Syntheses, characterization and crystal structures of [Cu(PCHO) 2(2,2′-bipy)][BF4], [Cu2(PCHO) 4(4,4′-bipy)][BF4]2 and [Cu 2(PCHO)4(bptz)] [BF4]2

Article abstract of DOI:10.1016/j.ica.2005.08.008

Treatment of [Cu(PCHO)₂(NCMe)][BF₄] (1) (PCHO = o-(diphenylphosphino)benzaldehyde) with 2,2′-bipyridine produces the complex [Cu(PCHO)₂(2,2′-bipy)][BF₄] (4), while the reactions of 1 with 4,4′-bipyridine and 3,6

Full text of DOI:10.1016/j.ica.2005.08.008

Inorganica Chimica Acta 359 (2006) 659–664
www.elsevier.com/locate/ica
Note
Syntheses, characterization and crystal structures of
[Cu(PCHO)2(2,20-bipy)][BF4], [Cu2(PCHO)4(4,40-bipy)][BF4]2
and [Cu2(PCHO)4(bptz)] [BF4]2 (PCHO = o-(diphenylphosphino)
benzaldehyde and bptz = 3,6-bis(20-pyridyl)-1,2,4,5-tetrazine)
a,
b
b
Wen-Yann Yeh *, Gene-Hsiang Lee , Shie-Ming Peng
a
Department of Chemistry, National Sun Yat-Sen University, 70 Lien-Hai Road, Kaohsiung 804, Taiwan
b
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
Received 21 April 2005; received in revised form 27 July 2005; accepted 3 August 2005
Available online 19 September 2005
Abstract
Treatment of [Cu(PCHO)2(NCMe)][BF4] (1) (PCHO = o-(diphenylphosphino)benzaldehyde) with 2,20-bipyridine produces the com-
plex [Cu(PCHO)2(2,20-bipy)][BF4] (4), while the reactions of 1 with 4,40-bipyridine and 3,6-bis(20-pyridyl)-1,2,4,5-tetrazine (abbreviated
as bptz) afford the dinuclear complexes [Cu2(PCHO)4(4,40-bipy)][BF4]2 (5) and [Cu2(PCHO)4(bptz)][BF4]2 (6), respectively. The crystal
structures of 4–6 have been determined by an X-ray diffraction study. The coordination about the Cu+ ion is trigonal for 5 and tetra-
hedral for 4 and 6, and there is no bonding between the aldehyde groups and the Cu+ ion in these compounds.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Cu(I) complexes; Phosphine ligands; Pyridine ligands
1. Introduction
PCHO afforded [Cu(PCHO)3][BF4] (2), showing a Cu–
aldehyde interaction. In contrast, treating 1 with the biden-
tate phosphine (PPh2C5H4)2Fe (abbreviated as DPPF) led
to dissociation of one PCHO ligand to produce the tetrahe-
dral complex [Cu(PCHO)(DPPF)][BF4] (3) containing an
g2-P,O chelate. It was postulated that the steric properties
of the neutral ligands play an important role in determining
the cation stoichiometry [16]. To extend this scope, we
present here the results concerning the substitution reac-
tions of 1 with N-heterocyclic ligands.
The multifunctional, hemilabile ligands [1], which con-
tain 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 [2]. The o-(diphenylphosph-
ino)benzaldehyde molecule (abbreviated as PCHO) is one
of the simplest bidendate P,O-donor agents [3]. Four
modes of bonding have been observed in the interaction
of PCHO with transition metal centers: g1-P donor [4,5],
g2-P,O chelating [6,7], g3-P,CO chelating [8], and P-acyl-
hydride mode [9–14], which involves oxidative addition of
the formyl C–H bond on the metals. Recently, we prepared
the trigonal complex [Cu(PCHO)2(NCMe)][BF4] (1) [15]
and found that replacement of the acetonitrile ligand by
H
H
H
H
O
O
O
O
+
Cu
P
P
Ph2
+
Cu
+
Cu
P
P
-
Ph2
Ph2
Ph2
Ph2
-
BF4
-
BF4
MeCN
P
BF4
Ph2
Ph2
P
Ph2
P
P
O
O
Fe
3
H
H
*
Corresponding author. Tel.: 886 7 5252000; fax: 886 7 5253908.
E-mail address: wenyann@mail.nsysu.edu.tw (W.-Y. Yeh).
2
1
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.08.008

660
W.-Y. Yeh et al. / Inorganica Chimica Acta 359 (2006) 659–664
2. Results and discussion
The FAB spectrum of 4 displays the molecular cation
at m/z 799. The H NMR spectrum presents a 2H singlet
1
The reaction of 1 and 2,20-bipyridine in THF solvent
generated an orange precipitate, from which air-stable, or-
ange-yellow crystals of the complex [Cu(PCHO)2(2,20-bi-
py)][BF4] (4) were obtained in 56% after recrystallization.
On the other hand, treating 1 with 4,40-bipyridine in a
2:1 molar ratio produced pale yellow crystals of the dinu-
clear complex [Cu2(PCHO)4(4,40-bipy)][BF4]2 (5) in 63%.
We then investigated the reaction of 1 with the multiden-
tate ligand 3,6-bis(20-pyridyl)-1,2,4,5-tetrazine (abbreviated
as bptz), which took place in CH2Cl2 at ambient tempera-
ture to yield a brown solution, and the dinuclear complex
[Cu2(PCHO)4(bptz)][BF4]2 (6; 42%) was obtained as air-
stable, dark brown crystals after diffusion into diethyl
ether. The reactions are summarized in Scheme 1. In con-
trast to compounds 2 and 3, the formation of 4–6 does
not alter the PCHO coordination. This difference is likely
for steric reasons, since the planar N-heterocyclic ligands
are less space-congested than the tertiary phosphines.
Compound 5 is formally a 16-electron species, while 4
and 6 are 18-electron. They have been characterized by ele-
mental analysis, mass, IR and NMR spectroscopy. The
crystals suitable for an X-ray diffraction study were grown
by diffusion of diethyl ether (for 4 and 5) or n-hexane (for
6) into a dichloromethane solution of the compound at
ambient temperature.
at d 9.51 for the pendant formyl protons, two 2H dou-
blets at d 8.84 (JH–H = 5 Hz) and 8.31 (JH–H = 8 Hz)
and two 2H multiplets at d 8.05 and 7.40 for the bipyri-
dine protons, and a 28 H multiplet in the range d 7.65–
6.82 for the phenyl protons. In addition, the
31P{1H}NMR spectrum shows a broad signal at d 4.51
for the phosphine ligands. The spectral data are consis-
tent with a C2 symmetry for 4 in solution. The ORTEP
diagram for the cation of 4 is depicted in Fig. 1. The
coordination about the Cu+ ion can be described as an
irregular tetrahedron, where the angles around the copper
atom range from 78.3(2)° for N1–Cu–N2 to 126.92(6)°
for P1–Cu–P2. The benzaldehyde rings are about parallel
with a dihedral angle of 3.5°, and the mean separation of
˚
˚
the planes is 3.60 A. This value is compatible with 3.35 A
for the interplane distance in graphite and can be de-
scribed in terms of a van der Waals type interaction
[17]. The pyridine ligand chelates the Cu+ ion with the
˚
N1–Cu length (2.110(5) A) being slightly longer than
˚
the N2–Cu length (2.091(5) A). The two pyridine rings
are not coplanar, showing a dihedral angle of 8.6(6)°,
˚
and the Cu atom is 0.17(4) A away from the mean plane
of the N1, C6, C5 and N2 atoms. The O1ꢀ ꢀ ꢀCu and
˚
O2ꢀ ꢀ ꢀCu distances are 3.13 and 3.10 A, respectively, too
long to support a Cu–O interaction.
H
O
N
N
P
P
Ph
+
Cu
2
_
N
BF
4
+
1
Ph
2
N
4
O
H
H
H
O
O
N
N
Ph
P
P
P
2
Ph
2
+
+
_
2 BF
Cu
N
N
Cu
4
+
2 1
Ph
2
P
Ph
2
O
O
5
H
H
H
O
H
P
Ph
N
2
+
Cu
N
O
Ph
2
_
P
2 BF
N
N
N
N
N
N
N
4
+
2
1
P
P
Ph
Ph
N
2
O
H
+
Cu
N
2
N
6
O
H
Scheme 1.

W.-Y. Yeh et al. / Inorganica Chimica Acta 359 (2006) 659–664
661
+
˚
8.27 A. The N3 atom is disordered at its site. Each Cu
ion adopts a distorted tetrahedral geometry similar to 4,
such that the N1–Cu–N2 and P1–Cu–P2 angels are
77.72(2)° and 128.57(6)°, respectively. The mean Cu–N dis-
˚
˚
tance is 2.09 A and Cu–P distance is 2.27 A. The planar
benzaldehyde groups are about parallel with a dihedral an-
˚
gle of 2.7°, and the mean separation of the planes is 3.58 A.
˚
The O1ꢀ ꢀ ꢀCu and O2ꢀ ꢀ ꢀCu distances are 3.00 and 3.02 A,
respectively. We note that the geometry about the copper
atom
is
similar
to
the
related
complex
[Cu2(PPh3)4(bptz)][BF4]2 containing triphenylphosphine li-
gands [19].
Complex 5 exhibits the expected C2h symmetry in solu-
tion. The 1H NMR spectrum at 25 °C shows a broad signal
at d 9.82 for the formyl protons, two doublet signals
(JH–H = 6 Hz) at d 8.52 and 7.92 for the bipyridine protons,
and a multiplet in the range d 7.71–6.99 for the phenyl pro-
tons. The 31P resonance is recorded at d 1.77 as a broad sig-
nal. The structure of 5 consists of discrete cations
[Cu2(PCHO)4(4,40-bipy)]2+ and tetrafluoroborate counter
anions. There is a crystallographic center of symmetry im-
posed on the molecule. The ORTEP drawing for the cation
is illustrated in Fig. 3. The complex contains two
ꢁ
Fig. 1. Molecular structure of 4. The BF4 anion has been artificially
omitted. Only the ipso carbons of the C6H5 groups are shown for clarity.
Selected bond distances (A) and bond angles (°): Cu–P1 2.269(2), Cu–P2
2.291(2), Cu–N1 2.110(5), Cu–N2 2.091(5), C11–O1 1.177(7), C30–O2
1.187(7), Cuꢀ ꢀ ꢀO1 3.13, Cuꢀ ꢀ ꢀO2 3.10 and P1–Cu–P2 126.92(6), N1–Cu–
N2 78.3(2), P1–Cu–N1 113.5(1), P1–Cu–N2 111.0(2), P2–Cu–N1 107.3(1),
P2–Cu–N2 109.3(1), Cu–P1–C17 117.1(2), Cu–P2–C36 117.8(2), C31–
C30–O2 124.0(6), C12–C11–O1 125.4(6).
˚
CuðPCHOÞ2 moieties bridged by a 4,40-bipyridine ligand,
þ
The FAB spectrum of 6 reveals an intense parent ion
peak for the [Cu2(PCHO)4(bptz)]2+ cation at m/z 761.
The H NMR spectrum at 25 °C shows a broad signal at
d 9.62 for the free formyl protons and several multiplets
in the range d 9.23–6.90 for the aromatic protons. The
31P resonance for the coordinated phosphine groups is re-
corded at d 5.63. A thermal ellipsoid plot of the dinuclear
cation [Cu2(PCHO)4(bptz)]2+ is shown in Fig. 2. There is
a crystallographic center of symmetry imposed on the mol-
˚
where the Cuꢀ ꢀ ꢀCu distance is 11.09 A. With the N1, P1
1
and P2 atoms forming the basal trigonal plane, the interli-
gand bond angles surrounding the Cu atom are within 5° of
the trigonal expectation of 120°, and the three angles sum
to 359.9°. The Cu atom is slightly displaced from the basal
˚
trigonal plane by 0.03 A, which is within those measured
˚
˚
for 1 (0.01 A) and 2 (0.08 A). The mean Cu–P distance of
˚
2.24 A is same as 1, but is slightly shorter than the tetrahe-
þ
˚
˚
ecule. The molecular cation consists of two CuðPCHOÞ2
dral complexes 4 (2.28 A) and 6 (2.27 A). The pyridine ring
is about perpendicular to the CuP2 plane with a dihedral
angle of 88°. Each benzaldehyde group is planar with the
formyl oxygen pointing to the copper center. However,
groups with each chelated by two nitrogen atoms of the
bridging bptz ligand in a commonly encountered anti ori-
entation [18], and the two Cu+ ions are separated by
ꢁ
Fig. 2. Molecular structure of 6. The BF4 anions have been artificially omitted. Only the ipso carbons of the C6H5 groups are shown for clarity. The N3
˚
atom is disordered at its site. Selected bond distances (A) and bond angles (°):Cu–P1 2.281(2), Cu–P2 2.250(2), Cu–N1 2.087(4), Cu–N2 2.095(4), C7–O1
1.205(7), C26–O2 1.214(8), Cuꢀ ꢀ ꢀO1 3.00, Cuꢀ ꢀ ꢀO2 3.02 and P1–Cu–P2 128.57(6), N1–Cu–N2 77.7(2), P1–Cu–N1 112.6(1), P1–Cu–N2 110.3(1), P2–Cu–
N1 111.0(1), P2–Cu–N2 114.6(1), Cu–P1–C13 119.5(2), Cu–P2–C32 114.5(2), C27–C26–O2 125.6(5), C8–C7–O1 124.6(6).

662
W.-Y. Yeh et al. / Inorganica Chimica Acta 359 (2006) 659–664
ꢁ
Fig. 3. Molecular structure of 5. The BF4 anions have been artificially omitted. Only the ipso carbons of the C6H5 groups are shown for clarity. Selected
˚
bond distances (A) and bond angles (°): Cu–P1 2.2386(7), Cu–P2 2.2397(6), Cu–N1 1.996(2), C12–O1 1.207(3), C31–O2 1.218(3), Cuꢀ ꢀ ꢀO1 2.67, Cuꢀ ꢀ ꢀO2
2.83 and P1–Cu–P2 124.85(2), P1–Cu–N1 116.59(6), P2–Cu–N1 118.50(6), Cu–N1–C1 124.0(2), Cu–N1–C5 119.6(2), Cu–P1–C6 111.69(8), Cu–P2–C25
117.84(7), C30–C31–O2 124.6(3), C11–C12–O1 125.8(2).
the two benzaldehyde rings are not in close proximity,
while they are parallel and have a van der Waals type inter-
action in 1, 2, 4 and 6. Such difference is reflected to the
O1ꢀ ꢀ ꢀCuꢀ ꢀ ꢀO2 angle, which is 115.7° for 1, 108.8° for 2,
113.8° for 4 and 114.9° for 6, but is 169.7° for 5. The
O1ꢀ ꢀ ꢀCu distance (2.67 A) and O2ꢀ ꢀ ꢀCu distance (2.83 A)
are much shorter than those in 4 and 6 and could suggest
a certain extent of dipole–ion interaction [20].
In conclusion, our studies have provided a useful range
of structural data for [Cu(PCHO)2X] complexes, in which
X presents P- or N-donor ligands with different steric pro-
files. It is promising that, by selective oxidation of the Cu+
ions, the dinuclear complexes 5 and 6 might provide simple
models for the study of the magnetic interaction of un-
paired d electrons [21]. The investigation is progressive in
our laboratory.
20 ml Schlenk tube. The solution was gently heated to re-
flux for 40 min and then cooled to ambient temperature
to produce an orange precipitate. The mixture was filtered,
and the solid was extracted with dichloromethane. The
dichloromethane solution was carefully layered with
diethyl ether to afford [Cu(PCHO)2(2,20-bipy)][BF4] (4)
(15 mg, 56%) as an air-stable, orange-yellow crystalline so-
lid. Anal. Calc. for C48H38BCuF4N2O2P2: C, 64.99; H,
4.32; N, 3.16. Found: C, 65.25; H, 4.30; N, 3.01%. Mass
(FAB): m/z 799 (Cu(PCHO)2(2,20-bipy)+; 63Cu). 1H
NMR (CD2Cl2, 25 °C): d 9.51 (s, 2H, CHO), 8.84 (d, 2H,
JH–H = 5 Hz, bipy), 8.31 (d, 2H, JH–H = 8 Hz, bipy), 8.05
(m, 2H, bipy), 7.40 (m, 2H, bipy), 7.65–6.82 (m, 28H,
Ph). 31P{1H} NMR (CD2Cl2, 25 °C): d 4.51 (br). IR
(CH2Cl2, cmꢁ1): 1690 (C@O).
˚
˚
3.3. Preparation of 5
3. Experimental
Compound 1 (45 mg, 0.06 mmol), 4,40-bipyridine (5 mg,
0.03 mmol) and dichloromethane (3 ml) were placed in an
oven-dried 20 ml Schlenk tube. The solution was stirred
at ambient temperature for 8 h and carefully topped with
diethyl ether (10 ml). [Cu2(PCHO)4(4,40-bipy)][BF4]2 (5)
(41 mg, 63%) was obtained as air-stable, pale yellow crys-
tals. Anal. Calc. for C86H68B2Cu2F8N2O4P4: C, 63.84; H,
4.24; N, 1.73. Found: C, 64.05; H, 4.27; N, 1.68%. Mass
3.1. General methods
All manipulations were carried out under an atmosphere
of dinitrogen with standard Schlenk techniques. Com-
pound 1 [15] and bptz [22] were prepared by the literature
methods. 2,20-Bipyridine and 4,40-bipyridine were pur-
chased from Aldrich and used as received. The solvents
were dried over appropriate reagents under dinitrogen
1
63Cu). H NMR (CDCl3,
þ
(FAB): m/z 643 (CuðPCHOÞ2
;
and distilled immediately before use. H and 31P NMR
25 °C): d 9.82 (br, 4H, CHO), 8.52 (d, 4H, JH–H = 6 Hz,
bipy), 7.92 (d, 4H, bipy) 7.71–6.99 (m, Ph). 31P{1H}
NMR (CDCl3, 25 °C): d 1.77 (s). IR (CH2Cl2, cmꢁ1):
1674 (C@O).
1
spectra were obtained on a Varian Unity INOVA-500 spec-
trometer. Fast-atom-bombardment (FAB) mass spectra
were recorded on a JEOL JMS-SX102A mass spectrome-
ter. Elemental analyses were performed at the National Sci-
ence Council Regional Instrumentation Center at National
Chen-Kung University, Tainan, Taiwan.
3.4. Preparation of 6
Compound 1 (45 mg, 0.061 mmol) and bptz (7.2 mg,
0.031 mmol) were placed in a Schlenk flask under dinitro-
gen, and dichloromethane (5 ml) was introduced. The
resulting mixture was stirred at ambient temperature for
3 h, yielding a dark brown solution. The solution was
3.2. Preparation of 4
Compound 1 (22 mg, 0.03 mmol), 2,20-bipyridine (7 mg,
0.045 mmol) and THF (4 ml) were placed in an oven-dried

W.-Y. Yeh et al. / Inorganica Chimica Acta 359 (2006) 659–664
663
Table 1
Crystallographic data for 4–6
4
5
6
Formula
C48.75H39.5BCl1.5CuF4N2O2P2
C86H68B2Cu2F8N2O4P4
C91H74B2Cl6Cu2F8N6O4P4
Crystal system
Formula weight
T (K)
monoclinic
950.79
295
monoclinic
1618.00
150
triclinic
1952.84
150
ꢀ
Space group
P21/n
P21/c
P1
˚
a (A)
9.8664(2)
25.4346(4)
19.9104(3)
90
100.9735(9)
90
4905.1(2)
4
1.287
10.5686(4)
17.9957(7)
20.6877(8)
90
99.936(1)
90
3875.6(3)
2
1.387
13.072(1)
13.763(1)
14.896(1)
109.170(2)
90.921(2)
117.925(2)
2189.9(3)
1
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
Dcalc (Mg/m3)
1.481
0.814
l (mmꢁ1
)
0.646
0.703
Final R indices (I > 2r(I))
Goodness-of-fit on F2
0.0833/0.2487
1.023
0.0463/0.1110
1.035
0.0815/0.1838
1.210
diffused into diethyl ether (15 ml) to afford air-stable,
brown crystals of [Cu2(PCHO)4(bptz)][BF4]2 (6) (22 mg,
42%). Anal. Calc. for C88H68B2Cu2F8N6O4P4: C, 62.24;
Acknowledgment
We are grateful for support of this work by the National
Science Council of Taiwan.
H, 4.04; N, 4.95. Found: C, 63.02; H, 3.98; N, 4.90%. Mass
1
(FAB): m/z 761 (M2+
;
63Cu). H NMR (CD2Cl2, 25 °C): d
9.62 (br, CHO), 9.23–6.90 (m, Ph and bptz). 31P{1H} NMR
(CD2Cl2, 25 °C): d 5.63 (br). IR (CH2Cl2, cmꢁ1): 1688
(C@O).
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