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On the Formation of УFree RadicalsФ from Alkylcobalt Complexes.

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flections may have suffered a phase change so that the information in the
appropriate frequency range is transferred with reversed contrast.
The second stage in image analysis involves image reconstruction, where the
electron micrograph now serves as object. Filtering of Fourier frequencies in
reciprocal space (secondary diffraction pattern) is performed generally with
the aid of a computer. The various stages of frequency filtering are very complex and must be treated with careful consideration of the physics involved.
Otherwise, artifacts can easily be introduced. The safest way to guard against
this is to compare the original image (which must be of very high quality)
with the computer-treated image, and to ensure that defects have not been
introduced which were not in the original. Details regarding these procedures will be published elsewhere [16].
Received: September 22, 1988;
supplemented: December 2, 1988 [Z 2974 IE]
German version: Angew. Chem. 101 (1989) 332
.,
CAS Registry numbers:
la, 118891-82-0; lb, 69079-52-3.
R 0 + OCo(dmgH)2py
[ I ] L. D. Marks, D. J. Smith, Nafure (London) 303 (1983) 316; J.-0. Malm,
J.-0. Bovin, A. Petford-Long, D. J. Smith, G. Schmid, N. Klein, Angew.
Chem. I00 (1988) 580; Angew. Chem. Int. Ed. Engl. 27 (1988) 555.
[2] H. Durst, 1. G. Voigt-Martin, Makromol. Chem. Rapid Commun. 7 (1986)
785; 1. G. Voigt-Martin, H. Durst, Liq.Cryst. 2 (1987) 585; I. G. VoigtMartin, H . Durst, H. Krug, Macromolecules, in press.
131 1. G. Voigt-Martin, H. Durst, Liy. Cryst. 2 (1987) 601.
[4] 1. G. Voigt-Martin, H. Durst, B. Reck, H. Ringsdorf, Macromolecules 21
(1988) 1620.
[5] 1. G. Voigt-Martin, H. Durst, Macromolecules 22 (1989) 168.
161 H. Finkelmann, Angew. Chem. 99 (1987) 840; Angew. Chem. I n f . Ed.
Engl. 26 (1987) 816: H. Finkelman, G. Rehage, Ado. Polym. Sci. 60/61
(1984) 174.
171 W. Kreuder, H. Ringsdorf, Makromol. Chem. Rapid Commun. 4 (1983)
807.
[S] Synthesis and characterization of 1 : W. Kreuder, H. Ringsdorf, P.
Tschirner, Makromol. Chem. Rapid Commun. 6 (1985) 367.
[9] G. Wenz, Makromol. Chem. Rapid Commun. 6 (1985) 577.
[lo] 0. Hermann-Schanherr, J. H. Wendorff, W. Kreuder, H. Ringsdorf, Makromol. Chem. Rapid Commun. 7 (1986) 97.
[I 11 S. Chandrasekhar, B. K. Sadashiva, K. A. Suresh, Pramanu 9 (1977) 471 ;
Chem. Abstr. 88 (1978) 3 0 5 6 6 ~ .
[I21 J. Billard, J. C . Dubois, Nguyen Huu Tinh, A. Zann, Nouv. J. Chim. 2
(1978) 535; C. Destrade, P. Foucher, H. Gasparoux, Nguyen Huu Tinh,
A. M. Levelut, J. Malthete, Mol. Crysf. Liy. Cryst. 106 (1984) 121.
[I31 A. M. Levelut, J . Phys. Lefr. 40 (1979) 81.
1141 D. Goldfarb, R. Poupko, 2. Luz, H. Zimmermann, J. Chem. Pfiys. 79
(1983) 4035.
[IS] J. Amoros, M. Amoros: Molecular Ctystals: Their Transform and Diffuse
Scattering. Wiley, New York 1983; J. Cowley: Diffraction Physics, North
Holland, Amsterdam 1986.
1161 1. G. Voigt-Martin, H. Durst, H. Krug, Mucromolecules, in press,
[17] M. Gharbia, M. Cagnon, G. Durand, J. Phys. Left. 46 (1985) 683; cf. A.
M. Levelut, J . Chem. Phys. 80 (1983) 149.
[IS] H. Ringsdorf, B. Schlarb, J. Venzmer, Angew. Chem. 100 (1988) 117; Angew. Chem. In!. Ed. Engl. 27 (1988) 113; H. Ringsdorf, G. Schmidt, J.
Schneider, Thin Solid Films 152 (1987) 207.
1191 T. Iwayanagi, T. Ueno, S. Nonogaki, H. Ito, C. G. Willson: "Muterials
and Processes for Deep U. V. Lithography", Adv. Chem. Ser.. in press.
[20] L. Y. Chiang, J. P. Stokes, C. R. Safinya, A. N. Bloch, Mot. Cryst. Liy.
Crysf. 125 (1985) 279; B. Mourey, J. N. Perbet, M. Hareng, S. Le Berre,
ibid. 84 (1982) 193.
[21] P. Davidson, A. M. Levelut, H. Strzelecki, V. Gionis, J . Phys. Lefr. 44
(1983) 823.
On the Formation of "Free Radicals" from
Alkylcobalt Complexes**
By Bernd Giese,* Jens Hartung, Jianing He,
Otfmar Hiiter, and Andreas Koch
Alkylcobaloximes of type 1 are becoming of increasing
importance in organic synthesis, since their photolysis gen[*I
[*'I
Prof. Dr. B. Giese, Dip1.-Ing. J. Hartung, Dipl.-lng. J. He,
Dip1.-lng. 0. Hiiter, Dipl.-Ing. A. Koch
Institut fur Organische Chemie der Technischen Hochschule
Petersenstrasse 22, D-6100 Darmstadt (FRG)
This work was supported by the Stiftung Volkswagenwerk.
Angew. Chem. In[. Ed. Engl. 28 (1989) No. 3
erates radicals which can be used for both carbon-carbod'] and carbon-heteroatom bond-forming reactions."c.21
Preparatively useful reactions include cyclizations""' and
intermolecular additions to olefins,[lb'dl which, depending
on the reaction conditions and the substituents, afford alkanes 2 and/or alkenes 3 (H,dmg = 2,3-butanedionedioxime).
4
H2C=CHX
>
RCH2-CHX-Co(dmgH)2py
6
5
On the basis of ESR measurements, it has been concluded that alkyl radicals generated from alkylcobaloximes
in a matrix still undergo an interaction with the Co" complex 5.I3I By carrying out reactivity and selectivity studies
on alkylcobaloximes in organic solvents, we have now
been able to show that C-C bond formation involves the
reaction of free radicals that do not differ from those generated from other radical sources.
7
8
T
9
10
11
U
12
In order to determine the reactivity, the hexenylcobaloxime 9 was photolyzed in the presence of various quantities
of CCI, at 26°C using a 300 W sun lamp. From the ratio of
the products 12 and 7 and the known rate of cyclization of
the hexenyl radical
the rate of abtraction of chlorine
from CCI, could be determined as 6.9 x lo3 M - ' s-'. This
value agrees remarkably well with the literature value for
the hexenyl radical, which was generated from the corresponding azo compound."]For intermolecular addition
reactions with the alkene 16, the reaction rates for the intermediates generated by reduction of the cyclohexyimercury salt 13f61
and by photolysis of the cyclohexylcobaloxime 14 were also identical within the limits of experimental error (Table 1). Since the mercury salt gives rise to uncomplexed radicals, these reactivity experiments lead to
the conclusion that free radicals are formed in the photolysis of cobaloximes.
These findings were supported by stereochemical studies. Thus, in the cyclization of the l-methylhexenylcobal-
0 VCH Yerlagsgesellscha/l mbH. D-6940 Weinheim, 1989
0570-0833/89/0303-0325 $ 02.50/0
325
C6H11HgOAc
13
1
NaBH,
H2C=CXY
16
hv
C6Hl ,Co(drngH)2L
+ C6Hl ," dC6Hl
0
-CH,-CXY
k re1
14
10
Zn
Tvt.
B,2
C6H11Br
15
Table 1. Reactivity k,, (20°C) of the alkenes 16 in C-C coupling with the
cyclohexyl radical 10 which was generated from different precursors. L in
14 = pyridine.
Alkene 16
X
Y
k,,, with different radical sources
13
14
15
(NaBH4) [a]
(hv) [a]
(Zn/Vit. BI2)[b]
CH3
EtO
CH3
H
CH,
H
CI
CI
0.04
0.14
0.2 1
0.27
0.58
= 1.00
3.1
8.8
Cds
CN
C02Et
C02Et
CN
CN
C02Et
CN
-
the alkanes 24 and the alkenes 25 in a ratio which depends on the substituent X and the solvent. The data show
that the photochemical reaction of the cobaloxime 14
( z 1) with alkenes (Reaction 0)
and the irradiation of the
adduct cobaloxime 23 (g6) (Reaction @) have identical
product ratios. The amount of alkanes 24 in the product
mixture increases with increasing electron withdrawing
character of the substituent X and upon changing from an
aprotic to a protic solvent. Furthermore, when the experiments were carried out in CH,OD a deuterium atom was
incorporated. This indicates an ionic cleavage of the cobalt-carbon bond in the formation of alkanes. The alkenes
25 are formed by elimination of hydridocobaloxime from
the cobaloxime 23.I9]
+
C6Hl 1CH2-CHBrX
NoCo(drngH)2py
21
+
22
C6Hl ,CH2-CHX-Co(dmgH)2py
23
0.04
-
0.13
-
= 1.00
0.22
0.27
0.61
= 1.00
2.6
II
-
~
@
H2C=CHX
1..
hv
dC ~ H , ~ C H ~ - C H Z+X C6HllCH=CHX
C6Hl1Co(drngH),py
@
14
25
24
[a] Solvent: CH2C12.[b] Solvent: DMF
oxime 17, formation of the cis-disubstituted cyclopentane
is favored (18a : 18b = 78 :22, 26°C) and, independent of
their configuration, the tert-butylcyclohexylcobaloximes
19a and 19b react with CCl, to afford the chlorides 20a
and 20b in the ratio 77 :23. These stereoselectivities correspond with those of free, uncomplexed radicals."'
18a
17
18b
78 : 22
t B u n C o ( d m g H ) 2 L
+
19a
1gb Co(dmgH)2L
Reaction @
E:Z(25)
Reaction @
E:Z(25)
X
Solvent
24:25
C02Et
CH2C12
CH3C02H
0:lOO
58:42
20:l
20.1
58:42
20:l
20:l
CHIC^^
29:71
90:lO
1.4:l
2.4:l
23:77
88: 12
2.0: I
CN
CH3C02H
24:25
0:lOO
1.1:1
Uncomplexed free radicals are also involved in the vitamin B12 catalyzed C-C coupling of alkyl halides with alkenes. This is shown by the reaction rates of the alkenes 16
when the cyclohexyl radical is generated by the method of
Scheffold et al.'''] from cyclohexyl bromide 15, vitamin
B,*, and Zn (Table 1). Furthermore, the stereoselectivity is
independent of whether the radical intermediate is prepared from tert-butylcyclohexyl bromide with vitamin B I Z
or with tributylstannane.
The proof of the occurrence of uncomplexed radicals
presented here is important for the design of syntheses us-
I
Vit.
+
+
t
B
u
n
C
I
20b
t
B
26
Br
u
q
a
/Zn
XCH=CYZ
or
au3SnH
27
+
t B u n C H X - C H Y Z
77 : 23
CHX-CHYZ
28a
According to these results, the C-C coupling products 2
and 3 are formed via the free radical 4 in the photolysis of
the cobaloxime 1. The question remains as to whether the
"adduct cobaloxime" 6 is an intermediate in this reaction.
In order to answer this question, we prepared independently the cobaloximes 23 from the corresponding bromides 21 and the Co' complex 22.['l Photolysis of 23 affords
326
0 VCH Verlagsgesellschaji mbH, 0-6940 Weinheim. 1989
X
H
CN
Me
Me
iPr
Alkene 27
Y
C02Et
H
H
C02Et
C02Et
0570-0833/89/0303-0326 $ 02.50/0
Z
C02Et
CN
CN
C02Et
C02Et
2Bb
Vit. B C 2
28a :28b
Bu,SnH
28a :28b
61 :39
44: 56
56:44
40 :60
27 : 73
21 :13
30:70
30:70
11:89
12:88
Angew. Chem. In(. Ed. Engl. 28 (1989) No. 3
ing cobaloximes and has implications for the discussion of
vitamin Biz catalyzed reactions in fiving organisms.["]
properties of the basis gel: chemical structure and surface
of the basis gel, and the nature, chain length, and density
of the hydrophobic ligands. In this study, we have determined the mobility of n-alkyl ligands on silica gel using
I3C CP/MAS NMR spectroscopy and have correlated this
with the unusual retention behavior of paracelsin peptides
on these RP carriers. The natural mixture of sequenceanalogous eicosapeptides (Scheme 1) which was used is of
great interest because of its antibiotic and membrane active properties, such as hemoIysis of erythrocytes and voltage dependent ionic conductivity in liquid bilayer membrane~."-~]
Received: October 20, 1988 [ Z 3018 IE]
German version: Angew. Chem. I01 (1989) 334
[ I ] a) M. Tada, M. Okabe, Chem. Lett. 1980. 201; b) 9. P. Branchaud, M. S.
Meier, Y . Choi, Tetrahedron Letr. 29 (1988) 167: c) A. Ghosez, T. Gbbel,
8. Giese, Chenr. Ber. 111 (1988) 1807; d) Salophen C o complexes have
also been used: V. F. Patel, G . Pattenden, J. Chem. SOC.Chem. Commun.
1987. 87 1.
121 a) B. P. Branchaud, M. S. Meier, M. N. Malekzadeh, J . Org. Chem. 52
(1987) 212; b) V. F. Patel, G.Pattenden, Teirohedron Lett. 28 (1987) 1451.
1
2
3
4
5
6
7
8
9
10
11 12 13 14 15 16 17 18
19
20
Ac-Aib-Ala-Aib-Ala-Aib-Ala-Gln-Aib-Val
-Aib-Gly-Aib-Aib-Pro-Val-Aib-Aib-Gln-Gin-Pheol
A
Ac-Aib-Ala-Aib-Ala-Aib-Ala-Gln-Aib-Leu-Aib-Gly-Aib-Aib-Pro-Val-Aib-Aib-Gln-Gln-Pheol
B
Ac-Aib- Ala-Aib-Ala-Aib-Aib-Gln-Aib-Val -Aib-Gly-Aib-Aib-Pro-Val-Aib-Aib-Gln-Gln-Pheol
C
Ac-Aib-Ala- Aib-Ala-Aib-Aib-Gln-Aib-Leu
Aib-Gly-Aib-Aib-Pro-Val-Aib- Aib-Gln-Gln-Pheol D
Scheme 1. Structure of the paracelsin peptides A-D.A c = Acetyl; Aib = a-aminobutyric acid ( 2 methylalanine), Pheol = phenylalaninol; all chiral components have the L configuration.
131 a) P. Maillard, C. Gianotti, Can. J. Chem. 60 (1982) 1402; b) D. W. R.
Rao, M. C. R. Symons, J. Chem. Sac. Faraday Trans. I 1984. 423.
[41 C. Chatgilialoglu, K. U. Ingold, J. C. Scaiano, J. Am. Chem. SOC.I03
(1981) 7739.
151 D. R. Jewell, L. Mathew, J. Warkentin, Can. J . Chem. 65 (1987) 31 I.
161 B. Giese, Angew. Chem. 95 (1983) 77 1 ; Angew. Chem. lnt. Ed. Engl. 22
(1983) 753.
171 a) A. L. J. Beckwith, 1. A. Blair, G. Phillipou, J. Am. Chem. SOC. 96 (1974)
1613; b) F. D. Greene, C. C . Chu, J. Walia, J. Org. Chem. 29 (1964) 728.
[8] The structures of the cobaloximes 23 (X = CO,Et, CN) were confirmed
by elemental analyses and IR and NMR spectroscopy. The 'H NMR
data (300 MHz, CDCl,) are particularly characteristic: 23 (X = C02Et):
6=0.55-1.17 (m, 8 H , cyclohexyl +CHZ), 1.22 (1. 3H, J=7.5 Hz, CH,,
ethylester), 1.50-1.64 (m, 5H, cyclohexyl CHI), 2.09-2.13 (m, 1 H,
Co-CH), 2.18 (s, 6 H , CH,, Hdmg), 2.21 (s, 6 H , CH2, Hdmg), 3.89-3.91
(m, 2 H, CH2, ethyl ester), 7.27-7.30 (rn, 2H, pyridine), 7.68-7.73 (m, 1 H,
pyridine), 8.49-8.51 (m, 2H, pyridine), 17.89 (s, 2H, OH).-23
(X = CN): 6=0.48-2.20(m, 14H), 2.23 (s, 6 H , CH,), 2.26 (s, 6 H , CH,),
7.28-7.34 (m, 2 H , pyridine), 7.71-7.77 (m, l H , pyridine), 8.45-8.49 (m,
2 H, pyridine), 18.05 (s, 2 H, OH).
[9] For the elimination mechanism see S. Derenne, A. Gaudemer, M. D.
Johnson, J. Organomet. Chem. 322 (1987) 22.
[lo] R. Scheffold, M. Dike, S. Dike, T. Herold, 1.Walder, J. Am. Chem. SOC.
102 (1980) 3642; R. Scheffold, L. Walder, C. Weymuth, Pure Appl. Chem.
59 (1987) 363; R. Scheffold, Nachr. Chem. Tech. Lab. 36 (1988) 261.
[ I 11 In enzyme reactions, both the position and the conformation of the radical may be determined by the enzyme. see J. Retey, J. A. Robinson: Stereospecificiy in Organic Chemistry and Enzymology, Verlag Chemie,
Weinheim 1982; J. Halpern, Science (Washington, D.C.)227 (1985) 869.
+
Correlation of the Dynamic Behavior
of n-Alkyl Ligands of the Stationary Phase with
the Retention Times of Paracelsin Peptides
in Reversed Phase HPLC
By Betfina pfleiderer, Haus Albert, Klaus D . Lork,
K ~ UKS. Unger, Hans Briickner. and Ernst Bayer*
In reversed phase high performance liquid chromatography (RP-HPLC), the retention of substances and the selectivity of the separation are influenced by the following
[*I Prof. Dr. E. Bayer, DipLChem.
B. Plleiderer, Dr. K. Albert
Institut fur Organische Chemie der Universitnt
Auf der Morgenstelle 18, D-7400 Tiibingen (FRG)
Dr. K. D. Lork, Prof. Dr. K. K. Unger
Insfitut fur Anorganische Chemie und Analytische Chemie der Universitat
J.-J.-Becher-Weg 24, D-6500 Mainz (FRG)
Prov.-Doz. Dr. H. Briickner
lnstitut fur Lebensmitteltechnologie der Universitat Hohenheim
Postfach 700562, D-7000 Stuttgart 70 (FRG)
Angew. Chem. Int. Ed. Engl. 28 (1989) No. 3
RP materials with n-alkyl chain lengths 1 < n < 20 were
prepared by reacting LiChrospher (Si 100, 10 pm) with the
appropriate n-alkyldimethyl~hlorosilane.'~~
The ligand
density was 3.5k0.2 mol m-'.
Since changes in the mobility of n-alkyl groups are revealed by the relaxation behavior of the carbon atoms,
they can be characterized through determination of the
spin-lattice relaxation times T,IS1or the relaxation times in
the rotating coordinate system T I P H . ' ~ ]We chose the T]pH
values of the protons as a measure of the mobility of the
alkyl chains, since TlpHgives information about rates of
motion in the kHz range,161and because relatively small
changes in the mobility result in large changes in the TlpH
times. In contrast, the TI times, which are sensitive in the
MHz range, exhibit only small differences."' In the range
of slow molecular motions, the TIpHvalues are averaged
completely by 13C-IH dipolar interactions.[*] However, the
high mobility of the alkyl chains, which exhibit liquid-like
behavior, and the additional rapid rotation of the probe at
the magic angle (MAS, v,,=4000-5000 Hz) lead to a drastic reduction in the dipolar interactions, so that averaging
by spin diffusion does not occur in these systems. This
phenomenon has been observed by Alemany et al. for
highly mobile molecules.[g~'ol
Solid-state N M R spectroscopy on C8 and CISphases has
shown that the total mobility of the CI8 chain is smaller
than that of the Cs chain.'"] For a more thorough investigation, materials with n = 4 , 5, 6, 8, 10, 12, 14, and 18 were
selected for TlpHmeasurements using I3C CP/MAS N M R
spectroscopy. Figure 1 shows the dependence of the relaxation times TlpHof the terminal methyl groups of the stationary phase upon the alkyl chain length n. Analogous behavior was observed for the (n - 1) and (n - 2) methylene
groups of the respective n-alkyl ligands. Surprisingly, a
maximum in the TlpHvalue of ca. 80 ms occurs for a chain
length of n = 6-8. The TlpHvalues of the alkyl chain carbon
atoms of the C4 and C, phases are given for comparison in
Table 1. In the case of the Cs phase (and also the C, and
C6 phases), they increase in the direction of the terminal
methyl group, whereas in the C4 phase they are practically
identical for all positions.
The temperature dependence of the relaxation times revealed that a n increase in the TlpHvalues corresponds to a
higher mobility of the n-alkyl chain. Thus, the relatively
small TlpHvalues of the C4phase indicate a low motional
0 VCH Verlagsgesellschafl mbH. 0-6940 Weinheim. 1989
0570-0833/89/0303-0327 $ 02.50/0
327
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