Synthesis of a new tetradentate bis(imino-phosphine) ligand and its complexation with copper(I) ions

Article abstract of DOI:10.1016/j.ica.2011.02.015

Schiff base condensation of m-phenylenediamine with two equivalents of o-(diphenylphophino)benzaldehyde products the potentially tetradentate molecule 1,3-(Ph₂P(o-C₆H₄)CHN)₂C ₆H₄ (1) in high yield. The reaction of 1 and [Cu(NCMe)₄]BF₄ affords the dinuclear complex [(1,3-(Ph₂P(o-C₆H₄)CHN)₂C ₆H₄)₂Cu₂](BF₄) ₂ (2) through coordination of the imino-phosphine groups. The structure of 2 has been determined by an X-ray diffraction study.

Full text of DOI:10.1016/j.ica.2011.02.015

Inorganica Chimica Acta 370 (2011) 456–459
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Inorganica Chimica Acta
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Synthesis of a new tetradentate bis(imino-phosphine) ligand and its
complexation with copper(I) ions
⇑
Chi-Shian Chen, Wen-Yann Yeh
Department of Chemistry and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Schiff base condensation of m-phenylenediamine with two equivalents of o-(diphenylphophino)benzal-
dehyde products the potentially tetradentate molecule 1,3-(Ph2P(o-C6H4)CH@N)2C6H4 (1) in high yield.
The reaction of 1 and [Cu(NCMe)4]BF4 affords the dinuclear complex [(1,3-(Ph2P(o-C6H4)CH@N)2C6H4)2-
Cu2](BF4)2 (2) through coordination of the imino-phosphine groups. The structure of 2 has been deter-
mined by an X-ray diffraction study.
Received 15 December 2010
Accepted 9 February 2011
Available online 15 February 2011
Keywords:
Ó 2011 Elsevier B.V. All rights reserved.
Tetradentate ligand
Dicopper(I) complex
Imino-phosphine
1. Introduction
tion of m-phenylenediamine with two PPh2(o-C6H4)C(@O)H mole-
cules and loss of two H2O. The starting compound PPh2(o-C6H4)-
The multifunctional, hemilabile ligands [1–4], which contain
both soft (such as P, S) and hard (such as N, O) donor atoms, have
attracted considerable interest for their unusual coordination
chemistry and their increasing importance in catalysis [5–8], with
the reactivity being controlled by the differential donor properties
of the ligands [9]. One of the early notable successes associated
with complexes of P^O-ligands was their application in the Shell
higher olefin process which utilizes a nickel-catalyzed oligomeri-
zation of ethylene [10]. In addition, the hemilabile property of
pyridyl group has made the complexes [Pd(allyl)(Ph2P(o-C6H4)-
CH@NC2H4(o-C5H4N))]+ very active in allylic alkylation reactions
[11]. As part of our interest in the design and coordination
chemistry of multifunctional ligands [12–16], herein we present
the synthesis of a new tetradentate P2N2 ligand and its coordina-
tion to copper(I) ions.
C(@O)H presents a 31P resonance at ꢀ11.4 ppm for the phosphorus
atom and an 1H resonance at 10.50 ppm for the formyl proton. The
31P{1H} NMR spectrum of 1 displays a slightly downfield signal at
ꢀ13.18 ppm for the phosphine ligands, and the 1H NMR spectrum
(Fig. 1) shows missing of the formyl proton resonance and a new
2H doublet signal (JP–H = 5 Hz) appearing at 9.01 ppm, assigned to
the imine protons.
Compound 1 contains two imino-phosphine moieties con-
nected to the 1,3-positions of a benzene ring. Due to rigidity of
the arene spacer, the two N^P groups are restricted to bind sepa-
rate metal atoms (or ions) instead of acting as a tetradentate che-
lating agent to coordinate one metal center. Such that, treatment of
1 with equimolar [Cu(NCMe)4]BF4 in dichloromethane at ambient
temperature produces an orange-red solution, from which air-
stable, red crystals of the dimetallic complex [(1,3-(Ph2P(o-
C6H4)CH@N)2C6H4)2Cu2](BF4)2 (2) were obtained in 80% yield by
adding diethyl ether. The ESI mass spectrum displays the ion peak
+
ꢀ
at m/z 1517 corresponding to the [M ꢀ BF4
]
fragment. A related
2. Results and discussion
N2P2 ligand, 1,2-(Ph2P(o-C6H4)CH@N)2C2H4, forms a mononuclear
copper(I) complex with a tetraligate coordination at the Cu center
from the four donor atoms [17].
Schiff base condensation reaction of m-phenylenediamine with
two equivalents of o-(diphenylphophino)benzaldehyde (PPh2(o-
C6H4)C(@O)H) in refluxing benzene produces the potentially tetra-
dentate molecule 1,3-(Ph2P(o-C6H4)CH@N)2C6H4 (1) in 90% yield
(Scheme 1), as an air-stable yellow solid. The FAB mass spectrum
of 1 gives the molecular ion at m/z 652, corresponding to combina-
Single crystals of 2 were grown by slow diffusion of diethyl
ether into a dichloromethane solution at ambient temperature.
The ORTEP drawing for the cation of 2 is illustrated in Fig. 2, where
a crystallographic center of symmetry is imposed on the molecule.
The complex consists of a dimeric [CuI ꢁ12] structure with each
2
copper ion bonded to two phosphorus and two nitrogen atoms
from different molecule of 1. The coordination about the Cu+ ion
can be described as an irregular tetrahedral, such that the angles
⇑
Corresponding author. Fax: +886 7 5253908.
E-mail address: wenyann@mail.nsysu.edu.tw (W.-Y. Yeh).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.015

C.-S. Chen, W.-Y. Yeh / Inorganica Chimica Acta 370 (2011) 456–459
457
O
H
N
N
+ 2 H2O
+ 2
Ph2P
NH2
NH2
PPh2
Ph2P
1
N
N
PPh2
PPh2
Ph2P
Ph2P
-
[Cu(NCMe)4] BF4
2
+ 2
1
Cu+
Cu+
2 BF4
N
N
2
Scheme 1. Preparation of 1 and 2.
Fig. 1. 1H NMR spectra of 1 and 2 in CD2Cl2 at 24 °C.
0
around the copper atom range from 90.1(1)° for P1–Cu1–N1 to
133.1(1)° for P1–Cu1–N2. The two imino-phosphine links are
coordinated to the copper ion asymmetrically with the bond dis-
tances Cu1–N1 2.107(4), Cu1–N2 2.068(4), Cu1–P1 2.275(2) and
Cu1–P2 2.231(1) Å, and the bite angles P1–Cu1–N1 90.1(1)° and
P2–Cu1–N2 97.7(1)°. The bond distances N1–C19 1.271(6) and
N2–C26 1.285(7) Å retain a N@C double bond character for the
imine moieties. It is interesting that the two benzene spacers are
in the anti-position and parallel to each other with the interplane
distance of 3.18 Å (Fig. 3), and the two Cu(I) ions are separated
by 7.44 Å.
p
⁄ orbital of the N@C double bond, while shielding of Hb might
be attributed to ring-current from the opposite arene species.
We recently prepared the molecule 2,6-(Ph2P(o-C6H4)CH@N)2-
C5H3N (3) and showed its reaction with Cu+ ions to give [(2,6-
(Ph2P(o-C6H4)CH@N)2C5H3N)2Cu2](BF4)2 (4) (Eq. (1)), in which
the two pentadentate ligands wrap the Cu(I) ions in a double-heli-
ꢀ
cal fashion [18]. Furthermore, complex 4 reacted with NO2 ions
with the activity mimicking the biological denitrification process
[19]. The Cu(I) ions in 2 are each coordinated by two ‘‘soft’’ phos-
phorus and two ‘hard’ nitrogen atoms, and are also expected to car-
ry out similar ligand substitution reactions. However, attempts to
react 2 with [Ph3PNPPh3]NO2, KN3, O2 or CNC6H4NC were unsuc-
cessful. This is likely due to the kinetic reasons that the two close
benzene spacers of 2 block the incoming ligands to attack the cop-
per ions. In addition, steric constraints of the P2N2 ligands might
hinder dissociation of the imine groups for undergoing substitution
reactions.
The 31P{1H} NMR spetrum of 2 presents a sharp singlet at
ꢀ9.39 ppm. The 1H NMR spectrum (Fig. 1) shows that the imine
0
0
proton resonance (Ha ) and one arene proton resonance (Hb ) are
shifted upfield to 8.06 and 5.60 ppm, respectively, in comparion
with the free ligand 1. Shielding of the imine protons is likely
due to back-donation of electrons from the d10 Cu(I) ion to the

458
C.-S. Chen, W.-Y. Yeh / Inorganica Chimica Acta 370 (2011) 456–459
ꢀ
Fig. 2. Molecular structure of 2 with 30% probability ellipsoids. The BF4 counter ions and hydrogen atoms have been artificially omitted. Selected bond distances (Å) and
angles (°): Cu1–N1 2.107(4), Cu1–N2 2.068(4), Cu1–P1 2.275(2), Cu1–P2 2.231(1), N1–C19 1.271(6), N2–C26 1.285(7) and P1–Cu1–P2 120.67(5), P1–Cu1–N1 90.1(1), P1–
Cu1–N2 133.1(1), P2–Cu1–N1 113.2(1), P2–Cu1–N2 97.7(1), N1–Cu1–N2 99.0(2), C19–N1–C20 115.0(4), C24–N2–C26 115.7(4).
3. Experimental
3.1. General remarks
All manipulations were carried out under an atmosphere of
purified dinitrogen with standard Schlenk techniques. [Cu(-
MeCN)4]BF4 was prepared as described in the literature [20]. m-
Phenylenediamine and o-(diphenylphophino)benzaldehyde (Al-
drich) were used as received. Solvents were dried over appropriate
reagents under dinitrogen and distilled immediately before use. 1H
and 31P{1H} NMR spectra were obtained on a Varian Unity INOVA-
500 spectrometer. Fast-atom-bombardment (FAB) and electro-
spray ionization (ESI) mass spectra were recorded on a JEOL JMS-
SX102A mass spectrometer and a Waters ZQ-4000 mass spectrom-
eter, respectively. Elemental analyses were performed at the Na-
tional Science Council Regional Instrumentation Center at
National Chen-Kung University, Tainan, Taiwan.
3.2. Preparation of 1
Fig. 3. Skeleton of 2 showing parallel of the two arene spacers.
Under a dinitrogen atmosphere, m-phenylenediamine (109 mg,
1 mmol), o-(diphenylphophino)benzaldehyde (600 mg, 2.06
mmol) and benzene (30 ml) were placed in an oven-dried 250 ml
Schlenk flask, equipped with a magnetic stir bar and a reflux con-
denser. The reaction mixture was refluxed for 8 h, yielding a yellow
solution. The solution was filtrated and concentrated to ca. 15 ml
under dinitrogen and layered with n-hexane (50 ml) overnight. A
yellow solid was obtained, characterized as 2,6-(Ph2P(o-C6H4)CH@
In conclusion, we have prepared a new polyfunctional molecule
1 and shown its coordination with Cu+ ions to generate a dimetallic
complex 2, which displays a quite different geometry and reactiv-
ity comparing with 4. We are currently investigating the viability
of 1 as a bridging ligand to assemble supramolecules or coordina-
tion polymers.
N
N
+
Cu
P
N
Ph2
Ph
Ph
P
2
N
N
N
2 P
ð1Þ
+
+ 2 Cu+
2
Cu
Ph2
Ph2P
PPh2
P
N
4
N
N
3

C.-S. Chen, W.-Y. Yeh / Inorganica Chimica Acta 370 (2011) 456–459
459
Table 1
(k = 0.71073 Å). The data were collected at 200 K. The h range for
data collection is 2.06–25.37°. Of the 25 806 reflections collected,
7365 reflections were independent. All data were corrected for Lor-
entz and polarization effects and for the effects of absorption. The
structure was solved by the direct method and refined by least-
square cycles. The non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included but not refined. All calcula-
tions were performed using the SHELXTL-97 package [21]. The
data collection and refinement parameters are presented in
Table 1.
Crystallographic data for compound 2.
Formula
C88H68B2Cu2F8N4P4ꢁ2CH2Cl2
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
1775.90
triclinic
ꢀ
P1
12.3888(3)
12.9899(3)
13.9411(4)
96.275(2)
99.964(2)
110.410(1)
2035.70(9)
200(2)
a
(°)
b (°)
c
(°)
V (Å3)
T (K)
Z
Acknowledgment
1
l
(mmꢀ1
)
0.800
0.0766, 0.1879
1.100
The authors are grateful for support of this work by the National
Science Council of Taiwan and thank Mr. Ting-Shen Kuo (National
Taiwan Normal University, Taipei) for X-ray diffraction analysis.
Final R1/wR2
Goodness-of-fit
Appendix A. Supplementary material
N)2C6H4 (1; 586 mg, 90%). Anal. Calc. for C44H34N2P2: C, 80.97; H,
5.25; N, 4.29. Found: C, 81.20; H, 5.54; N, 4.13%. Mass (FAB): m/z
652 (M+). 1H NMR (CD2Cl2, 24° C): 9.01 (d, JP–H = 5 Hz, 2H, N@CH),
8.18 (m, 2H, C6H4) 7.52–6.72 (m, 29H, Ph, C6H4), 6.70 (d,
JH–H = 8 Hz, 2H, C6H4), 6.46 (s, 1H, C6H4) ppm. 31P{1H} NMR (CD2Cl2,
24 °C): ꢀ13.18 (s) ppm.
CCDC 804438 for compound 2 contains the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic 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.2011.02.015.
3.3. Preparation of 2
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dichloromethane (10 ml) were placed in an oven-dried 50 ml
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ether (30 ml). The air-stable, red crystals of [(2,6-(Ph2P(o-
C6H4)CH@N)2C6H4)2Cu2](BF4)2 (2; 208 mg, 80% based on the Cu
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3.4. Structure determination for 2
A crystal of 2 found suitable for X-ray analysis was mounted in a
thin-walled glass capillary and aligned on the Nonius Kappa CCD
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