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Is There an Energy Difference between Enantiomorphic Structures.

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E = 4.39); the absorption curve of (2) is shifted somewhat
toward longer wavelengths compared with that of ( I )
1350 (log E = 3.48) and 253 n m (log E = 4.60); in ethanol].
T h e ‘ H - N M R spectrum of (2) ([D~lacetone;25 “C) consists of two sharp singlets at z = 6.48 and 2.93 (intensity
ratio 3 3 ) for the N-methyl and ring protons, respectively.
The corresponding signals of ( 1 ) occur a t z = 6.13 and
3.1 2 141.
A complex anion [AgL2]3- was later also considered as a
possible product (31.
On the basis of further studies we have now been able t o
show that this reaction actually leads to the complex
Agp[Ag2Lz1 containing two sets of differently bonded silver
atoms. Sulfide ions react successively with the microcrystalline salt disilver bis(cis-1,2-dicyano-1,2-ethylenedithio)diargentate(i), which is practicalIy insoluble in water,
according t o the equations
Experimental:
C r ( C 0 ) 5 C ~ H & ( I ) is prepared in 90 % yield by heating
bis(l,3 -dimethyl-4-imidazolium)decacarbonyldichromate(-I) (CgHgN2)2[Crz(CO)lol to 12OoC in a high vacuum “11,
in a modification of a previous method [4J.
A solution of ( I ) (1.0 g, 3.47 mmoles) and acetonitrile
(0.16 g, 4 mmoles) in dry, degassed T H F (75 ml) in a
Duran glass Schlenk tube fitted with reflux condenser is
exposed t o the light emitted by a high-pressure mercury
vapor lamp (Hanovia, type L, 450 W); the lamp is enclosed
in a water-cooled quartz jacket during irradiation. The
reaction solution rapidly comes t o boiling. After 4 h, the
solution is filtered under suction through a G 4 frit covered
with filtration aid and the filtrate is evaporated t o dryness
in Y L I C U U . Unreacted ( I ) can be dissolved out of the pale
yellow residue with diethyl ether. T h e remaining yellow
crystals of (2) are recrystallized from THF!n-hexane; yield
50mg(% 8%).
Received: June 16, 1970
[Z 249 IE]
German version: Angew. Chem. 82. 775 (1970)
[*I Dr. K. Ofele and Dr. M. Herberhold
Anorganisch-chemisches Laboratoriurn
der Technischen Universitat
8 Munchen 2, Arcisstrasse 21 (Germany)
[11 This work was supported by the Deutsche Forschungsgemeinschaft.
[2] E. 0. Fischer and A . Maasbol, Angew. Chem. 76, 645
(1964); Angew. Chem. internat. Edit. 3,580 (1964); Chem. Ber.
100, 2445 (1967); R . Aumann and E. 0. Fischer, Angew. Chem.
79, 900 (1967); Angew. Chem. internat. Edit. 6, 879 (1967);
E. 0.Fischer u. H . J . Kollmeier, ibid. 82, 325 (1970) and 9, 309
(1970), respectively.
[3] E. M . Badley, J . Chart, R . L. Richards, and G. A . Sim,
Chem. Commun. 1969, 1322; E. M . Badley, D. Phil. Thesis,
University of Sussex 1969.
141 K . Ofele, J. organometallic Chem. 12, P 42 (1968).
[5] K . OfeIe, Angew. Chem. 81, 936 (1969); Angew. Chem.
internat. Edit. 8, 916 (1969).
161 K . Ofele, Angew. Chem. 80, 1032 (1968); Angew. Chem.
internat. Edit. 7, 950 (1968).
[7] K . Ofere, J. organometallic Chem. 22, C 9 (1970).
I81 U.Schollkopf and F. Gerhart, Angew. Chem. 79, 578, 990
(1967); Angew. Chem. internat. Edit. 6,560, 970 (1967); H . - W.
Wanzlick and H:J. Schonherr, ibid. 80, 154 (1968) and 7, 141
(1968), respectively; H.-J. Schonherr and H.- W. Wanzlick,
Chern. Ber. 103, 1037 (1970).
191 E . 0.Fischer and H . J . Beck, Angew. Chem. 82,44 (1970);
Angew. Chem. internat. Edit. 9, 72 (1970).
[lo] Atlas CH 4; ion source TO 4; 50 eV. Measurements by
Dr. J . Miiller, Munchen.
[ l l ] Carried out by Dip].-Chem. W. Golla.
The reaction steps (1) and (2) overlap; however, (1) is much
faster. Iodide coordinates only with the cationic silver. In
contrast, cyanide is able to displace the dithiolate ligand
when present in excess.
The anion IAg2Lz12- reacts with tetraethylammonium
ions t o give a salt that is sparingly soluble in water. The
yellow crystals have a sharp melting- and decomposition
point of 219 OC; they dissolve most readily in acetone and
are sensitive t o light, especially when moist.
We have also succeeded in preparing addition compounds
of the silver salt and i n determining their composition by
elemental analysis; e.g. Agz[AgzL2].2 K C N , Ag21Ag2L21.
~ “ ( C Z W ~ I C NAgzIAgzLz1.2
,
AgNO3, AgzIAgnLzl.2(en).
Reaction of L2- with Ag‘ always leads first t o the soluble
anionic complex,
2 LZ-+ 2 Ag+ + LAgzL212which is precipitated by a n excess of silver ions.
On further addition ofligand the cationic silver is eventually
also coordinated.
Agz[Ag2L21
+ 2 Lz-
+
2 [AgzLzIz-
Received: June 29, 1970
[Z 250 IE]
German version: Angew. Chem. 82, 775 (1970)
[*I Dr. H. Wernet
Eduard-Zintl-Institut fur Anorganische und
Physikalische Chemie der Technischen Hochschule
61 Darmstadt, Hochschulstrasse 4 (Germany)
[l] G. Biihr and G. Schleizrer, Chem. Ber. 90, 438 (1957).
[21 G . Buhr, Angew. Chem. 73, 628 (1961).
[31 J. A . McCleverty, Progr. Inorg. Chem. 10, 49 (1968).
Is There an Energy Difference between
Enantiomorphic Structures ?
The “Silver Salt” of
cis-l,2-Dicyano-l,2-ethylenedithiol
By Hermann Wernet [*I and Gerhard Bahr (deceased)
(L2-)
The reaction of cis-l,2-dicyano-l,2-ethylenedithiolate
with silver ions in aqueous solution was initially described
as simple salt formation [1,21.
NC-C-S
f 2 Ag+
G-)
740
--f
Agz
By Wolfram Thiemann and Klaus Wagenet-[*]
Sodium ammonium DL-tartrate consists of enantiomeric,
optically active molecules (ratio of configurations 1:1)
which are precipitated a s a racemic mixture of pure,
enantiomorphic crystals (containing only D or only L molecules) from its saturated aqueous solution below 27 OC [I].
We used this salt in the following experiment: A saturated
solution of about 30 g of racemate was allowed t o reach
equilibrium with precipitated material at 25.5 O C . After
removal of the precipitate, the solution was diluted with
pure solvent (water) until the solubility limit was about
Angew. Chem. internat. Edit. f Vol. 9 (1970)
1 NO. 9
0 “C. When the temperature of the solution was allowed to
fall slightly below the new solubility limit only a smaI1
precipitate was formed (about 50 mg). After equilibration
under carefully controlled conditions, the precipitate and
solution were separated, the precipitate was dissolved in
water, and its optical activity was measured with respect to
the solution as standard. After many preliminary experiments, ten measurements performed under very strict
conditions all gave the same negative optical rotation r21 of
the precipitate, namely ct N 10-3 ’.
I n o u r search for a n explanation of this remarkable phenomenon we considered the following possible causes:
1 . Systematic errors in the measuring technique; they could
be ruled out by switching the cells, repeated measurements,
etc. - 2. Optically active impurities; this could be discounted on the basis of fractional (chromatographic) purification processes. - 3. Bacterial contamination of the
solution, which would result in preferential degradation of
the dextrorotatory [21 (natural) tartrate. We devoted the
most attention to this last possible source of error and
found: a) Concentrated solutions in open vessels are not
infected a t all within a week. b) If the observed activity
were nevertheless due to an attack by bacteria then any
variation in the time between precipitations would alter
the magnitude of the effect. This was not the case. c) Addition of the bactericide toluene to the solution had n o
influence o n the effect. - 4 . The thought that external fields
(such as the earth’s magnetic field) could lead to D / L discrimination is untenable.
At the present time, the only remaining interpretation of
our findings involves the assumption of different heats of
solution for D and L crystals of sodium ammonium tartrate.
And this means effectively that the lattice energies of the
enantiomorphic crystals must differ, which in turn can only
result from an asymmetric contribution t o the interaction.
Our measurements would indicate a relative difference in
the heats of solution (or lattice energies) of a few 10-5. We
are currently examining the consequences of this phenomenon by other techniques and for other systems.
Received: July 10 1970
[Z 251 IE]
Get-man version: Angeu. Chem. 82. 776 (1970)
[*I Dr. W. Thiemann and Prof. Dr.
K. Wagener
Institut fur Physikalische Chemie der
Kernforschungsanlage Julich GmbH and
Lehrstuhl fur Riophysik der
Technischen Hochschule Aachen
517 Jiilich 1, Postfdch 365 (Germany)
[l] E . L . Niel: Stereochemistry of Carbon Compounds.
McGraw-Hill, New York 1962, p. 44-45.
[ 2 ] Sign and magnitude of the optical rotation of a compound
depend upon the wavelength of the polarized light. We used a
Cary 60 spectropolarimeter, prod wed by Cary Tnstrumentcl
Varian, and worked at h = 280 nm.
Errata
In the communication “Aminoazimines by Addition of
Aminonitrenes to a-Carbonylazo Compounds” by K . H.
Koch and E. Fnhr, Volume 9, August 1970, the following
corrections should be made:
On page 634, right-hand column, line 30 “alcohol-free glacial
acetic acid” should read “alcohol-free ethyl acetate”.
On page 635, left-hand column, line 1 “(la)--(lf)” should
read “(ld)--(lf)”.
C O N F E R E N C E R E PORTS
The overall reaction is that shown in eq. (4).
Homolytic Reactions of the Alkyl-Metal Bond
By Alwyn G . Dnvies[*l
X Y + MRn
Bimolecular homolytic substitution ( S H ~ )reactions are
normally recognized to occur a t peripheral hydrogen atoms
[eq. (l)] or, less commonly, at halogen, oxygen, or sulfur
atoms.
X . + H-R
k
4
H-X+
R.
(1)
Recent stereochemical, kinetic, and ESR studies have shown
that this process will also take place, often much more
rapidly, at a multivalent metallic center [eq. (2); M = e.g.
Mg, Zn, Cd, B, AI, Sn, P, As, Sb, Bi], and provides the key
to t h e interpretation of many organometallic reactions.
Reaction (2) can also occur as a propagation step in a chain
process if a reagent X Y is chosen so that the chain carrier X *
is rapidly regenerated by the reaction (3).
R-+XY
+
R Y + P
Angew. Chem. internat. Edit. 1 Vol. 9 (1970) No. 9
X-MRn-l+
RY
(4)
Chain reactions of this type have been established for the
radicals R’C(CH3)zO. r41, C6H5S‘ [51, (CH3)2N-[6], and
succinimidyl[71 where the reagent XY is R’C(CH3)2OCI,
C ~ H S S H ,(CH&NCl, and bromosuccinimide respectively.
The reaction which has been studied most thoroughly, however, is the autoxidation of a n organometallic compound,
where the overall addition process (5) involves the propagation steps (6) and (7) 18991.
O r + MRn
ROO.
P +0
Reaction (2) can be studied as a step in a non-chain process
if the radical X . (e.g. (CH3)3CO.[ll, (CH3)3CS*r21, or
(CH3)zN- 131) is generated photolytically (from
or
(CH3)3C-O-O-C(CH3)3,
(CH&C-S-S-C(CH&,
(CH~)ZN-N=N-N(CH~)Z, respectively) in the cavity of an
ESR spectrometer, when the spectrum of the displaced
radical R . can be observed.
4
+
ROOMRn-I
+ MRn +
2
+ ROO.
ROOMRn-1
(5)
+ R’
(6)
(7)
The absolute rate constants, k2, for a number of these s H 2
replacements at metal centers have been determined by a
variety of techniques. Some of the values obtained, compared
Table. Rate constants kl and kz (mole-Is-’) for a few S H reactions
~
(Bu = butyl).
X.
(3)
74 1
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