Electron donor-acceptor compounds. Synthesis and structure of 5-(1,4-benzoquinone-2-yl)-10,15,20-trialkylporphyrins

Article abstract of DOI:10.1515/znb-1998-0914

A series of 5-(benzoquinone)-10,15,20-trialkylporphyrins was synthesized via cross condensation of the respective aldehydes, 2,5-dimethoxybenzaldehyde and pyrrole followed by demethylation with BBr₃ and oxidation with PbO₂. This meth

Full text of DOI:10.1515/znb-1998-0914

Electron Donor-Acceptor Compounds. Synthesis and Structure of
5-(l,4-Benzoquinone-2-yl)-10,15,20-trialkylporphyrins
Steffen Runge, Mathias O. Senge*
Institut für Organische Chemie (WE02), Fachbereich Chemie, Freie Universität Berlin,
Takustraße 3, D-14195 Berlin, Germany
Z. Naturforsch. 53b, 1021-1030 (1998); received June 15, 1998
Porphyrins, Quinones, Electron Transfer Compounds, Crystal Structure, Conformation
A series of 5-(benzoquinone)-10,15,20-trialkylporphyrins was synthesized via cross conden-
sation of the respective aldehydes, 2,5-dimethoxybenzaldehyde and pyrrole followed by de-
methylation with BBr3 and oxidation with Pb02. This method worked reasonably well for
compounds bearing the benzoquinone substituent and butyl, isopropyl, 1 -methylpropyl and
2-ethylpropyl residues (2a-d). The free base porphyrin quinones were converted into the
zinc(II) complexes (3a-d) all of which showed remarkable stability for porphyrin quinones.
The zinc(II) complex 3c bearing isopropyl residues was investigated by X-ray crystallography
and showed a supramolecular structure consisting of polymeric chains facilitated by coordina-
tion of a benzoquinone oxygen to a neighboring zinc(II) center. Attempts to synthesize a 5-
(benzoquinone)-10,15,20-tris(terr-butylporphyrin) resulted in the formation of a yellow por-
phomethene (4), which could not be oxidized further. A crystal structure analysis of 4, the
first for a free base porphomethene, shows an extremely twisted conformation with syn-
orientation of the three rm-butyl groups. The results indicate that new methods will have to
be developed for the synthesis of nonplanar porphyrin quinones.
Introduction
Electron transfer involving porphyrin-type do-
nors and quinone acceptors presents one of the
underlying principles of photosynthesis. The eluci-
dation of the first crystal structure of a bacterial
photosynthetic reaction center has provided a de-
tailed picture of the geometrical arrangem ent of
the cofactors involved [1], Despite enormous ef-
forts aimed at the synthesis and characterization
of suitable porphyrin-quinone model compounds
many questions regarding the photoinduced elec-
tron transfer remain unanswered or are discussed
controversially [2-4]. Open problems involve the
sequence, activation, efficiency, and speed of the
electron transfer in multicomponent biomimetic
systems. One question, which has been completely
overlooked so far, involves the influence of the
tetrapyrrole macrocycle conformation on electron
transfer processes. During the last years convinc-
ing evidence was accumulated that the conform a-
tional flexibility of porphyrins [5] and nonplanar
macrocycles plays an im portant role in fine-tuning
1a R = CH2CH2CH2CH3
1b R = CH2CH2(CH3)2
1c R = CH(CH3)2
2a R = CH2CH2CH2CH3
2b R = CH2CH2(CH3)2
2c R = CH(CH3)2
1d R = CH(CH2CH3)2
2d R = CH(CH2CH3)2
3a R = CH2CH2CH2CH3
3b R = CH2CH2(CH3)2
3c R = CH(CH3)2
4
R = C(CH3)3
* Reprint requests to Priv.-Doz. Dr. M. O. Senge.
E-mail: mosenge@chemie.fu-berlin.de
3d R = CH(CH2CH3)2
0932-0776/98/0900-1021 $06.00 © 1998 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com
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1022
St. R unge-M . O. Senge • Electron Donor-Acceptor Compounds
the physicochemical properties of tetrapyrrole-
based cofactors in vivo [6 ]. Since conformational
distortion of porphyrins results in significant alter-
ations in their redox chemistry, photophysics and
photochemistry, it follows that conformational ef-
hindered 5-triptycenequinone-10,15,20-tripentyl-
porphyrins [14]. For sterically demanding
tetraalkylporphyrins a modification of the Lindsey
conditions proved necessary [1 1 a].
Initial attem pts to utilize the Lindsey conditions
fects should exert considerable influence on pho- for the synthesis of our target compounds did not
toinduced electron transfer reactions. As early as
1988 Jortner and coworkers invoked conform a-
tional effects in the special pair as one possible
meet success. We finally adapted the conditions
et al. for the synthesis of sterically
used by Ema
demanding 5,10,15,20-tetraalkylporphyrins [11a]
explanation for the unidirectionality of the elec- and were able to prepare the series of 5-(2,5-di-
tron transfer along the L-branch of the photosyn-
thetic reaction center [7], Nevertheless, most of id) using valeraldehyde, isovaleraldehyde, isobu-
methoxyphenyl)-10,15,20-trialkylporphyrins (la-
the model compounds prepared to date are based
on simple, planar octa-/3-alkylporphyrins or tetra-
meso-arylporphyrins. More elaborate systems
have been based on phytochlorin derivatives [8 ].
We have now embarked on a program aimed at
the synthesis of covalently linked porphyrin qui-
nones with tailor-made distortion modes suitable
for investigation of the influence of the macrocycle
conformation on the electron transfer. The two
most common perturbation modes for porphyrins
are saddle distortion and ruffling of the macrocy-
cle [9,10]. The latter involves significant out-of-
plane distortion of the raeso-carbons and in-plane
rotation of the pyrrole rings. Such porphyrins are
easily accessible via the synthesis of 5,10,15,20-
tetraalkylporphyrins with bulky alkyl residues
[11]. While numerous porphyrin-quinones with 5-
tyraldehyde, and 2 -ethyl-butyraldehyde as source
for the m eso-alkyl groups. The choice of alkyl al-
dehydes for la-ld was governed by our earlier
work on symmetric tetraalkylporphyrins [1 1 c].
Using a variety of alkyl groups we have shown that
while tetraalkylporphyrins with residues such as
butyl, isopropyl, 2 -methylpropyl or 1 -ethylpropyl
are planar or moderately distorted, tert-butyl
groups induce significant ruffling in the porphyrin.
The respective metal complexes showed a higher
degree of conformation flexibility and by using the
substituents shown we hoped to gain access to a
series of porphyrin quinones with graded degree
of conformational distortion. For the synthesis of
compound lb we also applied the Adler-Longo
method. This resulted in an almost doubled yield,
albeit offset by a more time consuming work-up.
Application of this method to the synthesis of the
more sterically hindered porphyrins with isopropyl
(lc) or 1 -ethyl-propyl groups (Id) failed.
quinone-10,15,20-triflry/porphyrin
framework
have been synthesized [3], we chose 5-(benzoqui-
none-2-yl)-10,15,20-trialkylporphyrins as initial
targets to investigate if published synthetic m eth-
ods can easily be applied for the synthesis of non-
The next step towards the synthesis of the de-
sired porphyrin quinones involved removal of the
planar-porphyrin quinones or if new synthetic stra- methyl protection group with boron tribromide to
yield the respective hydroquinones [15] which
were oxidized in situ with lead(IV) oxide [16].
Using this m ethod, the free base porphyrin qui-
nones 2a-2d were obtained in 60-65% yield. Fi-
nally, the free base porphyrins were converted to
the respective zinc(II) complexes (3a-3d) with zin-
c(II) oxide using the method developed by Dieks
et al. [17]. Both the free bases and zinc(II) com-
plexes are relative stable compared to other por-
phyrin quinones.
Despite numerous attempts we were able to
grow crystals suitable for single-crystal X-ray crys-
tallography only for compound 3c. A view of the
molecular structure is given in Fig. 1. Although of
low resolution, the structure illustrates several im-
tegies have to be developed by us.
Results and Discussion
Although crude and requiring laborious chro-
matographic work-up, the standard m ethod for the
synthesis of covalently linked (protected) triarylp-
orphyrin quinones is a mixed condensation of the
required aldehydes and pyrrole. This approach fol-
lows the procedures developed by Adler-Longo
[12] and Lindsey [13] for symmetric porphyrins.
The choice of method depends on the reactivity of
the required aldehydes and on the stability of the
porphyrin quinone precursor formed. This ap-
proach has been used to synthesize sterically un-
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5 t. R unge-M . O. Senge • Electron Donor-Acceptor Compounds
1023
0.26 A, C15 = 0.22 A, C20 = 0.16 Ä). As expected,
the sterically less demanding benzoquinone sub-
stituent leads to the smallest Cm-displacements at
C20. The perturbation of the macrocycle is also
indicated by the pyrrole tilt angles against the 4N-
plane which are 9.0°, 8.4°, 8.2°, and 6 .6 ° for the
pyrroles with N21, N22, N23, and N24, respec-
tively. For comparison, (pyridine)(5,10,15,20-tetra-
(isopropyl)porphyrinato)zinc(II) is slightly more
ruffled (ZI24 = 0.19 Ä) with Cm-displacements of
0.34 A [11c]. In solution all compounds exhibit
very similar absorption spectra within each series
(1, 2 or 3) with a slight bathochromic shift for com-
pounds c and d. Since the degree of distortion cor-
relates with absorption maxima [6 ] the compounds
will have very similar conformations ranging from
planar to moderately ruffled.
Fig. 1. Computer generated plot of the monomeric unit
in the crystal structure of 3c. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (A) and angles
(°): Zn-N21 2.074(13), Zn-N22 2.026(15), Zn-N23
2.053(12), Zn-N24 2.024, Zn-02(ax) 2.265(13), C52-01
1.26(2), C55-02 1.25(2), N24-Zn-02 98.1(5), N22-Zn-02
92.1(5), N23 Zn-02 103.8(5), N21-Zn-02 85.6.
The crystal structure of 3c is characterized by
the form ation of a supram olecular system con-
sisting of polymeric chains of molecules. The
chains are formed via coordination of one benzo-
quinone oxygen atom (0 2 ) to the zinc center of a
neighboring molecule [Z n-02
= 2.265(13) Ä].
Thus, the zinc(II) centers are pentacoordinated
and displaced from the 4N-plane by 0.17 A. This
arrangem ent leads to chains consisting of porphy-
rin units in a zig-zag array (Fig. 3). Polymeric
chains involving peripheral heteroatom s and por-
phyrin metal centers have been described before
[18] but the present example shows how easily
such effects can take place in porphyrin quinones
with all the associated implications on photophysi-
cal studies of such compounds. In this context it
should be m entioned that isolated quinones have
been shown to coordinate to isolated porphyrins
forming highly ordered 3d-systems [19].
portant points. The distance between the donor
(defined as the center of the four pyrrole nitrogen
atoms) and the quinone (defined as the geometric
center of the six ring carbon atoms) is 6.36 A,
while the benzoquinone ring forms an angle of
76.5° with the 4N-plane of the tetrapyrrole. The
overall conformation of 3c is characterized by a
m oderate degree of ruffling (see Fig. 2). The
average deviation of the 24 macrocycle atoms
(z!24) from their least-squares plane is 0.124 A,
while the largest out-of-plane displacements are
observed for the Cm-atoms (C5 = 0.33 A, CIO =
Fig. 2. View of the deviations of macrocycle atoms from
the 4N-plane in 3c [Ä x 102].
Fig. 3. Partial view of the polymeric chains formed in the
crystal structure of 3c.
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1024
St. R unge-M . O. Senge • Electron Donor-Acceptor Compounds
The success in the synthesis of 2a-2d and 3a-3d,
involving porphyrins with no or only a m oderate
degree of conformational distortion, prom pted us
to attem pt the synthesis of a severely ruffled por-
phyrin quinone, namely 5-(l,4-benzoquinone-2-
yl)-10,15,20-tris(terr-butyl)porphyrin. The synthe-
sis of the symmetric 5,10,15,20-tetrakis(terf-bu-
tyl)porphyrin bearing four m eso tert-butyl groups
is easily achieved [1 1 ] and thus, we expected no
problems with the synthesis of a porphyrin bearing
three meso rm -butyl groups and one sterically less
demanding aryl group. Surprisingly, all attem pts to
obtain
a
5-(2,5-dimethoxyphenyl)-10,15,20-tris-
(rert-butyl)porphyrin from the reaction of pivalal-
dehyde, 2,5-dimethoxybenzaldehyde and pyrrole
failed. In all cases, a small am ount of a yellow
compound was the sole soluble product that could
be separated from the reaction mixture.
On the basis of spectroscopic data and a crystal
structure determ ination (Fig. 4) the yellow com-
pound was identified as the porphom ethene
(5,10,15,22-tetrahydroporphyrin) 4. Despite addi-
tion of D DQ during the reaction, only one oxida-
tion step had occurred involving the sterically least
hindered 2 0 -position of the porphyrinogen (the
primary product of the aldehyde and pyrrole con-
densation reaction). Subsequent attem pts to oxi-
dize 4 to the porphyrin using p-chloranil, bromine,
lead(II) oxide or D D Q while heating under reflux,
either gave no change or resulted in complete de-
composition of the product. Similarly, attem pts to
prepare 5-phenyl-10,15,20-tris(terr-butyl)porphy-
rin utilizing analogous reactions did not give the
desired result.
The molecular structure of 4 exhibits a very
nonplanar macrocycle conform ation (Fig. 4). The
average deviation of the 24 macrocycle atoms
from their least-squares plane is 0.442 A. Indivi-
dual pyrrole tilt angles with the 4N-plane are quite
different; the angles are 23.4°, 47.3°, 48.7°, and
97.8° for the pyrroles with N21, N22, N23, and
N24, respectively. The porphom ethene character
of the compound is clearly evidenced by the dipyr-
rom ethene structure of the N21,N24-dipyrrin unit.
The eleven atoms comprising this dipyrrom ethene
are planar with an average deviation from their
least-squares plane of 0.026 A. One notable fea-
ture of this structure is sy/i-orientation of the three
rm -butyl groups involving the three sp3 -hybrid-
ized meso positions. To our knowledge, this struc-
Fig. 4. Upper panel: Top view of the molecular structure
of 4 (50% occupancy ellipsoids). All hydrogen atoms
have been omitted for clarity. Lower panel: Side view of
4 with the Cm- and nitrogen hydrogen atoms.
ture presents the first example of a crystal struc-
ture of a free base porphom ethene. Only two
examples of m etalloporphomethenes obtained via
oxidation of 5,5,10,15,15,20,20-octaethylporphyri-
nogen have been described in the literature [2 0 ].
Note, that porphom ethenes are putative interm e-
diates of the biosynthetic pathway leading to por-
phyrins and this structure presents the first view
of such a compound.
One possible explanation for the vexing result
that a seemingly sterically less hindered compound
[the putative 5-(2,5-dimethoxyphenyl)-10,15,20-
tris(terf-butyl)porphyrinogen] can not be oxidized
to the porphyrin while the more hindered
[5,10,15,20-tetrakis(ferr-butyl)porphyrinogen] can,
might be found in the specific configuration of the
intermediates. Possibly, the first oxidation step
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S t. R unge-M . O. Senge • Electron Donor-Acceptor Compounds
1025
and dried methylene chloride. Boron trifluoride
diethyletherate (0.5 ml) was added dropwise and
the mixture stirred for 12 h. For oxidation 0.16 mol
D D Q was added followed by stirring for 1 h. The
reaction mixture was filtered through alumina
(neutral, Brockmann grade III) and chrom ato-
graphed on silica gel, eluting with CH2 Cl2/n-hex-
ane (1:2, v/v). In order of elution the following
four fractions were obtained: 5,10,15,20-tetraal-
kylporphyrin, 5-(2,5-dimethoxyphenyl)-10,15,20-
trialkylporphyrin, a mixture of 5,10- and 5,15-
leading to 4 and involving the dimethoxyphenyl-
■quadrant results in the formation of a porpho-
zmethene with a configuration more difficult to oxi-
udize than those formed during the synthesis of
:5,10,15,20-tetrakis(terf-butyl)porphyrin. Recently,
■we had similar experiences during the synthesis of
«extremely ruffled dodecaalkylporphyrins where
"we found indications that the oxidizability of por-
^phodimethenes strongly depends on their configu-
ratio n [2 1 ].
bis(2,5-dimethoxyphenyl)-dialkylporphyrin,
5.10.15-tris(2,5-dimethoxyphenyl)-20-alkylpor-
and
O ur present results indicate that it is possible
to synthesize meso-substituted porphyrin quinones
bearing sterically undemanding alkyl residues via
modification of existing methodologies. N everthe-
less, cross condensation methods fail for the prep-
aration of highly ruffled porphyrin quinones. Such
com pounds will have to be prepared via either bi-
ladiene-fl,c cyclization reactions, MacDonald con-
densations or preferably, via modification of por-
phyrins [21]. Such approaches are currently tested
in our laboratory.
phyrin. The second fraction, containing the desired
product, was further purified by recrystallization.
M ethod B: Pyrrole (0.2 mol), aldehyde (0.15
mol), and 2,5-dimethoxybenzaldehyde (0.05 mol)
were dissolved in 750 ml refluxing propionic acid
and heated for 45 min under reflux while bubbling
air through the solution. The reaction mixture was
concentrated and the residue dissolved in methy-
lene chloride. A fter neutralization with saturated
sodium carbonate solution, washing with water,
and drying over sodium sulfate the product was
purified as described for m ethod A.
Experimental
General
5.10.15- Tributyl-20- (2,5-
dim ethoxyphenyl)porphyrin (la)
All chemicals used were of analytical grade and
were purchased from Aldrich Co. unless stated
otherwise. - M elting points were measured on a
Biichi melting point apparatus and are uncor-
rected. - Silica gel 60 (Merck) was used for col-
umn chromatography. Analytical thin-layer chro-
m atography (TLC) was carried out using Merck
silica gel 60 plates (precoated sheets, 0 .2 mm thick,
fluorescence indicator F254). - 1H-NMR spectra
were recorded at frequencies of 250 MHz (AC
250) or 500 M Hz (Bruker, AM X 500). All chemi-
cal shifts are given in ppm, referenced on the d
scale downfield from the TMS signal used as in-
ternal. standard. - Electronic absorption spectra
were recorded with a Specord S10 (Carl Zeiss)
spectrophotom eter using dichloromethane as
solvent. - Mass spectra were recorded with a Var-
ian MAT 711 mass spectrom eter using E l tech-
nique with a direct insertion probe and an excita-
tion energy of 80 eV. - Elemental Analyses were
perform ed with a Perkin-Elmer 240 Analyzer.
Yield: m ethod A: 0.26 g (0.43 mmol, 3%); pur-
ple crystals from CH 2C12/az-hexane; m. p. 165-170
C °C. UV/vis (CH 2C12): 2max (lg e) = 230 nm
(3.85), 303 (3.95), 354 (4.11), 418 (5.47), 517 (4.02),
552 (3.67), 597 (3.15), 654 (3.61). ]H NM R (250
MHz, CDC13, TMS): ö = -2.61 (s, 2H, NH ), 1.10-
1.19 (q, J = 7.4 Hz, 9H, CH 2 CH 2 CH 2C //3), 1,74-
1.92 (hept, J = 7.2 Hz, 6 H, CH2 C H 2C //2CH3),
2.44-2.60
(hept,
J
=
7.9
Hz,
6 H,
CH2C //2 CH2 CH3), 3.50 (s, 3H, O C //3), 3.91 (s,
3H, O CH 3), 4.90-5.02 (quin, J = IA Hz, 6 H,
C //2CH2 CH2 CH3), 7.26 (s, 1H, H„henvl), 7.28-7.29
(d, J = 3.0 Hz, 1H, H phenyl), 7.58-7.59 (d, J = 2.2
Hz, 1H, Hphenyi), 8.79-8.81 (d, J = 4.4 Hz, 2H, ß-
H), 9,35-9,37 (d, J = 5.1 Hz, 2H, ß-H ), 9.47-9.53
(q, J = 4.9 Hz, 4H, ß-H ). MS (40 eV), m /z (%):
614 (100) [M+], 571 (6 8 ) [M+ - CH 3/CO], 528 (7)
[M+ - CH 3/CO], 499 (5) [M+ - C2 H 5],
C4oH46N 40 2
Calcd
614.3710
Synthesis o f 5,10,15-Trialky1-20-
(2,5-dim ethoxyphenyl)porphyrins
Found 614.3635 (HRM S)
M ethod A: Pyrrole (0.04 mol), aldehyde (0.03
mol), and 2,5-dimethoxybenzaldehyde (0 .0 1 mol)
were dissolved under argon in 2 0 0 ml degassed
C4oH46N40 2 (614.8)
Calcd C 78.14 H 7.54 N 9 .ll 0 5.20%,
Found C 78.04 H 7.42 N 8.98 0 5.57%.
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1026
St. Runge-M . O. Senge • Electron Donor-Acceptor Compounde
5-(2,5-Dim ethoxyphenyl)-10,15,20-tris(2-m ethyl-
5-(2,5-D im ethoxyphenyl)-l 0,15,20-tris(1-ethyl-
propyl)porphyrin (lb )
propyl)porphyrin (Id)
Yield: method A: 0.281 g (0.43 mmol, 3% ); pur-
ple crystals from CH2Cl2//7-hexane: m. p. 290 °C. -
UV/vis (CH 2C12): Amax (lg e) = 230 nm (4.43), 302:
(4.31), 366 (4.44), 419 (5.53), 518 (4.15), 552 (3.85).
Yield: method A: 0.26 g (0.429 mmol, 3%);
method B: 1.43 g (2.3 mmol, 5%); purple crystals
from C H 2Cl2/n-hexane; m. p. 185-189 °C. - UV/
vis (CH2 C12): Amax (lg e) = 230 nm (4.33), 301
(4.18), 367(4.26), 418 (5.36), 516 (3.97), 549 (3.47),
597 (3.76), 655 (3.84).
-
'H NMR (250 M H z.
CDC13, TMS): (3 = -2.43 (s, 2H, NH), 0.93-0.98 ( t,
J = 7.5 Hz, 12H, CH(CH 2C //3)2), 0.99-1.03(t, J =
7.5 Hz, 6 H, CH(CH2C //3)2), 2.67-3.01 (m, 12H,„
C H (C //,C H 3)2), 3.50 (s, 3H, O C //3), 3.90 (s, 3H,„
O C //3), 4.83-5.05 (m, 3H, C //(C H 2CH 3)2), 7.25
(s, 1H, H phenyI), 7.28-7.29 (d, J = 2.5 Hz, 1H, H phe.
nyl), 7.56-7.57 (d, J = 3.4 Hz, 1H, H phenyl), 8.75-
8.77 (d, J = 4.2 Hz, 2H, H ^ ^ e ) , 9.45-9.47 (d,.
J = 4.3 Hz, 2H, % pyrrole), 9.57-9.59 (d, J = 4.3
Hz, 2H, H ^ pyrrole), 9/62-9.64 (d, J = 5.2 Hz, 2H,
593 (3.36), 650 (3.49).
-
!H NM R (250 MHz,
CDC13, TMS): (5 = -2.62 (s, 2H, NH ), 1.17-1.19 (d,
J = 5.2 Hz, 12H, CH2 C H (C //3)2), 1.20-1.22 (d, J =
6.0 Hz, 6 H, C H (C //3)2), 2.69-2.84 (sept, J = 6.0
Hz, 3H, CH 2C //(C H 3)2), 3.49 (s, 3H, O C //3), 3.91
(s, 3H, O C //3), 4.81-4.84 (d, J = 7.0 Hz, 4H,
CH 2C H (C H 3)2), 4.88-4.91 (d, J = 7.0 Hz, 2H,
C //2 C H (CH 3)2), 7.26 (s, 1H, H phenyl), 7.28-7.29
(d, J = 2.3 Hz, 1H, H phenyl), 7.58-7.59 (d, J = 2.3
Hz, 1H, H phenyl), 8.79-8.81 (d, J = 4.6 Hz, 2H, H^.
pyrrole), 9.35-9.37 (d, J = 4.2 Hz, 2H, Hß.pyrroje),
9.47-9.53 (q, J = 5.1 Hz, 4H, H ^ y ^ e ) . - MS (40
eV), m /z (%): 614 (16) [M+], 571 (23) [M+-
c2H3o].
Hß-pyrroie)- - MS (40 eV), m /z (%): 656 (100) [M+],
627 (97) [M+ - CHO], 585 (14) [M+ - C3H 4 0 ].
c 43h 52n 4 o 2
Calcd
656.4179
Found 656.4092 (HRM S)
C4oH46N 40 2
Calcd
614.3710
C43H 52N4 0 2 (656.9)
Found 614.3636 (HRM S)
Calcd
C 78.62 H 7.97 N 8.52 0 4.87%,
Found C 78.58 H 8.15 N 8.1 0 5.17%.
C40H 46N4 O 2 (614.8)
Calcd
C 78.14 H 7.54 N 9 .ll 0 5.20%,
Synthesis o f 5-(l,4-benzoquinone-2-yl)-l0,15,20-
trialkyIporphyrins
Found C 78.50 H 7.52 N 9.16 0 4.82%.
5-(2,5-Dim ethoxypheny l)-10,15,20-
tri(isopropyl)porphyrin (lc)
The respective porphyrin (0.4 mmol) was dis-
solved in 100 ml methylene chloride. The solution
was cooled to -50 °C and 2.5 ml BBr3 were added
dropwise under argon. The green solution was
slowly warmed to room tem perature and stirred
for 10 h. A fter cooling to 0 °C the m ixture was
neutralized with saturated aq. solution of sodium
hydrogencarbonate. The organic phase was diluted
with methylene chloride to 250 ml, washed twice
with 1 0 0 ml water, and dried over sodium sulfate.
The hydroquinol formed was immediately oxi-
dized by addition of 1 g P b 0 2 and purified by col-
umn chromatography on silica gel eluting with
neat CH 2C12. The main fraction was concentrated
and further purified by recrystallization.
Yield: method A: 0.164 g (0.29 mmol, 2%); pur-
ple crystals from CH 2Cl2/«-hexane; m. p. 280 °C. -
UV/vis (CH 2C12): Amax (lg e) = 230 nm (3.96), 302
(3.99), 354 (4.11), 419 (5.38), 519 (3.84), 556 (2.87),
598 (2.70), 654 (2.86).
-
!H NM R (250 MHz,
CDC13, TMS): <3= -2.19 (s, 2H, N H ), 2.34-2.38 (d,
J = 7.0 Hz, 6 H, C H (C //3)2), 2.35-2.38 (d, J = 7.0
Hz, 12H, C H (C //3)2), 3.47 (s, 3H, O C //3), 3.89 (s,
3H, O CH 3), 5.43-5.62 (m, 3H, C H (CH 3)2), 7.23
(s, 1H, H phenyl), 7.26-7.27 ( d ,/= 2.5 Hz, 1H, H phe.
nyl), 7.54-7.56 (d, J = 2.5 Hz, 1H, H phenyl), 8.71-
8.73 (d, J = 5.1 Hz, 2H, H ^ pym>le), 9.41-9.43 (d,
J = 5.01 Hz, 2H, H^.pyrro,e), 9.54-9.56 (d, J = 5.01
Hz, 2H, Hß_pyrrole), 9.59-9.61 (d, J = 5.01 Hz, 2H,
H ^ pyrrole). - MS (40 eV), m /z (% ): 572 (100) [M+],
557 (73) [M+ - CH3], 499 (5) [M+ - C3H 80 ].
5 -(l ,4-Benzoquinone-2-yl)-10,l 5,20-
tributylporphyrin (2 a)
Yield: 0.114 g (0. 195 mmol, 60%); purple crys-
tals from CH 2Cl2/n-hexane; m. p. > 300 °C. - UV/
vis (CH 2 C12): Amax (lg e) = 248 nm (4.62), 304
(4.33), 368 (4.54), 415 (5.66), 516 (4.32), 547 (3.95),
c 37h 40n 4 o 2
Calcd
572.3241
Found 572.3157 (HRM S)
596 (3.87), 656 (3.81).
-
'H NMR (250 MHz,
C37H40N4 O 2 (572.7)
CDC13, TMS): d = -2.63 (s, 2H, N H ), 1.08-1.17
(q. J = 7.1 Hz, 9H, C H ,C H 2CH2C //3), 1.71-1.87
Calcd
C 77.59 H 7.03 N 9.78 0 5.58%,
N 9.61 0 6.18%.
Found C 77.21 H 7.
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St. R unge-M . O. Senge • Electron Donor-Acceptor Compounds
1027
(m, 6 H, CH 2 C H 2C //2 CH3), 2.40-2.57 (m, 6 H,
CH2 C //2 C H 2 C H 3), 4.86-4.95 (m, 6 H,
C //2 CH2 C H 2 CH3), 7.26 (s, 1H, H Dhenvl), 7.26-7.27
MHz, CDC13, TMS): ö = -2.19 (s, 2H, N H ), 2.33-
2.36 (d, J = 7.8 Hz, 12H, C H (C //3)2), 2.36-2.39
(d, J = 7.8 Hz, 6 H, C H (C //3)2), 5.39-5.49 (m, 3H,
C //(C H 3)2), 7.22-7.24 (d, J = 2.0 Hz, 2H, H p h e n y i),
(d. J = 1.7 Hz, 1H, H phenyl), 7.53-7.54 (d, J = 1.9
Hz, 1H, H phenyl), 8.88-8.91 (d, J = 5.0 Hz, 2H, H^. 7.49-7.50 (d, J = 2.0 Hz, 1 H , H phenyl), 8.81-8.83
(d, J = 4.1 Hz, 2H, H^.pyrrole), 9.48-9.50 (d, J = 5.1
Hz, 2H, Hy3_pyrrole), 9.52-9.54 (d, J = 5.1 Hz, 2H,
H^py^oie), 9.58-9.60 (d, J = 5.1 Hz, 2H, H^.pyr.
role). - MS (40 eV), m /z (% ): 544 (100) [M+ + 2H],
529 (40) [(M+ + 2H) - CH 3],
p yrrole), 9.41-9.43 (d, J = 5.0 Hz, 2H, H^.pyrroie),
9.45 (s, 2H, Hß_pyrrole), 9.48-9.50 (d, J = 5.0 Hz,
2H, H^.pyrrole). - MS (40 eV), m /z (%): 585 (100)
[M+ + 2H], 543 (21) [(M+ + 2H) - C3H 7], 533 (21)
[(M+ + 2H) - Q H /C O ],
C 3 8 H 4oN 4 0
2
C35H 34N4 0
2
Calcd
586.3337
Calcd
544.2878
Found 544.2838 (HRM S)
Found 586.3308 (HRMS)
C38H 40N4 O 2 (584.8)
C35H 34N40 2oH ?0 (560.7)
Calcd
C 78.05 H 6.89 N 9.58 0 5.47%,
Calcd
C 74.97 H 6 .ll N 9.99 0 5.89%,
Found C 77.74 H 6.93 N 9.09 0 6.24%.
Found C 74.99 H 6.22 N 9.65 0 5.14%.
5-(l,4-Benzoquinone2-yl)-10,15,20-tris(2-
m ethylpropyl)porphyrin (2 b)
5-(1,4-B enzoquinone-2-yl)-10,l 5,20-tris (1-ethyl-
propyl)porphyrin (2 d)
Yield: 1.105 g (1.89 mmol, 65%); purple crystals
from CH 2 Cl2/«-hexane; m. p. > 300 °C. - UV/vis
(CH 2C12): Amax (lg e) = 249 nm (4.64), 305 (4.41),
367 (4.60), 399 (5.16), 416 (5.74), 516 (4.28), 547
(3.59), 594 (3.44), 655 (3.42). - 'H NMR (250
MHz, CDC13, TMS): ö = -2.62 (s, 2H, NH ), 1.15-
1.17 (d, J = 4.3 Hz, 12H, CH2 C H (C //3)2), 1.18-
1.20 (d, J = 4.3 Hz, 6 H, CH2 C H (C //3)2), 2.64-2.81
(sept., J = 7.0 Hz, 3H, CH2 C //(C H 3)2), 4.78-4.81
(d, J = 7.0 Hz, 4H, C //2CH (CH 3)2), 4.85-4.87 (d,
/ = 7.0 Hz, 2H, C //2 C H (CH 3)2), 7.25 (s, 1H, H phe_
nyl), 7.26-7.27 (d, J = 1.8 Hz, 1H, H phenyl), 7.53-
7.54 (d, / = 1.8 Hz, 1H, H phenyl), 8.90-8.92 (d, J =
5.1 Hz, 2H, H^.pyrro.e), 9.41-9.43 (d, J = 5.3 Hz,
2H, H ^ pyrrole), 9.44-9.46 (d, J = 5.3 Hz, 2H, H/3.
p yrro le), 9.49-9.51 (d, J = 5.3 Hz, 2H, H^pyrrote). -
MS (40 eV), m /z (%): 584 (8 8 ) [M+ + 2H], 543
(100) [(M+ + 2H) - C3H 7], 499 (9) [(M+ + 2H) -
2x C3H 7], 457 (26) [(M+ + 2H) - 3x C3H 7],
Yield: 0.18 g (0.287 mol, 65%); purple crystals
from CH 2Cl2/«-hexane; m. p. > 300 °C. - UV/vis
(CH2 C12): Amax (lg e) = 248 nm (4.40), 306 (4.13),
368 (4.32), 417 (5.42), 516 (4.06), 555 (3.61), 594
(3.59), 659 (3.46). - 'H NM R (250 MHz, CDC13,
TMS): <3 = -2.41 (s, 2H, N //), 0.90-0.97 (t, J = 7.7
Hz, 12H, C H (C H 2C H 3)2), 0.95-1.01 (t, / = 7.7 Hz,
6 H,
CH (C H 2 C //3)2),
2.68-2.93
(m,
(m,
12H,
3H,
C H (C //2 CH 3)2),
4.84-5.05
C //(C H 2CH 3)2), 7.23 (s, 1H, H phenv,), 7.25-7.26
(d, > = 2.5 Hz,1H. Hphenyi), 7.50-7.51 (d, J = 2.5
Hz, 1H, H phenyl), 8.86-8.89 (d, J = 5.2 Hz, 2H, H^.
p yrrole), 9.51-9.53 (d, J = 5.2 Hz, 2H, Hß_pyrrole),
9.54-9.56 (d, J = 5.2 Hz, 2H, H ^p y ^e), 9.61-9.63
(d, J = 6.1 Hz, 2H, H^.pyrrole). - MS (40 eV); m /z
(% ): 628 (100) [M+ + 2H], 599 (42) [(M+ + 2H) -
C2H 5], 558 (22) [(M+ + 2H) - C2H 5 - C3H 5], 529
(11) [(M+ + 2H) - C5H 9 0 2],
c 41h 46n 4o 2
c38H40N4o2
Calcd
628.3777
Calcd
586.3307
Found 628.3789 (HRM S)
Found 586.3327 (HRMS)
C41H 46N4 0 2 (626.8)
C38H 40N4 O 2 (584.8)
Calcd
C 78.56 H 7.39 N 8.94 0 5.10%,
Calcd
C 78.05 H 6.89 N 9.58 0 5.47%,
Found C 78.56 H 7.30 N 8 . 6 8 0 5.46%.
Found C 77.66 H 6.92 N 9.18 0 6.24%.
Synthesis o f {5-(l,4-benzoquinone-2-yl)-10,15,20-
trialkylporphyrinato)zinc(II)
5-(l,4-B enzoquinone-2-yl)-l 0,15,20-
tri(isopropyl)porphyrin (2 c)
Yield: 0.12 g (0. 214 mmol, 61%); purple crystals
from CH 2 Cl2/«-hexane; m. p. > 300 °C. - UV/vis
(CH 2 C12): 2max (lg e) = 248 nm (4.45), 306 (4.19),
371 (4.36), 400 (4.90), 416 (5.73), 516 (4.14), 547
A pproximately 0.085 mmol of the porphyrin
quinone was dissolved in 50 ml methylene chlo-
ride. Zinc oxide (250 mg) and three drops of triflu-
oroacetic acid were added under stirring. A fter
1 0 minutes the color changed from green to violet
(3.72), 597 (3.68), 659 (3.54).
-
lH NMR (250
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1028
St. R unge-M . O. Senge ■Electron Donor-Acceptor Compounds
and the reaction mixture was filtered through sil-
ica gel, followed by recrystallization.
C38H 38N4 0 2Zn (648.1)
Calcd
C 70.42 H 5.91 N 8.64%,
Found C 70.34 H 5.83 N 8.31% .
{5-(l,4-B enzoquinone-2-yl)-10,15,20-
tributylporphyrinatojzinc(U ) (3a)
{5-(l,4-Benzoquinone-2-yl)-10,15,20-
tri(isopropyl)porphyrinato}zinc(U ) (3c)
Yield: 0.05 g (0. 071 mmol, 85%); red crystals
from CH2Cl2//?-hexane; m. p. > 300 °C. - UV/vis
Yield: 0.047 g (0.0738 mmol, 83%); purple crys-
tals from CH2Cl2/«-hexane; m. p. >300 °C. - UV/
(CH2 C12): 2max (lg e )
=
249 nm (4.58), 307 (4.35),
350 (4.22), 399 (4.81), 418 (5.69), 549 (4.23). - !H
NMR (250 MHz, CDC13, TMS): (3 = 1.02-1.08 (t,
J = 7.7 Hz, 3H, CH2CH2 CH2 C //3), 1.07-1.13 (t,
vis (CH2 C12): Amax (lg e)
(4.21), 351 (404), 400 (4.68), 419 (5.77), 550
(4.14). - ]H NM R (250 MHz, CDC13, TMS):
- 250 nm (4.44), 308
6
=
J
= 7.7 Hz, 6 H, CH 2C H 2 CH2 C //3), 1.62-1.80
2.42-2.45 (d, J = 6.9 Hz, 12H, C H (C //3)2), 2.46-
2.48 (d, J = 6.9 Hz, 6 H, C H (C //3)2), 5.61-5.72
(sept., J = 6.7 Hz, 3H, C //(C H 3)2), 7.14-7.16 (d,
J = 1.7 Hz, 1H, H phenyl), 7.18-7.20 (d, J = 1.7 Hz,
1H, H phenyl), 7.38-7.39 (d, J = 2.5 Hz, 1H, H phenyl),
8.94-8.96 (d, J = 5.1 Hz, 2H, H ^ pyrrole), 9.70-9.72
(d, J = 5.2 Hz, 2H, H^_pyrrole), 9.74-9.76 (d, J = 5.2
Hz, 2H, H ^p y ^e), 9.77-9.79 (d, J = 5.2 Hz, 2H,
(sext., J = 7.5 Hz, 2H, CH 2 CH2 C //2 C H 3), 1.64-
1.84 (sext., J = 7.5 Hz, 4H, CH2 CH2C //2CH 3),
2.14-2.27
CH2 C //2 CH2 CH3), 2.29-2.42 (quin., J = 7.5 Hz,
4H, CH2 C //2 CH2CH3), 4.26-4.33 (t, J = 7.5 Hz,
2H, C //2CH2 CH2 CH3), 4.48-4.71
C //2 CH2 CH2 CH3), 7.27 (s, 1H, H phenyl), 7.28-7.29
(d, J = 1.7 Hz, 1H, H phenyl), 7.53-7.54 (d, J = 1.7
Hz, 1H, H phenyl), 8.92-8.94 (d, J = 4.3 Hz, 2H, H ^
p yrrole), 8.93-8.95 (d, J = 4.3 Hz, 2H, H ^ pyrrole),
8.98-9.00 (d, J = 4.3 Hz, 2H, H ^ pyrrole), 9.37-9.39
(d, J = 5.1 Hz, 2H, H/J.pyrro.e), - MS (40 eV), m /z
(%): 648 (100) [M+], 605 (73) [M+ - C3H 7], 562
(14) [M+ - 2x C3H 7], 519 (13) [M+ - 3x C3H 7],
(quin.,
J
=
7.5
Hz,
2H,
8
(m, 4H,
FI/3-pyrrole ).
-
'MS (40 eV), m /z (%): 606 (97) [M+],
591 (37) [M+-CH3],
c 35H 32n 4 o 2
Calcd
606.1959
Found 606.1973 (HRMS)
C35H 32N4 0 2Zn (606.1)
Calcd C 69.36 H 5.32 N 9.24%,
c 38h 38n 4 o 2
Found C 68.39 H 5.46 N8.91% .
Calcd
648.2443
Found 648.2452 (HRM S)
{5-(l,4-Benzoquinone-2-yl)-10,15,20-tris(l-ethyl-
propyl)porphyrinato}zinc(II) (3d)
C38H 38N4 0 2 Z noH 20 (702.2)
Calcd
C 65.00 H 5.45 N 7.0% ,
Yield: 0.046 g (0.0667 mmol, 83%); red crystals
from CH2 Cl2/«-hexane; m. p. > 300 °C. - UV/vis
(CH 2C12): Amax (lg e ) = 253 nm (3.94), 311 (3.78),
Found C 65.26 H 5.59 N 7.52% .
{5-(l,4-Benzoquinone-2-yl)-10,15,20-tris(2-m ethyl-
propyl)porphyrin atojzin c(ll) (3b)
419 (5.28), 552 (3.82).
-
lH NM R (250 MHz,
CDC13, TMS): (3 = 0.91-0.97 (t, J = 7.6 Hz, 18H,
Yield: 0.046 g (0.071 mmol, 85%); red crystals
from CH2Cl2/n-hexane; m. p. > 300 °C. - UV/vis
(CH2C12): ^max (lg e) = 249 nm (4.58), 306 (4.30),
399 (4.80), 418 (5.74), 549 (4.18). - !H NM R (250
MHz, CDC13, TMS): (3 = 1.09-1.16 (m, 18H,
CH2 C H (C //3)2), 2.59-2.76 (sept., J = 7.0 Hz, 3H,
CH2 C //(C H 3)2), 4.53-4.56 (d, J = 6 . 8 Hz, 2H,
C //2 CH (CH 3)2), 4.66-4.68 (d, J = 6 . 8 Hz, 2H,
CH 2CH (C H 3)2), 4.67-4.69 (d, J = 6 . 8 Hz, 2H,
C //2 CH (CH 3)2), 7.26 (br s, 2H, H phenyl), 7.53-7.54
(d, J = 1.7 Hz, 1H, H phenyl), 8.97-8.99 (d, J = 5.2
Hz, 2H, H ^ pyrrole), 9.25 (s, 4H, H ^ p y ,^ ), 9.47-
9.49 (d, J = 5.2 Hz, 2H, H ^ pyrrole). - MS (40 eV),
m /z (%): 648 (11) [M+], 605 (24) [M+ - C3H 7], 562
(8 ) [M+ - 2x C3 H 7], 519 (13) [M+ - 3x C3H 7].
CH (CH2 C //3)2),
C H (C //2 CH 3)2),
C //(C H 2 CH3)2), 7.22 (s, 2H, H phenyl), 7.49 (br s,
1H, H phenyl) 8.96-8.98 (d, J JTo H z, 2H,
pyrrole), 9.74 (br s, 6 H, H^.pyr^e). - MS (40 eV),
m /z (% ): 606 (97) [M+], 591 (37) [M+-CH3],
2.71-3.03
4.98-5.15
(m,
(m,
12H,
3H,
C41H 44N40 2Zn
Calcd
690.2946
Found 690.2912 (HRMS)
C41H 44N40 2Zn (690.2)
Calcd C 71.35 H 6.42 N 8.12% ,
Found C 71.95 H 6.51 N7.98% .
Synthesis o f 5,10,15,22-Tetrahydro-20-(2,5-dimeth-
oxyphenyl)-5,10,15-tris(tert-butyl)porphyrin (4)
C38H 38N4 0 2Zn
Calcd
648.2443
2-Ethyl-butyraldehyde (0.03 mol), pyrrole and
2,5-dimethoxybenzaldehyde were reacted as de-
Found 648.2465 (HRM S)
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St. R unge-M . O. Senge • Electron Donor-Acceptor Compounds
1029
scribed above for method A. A fter filtration of the
reaction mixture through neutral alumina, fol-
lowed by column chrom atography on silica gel
(CH 2Cl2//i-hexane, 1:2, v/v) a red solution was ob-
tained as main fraction. Yield: 0.08 g (0.13 mmol,
1%); yellow crystals from C H 2 Cl2/«-hexane; m. p.
Table I. Summary of crystal data, data collection and re-
finement for the crystal structure determinations.
Compound
Chemical formula
Mol. wt.
3c
4
[C35H32N40 2Zn],
606.02
,
C4()H5f)N40 2
618.84
Color
Habit
Crystal size (mm)
Space group
pale yellow
parallelepiped
0.25 x 0.05 x 0.05
P2]/n
blue
plate
0.34 x 0.26 x 0.05
P2,
230-235 °C.
-
UV/vis (C H 2 C12): Amax (lg e) =
232 nm (3.49), 291 (3.10), 454 (3.52). - ’H NMR
(250 MHz, CDC13, TMS): Ö = 0.96-0.97 (d, J = 1.7
Hz, 9H, C (C //3)3), 1.09-1.10 (d, J = 2.5 Hz, 18H,
C(CH 3)3), 3.56 (s, 3H, OC//3), 3.67 (s, 1H, C m-H),
3.69 (s, 1H, C m-H ), 3.77 (s, 1H, C m-H ), 3.88 (s, 3H,
11.359(10)
10.998(8)
12.60(2)
111.82(9)
1462(3)
2
15.623(4)
14.838(6)
16.283(3)
109.32(2)
3562(2)
4
a (A)
b (A)
c (A)
ß(°)
V (A )
Z
OC// ), 5.89-5.90 (d, J = 2.6 Hz, 4H, H ^ p y ^ ) ,
3
1.377
1.472
0.93, 0.64
CuKa
1.54178
130(2)
1.154
0.553
0.97, 0.87
CuKa
1.54178
130(2)
dcaic (Mg m~3)
H (mm ')
Tmax, Tmin
Radiation
A (A)
6.09-6.11 (t, J = 3.2 Hz, 2H, H^.pyrrole), 6.26-6.28
(d, J = 3.2 Hz, 2H, H/3.pyrrole), 6.85 (s, 1H, H phenyI),
6.87-6.89 (t, J = 1.7 Hz, 2H, H phenyl), 8.69 (br s,
1H, NH), 8.75 (br. s, 2H, NH). - MS (40 eV); m /
z (%): 618 (5) [M+], 561 (74) [M+ - C4H 9],
T (K)
Diffractometer
Syntex P2[
57.12
Syntex P2,
57.03
n
u max
±h,+k,+l
5238
4797
Octants collected
Collec. reflections
Indep. reflections
Reflections with
F > 4.0 Ct(F)
±h,+k.+l
2225
2101
c 41h 46n 4 o 2
Calcd
618.3934
1638
2877
Found 618.3946 (HRM S)
0.0880
0.1310, 6.9324
196
0.008
1.176
0.0974
0.2318
0.1285
0.2567
1.105
0.0699
0.1537, 0.1052
417
0.001
0.306
0.0957
0.2334
0.1628
0.3081
1.056
flint
C41H46N40 2 (626.8)
y
Calcd
C 77.63 H 8.14 N 9.05 0 5.17%,
No. of parameters
Found C 77.13 H 8.41 N 9.01 0 5.45%.
dlomax
d lQ m a x (£ Ä-3)
fl 1 [F > 4.0 a(F)]
wR2 [F > 4.0 a(F)]
fl 1 (all data) a
wR2 (all data)
Crystallography
X-ray quality crystals were grown by liquid dif-
fusion. The crystals were rem oved from solution
and covered with a layer of Paraton N®. A suitable
crystal was selected, attached to a glass fiber and
immediately placed into the low-tem perature ni-
trogen stream as described by Hope [22]. Cell
S
a fll = ZIIF0-FCII/2F0I, wR2 = [2 (w (F 02-
w 1 = cr(F 02) + (xP)~
Fc2)2)/2[ w (F02) ]1/2;
+ yP.; w here P -: (F02 + 2F c2)/3.
param eters were determ ined from 25-30 auto- hydrogen atoms were refined with anisotropic
matically centered reflections in the range 2 0 ° < 6 thermal parameters. The crystals of 3c were of low
< 25°. During the data collections two standard
reflections were measured every 198 reflections
quality with fairly broad reflections profiles. Des-
pite repeated attem pts to grow better crystals and
and showed only statistical variation of the inten- several attem pted data collections the present
sities (<1%). The intensities were corrected for structure is the result of the best crystals found.
Lorentz and polarization effects. For both struc- Except for the zinc, nitrogen and benzoquinone
tures an absorption correction was applied using carbon and oxygen atoms all nonhydrogen atoms
the program XABS2 [23], while extinction effects
were refined with isotropic thermal parameters.
were disregarded. The structure of 3c was solved
The m eso-carbon atoms were refined with a com-
via a Patterson synthesis followed by structure ex- mon isotropic therm al param eter. The residual
pansion, while the structure of 4 was solved using electron density is located near the zinc center.
Direct Methods. For both structure solutions the
program SHELXS-93 was used [24], Refinements
were carried out by full-matrix least-squares on
IF2I using the program SHELXL-93 [25a] for 4 and
SHELXL-97 [25b] for 3c. Hydrogen atoms were
included at calculated opositions using oa riding
model with C-H = 0.96 A and N-H = 0.9 A. Details
for the crystal data, data collection and refinement
Complete details on the crystal structure investi-
gations, including atomic coordinates, thermal
parameters and complete bond lengths and angles
have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK). Copies can be ob-
tained on request by quoting the publication cita-
tion and the deposition num bers CSD-102147 for
are given in Table I. For the structure of 4 all non- 3c and CSD-102148 for 4.
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1030
St. Runge-M . O. Senge • Electron Donor-Acceptor Compounds
A ckn owledgements
Fonds der Chemischen Industrie and enjoyed the
continuing support of Prof. H. Kurreck. We grate-
This work was generously funded by the
Deutsche Forschungsgemeinschaft (Se543/2-4
and Heisenberg-Scholarship Se543/3-l) and the
fully acknowledge the cooperation of the UC
Davis crystallographic facility (M. M. Olmstead,
director).
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