From insertion of rhodium acetate paddlewheels into functionalized 7-azaindole hydrogen-bonded dimers to infinite architectures

Article abstract of DOI:10.1039/c1dt10359h

In order to take advantage of the peculiar mode of interaction consisting in the combination of hydrogen and coordination bonding displayed by the 7-azaindole core towards tetraacetate paddlewheel type complexes, a series of new derivatives, bearing perip

Full text of DOI:10.1039/c1dt10359h

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PAPER
From insertion of rhodium acetate paddlewheels into functionalized
7-azaindole hydrogen-bonded dimers to infinite architectures†
Dmitry Pogozhev, Ste´phane A. Baudron* and Mir Wais Hosseini*
Received 2nd March 2011, Accepted 4th May 2011
DOI: 10.1039/c1dt10359h
In order to take advantage of the peculiar mode of interaction consisting in the combination of
hydrogen and coordination bonding displayed by the 7-azaindole core towards tetraacetate
paddlewheel type complexes, a series of new derivatives, bearing peripheral interacting sites at the
position 3, have been prepared and their self-assembly into dimeric H-bonded species was established in
the solid state. Furthermore, the heterochelate mode of binding was exploited both in the solid state
and in solution using [Rh2(OAc)4] paddlewheel to generate discrete capped complexes resulting from
the coordination of the pyridyl nitrogen atom to the axial position of the Rh(II) cations and hydrogen
bonding between the pyrrolic NH and an oxygen atom of one of the equatorial acetate groups. The
extension to infinite hybrid networks was achieved using derivatives bearing self complementary
H-bond donor and acceptor groups such as a carboxylic moiety.
Introduction
Over the last two decades, the design and preparation of periodic
extended architectures called molecular networks1 have been
attracting considerable attention. For the design of these giant
architectures which may be regarded as hypermolecules, molecular
tectonics2 based on combinations of complementary building
blocks or tectons3 capable of mutual interconnection appears to be
an efficient approach.4 Among various structural characteristics
defining molecular networks such as their dimensionality and
geometry, the search for new assembling strategies resulting
Scheme 1 Most common coordination modes of 7-azaindole (left) and
from the number of components, their modes of interaction
and their sequence, is a matter of current interest. Although the
majority of cases reported are usually based on a single type of
attractive interaction such as van der Waals contacts,5 hydrogen6
or coordination bonding,7 examples of combined interactions have
been also reported.8 For the latter case, two strategies may be
considered. The first one is based on the one-pot preparation of
periodic architectures combining at least two different interac-
tion modes. For the second strategy, allowing the hierarchical
construction of molecular networks, the use of differentiated
interactions and their sequence are key features.9 With respect to
the second strategy, the 7-azaindole (7-azaH) moiety (Scheme 1)
appeared to us as an interesting platform. Indeed, the latter offers
the possibility of exploiting its simultaneous coordination and
H-bonding propensity giving rise to a heterochelate mode of
interaction (Scheme 1, left) for the design of metallatectons bearing
7-azaindolate (right).
at the position 3 peripheral interacting groups allowing thus
the construction of extended architectures through self-assembly
processes.
The nitrogen based heterocyclic molecule 7-azaindole
(Scheme 1) has received considerable interest not only for its
pharmaceutical applications,10–11 but also for its rich coordination
chemistry.12–20 Indeed, both 7-azaindole and its conjugate base,
7-azaindolate (7-aza-), (Scheme 1) have been shown to form a
variety of complexes with metal cations. Neutral 7-azaH offers
both a coordinating pyridyl group and H-bond donor site of the
NH type. Thus, such a ligand may be regarded as a heterochelate
combining two distinct types of interactions. Indeed, upon ligation
to a M-X fragment, hydrogen bonding between the NH group
and the anion X- is observed in all structurally characterized (7-
azaH)MX complexes (Scheme 1, left).17–19 For 7-azaindolate, a
monoanionic ligand, in principle, at least, two coordination modes
Laboratoire de Chimie de Coordination Organique, UMR CNRS 7140,
Universite´ de Strasbourg, F-67000, Strasbourg, France. E-mail: sbaudron@
unistra.fr, hosseini@unistra.fr; Fax: +33 368851325; Tel: +33 368851325
† CCDC reference numbers 815819–815825. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10359h
2
(m or h ) with metal cations may be envisaged (Scheme 1, right).
However, owing to the bite angle between the two N atoms, with
the exception of a mononuclear complex formed with europium,16
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all other complexes reported are polynuclear species resulting from
coordinating peripheral group,9,25 or hydrogen bonded networks
in the case of a self-complementary hydrogen bonding peripheral
moiety (Scheme 2d).8 To address this issue, we report herein
on the synthesis, characterization and coordination chemistry
towards the [Rh2(OAc)4] paddlewheel unit of five 7-azaindole
based ligands 1–5 (Scheme 3) bearing a peripheral p-benzonitrile,
a tricyanovinylene group, a 5-phenyldipyrrin, a m- or p-benzoic
acid group respectively.
1
1
m-h :h coordination mode, i.e. the anionic ligand bridges two
metal centres.13–15 In particular, paddlewheel type complexes have
been reported with Cu, Mo, Nb, Re and W for example.13
Interestingly, for the paddlewheel type complexes formed be-
tween 7-azaH and bimetallic [M2(O2CR)4]n+ (M = CuII, RhII, n =
0; M = RuII/III, n = 1; R = CH3, C2H5) species,17 the double mode
of interaction (Scheme 2a), i.e. formation of a coordination bond
between the pyridyl moiety of 7-azaH and the axial position of
the metal cations and hydrogen bond between the NH group and
one of the oxygen atoms of the equatorial carboxylate groups,
is observed (Scheme 2a). One might draw an analogy between
the binuclear complex (Scheme 2c) and the self-complementary
hydrogen bonded dimers (Scheme 2b).20 In other words, the
coordination to the [M2(O2CR)4]n+ paddlewheel can thus be
regarded as an expanded version of the hydrogen bonded dimers
observed for the free ligands.
Scheme 3 Functionalized 7-azaindole derivatives 1–5 and their precur-
sors and hydrogen assignments.
Results and discussion
Scheme 2 Schematic representation of (7-azaH)MX metal complex (a),
a 7-azaH hydrogen bonded dimer (b), a binuclear complex featuring
both coordination and H bonds (c) and a 1D network resulting from
interconnection of consecutive binuclear cores through a dihapto mode of
H-bonding (d).
Design of the ligands
Compounds 1–5 are 7-azaindole derivatives bearing peripheral
interaction sites at position 3. While ligand 1 bears a nitrile
group at the para position, compound 2 is equipped with a
tricyanovinylene moiety. Ligand 4 and 5, bearing a carboxylic
acid unit, are positional isomers. Finally, compound 3 combines
the 7-azaindole core with a dipyrrin unit. Whereas for compounds
1 and 2, one would expect mainly a coordinating behaviour for
the peripheral group, for the other three ligands, owing to the
self-complementary nature of the groups, one would also expect
H-bonding in addition to coordination propensity.
Although paddlewheel type complexes and in particular
[Rh2(OAc)4] have been exploited for the formation of supramolec-
ular architectures,21–22 and the above mentioned interaction motif
observed with other amino functionalized nitrogen based hete-
rocyclic ligands,23–24 to the best of our knowledge, the double
recognition feature, which can be regarded as a heterochelate mode
of interaction, has not been used for the formation of extended
architectures. This is probably related to the fact that, while the
coordination chemistry of 7-azaH has been widely investigated,
the one of its functionalized derivatives, with the exception of
N-alkylated compounds,12 is almost unexplored. Introduction
of an additional peripheral group at this position would lead
to the formation of interesting functionalized complexes or
metallatectons,2–4 based on the heterochelate interaction. Such
derivatives would be interesting candidates for the sequential
construction of heterometallic architectures in the case of a
Synthesis and characterization of the ligands
Ligand 1, 4 and 5 were prepared by the Pd-catalyzed Stille coupling
between 1-tert-butyldimethylsilyl-3-trimethylstannyl-7-azaindole,
6,26 and p-bromobenzonitrile (7) or m- (8) or p- (9) bromobenzoic
acid methyl ester in 17, 48 and 29% yield respectively (Scheme 3).
By analogy with the reported 3-tricyanovinylindole analogue,27
ligand 2 was prepared in 93% yield by reaction of TCNE with
7-azaindole in the presence of pyridine (Scheme 3). Finally,
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the dipyrrin appended derivative 3 was prepared as previously
described.20d
All reported ligands were characterized in solution by 1H- and
13C-NMR and IR spectroscopy. In the case of 1 and 2, they were
also studied in the solid state by single-crystal X-Ray diffraction
(Fig. 1).
acceptor sites located on the O atoms of carboxylate ligands. Since
azaindole derivatives 1–5 offer a coordinating site (N atom of the
pyridyl moiety) as well as a H-bond donor unit (NH group of the
five membered ring), upon their coordination to the tetraacetate
paddlewheel, four isomers can be envisioned, two being achiral
(Fig. 2a and 2b) and two enantiomers (Fig. 2c and 2d).
Fig. 2 Schematic representation of all four possible isomers result-
ing from the chelation of the [Rh2(OAc)4] paddlewheel complex by
7-azaH. Whereas isomers a and b possessing a centre and a plane of
symmetry respectively are achiral, isomers c (K) and d (D) are chiral and
enantiomers.
At room temperature, upon reaction in either DMF or THF
of two equivalents of ligands 1–3 with [Rh2(OAc)4],28 complexes
10–12 were obtained in 35 to 65% yield. All three complexes were
characterized both in solution by classical methods and in the
solid state by X-ray single-crystal diffraction.
Fig. 1 Structures of the H-bonded dimers formed by the self-complemen-
˚
tary ligands 1 (a) and 2 (b). For 1: N1—N2i = 2.897(2) A, N1–H1A—N2i =
◦
◦
˚
166.5 ; for 2: N1—N2ii = 2.890(2) A, N1–H1A—N2ii = 168.1 . i = 1 - x,
-y, -z; ii = -x, 3 - y, -z.
Crystals of 10 were obtained by slow diffusion of water vapour
into a DMF solution of the complex. Compound 10 crystallizes as
Crystal structure of ligands 1 and 2
¯
a DMF solvate, (10)·(DMF)2, in the triclinic space group P1 with
one complex on an inversion center and one solvent molecule
Compounds 1 and 2 are self-complementary units offering both H-
bond donor (NH) and acceptor (N) sites. In the solid state, unlike
the commercially available 7-azaindole which self-organizes into
a tetrameric unit,15 both compounds 1 (Fig. 1a) and 2 (Fig. 1b)
form hydrogen-bonded dimers, as observed for other derivatives
functionalized at the 3 position.20 Both compounds crystallize in
the monoclinic space group P21/c with one molecule in general
position.
¯
in general position. Crystals of 11 (triclinic, P1) were obtained
upon diffusion of n-pentane vapour into a dioxane solution of the
complex. The binuclear species 11 crystallizes as a dioxane solvate,
(11)·(Dioxane)4, with one complex on an inversion center and two
solvent molecules in general positions. Crystals of (12)·(Dioxane)4
were obtained by diffusion of n-pentane vapour into a dioxane
solution of the complex. The complex 12 crystallizes in the
monoclinic space group P21/n with one complex on an inversion
center and two dioxane molecules in general positions. For all
three dimers, the Rh–Rh distance is similar to one reported for
other paddlewheel type complexes.24 In all three cases, the axial
positions on the RhII cation are occupied by the pyridyl nitrogen
atom of the 7-azaindole moieties (Fig. 3). The functionalized 7-
azaindole unit and two acetate groups are coplanar, in contrast
with what is observed for the parent [Rh2(O2CC2H5)4(7-azaH)2]
complex (dihedral angle of 8.2 and 23.5◦) and the ruthen◦ium
analogue [Ru2(OAc)4(7-azaH)2](PF6) (dihedral angle of 43 ).17
The NH of the five membered heterocycle is hydrogen bonded
to an oxygen atom of an equatorial acetate group (Fig. 3) as
previously described for [Cu2(OAc)4(7-azaH)2] and [Cu2(OAc)2(7-
aza)2(7-azaH)2] complexes.17b,c Only the centrosymmetric iso-
mer (Fig. 2a and 3) has been obtained as for the parent
It is worth noting that, for the dipyrromethane precursor of 3,
the same type of arrangement is observed in the solid state.20d
For both dimers, the geometrical parameters of the observed
R2 (8) motifs1b are similar. While, for compound 1, the benzonitrile
2
group is tilted with respect to the heterocycle by 24.5◦, for 2, the
tricyanovinylene group is almost coplanar with the 7-azaindole
moiety (dihedral angle = 3.0◦). In the latter case, owing to the
˚
rather flat nature of the dimer, p-stacking with a 3.32 A distance
between two adjacent dimeric units is observed.
Synthesis and crystal structures of discrete paddlewheels 10–12
As stated above, paddlewheel type complexes offer both two free
coordination sites at the apical positions of the two metal centres
adopting a square based coordination geometry and H-bond
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Fig. 4 1H-NMR spectra in acetone-d6 of ligand 2 (bottom) and the
paddlewheel complex 11 (top) showing downfield shifts of Ha, Hb, Hc
and Hd hydrogen atoms. For assignment see Scheme 3.
Fig. 3 Crystal structure of complexes 10 (a), 11 (b) and 12 (c). Hydrogen
atoms and solvent molecu◦les have been omitted for clarity. Selected bond
˚
lengths (A) and angles ( ): for 10, Rh1–Rh1 = 2.4076(4); Rh1–N1 =
Fig. 5 1H-NMR spectra in CDCl3 of ligand 3 (bottom) and the complex
12 (top) showing that upon coordination to the paddlewheel complex
while signals of the dipyrrin moiety remain unaffected, Ha, Hb, Hc and
Hd hydrogen atoms of the 7-azaH unit are strongly downfield shifted. For
assignment see Scheme 3.
2.279(2), N2—O2 = 2.795(3), N2–H2—O2 = 146.6; for 11, Rh1–Rh1 =
2.4031(4), Rh1–N1 = 2.290(2), N2—O2 = 2.720(4), N2–H2—O2 = 147.5;
for 12: Rh1–Rh1 = 2.4036(7); Rh1–N4 = 2.268(3), N3—O1 = 2.896(5),
N3–H3—O1 = 143.4.
[M2(O2CR)4(7-azaH)2]n+ complexes.17 It is interesting to note that
these ligands are polytopic and thus upon reaction with rhodium
acetate, both coordination poles do compete for ligation to the
RhII cations. This is particularly relevant in the case of 3 since
both coordination poles comprise a nitrogen based heterocycle
and a pyrrolic ring capable of hydrogen bonding. However, the
two rings are fused in the 7-azaH moiety while they are free to
rotate in the dipyrrin unit and the two nitrogen atom are not in
an N–C–N arrangement, giving a preferred interaction with the
7-azaH group. This free rotation of the coordinating and hydrogen
bonding rings in dipyrrin ligands has been recently used for the
formation of [2 + 2] metallamacrocycles with silver cations.29
Synthesis and crystal structures of infinite 1D networks 13 and 14
Crystals of the infinite 1D network 13 were obtained in 82%
yield from 1-propanol upon slow evaporation. 13 crystallizes in
¯
the triclinic space group P1 with one paddlewheel unit on an
inversion center. Owing to the disorder observed for the solvent
molecules, the SQUEEZE command was applied.30 As observed
for paddlewheel complexes 10–12 mentioned above (Fig. 3), here
again the same type of interactions between the 7-azaH unit and
rhodium acetate is obtained. The binuclear complex bearing at its
periphery two self-complementary carboxylic acid groups oriented
in a divergent fashion leads to a 1D hydrogen bonding network
2
with the formation of the R2 (8) motif. It is worth noting that,
under the conditions used, neither coordination through O–Rh
bond of the carboxylic acid to the axial position of the RhII cations
nor the substitution of equatorial acetate groups are observed. The
latter point results from the inertness at room temperature of the
rhodium acetate complex towards carboxylate exchange processes.
The prevalence of the nitrogen over the oxygen coordination to the
axial position of RhII centre might be explained by a better affinity
of the metal cations for the pyridyl group and the simultaneous
formation of H-bond. Although, as mentioned above (Fig. 2),
in principle the chelation of the paddlewheel complex by 7-
azaH derivatives might lead to four different isomers, for all
three discrete complexes 10–12, a centrosymmetric organisation
is observed (Fig. 3). However, for the infinite networks based on
achiral units, two possibilities based either on the syn (Fig. 2b) or
the anti (Fig. 2a) configuration may be envisaged (Fig. 8). In the
case of the network 13 (Fig. 6) again only the centrosymmetric
anti isomer (Fig. 2a) is observed.
Behaviour in solution of complexes 11 and 12
Owing to a better solubility in organic solvents, only paddlewheels
1
11 and 12 were studied in solution by H-NMR spectroscopy
which revealed that both species are stable in liquid media. For
the complex 11 in acetone-d6, proton signals corresponding to
the 7-azaindole moiety are strongly deshielded when compared to
free ligand 2 (Fig. 4). As expected, the observed shifts are more
pronounced for the hydrogen atoms Ha, Hb and Hc belonging to
the pyridyl ring of the ligand.
A similar behaviour is observed for 12 in CDCl3. When
compared to the free ligand 3, while signals of the phenyldipyrrin
group remains unaffected, those of the 7-azaH moiety are strongly
downfield shifted upon coordination to the paddlewheel complex
(Fig. 5). These observations clearly indicate that, in solution and
at room temperature, no shift in the coordination mode between
the 7-azaH and dipyrrin units occurs.
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Fig. 6 A portion of the structure of the 1D network 13 resulting from the formation of H-bonds in a dihapto mode between carboxylic units belonging
◦
˚
to consecutive paddlewheel type units. C–H hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles ( ): Rh1–Rh1 = 2.4072(3);
Rh1–N1 = 2.263(2); N2—O6 = 2.834(3); N2–H2—O6 = 142.4; O2—O1i = 2.630(3); O2–H2A—O1i = 169.4. i = 1 - x, 1 - y, -z.
Crystals of the network 14 were obtained in 62% yield from
a DEF/EtOH/H2O mixture. 14 crystallizes as a DEF solvate,
14·(DEF)2, with one complex on an inversion center and a solvent
molecule in general position. For the latter, the carbonyl group
is found to be disordered over two positions. The observed
interactions between the paddlewheel and the ligand 5 are similar
to what is observed for 10–12 and for 13, i.e. chelation through
simultaneous formation of coordination (N–Rh) and hydrogen
(NH ◊ ◊ ◊ O) bonds. Again, as in the case of 13, for 14 a H-bonded 1D
network (Fig. 7) with centrosymmetric organisation of the units is
obtained (Fig. 8a). In marked contrast with what is observed for
13, the self-complementary peripheral carboxylic groups in 14 do
not interact directly through a dihapto mode of hydrogen bonding
2
leading to the R2 (8) motif but they rather form a tetramolecular
4
R4 (14) motif resulting from the insertion of two solvent molecules
between carboxylic moieties belonging to consecutive units.
Fig. 8 Two possible supramolecular isomers upon coordination of
[Rh2(OAc)4] to a 7-azaindole derivative bearing a peripheral self-com-
Conclusions
plementary hydrogen bonding group. Only a projection is presented here,
based on the two achiral isomers (see Fig. 2).
In conclusion, the coordination chemistry towards the
[Rh2(OAc)4] paddlewheel type complex of five 7-azaindole deriva-
tives bearing at position 3 a p-benzonitrile (1), a tricyanovinylene
group (2), a phenyldipyrrin (3), a m- (4) and p-benzoic acid
(5) has been investigated. In the solid state, the free ligands
1 and 2 self-organize into hydrogen bonded dimers with the
paddlewheel with derivatives 4 and 5. Indeed, upon interaction
with the paddlewheel complex, both compounds 4 and 5 bearing
a peripheral self-complementary hydrogen bonding benzoic acid
group lead to the formation of self-complementary metallatectons
which self assemble into 1D networks either though direct H-
bonding by a dihapto mode of recognition in the case of 4 or by
insertion of solvent molecules bridging consecutive units in the
case of 5. The construction of heterometallic infinite architectures
using the above mentioned complexes combining the [Rh2(OAc)4]
paddlewheel and ligands 1–5 with other metal centres is currently
under investigation.
2
R2 (8) motif. In the presence of [Rh2(OAc)4] paddlewheel, ligands
1–3 interact with the paddlewheel core through simultaneous
coordination of the pyridyl nitrogen atom to the axial positions
of RhII centres and H-bonding between the NH group and an
oxygen atom of one of the four equatorial acetate moieties. The
above mentioned heterochelation process was used to generate
infinite 1D H-bonded networks upon combining the [Rh2(OAc)4]
Fig. 7 A portion of the structure of the 1D network 14 resulting from the interconnection of consecutive paddlewheel type units through DEF solvent
molecules forming H-bonds with carboxylic moieties belonging to consecutive complexes. C–H hydrogen atoms have been omitted for clarity. Note that
only one of the two positions of the carbonyl group of the DEF molecule is shown and that, owing to this disorder, the hydrogen atom of of the C( O)H
◦
˚
group has not been introduced in the structure refinement. Selected bond lengths (A) and angles ( ): Rh1–Rh1 = 2.4055(4); Rh1–N1 = 2.274(2); N2—O4 =
2.781(3); N2–H2—O4 = 145.8; O1—O7Ai = 2.554(5); O1–H1A—O7Ai = 155.0; O2—C19ii = 3.536(5). i = 2-x, 1-y, 1-z; ii = x, 1+y, z.
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129.6, 127.6, 127.2, 126.9, 124.8, 117.6, 117.0, 113.8. IR(ATR)
n/cm-1 3144–2551 (OH), 1698 (C O), 1303 (C–O). Found: C,
69.50; N, 11.37; H, 4.06%. C14H10N2O2 requires C, 70.58; N, 11.76;
H, 4.23%. HRMS (ESI), m/z: [M + H]+ calcd for C14H11N2O2:
239.082, found 239.080.
Experimental
Synthesis
The intermediate 6, ligand 3 and the [Rh2(OAc)4] paddlewheel
complex were prepared as described.20d,26,28 Other commercially
available reagents were used as received. All solvents were dried
using standard procedures. 1H- and 13C-NMR spectra were
acquired at 25 ◦C on a Bruker AV 300 with the deuterated solvent
as the lock and residual solvent as the internal reference. NMR
chemical shifts d are given in ppm and referenced internally to the
residual solvent resonance. J values are given in Hz. Elemental
analyses were performed at the Service Commun d’Analyses,
Universite´ de Strasbourg (France).
Ligand 5. Under argon, a THF (50 mL) solution of 6
(1 g, 2.53 mmol), 4-bromo-benzoic acid methyl ester 9 (0.82 g,
3.81 mmol), LiCl (0.321 g, 7.57 mmol) and (Ph3P)4Pd (0.1 g)
was refluxed for 72 h. Addition of Et2O afforded a precipitate
which was filtered. The filtrate was evaporated and the residue
was purified by chromatography (SiO2, CHCl3/pentane: 1/3).
The isolated white powder was dissolved in a minimum amount
of MeOH and mixed with an aq. NaHCO3 solution (100 mL).
This suspension was refluxed until dissolution of the solid. Then,
an aq. HCl solution was added until the pH reached 3–5. Aq.
NaHCO3 was added to the solution until the pH reached 7–8.
The resulting white precipitate was filtered off and was washed
with Et2O (100 mL) to afford 5 as a white powder (0.175 g, 29%).
dH(300 MHz, DMSO-d6) 12.81 (s, 1H), 12.10 (s, 1H), 8.38 (d, J 7.8,
1H), 8.30 (d, J 4.7, 1H), 8.06 (d, J 2.5, 1H), 7.99 (d, J 8.2, 2H), 7.88
(d, J 8.2, 2H), 7.19 (dd, J 4.6 and 8.0, 1H). dC(75 MHz, DMSO-d6)
167.7, 149.6, 143.6, 140.1, 130.4, 128.2, 127.9, 126.2, 125.7, 117.5,
116.8, 113.7. IR(ATR) n/cm-1 3226 (OH), 1691 (C O), 1314 (C–
O). Found: C, 69.24; N, 11.11; H, 4.26%. C14H10N2O2 requires C,
70.58; N, 11.76; H, 4.23%. HRMS (ESI), m/z: [M + H]+ calcd for
C14H11N2O2: 239.082, found 239.081.
Ligand 1. A THF solution (50 mL) of 6 (1 g, 2.53 mmol), 4-
bromo-benzonitrile 7 (0.69 g, 3.80 mmol), LiCl (0.21 g, 7.59 mmol)
and (Ph3P)4Pd (0.2 g) was refluxed for 72 h under argon. After
addition of Et2O, the precipitate was filtered off and the solution
evaporated. The crude product was purified by column chromatog-
raphy (SiO2, CHCl3/pentane: 1/3). The resulting product was
dissolved in THF and an HCl solution in dioxane (4 M, 10 mL)
was added. The mixture was stirred for 1 h and the resulting
precipitate was filtered and washed with ether to afford 1 (0.092 g,
16%). dH(300 MHz, DMSO-d6) 12.20 (s, 1H), 8.38 (dd, J 1.4 and
8.4, 1H), 8.31 (dd, J 1.4 and 4.6, 1H), 8.15 (d, J 2.5, 1H), 7.96
(d, J 8.2, 2H), 7.86 (d, J 8.2, 2H), 7.21 (dd, J 4.8 and 8.1, 1H).
dC(75 MHz, DMSO-d6) 149.7, 143.8, 140.6, 133.2, 128.2, 126.8,
126.6, 119.7, 117.4, 117.1, 113.0, 107.9. IR(ATR) n/cm-1 2218
(CN). Found: C; 75.97; N, 19.17; H, 4.25%. C14H9N3 requires C,
76.70; N, 19.17; H, 4.14%.
Complex 10. In a tube (16 ¥ 1 cm), a DMF (5 mL) solution of
1 (25 mg, 0.114 mmol) was mixed with a DMF solution (5 mL) of
[Rh2(OAc)4] (25.2 mg, 0.057 mmol). Upon slow diffusion of water,
red crystals of the desired complex 10 were obtained (35.5 mg,
60%). IR(ATR) n/cm-1 2220(CN) 1437(COO-), 1591 (COO-).
Found: C, 48.38; N, 11.04; H, 4.64%. C42H44N8O10Rh2 requires
C, 49.14; N, 10.91; H, 4.32%.
Ligand 2. A benzene (10 mL) solution of 7-azaindole (0.5 g,
4.23 mmol) was added to a refluxing benzene solution (8 mL) of
TCNE (0.3 g, 2.34 mmol). The solution immediately turned black.
Addition of few drops of pyridine resulted in the precipitation of a
green solid. The mixture was further refluxed for 2 h. The solution
was then filtered and the solid washed with benzene and cold
CHCl3 to afford 2 (0.48 g, 93% based on TCNE). dH(300 MHz,
DMSO-d6) 13.78 (br s, 1H), 8.78 (s, 1H), 8.49 (dd, J 1.4 and
4.5, 1H), 8.44 (dd, J 1.5 and 8.2, 1H), 7.45 (dd, J 4.5 and 8.2,
1H). dC(75 MHz, DMSO-d6) 149.5, 146.5, 137.4, 133.5, 129.4,
119.6, 117.1, 115.0, 114.3, 113.9, 107.7, 81.4. lmax(CH2Cl2)/nm
(e/mol-1 L cm-1): 228 (14000), 281 (6000), 423 (8000), 478 (3000).
IR(ATR) n/cm-1 2223 (CN). Found: C, 65.16; N, 31.62; H, 2.67%.
C12H5N5 requires C, 65.75; N, 31.95; H, 2.30%.
Complex 11. A solution of 2 (25.7 mg, 0.117 mmol) in THF
(10 mL) was mixed with a THF solution (10 mL) of [Rh2(OAc)4]
(25.8 mg, 0.058 mmol). The solution was evaporated and the
residue was dissolved in dioxane. Red crystals were grown by slow
diffusion of n-pentane vapours into a dioxane solution of the
complex (25.5 mg, 35%). dH(300 MHz, CDCl3) 11.84 (br s, 2H),
9.23 (dd, J 1.0 and 5.1, 2H), 9.03 (dd, J 1.1 and 8.2, 2H), 8.88 (d,
J 3.3, 2H), 7.81 (dd, J 5.2 and 8.4, 2H), 1.98 (s, 12H). dC(75 MHz,
CDCl3) 192.6, 151.0, 147.8, 133.8, 133.2, 130.9, 120.8, 119.3, 114.0,
113.5, 112.0, 108.0, 78.5, 24.2 ppm. dH(300 MHz, acetone-d6) 8.93
(s, H), 8.59 (dd, J 1.5 and 8.1, 1H), 8.52 (dd, J 1.5 and 4.7, 1H), 7.48
(dd, J 4.7 and 8.1, 1H), 2.05 (s, 6H). IR(ATR) n/cm-1 2224 (CN),
1415 (COO-), 1588(COO-). The solvated nature of this compound
led to non-reproducible elemental analysis.
Ligand 4. A THF solution (150 mL) of 6 (3.40 g, 8.60 mmol),
3-bromo-benzoic acid methyl ester 8 (3.64 g 16.93 mmol), LiCl
(1.28 g, 30.29 mmol) and (Ph3P)4Pd (0.2 g) was refluxed for 72 h
under argon. After evaporation, the residue was first dissolved in
a minimum amount of MeOH and then an aq. NaHCO3 solution
(150 mL) was added. The suspension was refluxed until dissolution
of the solid. The pH of the solution was adjusted to 3–5 by addition
of an aq. HCl solution. Aq. NaHCO3 was added until pH 7–8 was
reached affording a white precipitate. After filtration, the solid
residue was washed with MeOH and Et2O to afford 4 as a white
powder (0.99 g, 48%). dH(300 MHz, DMSO-d6) 13.06 (s, 1H),
12.01 (s, 1H), 8.31–8.25 (m, 3H), 7.98–7.95 (m, 2H), 7.83(dt, J 1.5
and 7.6, 1H), 7.56 (t, J 7.6, 1H), 7.19 (dd, J 4.7 and 7.9, 1H).
dC(75 MHz, DMSO-d6) 167.9, 149.5, 143.5, 135.8, 132.1, 130.9,
Complex 12. A THF solution (30 mL) of dipyrrin 3 (50 mg,
0.149 mmol) was added to a THF solution (20 mL) of [Rh2(OAc)4]
(32.85 mg, 0.074 mmol). The reaction mixture was stirred for 5 min
and the solvent was removed under vacuum. Red crystals were
grown by slow diffusion of n-pentane into a dioxane solution of
the complex (71 mg, 65%). dH(300 MHz, CDCl3) 10.56 (s, 2H),
9.07 (d, J 4.3, 2H), 8.62 (dd, J 1.0 and 7.9, 2H), 7.84–7.81 (m,
4H), 7.71(d, J 2.4, 2H), 7.68 (t, J 1.1, 4H), 7.65–7.62 (m, 4H),
7.57 (dd, J 5.1 and 7.9, 2H), 6.77(dd, J 1.0 and 4.2, 4H), 6.44 (dd,
J 1.4 and 4.2, 4H), 2.00 (s, 12H). The signal of the pyrrolic NH
7408 | Dalton Trans., 2011, 40, 7403–7411
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©

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Table 1 Crystallographic data for 1–2, 10–12
1
2
(10)·(DMF)2
(11)·(Dioxane)4
(12)·(Dioxane)4
Formula
FW
C14H9N3
219.24
C12H5N5
219.21
C42H44N8O10Rh2
1026.67
C48H54N10O16Rh2
1232.83
C68H76N8O16Rh2
1467.21
Crystal system
Monoclinic
P21/c
10.4831(15)
14.485(2)
7.2366(11)
Monoclinic
P21/c
8.9962(4)
5.4962(3)
20.0699(8)
Triclinic
P1
Triclinic
P1
Monoclinic
P21/n
8.7968(4)
36.9943(15)
10.26665(4)
¯
¯
Space group
˚
a/A
8.0638(2)
11.2180(3)
12.0060(3)
78.2360(10)
84.2670(10)
85.0210(10)
1055.47(5)
1
173(2)
0.850
13745
4812 (0.0376)
0.0344
8.8730(2)
10.5971(2)
14.7313(3)
107.5620(10)
90.5040(10)
101.4450(10)
1290.84(5)
1
173(2)
0.719
28199
7590 (0.0353)
0.0492
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
104.049(4)
99.713(2)
100.402(2)
3
˚
V/A
1066.0(3)
4
173(2)
0.085
978.13(8)
4
173(2)
0.098
3286.1(2)
2
173(2)
0.577
Z
T/K
m/mm-1
Refls. coll.
Ind. refls. (Rint
9130
6991
18888
)
3027 (0.0451)
0.0567
0.1340
0.1243
0.1641
0.932
2212 (0.0307)
0.0382
0.1032
0.0555
0.1219
1.126
7311 (0.0501)
0.0605
0.1074
0.0885
0.1199
1.159
R1 (I > 2s(I))a
wR2 (I > 2s(I))a
R1 (all data)a
wR2 (all data)a
GOF
0.0848
0.0434
0.1064
1.165
0.1363
0.0592
0.1533
1.102
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ/ |Fo|; wR2 = [ w(Fo - Fc2)2/ wFo
]
.
2
4 1/2
Table 2 Crystallographic data for 13 and 14
is not observed. dC(75 MHz, CDCl3) 192.3, 148.7, 144.9, 143.6,
140.8, 135.3, 131.8, 129.6, 129.1, 126.2, 122.9, 121.0, 120.3, 117.6,
117.4, 116.2, 113.8, 24.2. lmax(CH2Cl2)/nm (e/mol-1 L cm-1): 228
(94000), 269 (52000), 437 (40000), 458 (34000). IR(ATR) n/cm-1
1412 (COO-), 1592 (COO-). Found: C, 55.33; N, 7.99; H, 4.82%.
C68H76N8O16Rh2 requires C, 55.66; N, 7.63; H, 5.22%.
13
14·(DEF)2
Formula
FW
C36H32N4O12Rh2
918.48
C46H54N6O14Rh2
1120.78
Crystal system
Triclinic
P1
Triclinic
¯
¯
Space group
P1
˚
a/A
7.7872(2)
11.7497(3)
13.7757(4)
110.5140(10)
96.1150(10)
96.0720(10)
1159.85(5)
1
173(2)
0.766
18223
5262 (0.0290)
0.0323
8.4005(2)
10.4754(3)
13.6491(4)
77.8610(10)
88.822(2)
88.1780(10)
1173.53(6)
1
Complex 13. A 1-propanol solution of 4 (25 mg, 0.105 mmol)
and [Rh2(OAc)4] (22.2 mg, 0.052 mmol) was left to stand for two
weeks to afford red crystals of 13 (39.5 mg, 82%). IR(ATR) n/cm-1
3259 (OH), 1710 (C O), 1232 (C–O), 1440 (COO-), 1589(COO-).
Found: C, 47.77; N, 6.80; H, 4.08%. C36H32N4O12Rh2 requires C,
47.08; N, 6.10; H, 3.51%.
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
T/K
173(2)
0.777
17206
5351 (0.0364)
0.0309
0.0768
0.0389
0.0906
1.190
m/mm-1
Complex 14. A DEF/EtOH/H2O: 3/2/2 solution of 5 (25 mg,
0.105 mmol) and [Rh2(OAc)4] (22.2 mg, 0.052 mmol) was left to
stand for two weeks. Red crystals, insoluble in common organic
solvents, were obtained (37.8 mg, 62%). IR(ATR) n/cm-1 3295
(OH), 1720 (C O), 1221 (C–O), 1435 (COO-), 1582 (COO-).
Found: C, 49.06; N, 7.07; H, 4.94%. C46H54N6O14Rh2 requires C,
49.29; N, 7.50; H, 4.86%.
Refls. coll.
Ind. refls. (Rint
)
R1 (I > 2s(I))a
wR2 (I > 2s(I))a
R1 (all data)a
wR2 (all data)a
GOF
0.0904
0.0393
0.0933
1.035
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fc|/ ꢀFo|; wR2 = [ w(Fo - Fc2)2/ wFo
] .
2
4 1/2
X-Ray diffraction
Acknowledgements
Data (Tables 1 and 2) were collected on a Bruker SMART CCD
diffractometer with Mo-Ka radiation. The structures were solved
using SHELXS-97 and refined by full matrix least-squares on F2
using SHELXL-97 with anisotropic thermal parameters for all
non hydrogen atoms.31 The hydrogen atoms were introduced at
calculated positions and not refined (riding model). In the case of
the structure of 13, the SQUEEZE command was employed owing
to the presence of highly disordered solvent molecules.30
CCDC 815819–815825 contain the supplementary crystal-
lographic data for compounds 1–2 and 10–14. For crystal-
lographic data in CIF or other electronic format see DOI:
10.1039/c1dt10359h
We thank the Universite´ de Strasbourg, the Institut Universitaire
de France, the Ministry of Education and Research, the C.N.R.S.
and Marie Curie Est Actions FUMASSEC Network (Contract
N◦ MEST-CET-2005-020992) for financial support.
Notes and references
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Dalton Trans., 2011, 40, 7403–7411 | 7409
©

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