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Competing Occurrence of Isomeric (Dialkyltartrato)zirconocene Dimers with Dimetallatricyclic and Ten-Membered Dimetallamonocyclic Frameworks.

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[I] V. Schurig, H. P. Nowotny, Angew. Chem. 102 (1990) 969; Angew. Chem.
Int. Ed. Engl. 29 (1990) 939.
(21 T. J. Ward, D. W. Armstrong, J. Liq. Chrumatugr. 9 (1986) 407.
108 (1986) 4514.
[3] I. Tabushi, Y. Kuroda, T. Mizutani, J. Am. Chem. SOC.
[4]a) P. E. Hare, E. Gil-Av, Science 204 (1979) 1226; b) V. A. Davankov, A. A.
Kurganov, A. S. Bochkov, Adv. Chromatugr. 22(1983) 71; c) E. Armani, L.
Barazzoni, A. Dossena, R. Marchelli, J. Chromotogr. 441 (1988) 287.
[S] R. P. Bonomo, V. Cucinotta, E DAlessandro, G. Impellizzeri, G. Vecchio,
E. Rizzarelli, Inorg. Chem., 30 (1991) 2708.
[6] G. Borghesani, F. Pulidori, M. Remelli, R. Purello, E. Rizzarelli, J. Chem.
SUC.Dotfon Trans. 1990, 2095.
[71 I. Tabushi, N. Shimizu, T. Sugimoto. M. Shiozuka, K. Yamamura, J. Am.
Chem. Soc. 99 (1977) 7100.
[8] P. Gans, A. Sabatini, A. Vacca, J. Chem. SOC.
Dalton Trans. 1985, 1195.
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Competing Occurrence of Isomeric
(Dialky1tartrato)zirconoceneDimers with
Dimetallatricyclic and Ten-Membered
Dimetallamonocyclic Frameworks **
By Gerhard Erker, * Stefan Dehnicke, Mathias Rump,
Carl Kriiger, Stefan Werner, and Matthias Nolte
Dinuclear (dialky1tartrato)titanium alkoxides are starting
substances for the generation of important enantioselective
catalysts.['] It is still an open question, however, whether the
catalytically active species is derived only from the dimetallatricyclic structure type 1 found in the solid
or
whether the isomeric ten-membered dimetallamonocyclic
structure 2I4]is also present in equilibrium. We have investigated the structure and dynamic behavior of (dialkyltartrato)zirconocenes as catalytically inactive model systems for
1/2 and have made a surprising observation.
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for determining whether the method can be extended to other amino acids, are warranted.
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1
Experimental Procedure
P-CDhm was prepared from dried 6-0-(p-tosyl)-P-cyclodextrin171 (1 g,
0.77 mmol), converted into the iodo derivative by reaction with NaI (10-fold
excess) in anhydrous D M F (40 mL) at 90°C for 5 h under stirring, then allowed
to reacted with histamine (10-fold excess) in DMF at 60" for 24 h under nitrogen. After purification on CM-Sephadex C-25, P-CDhm was obtained with a
total yield of 40%. P-CDhm was characterized by 'H and I3C NMR and by
elemental analysis IS].
Chromatographic separations were performed on a Waters model 6000A
HPLC pump, using a Radialpak C,* cartridge (10 x 0.8 cm) and a model 440
UV detector, set at 280 nm. The mobile phase was prepared as described previously [4c]. P-CDhm can be subsequently recovered from the eluent, after precipitation of copper(rr) as CuS, by filtration and HPLC purification using a
Technosphere 5 Amino (30 x 0.4 cm) column and a mixture of CH,CN and
water ( l j l ) as eluent.
Potentiometric titrations were carried out in aqueous solution by means of two
fully automated computer-controlled meters (Metrohm E654) using a combined glass electrode (Metrohm 125). All potentiometric data were handled by
the program SUPERQUAD [8].
CD Measurements were performed on a JASCO J-500A spectropolarimeter
equipped with a DP-SOON data processor.
Received: February 4, 1991
revised: May 29, 1991 [Z 4419 IE]
German version: Angew. Chem. 103 (1991) 1363
Angew. Chem. Inl. Ed. Engl. 30 (1991) No. 10
0 VCH
2
Reaction of (2 R, 3 R)-( +)-diisopropyl tartrate (4a) with
dimethylzirconocene (3) results in loss of methane and dimerization to give the dimetallatricyclic complex 5 a. The
dimetallatricyclic structure is confirmed in the solid state by
the crystal structure analysis (Fig. 1) and in solution by the
symmetry properties of the complex revealed by the lowtemperature NMR spectra. For example, the '€3 NMR spec[*] Prof. Dr. G. Erker, DipLChem. M. Rump
Organisch-Chemisches Institut der Universitat
Corrensstrasse 40, W-4400 Miinster (FRG)
Dr. S. Dehnicke
Institut fur Organische Chemie der Universitat Wurzburg
Prof. Dr. C. Kruger, Dip1.-Chem. S. Werner, DipLChem. M. Nolte
Max-Planck-Institut fur Kohlenforschung, W-4330 Mulheim a. d. Ruhr
(FRG)
[**I This work was supported by the Fonds der Chemischen Industrie, the
Alfried Krupp von Bohlen und Halbach-Stiftung, and the Bundesminister
fur Forschung und Technologie.
Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
0S70-0833/91j1010-1349 $330+.25/0
1349
trum (4.7 T) of 5 a at 233 K in CD,CI, shows two sets of
signals for the methine protons of the isopropoxy groups at
6 = 5.2 and 4.9 in a ratio of 1 : 1 ; the framework methine
protons (the protons of the CH(E)CH(E) unit, E =
- CO,CHMe,) appear as an AX system at 6 = 4.67 and 4.1 7
('J = 8.3 Hz). When the monitoring temperature is raised,
pairwise coalescence of the signals of the ester groups, as well
as those of the framework methine protons, is observed.
Above the coalescence temperature of 255 K, the framework
methine protons appear as a singlet. An activation barrier of
AG* = 12 1 kcalmol-' at 255 K was estimated for the
underlying exchange process from the temperature-dependent 'H NMR spectra (CH(E) coalescence).
AX spin system on cooling, whereas, in the case of meso-5a
and meso-5 b, a corresponding intramolecular exchange process cannot be frozen out on the NMR time scale. Down to
the lowest temperature attainable, the signals of the framework methine protons of the meso diastereomers remain unchanged (6 = 4.39 (202 K), meso-5a; 6 = 4.49 (213 K),
meso-5 b). This simple stereochemical variation results, at
least for the dimeric (dialkyltartrato)zirconocenes, in a dram tic change in the activation barrier for the intramolecular
eq iilibration process; possibly, the diastereomers ruc-5 and
m, so-5 have completely different structures. The NMR spectra of these meso compounds are fully consistent with a tenmembered dimetallacylic structure.
4
3
Fig. 1. Molecular structure of the dimetallatricyclic complex 5 a. Selected bond
distances [%.I and angles I"]: Z r l - 0 1 2.239(5), Z r l - 0 6 2.066(6), Z r 1 - 0 7
2.268(5), Zr2-01 2.244(6). Z r 2 - 0 7 2.258(5). Zr2-012 2.032(6); C1-01-Zr2
127.8(5), Z r l - 0 1 - Z r 2 113.7(2), Z r l - 0 1 - C 1 118.2(5), C21-07-Zrl 127.2(5),
Z r l - 0 7 - Z r 2 112.1(2), Zr2-07-C21 116.8(5). Folding of the central Zr,O,
four-membered ring. 157"; angle of the Cp centroids with Zr 1 and Zr2, 122.5
and 121.2". respectively.
A quite analogous dynamic behavior in solution has long
been known for the "Sharpless system" 1 (AG* z
15 kcalmol-').[2a.b1As in the case of our zirconocenes, it is
also an open question there whether an inter- or an intramolecular equilibration is involved. Therefore, we allowed dimethylzirconocene to react with (2 S, 3 S)-(-)-diisopropyl tartrate to give e n t d a . 'H NMR spectroscopy can be
easily used to follow and to analyze kinetically the intermolecular exchange reaction of the monomeric five-membered metallacyclic complex trans-Cp,hOCH(E)CH(E)O,
starting from the racemate prepared from the components
5 a and ent-5a, by monitoring the appearance of, for example, the singlet of the framework methine protons of the
complex meso-5a at 268 K in CD,CI, (equilibrium ruc-5a/
meso-5a z 1 : 1, AG* = 21
1 kcalmol-' at 268 K).'']
The products of the reaction of dimethyl tartrate (4 b) with
dimethylzirconocene behave analogously. At 233 K, the 'H
NMR spectrum of the optically active (dimethy1tartrato)zirconocene dimer 5 b displays an AX spin system (6 = 4.81,
4.1 1, ' J = 9.5 Hz) for the framework methine protons,
which coalesces above 255 K to a singlet (AG&= =
12 1 kcalmol-' at 262 K). The intermolecular exchange
reaction 5 b + ent-5 bgmeso-5 b proceeds about seven orders of magnitude slower (AG2,er = 20 & 2 kcalmol-' at
268 K).
The chiral (ruc-5a, ruc-5 b) and achiral (meso-5a, meso5b) diastereomeric (tartrato)zirconocene dimers show very
different dynamic behavior. In the case of the racemic compounds (see above), the singlet of the framework methine
protons (6 = 4.45, ruc-5a; 6 = 4.56, ruc-5b) is split into an
5
5
ent-5
4,5:E
= -C02CHMe2
meso-5
(a) : -CO,CH,
(b)
For the chiral compound 5b, obtained by reaction of
dimethylzirconocene with (2 R, 3 R)-(+)-dimethyl tartrate,
we demonstrated that external effects alone could cause a
change in the preferred dimeric structure. The NMR spectra
(see above) of 5 b indicate a C,-symmetric dimetallatricyclic
structure in solution (CD,CI,). In the solid state, on the
other hand, the ten-membered dimetallamonocyclic structure is favored, as shown by the crystal structure analysis of
5 b (Fig. 2, crystals from CH,CI,).
+
1350
0 VCH
Verlagsgesellschafi mbH, W-6940 Weinheim, I991
Fig. 2. Molecular structure of the ten-membered dimetallacyclic complex 5 b.
Selected bond angles ["I: 0 2 - Z r l - 0 1 2 99.4(2), 01-Zr2-011 100.8(2)". Angle
of the Cp controids with Z r l and Zr2 126.7 and 127.4", respectively.
0S70-0833/9I/lOlO-l3S0$3.50+.2S~O Angew. Chem. Inl. Ed. Engl. 30 (1991) No. 10
In the crystal, 5 b displays a crown-shaped ten-membered
ring framework. The ester groups are arranged pairwise in a
nearly C,-symmetric fashion. For both pairs, the Zr-0 (carbonyl) distances are too large for an interaction (Zr 1-05,
3.88; Z r 2 - 0 3 4.48, Z r l - 0 1 5 4.18, Zr2-013 4.00A). Noteworthy are the short bonds of the zirconium atoms to the
ring oxygen atoms ( Z r l - 0 2 1.952(3), 25-1-012 1.952(8),
Zr 2-0 11 1.941 (3), Zr 2-0 1 1.974(6) A) and the substantially increased Zr-0-C angles in the metallacycle (Zr 1-02-C 2
152.9(2), Zr1-012-CI2 158.8(3), Zr2-01-C1 148.2(2),
Zr 2 - 0 1 1-C 1 I 169.9(4)”). Accordingly, the formation of energetically favorable metal-oxygen K interactions can compensate for the energy difference between a ten-membered
dimetallacyclic and the commonly observed dimetallatricyclic structure.@]
If it is equally facile to effect the change between a tenmembered dimetallacyclic and a dimetallatricyclic structure
through external influences in the case of the dinuclear (dia1kyltartrato)titanium catalysts,[*.31 then the question of the
detailed structure of the active species in these important
enantioselective catalyst systems is again open. Since, in such
a case, it is problematic to draw conclusions about the structural parameters from direct observation, we are trying to
obtain this information on modified catalyst systems in
which stereochemical probes are incorporated.
Experimenlal Procedure
5a: Reaction of 3 (1.52 g, 6.04 mmol) with 4 a (1.39 g, 5.92 mmol) ([@ =
+ 17.0) in 80 mL of CH,CI, gave, after removal of the solvent and recrystalliza=
tion twice from toluene, 2.50 g (93 “A)of 5 a ; m.p. 146-153°C (dec.).
+ 28.0 (c = 0.82, CH,CI,). Correct C, H analysis. ‘H NMR (200 MHz,
CD,CI,. 300 K): 6 = 6.25 (s, 20 H; Cp), 5.09 (sept, 4 H ; CHMe,), 4.45 (s, 4 H ;
CH(meta~~acyc~e),
1.36 (d, 12 H ; CH,), 1.34 (d, 12 H; CH,).
crystal size, 0.25 x 0.36 x
Crystal structure analysis of Sa: C,,H,,O,,Zr,,
0.29 mm: M = 907.3, u = 9.692(1), b = 9.784(1), c = 21.105(2) A, p =
93.88(1) , V = 1996.9
= 1.51 gcrn-,. p = 5.71 cm-‘, 2 = 2. space
group P2,. i = 0.71069 A, Enraf-Nonius CAD4 diffractometer. 4933 measured reflections (fh. + k , + 0,[(sinB)/i.],,, = 0.65 k ’ ,4803 independent
and 4439 observed reflections (I> 20(l)), 487 refined parameters, R = 0.053,
R, = 0.062. residual electron density 1.82 e k ’ .
ent-5a- Reaction of 3 (1.72 g, 6.84 mmol) and e n r 4 a (1.60g, 6.84 mmol)
([XI? = - 16.5) gave 2.72 g (88 %) of ent-5a; m.p. 149-151 “C (dec.);
=
28.2 (c = 0.93. CH,CI,). Correct C, H analysis.
5 b : Reaction of 3 (2.14g. 8.51 mmol) and 4 b (1.52 g, 8.51 mmol)
= + 21) gave 3.08 g (91 YO)of 5 b ; m.p. 149°C (dec.); [%]is = f6.5
(c = 1.11. CH,CI,). Correct C, H analysis. ‘H NMR (200 MHz, 300 K,
CD,CI,): 6 = 6.24 (s, 20 H ; Cp), 4.56 (s, 4 H; CH) 3.71 (s, 12 H ; CH,) 13C
NMR (50 MHz. 300 K, CD,CI,): 6 = 173.9 (C=O). 112.9 (Cp), 84.8 (CH),
crystal size,
52.0 (OCH,). Crystal structure analysis of 5 b : C,,H,,O,,Zr,;
0.39x0.49x0.49mm,
M=795.1, u=8.222(1), b = 18.842(2), c =
11.240(1)A. [j= 107.85(1)’. V = 1657.4A’. @,a,,d= 1.59gcm-’, p =
6.76 cm- I, Z = 2. space group P2,. 2. = 0.71069 A, Enraf-Nonius CAD4 diffractometer. 4092 measured reflections ( k h, + k , + I). [(sinB)/l.],,, =
0 . 6 5 k ’ . 3892 independent and 3805 observed reflections ( I > 2u(/)), 416
refined parameters, R = 0.022, R, = 0.029, residual electron density
0.22 e k ’ . Further details of the crystal structure investigations are available
on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2. (FRG) on quoting the depository number CSD-55411, the names of
the authors, and the journal citation.
eat-5b: Reaction of 3 (1.34g, 5.34 mmol) and ent-4b (0.95 g, 5.34rnmol)
([@ = - 2l)gave2.12g(quant.)ofent-5b;correctC.Hana1ysis:m.p. 149°C
(dec.); [TI? = - 6.1 (c = 0.95. CH,CI,).
~
Received: May 21. 1991 [Z 4637IEl
German version: Angew. Chem. 103 (1991) 1371
J. Am. Chem. SOC.102 (1980) 5974; b)
M. Hayashi. T. Matsuda, N. Oguni, J Chem. Soc. Chem. Commun. 1990.
1364.
[2] Proposals for the dinuclear catalytically active species: a) M. G. Finn.
K. B. Sharpless. in J. D. Morrison (Ed.): Asymmetric Synthesis, Vol. 5, Academic Press, New York 1985, p. 247; b) S. S. Woodard. M. G. Finn, K. B.
Sharpless. J Am. Chem. SOC.113 (1991) 106; M. G. Finn, K. B. Sharpless,
111 a) T. Katsuki, K. 9. Sharpless,
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 10
0 VCH
ihid. 113 (1991) 113; c) I. D. Williams, S . F. Pedersen. K. B. Sharpless,
S . J. Lippard, ibid. 106 (1984) 6430; S . F. Pedersen, J. C. Dewan. R. R. Eckman, K. B. Sharpless, ibid. 109 (1987) 1279; d) K. A. Jorgensen. R. Wheeler.
R. Hoffmann, ibid. 109 (1987) 3240; e) C. Puchot, 0. Samuel, E. Dunach,
S . Zhao, C. Agami, H. B. Kagan, ibid. 108 (1986) 2353.
[3] An opposing proposal has been given: E. J. Corey, J. Org. Chem. 55 (1990)
1693. See also: S. Takano, Y. Iwabuchi. K. Ogasawara. J. Am. Chem. Soc.
113 (1991) 2786.
[4] K. B. Sharpless. S . S . Woodard, M. G . Finn, Pure Appl. Chem. 55 (1983)
1823. See also: R. 9. Ortega. R. E. Tapscott, C. F. Campana. Inorg. Chem.
21 (1982) 672; P. G . Potvin, P. C. C. Kwong, M. A. Brook. J. Chrm. SOC.
Chem. Commun. 1988. 773; P. G. Potvin, P. C. C. Kwong, R. Gau, S . Bianchet, Can. J Chem. 67 (1989) 1523.
[5] A similar exchange experiment with labeled (“two-dimensionally chiral”)
metallacyclic (catecho1ato)zirconocenes:G. Erker, R. Noe. J. Chem. SOC.
Dullon Trans. 1991, 685.
161 D. W. Stephan, Organomerullics 9 (1990) 2718; T. T. Nadisdi, D. W.
Stephan. Can. J. Chem. 69 (1991) 167; see for comparison: J. C. Huffman.
K. G. Moloy, K. G. Caulton, Inorg. Chem. 27 (1988) 2190; 9. Bachand.
J. D. Wuest, Orgunometallies 10 (1991) 2015.
Bis(hydroperoxy)naphthaldiimide as
a “Photo-Fenton Reagent”:
Sequence-Specific Photocleavage of DNA
By Seiichi Matsugo, Shosuke Knwanishi, Koji Yamamoto,
Hiroshi Sugiyama, Teruo Matsuura, and Isao Saito *
Dedicated to Professor Kurt Schaffner
on the occasion of his 60th birthday
In view of the high level of interest in the role of the
hydroxyl radical (HO’) in biological systems,[’] several approaches toward the development of efficient methods for
HO’ generation without using transition-metal ions and hydrogen peroxide have been investigated.‘’. 31 Our objectives
are to design an efficient organic precursor that generates
pure HO’ by low-energy irradiation, such as long-wavelength UV (>350 nm) or visible light irradiation. Such
molecules, referred to as “photo-Fenton reagents”, are particularly attractive as a controllable and mechanistically less
complicated HO’ source for applications in a number of
biologically important reactions such as cross-linking of biopolymers[41 and cleavage of DNA[’] and proteins.161The
design criteria include the ease of synthesis, stability at ambient temperature, solubility in aqueous solvents, and ability
to produce free HO’ by irradiation with long-wavelength
light. Our initial studies have indicated that hydroperoxyphthalimides can photogenerate HO’ upon irradiation at
d > 280 nm.[31In the present work, a naphthaldiimide derivative bearing a symmetrical bis-hydroperoxy group was designed in order to improve the efficiency of HO’ generation
per molecule and to enhance the absorption at longer-wavelengths. It acts as an effective photogenerator of HO‘ and
can induce sequence-specific cleavage of duplex DNA at the
5’ site of 5’-GG-3’ sequences.
Bis(hydroper0xide) 1 was prepared from the corresponding dimethyl ketal2 by treatment with excess ethereal hydro[*] Prof. Dr. 1. Saito, Dr. H. Sugiyama, Prof. T. Matsuura
Department of Synthetic Chemistry, Faculty of Engineering
Kyoto University
Kyoto 606 (Japan)
Dr. S. Matsugo
Kobe University of Mercantile Marine
Kobe 658 (Japan)
Dr. S . Kawanishi, K. Yamamoto
Department of Public Health, Faculty of Medicine
Kyoto University
Kyoto 606 (Japan)
Verlugsgesellschufl mbH, W-6940 Weinheim, 1991
0570-0833/9//1010-1351~
3.50+ ,2510
1351
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dimetallatricyclic, dimetallamonocyclic, framework, occurrence, dimer, zirconocene, competing, membered, ten, isomeric, dialkyltartrate
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