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Synthesis of Ethylene-Olefin Copolymers by Means of Soluble Organometal Catalysts.

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Furthermore, alkylsubstituted a-chloroenamines react
readily with electron-rich aromatics in electrophilic
substitutions without the need of an acid catalyst. This
reaction, called aminoalkenylation. allows for the spe-
R' = Alkyl, A r y l , V i n y l
R2 = H, A l k y l
R3,R4 = Alkyl, C y c l o a l k y l
Combinations of the known vanadium halides with
organoaluminum compounds are particularly suitable as
catalyst systems. It is assumed that the active species are
relatively short-lived soluble complexes of trivalent vana-
( 4 , NR3R4
+ /R3
cific and direct introduction of enamine functional
groups on nucleophilic carbon centers ( 4 ) .
dium (half-life < 10 min, according to the aluminum
compound used). Further. the activity of the catalyst is
dependent on the amount and the nature of the diene.
Keteneimmonium salts (2) cycloadd to various unsaturated substrates t o give four-membered rings (51
in high yields. Even with ethylene the reaction takes
place at room temperature with high yield. All additions
are directio- and stereospecific.
The synthesis is best carried out in a closed system under
slight excess pressure ( < 5 atm). Addition of the reactants
must be controlled. The molecular weight is regulated by
Like enamines, a-chloroenamines I I ) also react as
nucleophiles at the a-carbon atom with various electrophilic reagents. P . 8.Brz. to yield compounds of type 1 6 ) .
i n ethylene-diene copolymers it was found that the
polyethylene crystallinity decreases continuously with
R ' R ~ C = C-C=CR'R~
Furthermore, with magnesium in boiling T H F they
form a new type o f Grignard reagent (71 ,which can
be hydrolyzed to enamines o r coupled with ( I ) to give
a new class of activated dienes (81.
increase in the proportion of diene and that with 45-50
wt.-% of diene the polymers are amorphous. The modulustemperature curves pass through a minimum at ca. 5 G - 6 0
wt.-% of diene. Owing to the rigidity of the ethylene
I.ecture at Sruttgart an M a y 18. 1972 IVH 348 1El
German version. Angew. Cheni. 84. 901 (1977)
Synthesis of Ethylene-Olefin Copolymers by Means
of Soluble Organometal Catalysts
By H u m Schnecko"'
Besides the known ethylene-propylene copolymers and the
terpolymers of these two monomers with small amounts of
non-conjugated dienes (EPDM) it is possible also to prepare copolymers from ethylene and these dienes [especially
bicyclic derivatives of norbornene such as dicyclopentadiene ( I ) and ethylidenenorbornene (2) or hexahydromethyl-I ,4-methanonaphthalene ( 3 ) ] in any desired molar
ratio, and also terpolymers with diene contents appreciably
higher than customary hitherto ( i . e . up to >60 wt.-":).
[*] Prof. Dr. H. Schnecko
645 Hansu ( G e r m a n y )
Angen. Chem. mtei-nnr. Edit. J Vol. I I (1972) j/ N o . Y
comonomers the glass transition temperature T, lies in
the region of O T , whereas with propylene as comonomer
customary values of ca. - 55 "C are found for Tc;.Thus
terpolymers starting from equimolar amounts of ethylene
and propylene plus diene are characterized by appreciably
lower softening ranges (ca. - 45 "C), which. however. are
shifted upwards again with increasing diene content; at
> 30 wt.-% of diene the T, values once more rise above
0 "C.
From IR spectra and measurement of oxygen uptake it
can be shown that autoxidative cross-linking of the pro-
ducts readily occurs, this leading to insolubility. Polymers
of this type can thus, for instance, be used as coatings, and
pigmented or colorless Iacquets with good properties can
be obtained.
Lecture at Clausthal-Zelierfeld on June 2. 1972 [VB 350 IE]
German version: Angew. Chem. 84. 902 (1972)
Chirooptical Properties of the Cystine Disulfide
By R. Schwyzer"]
In synthetic [2,7-cystine}gramicidin S the cyclodecapeptide
is bridged by a disulfide group. NMR studies show that, as
in gramicidin S, the peptide chain of the compound exists
in the antiparallel B-conformation. Shielding effects indicate P-helical"] chirality for the disulfide bridge. In molecular models the dihedral angle cp amounts to about 120".
According to theory[*] the P-helical arrangement, linked
with19O0l< Icp I< 1180", requires that the contribution of
the longest-wavelength absorption band to the rotation
should be negative, and we have confirmed this experimentally by measurement of the circular dichroism (Imin
271.5 nm, rotational strength R = -12.3 x lo-*' erg cm3).
In addition, the theoretically required second Cotton
effect with the opposite sign can be clearly seen for this
compound (hm,,=230 nm, R = + 58.6 x
measurement in ethanol).
[*] Prof. Dr R. Schwyzer
Institut fur Molekularbiologie und Biophysik der Eidgenossischen
Technischen Hochschule
CH-8049 Zurich (Switzerland)
Theory further requires that disulfide bonds with cp = & 90"
absorb at. ca. 250 nm, and also that when the arrangement
of the disulfide bond is chiral none of the optical activity
inherent in the disulfide bond should appear. This requirement seems to be satisfied with cyclo-L-cystine.According
to 'H- and I3C-NMR measurements the molecule has a
diketopiperazine ring in the chair form and a chiral disulfide
bridge. In molecular models cp =go". In the ultraviolet
spectrum, absorption is observed at 247 nm, but there is
no long-wave Cotton effect. We assign a strong negative
Cotton effect at 228 nm (CD in ethanol) to the n, z* transition of the peptide-carbonyl group. We interpret the sign
and rotatory power ( R = 4 5 . 5 ~ 1 0 - ~of~ )this band as
indicating the existence of cyclo-L-cystine as the P-helical
diastereomer, but this would require confirmation by
other techniques.
These investigations support the theoretical treatment and
confirm the quadrant rule : 0" < cp < 90°, 180" < cp ~ 2 7 0 :"
R( + )=P-helical ; 90" < cp < 180", 270" <cp < 360" : R( +) =
M-helical. The chirality of the disulfide bond cannot be
deduced from measurements of the circular dichroism
(CD) and rotatory dispersion (ORD) alone without a
knowledge also of the (approximate) dihedral angle.
Lecture at Freiburg on May 29,1972 [VB 354 IE]
German version: Angew. Chem. 84,902 (1972)
[f] R. S. Cnhn, Sir Christopher lngold, and K Prelog, Angew. Chem.
78,413 (1966); Angew. Chem. internat. Edit. 5, 385 (1966).
[2] J. Linderberg and J. Michl, J. Amer. Chem. SOC.92, 2919 (1970).
[3] U . Ludescher and R. Schwyzer, Helv. Chim. Acta 54, 1637 (1971);
B. Donzel, B. Kamber, K . Wiithrich, and R. Schwyzer, ibid. 55, 947
(1972).--See also M . Carmack and L. A. Neubert, J. Amer. Chem. SOC.
89, 71 34 (1967); D. L. Cofemanand E. R. Blout, ibid.90, 2405 (1968).
State. Rev. Macromol. Chem. 8, 49-104
B (1972); 190
[Rd 525 IE -G]
The labeling of receptor sites in biological material with
photochemically generated reagents is the theme of a report
by J . R. Knowles. This method aims to simulate the natural
The properties of collagen and gelatin in the solid state
are reviewed in an article by 1. V. Yannas. The structural
unit ofsolid collagen in its various forms is the tropocollagen
"molecule", a right-handed superhelix itself consisting of
three left-handed protein helices connected by N-H-0
bridges. Furthermore, these protein chains are apparently
built up from two alternating types of subunits, one of
which is rich and the other poor in imino acids (proline,
hydroxyproline). Gelatin is the amorphous form of collagen.
The report contains sufficient relative data, summarized
and in some cases also interpreted, to form a basis for an
adequate physico-chemical description of collagen and
gelatin in the solid state. [Collagen and Gelatin in the Solid
+ Iigand $ [receptor-ligand]
with a reagent that structurally resembles the ligand and
interacts specifically with the receptor. In the reaction
the reagent should not behave specifically; it must be
capable of insertion into C-H bonds. These conditions
are fulfilled by photochemically generated carbenes and
nitrenes. Examples of applications are the labeling of
antidinitrophenyl- and anti-2-nitro-4-azidophenyl antiAngew. Chem. internat. Edit.
/ Voi. I I
1 No. 9
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synthesis, organometal, mean, ethylene, copolymers, olefin, soluble, catalyst
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