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Cyclooctatetraenylene Vinylenes.

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Table 2. Calculated structures for Za, 2 b, 3a, 3b. The structural data are given
at HF/6-31G(d), the relative energies at MP2/6-31+ +G(d)//HF/6-31G(d).
For details see Table 1.
1.503
1.354
135.1
104.0
0.0
61.2
6.1 (9.9)
0
- 0.976
-0.289
0.101
0.059
0.104
1SO4
1.355
135.4
103.6
9.1
61.4
6.7 (10.3)
0
-0.982
-0.288
0.102
0.063
0.105
1.511
1.347
132.7
103.2
166.6
62.8
6.9 (5.3)
0
- 0.972
-0.285
0.116
0.063
0.078
1.513
1.347
132.8
102.8
180.0
63.0
7.3 (5.6)
0
- 0.975
-0.284
0.117
0.065
0.078
[a] Dihedral angle between the planes H7-Cl-HS and Cl-C2-C3. [b] Relative to
the energy of 1 b (see Table 1).
only planar 2 and 3, reported energy differences of 26.4 and
30.6 kcal mol- ' relative to l.L3 The slightly higher stability
of the cis isomers 2a and 2b over the trans forms 3a and 3 b
may be explained by the better interactions between the n combination of the terminal lone-pair orbitals with the C-C
n* bond, which is also found for isoelectronic difluoroethylene.['' In agreement with this interpretation, the terminal C-C bonds are shorter and the central C-C bond is
longer in 2a and 2b than in 3a and 3 b (Table 2). In fact, the
relative energies of the most stable conformations of 1, 2,
and 3 are even quantitatively nearly the same as found for
b1
isoelectronic 1,I-, 1,2-cis, and 1,2-trans difl~oroethylene.[~
Why are the Y-shaped dianions 1 b and 1 c more stable
than the cis and trans isomers 2a-3b? The comparison of
the optimized structures which are true minima on the
C,Hie potential-energy surface provides a reasonable answer. The negative charge is distributed over three carbon
atoms in 1 b and l c , while it is concentrated mainly on two
carbon atoms in the cis and trans forms. Moreover, the calculation of the charge distribution using the NBO analysisL8. indicates a small positive charge at the central carbon atom of 1 b and 1 c indicating attractive interactions
between C1 and the terminal carbon atoms (Table 1). Internal coulombic stabilization as the cause of the higher stability of 1 has already been suggested by Klein,[41although he
considered only the D,, form l a . Wibergl5I dismissed the
idea of charge stabilization on the ground of the small size of
the positive charge at C1. However, important is not the
absolute size but the difference in charge interactions between l b and the isomeric forms 2a-3b. In l b, there are
small but attractive coulombic interactions between all carbon atoms directly bonded to each other. In 2 a, 2 b, 3 a, and
3 b, all carbon atoms are negatively charged and the coulombic interactions are purely repulsive. Although 2 and 3 have
a K bond which is missing in 1, the additional binding energy
of the K bond is lower than the sum of the stabilizations of
the three lone pairs in 1, as a result of the adjacent K vacancy.
We also refer to recent theoretical studies which show that K
delocalization in benzene and other ring compounds is destabilizing, and that it is the energy of the o bonds which enforces bond equalization.[16'
The analysis of the geometries and electronic structures of
the conformational energy minima 1 b-3 b clearly shows that
the higher stability of the Y-shaped structures l b and l c
relative to the cis and trans isomers 2a-3b is caused by
maximally distant localization of the n electrons, not delocalization or even aromaticity. All isomers adopt nonplanar
Angew,. Chem. Int. Ed. Engl. 30 (1991) No. 8
0 VCH
geometries with strongly pyramidalized methylene groups to
further separate the lone-pair electrons; this is achieved optimally in 1 b. There is no Y-aromaticity in the trimethylenemethane dianion!
Received: February 4, 1991 [Z 4423 IE]
German version: Angew. Chem. 103 (1991) 1038
CAS Registry number: 1, 41792-83-0.
[l] J. Klein, A. Medlik-Balan, J. Chem. Soc. Chem. Commun. (1973) 275.
[2] P. Gund, J. Chem. Educ. 49 (1972) 100.
[3] a) 1. Agranat, A. Skancke, J. Am. Chem. Soc. 107(1985) 867; b) S. Inagaki,
Y. Hirabayashi, Chem. Left. (1982) 709; c) S. Inagaki, H. Kawata, Y.
Hirabayasi, 1 Org. Chem. 48 (1983) 2928.
[4] J. Kleiu, Tefrahedron 39 (1983) 2733; ibid. 44 (1988) 503.
[5] K. B. Wiberg, J. Am. Chem. Soc. 112 (1990) 4177.
[6] The Convex verrsions of the program packages CADPAC 4.0 and GAUSSIAN 90 have been used.
171 The geometries and force-constant matrices of 1a, 1b, and 1c have been
calculated at the following levels of theory. and the number of imaginary
frequencies for 1 a isgiven in parentheses: HF/3-21G (3). HF/6-31G(d)(3),
HF/6-31 + + G(d) (4), MP2/6-31G(d) (4). Since the differences in the optimized geometries were found to be insignificant, the optimizations for
isomeric forms of 2 and 3 have been carried out only at HF/6-31G(d).
[S] NBO 3.&fOr a description of the method see: A. E. Reed, L. A. Curtiss,
F. Weinhold, Chem. Rev. 88 (1988) 899.
I
Am. Chem. Soc. 95 (1973) 3087; b) G. Frenking, W.
[9] a) N. D. Epiotis, .
Koch, M. Schaale, J. Comput. Chem. 6 (1985) 189.
[lo] The calculated result that l b and l c have small positive charges at the
central carbon atom has been found at all levels of theory employed here.
It has also been found for 1 a using a different technique for analyzing the
molecular wave function (ref. 151).
[ l l ] In ref. IS], the optimized structure of a dilithio derivative of isobutene is
shown, which exhibits a nonplanar C,H, geometry with weakly pyramidalized CH, groups which is very similar to 1b. This was interpreted [5] as
resulting from a tendency to maximize the coulombic attraction between
the lithium cations and the anion. Our results show that isolated 1 adopts
an even more strongly pyramidalized structure.
[12] R. F. W. Bader, "Atoms in Molecules: A Quantum Theory", Oxford University Press, Oxford 1990.
[13] The VZp(r)plot shown in Figure 2 for 1 bcorresponds to the C1 -C2 bond.
The results for the C1 -C3 and C1 -C4 bonds are nearly identical.
[I41 rb denotes a point of minimum electron density p ( r ) along the bond path,
while p ( r ) is a maximum in any direction perpendicular to the internuclear
axis [12].
[IS] T. S. Slee, P. J. MacDougall, Can. J: Chem. 66 (1988) 2961.
[I61 a) S. S. Shaik, P. C. Hiberty, J.-M. Lefour, G. Ohanessian, J. Am. Chem.
Soc. 109 (1987) 363; b) K. Jug, A. M. Koster, ibid. 112 (1990) 6772.
1171 A nonplanar geometry has been predicted for 1 using semi-empirical methods: M. N. Glukhovtsev, B. Ya. Simkin, Izv. Sev.-Kavk. Nauchn. Tsenfra
Vyssh. Shk., Esfest)).Nauki2 (1989) 115; Chem. Absfr. 113 (1990) 5348f.
Cyclooctatetraenylene Vinylenes""
By Petra Auchter-Krummei and Klaus Mulien*
Dedicated to Professor Heinz A . Staab
on the occasion of his 65th birthday
The chemistry of stilbene, the higher ohgo(para-phenylene
vinylenes) (l),['- and the poly(pheny1ene vinylenes) (2)[3,41
have been studied intensively from point of view of their
synthesis, physical organic chemistry, and applications.[51
The outstanding redox and photochemical properties of the
benzene homologue, cyclooctatetraene
makes
the successive replacement of the phenylene units in the linear n systems of 1 and 2 by cyclooctatetraene attractive. We
[*] Prof. Dr. K. Miillen, Dipl.-Chem. P. Auchter-Krummel
Max-Planck-Institut fur Polymerforschung
Ackermannweg 10, W-6500 Mainz (FRG)
[**I Polyarylenes and Polyarylene Vinylenes, Part 6. This work was supported
by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen
Industrie. Part 5 : K.-H. Koch, K. Miillen, Chem. Ber. 124 (1991). No. 9.
Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
0S70-0833/91/0808-1003$3.50+ .2Sj0
1003
@
\
/
1
2
i.--”..o-”
11.R.
1 0 a . R ’ - R 2 =H
1 0 b . R ’ . CH,, R 2 = C H 0
show that, starting from 1,5-difunctionalized cyclooctatetraene, derivatives of the type 3 and 4, can be synthesized
which exhibit extended a conjugation. Cyclic voltammetric
and NMR spectroscopic investigations confirm the role of
the title compounds as “charge storage” units and as substrates for thermally inducible charge transfer.
\ /
CH,
\ /
/ \
\ /
12 . R = CH,
units (13a from 6c and 8 70%; 14 from 5a and 9a 12%).
The “trimer” 11 and the monoaldehyde 10b are both
formed from 6c and 5b; l o b , however, requires 2 equiv of
6b.
- E / Z isomeric mixtures are formed; attempts at iodine-catalyzed formation of the all-E isomers (all structural formulas
represent all-E isomers) led to decomposition, but separation of the isomers by chromatography is possible.
- The attempt to obtain a polymer from 6c and 9a affords
the compound 4 with n NN 5 as a THF-soluble fraction (30 YO
w/w). According to the IR spectra, the higher molecular
weight fractions have the same overall structure as the shorter chain products.
The analogies to the benzene-like oligo( phenylene vinylenes) (1) are useful in the description of the chemical and
physical properties of the compounds 10a, 11, and 12 (type
3) and 13a, 14, and 15 (type 4). As in the oligo(pheny1ene
(E/z)-13 a is slowly transformed into the ( E /
~inylenes),~’~]
E ) isomer (36 days, 32 %) on irradiation with a mercury high
pressure lamp (380 W, Q-600, Pyrex filter). Neither (E/E)13a nor (E/E)-14 are changed by irradiation at 1 2 300 nm
over the same period. The question whether photochemically initiated Z / E isomerizations of stilbene and
are
diabatic or adiabatic makes a comparison of these compounds with the COT system 13a desirable.
-
3. R = CH,
4,R=CH3
The known cyclooctatetraene carbaldehyde 5 a and its
easily accessible phosphonium salt 5 b serve as building
blocks for olefination by Wittig or McMurry reactions.[’]
Suitable 1,5-difunctionalized cyclooctatetraenes are not
known. We therefore prepared the diester 6a by thermolysis[’] of the semibullvalene 7[’01 and then transformed 6 a
into the difunctional starting compounds 6b and 6c. The
other starting compounds, 8 and 9a, are easily accessible.
The stepwise construction of a linear a system via the dialdehyde 13b, also requires a compound in which one functionality has been protected, such as the ketal 9b.
5a , R = C H O
5b.R = CHzPPh3Br
7 .R’= CH,,
R2= COOCH,
6 a . R ’ = CH3.R2= COOCH,
6 b . R ’ = CH3.R2= CH2OH
6 C . R ’ = CH,. RZ=CHO
8 .R1=H. R2: CH2PPh3Br
9a.R’=Rz=CHzPPh3Br
9b.R‘.
xO)
H
O
.R2=CHzPPh,CI
13a. R’= CH,,
RZ: H
13b.R1=CH3,RZ=CH0
The following characteristics are typical for the construction of the
- The Wittig reaction gives better yields than McMurry coupling (10a[’21from 5a and 5b (KOtBu, THF, 25”C, 65%;
10a from 2 equiv of 5a (TiClJ, Zn/Cu, THF, 60°C) 19 %).
- Chains with terminal phenyl units are distinctly more easily accessible than those with terminal cyclooctatetraene
1004
0 VCH Verlagsgeseilschaf[mbH, W-6940 Weinheim,1991
0S70-0833~9f~0808-f004$3.50+
,2510
14
15.R -
CH,
Angew. C h m . Inf.Ed. Engl. 30 (1991) NO.8
Table 1. Selected physical and spectroscopic data for 6c, 10a. (E)-lob, 11, I t ,
(E,E)-13a, (E,E)-I3b, (E,E)-14, (E,E,E,E)-15,(E,E)-13aZe/2K0, (E,E)-1420/
2Ke, (E,E)-144e/4K@[a].
6 c : m.p. = 140°C; MS (EI, 70eV): m/z 188.0837 ( M e ) .
IOa: MS (€1. 70eV) mjz = 232.1252 ( M a ) ; 'HNMR: 6 = 6.18 (s, H9,10),
.60-5.65 (m, 14H); ''CNMR (75 MHz, CDCI,): 6 = 141.2, 132.6, 131.9.
131.7, 131.4. 130.8, 130,6.
(&lob: MS (FD, 4kV): m/z 289.1 (24.5%), 288.2 (100%. M e ) ; 'HNMR
(CDCI,): 6 = 9.49 ( s , CHO), 6.69 ( s , 1 H), 6.2, 6.1 (AB, JAB= 18.2 Hz), 5.985.7 (m, 10H). 1.92 (s, CH,), 1.8 (s, CH,).
11: MS (FD. 4kV): m/z 389.2 (27%), 388.2 (loo%, M e ) , 232.1 (9%);
'HNMR (CDCI,): 6 = 6.2, 6.08 (AB, JAR
= 15.8 Hz). 5.98-5.78 (m, 18H).
1.84(s.2CH3);"CNMR(CDCI3):6 = 141.3,140.4,139.3,134.0.132.5,131.7,
131.1, 131.0. 130.6. 124.4, 23.7.
12: MS (FD. 4 kV): m/z 545.3 (51%), 544.3 (100%. M e ) .
(E,E)-13a: m.p. = 156°C: 'HNMR: 6 = 6.46, 6.85 ( 3 J = 16.0 Hz;
H9,9.10.10), 5.92 (s, 4H ) [el, 1.93 (s, 6 H ; CH,); "CNMR (50MHz) [b]:
6 = 139.5 (C1,5), 140.5 (C3.7). 124.7, 134.2 (C2,4,6,8), 131.5 (C9.9). 128.8
(C10,lO). 137.5 (Cl l , l l ' ), 23.3 (CH,).
(E.E)-13b: m.p. = 132°C; MS: m j z : 392.1776(Me). ' HNM R : 6 = 6.92, 6.47
( 3 J = 15.2 Hz;H9.10,9,10), 6.01 (s, 2H) [el. 5.94 (s, 2H) [el, 1.96 (s, 6 H ;
CH,), 9.95 (s. 2H ; CHO).
(E,E)-14: m.p. = 178°C. 'HNMR (CDCI,): 6 = 6.37, 6.85 ( 3 J = 16.2 Hz;
H9,10,9,10). 5.77-6.14 (m, 14H) [e];''CNMR [d]: 6 = 141.4 (C3.37, 131.5
(C7,7'), 130.6, 131.6, 131.8, 132.1, 132.8 (C1,2,4-6,8,1',2,4-6.8'),
130.7
(C9,9), 128.2 (C10,10), 136.5 (C 11,ll').
(E,E,E,E)-I5: MS: m/r 592.3128; ' HNM R (CDCI,): 6 = 6.78, 6.4 (AB,
JA8= 16.0 Hz. H9,9',10,10), 6.86, 6.37 (AB, JAB= 15.5 Hz, H 15,15',16,16'),
6.1-5.7 (m,18H). 1.95 (s, 2CH,).
(E,E)-13aZe/2Ke: 'H NMR: 6 = 6.42, 7.3 ('J = 15.5 Hz; H9,10,9,10), 5.96
( s . 4H) [el. 2.84 (S. 6H ; CH,); "CNMR [c]: 6 = 101.9 (C1,5). 106.1 (C3,7),
96.1 (C2.4.6.8). 146.4 (C9,9), 109.2 (C10,10), 143.6 (CllJl'), 34.8 (CH,).
(E.E)-1420/2Ke: 'HNMR: 6 = 7.13, 7.08 ( ' J = 11.0 Hz, 4H) [g], 6.29, 6.68
and 6.3.7.41 ('J = 16.4 and 14.6 Hz; H 9,10,9.10), 5.67-6.15 (m, 12H) [el, 5.5
(t, 2 H) [el;
NMR: 6 = 143.1 or 144.2 (C 3) [fl, 101.6 (C Y),90.0,94.0,97.8,
101.0. 105.7, 123.0, 126.0, 127.2, 130.4, 132.0. 132.8, 147.2 C 1-10,l'-10) [f],
143.1 oder 144.2 (C 11) [f], 129.2 (C 11').
(E,E)-14'@/4Ke [a]: 'HNMR (400 MHz): 6 = 7.06 (s, 4H) [g], 6.34, 7.29
( ' J = 15.2 Hz. 4H), 6.16 (d, J = 12 Hz; 4H) [el, 5.92 (t, J = 11 Hz; 4H) [el,
5.84 (t. J = 10 Hz: 4H) [el, 5.6 (t, J = 10 Hz; 4H) [el; I'CNMR: 6 = 100.5
(C3,3'). 90.2, 93.1, 95.1, 97.6 (Cl-X,l'-S'), 143.9 (C9,9), 108.2 (C10,10),
137.4 (C 11.11').
[a] All NMR spectra, unless stated otherwise, are recorded in [DJTHF, the
neutral compounds at 25°C and ions at - 30°C. [b] Assignment of the signals
by H, C COSY NMR spectra ('H: 300 Hz, "C: 75 MHz). [c] Assignment of the
signals by correlation with chemical shifts with Hiickel charge densities. [d]
Assignment of the signals by selective 'H decoupling. [el Eight ring protons. [q
Assignment not possible. [g] Arene protons.
The electrochemical reduction of the title compounds by
cyclic voltammetry convincingly documents their unusual
redox systems (Table 2).
- In the homologous series of 1, completely reversible oneelectron transfers are observed. Increasing the chain length
increases the number of redox steps, shifts the reduction
potential to more negative values, and causes the potential
difference between the first and second reduction, AE =
Table 2. Cathodic peak potentials (EPJof cyclooctatetraenylene vinylenes as
determined by cyclic voltammetry [a].
TpC] E,. [V] (No. of electrons transferred)
COT [b]
101 [b]
12 [b]
13a [c]
14 [cl
WI
0
0
-10
0
0
0
- 2.12 [el (2e)
- 1.94 [el (2e) - 2.35
- 2.01 [el (4e) - 2.17
- 2.18 [el (2e)
- 1.97 [el (2e) - 2.11
- 1.96 [el (4e)
[d] (1 e) - 2.75 (1 e)
[el ( 2 e ) - 2.52 [d] (le)
- 2.67
(le)
[el ( 2 e )
Coulomb repulsioml']
For the reduction of cyclooctatetraenylene vinylenes, the
first wave corresponds to an electrochemically irreversible,
but chemically reversible, two-electron transfer (see Table 2).
This situation is similar to that of COT
"I there
the reason for the small potential difference AE is the electronic stabilization of the dianion, and the lack of electrochemical reversibility is due to the planarization of the ring
at the radical anion stage. Thus as a first approximation, the
first two-electron transfer in 10a, 11,12,13a, 14, and 15 may
be understood as a charging of the COT unit.
- The dominance of COT units as electrophores-in
spite of
potentially extended n conjugation-is also shown by the
successive reductions. Finally each COT ring has taken up
two electrons, and the "tetra-COT" system 12 is transformed
into an octaanion!
- The difference in behavior between the "bis-COT' compounds 1Oa and 14, which are distinguished from one another by the length of the bridging group between two COT
units, is characteristic. Compound 14 is reduced in two separate, irreversible, two-electron transfers, whereas in 10a a
reversible one-electron transfer follows an irreversible twoelectron transfer. Evidently the addition of electrons to one
of the COT units in 10a leads at least to a partial planarization of the second ring. Staley et al. ['8, '91 reached a similar
conclusion for the dianion formation in a series of "bis
COT" compounds.
The reduction with alkali metals allows a characterization
of the resulting diamagnetic ions by spectroscopy.[201A correlation of the I3C NMR chemical shifts of (E,E)-13a2@/
2Ke with the local n charge density (Table I ) suggests that
the excess charge is localized mainly on the eight-membered
ring and the olefinic centers ClO(10). No significant charging of the phenyl units is suggested by the 'H NMR signals
of the tetraanion salt (E,E)-144e/4Ke (Table 1). Complete
alkali-metal reduction of 10a yields a tetraanion. The 'H
NMR signals of the olefinic protons occur at low field due to
the diatropism (6 = 6.95, (s)) of the two eight-membered
rings.
-
14''
The occurrence of two AB systems for the olefinic protons
in the 'H NMR spectrum of the dianion salt (E,E)-14'@/
2K@(200 MHz, - 30 "C) suggests an "unsymmetric" charge
distribution. The charge is localized on one COT ring. The
spectra show no change at different temperatures, even up to
50 "C (90 MHz), which excludes a thermally induced charge
fluctuation below this temperature, although delocalization
of charge should be the preferred electrostatic configuration.
Such a charge redistribution in the anion implies that the
second COT ring becomes coplanar in the intermediate
stage, which results in an activation energy caused by geometric factors.['*.
That at low temperatures (- 80°C) the charge in dianion
10a is mainly localized on one ring may be deduced from the
'H NMR spectrum ([DJTHF, 200 MHz). Only one AB spin
1 9 3 2 1 1
[a] lo-, M solution in THF; electrolyte: Bu,NPF,. [b] Gold working electrode
[c] Platinum working electrode [d] Reversible [el Electrochemically reversible.
Angew. Chem. Int. Ed. Engl. 30 (1991) No. X
E, - E2 to approach a minimum as a result of the decreasing
0 VCH
Verlagsgesellschaft mbH, W-6940 Weinheim. 1991
0S70-0833/91/0X08-100S$3.50+ .2S/O
1005
system is observed for the olefinic protons (H9 and HIO),
6 = 6.78 and 6.57, 3J = 14.8 Hz). Due to an increase in temperature the shape of the lines changes. Coalescence occurs
at - 15 "C, and at temperatures > 25 "C a sharp singlet is
observed (6 = 6.67). The Gibbs activation energy of this process that can be understood as an intramolecular charge redistribution, isestimated at AG,?15sc) = 12.8 0.3 kcalmol-'.
In agreement with the cyclic voltammetry findings, the
charge redistribution apparently occurs more easily in
10aZ6/2K* than in 1420/2K@.
Whereas (2)-stilbene is rapidly transformed into the E
isomer on reduction with alkali metals,[221at - 80 "C (E,Z)13a can be converted into a dianion with its configuration
intact, which isomerizes only very slowly into the E,E isomer
(20 % after 13 weeks at - 80 "C).
Received: February 25, 1991 [Z4460 IE]
German version: Angew. Chem. 103 (1991) 996
[l] J. Heinze, J. Mortensen, K. Mullen, R. Schenk, J. Chem. SOC.Chem. Commun. 1987, 701; R. Schenk, H. Gregorius, K. Mehrholz, J. Heinze, K.
Mullen, J. Am. Chem. Soc., in press.
[2] G. Drehfahl, R. Kiihmstedt, H. Oswald, H.-H. Horhold, Makromol.
Chem. 131 (1970) 89.
[3] R. A. Wessling, J. Polym. Sci. Polym. Symp. 72 (1985) 55.
[4] H.-H. Horhold, M. Helbig, D. Raabe, J. Opfermann, U. Scherf, R. Stockmann, D. WeiB, 2. Chem. 27 (1987) 126.
[5] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, M.
MacKay, R. H. Friend, P. L. Burns, A. B. Holmes, Nafure 347 (1990) 539.
[6] G. I. Fray, R. G. Saxton: The Chemistry of The Cyclooctatetraene and Its
Derivatives, University Press, Cambridge 1978.
[7] L. A. Paquette, Tetrahedron 31 (1975) 2855.
[S] G. H. Harmann, A. Streitwieser, J. Org. Chem. 38 (1973) 549.
[9] L. A. Paquette, S. V. Ley, R. H. Meisinger, R. K. Russel, M. Oku, J. Am.
Chem. SOC.96 (1974) 5806.
[lo] J. Sellner, H. Schuster, H. Sichert, J. Sauer, H. Noth, Chem. Ber. 116(1983)
3751.
[11] All new compounds were characterized by elemental analysis and spectroscopic data. For typical examples see Table 1.
[12] The dianion of 10a is already known [19], but the neutral compound and
its electron transfer reactions have not been described.
[13] The electron absorption spectra of the compound types 3 and 4 are distinctly different. Compounds 10a, 11, and 12 have a broad poorly structured band at large wavelengths, which broadens further and undergoes a
= 328 nm
bathochromic shift on lengthening the chain (10a: E.,
( E = 3135); 11: 332 (5487); 12: 431 (4298)), whereas 13, 14, and 15 are
characterized by a narrow band at short wavelenths as well as an intensive,
broad bandat longer wavelengths(l3: I.,,, = 293 nm(&= 30799); 14: 365
(26483); 15: 354 (91 678)). On going from 14 to 15 the longer wavelength
band increases in intensity, but, in complete contrast to the compound of
the homologous series I, undergoes a slight hypsochromic shift.
[14] K. Sandros, M. Sundahl, 0. Wennerstrom, U. Norinder, J. Am. Chem.
SOC.112 (1990) 3082.
[15] A. J. Fry, C. S . Hutchins, J. Am. Chem. Soc. 97(1975) 591; R. D. Allendoerfer, R. H. Rieger, ibid. 87 (1965) 2336; H. Kiesele, J. Heinze in H. Lund,
M. Baizer (Ed.): Organic Electrochemistry, Dekker, New York 1991,
p. 331.
[16] Since the first transfer of charge is irreversible in the case of COT, the cyclic
voltammogram shows one wave, which does not imply a thermodynamically favored second transfer, because the second is shifted toward the
negative by 120-150 mV with respect to the first.
[17] J. Heinze, M. Dietrich, K. Hinkelmann, K. Meerholz, F. Rashwan,
DECHEMA Monogr. 112 (1989) 61; Chem. Abstr. 110 (1989) 221 3591.
[18] B. Eliasson, S . W. Staley, Prepr. Am. Chem. Soc. Div. Per. Chem. 30 (1985)
620; Chem. Abstr. 104 (1985) 50494a.
[19] S . W Staley, C . K. Dustman, K. L. Facchine, G. E. Linkowsky, J. Am.
Chem. Soc. 107 (1985) 4003.
1201 The amount of charge on the anions can be shown chemically by trapping
experiments. Thus the hexaanion 116e (as potassium salt) forms a hexamethyl derivative on reaction with dimethyl sulfate, which can be detected
by mass spectrometry.
[21] G. Krummel, W. Huber, K. Miillen, Angew. Chenz. 99(1987) 1305;Angew.
Chem. Inr. Ed. Engl. 26 (1987) 1290.
[22] F. Gerson, H. Ohya-Nishiguchi, M. Szwarc, G. Levin, Chem. Phys. Leu.
53 (1977); T. A. Ward, G. Levin, M. Szwarc, J. Am. Chem. Soc. 97 (1975)
258.
1006
0 VCH
Verlagsgesellschaft mbH. W-6940 Weinheim, 1991
Formation of Doubly Vinyl-Bridged Binuclear
Iridium Complexes by C-H Activation **
By Angelika Nessel, Oliver Niirnberg, Justin WOK
and Helmut Werner*
Dedicated to Professor Kurt Dehnicke
on the occasion of his 60th birfhday
Vinyl transition-metal complexes can be formed from
nonactivated olefins in general only under drastic reaction
conditions. Bergman and Stoutland['' reported in 1985 that
photolysis of [Cp*IrH,(PMe,)] (Cp* = C,Me,) in presence
of ethene leads not only to the formation of the expected
olefin compound [Cp*Ir(C,H,)(PMe,)] (l),but also to the
hydrido(viny1) complex [Cp*IrH(HC=CH,)(PMe,)] (2),
which on heating to ca. 180°C isomerizes to give 1. We now
describe binuclear doubly vinyl-bridged iridium complexes
that are obtained from well-known, easily accessible precursors and H,C=CHtBu in presence of base without photochemical activation.
2
1
Previously, Maitlis et al. have shown[21that [Cp*IrCl,],
reacts with ethene and Na,CO,/EtOH
to give
[Cp*Ir(C,H,),] . The mesitylene osmium complex 3 behaves
analogously and on treatment with C,H, and Na,CO,/
EtOH affords compound 4.l3IIf, however, ethene is replaced
by 3,3-dimethyl-1-butene the carbonyl(hydrido)methyl complex 5 is formed.t41Labeling experiments confirm that the
ligands CO, CH,, and H are really generated by stepwise
fragmentation of ethanol in the coordination sphere of the
metal.
Na2COS / EtOH
H~C-CH,
4
Na2COS / EtOH
H, C'-CHtSu
H
5
In contrast to our expectation, the reaction of [CpIrBr,],
(6,Cp = C,H,) with H,C=CHfBu and Na,CO,/EtOH does
not give [CpIrH(CH,)(CO)],[51 but leads to a mixture of
[*I Prof. Dr. H. Werner, Dipl. Chem. A. Nessel, Dipl. Chem. 0. Nurnberg,
Dr. J. Wolf
Institut fur Anorganische Chemie der Universitat
Am Hubland, W-8700 Wurzburg (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
(SFB347). the Fonds der Chemischen Industrie, and Degussa AG. We
thank M . Schulz for his support in determining the X-ray crystal structure.
0570-0833/91/0808-1006$3.50+.25/0
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 8
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