Versatile nuclearity in copper complexes with ortho functionalized 1,3-bis(aryl)triazenido ligands

Article abstract of DOI:10.1016/j.ica.2009.11.014

The synthesis, characterization and crystal structures of three new copper complexes derived from 1,3-bis(aryl)triazenido ligands bearing either a methoxycarbonyl, methylthio or a hydroxymethyl group in the ortho position of one of the aromatic rings are reported. In addition to the coordination of the triazenido fragment, the Lewis basic groups coordinate to the copper centers to form complexes with different nuclearity: {1-[2-(methoxycarbonyl)phenyl]-3-[4-methylphenyl]}triazene and {1-[2-(methylthio)phenyl]-3-[4-methylphenyl]}triazene form stable dinuclear and tetranuclear Cu(I) complexes, respectively. Reaction of {1-[2-(hydroxymethyl)phenyl]-3-[4-methylphenyl]}triazene with either Cu(I) or Cu(II) results in a novel Cu(II) hexanuclear macrocyclic complex.

Full text of DOI:10.1016/j.ica.2009.11.014

Inorganica Chimica Acta 363 (2010) 1150–1156
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Versatile nuclearity in copper complexes with ortho functionalized
1,3-bis(aryl)triazenido ligands
Juan José Nuricumbo-Escobar a, Carlos Campos-Alvarado a, Fernando Rocha-Alonso a,
Gustavo Ríos-Moreno b, David Morales-Morales c, Herbert Höpfl d, Miguel Parra-Hake a,
*
a Centro de Graduados e Investigación, Instituto Tecnológico de Tijuana, Apartado Postal 1166, Tijuana, B.C. 22000, Mexico
b Unidad Académica de Ciencias Químicas, Universidad Autónoma de Zacatecas, Campus Siglo XXI. Carretera a Guadalajara Km. 6, Ejido La Escondida, Zacatecas 98160, Mexico
c Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior Cd. Universitaria Coyoacán, México D.F. 04510, Mexico
d Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Cuernavaca 62209, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 July 2009
Received in revised form 23 October 2009
Accepted 8 November 2009
Available online 17 November 2009
The synthesis, characterization and crystal structures of three new copper complexes derived from 1,3-
bis(aryl)triazenido ligands bearing either a methoxycarbonyl, methylthio or a hydroxymethyl group in
the ortho position of one of the aromatic rings are reported. In addition to the coordination of the triazen-
ido fragment, the Lewis basic groups coordinate to the copper centers to form complexes with different
nuclearity: {1-[2-(methoxycarbonyl)phenyl]-3-[4-methylphenyl]}triazene and {1-[2-(methylthio)phenyl]-
3-[4-methylphenyl]}triazene form stable dinuclear and tetranuclear Cu(I) complexes, respectively. Reac-
tion of {1-[2-(hydroxymethyl)phenyl]-3-[4-methylphenyl]}triazene with either Cu(I) or Cu(II) results in a
novel Cu(II) hexanuclear macrocyclic complex.
Dedicated to Prof. Jonathan R. Dilworth
Keywords:
Triazenido ligands
Copper(I)
Ó 2009 Elsevier B.V. All rights reserved.
Copper(II)
Polynuclear complexes
Coordination macrocycle
1. Introduction
line or soft metals can be modulated by the choice of hard, but
weakly coordinating groups such as the methoxycarbonyl [8–11]
An approach toward the synthesis of complexes that exhibit
new chemical and physical properties is the design of ligands that
can be easily functionalized in order to modify the metal coordina-
tion sphere. A class of ligands that has attracted our attention are
1,3-bis(aryl)triazenides, since they exhibit a variety of bonding
modes with distinct properties [1,2]. Triazenido ligands can bind
through a single nitrogen to form monomeric complexes, through
chelation to form bidentate complexes, or through bridging be-
tween two metal centers to form metallacycles or infinite coordi-
nation polymers (Fig. 1) [3,4]. 1,3-Bis(aryl)triazenido ligands
(ArNNNAr)ꢀ are ‘‘short-bite” ligands when compared with the
more common (ArNCXAr)ꢀ (X = N, O, S) analogues [5]. It can be ex-
pected that the incorporation of donor groups (X) at the ortho posi-
tion of the 1,3-bis(aryl)triazenido ligands produces a markedly
different coordination chemistry. Thus, we have turned our atten-
tion to the application of 1,3-bis(aryl)triazenido ligands bearing Le-
wis basic ortho substituents [6,7], expecting that they form
additional chelate rings with the metal center and change their
coordination environment. The coordination properties of border-
and the hydroxymethyl group [11], or the choice of softer, but
more electron-donating substituents, such as the thiomethyl group
[11]. These weakly coordinating groups can behave as hemilabile
ligands [12], and allow for the generation of a free coordination site
for substrate activation, thus providing complexes with potential
catalytic applications.
In previous contributions we have reported the synthesis and
structures of Cu(I) and Pd(I) complexes with such ligands. Both
complexes are dinuclear with an almost planar 8-membered ring,
which consists of two N3 units and the metal centers (Fig. 2a)
[9,11]. Triazenido ligands form also tetranuclear complexes with
d10 metal ꢀions, in which the metal centers are linked exclusively
by the N3 fragments, thus forming a cage-like system (Fig. 2b)
[13,14].
In this paper, we report on the synthesis and structure of copper
complexes bearing 1,3-bis(aryl)triazenido ligands with a Lewis ba-
sic substituent in the ortho position of one of the aromatic rings
(Fig. 3). Depending on the nature of the ortho substituent, these
triazenes gave rise to dinuclear and tetranuclear copper(I) com-
plexes, and a hexanuclear copper(II) complex. We are unaware of
previously characterized macrocyclic hexanuclear copper com-
plexes with triazenido ligands.
* Corresponding author. Tel.: +52 664 6234043; fax: +52 664 6233772.
E-mail address: mparra@tectijuana.mx (M. Parra-Hake).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.11.014

J.J. Nuricumbo-Escobar et al. / Inorganica Chimica Acta 363 (2010) 1150–1156
1151
for elemental analyses were dried at room temperature under vac-
uum for at least 24 h.
Ar
N
Ar'
Ar
N
Ar'
Ar
N
Ar'
Ar
N
Ar'
N
N
N
N
H
N
N
N
N
M
MLn
LnM
MLn
Ln
2.2. Ligands
Fig. 1. A generic triazene and binding modes of triazenido ligands.
2.2.1. {1-[2-(hydroxymethyl)phenyl]-3-[4-methylphenyl]}triazene (3)
2-Aminobenzyl alcohol (500 mg, 4.1 mmol, 1 equiv.) dissolved
in water (5 mL) was mixed with 1 M HCl (5 mL, 12.3 mmol, 3
equiv.) at 0 °C, whereupon an aqueous solution (15%) of sodium ni-
trite (428 mg, 6.2 mmol, 1.5 equiv.) was added dropwise with stir-
ring. Once the amine was dissolved, a 15% solution of p-toluidine in
ethanol (439 mg, 4.1 mmol, 1 equiv.) was added at 0 °C, and the
resulting solution stirred for 30 min. Then, the reaction mixture
was neutralized with a 15% aqueous solution of NaOAc (32 mL)
to give a yellow precipitate, which was filtered and dried over
MgSO4. The product was purified by crystallization at ꢀ4 °C from
a 9:1 ethyl acetate/hexane solvent mixture to obtain a yellow crys-
talline solid (459 mg, 1.9 mmol, 46%). Mp = 90–92 °C. IR (KBr):
Since reports on catalytic applications of triazenido complexes
are rather scarce [15–17], we were also interested in exploring
the catalytic activity of our complexes. For this purpose, we se-
lected the cyclopropanation of styrene with ethyl diazoacetate
and examined the catalytic activity as a function of the complex
nuclearity and S/C (substrate/catalyst ratio).
2. Experimental
2.1. General remarks
3435, 3244, 2911, 1590, 1521, 1401, 1249, 1203, 1009, 813 cmꢀ1
.
Reactions with copper(I) were performed under argon atmo-
sphere, while those with copper(II) were realized under air. Unless
otherwise specified all chemicals were purchased from Aldrich
Chemical Co. and used without further purification. Copper(II)
acetate was purchased from MCB, and copper(I) acetate was
purchased from Strem. {1-[2-(methoxycarbonyl)phenyl]-3-[4-
methylphenyl]}triazene (1) and {1-[2-(methylthio)phenyl]-3-[4-
methylphenyl]}triazene (2) were synthesized according to
previously reported procedures [11]. NMR spectra were recorded
on Varian Gemini 200-BB FT equipment. 1H NMR (200 MHz) and
13C{1H} NMR (50 MHz) data are reported in ppm relative to Me4Si
as an internal standard. Coupling constants J are given in Hertz
(Hz). IR spectra were recorded on a Perkin–Elmer 1605 FT-IR spec-
trophotometer. UV–vis absorption spectra were determined on a
HP 8452A diode array spectrophotometer. Melting points were
measured in a Gallenkamp apparatus and are uncorrected. EI mass
spectra were obtained with a HP 5989 MS engine and HR-MS with
an Agilent LCTOF(2006), a high resolution TOF analyzer with win-
dows XP based OS and APCI/ESI ionization. Elemental analyses
were performed at NuMega Resonance Labs (San Diego). Samples
1H NMR (CDCl3, 200 MHz, 25 °C): d 7.66 (dd, J = 8.2, 1.2 Hz, 1H,
Ar), 7.31 (dt, J = 8.6, 1.8 Hz, 3H, Ar), 7.17 (m, 3H, Ar), 7.06 (dt,
J = 7.2, 1.2 Hz, 1H, Ar), 4.77 (s, 2H, –CH2), 2.33 (s, 3H, Ar–CH3).
13C{1H} NMR (CDCl3, 50 MHz, 25 °C): d 135.8 (CAr–N), 134.8 (CAr
–
N), 129.8 (2 CAr–H), 129.6 (CAr–H), 129.0 (CAr–H), 128.9 (C–CH3),
124.2 (CAr–H), 122.3 (C–CH2), 118.7 (CAr–H), 117.7 (CAr–H), 115.9
(C–CH3), 63.8 (–CH2), 21.0 (Ar–CH3). EIMS [m/z (%)]: 241 (8) [M]+,
119 (50) [M+-N2(C6H4)CH3], 91 (100) [M+-N3(C6H4)CH2OH].
2.3. Complexes
2.3.1. [Cu{H3C-p-(C6H4)-NNN-(C6H4)-o-COOCH3}]2 (4)
{1-[2-(Methoxycarbonyl)phenyl]-3-[4-methylphenyl]}triazene
(1) (149 mg, 0.555 mmol, 1 equiv.) was dissolved in CH3CN (5 mL)
and triethylamine (112 mg, 1.109 mmol, 2 equiv.) was added with
stirring. Then, a solution of Cu(OAc) (68 mg, 0.555 mmol, 1 equiv.)
in CH3CN (5 mL) was slowly added and the mixture stirred for
10 min at room temperature. A red-orange precipitate formed,
which was filtered to obtain a reddish microcrystalline air-stable
O
Ar
N
H3CO
Ar
N
N
N
N
N
M
N
N
Ar
N
Cu
Cu
N
O
OCH3
M
Ar
C
C
H3CO
O
N
Cu
Cu
N
N
Ar
N
N
N
N
Ar
OCH3
Ar
N
O
Ar
(a) M= Cu(I), Ag(I), Pd(I)
(b) Ar= 4-C6H4-CF3
Fig. 2. With d10 metal ions triazenido ligands form (a) dinuclear and (b) tetranuclear complexes.
N
N
N
N
N
N
N
H
N
N
H
H
SCH3
OCH3
O
HO
1
2
3
Fig. 3. Ortho functionalized triazenes 1–3 explored in this contribution for the formation of copper complexes.

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J.J. Nuricumbo-Escobar et al. / Inorganica Chimica Acta 363 (2010) 1150–1156
solid. Recrystallization by vapor diffusion of hexane into a concen-
trated solution of the product in CH2Cl2 at room temperature gave
red crystals, which were suitable for X-ray diffraction analysis
(149 mg, 0.224 mmol, 81%). Mp = 200–205 °C. IR (KBr): 2952,
4.70, N: 14.03%. HRMS Calc. for C84H78Cu6N18O6: 1812.2128.
Found: 1812.2020.
2.3.4. X-ray crystallography
1676, 1562, 1476, 1357, 1200, 753 cmꢀ1
.
UV–vis (CH2Cl2,
X-ray diffraction studies were performed on Bruker-APEX dif-
1.20 ꢁ 10ꢀ3 M): k
(e) 222 (1017), 324 (3402), 394 (3300), 458
fractometers equipped with
a
CCD area detector (kVo
=
Ka
(3000), 486 nm (2824 mL cmꢀ1 molꢀ1). 1H NMR (CDCl3, 200 MHz,
25 °C): d 7.99–7.89 (m, 2H, Ar), 7.70–7.76 (m, 2H, Ar), 7.57–7.42
(m, 6H, Ar), 7.20–7.07 (m, 6H, Ar), 3.78 (s, 6H, –O–CH3), 2.36 (s,
6H, Ar–CH3). Anal. Calc. (%) for C30H28Cu2N6O4: C: 54.29, H; 4.25,
N: 12.66. Found: C: 54.50, H; 4.64, N: 12.91%. HRMS Calc. for
C30H28Cu2N6O4: 662.0764. Found: 662.0743.
0.71073 Å, monochromator: graphite). Frames were collected at
T = 293 K (compound 4), T = 291 K (compound 5) and T = 100 K
(compound 6) via
[18]. The measured intensities were reduced to F2 and corrected
for absorption with SADABS SAINT-NT) [19]. Corrections were
xu-rotation at 10 s per frame (BRUKER-SMART)
(BRUKER-
made for Lorentz and polarization effects. Structure solution,
refinement and data output were carried out with the BRUKER SHEL-
XTL-NT program package [20,21]. Non-hydrogen atoms were refined
anisotropically, while hydrogen atoms were placed in geometri-
cally calculated positions using a riding model. The crystal struc-
2.3.2. [Cu{H3C-p-(C6H4)-NNN-(C6H4)-o-SCH3}]4 (5)
Complex 5 was prepared in the same manner as 4 using tria-
zene 2 to obtain a reddish microcrystalline solid that was first puri-
fied by column chromatography (florisil, CH2Cl2). Then, the product
was crystallized by vapor diffusion of pentane into a concentrated
solution of the product in CH2Cl2 at room temperature to give or-
ange crystals suitable for X-ray diffraction analysis (34 mg,
0.054 mmol, 55%). Mp = 199–201 °C. IR (KBr): 2919, 1576, 1462,
ture of compound
6 contains slightly disordered solvent
molecules (pentane), of which one is localized on a special position
(occ = 0.50). For their refinement DFIX, DANG, SIMU and DELU
instructions were used to constrain bond lengths, bond angles
and anisotropic displacement parameters.
A summary of selected crystallographic data and refinement
parameters for the structural analyses is given in Table 1.
1350, 1210, 819, 748 cmꢀ1. UV–vis (CH2Cl2, 9.53 ꢁ 10ꢀ4 M): k (
e)
272 (1421), 316 (4299), 398 (4215), 442 nm (4081 mL
cmꢀ1 molꢀ1). 1H NMR (CDCl3, 200 MHz, 25 °C): d 7.84–6.88 (m,
16H, Ar), 2.37 (s, 3H, Ar–CH3), 2.25 (s,3H, –SCH3), 2.24 (s, 3H, Ar–
CH3), 2.18 (s, 3H, –SCH3). Anal. Calc. (%) for C56H56Cu4N12S4: C:
52.57, H; 4.41, N: 13.14. Found: C: 52.40, H; 4.65, N: 13.22%. HRMS
Calc. for C56H56Cu4N12S4: 1279.5890. Found: 1280.0774.
2.4. Catalytic reactions
2.4.1. General procedure
Under argon, 2.8 mL of a solution containing 114 mg of ethyl
diazoacetate (1 mmol) in 1,2-dichloroethane were added during a
time period of 6 h via a syringe pump to 2 mL of a solution of the
catalyst and styrene (1 mL, 8.7 mmol) in 1,2-dichloroethane at
60 °C. After complete addition, the reaction mixture was stirred
at 60 °C for a further 16 h to ensure complete reaction. The mixture
was then cooled to room temperature, and purified through a short
silica gel plug, whereupon the solvent and unreacted styrene were
eliminated under reduced pressure. Yields were determined by GC
2.3.3. [Cu{H3C-p-(C6H4)-NNN-(C6H4)-o-CH3O}]6 (6)
Complex 6 was prepared in the same manner as 4 using ligand
3, to obtain an amber green microcrystalline solid, which was puri-
fied by column chromatography (florisil, CH2Cl2). The resultant
product was crystallized by vapor diffusion of pentane into a con-
centrated solution of the product in CH2Cl2 at room temperature to
give amber-green crystals suitable for X-ray diffraction analysis
(97 mg, 0.160 mmol, 68%). Mp > 300 °C. IR (KBr): 2919, 2832,
1598, 1578, 1504, 1370, 1215, 1034, 813, 754 cmꢀ1. UV–vis
(column b™-DEX 120, 30 ꢁ 0.25 mm ꢁ 0.25
lm, column tempera-
ture 110 °C, isothermally).
(CH2Cl2, 3.90 ꢁ 10ꢀ4 M): k
(e) 246 (3143), 334 (10030), 336
(9367), 390 nm (8712 mL cmꢀ1 molꢀ1). Anal. Calc. (%) for
3. Results and discussion
3.1. Syntheses and general characterization
3.1.1. Ligand 3
C84H78Cu6N18O6: C: 55.53, H; 4.33, N: 13.88. Found: C: 55.92, H;
Table 1
Crystallographic data and refinement parameters for compounds 4–6.
Triazenes 1 and 2 were synthesized according to previously re-
ported procedures [11], while triazene 3 was synthesized following
a modified literature procedure, which consisted in the diazotiza-
tion of 2-aminobenzyl alcohol with sodium nitrite, followed by
coupling with p-toluidine [11]. Triazene 3 was isolated in 93% yield
after crystallization from a 9:1 ethyl acetate/hexane solvent mix-
ture at ꢀ4 °C.
Compounds
4
5
6
Empirical
formula
Formula
weight
Crystal system Monoclinic
Space group
a (Å)
b (Å)
c (Å)
C30H28Cu2N6O4 C56H56Cu4N12S4 C84H78Cu6N18O6ꢂ3C5H12
663.66
1279.53
2033.32
Triclinic
P1
Tetragonal
P41212
17.0900(12)
17.0900(12)
33.542(3)
90
ꢀ
P21/c
The IR spectrum shows a broad band at 3435 cmꢀ1 for the OH
group and a single band at 3244 cmꢀ1 for the NH group of the tria-
zene fragment. The N3 system gave a band at 1590 cmꢀ1. The 1H
NMR spectrum shows two singlets in the aliphatic region, one inte-
grates for three protons at 2.33 ppm and is assigned to the p-tolyl
methyl group; the second singlet at 4.77 ppm integrates for two
protons and is assigned to the methylene group of the hydroxy-
methyl function. In the aromatic region there are four groups of
signals in the region from 7.06 to 7.66 ppm, which integrate for 8
hydrogen atoms. The 13C{1H} NMR spectrum shows a signal at
21.0 ppm for the p-tolyl methyl group, a signal at 63.8 ppm for
the methylene group of the hydroxymethyl function and signals
for 12 carbon atoms in the aromatic region (for assignation see Sec-
tion 2). EIMS confirms the molecular weight (241) for triazene 3.
4.030(1)
18.885(6)
18.184(5)
90
91.641(6)
90
1383.4(7)
2
1.593
293(2)
Mo K
1.586
0.0947
0.1004
12.9948(8)
14.5166(9)
16.659(1)
70.141(1)
72.990(1)
75.873(1)
2789.5(3)
2
a
(°)
b (°)
90
90
c
(°)
V (Å3)
Z
9796.7(14)
4
1.379
qcalc (g cmꢀ3
T (K)
)
1.523
291(2)
100(2)
k (Å)
a
0.71073 Mo K
a
0.71073 Mo K
a 0.71073
l
(mmꢀ1
)
1.704
0.0684
0.0765
1.341
0.0471
0.1182
R (%)a
Rw (%)b
a
R1
wR2 = [
=
R
||Fo| ꢀ |Fc||/
R|Fo|.
b
2
R
[w(Fo ꢀ Fc2)2]/
R .
[w(Fo2)2]]1/2

J.J. Nuricumbo-Escobar et al. / Inorganica Chimica Acta 363 (2010) 1150–1156
1153
3.1.2. Copper complexes
of the 4-methylphenyl function. The signal pattern in the aromatic
region is complex and indicates the presence of four different aro-
matic rings. As shown by the X-ray diffraction analysis, this is due
to different copper coordination modes: one part is tetracoordinat-
ed and the second has a coordination number of two (vide infra).
Copper complexes 4–6 were prepared in dry acetonitrile by a
combination of copper(I) acetate with the corresponding triazene
(1–3) in the presence of triethylamine (see Eq. (1) for the synthesis
of 4, as an example). The products were isolated by filtration and
purification was accomplished either by simple crystallization (4)
or by column chromatography (florisil/dichloromethane) and sub-
sequent crystallization (5, 6) to provide analytically pure com-
pounds in 81%, 55% and 68% yield, respectively. Compounds 4
and 5 were obtained in form of a reddish microcrystalline material,
while compound 6 gave amber-green crystals. As shown by spec-
troscopic studies and X-ray diffraction analysis, these reactions
lead to complexes with different coordination geometries and
nuclearities. The nuclearity of the complexes is dependent on the
nature of the ortho function within the triazenido ligand. Thus,
from the methoxycarbonyl-functionalized ligand a dinuclear com-
plex (4) was obtained, while the ligands with methylthio and
hydroxymethyl substituents gave tetranuclear (complex 5) and
hexanuclear (complex 6) species.
3.2. Description of the crystal structures
The molecular structures of 4–6 have been determined by X-ray
diffraction and are shown in Figs. 4–6. The most relevant crystallo-
graphic data are summarized in Table 1. Selected bond lengths and
angles are listed in Tables 2–4.
In compound 4 two copper atoms are bridged by two triazenido
ligands, in which the carbonyl oxygen atoms of the pendent Lewis
basic ester functions are coordinated to the copper centers. The ab-
sence of counterions indicates that the oxidation state of the start-
ing metal complex has been preserved.
In the dimeric structure of the Cu(I) complex 4 each ligand
bridges two metal centers (Fig. 4). This structure is therefore re-
N
N
N
CH3CN
+
CuOAc
H3CO
ð1Þ
O
N
Cu Cu
O
OCH3
N
N
H
Et3N
N
N
N
O
OCH3
Copper(I), having a d10 configuration, is expected to exhibit dia-
magnetic behavior. Accordingly, complexes 4 and 5 are amenable
to NMR analysis. However, we were surprised to find that complex
6 showed no signals in the 1H NMR spectrum, which suggests a
paramagnetic behavior, and the possibility that a Cu(II) complex
had formed by an oxidation reaction. Although complex 6 was pre-
pared under argon atmosphere, the Cu(I) product could not be iso-
lated under such conditions; therefore crystallization was
performed under air, which may have provided the oxidation con-
ditions. Since the second ionization energy of copper is not exces-
sive [22], deprotonation of the ligand to a dianionic species could
have promoted the oxidation of copper(I) to form a more stable
Cu(II) complex. Complex 6 was also obtained when the reaction
of 3 was performed with copper(II) acetate in open air conditions.
The solid-state IR spectra of compounds 4–5 lack bands in the
region for the triazene NH group, indicating the formation of a
monoanionic tridentate ligand by deprotonation of the triazene
precursor. In the case of compound 6 there is also no signal for
the OH group, which indicates the formation of a neutral copper(II)
complex in this case. This was confirmed by the absence of coun-
terions in the X-ray structure. The IR spectrum of complex 4 exhib-
its a strong band for the carbonyl group at 1676 cmꢀ1, which is
shifted to a wavenumber of lower energy when compared to the
carbonyl group in the free triazene (1684 cmꢀ1), thus indicating
coordination to the metal center. The 1H NMR spectrum of 4 shows
the characteristic signals for the methoxycarbonyl group at
3.78 ppm and the 4-methylphenyl function at 2.36 ppm; the aro-
matic hydrogens appear as a set of unresolved multiplets in the
range 7.99–7.07 ppm integrating for 16 hydrogens.
lated to a series of Cu(I), Ag(I) and Pd(I) complexes containing
unsubstituted bis(aryl)triazenido ligands, [Cu(PhNNNPh)]2 and
[Ag(PhNNNPh)]2 [23,24], ortho functionalized triazenido ligands,
[M(ArNNNAr)]2 (M = Cu(I) and Ag(I); Ar = o-C6H4–COOCH3) [9]
and [PdI(ArNNNAr)]2, (Ar = o-C6H4–COOCH3; o-C6H4–OMe) [11],
and ortho functionalized amidinato ligands, [Ag(RNCPhNR)]2
(R = o-C6H4–COOCH3, o-C6H4–SCH3) [25]. Complex 4 has an almost
planar 8-membered core formed by the two N3 units and the cop-
per centers (Fig. 4). The trans nitrogen atoms exhibit a N–Cu–N
The 1H NMR spectrum of complex 5 shows two signals for the
methylthio group, one at 2.25 ppm and one at 2.18 ppm. There
are also two signals at 2.37 and 2.24 ppm for the methyl group
Fig. 4. ORTEP diagram showing the structure of compound
4 with thermal
ellipsoids at the 50% probability level and the atom labeling scheme. Hydrogens
are omitted for clarity.

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J.J. Nuricumbo-Escobar et al. / Inorganica Chimica Acta 363 (2010) 1150–1156
Table 2
Selected bond distances (Å) and angles (°) for compound 4.
Bond distances (Å)
Cu(1)–N(3)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–Cu(1)
N(1)–N(2)
N(2)–N(3)
C(1)–N(1)
C(8)–N(3)
C(7)–O(1)
1.907(3)
1.910(3)
2.272(3)
2.4755(11)
1.310(4)
1.306(4)
1.437(5)
1.427(5)
1.216(5)
1.330(5)
1.433(5)
C(7)–O(2)
C(15)–O(2)
Bond angles (°)
N(1)–N(2)–N(3)
N(1)–Cu(1)–N(3)
Cu(1)–Cu(1)–N(1)
Cu(1)–Cu(1)–N(3)
Cu(1)–Cu(1)–O(1)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
N(2)–N(3)–C(8)
N(2)–N(3)–Cu(1)
Cu(1)–O(1)–C(7)
115.8(3)
169.80(13)
85.68(10)
86.21(10)
140.61(9)
106.44(12)
83.77(11)
169.80(13)
111.4(3)
125.4(3)
117.4(3)
Fig. 5. ORTEP diagram showing the structure of compound
5 with thermal
ellipsoids at the 50% probability level and the atom labeling scheme. Hydrogens
are omitted for clarity.
NNNC6H4CF3)]4 [14], and [Ag(H3COC6H4NNNC6H4OCH3)]4 [26], in
which four triazenido ligands are bound to four copper atoms
forming a 16-membered folded-ring system with metal–nitrogen
bondings (Fig. 5). Complex 5 contains a tetranuclear copper core.
The Cuꢂ ꢂ ꢂCu distances in complex 5 are 2.6702(6), 2.7029(7),
2.8006(6) and 2.6500(6) Å for Cu(1)–Cu(2), Cu(1)–Cu(3), Cu(2)–
Cu(3) and Cu(3)–Cu(4), respectively, which are longer than the
Cuꢂ ꢂ ꢂCu distances found in [Cu(MeNNNMe)]4 at 2.66(1) Å [23],
[Cu(F3CC6H4NNNC6H4CF3)]4 at 2.579(1) Å [14] and in [Cu(FC6H4
NNNC6H4F)]4 at 2.6070(9) Å [27]. Cuꢂ ꢂ ꢂCu distances in 5 are in gen-
eral above the range of weak bonding interactions [27]. Complex 5
contains two types of copper centers; assuming no Cuꢂ ꢂ ꢂCu interac-
tions, the first has a coordination number of 2 with two nitrogen
atoms coordinated to the 14 electron copper(I) center, and the sec-
ond has a coordination number of 4 with two nitrogen atoms and
two sulfur atoms coordinated to an 18 electron metal center. Each
of the four-coordinate copper centers is embedded in two chelate
rings resulting from the coordination of one nitrogen atom and
one sulfur atom from each of the bridging triazenido ligands. The
Cu–S distances vary from 2.4751(11) to 2.5621(12) Å, and the
bond angle of 169.80(13)°, indicating a small distortion from pla-
narity of the Cu-triazenido framework due to the coordination of
the carbonyl ester group. As in the Pd(I), Cu(I) and Ag(I) analogues,
the coordinated carbonyl oxygens in 4 lie slightly above and
below the planar core with Cu–Cu–O angle of 140.61(9)°. The
Cu–N(1) and Cu–N(3) bond lengths in 4 are identical, 1.910(3)
and 1.907(3) Å and the Cuꢂ ꢂ ꢂCu distance, 2.4755(11) Å, is signifi-
cantly shorter than the Cuꢂ ꢂ ꢂCu distance found in copper metal
(2.64 Å).
In the molecular structure of compound 5 four copper atoms are
bridged by four alternating triazenido ligands. Additionally, the
pendent Lewis basic thiomethyl groups are coordinated to the cop-
per centers (Fig. 5). As in 4, the absence of counterions indicates
that the oxidation state of the starting copper(I) complex has been
preserved.
The structure of complex 5 is similar to that of the tetranuclear
Cu(I) and Ag(I) complexes [Cu(MeNNNMe)]4 [13], [Cu(F3CC6H4
Fig. 6. (a) ORTEP diagram showing the structure of compound 6 with thermal ellipsoids at the 50% probability level and the atom labeling scheme. Hydrogens and methyl
groups are omitted for clarity. (b) View of the hexanuclear core in complex 6.

J.J. Nuricumbo-Escobar et al. / Inorganica Chimica Acta 363 (2010) 1150–1156
1155
Table 3
Table 4
Selected bond distances (Å) and angles (°) for compound 5.
Selected bond distances (Å) and angles (°) for compound 6.
Bond distances (Å)
Cu(1)–N(1)
Cu(1)–N(10)
Cu(1)–S(1)
Cu(1)–S(4)
Cu(2)–N(6)
Cu(2)–N(12)
Cu(3)–N(3)
Cu(3)–N(9)
Cu(4)–N(4)
Cu(4)–N(7)
Cu(4)–S(2)
Cu(4)–S(3)
Cu(1)–Cu(2)
Cu(1)–Cu(3)
Cu(2)–Cu(3)
Cu(2)–Cu(4)
N(1)–N(2)
Compound 6
1.946(3)
1.918(3)
2.5621(12)
2.5161(11)
1.894(3)
1.901(3)
1.898(3)
1.905(3)
1.950(3)
1.937(3)
2.5112(11)
2.4751(11)
2.6702(6)
2.7029(7)
2.8006(6)
2.7340(6)
1.295(3)
1.294(3)
1.296(3)
1.297(3)
1.304(3)
1.304(3)
1.316(3)
1.300(3)
Bond distances (Å)
Cu(1)–N(4)
Cu(1)–N(6)
Cu(2)–N(1)
Cu(2)–N(9)
Cu(3)–N(7)
Cu(3)–N(3)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(2)–O(1)
Cu(2)–O(2)
Cu(3)–O(3)#1
Cu(3)–O(3)
Cu(1)–Cu(1)#1
Cu(1)–Cu(2)
Cu(2)–Cu(3)
Cu(3)–Cu(3)#1
N(1)–N(2)
1.966(4)
1.990(4)
1.947(4)
1.991(3)
1.948(3)
1.978(4)
1.916(3)
1.919(3)
1.921(3)
1.925(3)
1.917(3)
1.918(3)
2.9323(11)
3.0282(7)
2.7819(7)
2.9878(10)
1.307(5)
1.307(5)
1.291(6)
1.290(5)
1.291(6)
1.301(5)
1.289(5)
N(2)–N(3)
N(4)–N(5)
N(5)–N(6)
N(7)–N(8)
N(8)–N(9)
N(10)–N(11)
N(11)–N(12)
N(2)–N(3)
N(4)–N(5)#1
N(5)–N(6)
N(5)–N(4)
N(7)–N(8)
N(8)–N(9)
Bond angles (°)
Bond angles (°)
N(1)–Cu(1)–N(10)
Cu(2)–Cu(1)–S(1)
Cu(3)–Cu(1)–S(4)
N(10)–Cu(1)–S(4)
N(6)–Cu(2)–N(12)
N(6)–Cu(2)–Cu(1)
N(3)–Cu(3)–N(9)
N(3)–Cu(3)–Cu(4)
N(4)–Cu(4)–N(7)
S(2)–Cu(4)–Cu(2)
S(3)–Cu(4)–Cu(3)
N(4)–Cu(4)–Cu(3)
N(7)–Cu(4)–Cu(3)
N(1)–N(2)–N(3)
168.75(12)
121.70(3)
163.92(3)
83.30(8)
157.29(12)
106.64(8)
156.14(12)
109.77(8)
165.37(11)
146.18(3)
164.67(3)
92.28(8)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–N(4)
O(2)–Cu(1)–N(4)
O(1)–Cu(1)–N(6)
O(2)–Cu(1)–N(6)
O(1)–Cu(2)–O(2)
O(1)–Cu(2)–N(1)
O(2)–Cu(2)–N(1)
O(1)–Cu(2)–N(9)
O(2)–Cu(2)–N(9)
O(3)#1–Cu(3)–O(3)
O(3)#1–Cu(3)–N(7)
O(3)–Cu(3)–N(7)
O(3)#1–Cu(3)–N(3)
O(3)–Cu(3)–N(3)
N(4)–Cu(1)–N(6)
N(1)–Cu(2)–N(9)
N(7)–Cu(3)–N(3)
Cu(1)–O(1)–Cu(2)
Cu(1)–O(2)–Cu(2)
Cu(3)#1–O(3)–Cu(3)
75.89(12)
167.84(14)
92.89(14)
96.06(15)
160.91(16)
75.61(12)
89.98(14)
164.14(14)
165.18(14)
99.99(13)
76.96(14)
167.27(14)
90.56(13)
93.86(14)
161.78(14)
96.04(16)
95.59(15)
98.84(14)
104.3(5)
81.16(8)
115.4(3)
115.5(3)
115.0(3)
N(4)–N(5)–N(6)
N(7)–N(8)–N(9)
N(10)–N(11)–N(12)
Cu(3)–Cu(4)–Cu(2)
Cu(1)–Cu(2)–Cu(4)
Cu(1)–Cu(3)–Cu(4)
Cu(2)–Cu(4)–Cu(3)
Cu(2)–Cu(1)–Cu(3)
Cu(1)–Cu(2)–Cu(3)
Cu(4)–Cu(2)–Cu(3)
114.9(3)
62.663(17)
166.33(2)
118.13(2)
62.663(17)
62.825(17)
59.159(16)
57.200(16)
103.9(5)
102.3(5)
Symmetry transformations used to generate equivalent atoms: #1 ꢀy+1, ꢀx+1,
ꢀz+3/2.
Cu–N distances from 1.894(3) to 1.950(3) Å. The N–Cu–N bond
angles are 156.14(12) and 157.29(12)° for the two-fold coordi-
nated copper atoms, and 165.37(11) and 168.75(12)° for the
four-fold coordinated copper atoms. The deviations from ideal lin-
ear and tetrahedral coordination geometries can be attributed to
coordination requirements.
In complex 6 three-folded dinuclear units of the composition
{[Cu(ArNNNAr)]2} are bridged by the methoxy groups of the ortho
functionalized triazenido ligands to form an overall hexanuclear
macrocyclic complex (Fig. 6).
mation of the cycle (Table 4). The Cuꢂ ꢂ ꢂCu distances in the range
of 2.7819(7)–3.0282(7) Å are larger than in the dinuclear complex
4, 2.4755(11) Å, and the tetranuclear complex 5, 2.6702(6)–
2.8006(6) Å. The Cu–N bond lengths vary from 1.947(4) to
1.991(3) Å and are also larger than the corresponding bond lengths
in 4 (1.907(3)–1.910(3) Å) and in 5 (1.894(3)–1.950(3) Å). Cu–O
bond lengths in 6 are in the range of 1.916(3)–1.925(3) Å and com-
pare well with the tetranuclear alkoxo bridged triazenido complex
[Cu(FC6H4NNNC6H4F)(OCH3)]4 at 1.919(3)–1.926(3) Å [27]. Cu–O
bond lengths in 6 are also similar to those in related hydroxo
As already mentioned, the absence of counterions indicates that
the copper centers have oxidation state 2+. Each metal center has a
coordination number of 4, with a rather distorted square-planar
geometry. The distortion is indicated by the deviations from the
ideal angles of a square-planar geometry (180° and 90°) with the
trans O–Cu–N bond angles in the range of 160.91(16)–
167.27(14)°, and the cis O–Cu–O and N–Cu–N bond angles in the
range of 75.61(12)–76.96(14)° and 95.59(15)–98.84(14)°, respec-
tively. This should be due to ligand bond requirements upon for-
and alkoxo bridged copper complexes: tetrakis[(
l-hydroxo)
(l-sulfathiazolato)copper(II)]tetrakis(dimethylsulfoxide) at 1.901
(9)–1.923(9) Å [28] and a tetranuclear complex formed by N-2-
pyridylsalicylaldimine at 1.965(6)–1.971(6) Å [29]. Cu–O–Cu an-
gles in 6 are in the range 102.3(5)–104.3(5)°, slightly larger than
the angles in the alkoxo bridged triazenido complex [Cu(FC6H4
NNNC6H4F) (OCH3)]4 at 102.0(1)° [27] and the copper complex of
N-2-pyridylsalicylaldimine at 102.9(3)° [29], due to structure
requirements for a larger cycle.

1156
J.J. Nuricumbo-Escobar et al. / Inorganica Chimica Acta 363 (2010) 1150–1156
Table 5
Acknowledgements
Cyclopropanation of styrene with ethyl diazoacetate catalyzed by complexes 4–6a.
Entry
Catalyst
S/Cb
Yieldc
cis/trans ratio
This work was supported by Consejo Nacional de Ciencia y
Tecnología (CONACyT) Grant 60467 and Consejo del Sistema Nac-
ional de Educación Tecnológica (COSNET) Grant 486-02-P. The
authors are indebted to Professor Patrick J. Walsh for fruitful
comments on this research. Analytical support by Daniel Chávez
is gratefully acknowledged. J.J.N.-E., G.R.-M., C.C.-A. and F.R.-A.
thank CONACyT for graduate fellowships. C.C.-A. thanks ESET,
LLC for complementary financial support.
1
2
3
4
5
6
4
4
5
5
6
6
100:1
100:0.1
100:1
100:0.1
100:1
100:0.1
32
25
72
75
88
89
38:62
36:64
30:70
33:67
30:70
34:66
a
At 60 °C.
Relative to ethyl diazoacetate.
b,c
Appendix A. Supplementary material
3.3. Catalysis
CCDC 741827, 741828 and 741829 contain the supplementary
crystallographic data for 4, 5 and 6. 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 associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2009.11.014.
In a set of experiments to evaluate the potential catalytic
activity of our complexes, cyclopropanation of styrene with ethyl
diazoacetate (EDA) was performed as a function of the complex
nuclearity and S/C (substrate/catalyst ratio) (Eq. (2)). The typical
experimental procedure is described in Section 2 and the results
are illustrated in Table 5.
References
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Reported herein are the structures of three new copper com-
plexes (4–6), which have been derived from 1,3-bis(aryl)triazenido
ligands bearing different Lewis basic groups in the ortho position of
one of the aromatic rings. Due to the variation of the Lewis basicity
and steric requirements of the varying coordinating functions,
complexes with different nuclearity have been obtained. While
the methoxycarbonyl group in 4 and the methylthio group in 5 sta-
bilize copper in the 1+ oxidation state forming dinuclear and tetra-
nuclear complexes, the methyleneoxy group in complex 6 seems to
prefer oxidation state 2+ with the formation of a novel hexanuclear
macrocyclic complex. Although the results from the evaluation of
the catalytic activity of 4–6 are scanty, they do indicate that might
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