monocyclopalladated derivative
*
Chen Xu, Jun-Fang Gong, Yan-Hui Zhang, Yu Zhu, Chen-Xia Du, Yang-Jie Wu
Department of Chemistry, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Key Laboratory of Applied Chemistry of Henan Universities,
Zhengzhou University, Daxue Road 75, Zhengzhou, Henan Province 450052, PR China
Received 10 January 2006; accepted 10 February 2006
Available online 20 March 2006
Abstract
The synthesis and characterization of a new 1,10-bisferrocenylimine [{(g5-C5H4)-CH@NCy}2Fe] 4 and its monocyclopalladated deriv-
ative 6 are reported. The compound 6 was found to be [PdCl{[(g5-C5H4)-CHO]Fe[(g5-C5H3)-CH@NCy]}(PCy3)], which was obtained
from the reaction of 4 with two mole equivalents of Li2PdCl4/NaOAc in methanol at room temperature and subsequent treatment of the
resulting product with tricyclohexylphosphine (PCy3). The X-ray single-crystal structures of the two new compounds are also described.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: 1,10-Bisferrocenylimine; Cyclopalladation; Tricyclohexylphosphine; Crystal structures; Hydrogen bonds
Cyclopalladated compounds containing a PdAC bond
intramolecularly stabilized by one donor atom were first
reported in the middle 1960s [1]. Forty years later, the chem-
istry of these compounds has developed into one of the most
fruitful fields in organometallic chemistry [2], and still
attracts a great deal of chemical interest. In the palladium-
catalyzed carbon–carbon bond and carbon–heteroatom
bond forming reactions, palladacycles have shown enor-
mous superiority in many respects due to their ready prepa-
ration, facile modification, high activity and comparative
stability [3]. For instance Bedford et al. recently demon-
strated that isolated or in situ formed trialkylphosphine
adducts of dimeric nitrogen-containing palladacycles 1
(Fig. 1, L@PCy3, PtBu3, e.g.) efficiently promoted the Suzuki
coupling of both activated and deactivated aryl chlorides [4].
We have also found that tricyclohexylphosphine (PCy3)
adducts of dimeric cyclopalladated ferrocenylimines 2–3
are very effective for Suzuki coupling of aryl chlorides with
phenylboronic acid [5]. These results are particularly inter-
esting since aryl chlorides are cheaper and more readily
available than the corresponding bromides and iodides.
On the basis of these findings, we synthesized a novel
1,10-bisferrocenylimine [{(g5-C5H4)-CH@NCy}2Fe] 4 and
studied its cyclopalladation with the aim of getting the
corresponding biscyclopalladated tricyclohexylphosphine
adducts. However, the double cyclopalladation of 4 with
two mole equivalents of Li2PdCl4/NaOAc followed by treat-
ment with tricyclohexylphosphine afforded [PdCl{[(g5-
C5H4)-CHO]Fe[(g5-C5H3)-CH@NCy]}(PCy3)] 6, which
arised from the monocyclopalladation of 4 and the hydroly-
sis of one imino group. Herein we report the synthesis, char-
acterization and crystal structures of 4 and 6 (Scheme 1).
The preparation of 4, 5 and 6 are as follows: To a solu-
tion of 1,10-diformylferrocene [6] in dry toluene was added
cyclohexylamine under nitrogen. Then the mixture was
refluxed with stirring in the presence of freshly activated
neutral Al2O3 for about 3 h until the carbonyl absorption
of 1,10-diformylferrocene disappeared according to IR
spectrum. After filtration and evaporation of the solvents,
the crude product was recrystallized from dichlorometh-
ane–petroleum ether giving brown-red crystals of 1,10-bisf-
errocenylimine 4 (yield: 93%) [7]. The following double
cyclopalladation reaction was carried out with 4 and two
mole equivalents of Li2PdCl4 and NaOAc in methanol at
*
Corresponding author. Tel./fax: +86 371 67766667.
E-mail address: wyj@zzu.edu.cn (Y.-J. Wu).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.02.008

C. Xu et al. / Inorganic Chemistry Communications 9 (2006) 456–459
457
H
(mC(O)H = 1684 cmꢀ1 for 1,10-diformylferrocene). The IR
spectrum of the reaction mixture of 5 with PCy3 was also
determined and three bands at 1693, 1637 and 1612 cmꢀ1
were observed. This suggested that the C(O)H group was
CH3
Y
N
N
CH3
Fe
Pd Cl
Pd Cl
PCy3
Fe
X
Pd
L
PCy3
1
formed during the reaction. The H NMR spectrum of 6
3
1
2
also confirms the existence of C(O)H group by the singlet
at d 9.91 ppm. The signals of two Cp rings appear at d
4.74, 4.61, 4.42 and 4.32 ppm, respectively, which are inte-
grated for seven protons. The above results indicate that 6
is a monocyclopalladated complex. The expected biscyclo-
palladated tricyclohexylphosphine adducts were not iso-
lated from the reaction of 5 with PCy3 .
Y = NR2, =NR L = PR3
X = TFA, OTf, Cl, etc.
Fig. 1. Examples of adducts resulting from the corresponding dimeric
palladacycles with phophines.
room temperature for 24 h. The formed red solids of 5
(yield: 83%) were collected by filtration and washed several
times with methanol. Without further purification, com-
plex 5 was treated with two equivalents of PCy3 in dry
CH2Cl2 at room temperature for 0.5 h. The product was
separated by passing through a short silica gel column with
CH2Cl2 as eluent, which the first band afforded complex 6
(yield: 42%) [8] after the evaporation of the solvent.
The IR spectrum of 1,10-diferrocenylimine 4 show mC@N
at 1639 cmꢀ1, which is similar to that of N-(cyclo-
hexyl)ferrocylideneamine [9], but shifted to higher energy
in comparison with those of ferrocenylarylimines [10].
Compared with 4, the C@N absorption (1622 cmꢀ1) of
compound 5 shifts to lower energy, indicating the coordi-
nation of nitrogen to palladium. Compound 5 was
tentatively assigned to be polymeric or dimeric biscyclopal-
ladated derivatives since no other bands (at about 1639 or
1679 cmꢀ1) were detected in the IR spectrum [11]. For
complex 6, two bands at 1612 and 1679 cmꢀ1 are detected
in the IR spectrum and these absorptions are ascribed to
the stretching of the C@N and C(O)H groups
The X-ray crystal structures [12] of compounds 4 and 6
were determined and perspective views of their molecular
structures are shown in Figs. 2 and 3, respectively. The
two Cp rings in 4 are parallel with a dihedral angle of 0ꢁ,
and the dihedral angle between two Cp rings in 6 is 3.3ꢁ.
Owing to the coordination of nitrogen to palladium, the
˚
C@N bond distance in 6 (1.275(7) A) is longer than that
˚
in 4 (1.264(3) A). The angle between the C5AC6 and
C5AAC6A is 180ꢁ for 4 and the corresponding angle
between the C1AC18 and C10AC11 is 75.3ꢁ for 6. Fig. 3
shows clearly that compound 6 is a monocyclopalladated
complex. The palladium adopts a distorted square planar
configuration defined by the N1, C6, P1, Cl1 atoms and
the angels around the Pd1 center are in the range of
81.05–96.52ꢁ. The coordinated PCy3 is trans to the imino
nitrogen with a PAPdAN angle of 169.71(12)ꢁ. The bicyclic
system formed by the palladacycle and the C5H3 moiety is
approximately coplanar (dihedral angle 7.7ꢁ). The
˚
˚
Pd1AN1 (2.173(4) A) and PdAP (2.2815(13) A) bond
˚
lengths are similar to those of complex 2 (2.170(5) A and
H
C
H
CHO
C
N
N
PCy3
N
Pd Cl
PCy3
Al2O3
Li2PdCl4/NaOAc
MeOH, r.t.
Fe
H2N
+
Fe
5
Fe
CH2Cl2, r.t.
H
C
toluene
reflux
CHO
OHC
4
6
Scheme 1.
˚
Fig. 2. Molecular structure of complex 4. Selected bond lengths (A) and angles (ꢁ): N(1)AC(6) 1.264(3), N(1)AC(7) 1.466(2), C(5)AC(6) 1.458(3),
C(6)AN(1)AC(7) 117.64(18), N(1)AC(6)AC(5) 123.72(19), C(4)AC(5)AC(6) 127.74(19).

458
C. Xu et al. / Inorganic Chemistry Communications 9 (2006) 456–459
˚
Fig. 3. Molecular structure of complex 6. Selected bond lengths (A) and angles (ꢁ): Pd(1)AC(6) 2.006(4), Pd(1)AN(1) 2.173(4), Pd(1)AP(1) 2.2815(13),
Pd(1)ACl(1) 2.3814(13), C(11)AN(1) 1.275(7), C(12)AN(1) 1.479(7) and C(6)APd(1)AN(1) 81.05(18), C(6)APd(1)AP(1) 96.52(14), N(1)APd(1)AP(1)
169.71(12), C(6)APd(1)ACl(1) 167.97(13), N(1)APd(1)ACl(1) 91.49(13), P(1)APd(1)ACl(1) 92.44(4), C(11)AN(1)AC(12) 122.3(5).
˚
˚
2.2833(16) A) [5], while they are longer than those of the
N1FꢁꢁꢁH1AJ = 2.612 A,N1AJ ꢁꢁꢁH1EAC1E = N1FꢁꢁꢁH1AJA
related Ph3P adducts [10c,13] [2.135(3), 2.153(6), 2.130(6),
2.114(4) A and 2.2569(9), 2.236(2), 2.247(2), 2.2356(13)
A] possibly due to the steric bulk of the PCy3 ligand.
In the crystal of 4 there exist intermolecular hydrogen
bond between the nitrogen atom of imino group and the
adjacent CAH group of Cp ring (N1AJꢁ ꢁ ꢁH1E =
C1AJ = 154.8ꢁ), which are attributed to construct the
2 D layer structure of complex 4. In complex 6, chlorine
atom not only forms hydrogen bond with the adjacent
CAH group of Cp ring, but also forms hydrogen bond
with the adjacent CAH group of tricyclohexylphosphine
˚
˚
˚
(Cl1Cꢁ ꢁ ꢁH5AA = Cl1Fꢁ ꢁ ꢁH5AB = 2.774A,Cl1Cꢁ ꢁ ꢁH5AA-
Fig. 4. The hydrogen bonds in complex 6.

C. Xu et al. / Inorganic Chemistry Communications 9 (2006) 456–459
459
[6] G.G.A. Balavoine, G. Doisneau, T.F. Khan, J. Organomet. Chem.
412 (1991) 381–382.
[7] Characterization data for 4: m.p. = 117–118 ꢁC. Found (calcd.) % for
C5A = Cl1Fꢁ ꢁ ꢁH5ABAC5B = 148.9ꢁ
and
Cl1Cꢁ ꢁ ꢁ
˚
H22K = Cl1Fꢁ ꢁ ꢁH22E = 2.794 A, Cl1Cꢁ ꢁ ꢁH22KAC22F =
Cl1Fꢁ ꢁ ꢁH22EAC22C = 168.5ꢁ) (Fig. 4), which are attrib-
uted to construct the 3D network structure of complex 6.
In conclusion, we have synthesized a novel 1,10-bisferr-
ocenylimine [{(g5-C5H4)-CH@NCy}2Fe] 4 and obtained
its monocyclopalladated complex [PdCl{[(g5-C5H4)-
CHO]Fe[(g5-C5H3)CH@NCy]}(PCy3)] 6. Applications
involving 6 in palladium-catalyzed reactions are currently
under investigation in our laboratory.
C
24H32FeN2: C, 71.34 (71.29); H, 7.94 (7.98); N 6.90 (6.93). IR (KBr,
cmꢀ1): 2923s, 2850m, 1639s (C@N), 1446m, 1385m, 1328m, 1245m,
1076m, 1047m, 886w, 824s; 1H NMR (400 MHz, CDCl3, ppm): 8.10
(s, 2H, ACH@NA), 4.61 (s, 4H, C5H4), 4.33 (s, 4H, C5H4), 3.03 (m,
2H, NACHC5H10), 1.82 (m, 4H, AC6H11), 1.70 (m, 6H, AC6H11),
1.55 (m, 4H, AC6H11), 1.31 (m, 6H, AC6H11). ESI-MS (M + H)+m/z:
405.
[8] Characterization data for 6: m.p. 250 ꢁC. Found (calcd.) % for
C
36H53ClFeNOPPd: C, 58.13 (58.08); H, 7.15 (7.18); N 1.83 (1.88). IR
(KBr, cmꢀ1): 2927s, 2851s, 1679m (CHO), 1612m (C@N), 1448m,
1369w, 1243w, 1063w, 822w, 740w. 31P{1H} NMR (162 MHz,
CDCl3, ppm): d 45.25. 1H NMR (400 MHz, CDCl3, ppm): 9.91 (s,
1H, ACHO), 8.00 (s, 1H, ACH@NA), 4.74 (s, 1H, C5H3), 4.61 (m,
4H, C5H4), 4.42 (s, 1H, C5H3), 4.32 (m, 2H, C5H3+NACHC5H10),
1.24–2.53 (m, 43H, PCy3 + AC6H11). ESI-MS (MꢀCl)+ m/z: 708.
[9] V. Kovacˇ, A. Visˇnjevac, V. Rapic´, B.K. Prodic´, J. Mol. Struct. 687
(2004) 107–110.
Acknowledgements
We are grateful to the National Natural Science Foun-
dation of China (Project 20472074) for financial support
of this work.
[10] (a) Y.J. Wu, Y.H. Liu, K.L. Ding, H.Z. Yuan, X.A. Mao, J.
Organomet. Chem. 505 (1995) 37–42;
Appendix A. Supplementary data
(b) J. Albert, M. Gome, J. Granell, J. Sales, X. Solans, Organomet-
allics 9 (1990) 1405–1413;
(c) R. Bosque, C. Lo´pez, J. Sales, X. Solans, J. Organomet. Chem.
483 (1994) 61–71.
Crystallographic data for the structures reported in this
article have been deposited with the Cambridge Crystallo-
graphic Data Center. CCDC No. 284579, 4; 287209, 6.
Copies of these information can be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk). Sup-
plementary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2006.02.008.
[11] Y.J. Wu, Y.H. Liu, L. Yang, Q.X. Zhu, Polyhedron 16 (1997) 335–
339.
[12] Crystals of 4 and 6 were obtained by recrystallization from dichlo-
romethane–petroleum ether at r.t.. Crystal data for 4: C24H32FeN2,
0.20 · 0.20 · 0.18 mm3, Monoclinic, C2/c, a = 20.795(4) A,
˚
˚
˚
b = 11.117(2) A, c = 9.5532(19) A, a = c = 90ꢁ, b = 99.92(3)ꢁ,
3
V = 2175.5(8) A , Z = 4, DCalc = 1.235 Mg/m3, l = 0.703 mmꢀ1
,
˚
F(000) = 864.
Crystal
data
for
6:
C36H53ClFeNOPPd,
0.20 · 0.18 · 0.16 mm3, Monoclinic, P2(1)/c, a = 10.491(2) A,
˚
˚
˚
References
b = 14.116(3) A, c = 24.020(5) A, a = b = 90ꢁ, c = 101.58(3)ꢁ, V =
3484.6(12) A , Z = 4, DCalc = 1.417 Mg/m3, l = 1.083 mmꢀ1
,
3
˚
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˚
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