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Electrostatic Activation of Nucleofuges Cationic Leaving Groups.

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of the substrate. The homolysis must therefore be induced by
a change in conformation of the enzyme protein. Probably
an equilibrium between substrate and product (succinylCoA), or the enzyme-bound intermediate, is immediately
established at the active site. The position of this "internal"
equilibrium is unknown and can differ considerably from the
equilibrium of the free substrates. To our knowledge this
communication reports the first direct proof of radicals in a
coenzyme B,, dependent rearrangement of the carbon skeleton.
Received: August 23, 1991 [Z4885 IE]
German version: Angeu. Chem. 1992, 104, 212
us to conduct the poly-onio substitutions with 4-dimethylaminopyridine (DMAP, symbolized by L in the reaction
equation^).'^'
The reaction of PCI, with two equivalents of DMAP in
ethyl acetate (EE) according to Equation (a) yielded the
bis(onio)-substituted phosphane 1a as isolable, hygroscopic
salt. (The spectroscopic data of this and all other new compounds are given in Table 1.) The dicationic structure of 1a
follows from its quantitative transformation into the analytically pure bis(trifluoromethanesu1fonate) (abbreviated
bis(triflate), 1 b) with Me,SiOTf (OTf = O,SCF,).
r
7
CAS Registry numbers:
Methylmalonyl-CoA mutase. 9023-90-9; coenzyme B,,, 13870-90-1
[l] Review: J. Retey in Vitamin B,,, Vol. 2 (Ed.: Df Dolphin), Wiley, New
York 1982, p. 357-379.
[2] S. Wollowitz, J. Halpern, J. A m . Chem. Soc. 1984, 106, 8319-8321; hid.
1988, 110, 3112-3120.
[3] G. Choi, S:C. Choi, A. Galan, B. Wilk, P. Dowd, Pror. Null. Acad. Sn.
USA 1990, 87 3174-3176.
[4] B. M. Babior. T. H. Moss, D. C. Could, J. Biol. Chem. 1972, 217, 43894392.
[S] B. M. Banor, T. H. Moss, W. H. Orme-Johnson. H . Beinert. J. B i d . Chern.
1974,249,4537-4544.
[6] S . A. Cockle, H. A. 0. Hill. R. J. P. Williams, S. P. Davies, M. A. Foster,
J. Am. Chem. Soc. 1972. 94, 275-217.
[7] T. H. Finlay, J. Valinsky. A. S. Mildvan, R. H. Abeles. J. Bid. Chem. 1973.
248, 1285-1290.
[S] K. L. Schepler, W. R. Dunham, R. H. Sauds, J. A. Fee, R. H. Abeles.
Biochim. Biophys. Artu 1975, 397, 510-518.
[Y] W. H. Orme-Johnson, H . Beinert, R. L. Blakley, J. Biol. Chem. 1974, 249,
2338-2343.
[lo] J. D. Brodie, A. D . Woodams, B. M. Babior, Fed. Proc. 1972, 31, 1578.
[I 11 The ESR spectrum was recorded on an ESP 300 E 10/12 ESR spectrometer
(Bruker Analytische Messtechnik) at a microwave frequency of 9.5 GHz
and microwave power of 5 mW. An N M R Gauss meter and a frequency
counter (model HP 5350B) was used to calibrate the magnetic field. A
cylindrical TM resonator served as sample head. The ESR spectra were
obtained at 77K.
[12] J. R. Pilbrow in Vitamin B,, (Eds.: B. Zagalak, W. Friedrich), de Gruyter,
Berlin, 1979, p. 505-510.
[I31 J. Rktey, P. Such, Y Zhao, unpublished.
Electrostatic Activation of Nucleofuges: Cationic
Leaving Groups**
By Robert Weiss* and Stefan Engel
We have shown that the redox potentials of quinonoid
oxidizing agents can be shifted dramatically to positive
values by cationic substituents."' The nature of the dependence of this phenomenon on the number and spatial arrangement of the positive poles revealed that it was dominated by an F effect.Iz1This effect causes a stabilization of the
dianionic (reduced) form of the quinones by the cationic
substituents. The electrostatic nature of the effect suggests
that it can be used to stabilize any anionic system, which
could have a direct bearing on the electrostatic activation of
anionic nucleofuges.
We now report on poly-onio-substituted phosphorus compounds among which cationic leaving groups are found for
the first time. Our experience with quinonoid systems[31led
[*] Prof. Dr. R. Weiss, Dr. S . Engel
Institut fur Organische Chemie
der Universitat Erlangen-Nurnberg
Henkestrasse 42
D-W-8520 Erlangen (FRG)
[**I This work was supported by the Fonds der Chemischen Industrie.
21 6
0 VC'H Verlugsgesellsrhafi mbH,
W-6940 Wernheim, 1992
l a (66%)
+2 Me,SiOTf
-2Me,SiCI
1
2a (98 %)
CH,CI,
ca.20°C. 2h
l b (91 %)
r
La1
2b (78%)
H3C,..,CH3
LQ =
&Y
T@
Both in the solid state and in solution, the salt 1 a loses one
equivalent of chlorine slowly at room temperature and fast
when heated. The novel bis(onio)phosphide 2 a results and
can be transformed into the corresponding triflate 2b by
anion exchange with Me,SiOTf. The spontaneous chlorine
loss is interpreted as an S,2 (C1) reaction with redox character,
in which the bis(oni0)phosphide functions as a potent cationic nucleofuge. If all the ionically and covalently bound chlo-
Table 1. Spectroscopic data of the compounds 1-7 [a]
la: IR: a[cm-'] = 3100 (w),1645 (ss), 1570 (s), 1410 (w), 1220 (w). 830 (m);
'H NMR: 6 = 3.17 (s, 12H), 7.47 (AABB, 8 H )
l b : IR: G[cm-'] = 3100 (w), 1650 (s), 1570 (s); 1405 (w). 1280 (s), 1215 (ss):
'H NMR: 6 = 3.31 (s, 12H), 7.67 (AABB, 8H); 830 (w)
2a: IR: C[cm-'] = 3050 (w). 1640 (ss), 1560 (ss), 1400 (s), 1210 (s), 825 (s);
' H N M R 6 = 3.23 (s, 12H), 7.56 (AA'BB, 8 H )
2b: IR: G[cm-'] = 3080 (w). 1650 (ss), 1550 (ss), 1405 (m), 1270 (ss), 1220 (s),
835 (W); ' H N M R : 6 = 3.17 (s, 12H), 7.41 (AA'BB, 8H); 3 1 P N M R
(400 MHz, CD3N0,, 26 ' C , H,PO,): 6 = -20.06
2c: IR: G[cm"] = 3060 (w), 1630 (ss), 1550 (ss), 1400 (m), 1200 (s), 800 (s);
' H N M R 6 = 3 . 1 7 (s, 12H). 7.49 (AABB, 8H); UVjVIS (CH,CN):
A[nm] = 215, 275
2d: IR: ?[crn-'] = 3050 (w), 1640 (ss), 1560 (ss), 1200 (s), 785 (m); ' H NMR:
6 = 3.21 (s, 12H), 7.50 (AA'BB', 8H); UVjVIS (CHJN): A[nm] = 278, 362
4b: IR- t[cm-'] = 3060 (w), 1640 (s), 1560 (s), 1400 (m), 1270 (ss), 1210 (ss),
1 0 2 5 ( ~ ) , 8 3 0 ( ~' )H; NMR:6 = 3 . 2 0 ( ~12H),4.00(d,
,
'J(P,H) =14Hz,3H),
7.47 ( A A B B , 8 H)
5: IR: G[cm-'] = 3060 (w). 1640 (ss), 1560 (ss), 1210 (w). 1030 (m), 810 (m);
' H NMR: 6 = 3.25 (s, 12H), 7.50 (AA'BB, 8 H )
7: IR: i.[cm-'] = 3090 (w). 1630 (ss), 1560 (ss), 1400 (m), 1270 (ss), 1205 (ss),
11 10 (m). 820 (m); ' H NMR: 6 = 3.21 (d, 12H), 7.47 (AA'BB, 8H);
NMR
(400 MHz, CD3N0,, 26 "C, H,PO,): 6 = -19.08
[a] All IR spectra were recorded in Nujol; all NMR spectra were measured at
60 MHz and 25 "C in CD,CN against TMS as standard.
'a570-0833192102o2-0216S3.50t.25/0
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 2
-
rine in 1a is exchanged for bromine or iodine [Eq. (b)], the
stable trihalogenides 2c, d form spontaneously in high yields
via the nonisolable dicationic salts 1c,d in an analogous S,2
(Hal) reaction at room temperature.
ITf, EE
9,
lyF’,L
,LO
a]OTp
7 (88%)
6
lc, X0 = Br”
Id, Xe = Ie
2c (77 Y o )
2d (82%)
The reduction P”’ -+ P’ summarized in Equations (a) and
(b) is without precedent. The driving force is the optimal
stabilization of the phosphide center in salts 2 by the F and
I effects of the cationic substituents. An increase in the oxidation state of phosphorus should increase the nucleofugality of the novel leaving groups 2. The idea was pursued with
derivatives of phosphoric and phosphorus acid analogous to
2. The attempt to synthesize the methoxy-substituted dication salt 4 (analogous to 1) from methyl dichlorophosphite 3
and two equivalents of DMAP at room temperature again
yielded a structurally novel, stable salt, bis(onio)phosphite 5,
as the only product [Eq. (c)]. Under the activating influence
Cl
-”
In this remarkable dealkylation reaction, the cation in salt
7 is a better leaving group than the triflate ion. Our results
show that the electrostatic stabilization of the electron density of a nucleofuge by two adjacent onio substituents is exceptionally effective. We anticipate that the method can be extended to other element combinations and charged states,
increasing the nucleofugality even further.
Experimental Procedure
All manipulations were performed in an inert nitrogen atmosphere in dried
solvents. No melting points were determined on account of the extreme hygroscopic nature of the samples. All reported compounds gave correct elemental
analyses.
General method to prepare the chloride salts: DMAP (20 mmol) was dissolved
in EE or CH,CI, (100mL) and treated with the approprlate P-Cl compound
(10 mmol). The precipitate was filtered off and dried at 0.01 Torr.
2 is obtained by gradual dropwise addition of a solution of DMAP (10 mmol)
in EE (75 mL) to a solution of PCI, in EE (5 mL). The triflates are prepared by
dissolving DMAP with the corresponding amount of Me,SiOTf.
Received: April 24, 1991 [Z4590 IE]
German version: Angew. Chem. 1991. 104. 239
CAS Registry numbers:
l a , 138784-98-2; l b , 138823-23-7; l c , 138785-02-1; I d , 138785-03-2; Za,
138784-99-3; 2b, 138785-01-0; Zc, 138785-04-3; 2d, 138785-05-4; 3,3279-26-3;
4a, 138785-06-5;4b. 138785-09-8; 5,138785-07-6; 6,677-24-7; 7.138785-11-2;
DMAP, 1122-58-3; PCI,, 7719-12-2; Me,SiOTf, 27607-77-8.
.
3
+ MeOTf
K I , ca. 2 0 T , 2h
4a
of the onio substituents, a demethylation similar to the Arbuzov reaction occurs, but already at the stage of the trivalent P(m) derivative. That the site of the cleavage in this S,
reaction is the C-0 and not the P a bond of 4 a is controlled
by the relative polarities and bond strengths of these bonds.
If the same reaction is performed in the presence of two mole
equivalents of Me,SiOTf according to Equation (d), good
yields of the corresponding dicationic salt 4 b are obtained.
111 R. Weiss,N. J. Salomon, G. E. Miess, R. Roth, Angew. Chem. 1986,9H, 925;
Angew. Chem. Int. Ed. Engl. 1986, 2.5, 917.
[2] R. Konig, Diplomarbeit, Universitat Erlangen-Nurnberg, 1989. “Field” is
used here in terms of a through-space interaction.
[3] S. Engel, Diplomarbeit, Universitat Erlangen-Nurnberg, 1988.
[4] G. Hofle, W Steglich, H. Vorbruggen, Angew. Chem. 1978,90,602; Angew.
Chem. In/. Ed. Engl. 1978, 17, 569.
[5] D. R. Cowsar, D. H. Lewis, G. W. Whitehead, Gov. Rep. Announce Index
( U S . ) 1978, 18,265; Chem. Absir. 1978, 90, P 109134f.
[6] M. Wakselman, E. Guibe-Jampel, Tefrahedron Lett. 1970, 11, 1521.
[7] H. P. Daskalov, M. Sekine, T. Hata, Tetrahedron Lett. 1980, 21, 3899.
TaNi,Te,, A Novel Layered Telluride, and
TaCo,Te,, a Structural Variant with
Peierls Distortion**
By Wolfgang Tremel*
Dedicated to Professor Joseph Grobe
on the occasion of his 60th birthday
4b (86 %)
The viability of this bis(triflate) confirms that the cationic
leaving group in 4 is better as nucleofuge than C1-, but worse
than OTf-. A reaction of 6, the phosphorus(v) derivative
corresponding to 3, with DMAP according to Equation
(e)[5,61yields as exclusive product the bis(onio)phosphate
triflate 7[’] besides one mol equivalent of methyl triflate,
which is detectable in solution (CH,CI,) and can be trapped
quantitatively. The latter is formed in an “Arbuzov reaction” in which the triflate ion functions as nucleophile and
the bis(onio)phosphate ion in 7 as cationic leaving group.
Angew. Chem. Inl. Ed. Engl. 31 (1992) No. 2
Early-transition-metal chalcogenides are-as
evident
from their structural chemistry and their physical properties-textbook examples of the inadequacy of simplified
[*I
Prof. Dr. Wolfgang Tremel[+]
Anorganisch-chemisches Institut der Universitat
Wilhelm-Klemm-Strasse 8, D-W-4400 Munster (FRG)
[‘I New address:
Institut fur Anorganische und Analytische Chemie der Universltdt
J. J.-Becherweg 24, D-W-6500 Mainz
[**I This research was supported by a grant from the Bundesministerium fur
Forschung und Technologie under contract No. 05339 GAB/3 and the
Fonds der Chemischen Industrie. I am grateful to Prof. Dr. B. Krebs for
further support and to the Starck Company (Dr. Peters) for a Ta donation.
0 VCH Vei-lagsgesellschafimbH, W-6940 Wernheim, 1992
0.570-0833192j0202-0217$3.50+.2.5/0
21 7
(e)
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