Iron(II) and zinc(II) monohelical binaphthyl salen complexes

Article abstract of DOI:10.1039/b508538a

A new chiral binaphthyl salen ligand with rigid polyaromatic sidearms gives monohelical Complexes (Fe^II and Zn^II) of predetermined handedness. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b508538a

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Iron(II) and zinc(II) monohelical binaphthyl salen complexes{
Alexander V. Wiznycia, John Desper and Christopher J. Levy*
Received (in Cambridge, UK) 16th June 2005, Accepted 28th July 2005
First published as an Advance Article on the web 23rd August 2005
DOI: 10.1039/b508538a
A new chiral binaphthyl salen ligand with rigid polyaromatic
II
Curved polyaromatics such as phenanthrenes meet this require-
II
sidearms gives monohelical complexes (Fe and Zn ) of
predetermined handedness.
ment and 4-hydroxy-3-phenanthrenecarboxaldehyde, 2, is well
suited for constructing the sidearms. This aldehyde is the key
precursor to the ligand (R)-3, and was synthesized in five steps
from naphthalene (Scheme 1). Friedel–Crafts acylation of
The helix is one of the most important chiral motifs in natural
systems and there is an increasing interest in the development of
helical transition metal complexes and related supramolecular
14
naphthalene to give 4 followed the general method of Haworth
but with significant improvement in the workup procedure,
allowing for facile separation of the desired compound from its
1
structures. The majority of investigations concern helicates, which
2
have two or more metal centers. By contrast, few studies focus on
1
5
regioisomer. Wolff–Kishner reduction of 4 to give 5 and
simpler mononuclear helices (monohelices), particularly those with
3
a single multidentate chiral ligand. The high asymmetry of these
subsequent cyclization with methanesulfonic acid to give 6
16
followed established procedures. Condensation of 6 with ethyl
formate to give 7 followed the procedure outlined by Cagniant and
complexes makes them attractive candidates as asymmetric
4
catalysts, and this has been explored in several studies.
1
7
Kirsch. Oxidation of 7 with triphenylmethanol in trifluoroacetic
19
1
8
Single-stranded monohelices are synthetically challenging targets
since multidentate ligands often prefer to bridge metal centers and
produce helicates. The preference is the result of the specific
geometric relationship between the donor atoms and the flexibility
acid gave 2 in good yield.
Condensation of (R)-1 with 2 in ethanol produced the neutral
2
0
ligand (R)-3 (Scheme 2). Single crystals (orange prisms) suitable
for X-ray analysis were grown by solvent diffusion of hexanes into
21
a methylene chloride solution of (R)-3. The dihedral angle
5
of the spacers between them. If the donors can orient themselves
to form strong binding interactions with a single metal and if the
ligand is pliable enough to allow for wrapping without strong
steric repulsions, then a monohelical complex is likely. To date
there have been no examples of monohelical metallosalen
complexes, although ‘stepped’ complexes such as those synthesized
between the naphthyl planes is 103.4u and all four donor atoms are
on one side of the molecule (Fig. 1). One half of the ligand has
6
7
8
by Katsuki et al., Jacobsen et al., and DiMauro and Kozlowski
9
strongly suggest the possibility. Also, Katz et al. and Takata
10
et al. have reported single-stranded polymeric salen helices.
Our approach to producing monohelices is to link two rigid
planar fragments (sidearms) to a chiral directing unit (the
backbone). The chirality of the backbone determines the handed-
ness of the helix (P or M). An excellent candidate for the backbone
precursor is the chiral 1,19-binaphthyl-2,29-diamine (1), which has
been shown to be effective at producing significantly twisted
1
1
tetradentate Schiff base ligands and complexes. The dihedral
angle between the naphthyl planes of the binaphthyl fragment is
correlated to the strength of the steric repulsions between them:
there is a flat-bottomed potential at 90u but a steep potential
Scheme 1 Synthesis of 2.
12
outside of the ca. 60u to 130u range. Thus, donors attached to
binaphthyl units have a great degree of flexibility in binding metals
with different sizes and coordination geometries, but the limita-
tions on the twisting and the steric bulk of the binaphthyl group
13
tend to disfavor the formation of dihelicates.
In order to form monohelices, the rigid sidearms attached to the
binaphthyl backbone need low steric bulk so that they can
approach one another and overlap upon complex formation.
111 Willard Hall, Department of Chemistry, Kansas State University,
Manhattan, Kansas, 66506, USA. E-mail: clevy@ksu.edu;
Fax: +1 785 532 6666; Tel: +1 785 532 6688
{ Electronic supplementary information (ESI) available: Full experimental
details and spectroscopic data. See http://dx.doi.org/10.1039/b508538a
II
Scheme 2 Synthesis of (R)-3 and its Zn and Fe complexes.
II
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grow single crystals suitable for X-ray analysis were unsuccessful
but the racemic compound, (R/S)-9, could be crystallized by
solvent diffusion of methanol into a methylene chloride solution.
2
6
The crystal structure shows racemic helices, with the R
enantiomer giving M helices and the S enantiomer producing P
helices (Fig. 3). The structure of the R enantiomer is similar to that
of the zinc complex, except that the iron has a distorted tetrahedral
geometry, with no coordinated solvent molecule. As a result, the
iron complex is more twisted and this is perhaps most evident from
the dihedral angle between the sidearms (74.5u), which is
significantly larger than in the zinc complex. The dihedral angle
between the naphthyl fragments (68.6u) is similar to the zinc
complex.
Fig. 1 Thermal ellipsoid plot (50% probability) of (R)-3. Selected bond
˚
lengths (A): C(01)–C(11) 1.488(3), C(02)–N(02) 1.411(3), N(02)–C(35)
.285(3), C(22)–C(35) 1.429(3), C(21)–O(21) 1.325(3).
In both complexes there is significant rotation of the aromatic
arms relative to the naphthyl units (the range is 63.9u to 83.8u)
indicating that there is little delocalization of p electrons between
these aromatic segments. A roughly perpendicular relationship
between the naphthyl units and the aromatic sidearms has been
1
nearly coplanar naphthyl and phenanthrene units (dihedral of
.6u), indicating that the p system is largely delocalized, as has been
7
22
seen for other binaphthyl salen ligands. The other half of the
molecule shows a dihedral angle of 27.4u, suggesting that packing
forces are enough to significantly disrupt the delocalization.
11
observed in other binaphthyl Schiff base complexes.
We have demonstrated the first synthesis of monohelical salen
complexes and have shown that the 1,19-binaphthyl backbone is
an effective helix-forming unit, producing only the helical form
predicted based on its chirality. The aromatic phenanthrene-based
sidearms are effective because they are rigid and planar and
therefore can approach each other in the helix without strong steric
repulsions. We are undertaking a series of theoretical calculations
and CD spectral analyses in order to understand the solution
chemistry of these complexes and are examining several metal
centers to establish their catalytic activity for asymmetric
transformations.
II
II
Both Zn and Fe complexes of (R)-3 can be produced using
2
3
the same general synthetic method. The ligand is allowed to react
with anhydrous MCl in the presence of excess NaOCH , which
2
3
deprotonates the phenolic hydrogens and prevents the build up of
hydrogen chloride. The zinc complex, (R)-8, is bright yellow and
the elemental analysis and NMR data indicate that the isolated
material has no coordinated water or solvent, which is very
2
4
unusual for a zinc salen complex. Single crystals were grown
from diffusion of methanol into a methylene chloride solution of
2
5
(
R)-8. The X-ray crystal structure shows that only M helices are
present and that methanol is coordinated to the zinc ion giving a
five coordinate metal center (Fig. 2). The dihedral angle between
the sidearms is 43.7u and the space-filling diagram indicates some
degree of overlap. The dihedral angle between the naphthyl
fragments is 66.9u, significantly smaller than in the free ligand, but
still within the region where binaphthyl-based steric repulsions are
relatively low.
II
The Fe complex, (R)-9, was isolated as an air and moisture
sensitive paramagnetic red-brown powder. Repeated attempts to
2 2
Fig. 3 (a) P and M helices in the structure of (R/S)-9?(CH Cl ). (b)
Thermal ellipsoid plot (50% probability) for the R,M molecule. Selected
˚
Fig. 2 (a) Thermal ellipsoid plot (50% probability) of (R)-8(CH OH).
3
bond lengths (A) and angles (u): Fe(2)–O(221) 1.907(2), Fe(2)–O(241)
˚
Selected bond lengths (A) and angles (u): Zn(1)–O(21) 1.9828(15), Zn(1)–
O(41) 1.9553(16), Zn(1)–O(61) 2.1542(18), Zn(1)–N(02) 2.0708(18),
Zn(1)–N(12) 2.0861(18), C(21)–O(21) 1.281(3), C(22)–C(35) 1.432(3),
C(35)–N(02) 1.301(3), N(02)–C(02) 1.427(3), C(41)–O(41) 1.297(3),
C(42)–C(55) 1.433(3), C(55)–N(12) 1.284(3), N(02)–Zn(1)–N(12)
1.879(3), Fe(2)–N(202) 2.010(3), Fe(2)–N(212) 2.022(3), C(221)–O(221)
1.311(4), C(222)–C(235) 1.424(5), C(235)–N(202) 1.285(4), C(202)–N(202)
1.422(4), C(241)–O(241) 1.306(4), C(242)–C(255) 1.412(6), C(255)–N(212)
1.290(5), C(212)–N(212) 1.426(5), N(202)–Fe(2)–N(212) 94.80(12),
O(221)–Fe(2)–O(241) 121.06(11). (c) and (d) Space filling plots of the
R,M molecule.
92.26(7), O(21)–Zn(1)–O(41) 100.52(7). (b) Space filling plot.
4
694 | Chem. Commun., 2005, 4693–4695
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with 5 M HCl gave a precipitate that was extracted into diethyl ether
This work is supported by the National Science Foundation
under grant number CHE-0349258 and by Kansas State
University.
(
3 6 150 mL). The extracts were combined, dried over MgSO
and dried in vacuo to give 7 (23.12 g, 86% yield). Anal. calc. for
: C 80.34, H 5.39. Found: C 80.07, H 5.47.
8 These reagents have been used in similar transformations: C. Bilger,
P. Demerseman and R. Royer, J. Heterocycl. Chem., 1985, 22, 735.
9 A mixture of 7 (22.82 g, 102 mmol) and triphenylmethanol (52.98 g,
04 mmol) in trifluoroacetic acid (400 mL) was refluxed for 2 h and then
4
, filtered,
15 12 2
C H O
1
Notes and references
1
2
1
2
3
C. Piguet, G. Bernardinelli and G. Hopfgartner, Chem. Rev., 1997, 97,
005.
H. C. Aspinall, Chem. Rev., 2002, 102, 1807; M. Albrecht, Chem. Rev.,
001, 101, 3457.
For monohelices from chiral ligands see ref. 4 and H. M u¨ rner, A. von
Zelewsky and H. Stoeckli-Evans, Inorg. Chem., 1996, 35, 3931; M. Seitz,
A. Kaiser, S. Stempfhuber, M. Zabel and O. Reiser, Inorg. Chem., 2005,
cooled. The solution was diluted with 800 mL water. The resulting
precipitate was collected and suspended into 1 M NaOH (400 mL),
stirred for 15 min and filtered to remove insoluble solids. The filtrate was
adjusted to pH 1 with 5 M HCl to give a yellow precipitate that was
2
2
collected, washed with H
ethanol and dried in vacuo to give 2 (5.68 g, 82% yield). Anal. calc. for
: C 81.07, H 4.54. Found: C 81.24, H 4.75.
0 A mixture of 2 (2.077 g, 9.3 mmol) and (R)-1 (1.329 g, 4.7 mmol) in
2
O (200 mL), recrystallized from boiling
15 10 2
C H O
44, 4630. Ansa-metallocenes are generally not included in the definition
of monohelices.
2
ethanol (100 mL) was refluxed for 18 h and the resultant suspension was
filtered while hot. The precipitate was washed with hot ethanol (40 mL)
and dried in vacuo to give (R)-3 (2.958 g, 91% yield) as a bright red solid.
4
5
Y.-Z Zhu, Z.-P Li, J.-A Ma, F.-Y Tang, L. Kang, Q.-L Zhou and A. S.
C. Chan, Tetrahedron: Asymmetry, 2002, 13, 161; K. Maruoka,
N. Murase and H. Yamamoto, J. Org. Chem., 1993, 58, 2938; N. End
and A. Pfaltz, Chem. Commun., 1998, 589; N. End, L. Macko,
Z. Margareta and A. Pfaltz, Chem. Eur. J., 1998, 4, 818; C. Guo, J. Qui,
X. Zhang, D. Verdugo, M. L. Larter, R. Christie, P. Kenney and
P. J. Walsh, Tetrahedron, 1997, 53, 4145.
Anal. calc. for C50
H 4.85, N 4.25. (S)-3 was synthesized using the same procedure, with
S)-1 in place of the (R)-1. Anal. calc. for C50 : C 86.68, H 4.66,
N 4.04. Found: C 86.66, H 4.88, N 4.12.
32 2 2
1 Crystal data for (R)-3. Bruker SMART 1000, C50H N O , M 5 692.78,
32 2 2
H N O : C 86.68, H 4.66, N 4.04. Found: C 86.93,
(
32 2 2
H N O
2
J. S. Fleming, K. L. V. Mann, S. M. Couchman, J. C. Jeffery,
J. A. McCleverty and M. D. Ward, J. Chem. Soc., Dalton Trans., 1998,
˚
˚
˚
orthorhombic, a 5 11.0977(6) A, b 5 16.4934(10) A, c 5 18.7071(11) A,
3
˚
V 5 3424.1(3) A , T 5 203(2) K, space group P2
h collection range 2.13 to 28.28u, m(Mo-Ka) 5 0.08 mm , 24779
reflections collected, 4512 unique (Rint 5 0.0886) which were used in all
1 1 1
2 2 (no. 19), Z 5 4,
2
047; J. S. Fleming, E. Psillakis, S. M. Couchman, J. C. Jeffery,
J. A. McCleverty and M. D. Ward, J. Chem. Soc., Dalton Trans., 1998,
37; E. Psillakis, J. C. Jeffery, J. A. McCleverty and M. D. Ward,
21
2
5
2
1
calculations. R 5 0.0646 (all data) and wR(F ) 5 0.1182 (all data).
J. Chem. Soc., Dalton Trans., 1997, 1645; M. V a´ zquez, M. R. Bermejo,
M. Fondo, A. M. Garc ´ı a-Deibe, J. Sanmart ´ı n, R. Pedrido, L. Sorace
and D. Gatteschi, Eur. J. Inorg. Chem., 2003, 1128; M. V a´ zquez,
M. R. Bermejo, M. Fondo, A. Garc ´ı a-Deibe, A. M. Gonz a´ lez and
R. Pedrido, Eur. J. Inorg. Chem., 2002, 465.
T. Katsuki, Synlett, 2003, 281; T. Katsuki, Adv. Synth. Catal., 2002, 344,
131; T. Katsuki, Peroxide Chem., 2000, 303; Y. N. Ito and T. Katsuki,
Bull. Chem. Soc. Jpn., 1999, 72, 603; R. Irie, T. Hashihayata, T. Katsuki,
M. Akita and Y. Moro-oka, Chem. Lett., 1998, 1041.
M. Palucki, N. S. Finney, P. J. Pospisil, M. L. Gueler, T. Ishida and
E. N. Jacobsen, J. Am. Chem. Soc., 1998, 120, 948; N. S. Finney,
P. J. Pospisil, S. Chang, M. Palucki, R. G. Konsler, K. B. Hansen and
E. N. Jacobsen, Angew. Chem., Int. Ed. Engl., 1997, 36, 1720.
E. F. DiMauro and M. C. Kozlowski, Org. Lett., 2001, 3, 1641.
Y. Dai, T. J. Katz and D. A. Nichols, Angew. Chem., Int. Ed. Engl.,
CCDC 276257. See http://dx.doi.org/10.1039/b508538a for crystal-
lographic data in CIF or other electronic format.
2 K. Bernardo, S. Leppard, A. Robert, G. Commenges, F. Dahan and
B. Meunier, New J. Chem., 1995, 19, 129; C.-M. Che, H.-L. Kwong,
W.-C. Chu, K.-F. Cheng, W.-S. Lee, H.-S. Yu, C.-T. Yeung and
K.-K. Cheung, Eur. J. Inorg. Chem., 2002, 1456.
23 Zinc chloride (0.065 g, 0.48 mmol), sodium methoxide (0.070 g,
1.30 mmol) and (R)-3 (0.300 g, 0.43 mmol) were suspended in a 2 : 1
mixture of benzene–ethanol (15 mL). After stirring for 12 h the reaction
mixture was concentrated to a yellow solid that was dissolved into
methylene chloride (15 mL). The solution was filtered to remove fine
insoluble material, and the clear filtrate was diluted with ethanol
(45 mL). Upon stirring for 3 h a yellow precipitate formed that was
collected and dried in vacuo to afford (R)-8 (0.213 g, 65%). Anal. calc.
2
6
7
8
9
1
996, 35, 2109.
0 Y. Furusho, T. Maeda, T. Takeuchi, N. Makino and T. Takata, Chem.
Lett., 2001, 1020.
1 C.-M. Che and J.-S. Huang, Coord. Chem. Rev., 2003, 242, 97.
2 L. Di Bari, G. Pescitelli and P. Salvadori, J. Am. Chem. Soc., 1999, 121,
998.
3 For an example of a dinuclear binaphthyl–Al salen helicate see:
T. M. Ovitt and G. W. Coates, J. Am. Chem. Soc., 1999, 121, 4072.
4 R. D. Haworth, J. Chem. Soc., 1932, 1125.
for C50
3.77. The synthesis of (R)-9 followed the same procedure as for (R)-7
except that anhydrous FeCl was used and THF was used in place of
CH Cl during workup. It was also necessary to concentrate the THF–
ethanol solution to 3/4 volume for precipitation of the product to occur.
The product, (R)-9, was a red-brown powder (0.156 g, 48% yield).
30 2 2
H N O Zn: C 79.42, H 4.00, N 3.70. Found: C 79.06, H 3.86, N
1
2
1
1
2
2
7
III
1
m
eff 5 5.05 m
except that (R/S)-3 was used in place of (R)-3 and concentration was not
necessary for product precipitation. Anal. calc. for C50 Fe: C
80.43, H 4.05, N 3.75. Found: C 80.73, H 3.80, N 3.57.
B
. (R/S)-9 was synthesized using an identical procedure
1
30 2 2
H N O
1
5 The 1- and 2-substituted naphthalene products are formed in
approximately equal amounts. Following is the modified workup of
the Haworth procedure for a reaction using 72 g of naphthalene. The
reaction mixture was poured into crushed ice (300 g) and acidified with
24 S. Mizukami, H. Houjou, Y. Nagawa and M. Kanesato, Chem.
Commun., 2003, 1148.
3 3 2 2
25 Crystal data for (R)-8(CH OH)?[0.75(CH OH)0.25(CH Cl )]. Bruker
5
M HCl (200 mL). Upon vigorous stirring a brown precipitate formed.
The mixture was filtered and the resultant solid washed with H
150 mL) and hexanes (150 mL). The solid was suspended in benzene
300 mL) at 60 uC for 15 min, allowed to cool, filtered and dried in vacuo
to give 4 (31.81 g, 37% yield).
SMART 1000, C52H36.75Cl0.5N O3.75Zn, M 5 832.68, orthorhombic,
2
3
˚
˚
˚
˚
2
O
a 5 12.3373(4) A, b 5 13.3410(5) A, c 5 23.6254(8) A, V 5 3888.6(2) A ,
T 5 203(2) K, space group P2 (no. 19), Z 5 4, 2h collection
(
(
1 1 1
2 2
21
range 1.72 to 28.32u, m(Mo-Ka) 5 0.72 mm , 41396 reflections
collected, 9192 unique (Rint 5 0.0421) which were used in all
calculations. R
2
5 0.0492 (all data), wR(F ) 5 0.0874 (all data) and
1
6 N. Harada, A. Saito, N. Koumura, H. Uda, B. de Lange, W. F. Jager,
H. Wynberg and B. L. Feringa, J. Am. Chem. Soc., 1997, 119, 7241;
V. Premasagar, V. A. Palaniswamy and E. J. Eisenbraun, J. Org. Chem.,
1
Flack 5 20.021(8). CCDC 276258. See http://dx.doi.org/10.1039/
b508538a for crystallographic data in CIF or other electronic format.
1
981, 46, 2974.
7 P. Cagniant and G. Kirsch, C. R. Seances Acad. Sci., Ser. C, 1976, 282,
65. This report only provides an outline of the reaction with no detail
26 Crystal data for (R)-9?CH
2 2
Cl . Bruker SMART 1000,
˚
32Cl FeN , M 5 831.54, triclinic, a 5 13.1443(12) A,
1
C
51
H
2
2 2
O
˚
˚
4
b 5 16.4557(15) A, c 5 18.9601(17) A, a 5 99.736(6)u,
b 5 104.006(6)u, c 5 94.156(4)u, V 5 3894.1(6) A , T 5 173(2) K,
space group P1, Z 5 4, 2h collection range 1.26 to 28.39u, m(Mo-
Ka) 5 0.57 mm , 49344 reflections collected, 17792 unique
3
˚
and no characterization of the product. A detailed report follows. To a
solution of 6 (23.53 g, 120 mmol) in benzene (350 mL) was added ethyl
formate (8.88 g, 120 mmol) and sodium methoxide (12.95 g, 240 mmol).
The reaction mixture was stirred for 12 h at room temperature and the
resulting precipitate collected and washed with benzene (2 6 50 mL).
The solid was then dissolved into 1 M NaOH (500 mL) and the aqueous
solution was washed with hexanes (3 6 100 mL). Acidification to pH 1
¯
2
1
1
(Rint 5 0.1024) which were used in all calculations. R 5 0.1632 (all
2
data) and wR(F ) 5 0.1642 (all data). CCDC 276259. See http://
dx.doi.org/10.1039/b508538a for crystallographic data in CIF or other
electronic format.
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 4693–4695 | 4695