Synthesis, characterization and crystal structures of monocyclopalladated and biscyclopalladated 1,1′-bisferrocenylpyrimidine-monophosphine complexes

Article abstract of DOI:10.1016/j.ica.2010.08.046

A new 1,1′-bisferrocenylpyrimidine ligand [{(η⁵-C ₅H₄)-N₂C₄H-2CH₃} ₂Fe] 1 was conveniently prepared via the coupling reaction of 1,1′-dichloromercuriferrocene and 4,6-dimethyl-2-

Full text of DOI:10.1016/j.ica.2010.08.046

Inorganica Chimica Acta 365 (2011) 469–472
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Note
Synthesis, characterization and crystal structures of monocyclopalladated and
biscyclopalladated 1,10-bisferrocenylpyrimidine–monophosphine complexes
Chen Xu a, , Ya-Peng Zhang b, Zhi-Qiang Wang a, Ting Liang b, Wei-Jun Fu a, , Xin-Qi Hao b, Yan Xu b,
⇑
⇑
Bao-Ming Ji a
a College of Chemistry and Chemical Engineering, Luoyang Normal University, Longmen Road No. 71, Luoyang City, Henan Province 471022, PR China
b Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450052, PR China
a r t i c l e i n f o
a b s t r a c t
A new 1,10-bisferrocenylpyrimidine ligand [{( 5-C5H4)–N2C4H–2CH3}2Fe] 1 was conveniently prepared
g
Article history:
Received 9 March 2010
Received in revised form 18 July 2010
Accepted 23 August 2010
Available online 26 September 2010
via the coupling reaction of 1,10-dichloromercuriferrocene and 4,6-dimethyl-2-iodopyrimidine, and its
monophosphine–palladacycle complexes 2–3 were also readily obtained from the cyclopalladation reac-
tions and bridge-splitting reactions. These compounds have been characterized by 1H NMR, IR, ESI-MS,
and elemental analysis. The complex 2 was found to be a biscyclopalladated complex, while the complex
3 was a monocyclopalladated complex. Additionally, their detailed structures have been determined by
X-ray single-crystal diffraction. The most striking common feature of the structures of 2–3 is intermolec-
ular C–HꢀꢀꢀCl hydrogen bonds, which are attributed to construct the 1D chain structures.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Palladacycle
1,10-Bisferrocenylpyrimidine
Monophosphine ligand
Crystal structure
1. Introduction
palladacycles [14–17]. In view of these findings and our continuous
interest in the cyclopalladation of ferrocenylpyrimidine, we syn-
Palladacycles are one of the most developed and studied classes
of organopalladium derivatives, which are widely applied in cou-
pling reactions as effective catalysts precursors [1,2]. Usually, they
are prepared in high yields through C–H activation, and most of
them are thermally stable, not sensitive to air and moisture.
Among them, cyclopalladated complexes containing N-donor ferr-
ocenyl ligand have been studied extensively in the past two dec-
ades [3–7]. However, double cyclopalladation of disubstituted
ferrocene is scarce, only a few biscyclopalladated complexes have
been reported [8–10]. To our knowledge, there was only one report
concerning the crystal structure of biscyclopalladated 1,10-ferroce-
nyldiimine complex [11].
thesized a 1
new 1,10-di(4,6-dimethyl-2-pyrimidinyl)ferrocene
and its monophosphine-cyclopalladated complexes 2–3 (Scheme
2). Interestingly, 2 was a biscyclopalladated complex, while 3
was a monocyclopalladated complex.
2. Experimental
2.1. General procedures
Solvents were dried and freshly distilled prior to use. All other
chemicals were commercially available expect for 1,10-dichloro-
mercuriferrocene and 4,6-dimethyl-2-iodopyrimidine which were
prepared according to the published procedures [18,19]. IR spectra
were collected on a Bruker VECTOR22 spectrophotometer in KBr
pellets. 1H NMR spectra were recorded on a Bruker DPX-400 spec-
trometer in CDCl3 with TMS as an internal standard. Mass spectra
were measured on a LC-MSD-Trap-XCT instrument. Elemental anal-
yses were determined with a Carlo Erba 1160 Elemental Analyzer.
We have studied the double cyclopalladation of 1,10-ferrocenyl-
diimine [{(g
5-C5H4)–CH@NCy}2Fe] and found the corresponding
tricyclohexylphosphine adduct is a monocyclopalladated complex
(A, Scheme 1) [12]. Furthermore, we have recently studied the
cyclopalladation of 4,6-dimethyl-2-pyrimidinylferrocene. Some of
the obtained monophosphine-cyclopalladated complexes (B,
Scheme 1) have been successfully used in palladium-catalyzed
Buchwald–Hartwig amination [13]. These precatalysts combine
the stability induced by the presence of a palladacycle framework
with the high activity commonly associated with phosphine li-
gands, and were far more active than the corresponding dimeric
2.2. Synthesis of 1,10-di(4,6-dimethyl-2-pyrimidinyl)ferrocene (1)
In a flask equipped with reflux condenser and gas inlet 1,10-
dichloromercuriferrocene (1 mmol), 4,6-dimethyl-2-iodopyrimi-
dine (2.2 mmol), NaI (3 mmol) and PdP(Ph3)4 (0.05 mmol), 15 ml
DMF were placed under N2 atmosphere. The reaction mixture
⇑
Corresponding authors. Tel./fax: +86 379 65523821.
E-mail address: xubohan@163.com (C. Xu).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.08.046

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C. Xu et al. / Inorganica Chimica Acta 365 (2011) 469–472
N
N
H
N
Fe
Pd
Fe
Cl
PCy3
Pd
Cl
L(monophosphine ligand)
OHC
B
A
Scheme 1. Examples of monophosphine-cyclopalladated complexes containing ferrocenyl ligand.
N
HgCl
N
N
Monophosphine
ligands L
[Pd]
N
N
Li2PdCl4
I
Fe
Fe
HgCl
N
1
N
N
L=
P
2
3
N
L
N
Cl
N
Pd
L
Pd
L
Fe
Fe
Pd
Cl
Cl
or
P
N
L=
N
N
N
2
3
(DCPAB)
Scheme 2. Preparation of compounds 1–3.
was then placed in an oil bath and heated at 130 °C for 8 h, cooled
and quenched with water. The organic layer was separated and the
aqueous layer was extracted with dichloromethane, then the com-
bined organic layers were washed with water, dried over MgSO4,
filtered, and the solvent was removed on a rotary evaporator.
The product was separated by passing through a short silica gel
column with CH2Cl2 as eluent. The second band was collected
and afforded the red solid 1, yield 83%. IR (KBr, cmꢁ1): 3048,
2921, 2852, 1556, 1516, 1487, 1419, 1340, 1222, 1173, 1105,
1026. 1H NMR (400 MHz, CDCl3): d 6.67 (s, 2H, Ar–H), 5.09 (s,
4H, C5H4), 4.33 (s, 4H, C5H4), 2.35 (s, 12H, –CH3). MS-ESI+: m/z
399.1 [M + H]+. Anal. Calc. for C22H22FeN4: C, 66.34; H, 5.57; N,
14.07. Found: C, 66.52; H, 5.43; N, 14.22%.
Calc. for C58H50Cl2FeN4P2Pd2: C, 57.83; H, 4.18; N, 4.65. Found: C,
57.97; H, 4.02; N, 4.46%.
2.3.2. [PdCl{[(g g
5-C5H4)]Fe[( 5-C5H3)–(N2C4H–2CH3)2]}(DCPAB)] (3)
Red solid, yield 51%. IR (KBr, cmꢁ1): 2921, 2842, 1595, 1556,
1490, 1438, 1370, 1359, 1271, 1173, 1036. The 1H NMR
(400 MHz, CDCl3): d 7.50–7.54 (m, 2H, Ph–H), 7.01–7.11 (m, 6H,
Ph–H), 6.71 (s, 1H, Ar–H), 6.67 (s, 1H, Ar–H), 5.09 (s, 1H, C5H3),
4.31 (s, 2H, C5H3), 3.69–3.75 (m, 4H, C5H4), 2.53 (s, 6H, –NMe2),
2.36 (s, 6H, –CH3), 2.32 (s, 6H, –CH3), 1.25–1.72 (m, 22H, PCy3).
MS-ESI+: m/z 897.3 [M–Cl]+. Anal. Calc. for C48H57ClFeN5PPd: C,
61.81; H, 6.16; N, 7.51. Found: C, 61.96; H, 6.05; N, 7.62%.
2.4. X-ray diffraction studies
2.3. General procedure for the synthesis of the monophosphine-
cyclopalladated ferrocenylpyrimidine complexes 2–3
Crystallographic data for 1–3 were collected on a Bruker SMART
0
APEX-II CCD diffractometer with Mo Ka radiation (k = 0.071073 ÅA).
The data were corrected for Lorentz-polarization factors as well as
A mixture of 1 (1 mmol), Li2PdCl4 (2.2 mmol) and NaOAc
(2.2 mmol) in 40 ml of dry methanol was stirred for 48 h at room
temperature. The red solids (yield: 88%) were collected by filtration
and washed several times with methanol. Without further purifi-
cation, it was treated with monophosphine ligands (2.2 mmol) in
dry CH2Cl2 at room temperature for 1 h. The product was separated
by passing through a short silica gel column with CH2Cl2 as eluent.
The first band was collected and afforded the corresponding mono-
phosphine-cyclopalladated ferrocenylpyrimidine complex.
for absorption. Structures were solved by direct methods and re-
fined by full-matrix least-squares methods on F2 with the SHELX
-
97 program [20]. All non-hydrogen atoms were refined anisotrop-
ically, while hydrogen atoms were placed in geometrically calcu-
lated positions. CCDC reference numbers 762578–762580 for
compounds 1–3, respectively.
3. Results and discussion
2.3.1. [Pd2Cl2{(
g
5-C5H3)–N2C4H–2CH3}2Fe (PPh3)2] (2)
3.1. Synthesis and characterization of compounds 1–3
Red solid, yield 59%. IR (KBr, cmꢁ1): 3411, 2901, 1576, 1547,
1487, 1428, 1359, 1330, 1183, 1065, 1036. 1H NMR (400 MHz,
CDCl3): d 7.82–7.87 (m, 12H, Ph–H), 7.39–7.43 (m, 18H, Ph–H),
6.68(s, 2H, Ar–H), 5.10 (s, 2H, C5H3), 4.80 (b, 2H, C5H3), 4.34 (s,
2H, C5H3), 2.34 (s, 12H, –CH3). MS-ESI+: m/z 1132.1 [Mꢁ2Cl]+. Anal.
The synthetic route of 1 and monophosphine-cyclopalladated
complexes 2–3 is demonstrated in Scheme 2. The palladium-cata-
lyzed cross-coupling reactions of organomercury compounds as a
source of ferrocenyl group with aryl halides were shown to be easy

C. Xu et al. / Inorganica Chimica Acta 365 (2011) 469–472
471
ergy. However, band at 1556 cmꢁ1 is still detected in the IR spec-
trum of 3 and the absorption is the same as free ligand 1. The 1H
NMR spectra of 1–3 are consistent with the proposed structures,
2 exhibits three peaks for Cp ring with the proton ratio of 2:2:2,
clearly showing that it was ortho-biscyclopalladated product, while
3 exhibits three peaks with the proton ratio of 1:2:4. The above re-
sults indicate that 3 is a monocyclopalladated complex.
The IR spectrum of the bridge-splitting reaction with mono-
phosphine ligands were also determined and band at 1556 cmꢁ1
was only observed in the reaction with DCPAB ligand. This sug-
gested that monocyclopalladated complex 3 was formed during
the reaction. This process would significantly reduce the steric hin-
drance around the coordinative nitrogen and the palladium due to
the steric bulk of the DCPAB ligand [11,12]. The expected DCPAB-
biscyclopalladated complex was not isolated. In order to further
investigate the structures of these compounds, their detailed struc-
tures have been determined by X-ray single-crystal diffraction.
Fig. 1. Molecular structure of compound
1 showing the intramolecular p–p
stacking interaction. H atoms are omitted for clarity.
3.2. Molecular structures of compounds 1–3
and convenient for the synthesis of monoarylsubstituted ferro-
cenes [13,21]. In most case THF-acetone has been used as solvent,
while 1,10-dichloromercuriferrocene was highly insoluble. So, we
have chosen DMF as solvent, in the present of PdP(Ph3)4 provided
coupled product 1 in good yield in the reaction of 1,10-dichloro-
mercuriferrocene and 4,6-dimethyl-2-iodopyrimidine.
The following double cyclopalladation reaction was carried out
with 1 and 2.2 equivalents of Li2PdCl4 and NaOAc in methanol at
room temperature for 24 h. The formed red solids (yield: 88%) were
collected by filtration and washed several times with methanol.
Because of its poor solubility in all common organic solvents, it
was characterized only by IR and assigned to be polymeric or di-
meric biscyclopalladated derivatives [12]. Compared with 1, the
C@N absorption (1527 cmꢁ1) of its pyrimidine ring shifted to lower
energy, indicating the coordination of nitrogen to palladium [12–
16]. Without further purification, it was directly subjected to
bridge-splitting reaction with monophosphine ligands to produce
the monophosphine-cyclopalladated complexes 2–3.
All the crystals were obtained by recrystallization from CH2Cl2–
petroleum ether solution at room temperature. The molecules are
shown in Figs. 1–3 (displacement ellipsoids are drawn at the 50%
probability level). The Cp ring of 1 are approximately coplanar with
the pyrimidine ring because of smaller steric hindrance [22–24],
the dihedral angels between them are 3.9° and 6.5°. The molecules
adopt a synperiplanar eclipsed conformation, with the two pyrim-
idine rings arranged in parallel fashion (Fig. 1). There are strong
intramolecular
p–p stacking interactions between the pyrimidine
rings (the interplane distances are about 3.626 Å) [25].
The single-crystal X-ray analysis further confirms that 2–3 are
biscyclopalladated and monocyclopalladated complexes, respec-
tively. The Pd atom in each complex is in a slightly distorted
square-planar environment bonded to the phosphorus atom, the
chloride atom, the pyrimidinyl nitrogen atom and the carbon atom
of the ferrocenyl moiety. In these complexes, the ferrocenylpyrim-
idine metallacycle is essentially flat. The Pd–N [2.230(3) and
2.247(5) Å] and Pd–P [2.2457(10)–2.2653(16) Å] bond lengths of
2–3 are obviously longer than those of the corresponding B
[2.2006(18)–2.240(3) Å and 2.2382(7)–2.2602(8) Å] [13]. In
Compounds 1 and 2–3 were fully characterized by elemental
analysis, IR, 1H NMR, and ESI-MS. In the IR spectra of 2–3, the
C@N absorptions of the pyrimidine rings also shifted to lower en-
Fig. 2. One-dimensional chain structure of 2 showing the intermolecular C–HꢀꢀꢀCl hydrogen bonds. Non-hydrogen-bonding H atoms are omitted for clarity.

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C. Xu et al. / Inorganica Chimica Acta 365 (2011) 469–472
Fig. 3. One-dimensional chain structure of 3 showing intramolecular p–p stacking interactions and the intermolecular C–HꢀꢀꢀCl hydrogen bonds. Non-hydrogen-bonding H
atoms and H2O are omitted for clarity.
addition, the above bond lengths in 3 also are longer than those of
2 possibly due to the steric bulk of the DCPAB ligand [12,13].
In complex 2, the FeII ion lying on a center of symmetry, the two
Cp rings adopt an antiperiplanar staggered conformation, with the
two pyrimidine rings pointing in the opposite directions (Fig. 2).
However, like 1, 3 adopts a synperiplanar conformation, with the
two pyrimidine rings arranged in parallel fashion (the interplane
distances are about 3.612 Å) (Fig. 3). The most striking common
feature of the structures of 2–3 is intermolecular C–HꢀꢀꢀCl hydrogen
bonds [13,14,26], their lengths are 2.815 Å [(CH3)C–HꢀꢀꢀCl] and
2.823 Å [(Cp)C–HꢀꢀꢀCl], respectively, which are attributed to con-
struct the 1D chain structures.
References
[1] R.B. Bedford, Chem. Commun. (2003) 1787.
[2] J. Dupont, M. Pfeffer, Palladacycles, Wiley–VCH, Weinheim, Germany, 2008.
[3] R. Bosque, C. López, J. Sales, Inorg. Chim. Acta 244 (1996) 141.
[4] Y.J. Wu, S.Q. Huo, J.F. Gong, X.L. Cui, L. Ding, K.L. Ding, C.X. Du, Y.H. Liu, M.P.
Song, J. Organomet. Chem. 637–639 (2001) 27.
[5] L.L. Troitskaya, Z.A. Starikova, T.V. Demeshchik, S.T. Ovseenko, E.V. Vorontsov,
V.I. Sokolov, J. Organomet. Chem. 690 (2005) 3976.
[6] X.M. Zhao, X.Q. Hao, B. Liu, M.L. Zhang, M.P. Song, Y.J. Wu, J. Organomet. Chem.
691 (2006) 255.
[7] M.E. Günay, C.J. Richards, Organometallics 28 (2009) 5833.
[8] R. Bosque, C. López, J. Sales, X. Solans, J. Silver, Dalton Trans. (1996) 3195.
[9] C. López, R. Bosque, J. Organomet. Chem. 524 (1996) 247.
[10] Y.J. Wu, Y.H. Liu, Polyhedron 16 (1996) 335.
[11] R. Bosque, C. López, X. Solans, M. Font-Bardia, Organometallics 18 (1999) 1267.
[12] C. Xu, J.F. Gong, Y.H. Zhang, Y. Zhu, C.X. Du, Y.J. Wu, Inorg. Chem. Commun. 9
(2006) 456.
Acknowledgments
[13] C. Xu, Z.Q. Wang, W.J. Fu, X.H. Lou, Y.F. Li, F.F. Cen, H.J. Ma, B.M. Ji,
Organometallics 28 (2009) 1909.
We are grateful to the National Natural Science Foundation of
China (Nos. 20902043 and 20902042) and the Natural Science
Foundation of Henan Education Department, China (No.
2009B150019) for financial support of this work.
[14] C. Xu, J.F. Gong, S.F. Yue, Y. Zhu, Y.J. Wu, Dalton Trans. (2006) 4730.
[15] C. Xu, J.F. Gong, Y.J. Wu, Tetrahedron Lett. 48 (2007) 1619.
[16] C. Xu, J.F. Gong, G. Tao, Y.H. Zhang, Y.J. Wu, J. Mol. Catal. 279 (2008) 69.
[17] M.R. Biscoe, B.P. Fors, S.L. Buchwald, J. Am. Chem. Soc. 130 (2008) 6686.
[18] M. Rausch, M. Vogel, H. Rosenberg, J. Org. Chem. 22 (1957) 900.
[19] G.M. Kosolapoff, C.H. Roy, J. Org. Chem. 26 (1961) 1895.
[20] G.M. Sheldrick, SHELXL-97, Program for refinement of crystal structure,
University of Göttingen, Germany, 1997.
Appendix A. Supplementary material
[21] I.P. Beletskaya, A.V. Tsvetkov, G.V. Latyshev, V.A. Tafeenko, N.V. Lukashev, J.
Organomet. Chem. 637–639 (2001) 653.
[22] M. Enders, G. Kohl, H. Pritzkow, J. Organomet. Chem. 622 (2001) 66.
[23] D. Braga, M. Polito, M. Bracaccini, D. D’Addario, E. Tagliavini, L. Sturba, F.
Grepioni, Organometallics 22 (2003) 2142.
[24] T. Mochida, K. Okazawa, R. Horikoshi, Dalton Trans. (2006) 693.
[25] S.M. Malathy Sony, M.N. Ponnuswamy, Cryst. Growth Des. 6 (2006) 736.
[26] L. Brammer, E.A. Bruton, P. Sherwood, Cryst. Growth Des. 1 (2001) 277.
CCDC 762578, 762579 and 762580 contain the supplementary
crystallographic data for compounds 1–3, respectively. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.08.046.