Templated synthesis and site-selective conversion of completely nonsymmetrical bis-metallosalphen complexes

Article abstract of DOI:10.1002/ejic.200900282

A metal-templated, stepwise approach toward fully nonsymmetrical bis-metallosalphen complexes is described. The synthesis comprises the selective monometalation of diimine precursors and subsequent introduction of the second metal ion by using various salicylaldehyde reagents. In the case of a bis-Zn(salen) derivative, the presence of different peripheral substituents on the two metallosalen units gave rise to a large difference in kinetic stability, which was used to selectively demetalate the more labile site. This result shows promise for the preparation of heterobimetallic structures. The first X-ray molecular structure of a completely nonsymmetrical bis-salphen complex is also reported.

Full text of DOI:10.1002/ejic.200900282

SHORT COMMUNICATION
DOI: 10.1002/ejic.200900282
Templated Synthesis and Site-Selective Conversion of Completely
Nonsymmetrical Bis-Metallosalphen Complexes
Ana M. Castilla,[a] Simona Curreli,[a] Nina M. Carretero,[a] Eduardo C. Escudero-Adán,[a]
Jordi Benet-Buchholz,[a] and Arjan W. Kleij*[a,b]
Keywords: Nonsymmetrical complexes / N,O ligands / Diastereoselectivity / Templated synthesis / Zinc
A metal-templated, stepwise approach toward fully nonsym-
metrical bis-metallosalphen complexes is described. The
synthesis comprises the selective monometalation of diimine
precursors and subsequent introduction of the second metal
ion by using various salicylaldehyde reagents. In the case of
a bis-Zn(salen) derivative, the presence of different periph-
eral substituents on the two metallosalen units gave rise to a
large difference in kinetic stability, which was used to selec-
tively demetalate the more labile site. This result shows
promise for the preparation of heterobimetallic structures.
The first X-ray molecular structure of a completely nonsym-
metrical bis-salphen complex is also reported.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
introduction of different aryl substituents in the second
salen unit. Here we report the Zn-templated synthesis of a
unique monometallic precursor and its conversion into fully
nonsymmetrical bis-metallosalphen complexes [salphen =
N,NЈ-1,2-phenylenebis(salicylideneimine)]. The presence of
different peripheral substituents on both Zn(salphen) mod-
ules creates a significant difference in the kinetic stability
of the Zn ions, which is demonstrated by a site-selective
demetalation of one of the Zn(salphen) units.
Introduction
Salen ligands are generally considered privileged, be-
cause many stereoselective transformations can be carried
out with these versatile structures.[1] Recently, the use of
(multimetallic) metallosalen complexes in material chemis-
try has emerged as a powerful approach towards functional
(supramolecular) systems with wide-ranging properties.[2,3]
Although synthetic salen chemistry has matured signifi-
cantly over the last decade,[4] the development of pro-
cedures for multinuclear salen complexes that allow particu-
lar control over the properties of each individual complexed
metal ion still represents a great challenge,[5] as a conse-
quence of the labile nature of the imine bond during synthe-
sis. The presence of different metallosalen units within the
multinuclear complex can provide a means for site-selective
functionalization that is potentially interesting for the devel-
opment of heteromultimetallic systems[6] useful in cascade
or orthogonal tandem catalysis. We recently reported on the
preparation of a small library of diimine precursors derived
from 3,3Ј-diaminobenzidine (see Scheme 1 for an example)
and their conversion into symmetrical bimetallic salphen
complexes with a nonsymmetry within each salen unit.[7,8]
We anticipated that a selective introduction of one metallo-
salen module onto the diaminobenzidene backbone could
lead to an interesting monometallic triimine precursor,
whose unreacted half-salen unit[7] subsequently tolerates the
Scheme 1. Synthesis of monometallic triimine precursors 1 and 2.
Results and Discussion
[a] Institute of Chemical Research of Catalonia (ICIQ),
Av. Paisos Catalans 16, 43007 Tarragona, Spain
Fax: +34-977-920-224
We recently reported the preparation of a series of di-
imines, including A and B (Scheme 1), derived from 3,3Ј-
diaminobenzidine.[7,8] These diimines can be prepared on a
larger scale and serve as valuable intermediates for symmet-
rical homobimetallic salphen complexes. We anticipated
that, under appropriate conditions, these diimines could
E-mail: akleij@iciq.es
[b] Institució Catalana de Recerca i Estudis Avançats (ICREA),
Pg. Lluís Companys 23, 08010 Barcelona, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900282.
Eur. J. Inorg. Chem. 2009, 2467–2471
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. W. Kleij et al.
SHORT COMMUNICATION
also serve to access monometalated precursors comprising Table 1. Synthesis of various fully nonsymmetrical homobimetallic
salphen complexes by using the monometallic synthons 1 and 2.[a]
one metallosalen unit and a (unreacted) half-salen unit at
the other end of the benzidene backbone. Different sol-
vents, reagents and conditions were initially screened for
selective formation of monometalated structures. Under di-
luted conditions and by using stoichiometric amounts of
both 3,5-dinitrosalicylaldehyde and Zn(OAc)2·2H2O, we
found that mono-Zn complexes 1–2 could be readily ob-
tained in moderate to good yields (40–80%) in repeated ex-
periments. Upon using either higher concentrations or
other reaction stoichiometries, mixtures of components
were obtained (i.e. unreacted diimine and mono- as well as
bimetallic structures), which complicated compound purifi-
cation.
The identity of mono-Zn compounds 1 and 2 can be eas-
1
ily deduced from their respective H NMR and 13C{1H}
NMR spectra. While diimines A and B produce only a sin-
gle imine resonance, compound 1 and 2 give rise to three
separate imine peaks consistent with the nonsymmetric na-
ture of these structures (Figure 1). Further analytical proof
for the structures of these compounds was provided by
MALDI-TOF mass spectrometry.
Complex
M
R
X
Y
Yield [%][b]
3
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Ni
H
H
H
H
H
H
H
H
H
H
H
tBu
Cl
NO2
Br
Cl
H
H
Br
Br
H
92
83
82
68
90
59[d]
67
81
76
76
68
41
4
5
6
tBu
H
7
8
allyl[c]
Me
H
9
H
H
10
11
12
13
14
tBu
OMe
H
allyl[c]
tBu
H
[e]
[e]
Zn
[a] Reactions were performed in THF/MeOH (4:1 v/v) at room
temp. [b] Isolated yield. [c] allyl: –CH2CH=CH2. [d] After
recrystallization from DMSO/Et2O. [e] See the scheme at the top
of the table.
Interestingly, both polar as well as nonpolar substituents
may be readily introduced on the periphery of the metallos-
alen unit in the second metalation step. The presence of
nonpolar groups renders the complex more soluble, and iso-
lated yields in these cases are, as a consequence, lower.
Mono-Zn complex 2 could also be directly converted into
bis-Ni(salphen) derivative 13 by using an excess of Ni(OAc)2·
4H2O and 3-tert-butylsalicylaldehyde in the second met-
alation stage. Here, the reaction sequence involves a trans-
metalation of the Zn(salphen) unit[10] and completion of the
half-salen unit with subsequent metalation by the Ni rea-
gent. This latter example demonstrates that various non-
Figure 1. Comparison between the aromatic regions (1H NMR,
[D6]DMSO) of compounds B, 2, 4, 9 and 12. The imine protons in
each compound are marked with an asterisk.
Mono-Zn complexes 1 and 2 were then used as starting symmetrical bis-metallosalphen can be accessed by using
materials for synthesizing completely dissymmetric bimetal- mono-Zn precursors 1 and 2. As for mono-Zn complexes 1
lic salphen structures (Table 1 and accompanying Figure). and 2, the nonsymmetrical nature of bimetallic species 3–
Combination of 2 with various salicylaldehydes and 14 is revealed in their NMR spectra by the presence of four
Zn(OAc)2·2H2O in THF/MeOH provided a synthetic route distinct peaks for the imine protons/carbons (Figure 1).
to homobimetallic compounds with ample scope. In all
Finally, we also examined the possibility of introducing
cases, the second metalation reaction is fast enough to pre- chirality in these nonsymmetrical homobimetallic struc-
vent potential imine hydrolysis and/or equilibration of the tures. Chiral binaphthyl derivative (S)-C (Table 1, Figure)
[11]
half-salen unit.[9] Thus, it is fair to say that the metal ions
was utilized to prepare chiral bis-Zn(salphen) complex
function as templating centres for the construction of both 14. Although the isolated (non-optimized) yield was only
the mono-Zn precursors 1 and 2, as well as complexes 3– moderate (Table 1), this result yet further illustrates the ver-
14 (Table 1).
satility of the presented approach toward nonsymmetrical
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2467–2471

Templated Synthesis of Nonsymmetrical Bis-Metallosalphen Complexes
bimetallic salphen structures and their potential use in mental conditions. Obviously, the nonmetalated site in 15
asymmetric synthesis.
could provide a means to access useful heterobimetallic
Single crystals of complex 12 were obtained from THF/ structures.[19]
MeOH and analyzed by X-ray diffraction (Figure 2). The
structure shows unambiguously the molecular nonsym-
metry: one Zn(salphen) unit carries an allyl substituent at
the 5-position. This allyl fragment may be of great use in
subsequent synthetic operations in order to arrive at larger
multinuclear salen structures through olefin metathesis re-
actions.
Figure 2. X-ray molecular structure of complex 12 with two axially
coordinating MeOH ligands. Co-crystallized solvent molecules, H-
atoms and disorder in one of the MeOH ligands, one of the NO2
groups and the allyl group are omitted for clarity.
Complex 11 constitutes an interesting combination of
two distinct Zn(salphen) modules. One of the Zn(salphen)
units has sterically demanding tert-butyl groups at the 3
and 3Ј positions: the presence of these tert-butyl groups is
generally considered necessary to prevent dimerization of
the Zn(salphen) complex through bridging of one of the
oxygen atoms of the N2O2 donor set.[12–14] We recently re-
ported that such monomeric Zn(salphen) complexes are
susceptible to decomposition in (aqueous) noncoordinating
solvents[15] and in the presence of protic N-heterocyclic li-
Scheme 2. Site-selective conversion of nonsymmetrical bis-
gands.[16] We therefore probed the selective demetalation of
complex 11,[17,18] having both a dimeric as well as mono-
meric site (Scheme 2), in a noncoordinating medium. Stir-
ring of a sample of 11 in aqueous CHCl3, however, did not
gave a selective demetalation of the structure, as illustrated
Zn(salphen) complex 11 into monometalated 15 by using imid-
azole; below the NMR spectra ([D6]DMSO) following this conver-
sion: (a) t = 0 h, 1.1 equiv. imidazole, (b) t = 4 h, 1 equiv. imidazole,
(c) t = 2 h, 2.1 equiv. imidazole, (d) t = 20 h, 2.1 equiv. imidazole;
* = imine resonances of complex 11, ᭹ = imine resonances of com-
plex 15, o = imidazole resonances.
1
by H NMR spectroscopy and MALDI-TOF mass spec-
trometry. Treatment of 11 with two equivalents of imid-
azole[16] in CH3CN proved to be more successful. In due
course, the monomeric site was demetalated with a calcu-
lated 85% conversion [Scheme 2, spectrum (d)] and a re-
markably high selectivity, providing a clean route towards
Conclusions
In summary, we present here the first stepwise and selec-
monometalated bis-salphen structure 15 (see Scheme 2). tive approach toward the construction of fully nonsymmet-
The formation of 15 could be substantiated by the presence rical bis-metallosalphen complexes with ample peripheral
of a diagnostic imine peak at 9.5 ppm and the presence of functionalization. The key intermediates, i.e. monometal-
a set of two distinct OH resonances located around ated triimine precursors 1 and 2, are prepared by a metal-
14.1 ppm (see also Supporting Information). This result templated approach. The Zn ions in these complexes serve
demonstrates that the two Zn(salphen) units in 11 possess to stabilize the salphen unit and prevent imine hydrolysis/
a significantly different kinetic stability under the experi- equilibration. In the second metalation step, again metal
Eur. J. Inorg. Chem. 2009, 2467–2471
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2469

A. W. Kleij et al.
SHORT COMMUNICATION
ppm. 13C{1H} NMR (100 MHz, [D6]DMSO): δ = 172.23, 172.16,
170.81, 166.95, 163.79, 162.69, 162.33, 162.14, 144.67, 142.46,
141.64, 141.54, 139.85, 139.47, 139.15, 138.67, 138.03, 137.54,
135.79, 135.46, 134.77, 134.60, 132.61, 131.67, 130.98, 130.64,
127.56, 125.74, 123.96, 122.53, 120.97, 119.52, 119.46, 117.36,
116.72, 115.40, 114.35, 112.75, 112.48, 102.53, 35.34, 35.07, 34.92,
29.53 [2ϫC(CH3)3], 29.20 ppm. MS (MALDI+, pyrene): m/z =
1094.2 [M + H]+. C52H47BrN6O8Zn2·0.5H2O (1103.74): calcd. C
56.59, H 4.38, N 7.61; found C 56.45, H 4.37, N 7.61.
templation facilitates selective formation of nonsymmetrical
derivatives 3–14. As an illustrative example, bis-Zn(salphen)
complex 11 has been used to take advantage over the sig-
nificant difference in kinetic stability between the mono-
meric and dimeric Zn(salphen) sites, which leads, under ap-
propriate conditions, to site-selective monodemetalation.
This observation may be considered a useful starting point
for the formation of heterobimetallic derivatives that may
find application in homogeneous catalysis. Currently, we are
exploring the utilization of our methodology for bimetallic
salen complexes valuable in catalytic applications.
Bis-Ni(salphen) Complex 13: To a solution of mono-Zn complex 2
(120.4 mg, 0.152 mmol) in THF (100 mL) was added a solution of
3-tert-butylsalicylaldehyde (49.3 mg, 0.277 mmol) in MeOH
(10 mL) and subsequently a solution of Ni(OAc)2·4H2O (111.7 mg,
0.449 mmol) in MeOH (10 mL). The dark red-brown solution was
stirred for 18 h, filtered, and the filtrate was concentrated. Tritura-
tion with MeOH (40 mL) furnished a brown solid after filtration
and drying. Yield: 103.9 mg (0.104 mmol, 68%). 1H NMR
(400 MHz, [D6]DMSO): δ = 9.04 (s, 1 H, CH=N), 8.80 (s, 1 H,
CH=N), 8.77 (s, 1 H, CH=N), 8.60 (s, 1 H, CH=N), 8.40 (m, 1 H,
ArH), 8.28 (s, 1 H, ArH), 8.13 (m, 1 H, ArH), 7.97–8.03 (m, 2 H,
ArH), 7.69–7.71 (m, 2 H, ArH), 7.46–7.51 (m, 2 H, ArH), 7.22–
7.30 (m, 3 H, ArH), 6.59–6.67 (m, 3 H, ArH), 1.40 [br. s, 27 H,
3ϫC(CH3)3] ppm. The compound is too insoluble for a decent
13C-NMR spectroscopic analysis. MS (MALDI+, pyrene): m/z =
1000.2 [M+], 2004.4 [2M + H]+. C52H48N6Ni2O8 (1002.36): calcd.
C 62.31, H 4.83, N 8.38; found C 62.07, H 4.96, N 8.43.
Experimental Section
Mono-Zn(salphen) Complex 2: To
(181.8 mg, 0.340 mmol) in CHCl3 (120 mL) was added sub-
sequently solution of 3,5-dinitrosalicylaldehyde (74.3 mg,
a solution of diimine B
a
0.350 mmol) in MeOH (10 mL) and a solution of Zn(OAc)2·2H2O
(74.9 mg, 0.341 mmol) in MeOH (10 mL). The colour of the homo-
geneous mixture first turned deep orange/red and then yellow (after
addition of the Zn reagent). The mixture was stirred at room temp.
for 18 h and was then filtered to furnish a red solid (Fraction 1:
115.6 mg, 43%). A second fraction was obtained by concentration
of the mother liquors and trituration of the residue with MeOH
and filtration. The second fraction was recrystallized from THF/
MeOH to finally yield the pure product (red solid, 58.6 mg). Total
yield: 174.2 mg (0.220 mmol, 65%). 1H NMR (400 MHz, [D6]-
DMSO): δ = 13.93 (s, 1 H, OH), 9.45 (s, 1 H, CH=N), 8.99 (s, 1
¯
Crystal Data for 12: C56H58N6O11.5Zn2, Mr = 1129.82, triclinic, P1,
a = 13.6205(8) Å, b = 14.3234(8) Å, c = 15.1813(11) Å, α =
78.444(2)°, β = 64.902(2)°, γ = 80.902(2)°, V = 2618.8(3) Å3, Z =
2, ρ = 1.433 gcm–3, µ = 0.985 mm–1, λ = 0.71073 Å, T = 100(2) K,
F(000) = 1176, θ(min) = 1.46°, θ (max) = 33.20°, 18360 reflections
collected, 11975 reflections unique (Rint = 0.0312), GOF = 1.049,
R1 = 0.0608 and wR2 = 0.1764 [IϾ2σ(I)].
4
H, CH=N), 8.96 (s, 1 H, CH=N), 8.88 (d, J = 3.1 Hz, 1 H, ArH),
4
4
8.72 (d, J = 3.1 Hz, 1 H, ArH), 8.23 (d, J = 1.5 Hz, 1 H, ArH),
3
3
4
7.99 (d, J = 8.7 Hz, 1 H, ArH), 7.75 (d, J = 8.6, J = 1.6 Hz, 1
3
4
3
H, ArH), 7.53 (d, J = 7.8, J = 1.4 Hz, 1 H, ArH), 7.40 (d, J =
7.8 Hz, 1 H, ArH), 7.35 (d, J = 8.3 Hz, 1 H, ArH), 7.30 (d, J =
8.0 Hz, 1 H, ArH), 7.26–7.28 (m, 2 H, ArH), 7.18 (d, J = 8.2, J
CCDC-724935 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
3
3
3
4
3
3
= 1.8 Hz, 1 H, ArH), 6.95 (t, J = 7.7 Hz, 1 H, ArH), 6.49 (t, J =
7.5 Hz, 1 H, ArH), 5.21 (s, 2 H, NH2), 1.464 [s, 9 H, C(CH3)3],
1.456 [s, 9 H, C(CH3)3] ppm. 13C{1H} NMR (100 MHz, [D6]-
DMSO): δ = 172.06, 166.95, 163.57, 162.50, 161.91, 159.46, 142.90,
142.38, 141.60, 139.45, 138.90, 138.52, 138.43, 136.39, 135.81,
134.69, 133.63, 131.65, 131.10, 130.91, 127.00, 123.91, 122.57,
119.48, 119.44, 119.11, 118.48, 117.30, 115.68, 114.90, 113.45,
112.75, 34.90, 34.49, 29.53, 29.26 ppm. MS (MALDI+, pyrene):
m/z = 775.2 [M – CH3]+, 791.1 [M + H]+, 797.2 [M + Li]+, 813.2
[M + Na]+. C41H38N6O7Zn (792.19): calcd. C 62.16, H 10.61, N
4.83; found C 61.98, H 10.83, N 5.05.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures and analytical data for all new com-
pounds, full structural details for 12 and NMR spectroscopic de-
tails for the conversion of 11 into 15.
Acknowledgments
Institució Catalana de Recerca i Estudis Avançats (ICREA) and
Institute of Chemical Research of Catalonia (ICIQ) foundation are
thanked for financial support. The Spanish Ministereo de Educa-
ción y Ciencias (MEC) is also thanked for a financial contribution
through project number CTQ2008-02050/BQU.
Bis-Zn(salphen) Complex 6: To a solution of mono-Zn complex 2
(41.5 mg, 0.0524 mmol) and 5-bromo-3-tert-butylsalicylaldehyde
(29.0 mg, 0.113 mmol) in THF (30 mL) was added a solution of
Zn(OAc)2·2H2O (28.8 mg, 0.131 mmol) in MeOH (10 mL) The re-
action mixture was stirred for 18 h at room temp. Then, the solvent
was removed under reduced pressure, and the residue was triturated
with MeOH (10 mL) and filtered. The orange solid product was
further air-dried. Yield: 39.2 mg (0.0358 mmol, 68%). 1H NMR
(400 MHz, [D6]DMSO): δ = 9.49 (s, 1 H, CH=N), 9.29 (s, 1 H,
[1] a) J. F. Larrow, E. N. Jacobsen, Top. Organomet. Chem. 2004,
6, 123; b) L. Canali, D. C. Sherrington, Chem. Soc. Rev. 1999,
28, 85; c) T. Katsuki, Chem. Soc. Rev. 2004, 33, 437; d) P. G.
Cozzi, Chem. Soc. Rev. 2004, 33, 410.
[2] S. J. Wezenberg, A. W. Kleij, Angew. Chem. Int. Ed. 2008, 47,
2354.
[3] A. W. Kleij, Chem. Eur. J. 2008, 14, 10520.
[4] A. W. Kleij, Eur. J. Inorg. Chem. 2009, 193.
[5] P.-H. Aubert, P. Audebert, M. Roche, P. Capdevielle, M.
Maumy, G. Ricart, Chem. Mater. 2001, 13, 2223.
[6] For a supramolecular approach toward heteromultimetallic
systems see: S. J. Wezenberg, E. C. Escudero-Adán, J. Benet-
Buchholz, A. W. Kleij, Inorg. Chem. 2008, 47, 2925.
4
CH=N), 9.14 (s, 1 H, CH=N), 9.04 (s, 1 H, CH=N), 8.88 (d, J =
4
3.1 Hz, 1 H, ArH), 8.73 (d, J = 3.1 Hz, 1 H, ArH), 8.37 (s, 1 H,
3
ArH), 8.34 (s, 1 H, ArH), 8.00–8.11 (m, 3 H, ArH), 7.90 (d, J =
4
3
8.8 Hz, 1 H, ArH), 7.62 (d, J = 2.6 Hz, 1 H, ArH), 7.34 (t, J =
3
4
7.8 Hz, 2 H, ArH), 7.26 (t, J = 7.6 Hz, 2 H, ArH), 7.23 (d, J =
3
2.7 Hz, 1 H, ArH), 6.49 (dt, J = 7.7, 4J = 2.7 Hz, 2 H, ArH), 1.49
[br., 18 H, two C(CH3)3 groups overlap], 1.46 [s, 9 H, C(CH3)3]
2470
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Templated Synthesis of Nonsymmetrical Bis-Metallosalphen Complexes
[7]
[16] E. C. Escudero-Adán, J. Benet-Buchholz, A. W. Kleij, Dalton
Trans. 2008, 734.
S. Curreli, E. C. Escudero-Adán, J. Benet-Buchholz, A. W.
Kleij, J. Org. Chem. 2007, 72, 7018.
[17] Although structure 11 can be easily demetalated in the presence
of imidazole under these conditions, the use of the nonsymmet-
ric bis-Zn(salphen) complexes in catalysis is not hampered,
since sufficient stabilization of the metal ions can be obtained
through coordination of solvent molecules and/or substrates
and introduction of appropriate substituents on the phenyl side
groups of the Zn(salphen) units.
[18] We have focused on the use of complex 11 for selective demet-
alation of the monomeric site; the other bis-Zn(salphen) com-
plexes (except for 6) have insufficiently large substituents on
each 3- or 3Ј-position of the bis-salen ligand, and therefore
the difference in stability between the two Zn(salphen) units is
considered too minimal for a selective conversion.
[19] Mono-Zn(salphen) complex 2 was also used as a starting point
for direct heterobimetallic complex formation by using
Ni(OAc)2·4H2O and various salicylaldehydes in CHCl3/MeOH
as medium. In all cases, both 1H NMR spectroscopy as well
as MALDI-TOF-MS clearly indicated the isolation of a mix-
ture of compounds due to transmetalation of the Zn(salphen)
module (see ref.[10]). As a result, both homo- and heterobimet-
allic species were observed.
[8]
S. Curreli, E. C. Escudero-Adán, J. Benet-Buchholz, A. W.
Kleij, Eur. J. Inorg. Chem. 2008, 2863.
In some cases, we observed imine equilibration of mono-Zn
[9]
complex 2 after prolonged standing in [D6]DMSO.
[10]
Transmetalation of Zn(salphen) complexes has been previously
reported: a) E. C. Escudero-Adán, J. Benet-Buchholz, A. W.
Kleij, Inorg. Chem. 2007, 46, 7265; b) S. J. Wezenberg, G. A.
Metselaar, E. C. Escudero-Adán, J. Benet-Buchholz, A. W.
Kleij, Inorg. Chim. Acta 2009, 362, 1053.
[11] a) A. R. van Doorn, D. J. Rushton, M. Bos, W. Verboom, D. N.
Reinhoudt, Recl. Trav. Chim. Pay-Bas. 1992, 111, 415; b) L.
Jin, Y. Huang, H. Jing, T. Chang, P. Yan, Tetrahedron: Asym-
metry 2008, 19, 1947.
[12] A. L. Singer, D. A. Atwood, Inorg. Chim. Acta 1998, 277, 157.
[13] A. W. Kleij, M. Kuil, M. Lutz, D. M. Tooke, A. L. Spek,
P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek, Inorg.
Chim. Acta 2005, 359, 1807.
[14] a) C. T. L. Ma, M. J. MacLachlan, Angew. Chem. Int. Ed. 2005,
44, 4178; b) J. K.-H. Hui, Z. Yu, M. J. MacLachlan, Angew.
Chem. Int. Ed. 2007, 46, 7980.
[15] S. J. Wezenberg, E. C. Escudero-Adán, J. Benet-Buchholz,
A. W. Kleij, Org. Lett. 2008, 10, 3311.
Received: March 26, 2009
Published Online: May 7, 2009
Eur. J. Inorg. Chem. 2009, 2467–2471
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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