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Crystal Structure of Tri(cyclooctatetraene)dititanium.

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Magnetic Anisotropy of the Amide Group
With this method we prepared the complexes V[COT]z,
Crz[COT]3, Mo2 [COT]3,W2[COT]3, Co [COT], and Ni [COT].
Received: August Sth, 1966
[Z 309 IE]
German version: Angew. Chem. 78, 942 (1966)
[l] Ger. Pat. 1191375 (April 28th, 1960/Dec. 19th. 1965),
Studiengesellschaft Kohle, Mulheim/Ruhr.
[2] W. Reppe er al., Liebigs Ann. Chem. 560, 1 (1948).
[3] Th. Katz, .I.
Amer. chem. SOC.82, 3784 (1960).
[4] H . Dietrich and H . Dierks, Angew. Chem. 78, 943 (1966);
Angew. Chem. internat. Edit. 5 , 899 (1966).
Crystal Structure of
Tri(cyc1ooctatetraene)dititanium
By Dr. H. Paulsen and K. Todt
Chemisches Staatsinstitut, Institut fur Organische Chemie,
Universitat Hamburg (Germany)
Studies of the long-range coupling [I], the intramolecular
nuclear Overhauser effect [21, the paramagnetic contact
shift [31, as well as by the benzene dilution method [41 showed
that in amides in which rotation about the N-CO bond is
restricted, protons in the arrangement A (cis to the carbonyl
group) are shielded more strongly than in arrangement B.
The corresponding CH3 N M R signal therefore occurs at
higher fields for form A than for form B. We have found
that this assignment is valid for freely rotating methyl groups,
but has to be differentiated for sterically fixed protons.
By Dr. H. Dietrich and Dr. H . Dierks
Fritz-Haber-Institut der Max-Planck-Gesellschaft,
Berlin-Dahlem (Germany)
The x-complex tri(cyc1ooctatetraene)dititanium ( 1 ) prepared
by Wilke et al. [11 crystallizes in thin, yellow leaflets, space
group F d d 2 (Ci”,, a = 14.41, b = 35.99, c = 7.25 A; V =
3760 A3, X-ray density 1.448 g/cm3, n = 8.
The crystals were studied by three-dimensional X-ray
diffraction (filtered copper K, radiation, multifilm technique). The reflection intensities were estimated visually by
means of a reference scale and were corrected for absorption.
t
A
O C H3
(1)
B
Integration of signal intensities as well as double resonance
experiments show that in ( I ) [51 the assignment of the double
resonance signals from both HZ and H! is reversed. Equatorial protons (H2 and Hl), which are in the plane of the
amide group, give a signal at lower field for form A than for
form B. On the other hand, the axial protons (such as H i
and the protons of the glycosidic OCH3 group), which are
outside the plane of the amide group, give a signal for form B
at lower field than that for form A, which corresponds to the
assignment for freely rotating methyl groups.
The figure gives a generalized representation of the anisotropic effect of the amide group. The possible proton positions are indicated by letters on the circles. Two regions can
be distinguished: the “plane region” in the plane of the
amide group with the positions aa‘ (equatorial protons), in
which a is shielded more strongly than a’, and the “out-ofplane region”, in which cc’ (axial protons) are opposed, and
position c’ is shielded more strongly than c. The positions
ee’ are equivalent to cc‘.
I
The molecules of ( I ) contain two titanium atoms and three
cyclooctatetraene rings and have a two-fold axis that passes
through the middle ring. The two outer rings are planar
(C-C distance 1.39 A) and are attached symmetrically
each to one titanium atom (all Ti-C distances 2.35 A).
The adjacent atoms C-12 and C’-12 of the middle ring
are apparently bonded to both titatium atoms although
the Ti-l/C-12 and Ti-2/C’-l2 distances are very long
(2.57 A).
The anomalous dispersion effect due to the two titanium
atoms plays a significant role in the structure refinement
presently being carried out, because the two-fold axis of the
molecule is also a polar axis of the crystal[zl. The present
value R = 11 % thus rises to 20 % if the structure factors for
inverted structures are used in the calculations.
Received: July 26th, 1966
[Z 303 IE]
German version: Angew. Chem. 78, 943 (1966)
m
d
d’
For compound (2) we assume a conformation in which the
methyl group is axialW H1 lies in the plane region and its
assignment is typical of aa’. The methyl group, since it lies in
the out-of-plane region, shows a typical cc‘ assignment. In
the fixed structure (3), H1 lies in the plane region and
(2)
I
CH3
[l] H . Breiland G . Wilke, Angew. Chem. 78,942 (1966); Angew.
Chem. internat. Edit. 5 , 898 (1966). We thank Prof. Wilke for
the tri(cyc1ooctatetraene)dititanium crystals.
[2] D. H . Teniplefon, A . Zalkin, and T . Weki, Amer. Crystallogr.
Ass. Meeting 1966, Abstr. p. 40.
Angew. Chem. internat. Edit. 1 Vol. 5 (1966)
/ No.
10
899
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