Synthesis, characterization, and structure of dinuclear copper(I) and silver(I) complexes of ortho-functionalized 1,3-bis(aryl)triazenide ligands

Article abstract of DOI:10.1016/S0277-5387(02)01413-4

The synthesis, characterization, and crystal structures of dinuclear copper(I) and silver(I) complexes with a functionalized 1,3-diaryl triazenide ligand are reported. The triazene ligand is substituted with carboxymethyl groups in the ortho positions of the aryl rings that can coordinate to electron deficient metals. Reaction of this ligand with Cu(OAc) and Ag(OAc) resulted in the formation of dinuclear complexes with an eight-membered ring core composed of the two triazenide ligands and two metals. In these complexes, only one carbonyl group of each triazenide ligand binds to the metal centers.

Full text of DOI:10.1016/S0277-5387(02)01413-4

Polyhedron 22 (2003) 563Á568
/
www.elsevier.com/locate/poly
Synthesis, characterization, and structure of dinuclear copper(I) and
silver(I) complexes of ortho-functionalized 1,3-bis(aryl)triazenide
ligands
Gustavo R´ıos-Moreno a, Gerardo Aguirre a, Miguel Parra-Hake a,*, Patrick J. Walsh b,*
a Centro de Graduados e Investigacio´n, Instituto Tecnolo´gico de Tijuana, Apartado Postal 1166 22000 Tijuana, B.C., Mexico
b P. Roy and Diane T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania,
231 South 34th Street, Philadelphia, PA 19104-6323, USA
Received 25 June 2002; accepted 2 December 2002
Abstract
The synthesis, characterization, and crystal structures of dinuclear copper(I) and silver(I) complexes with a functionalized 1,3-
diaryl triazenide ligand are reported. The triazene ligand is substituted with carboxymethyl groups in the ortho positions of the aryl
rings that can coordinate to electron deficient metals. Reaction of this ligand with Cu(OAc) and Ag(OAc) resulted in the formation
of dinuclear complexes with an eight-membered ring core composed of the two triazenide ligands and two metals. In these
complexes, only one carbonyl group of each triazenide ligand binds to the metal centers.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Triazene; Triazenide; Copper(I) complex; Silver(I) complex; Dinuclear structure
1. Introduction
complexes with cooperative interactions have been made
in asymmetric hydroformylation [3Á8], lanthanide/main
group systems based on BINOL [9Á11], asymmetric
alkylation of aldehydes [12], and others [13Á28].
Our interests have been in the synthesis and char-
acterization of bimetallic complexes bearing triazenide
/
Cooperativity in heterogeneous catalysts can lead to
greatly increased reactivity and catalyst lifetimes [1,2].
Such benefits are often ascribed to the interaction of
metal centers held in close proximity in the solid state.
Due to challenges associated with the study of hetero-
geneous catalysts, a long-standing goal in catalysis has
been to develop homogeneous models for heterogeneous
catalysts. The simplest model systems for heterogeneous
catalysts are bimetallic complexes in which the two
metal centers have a synergistic effect and exhibit
reactivity not observed with the related mononuclear
complexes. Recent advances in catalysis using bimetallic
/
/
ligands [29Á31]. While such ligands are isoelectronic
/
with amidinate [32,33] and carboxylate ligands [34], their
chemistry has been considerably less explored. We
recently demonstrated that the functionalized ligand
1,3-bis(2-carboxymethyl)benzene triazene (1), which is
easily synthesized in one step from commercially avail-
able materials [35], enforces a dinuclear structure [31].
Reaction of 1 with Cu2(OAc)4×/2H2O in the presence of
base resulted in the formation of 2 as shown in Eq. (1)
[31].
Dinuclear complexes of this type are of considerable
interest because of the controversy over whether a
* Corresponding authors. Tel.: ꢀ
/
1-215-573-2875; fax: ꢀ1-215-573-
/
6743.
E-mail addresses: mparra@tectijuana.mx (M. Parra-Hake),
pwalsh@sas.upenn.edu (P.J. Walsh).
metalÁ
/
metal bond exists in these systems [36] and
because of their interesting photophysical properties
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(02)01413-4

564
G. R´ıos-Moreno et al. / Polyhedron 22 (2003) 563Á568
/
ð1Þ
[37,38]. With this in mind, we set out to synthesize the
Cu(I) and Ag(I) complexes of the ligand 1. Herein we
report the synthesis and structure of the dinuclear
bis(triazenide) complexes of copper(I) and silver(I). In
contrast to the Cu(II) structure of 2 (Eq. 1)) [31], where
the ligand binds in a bis(bidentate) fashion, in the Cu(I)
and Ag(I) complexes each ligand binds in a bidentate
fashion to one metal and a monodentate fashion to the
other in the solid state.
2. Results and discussion
The synthesis of copper and silver complexes of ligand
1 is shown in Eq. 2). Combination of a solution of
copper(I) acetate in acetonitrile with a mixture of
triazene 1 and triethylamine under a nitrogen atmo-
sphere resulted in the formation of a redÁbrown
/
microcrystaline compound, 3. Solid 3 was isolated by
filtration and found to be air-stable. Purification was
accomplished using column chromatography on florisil
in dichloromethane followed by crystallization to pro-
vide analytically pure 3 in 65% yield. The silver complex
4 was prepared in a similar fashion. An orange solution
of 1 with triethylamine was combined with silver acetate
in methanol. The reaction mixture was heated to 40 8C
for 10 min and cooled to room temperature (r.t.). On
standing, pale yellow crystals of 4 formed and were
isolated in 94% yield by filtration.
Fig. 1. Structure of 3. Bond distances and angles are given in Table 1.
The structure was determined and an ORTEP diagram is
illustrated in Fig. 1 with bond distances and angles
displayed in Table 1. Details of the structure are
compiled in Table 3. The structure consists of two
copper centers bridged by two triazenide ligands. A
single ester carbonyl group is coordinated to each
copper center, with one ester of each ligand remaining
unbound. The structure is similar to the Cu(I) dinuclear
ð2Þ
X-ray quality crystals of the copper complex were
grown from CH2Cl2 by slow evaporation of the solvent.
complex [Cu(PhNNNPh)]2 (5) [37,39] and related to the
tetrameric Cu(I) complex [Cu(ArNNNAr)]4 (6, Fig. 2,

G. R´ıos-Moreno et al. / Polyhedron 22 (2003) 563Á
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565
Table 1
Selected bond distances (A) and angles (8) for complex 3
˚
Cu(1)ꢀ
Cu(1)ꢀ
Cu(1)ꢀ
Cu(1)ꢀ
C(15)ꢀ
/
Cu(1A)
2.4289(12)
1.909(4)
1.905(4)
2.163(4)
1.205(6)
1.312(5)
1.300(5)
1.183(6)
/N(1)
/N(3)
/O(3)
/O(3)
N(2)ꢀ
N(1)ꢀ
C(13)ꢀ
/
N(3A)
/
N(2)
/
O(1)
N(1)ꢀN(2)ꢀ
Cu(1A)ꢀCu(1)ꢀ
O(3)ꢀC(15)ꢀO(4)
N(1)ꢀCu(1)ꢀ
N(1)ꢀCu(1)ꢀ
N(3)ꢀCu(1)ꢀ
Cu(1A)ꢀ
Cu(1A)ꢀ
/
/
N(3A)
113.3(4)
145.00(12)
120.4(5)
102.2(2)
169.8(2)
87.9(2)
/
/
O(3)
/
/
/
/
O(3)
N(3)
O(3)
/
/
/
/
/
Cu(1)ꢀ
Cu(1)ꢀ
/
N(1)
N(3)
85.69(12)
86.56(12)
/
/
Fig. 3. Structure of 4. Bond distances and angles are given in Table 2.
˚
range from 1.973(6) to 2.088(6) A (average 2.020 A) [41].
˚
Arꢁ
/
4-C6H4ꢀ
/
CF3), in which each ligand bridges two
˚
In 6 the Cuꢀ
[40]. The NꢀN distances in 3 of 1.300(5) and 1.312(5) A
are very close, as is often observed with triazenide
ligands bound to late metals. The CuꢀCu distances in 3,
5, 6, and 2 are 2.439(12), 2.451(8), 2.579(1), and 2.531(1)
/N distances are 1.882(7) and 1.883(6) A
different copper centers [40]. Both 3 and 5 have planar 8-
member cores formed by the two N3 units and the
˚
/
copper centers (Fig. 2). In 3 and 5 the Nꢀ
angles are 169.88 and 171.88, respectively, indicating
that there is only a small distortion in the CuÁtriazene
framework of 3 due to the coordination of the ester
carbonyl group. The carbonyl oxygens of 3 lie above
/
Cuꢀ/N bond
/
/
˚
A, all of which are shorter than Cuꢀ
/Cu distances found
˚
in copper metal (2.64 A).
The silver(I) complex 4 also crystallized to form X-ray
grade pale yellow crystals. A structure determination
study was performed on one of these crystals and an
ORTEP diagram is illustrated in Fig. 3. Selected bond
lengths and angles are listed in Table 2 and crystal-
lographic data are in Table 3. The structure of 4 has the
same gross features as that of 3. The eight-membered
ring formed by the triazenide ligands and silver atoms is
nearly planar, with the oxygen of the carbonyl above
and below the planar core with a Cuꢀ
O distance of the coordinated carbon-
˚
yl oxygen is slightly elongated (1.205(6) A) with respect
/
Cuꢀ
/
O angle of
145.0(1)8. The Cꢀ
/
˚
to the free carbonyl group (1.183(6) A), as expected. The
Cuꢀ
/
N(1) and Cuꢀ
/
N(3) distances in 3 are very similar at
˚
1.909(4) and 1.905(4) A, and can be compared to the
˚
N distance in 2 of 1.991(2) A [31] and those in 5 of
Cuꢀ
/
˚
1.898(18) and 1.939(18) A [39]. The copperÁ
/
nitrogen
distances in 3 are shorter than those of the dinuclear
copper(II) triazenide complex Cu2(PhNNNPh)4, which
and below the plane of the ring [Agꢀ
/
Agꢀ
/
Oꢁ134.0(2)8].
/
Fig. 2. Structures of related triazenide and amidinate complexes.

566
G. R´ıos-Moreno et al. / Polyhedron 22 (2003) 563Á568
/
Table 2
Selected bond distances (A) and angles ( ) for complex 4
The pendent methoxy groups in the amidinate 10 are
o
˚
bonded to the silver with distances of 2.691(5)Á
/
2.894(6)
O distances in 10 are long, they
˚
A. Although the Agꢀ
/
Ag(1)ꢀ
Ag(1)ꢀ
Ag(1)ꢀ
Ag(1)ꢀ
C(13)ꢀ
/
Ag(1A)
2.704(2)
2.165(7)
2.203(7)
2.475(6)
1.222(10)
1.297(9)
1.296(9)
1.205(11)
have been shown to provide thermal stability to the
/N(3)
/N(1)
complex [44]. The Agꢀ
/
O distance in 4 is considerably
/O(3)
˚
shorter at 2.475(6) A and we believe that this interaction
stabilizes the complex based on its high melting point
/O(3)
N(1)ꢀ
N(2)ꢀ
/
N(2)
(204Á205 8C).
/
/
N(3A)
The strong IR stretch of carbonyl groups can provide
information about the strength of the interaction of this
group with metal centers. The interpretation of the IR
C(15)ꢀ
N(1)ꢀN(2)ꢀ
Ag(1A)ꢀAg(1)ꢀ
O(3)ꢀC(13)ꢀO(4)
N(3)ꢀAg(1)ꢀ
N(1)ꢀAg(1)ꢀ
N(1)ꢀAg(1)ꢀ
Ag(1A)ꢀ
Ag(1A)ꢀ
/
O(1)
/
/
N(3A)
117.8(7)
134.0(2)
120.8(9)
113.6(2)
167.2(3)
75.0(2)
/
/
O(3)
/
/
data for compounds 1Á4, however, is not as straightfor-
/
/
/
O(3)
N(3)
O(3)
ward as that involving simple dative ligands for two
reasons: (1) on formation of a complex, the triazene
must be deprotonated, which will result in a change in
/
/
/
/
/
Ag(1)ꢀ
/
N(3)
N(1)
82.3(2)
84.9(2)
/
Ag(1)ꢀ
/
the Cꢀ
/
O stretching frequency; (2) each ligand binds to
two metal centers. The IR spectrum of the unbound
diester 1 (CH2Cl2) contains strong absorptions for the
carbonyl groups at 1725 and 1697 cmꢂ1. Compound 3
exhibits two stretches at 1714 and 1684 cmꢂ1 in CH2Cl2
and at 1700 and 1671 cmꢂ1 in KBr. In the KBr
spectrum of 3, we believe that one carbonyl oxygen is
coordinated to copper and one is free, as observed in the
solid state structure. Because of the similarity between
the solution and solid state IR spectra, we propose that
one of the carbonyl oxygens of each ligand is bonded in
solution. For the purposes of comparison, the IR
spectra of 2 (Eq. (1)) exhibited a single absorption for
the carbonyl group at 1694 cmꢂ1. In the silver complex
4, the carbonyl stretches were observed at 1727 and 1684
cmꢂ1 (KBr) suggesting analogous behavior to 3.
The structure is closely related to the silver triazenide
complex [Ag(PhꢀNNNꢀPh)]2 (7 [42], Fig. 2) and the
pyridine adduct [(Py)Ag(ArꢀNNNꢀAr)]2 (8, Arꢁ4-
C6H4ꢀOEt) [43] which have the same core structures.
A polymeric derivative, 9, in which each ligand bridges
two different metals, has also been reported [40]. A
related amidinate dinuclear (10), in which the amidinate
ligand contains Lewis basic groups that coordinate to
the silver has recently appeared in the literature [38,44].
/
/
/
/
/
/
The core structure of 10 is similar to 4 and 7 (Fig. 2).
˚
N distances in 4 of 2.165(7) and 2.203(7) A are
The Agꢀ
/
˚
slightly longer than those of 7 (2.155(3) and 2.144(4) A)
and those found in the polymeric structure 9 (2.121(6)
˚
and 2.104(7) A). The Agꢀ
/
Ag distances in 4, 7, 8, and 9
The copper and silver complexes 3 and 4 are
1
diamagnetic and amenable to NMR analysis. The H
˚
are 2.704(2), 2.669(1), 2.726(1), and 2.834(1) A, respec-
tively.
and 13C{1H} NMR spectra of both the copper and silver
complexes are indicative of a single ligand environment
with equivalent ester and aryl groups. The equivalence
of the esters in solution could be explained if the
coordinated ester and free ester exchange rapidly on
the NMR time scale. In the hopes of understanding the
solution structure, a sample of the copper dinuclear
Table 3
Crystal data and structure refinement parameters for 3 and 4
Compound
3
4
Empirical formula
FW
C16H14CuN3O4
375.84
C16H14AgN3O4
420.17
˚
a (A)
16.579(3)
10.699(3)
8.3983(8)
15.9952(13)
12.4553(11)
90
complex 3 was cooled to ꢂ80 8C in the probe of a 200
/
˚
b (A)
˚
MHz NMR spectrometer. No significant changes in the
spectra were observed under these conditions. The
analogous experiment with the silver derivative 4 was
not possible due to the sparing solubility of this
compound in most solvents, including DMSO-d6.
In summary, we have synthesized dinuclear copper(I)
and silver(I) complexes of the functionalized triazenide
ligand 1 and characterized these compounds by X-ray
crystallography. IR data indicate that in solution, like
the solid state structures, the metal has a single
coordinated carbonyl oxygen. Variable temperature
NMR experiments with the copper dinuclear 3 are
consistent with a rapid exchange of the bound and
unbound carbonyl oxygens.
c (A)
17.567(3)
90
a (o)
b (o)
g (o)
90
90
108.942
90
3
˚
V (A )
3115.9(11)
8
Pbca
1582.5(2)
4
P21/c
Z
Space group
T (8C)
21
21
˚
Radiation, l (A)
Dcalc (g cmꢂ3
m (mmꢂ1
Final R indices
[I ꢀ2s(I)]
Mo Ka, 0.710373
1.602
1.428
Mo Ka, 0.710373
1.764
1.300
)
)
a
R1ꢁ
wR2ꢁ
R1ꢁ0.1122
wR2ꢁ0.1222
/0.0471
R1ꢁ
wR2ꢁ
R1ꢁ0.1415
wR2ꢁ0.1285
/0.0622
/
/0.0931
/0.0988
R indices
/
/
(all data)
/
/
a
R1ꢁ
/
a½½Fo½ꢂ
/
½Fc½½/a½Fo½; wR2ꢁ
/
[a[w(Fo2ꢂ
/
Fc2)2]/a[w(Fo2)2]]1/2
.

G. R´ıos-Moreno et al. / Polyhedron 22 (2003) 563Á
/568
567
We are currently preparing other novel triazene
ligands and their transition metal complexes.
4. Supplementary material
Crystallogrpahic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, for 3: CCDC No. 187742; for 4: CCDC
No. 187741. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
3. Experimental
Road, Cambridge, CB2 1EZ, UK (fax: ꢀ44-1223-
336033; email: deposit@ccdc:ac:uk or www: http://
www.ccdc.cam.ac.uk).
/
3.1. Synthesis and characterization of 3
Under an inert atmosphere, an acetonitrile solution of
ligand 1 [35] (0.085 g, 0.272 mmol, 1 equiv.) and
triethylamine (0.0412 g, 0.408 mmol, 1.5 equiv.) was
added to a stirred acetonitrile solution of Cu(OAc)
(0.050 g, 0.408 mmol, 1.5 equiv.). After mixing was
complete, a brown precipitate formed. The reaction
mixture was filtered to obtain a reddish brown micro-
crystalline solid, found to be air stable. The crude
product was purified by column chromatography (flor-
isil, CH2Cl2) and crystallized by slow evaporation from
Acknowledgements
This work was supported by Consejo Nacional de
Ciencia y Tecnolog´ıa (CONACYT) for Grant 36435-E
and support for GRM in the form of a fellowship and
CONACYT Proyecto Infraestructura (F264-E9207) for
funding of an X-ray diffractometer for Instituto Tecno-
lo´gico de Tijuana.
CH2Cl2. Yield (100.1 mg, 0.1333 mmol, 65.6%). M.p.ꢁ
239Á241 8C; IR(KBr): 2947, 1700, 1671, 1340, 1307,
1256, 1204, 1080, 765 cmꢂ1; (CH2Cl2): 1714, 1684, 1596,
1568, 1477, 1437, 1341 cmꢂ1 1H NMR (500 MHz,
CD2Cl2, 298 K): d 7.80 (dd, J1ꢁ7.8 Hz, J2ꢁ1.3 Hz,
1H), 7.55 (dd, J1ꢁ8.3, J2ꢁ0.7 Hz, 1H), 7.41 (dt, J1ꢁ
8.4 Hz, J2ꢁ1.5 Hz, 1H), 7.08 (dt, J1ꢁ7.1 Hz, J2ꢁ1.0
Hz, 1H), 3.43 (s, 3H) ppm; 1H NMR (200 MHz,
CD2Cl2, 193K): d 7.86 (d, Jꢁ7.7 Hz, 1H), 7.58 (d,
Jꢁ7.9 Hz, 1H), 7.50 (t, Jꢁ7.5 Hz, 1H), 7.16 (t, Jꢁ7.7
/
/
;
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/
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3 equiv.) and a solution of Ag(OAc) (0.100 g, 0.599
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1307, 1256, 1189, 1157, 1080, 767 cmꢂ1
[(CD3)2SO, 500 MHz, 298 K]: d 7.58 (dd, J1ꢁ
J2ꢁ1.0 Hz, 1H), 7.52 (dd, J1ꢁ8.1 Hz, J2ꢁ1.2 Hz,
1H), 7.48 (dt, J1ꢁ8.2 Hz, J2ꢁ1.34 Hz, 1H), 7.15 (dt,
J1ꢁ7.6 Hz, J2ꢁ
1.5 Hz, 1H), 3.58 (s, 3H) ppm; 13C
/
204Á
/
205 8C. IR(KBr): 2949, 1727, 1684, 1347,
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7.7 Hz,
;
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131.5, 129.6, 123.4, 123.3, 123.2, 51.7 ppm; Elemental
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10.00; Found: C, 45.35, H, 3.13, N, 9.87%.
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