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Thermal and Electrocatalytic Epimerization at Iron as the Chiral Center.

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With respect to medicinal applications of the isohematoporphyrin diglycosides 5-8, it was important to know
whether the polar sugar moiety would affect the photosensitizing activity. Of particular interest was the formation of
singlet oxygen, which is thought to be involved in the antitumor activity of Hpd."]
The trapping reaction with 2,s-dimethylfuran grsl under
standard conditions proved suitable for comparative, quantitative determination of the amount of ' 0 , formed.i91
by addition of acetic acid. Evaporation under vacuum afforded an oily residue.
which was applied with a 10-mL syringe to a SEP-PAK C,, cartridge (Waters,
Part. No. 51 910)- previously washed with methanol followed by water. The
porphyrin diglucoside 5 was completely adsorbed on the cartridge and retained.
so that inorganic components could be removed by washing with water and 5
could be subsequently eluted with methanol. Evaporation of the eluate gave
32 mg (87%) of red 5. m.p. 180'C. FD-MS: mi; 923 (100%. Me), UV:VIS
(MeOH): E.,..(logc) = 396 (5.00), 498 (3.77). 532 (3.62). 569 (3.46). 620 nm
(3.26). 'H NMR (300 MHz, [DJacetone, solution prepared by the SEP-PAK
cartridge method. see above): 6 = -4.0 (s, 2 H ; NH), 9.92, 10.01, 10.07, 10.10
(4s; mrso-H). "C NMR (75.47 MHz. broadband-decoupled, D:O): 6 = 9.2
(pyrrole CH,), 61.0, 61.1 (Glu-C6), 69.7, 69.9 (Glu-C4), 73.5 (Glu-C2). 76.1,
76.2 (Glu-C3, GIu-CS), 95 (br., me.so-C). 102.1, 102.8 (Glu-Cl). 179 (COOH).
Received: June 6, 1989 [Z 3378 IE]
German version: Angrw. Chem. I 0 1 (1989) 1550
9
10
11
The results in Fable 1 show that the new porphyrin diglycosides 5-8 are efficient photosensitizers. Each produces
roughly a hundredfold amount of chemically reacted '0, in
20 min. Thus, they are almost as efficient as the well-known
photosensitizer Rose Bengal.
Table 1. Comparison of ' 0 , formation under standard conditions: 2.5dimethylfuran 9 as trapping agent; quantitative determination (after inethanolysis) of the amount of crystalline hydroperoxide I 1 formed. Ca. 0.005 mmol of
photosensitizer and 1.44g(lSmmoi)of9in 160mLofbenzene:MeOH (3:l);
irradiation with a 150-W halogen lamp while 0, is bubbled through the solution
(20 min, 0 C).
Sensitrzer ([mg])
Isohematoporphyrin dimethyl ester 4 a (3.0)
Hemdtoporphyrin 3 (3.0)
Octaacetylporphyrin diglucoside 7 (4.8)
Octaacetylporphyrin digalactoside 8 (4.6)
lsohematoporphyrin diglucoside 5 (4.1)
Isohematoporphyrin digdlactoside 6 (4.4)
Rose Bengal (5.4)
Control without sensitizer
Yield of 11
based on 9
["h1
18
30
46
19
22
28
50
-
Detailed investigations of the photophysical properties of
the isohematoporphyrin diglucoside 5 and vinylogous porphyrinoids'". ' will soon be
Experimental Procedure
7: a-I-Acetobromoglucose (1.6 g, 3.9 mmol), sodium sulfate (3 g), and freshly
prepared silver carbonate [ S ] (1.6 g) were added under argon to a solution of
isohematoporphyrin dimethyl ester 4 a (172 mg, 0.27 mmol) in 250 mL of degassed, dry dichloromethane and the reaction mixture was stirred in the dark at
room temperature for 24 h (TLC monitoring, chloroform:methanol50: 1, silica
gel TCL plates F,,,. Merck). The reaction mixture was then filtered through
Celite and the filtrate was evaporated under vacuum. Column chromatography
of the residue on 200 g of silica gel (Merck, particle size 0.063-0.2 mm) with
chloroform gave 180 mg (51 %) of red, microcrystalline octaacetylisohematoporphyrin diglucoside dimethyl ester 7. m.p. 118'C. EI-MS: mi; 1287 (100%,
Me). 1200 (6, M e - CH,CH,COOCH,), 927 (60, M o -CH,O-glucose acetate). U V V I S (CHCI,): &(Iogt,) = 400 (5.25). 499 (4.15). 533 (3.98). 568
(3.80). 595 (3.1 I), 622 nm (3.64). 'H NMR (300 MHz, CDCI,): 6 = -3.84 (s,
2 H ; NH). 9.99, 10.01, 10.08. 10.10 (4s. 1 H each; meso-H). "CNMR
(75.47 MH7, broadband-decoupled, CDCI,): 6 = 11.67, 11.75, 11.84 (pyrrole
CH,). 19.44, 19.52, 20.46. 20.51, 20.65 facetyl-CH,), 51.70 (ester CH,), 61.99
(Glu-C6). 68.44 (Glu-C4), 71.06 (Glu-C2). 71.96 (Glu-CS), 72.87 (Glu-C3),
101.23 (GIu-Cl). 96.41. 96.63. 96.75, 96.90 (meso-C).
8 was synthesized analogously
5 : A solution of 7 (51 mg. 0.04 mmol) and potassium hydroxide (80 mg) in
75 mL of methanol and 6 mL of distilled water was refluxed for 24 h. The
reaction mixture was then allowed to cool to room temperature and neutralized
Angrn.. Chmi. 1111.Ed. Engl. 28 11989) No. I!
CAS Registry numbers:
3, 14459-29-1; 4a. 33070-12-1.4b. 3819-29-2.5, 122744-60-9: 6. 122744-61-0:
7. 122144-62-1; 8, 122744-63-2; 9, 625-86-5; 10, 45722-89-2; 11. 13249-74-6:
cx-u-acetobromogalactose,3068-32-4; cx-u-acetobromoglucose,572-09-8.
[I] T. J. Dougherty, Proc. SPIEInr. Soc. Opt. Eng. Scr. 5 , Vol. YY7(1988)2~-7:
A. Andreoni, R. Cubeddu (Eds.): Porphwin.5 in Tumor Therupx, Plenum
Press, New York 1984.
[2] I. L. Matthews, J. T. Newman, F. Sogandares-Bernal, M. M. Judy, H.
Skiles, J. E. Leveson, A. J. Marengo-Rove, T. C. Chanh. 7i.rin.sfusion
(Philudelphiu) 28 (1988) 81 -83.
131 G. W. Kenner, S. W. McCombre. K. M. Smith, Ju.sru.s Liehigs Ann. Chwn.
1973. 1329- 1338.
[4] The new compounds 5-8 were completely characterized by elemental
analysis and spectroscopic data.
[ S ] C. M. McCloskey, G. H. Coleman, Org. S w r h . Colt. &d. 3 (1955) 435.
[6] K. Bock, H. Thorgerson in G. A. Webb (Ed.): Annu. Rep. N M R Spwrru.sc.
13 (1982) 2-57.
171 K. R. Weishaupt, L. J. Gomer, T. J. Dougherty, Cancer Rex 36 (1976)
2326- 2329.
181 C. S. Foote, M. T. Wuesthoff, S. Wexler, 1. G . Burstain. R. Denny. G. 0.
Schenck. K.-H. Schulte-Eke, Rtruhedron 23 (1967) 2583 2599.
191 B. Frdnck. M. Dust, A. Stange, P. P. Hoppe, Nufurwb.\~,nsi.hufirn6Y
(1982) 401 -402.
[lo] M. Gosmann, B. Franck, Angew. Chem. 98 (1986) 1107- 1108: A n p w .
Chem. Int. Ed. Engl. 25 (1986) 1100-1101; B. Franck, M. Gosmann. G.
Kniibel, DOS 3 635820 (28. April 1988) BASF AG; Chem. A h t r . 109
(1988) 94748~.
I l l ] G. Knubel. B. Franck, A n p c Chem. /OO (1988) 1203-1204: A n g w .
Chem. Inr. Ed. Engl. 27(1988) 1170-1172.
[12] G. Schermann. R. Schmidt, A. Volker, H.-D. Brauer. H. Mertes. €3.
Franck, Photochen?. Photohiol. in press.
~
Thermal and Electrocatalytic Epimerization
at iron as the Chiral Center**
By Henri Brunner,* Konrad Fisch, Pefer G . Jones,
and Josef Salbeck
Optically active transition metal compounds in which the
transition metal is the chiral center can be synthesized with
the optically active aminophosphane ligands L and L'.('I
['I Prof. Dr. H. Brunner, Dip].-Chem. K. Fisch
Institut fur Anorganische Chemie der Universitit
Universitiitsstrasse 31. D-8400 Regensburg (FRG)
Prof. Dr. P. G. Jones
Institut fur Anorganische und Analytische Chemie der
Technischen Universitit Braunschweig
Dr. J. Salbeck
lnstitut fur Organische Chemie der Universitiit Regensburg
I"']Optically active transition metal complexes. Part 96. This work was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie and BASF AG. Ludwigshafen. Part 95: P. Bladon, P. L.
Pauson, H. Brunner, R. Eder, 1 Orxunomrr. Chrm. 355 (1988) 449.
,f' VCH Verlagsgesellschufi mhH, 0-6940 Weinheim. 1989
0570-0833lHYjIill-1521BO2.5Oj0
1521
Examples are the acetyl iron compounds ( R S ) and (SS)[CpFe(CO)(L)COCH,] (Cp = q-C,H,) and their analogues
containing the Iigand L . In all cases, the epimerization at the
iron atom occurs via dissociation of L and L'; because of the
participation of chiral dihapto-acyl intermediates and the
achiral rearrangement product [CpFe(CO),CH,], it is difficult to analyze this
Such complications d o not
occur in the epimerization of the methyl iron compounds 1
and 2.
The photochemical reaction of the prochiral compounds
[Cp'Fe(CO),CH,], Cp' = cyclopentadienyl or indenyl, with
L proceeds via exchange of one of the two enantiotopic C O
groups to give the compounds l a , b r 5 ] and 2a,b; the
diastereomeric ratio is 50: 50 in each case.[61The isomers can
be separated by preparative liquid chromatography and by
fractional c r y ~ t a l l i z a t i o n The
. ~ ~ ~absolute configurations of
1 a and 2a have been determined by X-ray structural analysis;[*l these compounds take u p remarkably similar conformations in the crystal (Fig. 1).
c4
c47
C46
C42
The thermal epimerization of 1 a and 2a in C,D, is first
order;['] in both cases it was followed by baseline-separated
' H NMR signals."'] The rate of epimerization is not
changed measurably when L is added, while in the presence
of L'. a complete phosphane exchange occurs which is also
first order. The epimerization of 2 a was shown to have a
large positive entropy of activation (75 J K - ' molF1).[lll
These results suggest a dissociative epimerization mechanism whose rate-determining step is the cleavage of the Fe-L
bond. The kinetic data for this process indicate that the
intermediate or transition state is an achiral species.['21
= 37 min, 50.0"C) epimerThe indenyl complex 2 a (l1,,
izes 10-20 times faster than the cyclopentadienyl complex
l a ( t , , z = 70min, 70.0"C). We suggest that this relatively
small acceleration is due to the increased steric interaction
between the indenyl and aminophosphane ligands which
favors phosphane dissociation. The absence of an "indenyl
effect" (higher reactivity of the indenyl system compared to
the analogous C p system because of ring ~ i i p p a g e l ' 141)
~.
must be due to the absence of associative processes.
Significant differences were observed in the electrocatalytic configuration transformation of the iron complexes 1 a
and 2a, depending on the pentahapto-bonded n ligand.
While the indenyl complex 2 a is epimerized completely within one minute at - 35 "C in T H F using sodium amalgam as
the reducing agent,['51 the Cp compound 1 a surprisingly
does not epimerize either at - 35 "C or at + 20 "C under the
same conditions. In contrast to the C p compound 1 a, the
indenyl compound 2a undergoes electron transfer to give a
19e-species which loses phosphane. The resulting 17e-radical
anion changes its configuration before phosphane association and transfer of the electron back to the catalyst o r substrate completes the catalytic cycle.
When the epimerization of 2a is oxidatively induced with
50 mol-% [Cp,Fe][PF,], it is incomplete at +20"C in THF
after 30min; however, under the same conditions the
epimerization of 1 a establishes thermodynamic equilibrium
1 a:l b = 62:38 after five minutes.
The cyclovoltammograms of 1 a and 2 a are in agreement
with the behavior of the complexes with respect to the starting reagents used; while the reduction of 2a shows an irreversible reduction wave at a peak potential of - 21 85 mV vs.
SCE, no corresponding behavior is observed for 1 a up to the
commencement of the reduction of the solvent at
-2570 mV. The reduction of the indenyl compound 2a is
accompanied by a further rapid reaction. The voltammograms are however almost identical for the oxidation of
2 a (+ 240 mV) and 1 a (235 mV); in each case these are irreversible oxidation processes followed by other rapid reactions.['6] All observed oxidation and reduction potentials lie
within the potential range of the starting reagents used for
the electrocatalysis.
Thus, in the case of the oxidatively or reductively induced
epimerization of l a and 2a, we have detected for the first
time a configuration transformation induced by electron
transfer" which is accelerated enormously in comparison
with the thermal reaction.
Received: June 21, 1989;
revised: August 2 , 1989 [Z 3405 IE]
German version: Angew. Chern. f01 (1989) 1558
CAS Registry numbers:
l a . 59727-90-1; 1 b. 59568-04-6; Za, 123075-70-7; 2b. 123163-87-1
c1
2a
Fig. 1. Structures of (-)e36-(R&)-l
1522
0 VCH
a and ( -)436-(RvcSc)-Zain the crystal.
Verlagsgesriischafi mhH, 0.6940 Weinheirn. 1989
[l] H. Brunner. Adv. [email protected]~nu~ner.
Chern. 18 (1980) 183.
[2] H. Brunner, H. Vogt, Chern. Be,. I14 (1981) 2186.
131 H. Brunner, H. Vogt, J. Orgunorner. Chem. 191 (1980) 181
0S70-0833/89/1lll-l522$02.50/0
Angew. Chem. lnt. Ed. Engl. 28 (1989) No. I 1
[4] H . Brunner, B. Hammer, Organumerailics2 (1983) 1595.
[5] H. Brunner. H. Vogt. J. ffrgmomet. Chem. 210 (1981) 223.
[6] The indenyl complex 2a.b was prepared analogous to the Cp complex
1 a, b. [5] Za, b is chromatographed on A1,0, in the absence of air; after
rcmoval of the startingmaterials, 2a, b is eluted with pentane-diethyl ether
(4: 1) as a brown zone. Removal of the solvents yields 2a, b as a powder.
[7] The diastereomers 1 a and 1 b were separated as previously described. [S]
The separation of Za and 2 b was carried out as follows: 1 g of the 1:l
mixture was stirred rapidly in 10 mL pentane. The mother liquor was
removed and the extraction of the residue repeated with 5 mL pentane. The
residue remaining contains 300 mg of the diastereomer Za in optically pure
form.
[8] ('rj..stulsrructurr unu/wrs of l a : C,,H,,FeNOP, M , = 483.1, space group
P2,2,2,.u = 1238.5(2), b = 1387.0(2),c = 1395.5(2) pm.Z = 4.Structure
solved using direct methods. Anisotropic refinement up to R = 0.028,
R,,= 0.029 for 3967 absorption-corrected reflexions up to 2 0 5 50" (Mo,,
irradiation). Absolute configuration determined by q-refinement: q =
+ 1.04(3)141. C r ~ s t u l s t r u c r u r e u n o l ~ ~ i s u f 2C,,H,,FeNOP,
a:
M, = 533.4,
space group P2,2,2,, u = 1050.4(2), h = 1152.0(1), c = 2245.4(2) pm,
Z = 4. The structure was solved using direct methods. Anisotropic refinement up to R = 0.051, R, = 0.041 for 3775 absorption-corrected reflexions up to 2 0 < 50' (Mo,, irradiation). Absolute configuration determined by q-refinement; q = +0.99(4). Further details regarding the
crystal structures can be obtained from the Fachinformationszentrum
Karlsruhe, Gesellschaft fur wissenschaftlich-technischeInformation mbH.
D-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the deposition
number CSD-54028, the authors and the literature reference.
[Y] Kinrric dutu fur the epimerizatiun o / l o : T = 70.0"C; k(1a) = (1.66 +
0 . 0 3 ) ~ 1 0 ~ ~ RS/SS,,=62/38;
s~':
Kc,=0.61. l a + L: T=70.O"C;
c ( l a ) = c(L) = 0.1 molL-';
k ( l a L) = (1.66 + 0 . 0 3 ) ~ 1 0 - ~ s - ' .
2a: T = 50.0"C; k(2a) = (3.19 i 0 . 1 0 ) ~l V 4 s - * ; RSjSS,, = 62/38;
K,, = 0.61. 2 a 5 L: T = 50.0'C; c(2a) = c(L) = 0.1 molL-'; k ( 2 a
L)=(3.10_f0.10)x10~4s~'.
2 a f L : T=50.OoC; c(2a)=0.1 mol
L-', c(L') = 0.3 mol L-'; k ( 2 a L ) = (1.81 5 0.06) x
s-I.
[lo] 'H NMR: l a und I b see [4]. 2 a (Zb) (C,D,, TMS int., 250 MHz):
6 = -0.71 (-0.62) (d, 3 H , J = S S H z , Fe-CH,), 1.52 (1.27) (d, 3H,
J = 7Hz,C-CH,).2.05(2.09)(d,3H,J=7.5Hz,N-CH,),4.50(4.43)(d,
2H, H-41, H-43). 4.83 (4.73) (t, 1 H, H-421, 5.86 (5.35) (m, l H , H-2).
5.93-7.63 (6.13-7.63) (m, lYH, phenyl and indenyl H).
[ll] A S * = +(75*5)JK-'mol-';
A H = ( 1 1 9 _ f 6 ) k J m o l - ' . The activation parameters were determined between 45.0-55.0 'C.
1121 P. Hofmann, A n p w . Chem. 89(1977) 551; Angew. Chem. Inr. Ed. Engl. I6
(1977) 536.
[13] M. E. Rerek. F. Basolo. J. Am. Chem. Soc. 106 (1984) 5908.
[14] M. E Rerek, F. Basolo, Organumetu/iics 2 (1984) 740.
[15] 2 a undergoes slight decomposition, as detected by the formation of free
phosphane. The degree of decomposition increases with increasing reaction temperature and reaction time.
1161 I n the case of 2a. a second reduction wave is observed at low feed rates
during the recording of the cyclovoltammogram in the opposite direction.
[I71 D. Astruc. Angen. Chem. 100 (1988) 662; Angew. Chem. Inr. Ed. Engl. 27
(1988) 643.
+
+
+
coordination and reactivity. We report here three different
modes of allene bonding in compounds 1-3.
We recently reported the preparation of 1 from
[W,(OtBu),] and allene in hydrocarbon solvents. [21 On the
basis of N M R spectroscopic data, we proposed a p-perpendicular allene coordination in which the C,H, moiety had
rehybridized to resemble that predictedf3] on theoretical
grounds for the transition state for allene racemiration.
Compound 1 reacts with CO (> 2 equiv.) in hydrocarbon
solvents to give complex 2, which shows two CO stretching
frequencies (1900 and 1830 cm-') in the IR spectrum and
four tBu groups in the H and 3C N M R spectra in the ratio
1:2:2:1. For the allene methylene groups one I3C N M R
signal and two 'H N M R signals are observed.
Compound 1 and excess allene react in hydrocarbon solvents at < 22 "C to give complex 3, which, by N M R spectroscopy, has six different OtBu groups, eight allenic protons,
and six allenic carbon atoms. The allenic proton resonances
form two separate ABCD spin systems.
We have been able t o obtain crystals suitable for an X-ray
analysis for 1-3 and find, contrary to our earlier prediction,''] that the allene is aligned parallel to the W -W axis in
1, whereas complexes 2 and 3 display other modes of bondin g .i41
Two views of compound 1 are shown in Figure 1 . The
structural parameters associated with the central W,C, moi-
Versatile Modes of Allene Bonding in the Structures
[W2(OtBu)6(C3H4)I9 [ w 2 ( o ~ B ~ ) ~ ( ~ 3 H ~9 ) ( ~ o ) 2 ~
and [W2(0tBu)6(C3H4)21
Of
By Roger H . Cayton, Stephanie 7: Chacon,
Malcolm H. Chisholm,' Mark J Hampden-Smith.
John C. Hufman, Kirsten Folting, Paul D. Ellis,
and Beth A . Huggins
The compounds [M,(OR),](M= M) provide templates for
developing organometallic chemistry.['' In particular, the
dinuclear center and the M = M bond allow novel modes of
[*I
Prof. M. H. Chisholm, Dr. R. H. Cayton, S. T. Chacon,
Dr. M. J. Hampden-Smith Dr. J. C. Huffman, Dr. K. Folting
Department of Chemistry and Molecular Structure Center
Indiana University
Bloomington, IN 47405 (USA)
Prof. P. D . Ellis. B. E. Huggins
Department of Chemistry, University of South Carolina
Columbia, SC 29208 (USA)
[**I This work was supported by the Department of Energy, Office of Basic
Sciences. Chemistry Division. and by the National Science Foundation.
An~qen.Chrm. I n / . Ed. Engl. 28 (1989) Nu. I 1
(3
l
Fig. 1. Two drawings of complex I emphasizing the p-parallel mode of alleneto-W, bonding. Pertinent distances [A] (average) and angles ["I; W-W 2.583(1),
C-C (allene) 1.47(1), W-CH, 2.13(1). W-C2.09(1). W - 0 I.YO(2);C-C-C 141(1).
ety indicate a n extensive degree of Wdn-C3pn orbital mixing. Indeed, the C-C distance of 1.47(1) 8, is essentially
identical to a C,,, - C,,, single-bond distance.C5l
The molecular structure of 2 is shown by a line drawing.
The allene ligand, which may be viewed as part of a
tungstaallyl(2 -)moiety, is o-bonded to one tungsten and
VCH Veriu~.~gesellsrhuf~
mhH, 0-6940 Wemherm, I989
0570-0833/89/1
IIl-I523 $02.50/0
1523
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