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cis- and trans-Bis-(-allyl)nickel Systems.

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cis- and trans-Bis-(7r-allyl)nickel Systems 11*
methylnickel (3b)
--78 "C as ~OIIOWS:
By H . Bonnemann, B. BogdanoviC, and G. Wilket*]
In 1961 we reported on bis-(x-al1yl)nickel (1) 121, the first
"pure'"31 ally1 derivative of a transition metal. From the
1H-NMR spectrum it could be shown that this complex
exists in cis-trans-isomeric forms ( l a ) and (Ib) [2bJ. X-ray
structure analysis 151 has proved that bis-(x-methal1yl)nickel
(2) 161 exists as trans-isomer [cf. ( l a ) ] in the single crystal.
2 R
<<
NiCH,
(3a). R
(3b), R
disproportionate quantitatively above
4
(I), R
(2). R
= CH3
j
.
Ni
=
H
= CH3
The Ni(CH& decomposes at once to give CH3 radicals and
elemental nickel. The bis-(x-a1lyl)nickel compounds ( I ) and
(2) obtained in this way can be isolated in crystalline form
at -100 "C. The crystals were dissolved in deuteriotoluene
at -78 "C and the IH-NMR spectra of the solutions were
measured as the temperature increased (the samples were
thawed over a period of 5 hours). The following proportions
of isomers were calculated from the spectra.
-70
-30
f30
-70
Measurement of atomic distances on a scale model shows
that o n transition of the trans- ( l a ) into the cis-form (Ib)
(180 O rotation of the allyl groups around the "0-bond axis")
the most favorable steric arrangement is obtained if the allyl
groups are also twisted by about 10 O around the axes p and @'
[see arrows in ( I b ) ] . The anti-protons (Hc) are farther from
[Ni(CH3)2]
+ 2.CH3
= H
-50
The 1H-NMR spectra of ( I ) and (2) are independent of
temperature, within experimental error, from -70 to f30 "C,
i.e. the proportions of the isomers in ( I ) ( 3 : l ) and (2)
(2.3 :1) remain substantially constant. The same proportions
are found if the crystalline complexes are dissolved at -70 O C
and their N M R spectra are measured immediately. For the
time being, the groups of signals in the 1H-NMR spectra [71
can be assigned to the cis- and trans-forms only o n the basis
of the following considerations of models.
+
R<.Ni:>R
7.8
3.1
3
3
3
:
:
:
:
:
1
1
1
1
1
0.5
1.2
2.3
2.3
2.3
: 1
: 1
: 1
: 1
: 1
From these results it follows that:
1. Bis-(x-allyl)nickel ( I ) and bis-(x-methallyl)nickel(2)
as mixtures of cis-trans-isomers.
occur
2. The trans-form is favored.
3. (x-Ally1)methylnickel (3a) decomposes largely stereospecifically to the trans-isomer (trans:cis = 7 . 8 : l instead of
3 :1) at -75 "C,whereas under similar conditions the (x-methal1yl)methyInickel (36) affords the cis-form preferentially
(trans: cis = 0.5 :1 instead of 2.3 :1).
4. At low temperatures the energetically favored equilibrium
of cis- and trans-forms is established only slowly from these
mixtures - with (2) more slowly than with ( I ) .
Final proof of the configuration of (2b) is currently being
sought by X-ray structure analysis of the crystalline bis-(nmetha1lyl)nickel obtained by disproportionation.
Received: June 26tn, 1967
[Z 553 IEI
German version: Angew. Chern. 79,817 (1967)
~
the nickel (less shielded) in (Ib) than in ( l a ) , while the synprotons (HB) and the meso-substituent approach the nickel
somewhat more closely (increased shielding) ;the assignments
given in the table then follow.
We obtained products with different proportions of isomers
in the following way: (x-Ally1)- (3a) 181 and (x-methally1)Intensity ratio
trans :cis
I
5.02
5
~
804
6.09
6.32
8.25
7.81
6.34
6.49
8.21
7.81
3.0: 1
8.36
8.61
[*] Dr. H. Bonnemann, Dr. B. BogdanoviC. and Prof. G. Wilke
Max-Planck-lnstitut fur Kohlenforschung
Kaiser-Wilhelm-Platz 1
433 Mulheim-Ruhr (Germany)
[I 1 H . Bonnemunn, Dissertation, Technische Hochschule Aachen.
1967.
121 [a] G. Wilke and B. BogdunoviC, Angew. Chem. 73, 756
(1961).
[b] B. Bogdunovit, Dissertation, Technische Hochschule Aachen,
1962.
[3] Newcomers to the field [4] have recently introduced the term
"isoleptic"; however, we feel that the use of this term is not
philologically sound.
[4] J. K. Beeconsall, B. E. Job, and S. O'Brien, J. chem. SOC.
(London) 1967 A , 423, ieport that the proportion of the isomers
is temperature-dependent between -40 "C [3: 1 in CDC13I and
$60"C [2.2:1 in benzene].
[5] H. Dietrich and R . Uftech, Z. Krist. 122, 112 (1965).
[6] [a] G. Wilke, Angew. Chem. 75, 10 (1963); p. 19; Angew.
Chem. internat. Edit. 2, 105 (1963), p. 114.
[b] W. Keim, Dissertation, Technische Hochschule Aachen, 1963.
[7] The spectra were measured on a Varian A 60 spectrometer
for solutions in deuteriotoluene at 30 "C with tetramethylsllane as
internal standard. We thank Dr. E. G. Hofftnunn and his collaborators for measurement and discussion of the spectra.
181 B. Bogdunovic, H . Bonnemann, and G. Wilke, Angew. Chem.
78, 591 (1966); Angew. Chem. internat. Edit. 5, 582 (1966).
Angew. Chem. internat. Edit.
1 Vol. 6 (1967) I No. 9
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