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Electrostatic Control of the Molecular and Crystal Structure of an Olefinic Double Betaine.

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The lack of optical induction when the optically active
catalysts 1-4 are used is the result of rapid racemization of
the catalytically active species. Surprisingly, optical induction is still not observed with the optically active complex 5,
whose planar chiral structure does not isomerize even at
200 "C. We interpret this result to mean that acetophenone
attacks the coordinated diphenylsilane from the side not facing the complex. The newly formed asymmetric center is thus
too far from the planar chiral group.
The complex [CpFe(CO),(CH,)] and also the complex
[IndFe(CO),(CH,)] can be used as hydrogenation catalysts.
For example, they catalyze the hydrogenation of a-methylstyrene to isopropylbenzene at 100 "C under H, (50 bar) in
However, owing to rapid deactivation of the comof the dimeric compounds
plexes employed-formation
[Cp'Fe(CO),], , which are catalytically inactive-only a few
catalytic cycles are achieved. The phosphane complexes 3
and 4 decompose during hydrogenation of a-methylstyrene
(90 "C, bar H,, THF) so rapidly that only a few percent of
hydrogenated product is formed. We explain the catalytic
hydrogenation by formation of an qZ-H, complex from the
unsaturated intermediate [Cp'Fe(CO)(COCH,)] under the
reaction conditions; this complex, formed in competition
with T H F and olefin complexes, reacts with a-methylstyrene
similarly to the reaction of the Fe-bonded SiH group with
acetophenone. Such q2-H, complexes have also been postulated to be formed during decomposition of [CpFe(CO),(CH,)] and [IndFe(CO),(CH,)] in the presence of hydrogen.r2*1
The majority of the reactions of organometallic compounds proceed via intermediates containing a free coordination site at the metal. It should be possible to use these free
coordination sites for catalysts of known structure.r211
[17] The [CpMn(CO),(sibdne)jcomplexes do not catalyze the hydrosilylation of
acetophenone with diphenylsilane; we have obtained evidence for a stoichiometric reaction.
[18] E. J. Crawford. P. K. Hanna, A. R. Cutler, J. A m . Chem. SOC.l i f (1989)
6891.
1191 1S O mL (1 1.6 mmol) of a-methylstyrene, 0.50 g (2.6 mmol) of [CpFe(CO),(CH,)] in 5 mL ofTHF, 50 bar H,. 110 " C ;degree of hydrogenation
90% ('H NMR integration).
[20] T. C. Forschner, A. R. Cutler, Inorg. Chim. Acfa 102 (1985) 113.
[21] Reports have appeared describing the use of [(arene)Cr(CO),(q'HSiHPh,)] complexes as catalysts for the activation of the Si-H bond of
diphenylsilane in thermal reactions: 0. B. Afanasova. E. Zubarev, T.M.
Sokolova, E. A. Chernyshew, Zh. Obshch. Khim. 57 (1987) 1909. E.
Chem. Commun. 1990, 681
Matarasso-Tchiroukhine, J. Chem. SOC.
Electrostatic Control of the Molecular and Crystal
Structure of an Olefinic Double Betaine **
By Robert Weiss,* Reinhardt Roth, Ruiner H . Lowuck,
and Mutthius Brerner
Dedicated to Professor Hans Jiirgen Bestmann
on the occasion of his 65th birthday
E/Z-isomeric olefinic double betaines of the type 1/2 were
previously unknown. The quadrupole system 2, which has
an alternating charge pattern, should be significantly more
stable than system 1, because of the more favorable electrostatic interactions between the charged substituents in 2.
Model calculations have shown that, depending on the substituents, this difference in stability can be up to
40 kcal mol-'.['] Here we describe the first synthesis of a
stable compound of type 1 as well as its unusual molecular
and crystal structure.
Received: May 23, 1990 [Z 3975 IE]
German version: Angew. Chem. 102 (1990) 1189
CAS Registry numbers
( - ) - I , 67375-04-6; (+)-1, 67291-26-3; (-)-2, 74984-64-8; (+)-2, 74945-73-6;
(-)-3, 59727-90-1; (+)-3, 59568-04-6; (-)-4, 123075-70.7; (+)-4, 123163.871; ( - ) - 5 , 129286-99-3; ( + ) - 5 , 129388-44-9; 6, 51276-65-4; CpFe(CO),CH,,
12080-06-7; Ph,SiH,, 775-12-2; acetophenone, 98-86-2; a-methylstyrene, 9883-9; isopropylbenzene, 98-82-8.
[l] J. L. Speier, Adv. Organomet. Chem. 17 (1979) 407.
[2] I . Ojima, K. Hirai in J. D. Morrison (Ed.): Asymmetric Synlhesis, Vol. 5 ,
Academic Press, Orlando, FL. USA 1985, p. 103.
[3] F. Seitz, M. S. Wrighton, Angew. Chem. lOO(1988) 281; Angew. Chrm. Inr.
Ed. Engl. 27 (1989) 289.
[4] K. Yamamoto, T. Hayashi, M. Kumada, J. Organornet. Chem. 46 (1972)
C65.
151 H. Brunner, U. Obermann, Chem. Ber. 122 (1989) 499.
[6] H. Brunner. H. Vogt, J. Orgunomet. Chem. 191 (1980) 181.
[7] H. Brunner, H. Vogt, J. Orgunomet. Chem. 2i0 (1981) 223.
[8] The structural formulas show the forms of 1-5 that are levorotatory at
1 = 436 nm. The Fe center has the R configuration, the C center,
the S configuration.
[9] 1.0 mL (8.0 mmol) of acetophenone, 1.6 mL (8.0 mmol) of diphenylsilane,
0.5-1.0 mol % of catalyst. The hydrosilylation can be monitored by 'H
NMR spectroscopy. The induction period can be from several minutes to
a few hours.
[lo] A simple rate law cannot be formulated for the epimerization, which occurs over hours[l4].
Ill] The half-lives for epimerizatlon of 3 and 4 in [D,]benzene are 70 min at
70'C and 37 min at SO°C[12]
[I21 H. Brunner, K. Fisch, P. G. Jones, J. Salbeck. Angew. Chem. I01 (1989)
1558; Angew. Chem. Int. Ed. Engl. 28 (1989) 1521.
[13] Replacement of the aminophosphane L by PPh, in complexes 1 - 4 does
not affect the catalytic activity.
[14] H. Brunner, H Vogt, Chem. Eer. 114 (1981) 2186.
1151 D. L. Lichtenberger, A. Rai-Chaudhuri,Inorg. Chem. 29 (1990) 975.
[16] H. Rabaa, JLY. Saillard, U. Schubert, J. Organomet. Chem. 330 (1987) 397.
1 132
Q VCH Verlagsge.~ellschofimhH. D-6940 Weinheim, f990
1
2
The starting point of the synthesis was our observation
that, in structure-determined analogy to p-chloranil,[21
dichloromaleic anhydride (3) can be substituted in a bis-onio
fashion by 4-dimethylaminopyridine (DMAP, 6). The yellow
4
3
L = N D N M a 2
e!
I.
e
coo
la
e!
I.
5
[*I Prof. Dr. R. Weiss, Dr. R. Roth, Dip1:Chem. R. H. Lowack,
Dr. M. Bremer
Institut fur Organische Chemie der Universitat
Henkestrasse 42, D-8520 Erlangen (FRG)
[**I This work was supported by the Fonds der Chemischen Industrie. R. H . L.
Thanks the Studienstiftung des deutschen Volkes for a doctoral fellowship.
$3.50+ .25/0
0570-0833~90jlOl0-1132
Angew Chem. Int. Ed. Engl. 29 (1990) No. 10
dication salt 4, obtained in good yields as an analytically
pure CH,CI, adduct, was fully chara~terized.~~]
The salt 4 can be converted, without loss of an onio substituent, into the corresponding maleic acid 5 by treatment
with a small excess of H,O in CH,CI,.r31 Reconversion of 5
to anhydride 4 by reaction with SOCI, confirms that the
energetically unfavorable Z configuration of the two onio
moieties is not affected by the hydrolysis. Double deprotonation of 5 finally yields the dihydrate of the Z double betaine
1 a.r41Recrystallization from boiling H,O affords the hexahydrate of 1a as crystals suitable for X-ray analysis.r51Figure 1 shows the molecular structure of l a . 6H,O in the
crystal.
Fig. 1. Structure of 1 a . 6H,O in the crystal. Selected distances [pm], angles I"],
and torsionangles("1:Cl-Cla 133.4(7),Cl-C2151.3(5),C2-02 125.1(5),C2-01
122.8(5). C1-N1 144.8(4), N1-C3 136.0(5), N1-C7 136.5(5), C3-C4 135.9(6),
C6-C7 135.4(6), C4-C5 140.6(6), C5-C6 142.1(6), C5-N2 133.1(5), N2-CS
146.8(6). N2-C9 146.8(6); C1a-C1-C2 125.2(2), C 1a-C1-N 1 120.1(2), C2-ClNl 11433); Cla-Cl-C2-02 125.5, Cla-Cl-C2-01 52.4, C3-Nl-Cl-Cla 62.9,
C7-N1-Cl-Cla 118.6. C8-N2-C5-C6 174.3, C9-N2-CS-C4 115.5, Nl-Cl-ClaN l a - 3 . 8 , C2-Cl-Cla-C2a 4.7.
The two carboxylate and the two pyridinium substituents
are twisted in a conrotatory fashion from coplanarity with
the central double bond. The torsion angles of the pyridinium moieties (e.g., C3-N1-C1-Cla) are 63", those of the carboxylate moieties (e.g., Cla-CI-C2-01) 52". The molecule
has overall C, symmetry (twofold axis perpendicular to the
double bond in the plane of the double bond). Thus, the
double betaine i s chiral in the crystalline state. Undoubtedly,
the electrostatic repulsion of the identically charged substituents in Z arrangement is responsible for the observed
deconjugation. X-ray structure analyses of alkali-metal
maleates show that, in those cases, one carboxylate group
remains coplanar with the double bond, while the other is
oriented almost orthogonally.r61 AM1 calculations, performed by us, predict that all substituents in l a should be
twisted by 90" from coplanarity. The flattened form of this
double betaine observed in the crystal, however, is presumably the result of a compromise between intramolecular
minimization of charge repulsion and intermolecular maximization of charge attraction in the crystal lattice.
Owing to this electrostatic attraction of oppositely
charged substituent pairs, 1a forms a novel stacked structure
in the crystal lattice. The basic motif is shown in Figure 2.
The structure displays the following characteristic features :
1. The asymmetric structural units form a racemate by alternating stacking of enantiomers along the c axis.
2. The charged ligands are each located within the electrostatic attraction region of an oppositely charged ligand of
the neighbor in the stack.
3. The midpoints of the central double bonds are separated
by 481 pm in the stack. Along the c axis, the projection of
each of these double bonds relative to the two identically
positioned neighboring systems is shifted parallel to the b
axis by 94 pm (cf. also Fig. 3). A direct interaction of the
olefinic double-bond moieties is not expected for this spatial arrangement.
4. The shortest intrastack contacts (225 pm) are formed between two carboxylate oxygen atoms of a given quadrupole l a and a partially positively charged DMAP a-H
atom of each of the two nearest neighbors in the stack.
Both the short distances and the spatial arrangement of
the interacting centers (linear O...H-C sequence, CO...H angle) show that these contacts must involve hydrogen bonds.['] As revealed in Figure 2, each molecule of
1a in the stack is anchored by four H-bond systems. As
shown by more detailed analysis using molecular models,
this favorable situation for interaction is due to the alternating stacking of enantiomers of l a to form the racemate.
In the projection along the c axis, the stacks of l a are
approximately X-shaped. In the crystal, these structural
units, containing lipophilic end groups (methyl groups of the
NMe, substituents) are joined together as shown in Figure 3.
The remarkable novel solid-state structure thereby resulting
contains as structural elements both an undulating layer lat-
P
0
Fig. 2. Hydrogen bonding and stacking of
four molecules of 1 a in the crystal (stereoview, projection along the b axis).
Angew. Chcm. i n f . Ed Engl 29 (1990) No. 10
8
0 VCH
Verlagsgesellschaft mbH, 0-6940 Weinherm, 1990
057~~-0833~90l1010-1133
$3.50+.25/0
1133
tice (distance between layers 0.33 nm) and rhomboidal channels (shorter diameter 0.7 nm, longer diameter 1.4 nm).
In the present case, as shown in Figure 3, the cavities are
filled with H,O molecules. Thus, it appears that this intriguing host lattice should be able to accept other polar and ionic
U
0
0
Fig. 3. Perspective drawing of the packing of the stacks of 1 a (projection along
the c axls) with the oxygen atoms of the molecules of crystal water.
guest molecules as well. Corresponding investigations have
already been initiated.
Received: March 9, 1990 [Z 3846 IE]
Publication delayed at authors’ request
German version: Angew. Chem. 102 (1990) 1164
CAS Registry numbers:
1 (Y = CO,H, X = NH,), 128191-80-0; l a . 6H,O (L = DMAP), 128191.786; l a (L = DMAP), 128191-79-7; 4 (L = DMAP), 128191-81.1; 5
(L = DMAP), 128191-82-2.
PI
The following reaction enthalpies were calculated for the isomerization of
1 to 2 by using the MNDO and AM1 methods: for Y = COO and
X = DMAP, -26.7 (MNDO) or -27.6 (AM1); for Y = C O O and
X = NH,, -37.7 (MNDO) or -51.1 kcal mol-’ (AM1).
I21 R. Weiss,N. J. Salomon, G. E. Miess, R. Roth, Angew. Chem. 98(1986)925;
Angew. Chem. Int. Ed. EngI. 25 (1986) 917.
[31 For further details, see R. Roth, Disserlutron, Universitit ErlangenNurnberg 1989.
[41 Colorless crystals, m.p. 170- 173 “C (dec.). IR (Nujol): C (cm-’) = 3400 (br,
m), 1650(sh), 1625(vs), 1570(m), 1210(m), 1190(m), 1070(w), 1030(w),
950(w), 930(w), 825(m), 780(w), 760(m). I3C NMR (100.6 MHz. D,O):
d = 41.06, 109.25, 138.65, 141.72, 157.62, 166.35.
151 Crystal structure data for 1 a . 6 H 2 0 : M, = 464.48, monoclinic, space
group CZ/r, a = 1773.5(7),b = 1479.7(5),c = 942 8(3) pm, = 108.75(3)”,
V=2.3428nm3,Z=4,@,,,,,,= 1.32gcm-’,MoK,radiation(T=293K),
graphite monochromator, Nicolet R3m/V diffractometer. 2310 unique reflections (4 < 2 8 < 52”), 1290 wlth F > 5o(n observed, 147 parameters
refined. The structure was solved by direct methods (SHELXTL PLUS).
Non-hydrogen atoms were refined anisotropically. Hydrogen atoms of the
water molecules were not included, the other hydrogen atoms were incorporatedusingarigidmodel.R=O.O72,R,=0085[w~’ = a 2 ( F j +O015F2].
Further details of the crystal structure investigation may be obtained from
the FachinformationszentrumKarlsruhe. Gesellschaft fur wissenschaftlichtechnische Information mbH, D-7514 Eggenstein-Leopoldshafen2 (FRG),
on quoting the depository number CSD-54565 the names of the authors,
and the journal citation.
161 W. G. Town, R. W. H. Small, Acta Crystaiiogr. Sect. B 29 (1973) 1950.
[71 R. Taylor. 0. Kennard, J. Am. Chem. SOC.104 (1982) 5063.
1134
0 VCH
Verlugsgeselischufi mbH, D-6940 Weinheim, 1990
Phenyl-Linked Quinone-Substituted Porphyrin
Trimers**
By Jonathan L. Sessler* and Vincent L. Capuano
Long-distance photoinduced electron-transfer (ET) reactions have attracted considerable attention due to their importance in many biological processes as well as their significance in solar energy conversion devices.“] Of notable
interest are those ET reactions which occur upon photoexcitation of the bacterial photosynthetic reaction centers
(RC’S).‘~’However, the complexity surrounding the reactive
components in the RC’s poses a significant challenge to the
understanding of the mechanisms operating throughout the
charge separation process.
While experiments performed on native RC’S[’-~Iand on
model systems[’361 have helped to clarify those factors, such
as distance, orientation, energetics, and medium, which control long-distance ET reactions, the unification of experiment with theory[’. has proven problematic. A particular
area of ambiguity concerns the role, if any, of the intermediate monomeric bacteriochlorophyll (BChl) in mediating the
initial ET step from the photoexcited special pair (SP*) donor to the bacteriopheophytin (Bph) acceptor.17]An attractive, but as yet experimentally unconfirmed, mechanism
casts this BChl prosthetic group in the role of a “superexchange” mediator, facilitating the long-range (1 7-A centerto-center) SP*-to-Bph ET p r o c e ~ s . [ ~ - ~ ~
Given the controversial nature of this hypothesis we have
over the past few years sought to develop a series of acceptor-substituted porphyrin-type model systems which contain
a variety of chromophores held in well-defined rigid arrangements. We have recently reported the synthesis and study of
several elaborated quinone-substituted porphyrin dimers in
which evidence for apparent porphyrin-based “superexchange”-mediated ET behavior was obtained.I6] More sophisticated systems, however, might allow for a further probing of this behavior as well as other related mechanistic
questions. We have recently turned our attention, therefore,
to the development of model systems containing more than
two porphyrin subunits.
In this communication we wish to report the synthesis and
photophysical properties of the bis-quinone phenyl-linked
trimeric porphyrin 1, which, to the best of our knowledge,
represents the first acceptor-substituted porphyrin trimer.” O1
In addition, we report the synthesis of the quinone-free control system 2.[”1
The syntheses of the title compounds 1 and 2 are based on
the condensation between the a-unsubstituted dipyrrylmethane 7 and the functionalized porphyrins 9 and 11, respectively, using a modified procedure for formation of porphyrin trimers.[’2] The central porphyrin is constructed in
the final bond-forming sequence. The starting materials 7,9,
and 11 were prepared using modifications of methods which
we and others have recently reported.[’. 61 Specifically,
dipyrrylmethane 3 was prepared by the acid-catalyzed condensation of 4-(hydroxymethy1)benzaldehyde (introduced in
the form of its diethyl acetal)[l3I with ethyl 3-ethyl-4-methyl2-pyrrolecarboxylate (75% yield) and was saponified and
decarboxylated in boiling ethylene glycol to give 4 as a pale
tan solid (m.p. 149- 151 “C, 95% yield).[141Compound 4 was
[*I Prof J. L. Sessler, V. L. Capuano
Department of Chemistry, University of Texas at Austin
Austin. TX 78 712 (USA)
[**I This work was supported by The Robert A. Welch Foundation, the
Camille and Henry Dreyfus Foundation (Teacher-Scholar Award to
J.L.S.), and The National Institutes of Health (GM 41 657 to JL.S.)
OS70-0833j9OjlOlO-11343 3.S0+.25/0
Angen,. Chem. I n [ . Ed. Engl. 29 (1990) No. 10
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