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Endoreceptors with Convergent Phenanthroline Units A Molecular Cavity for Six Guest Molecules.

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the Ag'-Ag' distances are 493 and 490pm. Finally, the
N-Ag' distances to the bipyridine N atoms are 244-251 pm.
The coordination sphere around the central Ag' ion can be
regarded as a distorted octahedron, that around each of the
two other Ag' ions as a heavily distorted trigonal pyramid.
A mononucleari' O1 and two dinucleari3"]Ag' complexes of
related macrobicyclic ligands have been reported earlier. The
cryptate 6 constitutes the first trinuclear Ag' complex. The
three metal ions are arranged in a row, held at well-defined
distances, and bound in two different environments, the central one being a tris-bipyridine Ag' site. Cryptand 3 offers the
possibility of preparing homo- or heterometallic trinuclear
metal cryptates that should display different binding, electrochemical, and photophysical properties for the terminal
and the central metal ions, making available a range of novel
features. For instance, a Cu'-Ag'-Cu' heterodinuclear complex has already been prepared. Further development of the
present work will also include the encapsulation of organic
substrates inside the cavities of macrobicycles 3 and 4 either
as free bases or as protonated and alkylated derivatives.
PI F. Ebmeyer, F. Vogtle, Chem. Ber. 122 (1989) 1725.
161 A. J. Mancuso, D. Swern, Synthesis 1981, 165.
[71 B. J. Hathaway, D. G. Holah, J. D. Postlethwaite, J. Chem. SOC.1961,
3215.
181 Crystal structure data for 3: C4,H,8N,,4 H,O, colorless crystals. monoclinic, space group P2Jc (No. 14); M , = 893.06; u = 1721.6(3),
b = 1631.0(2), c = 1719.6(3)pm. = 97.98(4)"; V = 4782(1) x lo6 pm3.
Z = 4; e..,., = 1.241 gcm-'; Cu,, ( A = 1.5418 A); p = 0.63 m m - I ;
F(OO0) = 1896; T = 296 f 1 K; crystal dimensions, 0.20 x 0.20 x
0.30 mm; CAD4 diffractometer (Enraf Nonius); corrections: Lorentz polarization, linear ca. 45% decrease (corrected with factors 1.00 to 1.53 on
I ) , empirical absorption correction (DIFABS) with minimum and maximum correction coeficients 0.884 and. 1.254; 28 = 4-100"; hkl range
h = - 1 17, k = - 1 -t 16, I = - 17 17; 6085 measured, 4918 unique
reflections, 3642 with I > 2.0 o(0. The structure was solved using
SHELXS. Refinement: full-matrix least-squares, R = 0.053, R, = 0.061
(w = w'[l.O-(AF/6 . U F ) ~ ]with
~ , w' = Chebychev polynomial for F, with
three coefficients (10.8, 4.3 und 7.95)), R,,, = 0.020. Crystal structure data
for 6 : [C,,H,,NI4Ag,](BF4),, pale yellow crystals, triclinic, space
group P-1 (No. 2); M , = 1405.02; a = 1358.0(1), 6 = 1433.3(3), c =
1576.7(2) pm, a = 106.95(1), = 99.98(1), y = 82.9911)"; V = 2894(1) x
lo6 pm3, Z = 2; Q..,.~ = 1.612 gem-,; Cu,, (A. = 1.5418 A); / I =
8.97mm-'; F(OO0)= 1396; T = 296 f 1 K; crystal dimensions, 0.15 x
0.15 x 0.20 mm; CAD4 diffractometer (Enraf Nonius); corrections:
Lorentz polarization, empirical absorption correction (DIFABS) with
minimum and maximum correction coefficients 0.759 and 1.532; 28 = 4130";hklrangeh = - 1 + 1 5 , k = - 1 6 - , 1 6 , / =- 1 8 - 18; 10488meaExperimental Procedures
. structure was
sured, 9596 unique reflections, 5415 with I > 3.0 ~ ( 4The
solved using SHELXS. Refinement: block-matrix least-squares (three
3: To a stirred solution of Tren (1: 0.047 g, 0.32 mmol) in 5 mL of anhydrous
= w'[I.O-(AF/6 . U F ) ~ ] ~
with
,
w' =
blocks), R = 0.058, R , = 0.070
acetonitrile was added dropwise at room temperature under argon a suspension
Chebychev polynominal for F, with three coefficients (16.3, - 0.097 and
of the dialdehyde 2 (colorless crystals, m.p. 228 "C; 0.1 g, 0.47 mmol) in acetoni12.9)), R,,, = 0.045. Non-hydrogen atoms refined anisotropically, H
trile ( 5 mL). The orange solid was filtered and recrystallized from methanol.
atoms calculated at their idealized positions (C-H distance 1.00 A) and
Colorless crystals; m.p. 280°C (CH,OH); yield 78%; UV-VIS (CHCIJ
included in the final structure factor calculations but not refined (CRYSCH,OH. 99:l): i.,,, [nm] ( E ) = 308 (85300) 263 (40 100); 'H NMR (200 MHz,
TALS and PLUTO programs). Further details of the crystal structure
CD,CI,. 25'C): 6 = 2.80 (m, 12H; CH,N<), 3.79 (m, 12H; CH,N=), 7.73
investigations are available on request from the Director of the Cambridge
(dd, 'J = 8.25 Hz, 4J = 2.40 Hz, 6 H ; H4), 7.89 (d, 'J = 8.25 Hz, 6 H ; H3),
Crystallographic Data Centre, University Chemical Laboratory, Lensfield
8.24 (s. 6 H ; CH = N), 8.40 (d, "5 = 2.40 Hz, 6 H ; H6); 13C NMR (50.3 MHz.
Road, GB-Cambridge CB2 1 EW (UK), on quoting the full journal citaCD,CI,/CD30D,99:1, 25°C); 6 = 53.5 (CH,N<), 58.3 (CH,N=), 121.3 (C3),
tion.
131.5 (C5),134.3 (C4), 150.3 (C2), 156.5 (C6), 159.8 (CH = N); MS (FAB',
191 The energy difference (steric energy) between the two conformations of the
m-nitrobenzylalcohol): mjz 821.4 ( M e H).
free ligand 3 and the conformation of the tris-Ag' complex 6 calculated by
4 . HBr: yield 52%; 'H NMR (200 MHz, CDCI,, CD,OD, 25°C): 6 = 2.7 (m.
MM2 can be estimated to be approximately 57 kJrno1-I [on an HP9000
12H; CH,N<), 3.3 (m, 12H; CH,NH-), 4.15 (s, 12H; Ar-CH,-NH), 8.00(d,
model 825SSRX; as option of the molecular modeling program
3J=8.25H~,6H;H3),8.40(dd,3J=8.25H~,4J=2.40,6H;H4),8.60(d, MOLEK9000 (version February 1991). P. Bischof, ISKA (Bensheim)].
'5 = 2.40.6H; H 5); MS (FAB', m-nitrobenzylalcohol): mi-. 833.6 ( M 6 + H):
I101 J. C. Rodriguez-Ubis, B. Alpha, D. Plancherel, J.-M. Lehn, Helv. Chim.
5 : yield 78%; UV-VIS (CHCI,/CH,OH, 99:l): ,ImaX[nm] ( E ) = 373 sh (15 loo),
Acta 67 (1984) 2264; b) B. Alpha, These de Doctoraf des Sciences, Uni303 sh (47300), 282 sh (49000), 263 (50200); 'H NMR (200 MHz, CD,CI,,
veriste Louis Pasteur, Strasbourg, 3987.
25°C): 6 = 3.19 (m, 12H; CH,N<), 3.90 (m, 12H; CH,N=), 8.05 (dd,
3J=8.20H~,4J=2.00H~,6H;H4),8.21(d,3J=8.20H~,6H;H3),8.70(~,
6 H ; CH = N), 8.94 (d, "J = 2.00 Hz, 6 H ; H6).
6 : yield 67%; UV-VIS (CHCI,/CH,OH, 99:l): A,, [nml ( E ) = 306 (73700),
274sh (47800); 'H NMR (200 MHz, CD,CN, 25°C): 6 = 3.10 (m, 12H;
CH,N<), 3.84 (m, 12H; CH,N=), 8.24 (dd, 'J = 8.20 Hz, 4J = 2.30 Hz, 6 H ;
H4), 8.42 (d, "J = 8.20Hz, 6 H ; H3), 8.77 (bc. S, 6 H ; CH = N), 9.63 (d.
Endoreceptors with Convergent Phenanthroline
4 J = 2.30 Hz, 6 H ; H6); 13C NMR (50.3 MHz, CD,CN, 25°C): 6 = 51.6
Units: A Molecular Cavity for Six Guest
(CH,N<), 58.8 (CH,N=), 123.9 (C3), 132.8 (C4), 140.9 (C5), 145.3 (C2),
154.0 ( C 6 ) , 162.0 (CH = N).
Molecules
-
-
(wj
+
**
Received: May 21, 1991 [Z 4636 IE]
German version: Angew. Chem. 103 (1991) 1365
CAS Registry numbers:
1, 4097-89-6; 2, 135822-72-9;3, 135852-89-0; 3.4H,O. 135822-73-0; 4.xHBr,
135877-62-2; 5, 135822-75-2; 6, 135852-91-4.
[l] J. E. Prne, G. Schwarzenbach, Helv. Chim. Acta 33 (1950) 963.
[2] a) J.-M. Lehn, S. H. Pine, E. Watanabe, A. K. Willard, J Am. Chem. Soc.
99 (1977) 676; b) B. Dietrich, M. W. Hosseini, J.-M. Lehn, R. B. Sessions,
Helv. Chim. Acta 68 (1985) 289; c) R. J. Motekaitis, A. E. Martell, I. Murase, J.-M. Lehn, M. W. Hosseini, Inorg. Chem. 27 (1988) 3630.
[3] a) J. Jazwinski, J.-M. Lehn, D. Lilienbaum, R. Ziessel, J. Guilhem, C.
Pascard, J. Chem. Soc. Chem. Cornmun. 1987, 1691; b) J.-M. Lehn, R.
Meric, J.-P. Vigneron, I . Bkouche-Waksman, C. Pascard, ibid. 1991, 62;
c) D. MacDowell, J. Nelson, Tetrahedron Lett. 29 (1988) 385; d) D. MacDowell, J. Nelson, V. McKee, Polyhedron 8 (1989) 1143; e) 0.Kocian, R. J.
Mortimer, P. D. Beer, Tetrahedron Lett. 31 (1990) 5069.
[4] See for instance: a) K. Kalyanasundaram, Coord. Chem. Rev. 46 (1982)
159; b) A. Juris, V. Balzani, F. Barigelleti, S . Campagna, P. Belser, A. von
Zelewsky. ibid. 84 (1988) 85; c) F. Barigelleti, L. de Cola, V. Balzani, P.
Belser. A. von Zelewsky, F. Vogtle, F. Ebmeyer, S . Grammenudi, J. Am.
Chem. SOC.1 1 1 (1989) 4662.
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 10
0 VCH
By Fritz Vogtle,* Ingo Liier, Vincenzo Balzani,
and Nicola Armaroli
The cagelike bridging of three 2,T-bipyridine units has so
far afforded ligands whose conformational flexibility allows
the nitrogen donor centers to be twisted."] The use of 1,lOphenanthroline instead of 2,2'-bipyridine promised to increase the preorganization of the binding sites directed toward the interior of large molecular cavities, as Lehri et a1.i2al
have described for smaller ligands. In this way, it should be
[*I Prof. Dr. F. Vogtle, Dipl.-Chem. I. Liier
Institut fur Organische Chemie und Biochemie der Universitlt
Gerhard-Domagk-Strasse 1, W-5300 Bonn J (FRG)
Prof. Dr. V. Balzani, Dr. N. Armaroli
Dipartimento di Chimica dell'Universita
via Selmi 2, 1-40 126 Bologna (Italy)
[**I This work was supported by the Bundesministerium fur Forschung und
Technologie (BMFT-0329120A). We thank Dr. G. Eckhardt and Dr. S.
Schuth, Universitat Bonn, for recording the FAB mass spectra and Prof.
Dr. E. Sleckhan and Dip1.-Chem. M . Frede, Universitat Bonn, for recording and interpreting the cyclic voltammograms.
Verlugsgesellschafi mbH, W-6940 Wernheim. 1991
0570-0833/9ljiO10-1333 $3.50+ ,2510
1333
possible to confine several organic guest molecules in the
interior of a single host molecule, thereby bringing them into
close proximity-a prerequisite for controlled reactions in
the cavities of tailored catalysts.
In the new endoreceptorsrZb12 and 3, the convergent arrangement of the donor centers realizes the desired extent of
endo preorganization of the binding sites, while the conformational flexibility made possible by the ether bridges
should result in little hindrance to the inclusion of guest
molecules. The synthesis of 2 and 3 was accomplished in a
one-step reaction of 2,9-bis(4-hydroxyphenyl)-l,1O-phenanthroline (l), introduced by Sauvage et al.,[31with 4[4a1and
5,[4b1respectively, in 11 % und 2.3 % yield. The 'H NMR
spectra, the FAB mass spectra, and the elemental analyses
are consistent with the host structures proposed; the formation of the corresponding macrobicyclic hosts containing the
spacers 6-10[4'-e1 was confirmed by FAB MS.
1
2:-
=4
3:-
=5
X
[Cu(CH,CN),]BF4 in CH,CN, followed by addition of a
solution of 11or 12 in CH,CI,, results in quantitative formation of complex 15 or 16, respectively, both of which are
stable in solution and to air. Elemental analysis gave the
correct empirical formulas for [15(BF4),] 3 H,O and
[16(BF4),] . 3 H,O and FAB MS and 'H NMR spectroscopy
established the presence of endo complexes. FAB mass spectra confirmed the composition of 15 and 16: peaks at m/z
2765 and m/z 2307 correspond to [15(BF4),]@ and
[16(BF4),]*, respectively; further peaks correspond to the
fragmentation products formed by stepwise loss of phenanM
throline and Cu'. The 'H NMR spectrum of 15 (5 x
in CD,CI,) indicates a symmetric arrangement of the guests
in the cavity: the signals of the OCH, protons are shifted to
higher field compared with those of the free ligand 2 by
A6 = 0.38 to give a single, somewhat broad signal at
6 = 5.00. The signals of the mutually interacting phenylene
groups of the bis(4-methylpheny1)phenanthroline (1 1) guest
and the bis(oxypheny1)phenanthroline unit of the ligand are
both shifted to higher field.[3b1The signals of the methyl
groups of the phenanthroline guest are shifted by AS = 0.06
to higher field (6 = 1.90) compared with those of the complex 11a; the signal intensities are those expected for a complex with three Cu* centers and three phenanthroline guests.
X
X
X
X
4 : X=Br
8 : X=Br
X
X
5 : X=CI
9 : X=Br
6 : X=CI
7 : X=Br
10: X=Br
Like the bipyridine cavities described earlier,[lbl 2 and 3
were expected to form inclusion compounds with trihydroxybenzenes. However, attempts to complex 1,3,5-trihydroxybenzene were unsuccessful, as were efforts involving
1,3,5-tris(4-hydroxyphenyl)benzene, which fits better into
the cavity. These results underline the demands of host/guest
complementarity.
Surprisingly, however, inclusion of 2,9-disubstituted 1 ,lophenanthrolines such as 11-14, as their Cu' complexes,
takes place in the interior of the macrobicyclic host 2. Treatment of a solution of 2 in dimethylformamide (DMF) with
In complex 16, the signals of the OCH, protons (6 = 4.78)
are shifted more strongly to higher field than those in 15
(AS = 0.6). The inclusion of neocuproine (12) also causes
high-field shifts of the signals for the phenylene protons of
the bis(oxypheny1)phenanthroline. The signals of the methyl
groups of neocuproine are at higher field compared with
those of complex 12a[3bl by AS = 0.2 and their intensity
ratios are those expected. Accordingly, 2 is a true endoreceptor. The convergent arrangement of the donor centers forces
the guest molecules to "dock" within the cavity. Steric factors prevent the guests from swinging freely.
R'120 : R = - C H ~
;R'=-H
130 : R=-CH3
;R ' = a
140: R = e O H
;R'=-H
The space available in the cavity of 2 is not unlimited,
however. Whereas three 2,9-disubstituted phenanthroline
molecules fit into the cavity, only two molecules of
bathocuproine (13, R = phenyl), which is larger, were found
by FAB MS to undergo inclusion under analogous conditions.
1334
0 VCH Verlagsgesell.schafimbH, W-6940 Weinheim, 1991
0570-0833/91/10l0-1334B 3.50+.25/0
Angew. Chem. hi.Ed. Engl. 30 (1991) No. 10
Although host 2 is sparingly soluble in CH,CI,, complexes 15 and 16, obtained by inclusion of 11 and 12, respectively,
are readily soluble. Attempts to synthesize 18, on the other
hand, led to a substance that was sparingly soluble in
CH,Cl, and could not be purified any further. 'H NMR
spectra indicate the presence of a mixture of 18 and 14a.
Table 1. Absorption and luminescence data for 11 a, 12a. 15, and 16 [a]
Complex
i:Fr
Ila
12a [fl
440
457
437
443
15
16
[nm] [b]
[nm] [c]
720
750
730
760
'p'"
x lo3 [d]
1.70
0.40
0.70
0.08
[ns] [el
237
73
170
50
[a] Room temperature, degassed CH,CI, solution. [b] Absorption maximum at
the longest wavelength. [c] From corrected emission spectra; estimated error
5 nm. [d] Quantum yield; estimated error ca. 25 %. [el Lifetime; estimated
error I 10 %. [fl See also [5b].
The absorption and luminescence data for I1 a and 12 a as
well as for 15 and 16 are summarized in Table 1 ;the emission
maxima are corrected. Figure 1 shows the absorption and
(uncorrected) luminescence spectra of 15 and 16. The photophysical properties of 12 a and similar complexes, including
the Cu' catenate, are well-investigated.r51The intense absorp-
hlnmlFig. 1. Absorption and (superimposed) uncorrected luminescence spectra of 15
(-)and
16 (---)in CH,CI,.
tion bands in the UV region are due to n-x * ligand-centered
transitions, while the bands appearing in the visible region
are assigned to metal-to-ligand charge-transfer (MLCT)
transitions. The three metal-containing chromophoric units
of the trinuclear complexes 15 and 16 are equivalent. The
luminescence bands of 15 and 16 should be assigned to an
MLCT-excited state involving the ligands 11 and 12, respectively. This assumption is based on the observed redshift of
the luminescence bands of 15 and 16 with respect to those of
11 a and 12a, respectively, which is expected on replacing a
ligand in I l a and 12a by the more basictse] bis(anisy1)phenanthroline unit of the macrobicyclic host. The tolyl substituents in 15 and 11 a protect the excited state against the
formation of short-lived exciplexes and this is reflected in an
increase in the luminescence intensity and lifetime compared
to those of 16 and 12a.15d1
Angew. Chern. Int. Ed. Engl. 30 (1991) No. 10
0 VCH
The stabilizing effect of tolyl substituents in the guest is
also evident in the cyclic voltammetry measurements on 15
and 16. Although adsorption effects at the glassy-carbon
working electrode make the investigation of the complexes
difficult, a chemically largely reversible reduction was detected for 15 and can be assigned to the formal transition
Cu' + Cuo. In contrast, 16 is reduced irreversibly.
The new type of complex offers the possibility of using the
methods developed by Sauvage et al.13d-'] to synthesize a
previously unknown type of catenane in which 2 would be
symmetrically interlaced with three crown ethers. The confinement and orientation of three guests in close proximity in
a single cavity, achieved here for the first time, opens up new
possibilities for the development of catalysts for selective
reactions between several oriented guests within a molecular
cavity.
Experimental Procedure
2: A solution of I (3.3 g, 9 mmol) in 250 mL of dry DMF and a solution of 4
(2.14 g, 6 mmol) in 250 mL of DMF were added simultaneously to a solution
of CsCO, (8 g) in 1.2 L of DMF under argon at 70°C over 15 h. The reaction
mixture was then stirred for an additional 15 h at 70°C. After removal of the
solvent, the residue was extracted into CHC1, and purified by chromatography
on silica gel (eluent: CH,CI,/MeOH, 10: 1) (R, value: 0.63); m.p. 282-285°C.
' H NMR (200 MHz, CDCI,/TFA): 6 = 5.38 ( s , 12 H), 7.35 (d. 12 H,
3J = 9 Hz), 7.63 ( S , 6 H). 8.08 (d, 12 H, ' J = 9 Hz), 8.37 (s. 6 H), 8.5 (d. 6 H.
3J = 8 Hz), 9.07 (d, 6 H, 'J = 8 Hz). FAB-MS (matrix: m-nitrobenzyl alcohol):
m/z 1321 ( M e
H). The extreme low solubility of 2 in pure CDCI, only
allowed an 'H NMR spectrum of unsatisfactory quality to be recorded; it is
clearly evident, however. that the shift of the OCH, protons is unchanged with
respect to the measurement in CDCIJTFA (6 = 5.39). the aromatic protons
absorb at 6 =7.17-8.33.
3: Synthesized analogously to 2. The product was obtained by column chromatography on silica gel (eluent: CH,CI,/MeOH. 40: 1) (R, value: 0.27); m.p.
263°C. 'H NMR (90 MHz, CD,CI,): 6 = 3.2 (t, 12 H, ' J = 5 Hz). 4.26 (t,
1 2 H , , J = 5 H z ) , 7.06 (d, 12H, ' J = 9 H z ) , 7.55 ( s , 6 H ) . 7.82 (d, 6 H .
'J = 8 Hz), 8.04 (d, 6 H, ' J = 8 Hz). 8.26 (d, 12 H, 'J = 9 Hz). FAB-MS (matrix :dithioerythritol/dithiothreitol+ 2 N HCI): m / z 1283 (100 %). ( M e + H),
1256 (1 7 %).
15- 17: [Cu(CH,CN),BF, (95 mg, 0.3 mmol) [6] in 15 mL of degassed CH,CN
was added to 2 (132 mg, 0.1 mmol) in 20 mL of degassed DMF with stirring
under argon. The solution turned red-brown. It was stirred for a further 10 min,
after which the phenanthroline guest (0.3 mmol), dissolved in 15 mL of
degassed CH,CI,, was added continuously over 1 h. After 3 h. the reaction
mixture was evaporated to dryness and the residue dissolved in CH,CI,. The
product was isolated by preparative layer chromatography (PLC) (eluent:
CH,Cl,/methanol. 10 : 1) and recrystallized from CH,Cl,/benzene. [15(BF.,),) .
3 H 2 0 : Fp = 302-303°C; [16(BF,),). 3 H,O: Fp = 285-287°C. I I a, l3a,
14a: Synthesized analogously to 12a [3 b].
The absorption spectra were recorded with a Perkin-Elmer 2.6 spectrophotometer; the luminescence spectra were obtained with a Perkin-Elmer 650-40
spectrofluorimeter. The emission lifetimes were measured with an Edinburgh
single photon counting apparatus. The quantum yields were determined with
[Os(bpy),12@as standard (@ = 5 x lo--' in CH,CN at room temperature) [7].
+
Received: June 4. 1991 [Z 46741El
German version: Angen,. Chem. 103 (1991) 1367
CAS Registry numbers:
1, 88498-43-5; 2, 136034-17-8; 3, 136059-97-7; 4. 18226-42-1; 5. 555-77-1; 11,
116287-98-0; Ila, 136059-96-6; 12.484-1 1-7; 13,4733-39-5;13a. 111290-82-5;
14a, 128039-68-9; 15, 136088-30-7; 16, 136088-32-9; 17. 136088-34-1.
[I] S. Grammenudi, F. Vogtle, Angen. Chem. 98 (1986) 1119; Angen. Chum.
Int. Ed. Engl. 25 (1986) 1122; b) F. Ebmeyer, E Vogtle, ibid. 10/ (1989) 95
bzw. 28 (1989) 79; c) J. M. Lehn, D. Lilienbaum. J. de Mendoza. E. Mesa.
J.-C. Rodriguez-Ubis, P. Vasquez, P.-M. Windscheif, R. Ziessel, K. Rissanen, F. Vogtle, ibid. 103 (1991) 1365 and 30 (1991) 1333; d) F. Ebmeyer,
F. Vogtle in: Bioorganic Chemistry Frontiers, Vol. 1, Springer, Berlin 1990,
p. 145.
[I] a) J.-C. Rodriguez-Ubis, B. Alpha, D. Planchel, J. M. Lehn, Hrlv. Chim.
Acta 67 (1984) 2264; b) J. M. Lehn, Angeu. Chem. 100 (1988) 91; Angew.
Chem. Int. Ed. Engl. 27 (1988) 89.
[31 a) C. 0. Dietrich-Buchecker, J. P. Sauvage, Tetrahedron Lert. 24 (1983)
5091; b) C. 0. Dietrich-Buchecker, P. A. Marnot, J. P. Sauvage, J. P.
Kintzinger. P. Maltese, Nouv. J. Chim. X (1984) 573; c) C. 0. DietrichBuchecker, P. A. Marnot, J. P. Sauvage, J. R. Kirchhoff, D. R. McMillin. J.
Chem. SOC.Chem. Commun. 1983.513; d) J. C. Chambron, C. 0. Dietrich-
Verlagsgesellschaft m b H , W-6940 Weinheim. 1991
0570-0X33~9lj1010-1335B3.50f.2510
1335
Buchecker, C. Hemmert, A. K. Khemiss, D. Mitchell, J. P. Sauvage,
J. Weiss, Pure Appl. Chem. 62 (1990) 8002; e) J. P. Sauvage, Arc. Chem. Res.
23 (1990) 319.
[4] a) E Vogtle, M. Zuber, R. G. Lichtenthaler, Chem. Ber. 106 (1973) 717; b)
K. Ward, J. Am. Chem. SOC.57 (1935) 914: c) H. Stetter, W. Bockmann,
Chem. Ber. 84 (1951) 834; d) B. Dung, F, Vogtle, J. Incfusiori Phenom. 6
(1988) 429: e) N. Sendhoff, W. Kikner, F, Vogtle. S . Franken, H. Puff,
Chem. Ber. 121 (1988) 2179.
1.51 a) A. K. Ichinaga, J. R. Kirchhoff. D. R. McMillin, C. 0. DietrichBuchecker, P. A. Marnot, J. P. Sauvage, Inorg. Chem. 26 (1987) 4290; b)
A. K. I. Gushurst, D. R. McMillin, C. 0. Dietrich-Buchecker, J. P.
Sauvage, ibid. 28 (1989) 4070; c) R. M. Everly, R. Ziessel, R. Suffert,
D. R. McMillin, ibid. 30 (1991) 559; d) R. M. Everly, D. R. McMillin, Phorochem. Phofobiof.50 (1 989) 71 1 ; e) N. Armaroli, V. Balzani, L. De Cola,
J. P. Sauvage, C. 0. Dietrich-Buchecker, J. M. Kern, unpublished; f)
N. Armaroli, V. Balzani, F. Barigeletti, L. De Cola, J. P. Sauvage,
C . Hemmert, J. Am. Chem. Soc. 113 (1991) 4033: g) Overview: V. Balzani,
F. Scandola: Supramolecular Photochemistry, Ellis Horwood, Chichester
1991.
[6] H. Meerwein, V. Hederich, K. Wunderlich, Arch. Pharm. Ber. Dtsch.
Pharm. Ges. 291 (1958) 541.
[7] E. M. Kober, J. V. Caspar, R. S . Lumpkin, T. J. Meyer, J. Phys. Chem. 90
(1986) 3722.
N
0
DCN'
Ph
PhC=N=CH-Ph
2
la
1
+
DCN'O
/
1
DCN'G
Ph
phQph
4a
DCN'e
eph
+
4b
CN
CN
Scheme 1. Products 4 a and b are formed in a 50 : 50 ratio
[3 + 21 Cycloadditions with Azirine Radical
Cations: A New Synthesis of N-Substituted
Imidazoles **
By Felix Muller and Jochen Mattay*
Dedicated to Professor Kurt Schaffer
on the occasion of his 60th birthday
Recently, much attention has been focused on the investigation of reactions involving photoinduced electron transfer
(PET), especially the PET-catalyzed ring opening of highly
strained carbo- and heterocycIes."l Here we report on the
reactions of azirines, a group of compounds frequently used
in 1,3-dipolar cycloaddition reactions,['' under photosensitized (electron-transfer) irradiation conditions.
Photochemical irradiation usually results in energy transfer to a substrate either by direct excitation or through a triplet
sensitizer. PET, however, generally proceeds by the irradiation of an electron acceptor. For this purpose cyanoarenes
such as 1,4-napthaIenedicarbonitrile(DCN) are very useful.
Since the n-n* transition of azirines such as 1 a occurs at
a wavelength of 280 nm,"] irradiation with light of 350-nm
wavelength does not lead to the direct excitation of the substrate. However, DCN is excited and abstracts an electron
from the azirine.t3] As observed for direct excitation,['] the
C-C bond of azirine is thereby broken. We regard the formation of the 2-azaallenyl radical cation 2 as an intermediate.
This species reacts with acrylonitrile under ring closure and
back electron transfer to give the five-membered ring 4. The
addition thus proceeds via a two-step mechanism. The photoinduced 1,3-dipolar cycloaddition of azirines described by
Padwa et aLf4]leads to a very high diastereoselectivity. Compound 4b is formed in a yield of 90%, whereas that of 4a is
just 10%. In contrast, we found a product ratio of 50:50
when DCN catalysis was used.
Scavenging with 2,2,2-trifluoroethanol resulted in 5 and 6
as products.r51Compound 5 is the trapped product of the
2-azaallenyl radical cation 2. The formation of 6 is easily
explained by the trapping of 3a/3b, which were formed
through reaction of 2 with acrylonitrile. Thus, dihydropyrroles 4 are not formed via a concerted [3 + 21 cycloaddition,
as is the case for direct irradiation.l4I
P h yN
H
3336
0 VCH
Erfagsgesellschafi mbH, W-6940 Weinheim, 1991
ThOCH,CF,
Ph
CN
5
6
The reaction does not proceed upon 350-nm irradiation in
the absence of DCN or in the presence of a triplet sensitizer
(benzophenone). When we compared the reactivity of 2 with
nitrile ylides generated by direct irradiation, we noted that
the reaction is favored for olefins substituted with electronwithdrawing groups; for instance, the reaction with vinyl
ethers does not lead to five-membered rings. If there is no
suitable reaction partner, azirines will dimerize, via [3 + 21
c y c l ~ a d d i t i o n [ ~to* ~give
] 9. Both nitrile ylides and 2-azaallenyl radical cations react with aldehydes and ketones to
form 3-dihydroo~azoles.[~~
R'
"yR2
R'\N
=?
A2
MeCN, DCN
[*] Prof. Dr. J. Mattay, DipLChem. F. Muller
Organisch-Chemisches Institut der Universitat Miinster
Orleansring 23, W-4400 Miinster (FRG)
[*'I Radical Ions and Photochemical Charge-Transfer Phenomena (Series A),
Part 31, and Cycloadditions (Series B), Part 35. This work was supported
by the Deutxhe Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and the state of Nordrhein-Westfalen. We also thank Bayer AG for
generous gifts of materials. F: M. would like to thank the Studienstiftung
des deutschen Volkes for a predoctoral grant. Series A, Part 30: J. Mattay,
M. Vondenhof, Top. Curr. Chem. 159 (1991) 219. Series B, Part 34: M.
Conrads, J. Mattay, Chem. Ber. 124 (1991) 1425.
PhN
q
yOCH,CF,
9a-c
la-c
k'
7a-b
Scheme 2. l a , R' = R Z = phenyl; l b , R' = phenyl, R2 = H; lc, R' = n-butyl, R2= H ; 7 a , R3 = phenyl, R4 = n-propyl, 7b, R3 = R4 = n-propyl.
0570-0833f9l~IOIO-l336
$3.50+.25/0
Angew. Chem. In/. Ed. Engl. 30 (1991) No. 10
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