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ence of the diazene, and that 1,2-di-p-tolyldiazene, which is
more difficult to reduce, reacts more slowly than 1,2diphenyldiazene. The hole in the valence band ( h + ) that is
created at the same time oxidizes the ether via an intermediate radical cation to an allyl-stabilized radical 'R3. Recombination of RI-N-NHR' with 'R3affords the final product 1.
The intermediacy of the radical 'R3 is deduced from the
formation of the dehydrodimers R3-R3 as side products.
Regioisomeric products, which could arise from the ally1
rearrangement of the dihydropyranyl radical, have not been
1984, 106,6222-6230; H. Al-Ekabi, P. de Mayo, J. Org. Chem. 1987,52,
141 S. Yanagida, K. Mizumoto, C. Pac,J. Am. Chem. Sac. 1986,108,647-654;
P. de Mayo, G. Wenska, J Chem. Sac. Chem. Commun. 1986, 941 -942.
[5] a) J. Bucheler, N. Zeug, H. Kisch, Angew. Chem. 1982, 94, 792-793;
Angew. Chem. Int. Ed. Engl. 1982, 21, 777; b)N. Zeug, J. Bucheler, H.
Kisch, J Am. Chem. SOC.1985,107,1459- 1465; c) S. Yanagida, T. Azuma,
Y Midori, C. Pac, H. Sakurai, J Chem. SOC.Perkin Trans. 2 1985, 14871493.
[6] a) This corresponds to the conversion of 3.6 monolayers of 1.2-diphenyldiazene per hour, if it is assumed that a monolayer consists of 1014 particlescm-*; for ZnS (see Experimental Procedure) 2.2 monolayers per
hour; see L. P. Childs, D. F. Ollis, 1. Catai. 1980,66,383 -389. The specific
surface area determined by N, adsorption for CdS and ZnS is 120 and
100m2g-', respectively. h) We thank Prof. Dr. G. Emig, University of
Erlangen-Numberg, for these measurements.
[7] This was also observed in the system henzaldehyde/3,4-DHP: A. G. Griesbeck, S. Stadtmuller, J Am. Chem. Sac. 1990, 112, 1281-1283.
[8] P. S. Engel, W.-X. Wu, J Am. Chem. Sac. 1989, 111, 1830-1835.
[9] G. 0 . Schenck, H. Formanek, Angew. Chem. 1958, 70, 505; R. C . Cookson, 1. D. R. Stevens, C. T. Watts, Chem. Commun. 1965, 259-260; G.
Ahlgren, Tetrahedron Lett. 1974, 2779-2782.
[lo] A. Kurian, C. V. Suryanarayana, J. Appl. Electrochem. 1972.2.223-229.
11 11 W. Hetterich, H. Kisch, Chem. Ber. 1989, 122, 621 -627.
M= Zn, Cd
Scheme 2. Postulated photocatalysis cycle.
The proposed mechanism is supported by the irradiation
(A 2 290 nm) of a dilute solution of 1,2-diphenyldiazene and
benzophenone in 3,4-DHP. This reaction also affords the
addition product l a regioselectively in a yield of 30% according to HPLC. In the excited triplet state, benzophenone,
which functions as sensitizer in this system, abstracts an H
atom from 3,4-DHP.['] The benzhydryl radicals that result
react with 1,2-diazenes to afford the corresponding hydrazyl
radicals,[81which recombine with the dihydropyranyl radicals to form l a .
The overall reaction corresponds to an addition of an
allylic C-H bond of a cyclic enol ether to a diazene group, a
reaction type that was hitherto known only for electron-poor
diazenes like azodicarboxylic acid esters.['] Thus, we have
shown for the first time that two different organic substrates
can be coupled to form a linear addition product on the
irradiated surface of a semiconductor.
By Peter Paetzold,* Laurence Gkret-Baurngarten, and
Roland Boese
Dedicated to Professor Hermann Stetter
on the occasion of his 75th birthday
As ab initio calculations show,"] the diboriranes 1 a-4a
(R = R = H) have a tendency to contract the B-B distance
and open the H-B-B angle with increasing electronegativity
of Y. This behavior is similar to that of the corresponding
heterocyclopropanes and disiliranes.
1 . Y = BR
I \
Y = CR,'
3 , Y = NR
4 , Y = O
Experimental Procedure
All manipulations were conducted under an inert atmosphere of N, with dry,
N,-saturated solvents. ZnS and CdS were prepared according to [lo] and [ll].
General procedure: 1,2-diphenyldiazene (0.5 g, 2.74 mmol), ZnS (0.5 g,
5.13 mmol), 3,4-DHP (3.00 mL, 33.2 mmol), and MeOH (85.0 mL) or 1,4-dioxane/H,O (70.0/15 mL) were suspended in an ultrasound bath in a Pyrex immersion lamp apparatus for 15 min and thereafter irradiated with a Hg high-pressure lamp (Phillips HPK 125 W) until no more diazene could he detected hy
thin-layer chromatography (about 15 h). ZnS was filtered off, and evaporation
to dryness (25 "C) yielded a yellow oil. 1a and I d : white solids after two recrystallizations from MeOH (yield: 30 and 20% respectively); l b and l c : after
column chromatography (Al,O,/petroleum ether) 1b was isolated (40%) as a
pale yellow oil that yields a white solid on crystallization from petroleum ether
(10%). l c is isolated as colorless oil (30%).
Received: March 10, 1992 [Z5233IE]
German version: Angew. Chem. 1992, 104, 1102
CAS Registry numbers:
1a, 142065-25-4;1 b, 142040-07-6;1c, 142040-03-7;1d, 142040-04-8;3,4-DHP,
110-87-2; 4,5-DHE, 1191-99-7; PhN=NPh, 103-33-3; p-tolyl N=N p-tolyl,
501-60-0; PhN=NtBu, 1775-83-3.
[l] M. A. Fox, Top. Curr. Chem. 1987, 142, 71-99.
[2] A. J. Frank, Z. Goren, I. Willner, J Chem. Sac. Chem. Commun. 1985,
1029-1030; T. Shiragami, C. Pac, S. Yanagida, J. Phys. Chem. 1990, 94.
504 -506.
[3] A. M. Draper, M. Ilyas, P. de Mayo, V. Ramamurthy, J Am. Chem. Sac.
Verlagsgesellschaft mbH, W-6940 Weinheim, 1992
In the case of the azadiborirane 3, experimental crystal
structure determinations are only available for two derivatives with amino groups bonded to boron.['. 31 Since the electronic effect of these substituents is strong, a comparison
with theoretical predictions makes little sense. An alkyl
derivative (3 b, R = R = fBu) proved to be disordered in the
crystal.[41We have now prepared the first oxadiborirane, title
compound 4b, by initially converting the chloroborane 5
into the diboryl oxide 6 [Equation (a)] and, subsequently, 6
into 4 b through reduction with Na/K alloy [Equation (b)].
The colorless crystalline product 4 b shows only one NMR
signal in C,D, for each of the atoms H, B, and C.[51For the
structure of the parent compound 4 a determined by ab initio
methods, an NMR shift of 6(' 'B) = 67.0 has been calculat[*] Prof. P. Paetzold, L. Gkret-Baumgarten
Institut fur Anorganische Chemie der Technischen Hochschule
Templergraben 55, D-W-5100 Aachen (FRG)
Dr. R. Boese
Institut fur Anorganische Chemie der Universitat-Gesamthochschule
Universitatsstrasse 5-7, D-W-4300 Essen (FRG)
[**I Trisyl = tris(trimethylsi1yl)methyl.
Angew. Chem. Int. Ed. Engl. 1992, 31, No. 8
+ 2 M
I \
- B - B - C(SiMe3),
edC6lby the IGLO method, which agrees well with the measured value for 4b of 65.7. The X-ray crystal structure analysis of 4b[71confirms the three-membered ring structure with
an almost linear C-B-B-C moiety (Fig. 1). The 0 atoms are
disordered about the crystallographic C , axis and are therefore found with half the electron density on each side of the
B-B' bond. This disorder leads to centrosymmetry, whichas the isotropic dislocation parameters show-is strictly
valid for the C(SiMe,), groups. The same parameters indicate such a strong displacement of the ring atoms out of the
ring plane that an exact description of the ring geometry
becomes impossible.
metal ("a-bridged x bonding"). In oxadisilirane B (R =
Mes), which is related to three-membered rings of type 4
through the diagonal relationship in the periodic system, a
Si-Si distance of 2.23 8, is found,["] which is closer in length
to a double bond than to a single bond, each of these bond
lengths being found in a typical range, in contrast to B-B
bonds. Certainly, the short B-B and Si-Si distances of oxadiborirane and oxadisilirane can also be accurately described
by a model with bent bonds and no x interaction.["] The
remarkably long E U ) distances of 1.545 and 1.510 A in 4b
do not agree well with those calculated for 4a (1.409"' or
1.403 A['') and prove to be drastically longer than the 1.32 A
measured for the open-chain compound, (RO),B-B(OR),
((RO), = -OCMe,-CMe,O-),
that can be used for comparison. Because of the disordered 0 atoms, the C-B-B' and
B-B'-C'angles of 4b (177.7 and 182.3', respectively) can only
be compared with the values of 173.9'[11 and 175.2°[61calculated for 4a, insofar as these angles accurately reflect the
tendency toward linearization of the chain R-B-B-R on
passing from 1 to 4; the corresponding angles for unknown
three-membered ring compounds of type 1 where R = R are
expected to be 150".
The oxadiborirane 4b proves to be quite inert. In contrast
to the azadiboriridine 3b (R = R = tBu), it reacts neither
with C0,['21 nor with RN, (R = Pr, Bu),[l3] BH3,[I4l or
E ~ B = N z B u , [ and
' ~ ~ not even with alkynes RC=CR (R = Et,
Me,Si), whose reaction with the B-B bond of diborane(4)
derivatives is considered typical. It is inert even towards 0,
and H,O. Attempts to cleave the 0 atom reductively with
phosphanes PR, (R = Me, Ph) as acceptors left 4b intact.
The only reaction that we could find for 4 b is the oxidative
addition of formic or acetic acid in the ratio 1 :1 according to
Equation (c), in which the crystalline products 7a, b are ob-
Fig. 1. Molecular structure of 4 b in the solid state. The ellipsoids correspond
to 50% probability of electron occupation, hatched and unhatched atoms are
equivalent by crystallographic centrosymmetry, the disordered oxygen atom is
drawn as an ellipse with dashed outline. and the hydrogen atoms are omitted
for clarity. Selected distances [A] and angles ["I (standard deviations in parentheses): B - B 1.601(7), B-0 1.545(5), B'-0 1.510(6), B-C 1.544(4); 0-B-B
57.4(3). B-0-B' 63.2(3), C-B-0 120.2(3),C-B-B 177.7(3).
7a, R = H
7b, R = Me
tained in yields of 82 or 71 %,
not the acidic proton, but the carboxyl C atom is oxidizing.
In spite of disorder in the region of the B-B' bond, this
bond length can be determined with satisfactory accuracy to
1.60 A. It is almost as short as the B-B bond in anion A
(1 .58 A; R =
which is-to our knowledge-the
shortest B-B bond measured up to now. It is noteworthy, in
Experimental Procedure
Bis[chloro(tris(trimethylsilyl)methyl}horyl] oxide 6: Li,O (0.1 7 g) was added to
a solution of 5 (3.57 g) [I71 in THF (30 mL). The mixture was stirred for 10 h
at room temperature before the solvent was removed in vacuo, the residue
dissolved in pentane (20 mL), and LiCl filtered off. At -80°C 6 crystallized
(3.10 g, 95%, m.p. 198 "C) (181. The same product was obtained with a similar
procedure from 5 and NaOSiMe, in the ratio 2: 1 (75%).
Bis[tris(trimethylsilyl)methyl~oxadihorirane 4b: A solution of 6 (3.10 g) in hexane (30 mL) was heated under reflux in the presence of Na/K alloy (3 mL) for
10 h. The excess alloy and alkali-metal salts were filtered off, and the filtrate was
evaporated to dryness. Sublimation at 120~Cj0.005Torr afforded 4b (1.55 g,
57%, m.p. 242°C).
Received: March 27, 1992 [Z5268IEI
German version: Angew. Chem. 1992, 104, 1071
this context, that B-B bond lengths are scattered over a wide
range; the B7-B8 distance in B,,H,, of 2.01 A,[91for example, is still considered bonding. The B-B bond distance
calculated for 4a of 1.594 (3-21G) or 1.562A (MP2/631 G*[61)is close to that measured for 4b. Theory"' draws a
picture of a diborane(2), RB=BR, that is bridged by an 0
atom in analogy to an olefin bonded side-on by a transition
Angew,. Chem. Inr. Ed. Engl. 1992, 31, No. 8
CAS Registry numbers:
4b, 142066-17-9; 6, 142066-18-0; 7a, 142066-16-8; 7b, 142066-19-1; HCO,H,
64-18-6; MeCO,H, 64-19-7.
[I] C. Liang, L. C. Allen, J. Am. Chem. Sor. 1991,113, 1878-1884; Calculations with the 3-21G hasis set.
121 F. Dirschl, E. Hanecker, H. Noth, W. Rattay, W. Wagner, Z . Nalurforsch. B 1986, 41, 32-31.
Verlagsgesel~schaf!mbH. W-6940 Weinheim. 1992
S 3.50-k .25/0
(31 K.-H. van Bonn, P. Schreyer, P. Paetzold, R. Boese, Chem. Ber. 1988,12f,
[4] R. Boese, B. Krockert, P. Paetzold, Chem. Ber. 1987, 120, 1913-1915.
[5] 4b: NMR(C,D,): 6('H) = 0.29; 6("B) = 65.7; S(I3C) = 4.33(q); according to experience the signal for the B-bonded C atoms is broad and was
not resolved.
[6] We thank P. von R. Schleyer and M. Buhl, Universitat Erlangen, for the
calculations with the 6-31G' hasis set at MP2 level, which they completed
for us before the paper of Allen et al. [l] appeared.
[7] Crystal data of 4b: a = 16.033(3), b = 8.906(2), c = 23.781(4) A, 6 =
109.06(1)", V = 3209.5(1.0) A', T =lo3 K, 2 = 4, pealed
= 1.036 gem-,,
C2/c (no. 15); Nicolet R3m/Vdiffractometer; p(Moxm)= 2.6 cm-'; range
3 s 28 5 40 '; 2098 independent reflections, 1798 of which observed with
Fo 2 4a(F); anisotropic temperature factors for non-hydrogen atoms;
163 refined parameters; R = 0.0424, R , = 0.0520. Further details of the
crystal structure investigation may be obtained from the Fachinfonnationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-W-7514 Eggenstein-Leopoldshafen 2 (FRG) on quoting the depository number CSD-320470, the names of the authors, and
the journal citation.
[8] H. Meyer, G. Schmidt-Lukasch, G. Baum, W. Massa, A. Berndt, Z . Naturforsch. B 1988, 43, 801 -806.
[9] J. S. Kasper, C. M. Lucht, D. Harker, Acra Crystaiiogr. 1950,3,436-455.
[lo] H. B. Yokelson, A. J. Millevolte, G. R. Gillette, R. West, J. Am. Chem. SOC.
1981, 109, 6865-6866,
[ l l ] I. A. Boatz, M. S. Gordon, J. Phys. Chem. 1989,93, 3025-3029.
[12] H. Notz, Z . Narurforsch. B 1984, 39, 1463-1466.
[13] P. Paetzold, B. Redenz-Stormanns, R. Boese, Angew. Chem. 1990, 102,
910-911; Angew. Chem. Int. Ed. Engl. 1990,29,900-903.
[14] P. Paetzold, B. Redenz-Stormanns, R. Boese, M. Biihl, P. von R. Schleyer,
Angew. Chem. 1990, 102, 1059-1060; Angew. Chem. Int. Ed. Engi. 1990,
29, 1059.
[15] P. Paetzold, B. Redenz-Stormanns,R. Boese, Chem. Ber. 1991,124,14352441.
[16] 7a: m.p. = 228°C (from pentane); NMR(C,D,): 6('H) = 0.30 (s, 54H),
4.85 (s, 2H); 6("B) = 32.7; 6(I3C) = 5.l(q), 84.3(t). -7b: m.p. =142"C
(from pentane); NMR(C,D,): S('H) = 0.27 (s, 54H), 1.54 (d, 3H), 4.12
(q, 1 H); 6("B) = 32.3; a("C) = 4.2(q), 30.5(q), 89.3(d).
[17] S. S. Al-Juaid, C. Eaborn, M. N. A. El-Kheli, P. B. Hitchcock, P. D. Likkiss, M. E. Molla, I. D. Smith, I.A. Zora, J. Chem. SOC.Dalton Trans.
[18] 6 : NMR(C,D6):6('H) = 0.32(~);6("B)=40.4;S('~C)= 5.2(q), 19.4(s).
troscopy shows only the intense So -t S, transition. Likewise, normally no information can be gleaned from fluorescence spectroscopy about the energetic situation of S, in
long-chain polyenes such as ,&carotene.
Experiments showed that shorter polyenes containing
fewer than nine double bonds generally fluoresce from the
first singlet state S,, a state forbidden for absorption, whereas longer carotenoids containing more than eight 71 bonds,
such as p-carotene, show an anti-Kasha emission from the S,
state.["] We now report the synthesis of novel, modified
carotenoids with nine and eleven 71 bonds, for which dual
fluorescence (that is, emission from the S, and the S, state)
occurs, and thus the energetic level of S, can be determined
at least approximately.
In the planning of the synthesis of modified, sufficiently
photostable carotenoids, we were first guided by the idea of
substituting the saturated ethano fragments in lycopene by
conjugatively stabilizing carbonyl groups (oxalyl fragments).
To achieve this we linked two C, end components with a C,
central component (dialdehydes 1-4) according to the synthesis principle c., + c, + c, = c, + 8 . As shown in Figure 1, the diones 7- 10 and the tetrones 11- 14 can be obtained
in this way (Table 1). Whereas the color of the diones 7-10
Dual Fluorescence of Novel Modified
By Hans Betterrnann,* Martin Bienioschek,
Hans Ippendog, and Hans-Dieter Martin*
Fig. 1. The synthesis of tetramethoxydiapocarotenediones 7- 10 and diapocarotenetetrones 11-14. Compounds 5 or 6 may be used to provide the carbony1 groups.
Carotenoids are counted among the most important and
also most numerous naturally occurring chromophores.".
In the photosynthesis of higher plants, algae, and bacteria
they assume a dual role: a) they absorb energy as accessory
pigments (antenna function); thus they aid in energy transfer
and b) they quench the triplet state of various chlorophylls
or remove reactive or excited oxygen species.
The key to the understanding of the energy transfer processes in carotenoids is a knowledge of their lowest excited
and TI
states, in particular the states S, (2'A,), S, (llBu),
(CZhsymmetry assumed). Unfortunately little is known
about the energy of S, and T,, in spite of intensive spectroscopic investigation^:^^ - lo] conventional absorption spec[*] Dr. H. Bettermann, DipLChem. M. Bienioschek
Institut fur Physikalische Chemie und Elektrochemie der Universitat
Universitatsstrasse 1, D-W-4000 Dusseldorf (FRG)
Prof. Dr. H.-D. Martin, Dipl.-Chem. H. Ippendorf
Institut fur Organische Chemie und Makromolekulare Chemie der Universitat Dusseldorf
[**I Chromophoric Systems, Part 5. This work was supported by the Deutsche
Forschungsgemeinschaft, the Fonds der Chemischen Industrie and BASF
AG. Part 4: H.-D. Martin, T. Werner, J. Mol. Strucr., 1992, 244, 91-96.
Verlagsgesellschaft mhH, W-4940 Weinheim. 1992
Table 1. Selected physical data of 6-14 [a].
6 : MS(70 eV): m/a 209 ( M + )
7: M.p. 174"C, MS(70eV): m/z 392 ( M ' ) , UV/VIS(CHCl,): A[nm](&)= 409
(64000), 433 (63 500)
8: M.p. 157"C, MS(70eV): m/z 444 ( M ' ) , UV/VIS(CHCl,): I[nm](&)= 457
(79 000), 484 (73 000)
9: M.p. 204"C, MS(70 eV): m/a 524 (M'), UVjVIS(CHC1,): I[nm](&)= 499
(99800), 530 (85900)
10: M.p. 216"C, MS(70eV): m/z 576 (M'), UV/VIS(CHCI,): A[nm](&)= 515
(119000), 555 (87500)
11: M.p. 1 9 7 °C MS(70eV): m/a 300 ( M I ) , UVjVIS(CHC1,): A[nm](&)= 442
(36900), 468 (33800)
12: M.p. 190°C MS(70 eV): m / z 352 (W),UV/VIS(CHCl,): A[nm](&)=
488 nm (59700), 510 (60900)
13: M.p. 217"C, MS(70 eV): m/z 432 (M'), UV/VIS(CHC13):A[nm](&)= 532
(85300), 555 (80800)
14: M.p. 240°C, MS(70 eV): m/z 484 ( M + ) ,UV/VIS(CHCI,): I[nrn](&)= 549
(112000), 580 (110000)
[a] All compounds have the correct elemental analysis. The compounds were
purified by column chromatography, and their purity tested by thin-layer chromatography.
0570-0833/92/0808-f042$3.S0+ ,2510
Angew. Chem. Int. Ed. Engl. 1992, 31, No. 8
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