Expression of the prohelicity of bis-cyclomanganated 2,3-diphenylquinoxaline through reactions with diaryldiazomethanes

Article abstract of DOI:10.1039/b111570g

The reactions of bis-cyclomanganated 2,3-diphenylquinoxaline with diazodiphenylmethane and 9-diazofluorene allowed the formation of a new oligomeric and dinuclear manganospiralene and the ready preparation of a pentacyclic helix comprising two (η⁵

Full text of DOI:10.1039/b111570g

Expression of the prohelicity of bis-cyclomanganated
2,3-diphenylquinoxaline through reactions with diaryldiazomethanes†
André de Cian,a Jean-Pierre Djukic,*a Jean Fischer,a Michel Pfeffer*a and Karl Heinz Dötz*b
a UMR 7513 CNRS, Université Louis Pasteur, 67070 Strasbourg, France.
E-mail: djukic@chimie.u-strasbg.fr; pfeffer@chimie.u-strasbg.fr
b Kekulé Institut für Organische Chemie und Biochemie der Universität Bonn, Gerhard-Domagk str. 1,
53121 Bonn, Germany. E-mail: doetz@uni-bonn.de
Received (in Cambridge, UK) 20th December 2001, Accepted 7th February 2002
First published as an Advance Article on the web 25th February 2002
The reactions of bis-cyclomanganated 2,3-diphenylquinoxa-
line with diazodiphenylmethane and 9-diazofluorene al-
lowed the formation of a new oligomeric and dinuclear
manganospiralene and the ready preparation of a penta-
cyclic helix comprising two (h5-fluorenyl)Mn(CO)3 frag-
ments, whose helicity can be locked upon one-dimensional
linear coordination to silver cation.
insertions of Ph2CN2 in a CAr–Mn bond result in an increase of
the torsion angle between the two phenyl groups and the
heterocycle, thus yielding a much less sterically congested
product 1c (Scheme 1). In complex 1c, the heterocycle is
embedded between the two endo phenyl rings (Fig. 1). The
stacking of the aromatic rings is characterised by interplanar
angles of ca. 20° and distances between centroids of vicinal
rings of ca. 3.4 Å. The phenylene rings are twisted by a value of
ca. 50° with respect to the central heterocycle, and are mutually
involved in CH–p interactions8 through the hydrogen atoms
located at C21 and C50 respectively.
The conformational stability of helicenes depends mostly on the
number of fused rings1 whose geometrical features contribute in
defining the overall ‘chirality’.2 Bis-cyclometallated 2,3-di-
phenyl-substituted quinoxalines and pyrazines such as those
studied by Steel and Caygill3 [M = Pd(II)]] can be considered
as dipallada-analogs of pentahelicenes as they possess the
structural features of pentahelicenes, i.e. a low barrier to
conformational change4 and the rich reactivity of the chelated
metal centers.5 Helicity in the solid state stems from the steric
repulsion existing between the two metallated phenyl groups
connected at the 2- and 3-positions of the diaza-benzene ring.
Such a chiral helical system is fluxional in solution and can be
qualified as being ‘prohelical’ rather than strictly helical. We
were interested in studying the stereochemical features of
reactions occurring in the coordination sphere of each chelated
metal in a such dinuclear substrate and in evaluating to what
extent this intrinsic ‘prohelicity’ could be advantageously used
in the stereoselective synthesis of polynuclear manganospir-
alenes.6
Complex 1b reacted smoothly with 9-diazofluorene in
refluxing toluene to yield a new, stable bimetallic product 1d
(79% yield) containing three 1,2-disubstituted aromatics and
The reaction of 2,3-diphenylquinoxaline 1a7 with
(Ph2CH2)Mn(CO)5 afforded the dinuclear complex 1b [eqn.
(1)].†
Fig. 1 ORTEP diagram of the structure of 1c drawn at the 30% probability
level. Hydrogen atoms are omitted for clarity; selected bond lengths (Å) and
absolute torsion angle (°): Mn(1)–N(1) 2.057(3), Mn(1)–C(4) 2.161(4),
Mn(1)–C(17) 2.203(3), Mn(1)–C(22) 2.401(3), Mn(2)–N(2) 2.043(3),
Mn(2)–C(33) 2.154(4), Mn(2)–C(46) 2.220(3), Mn(2)–C(51) 2.388(3);
C(22)–C(23)–C(52)–C(51) 8.5. Selected angles (°) between mean planes P1
(C34–C35–C36–C37–C38–C39), P2 (N1–C23–C52–N2–C25–C26–C27–
C28–C29–C24), P3 (N1–C23–C52–N2–C25–C24) and P4 (C51–C50–C49–
C48–C47–C46): P1–P2 22.3, P3–P4 53.5. Distance (Å) between centroids,
Cgn, of planes Pn: Cg1–Cg3 3.43.
(1)
Complex 1b reacted smoothly with an excess amount of
Ph2CN2 in a mixture of boiling toluene and heptane. The
reaction product, 1c, which was purified by conventional flash
chromatography and recrystallised, was recovered as an air-
stable dark-blue powder (60% yield). The structure of this
binuclear complex indicates clearly that the reaction of the two
equivalents of Ph2CN2 took place on opposite faces of the
substrate 1b, in an expected anti-fashion with respect to the
mean plane of the chelate (Fig. 1).‡ Two successive anti
† Electronic supplementary information (ESI) available: preparation pro-
cedure and spectroscopic data for 1b–d, crystal data for polymer 1e. See
http://www.rsc.org/suppdata/cc/b1/b111570g
Scheme 1 Two pathways in the sequential addition of Ph2CN2 to 1b.
638
CHEM. COMMUN., 2002, 638–639
This journal is © The Royal Society of Chemistry 2002

diffraction analysis showed that polymer 1e, spontaneously
crystallises as a conglomerate in the non-centrosymmetric space
group P212121. Similarly to 1d, the pentacyclic ligand of the
polymer 1e adopts a helical shape.
This study shows that bis-cyclomanganated 2,3-diphenyl-
1,4-diazabenzene compounds, through exaltation of their in-
trinsic prohelicity, are convenient substrates for the ster-
eoselective elaboration of helical molecules.
We thank the CNRS (France) and the DFG (Germany) for
financial support.
Notes and references
‡
For compounds 1c–e, the intrinsic low quality of the analysed crystals
yielded structures with poor resolution. Crystal data for 1c:
C
52H32Mn2N2O6, M = 890.72, monoclinic, P21/n, a = 15.6887(7), b =
16.7698(9), c = 15.9857(7) Å, b = 93.588(5)°, V = 4197.5(3) Å3, Z = 4,
Dc = 1.41 g cm23, m = 0.657 mm21, F(000) = 1824, l(MoKa) = 0.71073
Å, T = 294 K, dark blue, dimensions 0.20 3 0.14 3 0.10 mm. A total of
16 708 reflections were collected with 2.5 < q(°) < 27.51. R = 0.035, Rw
= 0.040, GOF = 1.040, maximum residual electron density 0.289 e Å23
.
3947 unique reflections had intensities I > 3s(I). CCDC reference number
176859.
For 1d: C52H28Mn2N2O6·CH2Cl2, M = 971.62, orthorhombic, Pbca, a =
14.8379(2), b = 35.4532(3), c = 16.3322(5) Å, V = 8591.6(3) Å3, Z = 8,
Dc = 1.50 g cm23, m = 0.769 mm21, F(000) = 3952, l(MoKa) = 0.71073
Å, T = 173 K, yellow, dimensions 0.16 3 0.13 3 0.10 mm. A total of
19 157 reflections were collected with 2.5 < q(°) < 27.48. R = 0.051, Rw
= 0.082, GOF = 1.415, maximum residual electron density 0.589 e Å23
3614 unique reflections had intensities I > 3s(I). CCDC reference number
176860.
For 1e: C53H31AgMn2N2O6·BF4·2CH3OH, M = 1176.48, orthorhombic,
P212121, a = 13.6186(5), b = 15.1375(7), c = 25.032(1) Å, V = 5160.5(4)
Å3, Z = 4, Dc = 1.51 g cm23, m = 0.930 mm21, F(000) = 2372, l(MoKa)
= 0.71073 Å, T = 173 K, red, dimensions 0.12 3 0.10 3 0.08 mm. A total
of 11 811 reflections were collected with 2.5 < q(°) < 27.48. R = 0.058,
Rw = 0.080, GOF = 1.513, maximum residual electron density 0.959 e
Å23. 3656 unique reflections had intensities I > 3s(I). CCDC reference
number 176861.
.
Fig. 2 ORTEP diagram of the structure of 1d drawn at the 40% probability
level. Hydrogen atoms and solvated CH2Cl2 are omitted for clarity; selected
bond lengths (Å) and angles (°): Mn(1)–C(15) 2.147(8), Mn(1)–C(7)
2.190(7), Mn(1)–C(14) 2.201(7), Mn(1)–C(13) 2.207(7), Mn(1)–C(12)
2.233(7); C(14)–C(15)–C(7) 105.5(6), C(15)–C(14)–C(13) 110.5(6),
C(14)–C(13)–C(12) 106.8(7), C(13)–C(12)–C(7) 107.9(6). Angle (°)
between mean planes P1 (C12–C13–C14–C15–C7) and P2 (C34–C35–C36–
C37–C38–C39): 12.7(4). Distance (Å) between centroids, Cgn, of planes Pn:
Cg1–Cg2 3.70.
5
two terminal (h -fluorenyl)Mn(CO)3 fragments.† In agreement
See http://www.rsc.org/suppdata/cc/b1/b111570g/ for crystallographic
data in CIF or other electronic format.
with analogous observations made for the reaction of XRe-
(CO)3L3 with C5H4N2,9 complex 1d likely results from the
formal insertion of a fluorenylidene moiety into the CAr–Mn
bond and a succession of subsequent haptotropic shifts that end
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5
by forming the final appended bis(h -fluorenyl)Mn(CO)3
complex (Scheme 2). The structure of 1d is helical in shape as
a result of the compact arrangement of the three central
1,2-disubstituted aromatics (Fig. 2). The two Mn(CO)3 moieties
point outwards to minimize steric interactions and allow
stabilising intramolecular p–p stacking.
The reaction of 1d with stoichiometric amounts of AgBF4 in
acetone cleanly afforded a new bright red linear hybrid
inorganic/organometallic polymer10 1e (Scheme 2).† Slow
recrystallisation of a crude sample of 1e from a THF–MeOH
solution by diffusion in n-heptane afforded red crystals. X-Ray
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Scheme 2 Reaction of 1b with 9-diazofluorene and reactivity of the product
1d towards coordination to Ag+.
CHEM. COMMUN., 2002, 638–639
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