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Measuring the Optical Activity of Chiral Imprints in Insoluble Highly Cross-linked Polymers.

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space group P2,/n, u = 11.015(2), h = 14.851(2). c = 15.752(2)
91.22(2)", V = 2576.3(5) A', e = 1.22 gcm-', Z = 4, p = 5.21 cm-'. wscan, range: 20 = 4-46'' in _+ hkl, scan width: 0.8 + 0.35 tan0, variable
scan speed: 90 s max., 3802 reflections collected, internal consistency:
0.019, 3317 unique reflections. 2891 reflections considered observed with
F 2 4a(F). Structure solution with direct methods, anisotropic decription
of non-hydrogen atoms, isotropic description of H-atoms. R = 0.052,
R, = 0.055 with w - ' = oZ(F) ,000235 F2, highest A/o = 0.048, highest
residual electron density: 0.68 e/h3.-Further details of the crystal structure determination are available from the Fachinformationszentrum
Information mbH,
Karlsruhe. Gesellschaft fur wissenschaftl~ch-technische
D-7514 Eggenstein-Leopoldshafen 2 (FRG). on quoting the depository
number CSD-54482, the names of the authors, and the journal citation.
1151 K3BP, contains a linear P = B = P anion, related to 8. its B-P bond length
being 1.767 which is somewhat longer than in 8 : H. G. von Schnenng,
M. Somer, M. Hartweg. K. Peters, Angew. Chem. 102 (1990) 63; Angew.
Chem. Int. Ed. Engl. 29 (1990) 65.
[16] R. Appel, F. Knoch, V. Winkhaus. J. Organomet. Chem. 307 (1986) 93.
[17] R. Appel, P. Folling, B. Josten, M. Siray, V. Winkhaus, F. Knoch. Angrw.
Chem. 96 (1984) 620, Angew. Chem. Int. Ed. Engl. 23 (1984) 619.
[18] P. Kolle, Dissertation, Universitit Miinchen 1987.
I191 R. W. Kirk. P. L. Timms. J. Chem. SOC.Chem. Commun. 1967, 18; E. F.
Pearson, R. V. McCormick, J. Chem. Phvs. 58(1973) 1619; E. F. Pearson,
C. L. Norris, W. H. Flygare, ihid. 60(1974) 1761; H. W Kroto, R. J. Suffolk, N. P. C. Westwood, Chem.-Phys.Lett 22(1973)495; C. Kirby, H. W.
Kroto, M. J. Taylor, J. Chem. Soc. Chem. Commun. 1978, 19; C. Kirby,
H. W Kroto, J. Mol. Spectrose. 83 (1980) 1.
[20] W. Rattay, Dissertation. Universitit Miinchen 1985.
[21] V. Hyna. Dissertation, Universitit Miinchen 1989.
Scheme 1
as binding groups) can be converted into the polymer
P - 1 - 0 . After detaching the template 2 the polymer P - 1 - 0 ,
whose voids each contain two projecting free boronic acid
groups, is obtained (see Scheme 1). This polymer can be used
to achieve highly selective chiral separations of both the racemate of the template 2t3] and D,L-mannose.~'"]
As these polymers are completely insoluble the chiral
voids cannot be characterized by direct methods, and the
usual method of investigating the racemate separation behavior only gives indirect information. If chiropticdl measurements could be made on such polymers this would certainly make possible major advances. Vogl, Pzno et aI.I41have
recently described a method for measuring the optical rotation of helical atropisomeric polymers in the solid phase. We
have investigated the possibility of applying this method to
macroporous polymers with chiral voids, and of using it, for
example, to determine the contribution of the chirdl imprints
to the specific rotation for the polymers P-1-•
and P-1- .
To measure the specific rotation of a solid it must be examined as a suspension in a medium whose refractive index is as
close as possible to that of the substance being investigated.
Where measurements are made in media with different refractive indices (Fig. l), different values are obtained for the
Measuring the Optical Activity of Chiral Imprints in
Insoluble Highly Cross-linked Polymers **
By Giinter Wuyf* and Giinter Kirstein
In recent years there has been increasing interest in the
technique of using template molecules to produce imprints in
cross-linked polymers, then applying these for molecular
recognition purposes.",
To prepare these, polymerizable
monomer molecules possessing suitable binding groups are
first attached to template molecules. The "template
monomer" is then converted into a macroporous polymer by
polymerizing in the presence of a large excess of a cross-linking agent. The template can then be removed, leaving microvoids in the polymer; the shape of the voids and the configuration of the binding groups are determined by the template
molecule. For example, the template monomer 1 (consisting
of phenyl-cc-D-mannopyranoside 2 as a template and two
4-vin ylphenylboronic acid residues attached by esterification
60 50 -
40 30[MI::,
1 S550 1 S 5 0 0
1 S350 1.5300
Fig. 1. Molar optical rotation [M:4o6
and optical transmission D (measured in
mA obtained from a photomuitipiier) for suspensions o f P - 1 - 0 in media with
different refractive indices [5]. c = 2.0.
[*] Prof. Dr. G. Wulff, Dr. G. Kirstein
Institut fur Organische Chemie und Makromolekulare Chemie der Universitit
Universititsstrasse 1, D-4000 Diisseldorf (FRG)
[**I Polymers with Enzyme-Analogous Structures, Paper 28. This work was
supported by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie. Paper 27: [I c].
@2VCH Verlugsgesell.~chuftmbH. 0-6940 Wernheim. 1990
optical transmission D and the specific rotation. Only in the
optimum range with 80-95 % transmission does one obtain
the maximum, and correct, value for the specific rotation of
To test the reliability of such measurements,
the refractive index of the medium was adjusted to the optimum value and the molar optical rotation was measured as
a function of the concentration (Fig. 2). It is also important
that the density of the medium should be as similar as possible to that of the solid, so as to avoid ~edimentation.'~.
Since birefringence effects can be mistaken for optical rota-
0S70-0833/90/0606-0~84$ 0 3 SO+ .2S/O
Angetis. Chem Int. Ed. Engl. 29 (1990) No. 6
" - -
546 nm
To investigate the effects of the template and of the void
structure on the optical rotation, the polymer P - 1 - 0 made
from the template monomer 1 was studied in greater detail.[,]
As can be seen from Figure 1 and Table 2, this gave a molar
rotation value
of - 60.6'. The measurements over a
range of concentrations (Fig. 2) showed good agreement between the values, with an average
value of - 61.7"
and a mean error for the average of m = 1.2". Taking into
account possible systematic errors, the overall limit of error
is estimated as 5-10%.
436 nm
578 nmm
Table 2. Optical rotation values for various polymers with voids. The measurements were made on suspensions in a mixture of 1,2-dichlorobenzene,
dichloroethane and tetra~hloroethylene.'~'
Fig. 2. Molar optical rotation of P - 1 - 0 as a function of suspension concentration c in a medium with a refractive index n i o = 1.5424. The average molar
rotation values ,t and the standard devraiions Q for the measurements at each
wavelength are as follows: 436 nm: 4 = 97.1", u = 2.4"; 546 nm: ? = 61.7".
u = 3.1'. 578 nm: 4 = 48.7", u = 3.0"; Na D-line: X = 43.3". u = 3.9".
tions,C4]an achiral macroporous polymer, which was otherwas first
wise similar to the polymers P - 1 - 0 and P-1-•
prepared from the monomer 3. From this polymer P-3-m
the cyclohexanol moiety 4 was then detached to give the
polymer P-3-[7. Neither polymer showed any optical rotation under optimal measurement condition^.^^] The achiral
polymer P - 3 - 0 , with free boronic acid groups, was then
esterified by reacting in turn with an excess of (9-or of
(R)-t-phenyl-l,2-ethanediol, [(9-5 and (R)-5 respectively],
achieving esterification of about 96% of the boronic acid
groups. Optical rotation measurements were then made on
this polymer also (see Table 1). The observed molar rotation
for the polymers containing the (S)and (R)
enantiomers were + 357" and - 366" respectively, thus giving absolute values which are identical within the limits of
error, and are also of the same order of magnitude as the
molar rotation value for the corresponding monomeric
phenyl ester 6. From these results one may proceed on the
assumption that optical rotation values can be determined
with reasonable accuracy on highly cross-linked macroporous polymers. It appears that the achiral matrix has only a
small effect on the contribution of optically active sidegroups to the observed rotation values.
Table 1. Optical rotation values for achiral polymers after reacting with optically active diols, and for reference samples [a]
0- CH
0- CH
Cs H5
- 24.0 f 1"
-366 i-15"
(95.0% re)
(95.8% ee)
+ 99.5"
- 100.3"
+ 159.0"
[a] Macroporous polymer P-3-•
prepared by removing the cyclohexanol
or (R)-l-phenyl-1,2-ethandiolS
residues from P-3-@ then loading with (9a level of 96.3% occupancy. Suspension medium: 6.60 g of 1,2-dichlorobenzene
plus 1.00 g of a mixture of 9.00 g of dichloroethane with 2.00 g of tetrachloroethylene. n i o = 1.5386. Polymer concentrations: 2.748 g in 100 mL for
the polymer containing (9-phenylethandiol and 1.758 gin 100 mL for that with
the ( R ) enantiomer. Measured rotations: 0.643" and - 0.422" respectively.
Angcn. Chrm. i n [ . Ed. EngL 29 (1990) No.6
P - 1 - 0 [b]
- 0.067"
+ 0.040"
- 76.4'
[Z = - 61.7"] [d]
[a] nbo = 1.5424, c = 2.00, D = 80%. [b] nbo = 1.5424, c = 2.58, D = 80%.
[c]n;' = 1.5401, c = 1.28, D = 95%. [ J X was calculated from the measurements at different concentrations (see Fig. 2). D is the optical transmission of
the suspension expressed as a percentage of that for the pure solvent.
If we compare the value of - 61.7" given in Table 2 for the
of the polymer P - 1 - n with the value
molar rotation
448.9" for the template monomer 1, it becomes apparent
that, in contrast to the situation in P - 3 - m , the molar
rotation value has decreased considerably as a result of the
polymerization. It must be assumed that this has been caused
by the polymer matrix. Its effect can be determined by splitting off the optically active template 2. Since optically active
boronic acid groups usually have rotation values greatly different from those of their esters,['] it is necessary to convert
P-1-c] with ethylene glycol 7 into the ester P-1-m in order
to allow a meaningful comparison. The polymer P-1-•
gives a positive molar rotation
= + 110.0'. This
shows that in P-1-•
the imprints generated in the polymer
make a positive contribution to the rotation value, and this
is responsible for the low molar rotation value found for
P - 1 - 0 . In this case the optical rotation is not caused by
individual chirdl centers, as is usual, but by the imprint as a
whole. Evidently, therefore, the contribution of chiral voids
to the rotation values in highly cross-linked polymers can be
measured satisfactorily.
Measuring the optical rotation in the solid phase allows
one to directly determine the properties of a chiral void in the
polymer. For example, it is possible to recognize different
binding situations of the template in the cavity. If the polymer P - 1 - 0 with empty voids is recharged with the template
2, the resulting polymer, in contrast to P - 1 - a , has a very
large positive rotation value of [MI::, = + 323". If this loaded polymer is heated in acetonitrile in the presence of a 3 A
molecular sieve, the molar rotation
changes to - 68",
i.e. about the same as for the original polymer P - 1 - a . Evidently most of the template molecules are at first bonded
only by a single point of attachment (formed by esterification of only one boronic acid group in the cavity), and this
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then changes to a double attachment. Results from calorimetric studies lend support to this assumption.“]
Further interesting results can be expected from studies of
the optical rotation, and of the circular dichroism where
appropriate, for polymers under different swelling conditions and at different temperatures. This method could also
become very important as a means of characterizing chiral
stationary phases for use in separating racemates. In cases
where a cross-linked polymer has been prepared with optically active side-groups there is often speculation about effects caused by an asymmetric rnatrix,[’l and it should now
be possible to measure this directly.
[{(CO),M),(p-C,H,)], M = Fe 1,[’] M = Ru 2,121an unsymmetrical syn-binding B of cycloheptatriene to the (L,M),
unit is known (d,
q2:q3;example: [(CpRh),(p-C,H,)] 313]).
Here we report on the synthesis, structure and dynamic behavior of syn-[(CpCo),(p-C,H,)] 6a and anti[(Cp*Co),(p-C,H,)] 6b (Cp = q-cyclopentadienyl, Cp* =
q-pentamethylcyclopentadienyl). In 6 b an anti-bound cycloheptatriene bridge C (q4:q4) has been realized for the first
Received: January 29, 1990 [Z 3764 IE]
German version. Angrn.. Cheni. 102 (1990) 706
[I] a) G. Wulff, A. Sarhan, Angeu- Chem. 8 4 (1972) 364, Angew. Chem. h l . Ed.
Engl. 11 (1972) 341 ;b) G. Wulff, A. Sarhan, K . Zabrocki, Tetrahedron Lett.
1973,4329; c) G . Wulff, S. Schauhoff, J Org. Chem., in press; d) K . J. Shea,
E. A. Thompson, S. D. Pandey, P. D. Beauchamp, J Am. Chem. Soc. 102
(1980) 3149; e) J. Damen, D. C . Neckers, h i d . 102 (1980) 3265; f ) B. Sellergren, M. Lepisto. K. Mosbach, ihid. 110 (1988) 5853; g) Review: G. Wulff
in W. T. Ford (Ed.): Polymeric Reagents and Cutalysrs, A C S Symp. Ser. 308
(1986) 186
[2] G. Wulff, B. Heide. G. Helfmeier, J Am. Chem. Soc. ION (1986) 1089; K J.
Shea, T. K . Dougherty. ihrd. iUN(3986) 1091; K . J. Shea, D. Y Sasaki, ibid.
111 (1989) 3442.
[3] G. Wulff, J. Vietmeier, H.-G. Poll, Makromol. Chem. 188 (1987) 731
[4] P. Pino, J. Bartus, 0. Vogl, Polym. Prepr. Am. Chem. Soc. Div Poljm.
Chem. 29jl (1988) 254; J. Bartus. L. S . Corley. G. D. Jaycox, 0. Vogl.
Polym. Prepr. Jpn. [Engl. Ed.] 36 (1987) Nr. 5-10, E23; for earlier studies
see also. P. Pino. Furtschr. Hochpo/.vm. Forsch. 4 (1965) 417.
[S] The measurements by Vogl, Pino et al. [4] were made using polymers with
a particle diameter 45 pm suspended in a medium with the same refractive
index contained in a 10 mm UV cuvette. The suspension was stirred to avoid
sedimentation. For our measurements, in order to obtain larger rotations,
we used a n ordinary thermostatically controlled polarimeter cuvette with an
optical path length of 100 mm. Sedimentation was prevented by aerating
with a peristaltic pump or by shaking occasionally. Suspension media with
different refractive indices were prepared by mixing twocomponents, namely 1.2-dichlorobenzene ( n i o = 1.5513) and a mixture of 1.2-dichloroethane
and tetrachloroethylene (9:2 wiw, .go = 1.4528). See also Figure 1
[6] The polymer P-I-@ used here was prepared by the usual method. [3]
24.43 g of ethylene glycol dimethacrylate. 4.60 g of 1 and 0.1 8 g of azo-bis(isobutyronitrile) were polymerized in 18 g of tetrahydrofuran for 9 h at
65 ‘C. The polymer contained 0.33 mmol g-’ of the template monomer I .
It was found possible to remove 8 8 % of the template. In calculating the
molar rotation values for P - 1 - 0 and P-1-m given in Table 2, the rotation
caused by the residual 12% of the template monomer was subtracted. The
molar rotation values relate to the fraction for whlch the given structure
[7] G. Wulff, H. Stellbrink, Red. Truv. Chim. Puys-Bas 109 (1990) 216.
[8] G. Wulff, G. Kirstein, H:G. Poll. unpublished.
[9] G. Blaschke. Angeiv. Chem. 92 (1980) 14; Angew. Chem. Int. Ed. Engl. 19
(1980) 13.
Dicobalt Complexes with syn- and anti-Coordinated
p-Cycloheptatriene Bridges **
By Hubert WadePohi,* Wolfgang Galm, and Hans Pritzkow
Dedicated to Professor Giinter Wilke
on the occasion of his 65th birthday
Fe(CO)3. Ru(CO),
CoCp. RhCp
Reaction of [CpCo(l -4-q-C7H,] 4a[41 with [CpCo(C2H4),] 5aIS1 affords the syn-binuclear complex 6 a
in good yields. From [Cp*Co(l-4-q-C7H,)] 4b and
[Cp*Co(C,H,),] 5bl6I the anti-binuclear complex 6b is exclusively formed. The ethene complexes 5 probably attack at
the uncomplexed CC double bond of the q4-bound cycloheptatriene ligand of 4. The two bulky Cp*Co groups prevent the formation of a Co-Co bond, which would lead to
the syn-binuclear complex, and force the anti-coordination.
The high stability of 4b prevents the formation of a “mixed”
Cp*/Cp derivative of 6. Hence, 4b reacts neither with 5a nor
[CpCo(C,Me,)],[’I both of which are sources of the CpCo
fragment. Reaction of 4 a or [CpRh(q4-C,H,)][3*71with 5b
yields 4 b only, via ligand exchange.
In binuclear complexes cycloheptatriene, as a six-electron
ligand, can bind in different ways to the metal atoms. Apart
from the symmetrical syn-coordination A (q3 q3;examples:
[*] Priv.-Doz. Dr. H. Wadepohl, W. Galm. Dr. H. Pritzkow
Anorganisch-Chemisches Institut der Universitit
Im Neuenheimer Feld 270, D-6900 Heidelberg (FRG)
[**I This work was supported by the Deutsche Forschungsgerneinschaft (Sonderforschungsbereich 247 der Universitiit Heidelberg).
V C H Verlug.sge,si~iIschuft
mhH. 0-6940 Weinheim, I Y Y O
The syn-orientation of the CpCo groups in 6a causes the
bridging ligand to appear as five ‘H-NMR signals in the
intensity ratio 2:2:1:2:1. Like 3, 6a is also non-ridgid in
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Angew. Chem. h i .
Ed. Engl. 29 (1990) No. 6
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