Synthesis and structural characterization of two novel copper(I) complexes with oxygen donor

Article abstract of DOI:10.1002/zaac.200600196

Two novel copper(I) complexes with Cu-O bonds, [Cu₂L ₂(PPh₃)₂](BF₄)₂ (1) and [Cu(L)(dppeo)](BF₄) (2) (L = 6-(4-diethylmethylphosphonatephenyl)-2, 2′-bipyridine, dppeo = bis(diphenylphosphino)ethane monoxide), have been prepared and their structures characterized. In the binuclear complex 1, the ligand L serves as tridentate donor with the N, N′ and O as coordination atoms, and the two Cu^I atoms are bridged through both P = O donor atoms in different ligand L with a triphenylphosphine molecule as auxiliary ligand. While in mononuclear complex 2, both ligands L and dppeo behave as bidentate with N∧N from L and P∧O from dppeo chelating to Cu^I atom.

Full text of DOI:10.1002/zaac.200600196

DOI: 10.1002/zaac.200600196
Synthesis and Structural Characterization of two Novel Copper(I) Complexes
with Oxygen Donor
Qian-Yong Cao*,a,b, Xin Ganc, and Wen-Fu Fu*,b,c
a Nanchang / P. R. China, Department of Chemistry, Nanchang University, Jiangxi 330047, China
b Beijing / P. R. China, Technical Institute of Physics and Chemistry, Chinese Academy of Science
c Yunnan / P. R. China, College of Chemistry and Chemical Engineering, Yunnan Normal University
Received July 9th, 2006.
Abstract. Two novel copper(I) complexes with Cu-O bonds,
P ϭ O donor atoms in different ligand L with a triphenylphosphine
molecule as auxiliary ligand. While in mononuclear complex 2,
[Cu2L2(PPh3)2](BF4)2 (1) and [Cu(L)(dppeo)](BF4) (2) (L
6-(4-diethylmethylphosphonatephenyl)-2,2Ј-bipyridine, dppeo
ϭ
ٙ
ϭ
both ligands L and dppeo behave as bidentate with N N from L
ٙ
bis(diphenylphosphino)ethane monoxide), have been prepared and
their structures characterized. In the binuclear complex 1, the
ligand L serves as tridentate donor with the N, NЈ and O as coordi-
nation atoms, and the two CuI atoms are bridged through both
and P O from dppeo chelating to CuI atom.
Keywords: Copper; Oxygen donor; Crystal structure
Introduction
have synthesized the new ligand, 6-(4-diethylmethylphos-
phonatephenyl)-2,2Ј-bipyridine (L), and found it can be
used as tridentate or bidentate ligand according to the
properties of the metal atom and auxiliary ligand. Here we
report two novel copper(I) complexes with Cu-O bond,
[Cu2L2(PPh3)2](BF4)2 (1) and [Cu(L)(dppeo)] (BF4) (2), and
their structural characterization.
Copper(I) complexes have received much attention for their
being less expensive and environmentally friendly, various
coordination structure, rich photochemical and photo-
physical properties [1Ϫ4]. Since the metal atom is generally
considered a borderline soft acid, the chemistry of copper(I)
is dominated by soft ligands (such as tertiary phosphine
donor ligands and sulfur donor ligands) and chelating
ligands (polypyridine ligands such as 2,2Ј-bipyridine,
1,10-phenanthroline and their substituted derivatives) [5, 6].
Copper(I) complexes with oxygen donor ligands, on the
contrary, are really rare [7Ϫ9], since the oxygen site is hard
donor which often prefers to complex with hard metals
such as early and high valent transition metals. Samuelson
and Pilloni have reported that bis(phosphine) monoxides
(BPMO) such as bis(diphenylphosphino)ethane monoxide
(dppeo) and diphenyl phosphino ferrocene oxide (odppf)
Experimental Section
General procedures
All reactions were performed under a dinitrogen atmosphere. Sol-
vents were distilled using standard techniques and saturated with
dinitrogen before use. [Cu(CH3CN)4](BF4), 4-bromophenyl-2,2Ј-
bipyridine (3) and dppeo were prepared by literature methods
[10Ϫ12].
ٙ
can serve as P O bidentate chelating ligands to copper(I)
Synthesis of ligand L (see scheme 1)
atoms [8, 9]. We envision that PϭO group substituted poly-
pyridine ligands may use as polydentate donor to construct
novel copper(I) complexes with Cu-O bond. Recently, we
6-(4-bromophenyl)-2,2Ј-bipyridine.
A
solution of
3
(1.0 g,
4.1 mmol), N-bromosuccinimide (0.72 g, 4.1 mmol) and small
amount of benzoyl peroxide in dry CCl4 (30 mL) was heated to
reflux for 3 h. The resulting solution was cooled to room tempera-
ture, then filtered to remove succinimide, and with small amount
of warm CCl4 washed twice the solid. On removal of the solvent, a
slight yellow solid was obtained which was used in the next reaction
without further purification. Yield: 0.96 g, 72 %; m.p. 128ϳ130 °C.
1H NMR (300 Hz, CDCl3): 4.58 (s, 2H), 7.55 (d, J ϭ 8 Hz, 2H), 7.66 (m,
1H), 7.88 (d, J ϭ 8 Hz, 1H), 8.01 (m, 1H), 8.14 (d, J ϭ8 Hz, 1H), 8.21
(m,2H), 8.63 (d, J ϭ 8 Hz, 1H), 8.78 (d, J ϭ 8 Hz, 1H), 8.95 (d, J ϭ 5 Hz,
1H).
* Dr Qian-Yong Cao,
Department of Chemistry, Nanchang University
Nanchang 330047, P. R. China
Fax: 791-8339575
E-mail: cqyong@ncu.edu.cn
Prof. Dr. Wen-Fu Fu
Technical Institute of Physics and Chemistry,
Chinese Academy of Science
Beijing 100080, P. R. China
fuwfu@sohu.com
6-(4-diethylmethylphosphonatephenyl)-2,2Ј-bipyridine (L). A solu-
tion of 4 (1.0 g, 3.08 mmol) in triethylphosphite (5 mL) was re-
fluxed for 3 h. The excess phosphite was removed by distillation
176
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Z. Anorg. Allg. Chem. 2007, 633, 176Ϫ179

Copper(I) Complexes with Oxygen Donor
collection as well as refinement are summarized in Table 1. Diffrac-
tion data were collected at room temperature with graphite mono-
chromatized Mo Kα radiation (λ ϭ 0.71073 A) on a Rigaku
Table 1 crystal data and structure refinement
˚
Complexes
Formula
Fw
1·CH2Cl2
2·0.5CH2Cl2
C40H40BCl2CuF4N2O3P2 C47.5H48BClCuF4N2O4P3
879.93
R-AXIS RAPID IP X-ray diffractometer for 1 and on a Bruker
SMART CCD area detector for 2. Diffracted data were corrected
for absorption correction using the ABSCOR [13] program (1) or
SADABS [14] program (2). The structures were solved by direct
methods using the program SHELXS 97 [15] and refined by full-
matrix least squares on F2 using the SHELXL 97 [16] program
package. The non-hydrogen atoms were refined anisotropically.
CCDC 227448 (1) and 605459 (2) contains the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: ϩ44 1223 336033).
989.59
Crystal system
Space group
Color
monoclinic
P21/c
monoclinic
Cc
yellow
0.30 x 0.26 x 0.20
9.735(3)
32.238(9)
16.681(5)
93.728(5)
5224(3)
2
brown-yellow
0.30x0.30x0.25
12.680(3)
22.195(4)
15.194(3)
104.74(3)
4135.3(14)
4
Crystal size, mm
˚
a /A
˚
b /A
˚
c /A
β /°
3
˚
V /A
Z
Dcalc /Mg/m3
T /K
1.413
293(2)
1.258
293(2)
Refls. No.
Theta range
µ /mmϪ1
F(000)
R, Rw
Goodness-of- fit
Flack’s parameters
36428
2.09-27.48
0.792
1808
0.0493, 0.1243
0.857
14652
1.76-26.38
0.616
2044
0.0640, 0.1712
1.066
Result and Discussion
Scheme 1 shows the details of the synthetic strategy adopted
for the synthesis of the key ligand 6-(4-diethylmethylphos-
phonatephenyl)-2,2Ј-bipyridine (L) with good yield. Com-
plexes 1 and 2 were prepared by reaction of equimolar
quantities of [Cu(CH3CN)4](BF4), ligand L and auxiliary
ligand PPh3 for 1 or dppeo for 2 in dichloromethane. Both
complexes are colored solids (brown-yellow for 1 and yel-
low for 2) and soluble in organic solvents such as dichloro-
methane, chloroform and acetonitrile. They are stable in air
and moisture.
0.00(2)
under high vacuum. The crude product was purified by column
chromatography on silica gel by using ethylacetate/methanol
(80/20) as eluent. Yield: 0.94 g, 80 %; m.p. 114ϳ115.5 °C.
1H NMR (300 Hz, CDCl3): 1.28 (t, J ϭ 7 Hz, 6H), 3.24 (d, J ϭ 22 Hz, 2H),
4.05 (m, 4H), 7.34 (m, 1H), 7.45 (m, 2H), 7.77 (d, J ϭ 8 Hz, 1H), 7.88 (m,
2H), 8.12 (d, J ϭ 8 Hz, 2H), 8.38 (d, J ϭ 8 Hz, 1H), 8.64 (d, J ϭ 8 Hz, 1H),
8.70 (d, J ϭ 8 Hz, 1H).
The single crystals of 1 and 2 suitable for X-ray analysis
were obtained from their dichloromethane solution by
vapor diffusion with diethyl ether. Their perspective views
are shown in Figures 1 and 2, and selected bond distances
and angles are summarized in Table 2. The molecular struc-
ture of 1 consists of two centrosymmetric dimeric units of
[CuL(PPh3)]ϩ, in which two symmetrically related copper(I)
atoms are held together by O donor atoms of the tridentate
ligands L. The Cu, O, P, C and N atoms form a twenty
membered ring. The copper(I) adopts a distorted tetra-
hedral coordination structure with two nitrogen and one
oxygen atoms from ligand L and one phosphorous atom
from auxiliary ligand PPh3. The angles around the copper
atom range from 80.10(11)° for N1-Cu-N2 to 125.24(7)° for
N(2)-Cu-P(1). The calculated long Cu-Cu(A) distance
Syntheses of [Cu2L2(PPh3)2](BF4)2 (1)
A mixture of equal mole of [Cu(CH3CN)4](BF4) and L (0.5 mmol)
in 30 mL dichloromethane was stirred for 1 hour, then equal mole
of PPh3 was added and reacted for additional 2 hours. The
resulting yellow reaction mixture was concentrated in vacuum, and
the crude product was precipitated by adding diethyl ether. The
yellow single crystals were obtained from the solution of dichloro-
methane by vapor diffusion with diethyl ether. Yield: 82 %. Anal.
Calc. for C39H38BCuF4N2O3P2 (795.04): C, 58.92; H, 4.82; N, 3.52.
Found: C, 59.05; H, 4.96; N, 3.48 %.
Synthesis of [Cu(L)(dppeo)] (BF4) (2)
The preparation of 2 was similar to that of 1, except deepo was
used in place of PPh3. Yellow solid, yield: 89 %. Anal. Calc. for
C47H47BCuF4N2O4P3 (947.14): C, 59.55; H, 4.96; N, 2.96. Found:
C, 59.48; H, 5.01; N, 3.02.
˚
8.503 A reveals no Cu-Cu contact in complex 1. The Cu-O
˚
˚
distance (2.178(2) A), Cu-N distance (2.052(3) A and
˚
˚
2.116(3) A) and Cu-P distance (2.1725(10) A) are normal,
and are within the values of reported related structures
[8Ϫ9, 17Ϫ18]. It is noteworthy here that the ligand L be-
haves as tridentate donor with two N atoms adopting nor-
mal chelating mode and O bridging mode. The dihedral an-
X-ray crystallography
Crystals of complexes 1 and 2 were obtained by vapor diffusion of
diethyl ether into CH2Cl2 solution. Crystal data and details of data
Scheme 1
Z. Anorg. Allg. Chem. 2007, 176Ϫ179
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www.zaac.wiley-vch.de
177

Q.-Y. Cao, X. Gan, W.-F. Fu
˚
Table 2 Selected bond distances /A and angles /°:
complex 1
Cu-N1
Cu-N2
P2-O3
N1-Cu-N2
N1-Cu-P1
N2-Cu-P1
2.052(3)
2.116(3)
1.465(2)
80.10(11)
130.47(8)
125.24(7)
Cu-P1
Cu-O3A
2.1725(10)
2.178(2)
a
N1-Cu-O3A
N2-Cu-O3A
P1-Cu-O3A
96.79(10)
99.01(9)
116.37(7)
Complex 2
Cu1-N1
Cu1-N2
P2-O1
N1-Cu1-N2
N1-Cu1-P1
N2-Cu1-P1
2.047(6)
2.081(6)
1.469(6)
81.1(2)
134.1(2)
125.8(2)
Cu1-P1
Cu1-O1
P3-O2
N1-Cu1-O1
N2-Cu1-O1
P1-Cu1-O1
2.164(2)
2.172(5)
1.436(8)
96.1(3)
115.7(2)
101.6(2)
a Symmetry code: Ϫx ϩ 1,Ϫy ϩ 1,Ϫz
Figure 1 The cation structure of [Cu2L2(PPh3)2](BF4)2 (1), the hy-
drogen atoms are omitted for clarity
Figure 3 UV-Vis spectra of free ligand L (0.85ϫ10Ϫ4 mol·LϪ1),
complex 1 (2.66ϫ10Ϫ5 mol·LϪ1) and complex 2 (4.95ϫ10Ϫ5
mol·LϪ1) in neat dichloromethane solution.
C31-C32-N1 in a plain conformation, and six membered
ring via Cu1-P1-C13-C14-P2-O1 in a chair conformation
which is very similar to the reported six-membered chelate
structure found in [Cu(dppeo)2](ClO4) [19]. The center
atom adopts distorted tetrahedron structure, and the bond
angles and the bond distances around the copper atom are
similar to those of 1. In ligand L, the bipyridine units are
almost co-planar with dihedral angles of 6.63°, and the tor-
sion angle between the pendant aromatic rings and adjacent
pyridine fragments is 40.53°. However the PϭO group in
Figure 2 The cation structure of [Cu(L)(dppeo)](BF4) (2), the
phenyl rings in dppeo (C1-C12 and C15 to C26) and all hydrogen
atoms are omitted for clarity
gle between two pyridine rings is 4.1 (2)°, and the torsion
angle between the pendant aromatic rings and adjacent
pyridine fragments is 38.9 (2)°. These values compared with
that of 2 indicates the centrosymmetric dimeric structure
for complex 1 is favorable in structure.
˚
ligand L is free, and the bond distance 1.436(8) A (P3-O2)
˚
is shorter than that in complex 1 (1.465(2) A, P2-O3). The
When the auxiliary ligand PPh3 changed into the
hemilabile ligand dppeo which containing both soft donor
tertiary phosphine and hard donor PϭO, we only obtained
the mononuclear complex 2. The crystal structure of 2 con-
sists discrete cations [Cu(L)(dppeo)]ϩ, tetrafluoroborate
anions and solvent dichloromethane molecules. In 2, both
ligands L and dppeo act as a bidentate chelating donor.
Chelating produces one five membered ring via Cu1-N1-
tetrafluoroborate anions in 2 are disorder, and no specific
interactions between the tetrafluoroborate anions and the
cationic complex are observed.
The UV-Vis absorption spectra for complexes 1 and
2
in dichloromethane are shown in Figure 3. For
comparison, the spectra of free ligand L are also given. For
complex 1, it is no doubt that the bands at 244 nm
(7.30 ϫ 10Ϫ4 dm3·molϪ1·cmϪ1
)
and 260 nm (sh,
178
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Z. Anorg. Allg. Chem. 2007, 176Ϫ179

Copper(I) Complexes with Oxygen Donor
5.91 ϫ 10Ϫ4 dm3·molϪ1·cmϪ1) are assigned to intraligand
(IL πǞπ*) transitions of the ligand, which based on simi-
larities with the absorptions of the free ligand. The band at
322 nm with large extinction coefficient (2.86 ϫ10Ϫ4
dm3·molϪ1·cmϪ1), which only red-shift 18 nm when
compared with band at 306 nm (sh) of the free ligand, and
occur at a shorter wavelength when compared with
analogous complexes such as [Cu(bpy)(PPh3)]ϩ and
[Cu(Phen)(PPh3)]ϩ [20]. We tentative assign this band to a
mixture transitions that involve IL transitions and metal-
to-ligand charge-transfer (MLCT) transitions. For complex
2, the low-energy broad absorption band with peak at
372 nm is characteristic for MLCT transition.
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Conclusion
Binuclear complex [Cu2L2(PPh3)2](BF4)2 (1) and mono-
nuclear copper(I) complex [Cu(L)(dppeo)](BF4) (2) with
6-(4-diethylmethylphosphonatephenyl)-2,2Ј-bipyridine (L)
have been prepared and characterized. For binuclear com-
plex 1, two symmetrically related copper(I) atoms are held
together by PϭO donor atoms of the tridentate ligands L,
while in complex 2, both ligands L and dppeo behave as
bidentate chelating ligands resulting mononuclear cop-
per(I) complex.
Acknowledgments. The work was supported by the State Key
Project (No. 2005CCA06800) and the National Natural Science
Foundation of China (NSFC Grant No. 50463001). We thank the
foundation (50418010) for NSFC/RGC Joint Research.
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