close

Вход

Забыли?

вход по аккаунту

?

Effect of Non-Planarity on the Paramagnetic Ring Current in the Dianion of 1 6;8 13-Propanediylidene[14]annulene.

код для вставкиСкачать
and ( 3 ) . On heating (3) with SbI, at 100°C for 24 hours
in a sealed tube no iodination took place, whereas 12 hours'
heating of (3) with SiI, at 100°C gave ( I ) in 5% yield. In
each case, however, the main reaction was disproportionation of (3) to (2) and SiFC1,Br ( 4 ) . On the other hand,
reaction of ( 3 ) and HSiI, at 100°C for 18 hours resulted
in 50% conversion according to Eq. (3); small amounts of
other products formed by progressive Br/I exchange that
could be detected spectroscopically were (in order of
decreasing amounts) : HSiBrJ and HSiBr, (by 'H-NMR),
SiFClI, IS), SiFBr,I, SiFBrI,, ( 2 ) , ( 4 ) , and SiFI, ("FNMR). ( I ) can be separated from the reaction mixture in
very pure form by fractional distillation, since, with exception of ( 3 ) (b.p. 59.5"C), all the main components of
the mixture boil at higher temperatures.
( I ) is a colorless, readily hydrolyzable liquid (b.p.,,,=
85"C, n;'= 1.507) which turns pink in color when exposed
to air or light. Its thermal stability is remarkable: the
substance remains unchanged after 8 hours' heating at
100°C in an ampoule. After 33-50 hours at this temperature, 5-8 % (3) and ( 5 ) could be detected in. the Raman
spectrum by means of their most intense lines at 361 and
316 cm- respectively.
',
All fundamental vibrations of ( I ) are Raman and IR
active. As expected, the Raman spectrum shows nine
polarized lines (Table 1); the IR absorptions of the four
stretching vibrations were also measured. The quoted
assignments are derived from a vibration analysis, which,
in combination with force constants and averaging methods
described in Ref. [7], lead to good agreement of calculated
and measured frequencies (stretching force constants :
f(SiF)= 5.7, f(SiCl)= 3.0, f(SiBr)= 2.42, f(SiI)= 1.76 mdyn/
A). In addition to the relatively strong mixing of bending
coordinates, the coupling of the lowest stretching vibration
(vSiI)with the highest bendingmode(GFSiC1)isnoteworthy.
Table 1. Fundamental vibrations of SiFClBrI in the IR (1000-250
cm- ') and Raman spectra.
vl
v2
v3
v4
v5
6
'
Vl
V8
v9
IR
(cm-')
Raman
Ini.
910s
587s
486s
3331x1
912
588
482
334
236
208
179
129
99
0.03
0.11
0.08
10
2.8
3.6
5.7
3.9
7.8
(cm-')
Depol.
factor (cm- ')
-
-
0.05
0.32
0.42
0.26
0.70
0.63
916
578
481
337
245
214
184
131
100
Assignment
vSiF
vSiCl
vSiBr
vSiI, GFSiCI
GFSiBr, GFSiCI
GFSiI
GClSiBr, GFSiCI
GClSiI, GClSiBr
GBrSiI, GClSiI
The "F-NMR spectra of (1)-(5) consist of singlets with
"Si satellites ;with increasing electronegative substitution,
the signals are shifted to higher field and the coupling
constants J(29Si'9F)decrease (Table 2).
[l]
Gmelins Handbuch der anorganischen Chemie, Silicon Part B.
Verlag Chemie, Weinheim 1959.
[2] W C. Schumb and H . H . Anderson, J. Amer. Chem. SOC.59, 651
(1937).
[3] C. Cerfand M.-B. Delhaye, Bull. SOC.Chim. Fr. 1964, 2818.
[4] M:B. Delhaye-Buisset, C. R. Acad. Sci. 244, 770 (1957).
[5] E. Hengge and F. Hiifler, Z. Naturforsch. 26a, 768 (1971).
[6] Ct: C. Schumb and H . H . Anderson, J. Amer. Chem. SOC. 58, 994
(1936).
[7] F. ffafler, Z. Naturforsch. 26a, 547 (1971).
[8j 6=77.33 ppm, J = 368.7 Hz: R . B. Johannesen, F . E. Brinckman,
and T D. Coyle, J. Phys. Chem. 72,660 (1968).
920
Table 2. Chemical shifts 6 (against CC1,F) and coupling constants
J(29Si19F)from the 19F-NMR spectra of fluorohalosilanes (1)-(5).
G(ppm)
J(Hz)
(1)
( 2 ) 181
f3)
(4)
(5)
74.5
380
76.5
365
81.5
351
87.0
332
70.0
401
Received: July 20, 1971 [Z 502 IEj
German version: Angew. Chem. 83,977 (1971)
Effect of Non-Planarity on the Paramagnetic
Ring Current in the Dianion of
1,6 ;8,13-Propanediylidene[14]annulene ['*I
By Fabian Gerson, Klaus Miillen, and Emanuel Vogel"
A concept of "ring current" induced in cyclic x-electron
systems"] (perimeters) is usually invoked to account for
the 'H-NMR chemical shifts of ring protons in these
systems[']. Theory predicts a "diamagnetic" or "paramagnetic" ring current according to whether the perimeter
has 4n+2 or 4n n-electr~ns[~~.
In a perimeter with 4n+2
electrons, the signals of the outer and inner ring protons
undergo a down-field and an up-field shift, respectively,
relative to the signals of olefinic protons. The reverse
is true for a perimeter with 4n electrons['1. Bond alternation
and deviations of the perimeter from planarity should
reduce the paramagnetic ring current much more effectively than the diamagnetic oneL3'.This statement has been
verified by us for 1,6;8,13-propanediylidene[l4]annulene
a bridged fourteen-membered perimeter with
4 x 3+2=14 n-electrons, and for its dianion ( i ) 2 e
having 4 x 4= 16 x-electrons. As shown by molecular
models, X-ray structurer51,and other spectroscopic studiesi6], the perimeter in (1) exhibits moderate deviations
from planarity. The same geometry can be assumed for
(1)2e, since the shape of the perimeter is fixed by the
bridging groups.
The dianion ( I ) ' @ has been produced by reduction of ( I )
with potassium in perdeuteriotetrahydrofuran ([ID,]-THF)
or 1,2-dimethoxyethane (DME). This method has also
been used for the preparation of the anthracene dianion
( 2 ) 2 g from the parent neutral hydrocarbon (2). The
relevant proton resonance data for ( i ) ,
(2),(2)2e
are listed in Table 1, along with the corresponding values
for trans-lob, 10c-dimethyl-lob, 10c-dihydropyrene (3) r71
and its dianion (3) 2e Is].
In the following briefdiscussion, the data for ( I ) and
will be compared with those for (3) and ( 3 ) 2 g . Unlike
( I ) and ( I ) ' e , the rigid fourteen-membered perimeter
in both (3)['*]and (3)2ers1achieves a high degree of
planarity.
Comparison of the T-values for the ring protons in the
neutral compounds ( I ) and (3) indicates that moderate
deviations of the perimeter from planarity affect the diamagnetic ring current to a small extent only. (The difference
of 0.7 ppm is partially due to unequal perimeter areas
in the two compounds["].) In contrast, as shown by an
analogous comparison for the ring protons in the dianions
and (3)2e3,even moderate deviations from a
[*] Prof. Dr. F. Gerson and Dip1.-Chem. K. Miillen
Physikalisch-Chemisches Institut der Universitat
CHA056 Basel, Klingelbergstrasse 80 (Switzerland)
Prof. Dr. E. Vogel
Institut fir Organische Chemie der Universitat
5 Koln I, Zulpicher Strasse 47 (Germany)
p*]This work was supported by the Schweizer Nationalfonds (Project
SR 2.120.69).
Angew. Chem. internat. Edit.
Vol. 10 (1971) 1 No. 12
coplanar arrangement have a striking effect on the paramagnetic ring current. It should be borne in mind that-on
going from the neutral compounds to their dianions-an
average shift of approximately 2 x 1 0 / 1 4 1.4
~ ppm per ring
proton is expected by a mere allowance for two additional
negative charges'']; such a shift (+ 1.6 ppm) indeed occurs
QyJA
'
\
(I)
\
I
impeded by line-broadening due to the presence of the
intermediate radical anion ( I )
Received: July 28,1971 [Z 505 IE]
German version: Angew. Chem. 83,1014 (1971)
[I] J . A . Pople, W G . Schnetder, and H . J . Eernstein: High Resolution
NMR. McGraw-Hill, New York 1959, Section 7-5.
[2] R. C . Haddon, K R. Haddon, and L. M . Jackman, Fortschr. Chem.
Forsch. 16, 103 (1971).
[3] K. G. Untch and J . A . Pople, J. Amer. Chem. SOC.88, 4811 (1966).
[4] E. Vogel, A . Vogel, H.-K. Kiibbeler and W Sturm, Angew. Chem.
82, 512 (1970); Angew. Chem. internat. Edit. 9, 514 (1970).
[5] G . Casalone, A . Gacarotti, A . Mugnoli, and M . Simonetta, Angew.
Chem. 82, 516 (1970); Angew. Chem. internat. Edit. 9, 519 (1970).
Table 1. Centers of gravity for proton resonances of ( I ) , ( l ) 2 e ,(2). ( 2 ) 2 e , (3) and (3)2e. 7-values in ppm.
The uncertainty in the number given for the bridge protons of
is due to a partial masking of the pertinent
signals by the resonances of the solvents (isotopic impurities in ID,]-THF, wing of the CH, band in DME).
Species
Shift
Ring
protons
Bridge
protons
Shift
Solvent,
temp. ("C)
Ref.
~~
(1)
(l)2e
CDCIJ 25
[D,]-THF/-60
+
141
this work
cs,/i25
[91
this work
( + 0.3)
-
:::}
(2)
(2)'e
+
-
1.6
(3)
- 11.0
13i2e
DM El - 60
-25.3
+
CDClJ 25
[D,]-THF/-65
[7,Sl
[8]
[6] F. Gerson, K . Miillen, and E. Vogel, J. Amer. Chem. SOC.,in press.
[7] V. Boekelheide and J . E. Phillips, J. Amer. Chem. SOC.89, 1695
(1967).
181 R. H . Mitchell, Ch. E . Klopfenstein, and V Boekelheide, J. Amer.
Chem. SOC.91,4931 (1969).
[9] N . Jonathan, S. Gordon, and 8.P. Dailey, J. Chem. Phys. 36, 2443
(1962).
[lo] A . W Hanson, Acta Crystallogr. 18, 599 (1965).
[ I l l See, e.g.,: L. Salem: The Molecular Orbital Theory of Conjugated Systems. Benjamin, New York 1966, Chapter 4.
J
l
11505.11
t
l
4.0
i
l
l
l
l
i
l
l
5.0
Fig. 1. Proton resonance spectrum of the dianion
in the ?-range
of 3.5-5.5 ppm; recorded for a [D,]-THF solution at -60°C and a
frequency of 60 MHz.
for the conversion of anthracene (2) to its dianion (2)2e.
The fact that the corresponding shift (+2.1 ppm) for the
conversion of ( I ) to
is only 0.5 ppm larger points
to an almost complete quenching of the paramagnetic
ring current in
On the other hand, an analogous
shift of more than + 10 ppm is observed in the case of (3)
and (3)" (Table 1).
Similar conclusions can be drawn from the shift of the
bridge protons, although their different positions in the two
bridged annulenes make a direct comparison more problematical than for the ring protons.
It is noteworthy that the resonance signals of the ring
protons in
extend over a range of 1.5 ppm (Figure I),
whereas the corresponding range for the neutral compound ( I ) is only 0.5 ~ p m [ ~This
] . increase for
points to larger differences in the chemical shifts. Unfortunately, an analysis of the spectrum of (I)'*
is
Angew. Chem. internat. Edit.1 Val. 10 (1971)
1 N o . 12
Crystal and Molecular Structure
of Bis(n-cyclopentadienyl)tetrasulfidotungsten( 1 ~ ) ~ " '
By Betty R. Davis, Ivan Bernal, and Hartmut Kopf"]
In 1969, KOpf1'] prepared the first metallocene tetrachalcogenide chelate (x-C,H,),MoS, and proposed from
NMR studies that the cyclic MoS, moiety was nonplanar
but nevertheless symmetrically disposed with respect to
the two cyclopentadienyl rings. This conclusion was based
on the evidence that the solution 'H-NMR spectrum of the
compound consists of a single, sharp line which showed no
broadening down to -95°C. Later, similar results were
found for (x-C,H,),WS,
In continuation of our
p] Prof. Dr. I. Bernal and B. R. Davis
Department of Chemistry
Brookhaven National Laboratory
Upton, L. I., N.Y. 11973 (USA)
Dr. H. Kopf
Institut fur Anorganische Chemie der Universitat
87 Wiirzburg, Landwehr (Germany)
[**I This work was performed under the auspices of the U. S.Atomic
Energy Commission.-It is to be regarded as Part 7 of the series: Organometallic polychalcogenide che1ates.- Part 6 : 141;Part 5 :H.KijpJ
A . W i d , and W Kahl, Angew. Chem. 83, 146 (1971); Angew. Chem.
internat. Edit. JO, 137 (1971).
92 1
Документ
Категория
Без категории
Просмотров
0
Размер файла
225 Кб
Теги
current, effect, paramagnetic, propanediylidene, annulene, planarity, non, ring, dianion
1/--страниц
Пожаловаться на содержимое документа