Facial discrimination in monoarylporphyrins: Synthesis and stereochemical behaviour of bis(ligated) monospirobifluorenylporphyrin ruthenium complexes

Article abstract of DOI:10.1016/j.inoche.2007.02.006

Condensation of dipyrromethane, pyrrole-2-carbaldehyde with either 9,9′-spirobifluorene or fluorene aldehyde yields new meso-monosubstituted, β-unsubstituted porphyrins. The large size of spirobifluorene hinders the rotation around the C_meso-C<

Full text of DOI:10.1016/j.inoche.2007.02.006

Inorganic Chemistry Communications 10 (2007) 627–630
www.elsevier.com/locate/inoche
Facial discrimination in monoarylporphyrins: Synthesis
and stereochemical behaviour of bis(ligated)
monospirobifluorenylporphyrin ruthenium complexes
a,
b
b,
*
*
´
Cyril Poriel , Audrey Martail , Gerard Simonneaux
a
` `
´
UMR CNRS 6226, Unite´ Sciences Chimiques de Rennes, Matiere Condensee et Systemes Electroactifs (MACSE), Campus de Beaulieu,
Bat. 10C, Avenue du Ge´ne´ral Leclerc, 35042 Rennes Cedex, France
b
UMR CNRS 6226, Unite´ Sciences Chimiques de Rennes, Inge´nierie Chimique et Mole´cules pour le Vivant (ICMV), Campus de Beaulieu,
Bat. 10C, Avenue du Ge´ne´ral Leclerc, 35042 Rennes Cedex, France
Received 16 January 2007; accepted 14 February 2007
Available online 20 February 2007
Abstract
Condensation of dipyrromethane, pyrrole-2-carbaldehyde with either 9,90-spirobifluorene or fluorene aldehyde yields new meso-mono-
substituted, b-unsubstituted porphyrins. The large size of spirobifluorene hinders the rotation around the Cmeso–Caryl bond to give, for bis-
ligated complexes, two different topological faces.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Monoarylporphyrin; Spirobifluorene; Fluorene; Ruthenium; Atropisomer; Nuclear magnetic resonance
Restricted rotation of phenyl rings resulting from steric
interactions with neighbouring groups is an area of intense
investigation [1]. The phenomenon of atropisomerism in
porphyrins with meso aryl substituents was first described
by Gottwald and Ullman [2]. Since then, studies of rota-
tional processes in porphyrins and metalloporphyrins have
enormously expanded in the intervening 20 years [3]. Thus,
restricted rotations have been reported for tetra-meso [4,5]
as well as di-meso [6–8] substituted porphyrins, mainly with
substituents in ortho position of the phenyl ring. A few
examples of atropisomerism in meta position have also
been described with bulky substituents such as fullerenes
or carboranes [9–11]. In principle, facial discrimination is
also possible in monoarylporphyrins due to a possible
interaction between pyrrole hydrogens and phenyl ortho
hydrogens. Such interactions in monosubstituted porphy-
rin lead to the formation of two different topological faces.
In this report, we described our stereochemical investiga-
tions in an unprecedented monoporphyrin substituted in
meso position with a bulky spirobifluorenyl group showing
such a case. Indeed, the large size of the spirobifluorene
(which can be considered as a phenyl ring substituted in
meta position) hinders the rotation around the Cmeso–Caryl
bond to give, for bis ligated ruthenium complexes, two dif-
ferent topological faces. Syntheses and stereochemical
studies of less hindered meso monofluorenylporphyrin were
also developed in order to ascertain this phenomenon.
A simple and straightforward method that provides an
access to meso-monosubstituted, b-unsubstituted porphy-
rins has been recently reported [12]. This procedure offers
meso-monosubstituted porphyrins with moderate yields
(2–12%) by condensation of aldehydes with dipyrrome-
thane and pyrrole-2-carbaldehyde (Scheme 1). Accordingly,
in a typical experimental procedure, dipyrromethane
(2.06 mmol), pyrrole-2-carbaldehyde and 9,90-spirobifluo-
rene-2-carbaldehyde [13] or fluorene-2-carbaldehyde
(2.06 mmol) dissolved in 1 L of distilled dichloromethane
were stirred with 100 ll of trifluoroacetic acid, under an
*
Corresponding authors.
E-mail address: gerard.simonneaux@univ-rennes1.fr (G. Simonneaux).
1387-7003/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.02.006

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C. Poriel et al. / Inorganic Chemistry Communications 10 (2007) 627–630
H
N
CHO
NH
N
N
CHO
TFA/p-chloranil
CH2Cl2
HN
H
H
N
N
MSP(H2)
1
3%
Scheme 1. Synthesis of MSP(H2) 1.
argon atmosphere, for 16 h. After addition of chloranil
(5.78 mmol), and 1 h more stirring, 1.5 mL of triethylamine
was added and the solvent was removed. During this
condensation, the disubstituted porphyrin is also obtained
as a by-product. However, the meso-monoporphyrin with
either fluorene (6% yield, called MFP for mono-
fluorenylporphyrin) or spirobifluorene (3% yield, called
MSP for monospirobifluorenylporphyrin) [14] can be easily
separated from the reaction mixture, by simple filtration
followed by column chromatography, due to the low
solubility of the 5,15-disubstituted derivative, i.e. 5,15-diflu-
oren-2-yl-porphyrin and 5,15-dispirobifluoren-2-yl-porphy-
(2 h) (see Scheme 2). Then, it was decided that complexa-
tion of methyldiphenylphosphine or t-butylisocyanide
offered the greater simplicity and efficiency because these
bis-ligated complexes can provide, depending of the sym-
metry, a porphyrin ring with two topologically different
faces. These complexes were prepared by adding an excess
of the free ligand (methyldiphenylphosphine or t-butyliso-
cyanide) to the Ru(CO) precursor 2 [17,18]. The 1H
NMR spectrum of the bis(t-butylisocyanide) complex
(MSP)RuII(t-BuCN)2 (3), displayed two identical high field
singlets at ꢀ0.65 and ꢀ0.83 ppm (each corresponding to
nine hydrogens) for the methyl resonances of the t-butyl
group (Fig. 3a). This result clearly showed the presence
of two different methyl sets and thus two different topolog-
ical porphyrin faces. This phenomenon has been attributed
to the large size of the bulky spirobifluorene group and is
due to the slow rotation of spirobifluorene group around
the Cmeso–Caryl bond.
1
rin. The H NMR spectrum of 5-(9,90-spirobifluoren-
2-yl)porphyrin (1) is presented in Fig. 1. Due to the local
symmetry of the molecule, two sets of meso hydrogens
are observed, one for the meso hydrogens in position 10
and 20 (10.26 ppm) and one for the meso hydrogen in posi-
tion 15 (10.22 ppm).
The UV–Visible spectrum of 1 is shown in Fig. 2. The Q
bands allow to determined that this porphyrin is a phyllo
type porphyrin as usually observed for meso-monosubsti-
tuted derivatives [15]. Indeed, the meso-monosubstitution
with an electrodonating group, i.e. spirobifluorene induces
a dissymmetry of the p electronic cloud of the porphyrin
which lead to this type of electronic structure.
To detect a possible facial discrimination with a bulky
spirobifluorene group in meso position [16], the ruthenium
complex (MSP)RuII(CO) (2) was first prepared by treat-
ment of 1 with Ru3(CO)12 in o-dichlorobenzene at 160 °C
To ascertain this interpretation, we decided to study the
complexation of methyldiphenylphosphine and again, the
bis-ligated complex exhibits two different topological faces.
1
Thus, the H NMR spectrum of the bis(methyldiphenyl-
phosphine) adduct (MSP)Ru(II)(PMePh2)2 (4) displayed
two identical triplets at d = ꢀ2.57 and ꢀ2.71 ppm (each
corresponding to six hydrogens) for the methyl resonance
of the phosphine ligands (Fig. 4a). It should be noted that
the multiplicity of these signals, i.e. triplets are due to vir-
tual coupling [19] with phosphorus as previously reported
for similar complexes [16].
Fig. 1. 1H NMR spectrum of MSP(H2) 1 (CDCl3).

C. Poriel et al. / Inorganic Chemistry Communications 10 (2007) 627–630
629
2
IV
Abs
3
1
III
II
Abs
I
1.5
0
450 487 525 562 600 637 675
Wavelength (nm)
0
225 300 375 450 525 600 675
Wavelength (nm)
Fig. 2. UV–Visible spectrum of MSP(H2) 1 (CH2Cl2).
a
b
-1.10
-0.40
-0.60
-0.90
-0.70 -0.80 -1.00
-0.50
-0.3 -0.4
-0.7
-0.9
-0.8 -1
-0.5 -0.6
-1.1
Fig. 3. High field portion of the 1H NMR spectrum (CDCl3) of (a) (MSP)RuII(t-BuCN)2 (3) and (b) (MFP)RuII(t-BuCN)2 (7).
CO
L
N
N
N
N
L
N
N
N
N
NH
N
N
Ru CO
3
12
Ru
L
Ru
RT
CHCl
160˚C
HN
3
1,2 dichlorobenzene
73%
92%
(MSP)RuII(CO)
(MSP)H2
1
2
CH3
CH3
CH3
C N
C
3
L=
L=
(MSP)RuII(t-BuNC)2
(MSP)RuII(PPh2CH3)2
Ph
P
Ph
4
CH3
Scheme 2. Synthesis of ruthenium complexes of 5-(9,90-spirobifluoren-2-yl) porphyrin.
a
b
-2.30 -2.40 -2.50 -2.60 -2.70 -2.80
-2.30 -2.40 -2.50 -2.60 -2.70 -2.80 -2.90 -3
Fig. 4. High field portion of the 1H NMR spectrum (CDCl3) of (a) (MSP)RuII(PMePh2)2 (4) and (b) (MFP)RuII(PMePh2)2 (8).
1
In order to study the influence of the meso substituent,
we also prepared 5-fluoren-2-yl-porphyrin (MFP) (5) and
their ruthenium complexes 6–8 following the same route
(Scheme 3). As described for 3, the (MFP)RuII(t-BuCN)2
(7) adduct (Scheme 3) should also theoretically exhibited
two signals for the methyl resonances due to the two differ-
ent topological faces of this complex. In contrast, only one
resonance (d = ꢀ0.63 ppm) for the isocyanide groups was
detected in H NMR (Fig. 3b). Indeed, in this case the
methyl groups of the isocyanide ligand are too far away
from the methylene C9 of the meso fluorene substituent
and thus do not allow to distinguish the different faces of
the porphyrin ring. The same behaviour is also observed
in the 1H NMR spectrum of (MFP)RuII(PMePh2)2 (8),
which showed only one resonance for the methyl resonance
of the phosphine ligands (d = ꢀ2.50 ppm, Fig. 4b).

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C. Poriel et al. / Inorganic Chemistry Communications 10 (2007) 627–630
H
N
CHO
CO
NH
N
N
N
N
L
N
N
N
N
N
N
Ru3CO12
CHO
L
Ru
Ru
L
TFA/p-chloranil
CH Cl
HN
RT/ CHCl3
160˚C
80%
H
N
H
N
2
2
fluorene-2-carbaldehyde
95%
5
6
CH
3
6%
C
N
C
CH
L=
L=
7
3
CH
3
Ph
Ph
CH
P
8
3
Scheme 3. Synthesis of 5-fluoren-2-yl-porphyrin derivatives.
In conclusion, we have prepared new bis ligated ruthe-
References
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can be considered as a meta substituted phenyl ring. In this
case, bis-ligated ruthenium monofluorenylporphyrin com-
plexes do not display any facial discrimination in 1H
NMR spectrum. The large size of the spirobifluorene group
that hinders the rotation around the Cmeso–Caryl bond,
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Appendix A. Supplementary data
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Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.
2007.02.006.