Isolation and structural characterization of a binuclear intermediate species pertinent to transmetalation of Zn(salphen) complexes and the formation of polynuclear salen structures

Article abstract of DOI:10.1021/ic8018265

Zinc(II) salphen complexes equipped with additional alkoxy donor groups at the 3-position of the salicylideneimine groups have been prepared to bind metal acetates in a second coordination sphere close to the central Zn(II) ion. The isolated binuclear mon

Full text of DOI:10.1021/ic8018265

Inorg. Chem. 2009, 48, 846-853
Isolation and Structural Characterization of a Binuclear Intermediate
Species Pertinent to Transmetalation of Zn(salphen) Complexes and the
Formation of Polynuclear Salen Structures
†
Leire San Felices, Eduardo C. Escudero-Ad a´ n, Jordi Benet-Buchholz, and Arjan W. Kleij*
†
†
,†,‡
Institute of Chemical Research of Catalonia (ICIQ), AV. Pa ¨ı sos Catalans 16,
4
3007 Tarragona, Spain, and Instituci o´ Catalana de Recerca i Estudis AVan c¸ ats (ICREA),
Pg. Llu ´ı s Companys 23, 08010 Barcelona, Spain
Received May 9, 2008
Zinc(II) salphen complexes equipped with additional alkoxy donor groups at the 3-position of the salicylideneimine
groups have been prepared to bind metal acetates in a second coordination sphere close to the central Zn(II) ion.
The isolated binuclear monosalphen complexes have been studied in detail using NMR and MS techniques. Further
synthesis has revealed that the formation of binuclear species from the parent salphen ligands is dependent on the
nature of the bridging group between the two salicylideneimine groups and is prevented by replacement of one of
2
the alkoxy substituents for a bulky t-Bu group. One of the binuclear Zn complexes was crystallographically
characterized and can be regarded as a structural model for the intermediate stage of the transmetalation of the
central Zn(II) center within these dinuclear compounds by other metal acetate salts. Furthermore, the X-ray diffraction
structure also relates well with some intermediate structural stages of the buildup of various polynuclear salen
structures.
Introduction
blocks in order to fine-tune the material properties. Recently
we have reported several studies devoted to the intriguing
reactivity of the salphen [salphen ) N,N′-phenylenebis(sali-
Salen ligands and complexes play a profound role in
homogeneous catalysis. In the past decade, salen structures
have, however, also emerged as highly useful components
of various (supramolecular) materials, among which are
1
6
cylideneimine)] family of Zn(II)-centered metallosalens. The
origin of this reactivity is found in the high Lewis acidity of
2
7
the Zn(II) ion, which allows strong binding of various N-
3
multimetallic systems for cooperative catalysis operations,
and O-donor systems. On the other hand, the Zn(salphen)
unit is kinetically labile, making it an excellent starting point
for the introduction of various other metal ions by means of
4
5
macrocyclic compounds, and new templating systems. For
all of these materials, it is vital to understand and to exploit
the reactivity and stability characteristics of the salen building
8
transmetalation (TM), as we have previously reported.
The presence of supplementary hydroxyl and alkoxy
substituents on the salen framework has been frequently used
to assemble bimetallic monosalen complexes and catalysts.
We recognized the ability of such donor fragments to access
bimetallic salphen complexes in order to be able to stabilize
and analyze in detail the presumed binuclear intermediate
*
Author to whom correspondence should be addressed. E-mail:
akleij@iciq.es.
†
9
ICIQ.
ICREA.
‡
(
1) For some reviews see: (a) Darensbourg, D. J. Chem. ReV. 2007, 107,
2
1
388. (b) McGarrigle, E. M.; Gilheany, D. G. Chem. ReV. 2005, 105,
563. (c) Baleizao, C.; Garcia, H. Chem. ReV. 2006, 106, 3987. (d)
Larrow, J. F.; Jacobsen, E. N. Top. Organomet. Chem. 2004, 6, 123.
2) (a) Wezenberg, S. J.; Kleij, A. W. Angew. Chem., Int. Ed. 2008, 47,
(
(
2
354. (b) Kleij, A. W. Chem.sEur. J. 2008, 14, 10520.
(5) (a) Akine, S.; Sunaga, S.; Taniguchi, T.; Miyazaki, H.; Nabeshima,
T. Inorg. Chem. 2007, 46, 2959. (b) Wezenberg, S. J.; Escudero-Ad a´ n,
E. C.; Benet-Buchholz, J.; Kleij, A. W. Inorg. Chem. 2008, 47, 2925.
(c) Kleij, A. W.; Reek, J. N. H. Chem.sEur. J. 2006, 12, 4218.
(6) (a) Escudero-Ad a´ n, E. C.; Benet-Buchholz, J.; Kleij, A. W. Inorg.
Chem. 2008, 47, 410. (b) Escudero-Ad a´ n, E. C.; Benet-Buchholz, J.;
Kleij, A. W. Dalton Trans. 2008, 734. (c) Wezenberg, S. J.; Escudero-
Ad a´ n, E. C.; Benet-Buchholz, J.; Kleij, A. W. Org. Lett. 2008, 10,
3311.
3) (a) Sammis, G. M.; Danjo, H.; Jacobsen, E. N. J. Am. Chem. Soc.
2
004, 126, 9928. (b) Mazet, C.; Jacobsen, E. N. Angew. Chem., Int.
Ed. 2008, 47, 1762.
(
4) (a) Akine, S.; Kagiyama, S.; Nabeshima, T. Inorg. Chem. 2007, 46,
9
2
2
525. (b) Hui, J. K.-H.; MacLachlan, M. J. Chem. Commun. 2006,
480. (c) Gallant, A. J.; MacLachlan, M. J. Angew. Chem., Int. Ed.
003, 42, 5307. (d) Sun, S.-S.; Stern, C. L.; Nguyen, S. T.; Hupp,
J. T. J. Am. Chem. Soc. 2004, 126, 6314.
846 Inorganic Chemistry, Vol. 48, No. 3, 2009
10.1021/ic8018265 CCC: $40.75  2009 American Chemical Society
Published on Web 12/31/2008

Characterization of a Binuclear Intermediate Species
8
of our TM protocol. Here, we report details about the
Scheme 1. Synthesis of the Binuclear Salphen Complexes 1-3, Ni
Complex 4, and Heterobimetallic Complex 5
synthesis and characterization of such binuclear complexes
and their relation to the operative TM mechanism. Addition-
ally, their resemblance with the key structural motifs found
in the intermediates leading to polynuclear salen-based
compounds is also discussed. Previously, MacLachlan and
1
0
co-workers reported on interesting bowl-shaped, macro-
cyclic heptanuclear Zn
7
(trisalphen) cluster complexes, of
O]6 may be regarded as an attractive
+
which the central [Zn
4
mimic for the active site of metalloenzymes such as
1
1
phospholipase C that comprises a trinuclear zinc cluster.
The heptanuclear structures are built up from a central tri-
Zn(salphen) unit. The hexa-hydroxy interior acts as a
6
+
4
template for the creation of the [Zn O] cluster, and the
cluster itself is held together via various OAc bridges
between the different metal centers. Upon reaction with
Co(II) acetate, a mixed metal assembly could be obtained
in which the Zn ions within the central cluster were
2
+
completely replaced by Co . Another relevant example of
a polynuclear salen structure in which an internal array of
O atoms acts as a template for the formation of a trinuclear
3
Zn oxime-based system was provided by Nabeshima and
1
2
co-workers. Here, the authors suggested a cooperative
mechanism for the formation of the trinuclear metallohost
2 2
molecules. Two of the Zn(II) ions are inserted into the N O
salamo donor pockets, while a third Zn(II) ion is coordinated
by two phenolic O atoms of the salen fragments and by two
2
µ -acetato ligands that each bridge to one of the other Zn(II)
centers, thereby completing their coordination sphere. The
identification of the templating mechanism that leads to such
polynuclear systems (cf. enzyme mimics) is thus intriguing,
and suitable model systems could help to further understand
the formation of such ensembles.
6
and pyridine. NMR analysis was therefore performed in d -
DMSO, and for all complexes, typical patterns were observed
that can be associated with the formation of a Zn(II)-centered
salphen complex (see the Supporting Information). Further-
more, the binuclear nature of 1-3 was supported by the
Results and Discussion
OEt
OAc
presence of a singlet peak [integral ratio of CH
3
/CH
3
)
1] around 1.8 ppm that was ascribed to the OAc ligands
Homobimetallic complexes 1-3 (Scheme 1) were pre-
pared in high isolated yields (76-98%) in a one-pot multistep
synthesis using the appropriate diamine precursor, 3-RO-
13
2
of a Zn(OAc) unit. Convincing evidence for the formation
of di-Zn(II) complexes was provided by MALDI-TOF mass
spectrometry (see the Supporting Information). For instance,
for 3, a high-intensity peak was noted at m/z ) 641.0, which
corroborates with the fragment ion [M - OAc] . Other
isotope clusters of low intensity were also found that are a
salicylaldehyde (R ) Me, Et) and 2 equiv of Zn(OAc)
O (or excess) in MeOH. Compounds 1-3 proved to be
sparingly soluble in many organic solvents except for DMSO
2
·
2H
2
+
(
(
(
7) (a) Kleij, A. W.; Kuil, M.; Tooke, D. M.; Lutz, M.; Spek, A. L.; Reek,
J. N. H. Chem.sEur. J. 2005, 11, 4743. (b) Dalla Cort, A.; Mandolini,
L.; Pasquini, C.; Rissanen, K.; Russo, L.; Schiaffino, L. New. J. Chem
2
result of the loss of the Zn(OAc) fragment and dimerization
of the mononuclear complex. Similar mass spectrometric
results were obtained for complexes 1-2.
2
007, 31, 1633.
8) (a) Escudero-Ad a´ n, E. C.; Benet-Buchholz, J.; Kleij, A. W. Inorg.
Chem. 2007, 46, 7265. (b) Wezenberg, S. J.; Metselaar, G. A.;
Escudero-Ad a´ n, E. C.; Benet-Buchholz, J.; Kleij, A. W. Inorg. Chim.
Acta 2008, in press (DOI: 10.1016/j.ica.2008.05.022).
Fortunately, crystals of 2 suitable for X-ray diffraction
could be obtained by dissolving the complex in hot MeOH
and slowly cooling the obtained solution. The molecular
structure for 2 is presented in Figure 1, a selection of bond
distances/angles and crystallographic data can be found in
Tables 1 and 2. The structure comprises a remarkable
nonsymmetrical, bis-Zn-monosalphen complex in which the
central metal center Zn(1) is in an approximate square-
9) See for some recent examples: (a) Handa, S.; Nagawa, K.; Sohtome,
Y.; Matsunaga, S.; Shibasaki, M. Angew. Chem. Int. Ed 2008, 47, 1.
(
(
b) Yang, X.; Jones, R. A.; Wong, W. K. Dalton Trans. 2008, 1676.
c) Chen, Z.; Morimoto, H.; Matsunaga, S.; Shibasaki, M. J. Am. Chem.
Soc. 2008, 130, 2170. (d) Handa, S.; Gnadadesikan, V.; Matsunaga,
S.; Shibasaki, M. J. Am. Chem. Soc. 2007, 129, 4900. (e) Chen, J.-
M.; Ran, W.-J.; Gao, F.; Duan, R.; Zhang, Y.-H.; Zhu, Z.-A. J. Coord.
Chem. 2007, 60, 2485.
2 2
pyramidal geometry comprising a tetradentate N O ligation
(
10) (a) Frischmann, P. D.; Gallant, A. J.; Chong, J. H.; MacLachlan, M. J.
Inorg. Chem. 2008, 47, 101. (b) Gallant, A. J.; Chong, J. H.;
MacLachlan, M. J. Inorg. Chem. 2006, 45, 5248.
11) Parkin, G. Chem. ReV. 2004, 104, 699.
12) Akine, S.; Taniguchi, T.; Nabeshima, T. J. Am. Chem. Soc. 2006, 128,
(13) A similar NMR shift is noted for the OAc groups of non-complexed
Zn(OAc) O in the same solvent. This implies that DMSO is able
(
(
2
·2H
2
to break up the binuclear complex, and observation of the non-
assembled individual components is thus evident.
1
5765.
Inorganic Chemistry, Vol. 48, No. 3, 2009 847

San Felices et al.
Figure 2. X-ray molecular structure determined for Ni(II) complex 4.
Hydrogen atoms are omitted for clarity except for the bonded water
molecule.
Figure 1. X-ray molecular structure determined for bimetallic complex 2.
Hydrogen atoms are omitted for clarity.
1
2
workers (see Figure 3). In both examples, the formation
of polynuclear Zn(II) complexes is mediated by the internal
set of O-donor atoms of the salen ligand. Furthermore, the
Table 1. Selected Bond Distances (Å) and Angles (deg) for Compounds
2
and 4 with esd’s in Parentheses
2
4
Zn center in both tetranuclear compound [Zn
4
] and trinuclear
Distances
1.9890(17)
2.0263(18)
1.985(2)
2.077(2)
2.074(2)
1.9903(19)
2.475(2)
2.010(2)
2.0496(18)
2.0723(18)
2.1867(19)
[
Zn ] are held further in place by two bridging acetate ligands
3
Zn(1)-O(1)
Zn(1)-O(2)
Zn(1)-O(5)
Zn(1)-N(1)
Zn(1)-N(2)
Zn(2)-O(2)
Zn(2)-O(4)
Zn(2)-O(6)
Zn(2)-O(7)
Zn(2)-O(8)
Zn(2)-O(9)
Ni(1)-O(1)
Ni(1)-O(2)
Ni(1)-N(1)
Ni(1)-N(2)
1.8485(6)
1.8439(6)
1.8562(7)
1.8569(6)
using the adjacent Lewis-acidic Zn(II) ions as anchoring
points.
The Lewis-acidic nature specifically found for the Zn(II)
complexes of the present studies was supported by several
additional experiments and analyses. First of all, under
similar reaction conditions as reported for 1-3 (an excess
of Ni(OAc)
2
2
· 4H O reagent), only the mono-Ni(II)salphen
complex 4 (Scheme 1) was produced in high yield (84%).
The X-ray molecular structure of 4 (Figure 2 and Tables 1
and 2) shows the expected square-planar arrangement of the
Angles
O(1)-Zn(1)-O(2)
O(1)-Zn(1)-O(5)
O(1)-Zn(1)-N(1)
N(1)-Zn(1)-N(2)
O(1)-Zn(1)-N(2)
O(4)-Zn(2)-O(6)
O(2)-Zn(2)-O(8)
O(7)-Zn(2)-O(9)
93.65(7)
105.35(9)
89.32(8)
78.40(8)
148.64(9)
166.29(7)
154.32(9)
156.74(7)
O(2)-Ni(1)-O(1)
O(2)-Ni(1)-N(1)
O(1)-Ni(1)-N(1)
O(2)-Ni(1)-N(2)
O(1)-Ni(1)-N(2)
N(1)-Ni(1)-N(2)
83.43(3)
178.64(3)
95.31(3)
95.34(3)
178.70(3)
85.92(3)
salphen ligand around the Ni(II) center with a H
trapped via H-bonding within the O cavity. Treatment of 4
with 1 equiv of Zn(OAc) · 2H O (or excess) in a mixture of
CHCl /MeOH yielded unreacted 4 (Scheme 1). However,
when binuclear complex 2 was treated with a slight excess
of Ni(OAc) · 4H O in THF at room temperature, formation
of a new orange complex was observed. Since both 2
bright yellow) and 4 (deep red) have distinct and typical
colors, the isolation of structure 5 (Scheme 1) was envisaged
in which the Ni(OAc) fragment is coordinated in a similar
fashion as for the Zn(OAc) fragment within bis-Zn(II)
2
O molecule
4
2
2
3
2
2
of the salphen ligand and one O atom of a bridging OAc.
The other metal center, Zn(2), is positioned within the
second” coordination sphere of the salphen ligand via the O
atoms of one of the OEt groups and one O donor of the
set. The rather distorted octahedral surrounding of Zn2
14
(
“
2
2 2
N O
2
is completed by one bidentate OAc ligand, one bridging OAc,
and one molecule of the crystallization solvent (MeOH). The
Zn-O distance Zn(2)-O(4) is 2.475(2) Å and is consider-
ably longer than the other Zn-O bond lengths. The bridging
acetate ligand allows axial coordination of Lewis-acidic Zn(1)
by O(5). As a consequence, the second Zn center (Zn(2))
becomes less symmetrically positioned; that is, it is pointing
further away from O(4) within the distorted octahedral
geometry and results in a significantly larger Zn-O bond
length as compared to the other Zn-O distances involving
Zn(2).
complexes 1-3. When isolated 5 was subjected to NMR
analysis, the color of the obtained solution immediately
turned deep red, which is a strong indication for the
(irreversible) formation of the Ni(II) complex 4. Indeed, for
several deuterated solvent systems (d -DMSO and d -
6
5
pyridine) a fast transmetalation was confirmed, and no signals
corresponding to 2 could be detected. In addition, the
concomitant formation of 1 equiv (by signal integration) of
2
Zn(OAc) was evidenced by the presence of a sharp singlet
1
resonance at 1.8 ppm in the H NMR spectrum. Further proof
for the presence of a mixed Zn-Ni salphen complex prior
to transmetalation was offered by MALDI-TOF-MS, which
The structure of 2 (Figure 1) resembles (in part) the key
structural unit found in the polysalen compounds reported
1
0
by MacLachlan and co-workers and Nabeshima and co-
(14) Please note: heterogeneous reaction.
848 Inorganic Chemistry, Vol. 48, No. 3, 2009

Characterization of a Binuclear Intermediate Species
4 7
Figure 3. Schematic representation of the polynuclear salen complex formation reported by MacLachlan (at the top, [Zn ] and [Zn ]) and Nabeshima
(
2 3
below, [Zn ] and [Zn ]). Note the importance of both the array of internal O-donor atoms and the (bridging) acetate ligands.
Table 2. Crystallographic Data and Structure Refinement for Complexes 2 and 4
complex 2
complex 4
empirical formula
fw
temperature, K
wavelength, Å
cryst syst, space group
unit cell dimensions (Å/deg)
C
29
H
31
N
2
O
9
Zn
2
26 6 2 5
C H26Cl N O Ni
682.30
100(2)
0.71073
717.90
100(2)
0.71073
triclinic, P1j
triclinic, P1j
a ) 7.7191(5), R ) 87.326(3)
a ) 9.2322(2), R ) 90.7480(10)
b ) 13.3739(7), ꢀ ) 77.487(4)
b ) 11.6101(3), ꢀ ) 95.5330(10)
c ) 14.4779(8), γ ) 78.697(3)
c ) 14.4864(4), γ ) 107.2580(10)
volume, Å3
1430.80(14)
1474.52(6)
Z
2
2
3
density (calculated), Mg/m
abs coeff, mm
1.584
1.734 mm
1.617
1.242 mm
-
1
-1
-1
F(000)
702
732
cryst size, mm3
0.10 × 0.05 × 0.02
0.40 × 0.20 × 0.15
θ range for data collection, deg
index ranges
2.88-31.14
2.83-39.29°
-11 e h e 9, -19 e k e 18, -20 e l e 20
-16 e h e 16, -20 e k e 18, -25 e l e 25
36349, 15411 [R(int) ) 0.0165]
88.2%
refln collected/independent
completeness to θ max
abs correction
max. and min. transmission
refinement method
22034, 8603 [R(int) ) 0.0841]
92.9%
none
SADABS (Bruker-Nonius)
0.8356, 0.6365
full-matrix least-squares on F
0.9661, 0.8457
full-matrix least-squares on F
2
2
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2(I)]
R indices (all data)
8603/0/384
1.006
R1 ) 0.0534, wR2 ) 0.1133
R1 ) 0.0883, wR2 ) 0.1283
0.860, -0.888
15411/0/371
1.046
R1 ) 0.0306, wR2 ) 0.0828
R1 ) 0.0347, wR2 ) 0.0856
1.199, -1.235
-
3
larg. diff. peak, hole, e Å
showed a typical isotopic distribution at m/z ) 583.0
corresponding to the fragment ion [5 - OAc] .
large effect on the coordination ability of the Zn(salphen)
complex to the Zn(OAc) module. Complexes 7 and 8 were
+
15
2
Additional control compounds were then prepared (Scheme
) to see whether the presence of both alkoxy groups is a
prepared in excellent isolated yields (86 and 87%, respec-
tively) and their respective H NMR spectra (recorded in
1
2
prerequisite for binding of the Zn(OAc)
2
fragment. Monoi-
6
d -DMSO) compared with those obtained for bimetallic
mines 6a and 6b were prepared using a method developed
by Atwood and co-workers. The difference between these
two monoimines is the bulkiness of the substitution at the
species 1-3. Remarkably, for 7, no resonance was detected
that could be assigned to an acetate fragment, and the other
spectroscopic data clearly pointed at the formation of a mono-
metallic species. Apparently, the bulky t-Bu group does not
1
6
3
-position of the salicylideneimine unit, which can have a
Inorganic Chemistry, Vol. 48, No. 3, 2009 849

San Felices et al.
Scheme 2. Synthesis of Zn(salphen) Complexes 7-10
1
7
allow formation of the bimetallic compound. This was further
confirmed by the isolation of 8: here, the relatively small
methyl group (Scheme 2) does not interfere with the
formation and isolation of the bimetallic complex. The latter
was completely characterized by a combination of analytical
tools (see Experimental Section).
features probably determine the course of the reaction.
Upon changing the bridging (rigid) phenyl unit for a more
flexible cyclohexyl group (Scheme 2), again only mono-
Zn(salen) 10 (69%) could be isolated. This result shows the
importance of having a rigidified structure as a crucial
prerequisite for bimetallic complex formation.
Two other complexes were also probed, namely, com-
pounds 9 and 10 (Scheme 2). Interestingly, when the
Bis-Zn(II) complex 2 contains two pending EtO groups
that help to stabilize the bimetallic species. When treated
metalating reagent Zn(OAc)
Zn(propionate) , selective isolation of mono-Zn(II) complex
(89%) was achieved. Although the X-ray molecular
structure determined for 2 reveals ample room for the
incorporation of a Zn(propionate) module into the salphen
structure, as observed for Zn(OAc) (Figure 1), solubility
2
was replaced for (excess)
with excess Ni(OAc)
2
2
· 4H O, it is converted into the het-
2
erobimetallic Zn(II)-Ni(II) salphen complex 5. The non-
symmetrical bis-Zn(II) complex 8 comprises only one of
these stabilizing groups and therefore should be more prone
to be directly converted into the transmetalation product, as
opposed to 2. Indeed, when 8 is treated under similar
conditions (Scheme 3), a fast color change from yellow to
deep red is observed, and complete dissolution of the initial
solid material occurs, unlike observed for the conversion 2
f 5. Analysis (NMR, MS) confirmed the exclusive forma-
tion of mono-Ni(II) complex 11 in high isolated yield (81%).
The latter result demonstrates that complex 2 thus allows
isolation of an intermediate stage of the transmetalation
reaction.
9
2
2
(
15) The location of this resonance corroborates well with the presence of
Zn(OAc) . Note that (paramagnetic) Ni(OAc) gives a broad signal
around 2.8 ppm under these conditions. The Ni(II) species 4 is unable
to bind Zn(OAc) sufficiently strong, and consequently no heterobi-
metallic compound was isolated after the washing step with MeOH
see the Experimental Section). The latter observation plus the fact
that 5 undergoes quantitative transmetalation upon dissolution to
is in line with the proposed
2
2
2
(
furnish 4 and 1 equiv of Zn(OAc)
2
formulation for 5 with a Ni/Zn stochiometry of 1:1. Furthermore,
comparison of the solid-state IR spectra between bis-Zn(II)-(salphen)
2
, mono-Ni(II)salphen 4, and complex 5 also revealed the formation
of a unique complex (see Supporting Information). Isolated 5 was
subjected to MALDI-TOF mass spectrometry: due to dissolution, some
transmetalation could not be avoided, but nonetheless complex 5 was
observed under the applied conditions. The mass spectrum also
exhibited a peak at m/z ) 637.0, which was ascribed to a bis-Ni(II)
salphen complex and at 460.1 (attributed to Ni complex 4). Finally,
the elemental analysis carried out for 5 proved to be also in line with
the proposed structure.
(16) Mu n˜ oz-Hern a´ ndez, M.-A.; Keizer, T. S.; Parkin, S.; Patrick, B.;
Atwood, D. A. Organometallics 2000, 19, 4416.
(17) Complex 9 is probably dimeric in nature because of the absence of
sufficient steric bulk at the 3- positions of the salicylideneimine groups.
See for instance:(a) Singer, A. L.; Atwood, D. A. Inorg. Chim. Acta
1998, 277, 157. Isolation of 9 should be interpretated as a (much)
faster precipitation of dimer 9 versus the envisioned, bimetallic
2
complex 9·Zn(propionate) .
850 Inorganic Chemistry, Vol. 48, No. 3, 2009

Characterization of a Binuclear Intermediate Species
Scheme 3. Synthesis of Ni(salphen) 11 via Transmetalation of 8
bridges between the two salicylideneimine fragments provides
only monometallic compounds, underlining the importance of
rigidity for bimetallic complex formation. The rigidity of the
salphen system leads to increased Lewis acidity behavior of
the Zn(II) ion: the Zn center is forced into an unfavorable
square-planar geometry, which increases its Lewis acidic
behavior. This was previously supported by PM3 calculations
that allowed access to the potential energy surface of Zn(sal-
phen) derivatives and showed a localized positive charge on
the Zn center. This Lewis acidity allows strong axial binding
7
Scheme 4. Mechanistic Proposal for the Transmetalation of
of axial ligands (cf., carboxylates and N-donor ligands). These
specific properties of the Zn(salphen) family of complexes help
to further rationalize the formation and reactivity of heptanuclear
Zn(salphen) Complex 2 by Ni(OAc)
2
Zn
7
cluster compounds based on a trisalphen macrocycle that
10
was recently reported by MacLachlan et al. The three central
6+
Zn ions template a stepwise construction of the central [Zn
unit following a sequence of axial coordination/bridging of the
OAc ligands and deprotonation of a single H O ligand. A similar
reasoning may be applied for a trinuclear oxime-based salen
structure reported by Nabeshima et al. Our current focus is
on the stepwise introduction of different metal ions in polysal-
4
O]
2
12
(ph)en structures using our developed TM protocol to afford
(catalytically active) heteromultimetallic complexes useful for
multistep organic syntheses.
Experimental Section
General Comments. All starting materials were purchased from
commercial sources and used without further purification. Compound
15
6
a was prepared using a previously reported method. Elemental
analyses were performed at the Unidad de An a´ lisis Elemental of the
University of Santiago de Compostela (Spain). All NMR measurements
were carried out on a Bruker-400 MHz spectrometer at ambient
temperature unless stated otherwise, and chemicals shifts are given in
parts per million versus TMS. Mass spectrometric data were obtained
from the Research Support unit of the ICIQ, and MALDI-TOF
experiments were carried out with pyrene as a matrix. IR spectra (solid
state) were recorded on a Bruker Tensor 27 apparatus.
The combination of all of the spectroscopic/spectrometric
and crystallographic results leads to the following mecha-
nistic proposal (Scheme 4). First, an initial coordination
complex is formed (cf., 5), after which one of the OAc
ligands of the Ni(OAc) fragment bridges to the Lewis-acidic
2
Zn(II) center (cf., X-ray structure of 2). Then, double acetate
transfer between the Ni and Zn center is anticipated. In the
final stage, a Zn(OAc)
sphere, and a mononuclear Ni(II)salphen complex is formed
cf., X-ray structure of 4 and NMR studies with complex
). This mechanism can also be projected onto the trans-
2
unit is expelled from the coordination
Synthesis of [Zn(3-MeO-salphen)] ·[Zn(OAc) ] (1). To a solu-
2
tion of 1,2-diaminobenzene (253.9 mg, 2.34 mmol) and 3-methoxy-
salicylaldehyde (920.0 mg, 6.05 mmol) in MeOH (40 mL) was added
(
5
a solution of Zn(OAc)
2
2
·2H O (1.39 g, 6.33 mmol) in MeOH (20 mL).
The initial orange solution turned immediately yellow, and a yellow
solid started to precipitate rapidly. The product was collected by
filtration after 6 h and dried to furnish 1.48 g of 1 (2.30 mmol, 98%).
metalation of similar Zn(salphen) complexes using various
8
other metal acetate salts.
1
H NMR (400 MHz, d -DMSO): δ 9.01 (s, 2H, CHdN), 7.89-7.91
6
Conclusion
3
4
(m, 2H, ArH), 7.38-7.40 (m, 2H, ArH), 7.05 (d, J ) 8.1 Hz, J )
In summary, we here describe the isolation of bimetallic
monosalphen structures that are relevant to both the transmeta-
lation of Zn(salphen) complexes as well as the buildup of
3
4
1
.5 Hz, 2H, ArH), 6.87 (d, J ) 7.6 Hz, J ) 1.4 Hz, 2H, ArH), 6.47
3
(t, J ) 7.8 Hz, 2H, ArH), 3.77 (s, 6H, OMe), 1.81 (s, 6H, OAc).
13
1
C{ H} NMR (100 MHz, 80/20 v/v d
5 6
-pyridine/d -DMSO): δ 178.79,
9,10
polynuclear compounds based on salen scaffolds.
The
165.32, 164.38, 153.93, 140.89, 128.70, 128.32, 120.07, 117.56,
1
15.16, 113.33, 56.19, 23.59. MS (MALDI-TOF, pyrene matrix): m/z
fundamental basis for the formation of bis-Zn-monosalphen
complexes is the Lewis acidity of the central Zn ion. This allows
the ligation of an axial ligand (i.e., OAc) and, therefore, isolation
of bimetallic complexes 1-3, 5, and 8. The in situ transmeta-
lation of 2 affords mononuclear Ni(II) complex 4 (Scheme 3),
which is coordinatively saturated and effectively will not provide
stable binuclear species. Additional experiments have revealed
that only one alkoxy group in the salphen structure is needed
to provide bimetallic species. Furthermore, metalation of more
flexible salen ligands incorporating, for instance, cyclohexyl
+
+
5
63.1 (M - OAc) , 903.1 (2 × [M - Zn(OAc)
2
] + Na) , 1003.1 (2
] +
2
O: C, 47.36; H, 4.28; N,
+
×
[M - Zn(OAc)
2
] + Zn(OAc)] , 1085.1 (M + [M - Zn(OAc)
2
+
Na] . Anal. calcd for C26
.25. Found: C, 47.38; H, 4.11; N, 4.20.
Synthesis of [Zn(3-EtO-salphen)] ·[Zn(OAc)
H N
24 2
O
8
Zn
2
·2H
4
2
] (2). To a solu-
tion of 1,2-diaminobenzene (0.56 g, 5.18 mmol) and 3-ethoxy-
salicylaldehyde (2.23 g, 13.42 mmol) in MeOH (130 mL) was added
a solution of Zn(OAc)
2
2
·2H O (2.56 g, 11.66 mmol) in MeOH (20
mL). The initial orange solution turned immediately yellow, and a
yellow solid started to precipitate rapidly. The product was collected
Inorganic Chemistry, Vol. 48, No. 3, 2009 851

San Felices et al.
1
by filtration after 2 h and dried to furnish 3.48 g of 2 (4.83 mmol,
5%). Crystals suitable for X-ray analysis were obtained from hot
4 (see its H NMR data) and 1 equiv of Zn(OAc)
2
(δ 1.8). MALDI-
+
9
TOF-MS (pyrene matrix): m/z 637.0 [M , bis-Ni(II) complex, calcd.
1
+
MeOH. H NMR (400 MHz, d
6
-DMSO): δ ) 9.01 (s, 2H, CHdN),
637.06], 583.0 [(M - OAc) , Zn/Ni complex, calcd. 583.04], 499.0
3
+
+
7
8
2
4
.88-7.90 (m, 2H, ArH), 7.37-7.39 (m, 2H, ArH), 7.05 (d, J )
[(M + K) , mono-Ni complex, calcd. 499.06], 483.1 [(M + Na) ,
4
3
4
+
.1 Hz, J ) 1.6 Hz, 2H, ArH), 6.87 (d, J ) 7.5 Hz, J ) 1.6 Hz,
mono-Ni complex, calcd. 483.08], 460.1 [M , mono-Ni complex,
calcd. 460.09]. IR (neat, cm ): 3035, 2970, 2931, 1738, 1633, 1612,
1585, 1555, 1500, 1459, 1394, 1378, 1323, 1294, 1254, 1211, 1179,
1120, 1097, 1026, 922, 778, 756, 733, 663. Anal. calcd for
3
3
-1
H, ArH), 6.42 (t, J ) 7.7 Hz, 2H, ArH), 4.05 (q, J ) 7.0 Hz,
3
H, OCH
CH
DMSO): δ 178.81, 165.83, 164.36, 153.05, 140.86, 129.19, 128.31,
2
CH
3
3
), 1.81 (s, 6H, OAc), 1.37 (t, J ) 7.0 Hz, 6H,
1
1
OCH
2
3 5 6
). C{ H} NMR (100 MHz, 80/20 v/v d -pyridine/d -
28
C H
28
N
2
O
8
NiZn ·1/2H
2
O: C, 51.45; H, 4.47; N, 4.29. Found: C,
1
20.43, 117.79, 117.55, 113.41, 65.07, 23.57, 15.93. MS (MALDI-
51.33; H, 4.55; N, 4.28.
+
TOF, pyrene matrix): m/z 466.2 [M - Zn(OAc)
Zn(OAc)
OAc) , 857.0 (M + Zn(OAc)
2
] , 489.2 [M -
Synthesis of Monoimine (6b). A mixture of 3-methyl-salicy-
laldehyde (1.00 g, 7.34 mmol) and 1,2-diaminobenzene (0.91 g,
8.42 mmol) in MeOH (30 mL) was stirred for 3 h and then cooled
to -25 °C, upon which the product crystallized. Filtration and
drying afforded yellow/orange needles of 6b (0.41 g, 25%).
+
+
2
+ Na] , 505.1 [M - Zn(OAc)
2
+ K] , 591.1 (M -
+
+
+
2
+ Na) , 1302.08 (2M) . Anal. calcd
for C28
H
28
N
2
O
8
Zn
9.92; H, 4.55; N, 4.10.
Synthesis of [Zn(3-EtO-salnaph)]·[Zn(OAc)
tion of 2,3-diaminonaphthalene (38.3 mg, 0.242 mmol) and
-ethoxy-salicylaldehyde (91.4 mg, 0.550 mmol) in MeOH (20 mL)
was added a solution of Zn(OAc) ·2H O (156.4 mg, 0.713 mmol)
2
·1.5H
2
O: C, 49.57; H, 4.61; N, 4.13. Found: C,
4
2
] (3). To a solu-
Subsequent fractions yielded mixtures of the mono- and bis-imine
1
products. H NMR (400 MHz, CDCl
3
): δ 13.28 (s, 1H, OH), 8.64
3
3
3
(s, 1H, CHdN), 7.38 (d, J ) 7.6 Hz, 2H, ArH), 7.13 (t, J ) 7.6
4
3
4
Hz, J ) 1.4 Hz, 1H, ArH), 7.07 (d, J ) 8.2 Hz, J ) 1.5 Hz, 1H,
2
2
3
in MeOH (5 mL). The initial orange solution turned immediately
yellow, and a yellow solid started to precipitate rapidly. The product
ArH), 6.90 (t, J ) 7.5 Hz, 1H, ArH), 6.80-6.84 (m, 2H, ArH),
1
3
1
4.04 (s, 2H, NH
2
), 2.35 (s, 3H, Me). C{ H} NMR (100 MHz,
was collected by filtration after 16 h and dried to furnish 132.7 mg
CDCl ): δ 162.36, 159.06, 140.84, 135.37, 134.12, 129.97, 128.05,
3
1
6
of 3 (0.184 mmol, 76%). H NMR (400 MHz, d -DMSO): δ 9.16
126.13, 118.84, 118.80, 118.39, 115.80, 15.52. MS (ESI): m/z 227.1
+
(
7
s, 2H, CHdN), 8.34 (s, 2H, ArH), 7.94-7.96 (m, 2H, ArH),
(M + H) . Anal. calcd for C14
14 2 2
H N O·1/5 H O: C, 73.15; H, 6.31;
3
4
.51-7.53 (m, 2H, ArH), 7.09 (d, J ) 8.1 Hz, J ) 1.4 Hz, 2H,
N, 12.19. Found: C, 73.31; H, 6.31; N, 12.24.
3
4
3
ArH), 6.90 (d, J ) 7.5 Hz, J ) 1.4 Hz, 2H, ArH), 6.45 (t, J )
7
6
Synthesis of Nonsymmetrical [Zn(3-EtO-salphen)] (7). To a
solution of 3-ethoxy-salicylaldehyde (0.15 g, 0.90 mmol) and the
monoimine 6a (0.23 g, 0.71 mmol) in MeOH (30 mL) was added
3
2 3
.7 Hz, 2H, ArH), 4.07 (q, J ) 7.0 Hz, 4H, OCH CH ), 1.85 (s,
3
13
1
H, OAc), 1.38 (t, J ) 7.0 Hz, 6H, OCH
2 3
CH ). C{ H} NMR
(
100 MHz, 80/20 v/v d
5
-pyridine/d -DMSO): δ 178.64, 166.18,
6
a solution of Zn(OAc)
2
2
·2H O (0.45 g, 2.05 mmol) in MeOH (10
1
1
65.48, 152.99, 140.52, 133.34, 129.28, 128.85, 127.22, 120.61,
18.09, 115.03, 113.43, 65.04, 23.55, 15.99. MS (MALDI-TOF-
mL). The initial orange-colored solution was stirred for 18 h and
then filtered, and the residue was dried to furnish complex 7 as a
1
+
yellow to orange solid (327.0 mg, 0.61 mmol, 86%). H NMR (400
MS, pyrene matrix): m/z 539.1 [M - Zn(OAc)
-
Zn(OAc)
-
2
+
+ Na] , 641.0 [M
+
MHz, d
6 5
-acetone/d -pyridine, 90:10 v/v): δ 9.05 (s, 1H, CHdN),
OAc] , 823.0 [M + (Zn(OAc)
2
+ Zn(OAc)] , 907.0 [M + 2 ×
4
+
+
9
.04 (s, 1H, CHdN), 7.74-7.84 (m, 2H, ArH), 7.51 (d, J ) 2.7
2
+ Na] , 1009.2 [2 × M - EtH + H] , 1073.2 [2 × {M
4
+
Hz, 1H, ArH), 7.31-7.36 (m, 2H, ArH), 7.28 (d, J ) 2.6 Hz, 1H,
ArH), 7.14 (d, J ) 8.0 Hz, J ) 1.7 Hz, 1H, ArH), 7.00 (d, J )
Zn(OAc)
2
} + K] . Anal. calcd for C32
H
30
N
2
O
8
Zn
2
2
·2.5H O: C,
3
4
3
5
1.49; H, 4.73; N, 3.75. Found: C, 51.58; H, 4.56; N, 3.79.
Synthesis of [Ni(3-EtO-salphen)] (4). To a solution of 1,2-
diaminobenzene (0.20 g, 1.85 mmol) and 3-ethoxy-salicylaldehyde
0.63 g, 3.79 mmol) in MeOH (30 mL) was added a solution of
Ni(OAc) ·4H O (0.99 g, 3.98 mmol) in MeOH (15 mL). The initial
4
3
7
.4 Hz, J ) 1.8 Hz, 1H, ArH), 6.46 (t, J ) 7.7 Hz, 1H, ArH),
3
4
.35 (q, J ) 7.0 Hz, 2H, OCH
2
CH
), 1.34 (s, 9H, C(CH
-pyridine): δ 172.60, 172.30, 167.47, 164.47,
3 3 3
), 1.60 (s, 9H, C(CH ) ), 1.37
3
13
1
(
t, J ) 7.0 Hz, 3H, OCH
2
CH
3
3 3
) ). C{ H}
(
NMR (100 MHz, d
5
2
2
1
1
6
63.79, 153.36, 142.80, 141.48, 141.03, 135.18, 130.72, 130.50,
mixture was stirred for 16 h, and then the microcrystalline dark
brown product was collected by filtration and dried. Yield: 716.6
mg (1.55 mmol, 84%). Crystals suitable for X-ray diffraction were
30.35, 128.20, 127.72, 122.56, 121.35, 119.76, 117.19, 113.38,
6.51, 36.69, 34.72, 32.31, 30.71, 16.58. MS (MALDI-TOF, pyrene
+
+
1
matrix):m/z534.3(M) ,1070.4(2M) .Anal.calcdforC H N O Zn·1/
obtained from CHCl
3
. H NMR (400 MHz, d
6
-DMSO): δ 8.88 (s,
30 34
2
3
3
MeOH: C, 66.64; H, 6.51; N, 5.12. Found: C, 66.69; H, 6.74; N,
5.23.
Synthesis of Nonsymmetrical [Zn(3-EtO-salphen)] ·[Zn(OAc)2]
2
7
H, CHdN), 8.16-8.18 (m, 2H, ArH), 7.33-7.36 (m, 2H, ArH),
3
4
3
.23 (d, J ) 8.2 Hz, J ) 1.4 Hz, 2H, ArH), 6.89 (d, J ) 7.5 Hz,
4
3
3
J ) 1.4 Hz, 2H, ArH), 6.57 (t, J ) 7.8 Hz, 2H, ArH), 4.03 (q, J
3
)
6.9 Hz, 4H, OCH
2
CH
H NMR (400 MHz, CDCl
m, 2H, ArH), 7.21-7.23 (m, 2H, ArH), 6.95 (d, J ) 8.1 Hz, 2H,
3
), 1.34 (t, J ) 7.0 Hz, 6H, OCH
2
CH
3
).
(8). To a solution of monoimine 6b (0.38 g, 1.68 mmol) and
3-ethoxy-salicylaldehyde (0.29 g, 1.75 mmol) in MeOH (40 mL)
was added a solution of Zn(OAc) ·2H O (0.88 g, 4.01 mmol) in
1
3
): δ 8.28 (s, 2H, CHdN), 7.72-7.74
3
(
2
2
3
3
ArH), 6.75 (d, J ) 6.8 Hz, 2H, ArH), 6.56 (t, J ) 7.8 Hz, 2H,
ArH), 4.07 (q, J ) 6.9 Hz, 4H, OCH CH ), 1.55 (t, J ) 6.9 Hz,
2 3
MeOH (10 mL). A yellow solution was initially obtained, and after
10 min, a suspension was noted. The product was collected by
filtration after 2 h and dried to yield 8 as a yellow solid (912.1 mg,
3
3
13
1
6
H, OCH
2
CH
3
). The product is too insoluble for a C{ H} NMR
+
1
analysis. MS (MALDI-TOF, pyrene matrix): m/z 483.0 [M + Na] ,
1.46 mmol, 87%). H NMR (400 MHz, d -DMSO): δ 8.99 (s, 1H,
6
+
9
43.1 (2 M + Na) . Anal. calcd for C24
H
22
N
2
O
4
Ni·1/2H
2
O: C,
CHdN), 8.98 (s, 1H, CHdN), 7.87-7.89 (m, 2H, ArH), 7.36-7.39
3
4
6
1.31; H, 4.93; N, 5.96. Found: C, 61.20; H, 4.82; N, 5.72.
Mixed Zn-Ni Complex (5). Complex 2 (98.1 mg, 0.143 mmol)
was suspended in THF (10 mL), and then Ni(OAc) ·4H O (47.7
(m, 2H, ArH), 7.28 (d, J ) 7.9 Hz, J ) 1.6 Hz, 1H, ArH), 7.20
3
3
4
(d, J ) 6.8 Hz, 1H, ArH), 7.06 (d, J ) 8.1 Hz, J ) 1.6 Hz, 1H,
ArH), 6.88 (d, J ) 7.5 Hz, J ) 1.7 Hz, 1H, ArH), 6.44 (t, J )
7.4 Hz, 1H, ArH), 6.41 (t, J ) 7.7 Hz, 1H, ArH), 4.09 (q, J )
7.0 Hz, 2H, OCH CH ), 2.20 (s, 3H, Ar-CH ), 1.81 (s, 6H, OAc),
1.37 (t, J ) 7.0 Hz, 3H, OCH
-pyridine): δ 179.20, 173.12, 166.70, 164.15, 164.07, 153.38,
141.09, 141.06, 135.63, 135.09, 132.51, 129.56, 128.16, 128.10,
3
4
3
2
2
3
3
mg, 0.192 mmol) was added. The initial yellowish suspension was
stirred for 18 h, concentrated, and triturated with MeOH. The
2
3
3
1
3
13
residue was dried to yield an orange to brown solid (53.8 mg, 0.0835
2 3
CH ). C{ H} NMR (100 MHz,
1
mmol, 55%). H NMR analysis was performed in both d
6
-DMSO
d
5
and d
5
-pyridine, affording exclusively (after dissolution) complex
852 Inorganic Chemistry, Vol. 48, No. 3, 2009

Characterization of a Binuclear Intermediate Species
1
2
20.85, 119.68, 119.43, 117.30, 117.27, 114.12, 113.41, 65.67,
(100 MHz, CDCl
126.45, 118.21, 114.81, 111.41, 64.87, 63.89, 27.76, 23.93, 14.57.
3
+ 10% v/v d -pyridine): δ 164.71, 151.89,
5
3.57, 18.52, 16.06. MS (MALDI-TOF, pyrene matrix): m/z 459.1
+
+
+
+
[
M - Zn(OAc)
2
+ Na] , 899.0 [2 M - 2 × Zn(OAc)
2
+ Na] .
MS (MALDI-TOF): m/z 472.2 (M) , 495.2 (M + Na) , 947.3 (2M
+
+
Anal. calcd for C27
26
H N
2
O
7
Zn
2
·1.5H
2
O: C, 50.02; H, 4.51; N, 4.32.
+ H) , 971.3 (2M + Na) . Anal. calcd for C24
H
28
N
2
O
4 2
Zn·2H O:
Found: C, 50.32; H, 4.36; N, 4.37.
C, 56.53; H, 6.33; N, 5.49. Found: C, 56.49; H, 6.02; N, 5.42.
Synthesis of [Zn(3-EtO-salphen)] (9). To a solution of 1,2-
diaminobenzene (0.19 g, 1.76 mmol) and 3-ethoxy-salicylaldehyde
Synthesis of Nonsymmetrical [Ni(3-EtO-salphen)] (11). To a
suspension of complex 8 (147.1 mg, 0.224 mmol) in THF (15 mL)
(
(
0.59 g, 3.55 mmol) in MeOH (80 mL) was added Zn(propionate)
1.00 g, 4.73 mmol) dissolved in warm MeOH (50 mL). The initial
2
was added a suspension of Ni(OAc)
2
2
·4H O (63.4 mg, 0.255 mmol)
in THF (5 mL). Upon addition of the Ni reagent, the reaction
mixture turned deep red over time (1-2 h), and complete dissolution
was noted. After 3 h, the solution was concentrated and triturated
with MeOH (25 mL) and filtered and the residue dried to give a
reaction mixture was heated to reflux and then allowed to cool to
ambient temperature. After 16 h, the obtained suspension was
filtered and the residue dried to furnish a yellow to orange solid
1
1
(
732.5 mg, 1.57 mmol, 89%). H NMR (400 MHz, d
6
-DMSO): δ
brown solid. Yield: 77.9 mg (0.181 mmol, 81%). H NMR (400
9
.01 (s, 2H, CHdN), 7.88-7.90 (m, 2H, ArH), 7.37-7.39 (m, 2H,
6
MHz, d -DMSO): δ 8.88 (s, 1H, CHdN), 8.87 (s, 1H, CHdN),
8.15-8.17 (m, 2H, ArH), 7.46 (d, J ) 7.4 Hz, J ) 1.3 Hz, 1H,
3
4
3
3
4
ArH), 7.05 (d, J ) 8.1 Hz, J ) 1.6 Hz, 2H, ArH), 6.87 (d, J )
7
4
3
.5 Hz, J ) 1.6 Hz, 2H, ArH), 6.42 (t, J ) 7.7 Hz, 2H, ArH),
ArH), 7.33-7.36 (m, 2H, ArH), 7.23-7.27 (m, 2H, ArH), 6.91 (d,
3
3
3
4
4
.05 (q, J ) 7.0 Hz, 4H, OCH
2
CH
3
), 1.37 (t, J ) 7.0 Hz, 6H,
). C{ H} NMR (100 MHz, d
J ) 7.4 Hz, J ) 1.6 Hz, 1H, ArH), 6.54-6.61 (m, 2H, ArH),
13
1
3
OCH
1
1
2
CH
3
5
-pyridine): δ 166.55,
4.12 (q, J ) 7.0 Hz, 2H, OCH
(t, J ) 7.0 Hz, 3H, OCH
DMSO/d
2
CH
3
13
), 2.16 (s, 3H, Ar-CH
3
), 1.30
). C{ H} NMR (100 MHz, d
-benzene 90:10 v/v): δ 164.29, 158.23, 156.23, 156.10,
3
1
63.95, 153.42, 150.70, 140.98, 136.30, 129.17, 128.01, 124.28,
2
CH
3
6
-
20.54, 118.68, 117.16, 113.35. MS (MALDI-TOF): m/z ) 466.3
6
+
(
M) . Anal. calcd for C24
H
22
N
2
O
4
Zn ·H
2
O: C, 59.33; H, 4.98; N,
149.48, 142.51, 142.39, 134.66, 131.84, 128.46, 127.89, 127.18,
5
.77. Found: C, 59.06; H, 5.22; N, 5.77.
Synthesis of [Zn(3-EtO-salen)] (10). A homogeneous mixture
of (1R,2R)-1,2-diaminocyclohexane (68.3 mg, 0.598 mmol), 3-ethoxy-
salicylaldehyde (0.20 g, 1.20 mmol), Zn(OAc) ·2H O (0.42 g, 1.91
mmol), and NEt (5 mL) in MeOH (40 mL) was shortly heated to
126.78, 120.90, 119.89, 119.33, 115.99, 115.95, 114.78, 114.45,
+
64.76, 16.20, 15.03. MS (ESI, MeOH): m/z 453.1 (M + Na) , 883.2
+
(2 M + Na) . Anal. calcd for C23
20 2 3
H N O Ni: C, 64.08; H, 4.68;
2
2
N, 6.50. Found: C, 64.00; H, 4.64; N, 6.40.
3
reflux. Then, the mixture was allowed to cool and was further stirred
for 2 h at ambient temperature, after which the mixture was filtered
Acknowledgment. Both ICREA and ICIQ are acknowl-
edged for financial support. Dr. Noem ´ı Cabello is thanked
for the MS studies.
and the solid residue dried to furnish 10 as a light yellow solid
1
(
195.6 mg, 0.413 mmol, 69%). H NMR (400 MHz, CDCl
3
+ 10%
v/v d
6
4
5
-pyridine): δ 8.28 (s, 2H, CHdN), 6.77-6.82 (m, 4H, ArH),
.44 (t, 3J ) 7.7 Hz, 2H, ArH), 4.21 (m, 2H, -CH-NdC),
.05-4.10 (m, 4H, OCH CH ), 3.06 (br, 2H, cyclohexyl-H), 2.37
Supporting Information Available: Relevant spectroscopic data
and copies of spectra and crystallographic data in CIF format. This
material is free of charge via the Internet at http://pubs.acs.org.
2
3
3
(
br, 2H, cyclohexyl-H), 1.93 (br, 2H, cyclohexyl-H), 1.46 (t, J )
), 1.34 (br, 2H, cyclohexyl-H). 13C{ H} NMR
1
IC8018265
6.7 Hz, 6H, OCH
2
CH
3
Inorganic Chemistry, Vol. 48, No. 3, 2009 853