Coordination modes of N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine with copper (I) and (II) halides

Article abstract of DOI:10.1016/j.ica.2003.08.020

The title ligand, N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine, was prepared via a condensation-reduction synthetic route. The compounds, CuCl(C₁₉H₁₉N₃O) and [CuBr(C₁₉H ₁₉N₃O)]⁺Br^-·3H₂O, were readily synthesized from the reaction of CuCl or CuBr₂ and the ligand in acetonitrile. The title copper(I) compound is an O-H?Cl hydrogen-bonded linear chain of tetrahedrally coordinated copper centers, and the title copper(II) compound exists as two strongly tetragonally distorted dibromide bridged metal cations in a dimer with the phenol hydroxyl groups weakly bound in a trans-fashion to one of the bridging bromides. In the copper(I) complex the phenoxy group acts only as a hydrogen bond donor, whereas in the copper(II) complex it acts both as a ligand and a hydrogen bond donor.

Full text of DOI:10.1016/j.ica.2003.08.020

Inorganica Chimica Acta 357 (2004) 619–624
www.elsevier.com/locate/ica
Note
Coordination modes of
N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine
with copper (I) and (II) halides
*
Marilyn M. Olmstead, Timothy E. Patten , Christina Troeltzsch
Department of Chemistry, University of California, Davis One Shields Avenue, Davis, CA, 95616-5295, USA
Received 21 August 2003; accepted 30 August 2003
Abstract
The title ligand, N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine, was prepared via a condensation–reduction synthetic
route. The compounds, CuCl(C19H19N3O) and [CuBr(C19H19N3O)]þBrꢀ ꢁ 3H2O, were readily synthesized from the reaction of CuCl
or CuBr2 and the ligand in acetonitrile. The title copper(I) compound is an O–H ꢁ ꢁ ꢁ Cl hydrogen-bonded linear chain of tetrahe-
drally coordinated copper centers, and the title copper(II) compound exists as two strongly tetragonally distorted dibromide bridged
metal cations in a dimer with the phenol hydroxyl groups weakly bound in a trans-fashion to one of the bridging bromides. In the
copper(I) complex the phenoxy group acts only as a hydrogen bond donor, whereas in the copper(II) complex it acts both as a ligand
and a hydrogen bond donor.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Hydrogen bonding; Tetragonally distorted octahedral Cu(II) complexes; Tetrahedrally coordinated Cu(I) complexes; Tridentate and
tetradentate ligands
1. Introduction
During the course of our studies on using monoan-
ionic tetradentate ligands to prepare copper(I)-based
atom transfer radical polymerization catalysts, we in-
vestigated the complexation of a bis(picolyl)amine-
based ligand [10–12] to copper(I) and copper(II) halides.
Iron (III) [13,14], copper (II) [15,16], and zinc (II) [17,18]
complexes of the ligand, N-(2-hydroxyphenyl)methyl-
bis-(2-pyridylmethyl)amine, have been studied previ-
ously as models for the metal centers of purple acid
phosphatase, galactose oxidase, and alkaline phospha-
tase. The ligand itself has been used as a sensitizer for
esterase determination [19]. Here we report a new syn-
thesis of the ligand, and the synthesis and structures of
its complexes with copper(I) and (II) halides.
Copper coordination complexes have been studied as
small molecule analogs of metalloproteins that mediate
dioxygen activation, electron transfer, and transport
processes [1]. Recently, copper complexes of various
amine-based ligands have gained considerable interest as
catalysts for atom transfer reactions and controlled/‘‘liv-
ing’’ radical polymerizations [2–4]. Tri- and tetradentate
amine ligands, and in particular tripodal tetradentate
amine ligands, have shown a great deal of versatility and
practicality for ATRP catalysis purposes. In complexes of
copper(I) and copper(II) with tripodal tetradentate am-
ines, variations in several structural parameters, such as
chelate ring size and the nature of the donor group, were
found to have dramatic effects upon the structure, redox
potential and spectroscopic features of the corresponding
complexes [5–9].
2. Experimental
2.1. Materials
* Corresponding author. Tel.: +1-(530)-7546181; fax: +1-(530)-
7528995.
E-mail address: patten@indigo.ucdavis.edu (T.E. Patten).
CuCl (Acros) was purified until colorless by grinding
into a fine powder using a mortar and pestle, stirring in
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.08.020

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M.M. Olmstead et al. / Inorganica Chimica Acta 357 (2004) 619–624
glacial acetic acid, consecutive washes of absolute eth-
anol and diethyl ether, and removal of volatile materials
under vacuum. Acetonitrile was dried using appropriate
procedures, and standard Schlenk techniques were used
to prepared the copper(I) complex. Bis(2-pyridylm-
ethyl)ammonium tetrafluoroborate was prepared via the
addition of fluorboric acid to a solution of bis(2-pyr-
idylmethyl)amine in ethanol followed by filtration of the
white precipitate product. All other chemicals were
purchased from Acros and used without further purifi-
cation.
removed under vacuum. The solid was then stirred in
100 ml of CH3OH at 0 °C, and 0.349 g (9.23 mmol) of
NaBH4 was added in small portions. Once all of the
NaBH4 was added, then the solution was heated at re-
flux for 15 min. The solution was cooled, partitioned in
equal amounts of Et2O and H2O, and then the aqueous
layer was extracted using 3 ꢃ 50 ml of Et2O. The Et2O
layers were dried over Na2SO4 and then concentrated to
yield a yellow oil that crystallized over several days.
1
Yield: 1.12 g (51%); H NMR (300 MHz, CD3CN): d
(ppm) 8.54 (m, 2H), 7.71 (m, 2H), 7.34 (m, 2H), 7.2–7.1
(m, 4H), 6.78 (m, 2H), 3.84 (s, 4H), 3.78 (s, 2H), 2.21
(br, 1H); 13C {1H} NMR (75 MHz, CD3CN): d (ppm)
158.5, 149.0, 136.9, 130.5, 129.1, 123.5, 123.3, 122.5,
118.9, 117.5, 116.3, 58.8, 56.6; IR (thin film, NaCl plate):
m (cmꢀ1) 3421 (br), 1591 (s).
2.2. Characterizations
1
13C {1H} and H NMR spectra were recorded on a
Varian Mercury 300 NMR spectrometer. Chemical
shifts were referenced to the proton or carbon signal of
the NMR solvent. FTIR spectra were obtained with a
Mattson Galaxy Series FTIR 3000. Elemental analyses
were performed by Midwest Microlabs.
2.4. Chloro-{N-(2-hydroxyphenyl)methyl-bis-(2-pyridyl-
methyl)amino}-copper(I) (1)
The ligand (1.21 g, 3.96 mmol) was dissolved in 25 ml
of dry acetonitrile, and then 0.392 g (3.96 mmol) of
Cu(I)Cl was added. The solution was stirred and heated
at reflux for 10 min. The solution was allowed to cool
overnight, and yellow crystals formed. The supernatant
was decanted and the crystals, suitable for X-ray anal-
ysis, were placed under vacuum to remove volatile
materials. Yield: 1.44 g (90%); m.p. (uncorrected) ¼ 157–
159 °C; Elemental composition (C19H19ClCuN3O):
Anal. Calc. for C 56.43, H 4.79, N 10.40. Found: C
55.92, H 4.80, N 10.70%; IR (thin film, NaCl plates) m
(cmꢀ1): 3170 (broad), 1599 (s).
2.3. N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)
amine
Salicaldehyde (1.00 ml, 9.38 mmol) was added to a
solution of 2.44 g of bis(2-pyridylmethyl)ammonium
tetrafluoroborate in 50 ml of benzene. A Dean-Stark
trap and reflux condenser were fitted to the flask and the
solution was heated and stirred at reflux until no further
water was collected ðꢂ0.15 ml). The white precipitate
was isolated by filtration and volatile materials were
Table 1
Crystal data and refinement details for complex-1 and complex-2 ꢁ 3H2O
Formula
C19H19ClCuN3O
C38H44 Br4Cu2N6O5
1111.53
Formula weight
Crystal system
Space group
404.36
monoclinic
C2=c
monoclinic
P21
Color and habit
ꢀ
yellow prism
15.2135(7)
9.2386(7)
26.4877(16)
106.485(2)
3569.9(4)
91(2)
blue needle
10.4714(15)
16.251(2)
12.513(2)
102.058(7)
2082.4(6)
91(2)
a (A)
ꢀ
b (A)
ꢀ
c (A)
b (°)
V (A )
Temperature (K)
3
ꢀ
ꢀ
Wavelength (A)
0.71073
8
0.71073
2
Z
Crystal dimensions (mm)
l(Mo Ka) (mmꢀ1
0.18 ꢃ 0.14 ꢃ 0.08
1.38
63
0.44 ꢃ 0.16 ꢃ 0.13
4.91
60
)
2hmax (°)
Reflections collected
Independent reflections
Reflections observed [I > 2rðIÞ]
Parameters
24490
5713
27201
11950
4260
228
11050
522
R1 (observed data)
wR2 (all data)
Goodness-of-fit
0.0366
0.0864
1.01
0.0281
0.0670
1.04

M.M. Olmstead et al. / Inorganica Chimica Acta 357 (2004) 619–624
621
2.5. Dibromo-{N-(2-hydroxyphenyl)methyl-bis-(2-pyr-
idylmethyl)amino}-copper(II) (2)
treatment with NaBH4 in methanol. This condensation–
reduction approach represents an alternative to the nu-
cleophilic substitution routes described previously
[13,15,16]. This reaction yielded satisfactory amounts of
the ligand that contained no other materials as judged
by its NMR spectra.
The addition of CuCl to an acetonitrile solution of
the ligand followed by heating the solution at reflux
formed complex-1 in good yield (Eq. (1)). An IR spec-
trum showed bands
The ligand (1.44 g, 4.72 mmol) was dissolved in 20
ml of dry acetonitrile, and then 1.06 g (4.76 mmol) of
anhydrous Cu(II)Br2 was added. The solution was
stirred and heated at reflux for 10 min. The solution
was allowed to cool overnight and a green powder
formed, which was recrystallized from tetrahydrofuran.
Yield: 1.63 g (64%). Crystals suitable for X-ray anal-
ysis were grown from methanol by evaporation of the
solvent.
2.6. X-ray structure determinations of 1 and 2 ꢁ 3H2O
Diffraction data were collected with a Bruker
SMART 1000 diffractometer, graphite-monochromated
Mo Ka radiation, and a nitrogen cold stream provided
by a CRYO Industries apparatus. Corrections for ab-
sorption were applied using the program SADABS 2.03
[20]. The structures were solved by direct methods
ð1Þ
corresponding to the presence of the phenolic O–H
group (3170 cmꢀ1) and the aromatic rings (1599 cmꢀ1).
The structure of complex-1 is monomeric, with the co-
ordination geometry about the metal center distorted
from tetrahedral geometry due to the constraint of
tethering the nitrogen donor groups (Fig. 1). Table 2
shows selected bond angle and bond length data for
complex-1. The two N–Cu–N angles between the di-
rectly tethered nitrogen donors are less than 109.5° (81.0
and 78.1) while the other N–Cu–N angle and the three
N–Cu–Cl angles are all greater than 109.5° (127.5° and
(
SHELXS-97 [21]) and refined by full-matrix least-
(
squares on F 2
SHELXL-97 [21]). All non-hydrogen at-
oms were refined with anisotropic thermal parameters.
Hydrogen atoms on water molecules were located on a
difference map and refined using distance restraints.
Other hydrogen atoms were added by geometry and
refined using a riding model. The maximum and mini-
mum peaks in the final difference Fourier map corre-
ꢀꢀ3
sponded to 0.53 and )0.33 eA for 1 and 0.97 and
ꢀꢀ3
)0.76 eA for 2 ꢁ 3H2O. Crystal data and refinement
details for 1 and 2 ꢁ 3H2O are shown in Table 1. Addi-
tional experimental information, including atomic po-
sitional parameters, is supplied in CIF format as
described in the supplementary material.
3. Results and discussion
The ligand used in this study, N-(2-hydroxyphenyl)-
methyl-bis-(2-pyridylmethyl)amine, was prepared by the
condensation of bis(2-pyridylmethyl)ammonium tetra-
fluoroborate with salicaldehyde to form the iminium salt
(Scheme 1). The iminium salt precipitated from the re-
action solution as it formed. The material was isolated
by filtration and then reduced to the amine product by
Fig. 1. Molecular structure of complex-1 showing the intermolecular
O–H ꢁ ꢁ ꢁ Cl hydrogen bonding and thermal ellipsoids at the 50%
probability level.
Scheme 1. Synthetic route for obtaining the ligand used in this study, N-(2-hydroxyphenyl)methyl-bis-(2-pyridylmethyl)amine.

622
M.M. Olmstead et al. / Inorganica Chimica Acta 357 (2004) 619–624
Table 2
dimeric with two copper complexes in the asymmetric
unit (Fig. 2). Unlike the copper(I) center in complex-1,
the copper(II) center can form tetragonally distorted
octahedral complexes, so the phenol can potentially act
both as a ligand and a hydrogen bond donor-acceptor in
complex-2. The presence of both a bromide ligand and a
bromide counterion to balance the 2+ charge of the
copper center indicates that the coordinated phenol
oxygen is protonated. Table 3 shows selected bond angle
and bond length data for complex-2 ꢁ 3H2O. The two
ꢀ
Selected bond lengths (A) and angles (°) for complex-1
Cu(1)–N(1)
Cu(1)–N(2)
2.0106(16)
2.3935(15)
2.0053(16)
2.2739(5)
Cu(1)–N(3)
Cu(1)–Cl(1)
Cl(1)–Cu(1)–N(1)
Cl(1)–Cu(1)–N(2)
Cl(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
116.65(5)
132.82(4)
112.91(5)
81.00(6)
127.48(6)
78.05(6)
ꢀ
copper centers are 4.00 A apart in the dimer. The
ꢀ
Cu ꢁ ꢁ ꢁ Br distances are 3.21 and 3.32 A and are very
long, indicating only a very weak interaction between
the two complexes forming the dimer. The trans Cu–O
ꢀ
distances are quite long at 2.428(2) and 2.427(2) A,
consistent with 4 + 2 tetragonal distortion [22]. The
copper–nitrogen distances for the amines trans to the
ꢀ
bromide are 2.022(2) and 2.045(2) A; and the other
116.7, 132.8, and 112.9, respectively). The three Cu-N
bond lengths (2.01, 2.01, and 2.39) and Cu-Cl bond
length (2.27) all fall within the expected range for similar
bis-(2-pyridylmethyl)amine complexes. Because the co-
ordination sphere of the copper(I) center is saturated by
the softer amine and chloride ligands, the pendant
phenol group can only act as a hydrogen bond donor-
acceptor. The phenolic hydrogen is hydrogen bonded to
a chlorine atom on a neighboring complex, d(H–
ꢀ
ꢀ
ꢀ
O) ¼ 0.84 A, d(H ꢁ ꢁ ꢁ Cl) ¼ 2.25 A, d(O ꢁ ꢁ ꢁ Cl) ¼ 3.08 A,
and \(OHCl) ¼ 173.3°, to form chains of complexes
throughout the crystal.
The addition of anhydrous CuBr2 to an acetonitrile
solution of the ligand followed by heating the solution at
reflux formed complex-2 (Eq. (2)). The structure of
complex-2 is
Fig. 2. Molecular structure of complex-2. The bromide counterions
and hydrogen-bonded water molecules have been omitted. Thermal
ellipsoids are drawn at the 50% probability level.
ð2Þ
Table 3
ꢀ
Selected bond lengths (A and angles ( °) for complex-2 ꢁ 3H2O
Cu(1)–O(1)
Cu(1)–N(1)
2.428(2)
2.003(3)
2.022(2)
2.007(2)
2.3981(5)
3.3190(6)
93.65(5)
95.74(7)
176.58(7)
97.94(7)
97.86(8)
89.59(8)
88.73(8)
82.71(10)
164.40(10)
83.22(10)
4.0029(8)
Cu(2)–O(2)
Cu(2)–N(4)
2.427(2)
1.997(2)
2.045(2)
1.990(2)
2.4125(5)
3.2137(6)
94.18(5)
96.62(7)
176.82(7)
98.05(7)
98.40(9)
88.77(8)
87.37(9)
81.74(10)
163.79(10)
83.26(9)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(2)–N(5)
Cu(2)–N(6)
Cu(1)–Br(1)
Cu(1)–Br(2)
Cu(2)–Br(2)
Cu(2)–Br(1)
Br(1)–Cu(1)–O(1)
Br(1)–Cu(1)–N(1)
Br(1)–Cu(1)–N(2)
Br(1)–Cu(1)–N(3)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
Cu(1) ꢁ ꢁ ꢁ Cu(2)
Br(2)–Cu(2)–O(2)
Br(2)–Cu(2)–N(4)
Br(2)–Cu(2)–N(5)
Br(2)–Cu(2)–N(6)
O(2)–Cu(2)–N(4)
O(2)–Cu(2)–N(5)
O(2)–Cu(2)–N(6)
N(4)-Cu(2)–N(5)
N(4)-Cu(2)–N(6)
N(5)-Cu(2)–N(6)

M.M. Olmstead et al. / Inorganica Chimica Acta 357 (2004) 619–624
623
copper–nitrogen distances are 2.003(3), 2.007(2),
ꢀ
4. Supplementary material
1.997(2), and 1.990(2) A. The Cu–Br distances are
ꢀ
2.4125(5) and 2.3981(5) A. The N–Cu–N and N–Cu–Br
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been de-
posited with the Cambridge Crystallographic Data
Centre as supplementary publications nos. CCDC-
218053 (complex-1) and CCDC-218054 (complex-
2 ꢁ 3H2O). Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336-033;
email: deposit@ccdc.cam.ac.uk or www: http://www.
ccdc.cam.ac.uk).
bond angles within the square plane total 360° within
experimental error (359.6° and 359.8°). The N–Cu–N
bond angles are less than 90° due to the geometrical
constraints of the bis-(2-pyridylmethyl)amine fragment
of the ligand (ranging from 81.8° to 83.3°), while the N–
Cu–Br bond angles are greater than 90° for the same
reason (ranging from 95.8° to 98.1°). The chloride
counterpart of complex-2 has been reported [16], and
the structure is largely similar to complex-2. As for
complex-2, there are two crystallographically indepen-
dent molecules within the unit cell. The copper–oxygen
ꢀ
distances are 2.570(4) and 2.457(5) A which are trans to
ꢀ
Acknowledgements
the long Cu ꢁ ꢁ ꢁ Cl bridge bonds of 3.104 and 3.039 A.
The copper–nitrogen distances for the amines trans to
Acknowledgment is made to the donors of the Pe-
troleum Research Fund, administered by the American
Chemical Society, for support of this research (Grant
#35150-AC7).
ꢀ
the chloride are 2.041(4) and 2.059(4) A ; and the other
copper–nitrogen distances are 1.987(5), 1.978(5),
ꢀ
1.980(5), and 1.978(5) A.
During recrystallization from methanol, water was
incorporated into the crystal, and formed a hydrogen-
bonded network with the complex and the bromide
counterions. A stereoview of the unit cell is shown in
Fig. 3. The phenolic hydrogen of one-half of the dimer is
hydrogen bonded to a bromide anion, d(H–O) ¼
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