Synthesis of triple-stranded complexes using bis(dipyrromethene) ligands

Article abstract of DOI:10.1021/ic101694z

The reaction of an α-free, β,β′-linked bis(dipyrromethene) ligand with Fe³⁺ or Co³⁺ led to noninterconvertible triple-stranded helicates and mesocates. In the present context, a stable α-free ligand 2 has been developed and complexat

Full text of DOI:10.1021/ic101694z

11550 Inorg. Chem. 2010, 49, 11550–11555
DOI: 10.1021/ic101694z
Synthesis of Triple-Stranded Complexes Using Bis(dipyrromethene) Ligands
Zhan Zhang and David Dolphin*
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia
V6T 1Z1, Canada
Received August 19, 2010
The reaction of an R-free, β,β0-linked bis(dipyrromethene) ligand with Fe3þ or Co3þ led to noninterconvertible triple-
stranded helicates and mesocates. In the present context, a stable R-free ligand 2 has been developed and
complexation of ligands 1 and 2 with diamagnetic Co3þ, Ga3þ, and In3þ has been studied. The triple-stranded M213
(M = Ga, In) and M223 (M = Co, Ga, In) complexes were characterized using matrix-assisted laser desorption
ionization time-of-flight spectrometry, 1H NMR and UV-vis spectroscopy, and X-ray crystallography. Again, the 1H
NMR analysis showed that both the triple-stranded helicates and mesocates were generated in this metal-directed
assembly. Consistent with our previous finding on coordinatively inert Co3þ complexes, variable-temperature NMR
spectroscopy indicated that the triple-stranded helicate and mesocate of labile In3þ did not interconvert in solution,
either. However, the diastereoselectivity of the M223 complexes was found to improve with an increase in the reaction
temperature. Taken together, this study complements the coordination chemistry of poly(dipyrromethene) ligands and
provides further insight into the formation of helicates versus mesocates.
Introduction
synthesis of nonpolar double-stranded helicates,9-13 trian-
gular helicates,14,15 and oligomeric linear complexes.16 How-
ever, these complexes were all constructed on the basis of
tetrahedral coordination of the dipyrromethenes with a diva-
lent metal. Curiously, neutral octahedral poly(dipyrromethene)
complexes have rarely been reported,17 even though mono-
nuclear octahedral ones3,4 and multinuclear double-stranded
ones9-13 have long been recognized. It is of interest to learn the
requirements for a poly(dipyrromethene) ligand to form supra-
molecular architectures with octahedral geometry and to devel-
op an efficient synthesis of ligands capable of generating such
attractive three-dimensional supramolecules.
As a result of a fully conjugated bipyrrolic system, depro-
tonated dipyrromethenes (also known as dipyrrins) are
known as useful monoanionic ligands that can, when co-
ordinated with di- or trivalent metals, generate attractive
uncharged complexes that have strong absorptions in the
visible region.1-5 As such, dipyrromethene complexes may
serve as functional subunits of synthetic light-harvesting
devices and, as a result, have drawn considerable attention
in the last few decades.6-8 In the pursuit of chromophoric
supramolecular complexes, poly(dipyrromethene)s, which
contain multiple dipyrromethene units connected by a
linker, have been investigated as building blocks for the
Recently, we reported the first examples of multinuclear
octahedral bis(dipyrromethene) complexes, Fe213 and Co213,
which are uncharged complexes with intensive UV-vis
*To whom correspondence should be addressed. E-mail: david.dolphin@
ubc.ca. Fax: 1-604-822-9678.
(1) March, F. C.; Couch, D. A.; Emerson, K.; Fergusson, J. E.; Robinson,
absorption.17 The reaction of ligand 1 and Fe3þ (or Co3þ
)
gives both triple-stranded helicates and mesocates. In con-
trast, diastereoselective formation of helicates is normally
W. T. J. Chem. Soc. A 1971, 440–448.
(2) Bruckner, C.; Karunaratne, V.; Rettig, S. J.; Dolphin, D. Can. J.
Chem. 1996, 74, 2182–2193.
(3) Murakami, Y.; Matsuda, Y.; Sakata, K.; Harada, K. Bull. Chem. Soc.
Jpn. 1974, 47, 458–462.
(4) Murakami, Y.; Sakata, K.; Harada, K.; Matsuda, Y. Bull. Chem. Soc.
Jpn. 1974, 47, 3021–3024.
(5) Thoi, V. S.; Stork, J. R.; Magde, D.; Cohen, S. M. Inorg. Chem. 2006,
45, 10688–10697.
(6) Yu, L. H.; Muthukumaran, K.; Sazanovich, I. V.; Kirmaier, C.;
Hindin, E.; Diers, J. R.; Boyle, P. D.; Bocian, D. F.; Holten, D.; Lindsey,
J. S. Inorg. Chem. 2003, 42, 6629–6647.
(10) Zhang, Y.; Wang, Z. M.; Yan, C. H.; Li, G. P.; Ma, J. S. Tetrahedron
Lett. 2000, 41, 7717–7721.
(11) Thompson, A.; Dolphin, D. J. Org. Chem. 2000, 65, 7870–7877.
(12) Chen, Q. Q.; Zhang, Y. J.; Dolphin, D. Tetrahedron Lett. 2002, 43,
8413–8416.
(13) Wood, T. E.; Dalgleish, N. D.; Power, E. D.; Thompson, A.; Chen,
X. M.; Okamoto, Y. J. Am. Chem. Soc. 2005, 127, 5740–5741.
(14) Thompson, A.; Rettig, S. J.; Dolphin, D. Chem. Commun. 1999, 631–
632.
(7) Sazanovich, I. V.; Kirmaier, C.; Hindin, E.; Yu, L. H.; Bocian, D. F.;
Lindsey, J. S.; Holten, D. J. Am. Chem. Soc. 2004, 126, 2664–2665.
(8) Wood, T. E.; Thompson, A. Chem. Rev. 2007, 107, 1831–1861.
(9) Zhang, Y. J.; Thompson, A.; Rettig, S. J.; Dolphin, D. J. Am. Chem.
Soc. 1998, 120, 13537–13538.
(15) Ma, L.; Shin, J. Y.; Patrick, B. O.; Dolphin, D. CrystEngComm 2008,
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(16) Miao, Q.; Shin, J.-Y.; Patrick, B. O.; Dolphin, D. Chem. Commun.
2009, 2541–2543.
(17) Zhang, Z.; Dolphin, D. Chem. Commun. 2009, 6931–6933.
r
pubs.acs.org/IC
Published on Web 11/11/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 24, 2010 11551
Figure 1. R-Free, β,β0-linked proligands 1-H2 2HBr and 2-H2.
3
Scheme 1. Synthesis of Proligand 2-H2
Figure 2. Stick model of the crystal structures of helicates Co223 and
Ga223. Note: The helicates were a racemic mixture. Phenyl groups and
hydrogen atoms have been omitted for clarity.
Table 1. Product Ratios at Different Reaction Temperaturesa
helicate/mesocate ratio
reaction temperature (°C) Co213 Ga213 In213 Co223 Ga223 In223
25
65
150
3:2
3:2
b
3:2
3:2
b
2:3
3:2
b
2:1
4:1
5:1
3:2
5:2
7:1
3:2
2:1
4:1
observed in the well-reported studies of double-stranded
complexes.9-13 More intriguingly, the isolated helicates (or
mesocates) did not convert to the corresponding diastereo-
meric mesocates (or helicates) even upon heating, suggesting
that this complexation process is not simply under thermo-
dynamic control, as is usually observed in a common metal-
directed self-assembly. In order to examine whether this
phenomenon is only a result of the well-known inertness of
Co3þ complexes or is prevalent for other metal complexes,
reactions of a stable ligand with metals, especially more la-
bile ones such as Ga3þ and In3þ, need to be investigated. Un-
fortunately, because of the presence of four unsubstituted R
a The ratios were determined using 1H NMR after chromatography.
b Not measured because the proligand rapidly decomposed at this
temperature.
Upon coordination with a diamagnetic trivalent metal
in the presence of a few drops of NEt3, both ligands 1 and
2 produced nonpolar triple-stranded complexes. To ac-
hive higher yields of the nonpolar products, methanol was
used as the reaction medium for the complexation of ligand
2. Under optimal conditions, the total yield of Ga223 com-
plexes (Figure 2) was almost double compared to that of
Ga213 complexes, while the yields of In213 and In223 com-
plexes were very similar. Surprisingly, when [Co(py)4Cl2]Cl,
which worked well with ligand 1, was used, the expected
complexes were generated in relatively low yields.
positions, proligand 1-H2 2HBr (Figure 1) is exceedingly
3
unstable in solution, which severely limits its usefulness. In
this study, we have designed and developed the synthesis of a
novel R-free, β,β0-linked bis(dipyrromethene), 2-H2, which is
pretty stable in both solution and the solid state. Using the
bis(dipyrromethene) ligands as models, we hoped our inves-
tigations could provide some insight into the self-assembled
formation of helicate versus mesocate and provide direction
for future ligand design.
Both helicate and mesocate were generated in all of the
reactions. Judging from integration of their H NMR
1
signal(s), the helicate/mesocate product ratios of diamag-
netic M213 (M = Co, Ga, In) complexes were essentially
not affected by the metal ion used when the reaction was
carried out at 65 °C (Table 1). Although the Fe213 and
Co213 helicates and mesocates can be isolated on silica
gel, the Ga213 and In213 complexes degraded under the
same conditions. Alumina facilitated the separation of
these complexes from the reaction mixture but was not
effective enough to allow separation of the M213 diaste-
reomers. In the case of the M223 complexes, the helicates
and mesocates, unfortunately, have very similar Rf values
on both silica gel and alumina and thus could not be
separated from each other using common chromatogra-
phy. However, carrying out the complexation of ligand 2
at 150 °C eventually led to the helicates as predominant
products. In contrast, changing the reaction temperature of
ligand 1 did not result in a significant change in the product
ratio. Ligands 1 and 2 also produced triple-stranded com-
Results and Discussion
Ligand Design and Preparation of the Complexes. The
fully R-free, β,β0-linked ligand 1 was synthesized by
condensing an R-free dialdehyde and fully R-free
pyrrole.17 To improve its stability and meanwhile to keep
the R-unsubstituted character, a functional group might
be introduced to the meso position of each dipyrro-
methene fragment. On the basis of the knowledge that
an aryl group, especially an electron-withdrawing one at
the meso position, can dramatically improve the stability
of dipyrromethenes, we decided to introduce a phenyl
group to these positions. Starting from β,β0-linked 4,
proligand 2-H2 was readily synthesized by reduction,
condensation, and oxidation (Scheme 1). It is note-
worthy, however, that oxidation with dichlorodicyano-
quinone (DDQ) produced not only the desirable 2-H2 but
also a small amount of the scrambled product 5-phenyl-
dipyrromethene. An attempt at using the less reactive
oxidant chloranil overnight failed to achieve conversion
from 5 to 2-H2. As anticipated, this bis(dipyrromethene)
displayed very good stability.
plexes with paramagnetic metals such as Fe3þ and Mn3þ
.
The presence of two types of nonpolar complexes with very
similar polarity on thin-layer chromatography (TLC) plates
suggests that both helicates and mesocates were formed.
Preliminary X-ray analysis showed that the crystals grown
out of the product mixture had a helical structure, indicating

11552 Inorganic Chemistry, Vol. 49, No. 24, 2010
Zhang and Dolphin
Figure 4. Bis(dipyrromethene) hydrobromide salts 6-9-H2 2HBr.
3
103°, only 2° greater than that of the Co213 helicate.
Figure 3. UV-vis spectra of M213 and M223 complexes. Note: The
complexes were prepared at 65 °C and are a mixture of helicate and
mesocate.
˚
The M-M distance is 7.765 A for the Co223 helicate,
leading to a helical pitch of 27.1 A. Similar to the cases of
˚
the Co213 and Co223 helicates, the mean Ga-N bond
length of the Ga223 helicate (2.051 A) compares well to the
that the helicates again might be the major products in these
cases. However, accurate helicate/mesocate ratios are still to
be determined, and the properties of these complexes are
under study.
˚
5
reported bond lengths of 2.054 and 2.053 A. The twist
˚
angle of the Ga223 helicate is 97°, smaller than those of the
Co213 and Co223 helicates but close to that of the Fe213
Characterization of the Complexes. Using 2-[(2E)-3-
(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile
(DCTB) as the matrix, matrix-assisted laser desorption
ionization time-of-flight mass spectroscopy showed that
all of the nonpolar complexes had a mass corresponding
to M2L3 (L = 1, 2), indicating that they were triple-
stranded. The 1H NMR spectra of the diamagnetic
M213 and M223 complexes are consistent with the fact
that both the helicate and mesocate were generated from
the same ligand and metal. Because a helicate has a D3
point group and a mesocate has C3h symmetry, the protons
of the methylene linker are homotopic in a helicate and
diastereotopic in a mesocate. Therefore, the singlet signal for
the methylene group belonged to the helicate, while the two
doublets, located at relatively higher field, represented the
mesocate. In particular, the helicates and mesocates of
Ga2L3 and In2L3 (L = 1, 2) can be unambiguously identi-
fied by the multiplicity of the methylene linker, but the two
doublets merged into one broad peak in the case of the
Co223 mesocate. In 1,2-dichlorobenzene-d4, a similar phe-
nomenon was also observed for the In223 mesocate.
Single crystals suitable for X-ray analysis were grown
out of the product mixture prepared at 150 °C by vapor
diffusion of hexane into a CH2Cl2 (or CHCl3) solution
(Table S1 in the Supporting Information). The crystal
structures showed that, consistent with the observation
helicate.17 The Ga-Ga distance is 8.038 A. Conse-
˚
˚
quently, the Ga223 helicate owns a helical pitch of 29.8 A.
The primary UV-vis spectral features of the triple-
stranded M213 and M223 complexes are intense absorp-
tion bands (ε > 105 M-1 cm-1) with maxima at around
3
500 nm (Figure 3). Compared to the corresponding
mononuclear analogues, the major band of the dinu-
clear triple-stranded complexes has a similar pattern but
a pronounced bathochromic shift of approximately
40 nm.3-5,18 The strong similarity between the M223
and M213 complexes indicates that the substituent effect
at the β or meso position on the ligand makes little
difference to the optical properties of these complexes.
Similar to the octahedral mononuclear complexes,3-5,18
the absorption spectra of transition-metal complexes are
characterized by a broad band with relatively weak
absorbance, while the main spectral feature of main-
group Ga3þ and In3þ helicates is a sharp, intense peak.
Scope of Bis(dipyrromethene) Ligands Capable of Gen-
erating Triple-Stranded Complexes. Both substituted R,
R0- and β,β0-linked bis(dipyrromethene)s have been re-
ported to form double-stranded helicates.8,11 To survey
their capability of generating neutral triple-stranded com-
plexes, substituted ligands 6-9 (Figure 4) with different
linker or R substituents were synthesized and examined.
When ligands such as 6-8 were employed, neutral M2L3
complexes were not detected in any of the reactions.
Interestingly, when β,β0-linked 9, which has two R posi-
tions unsubstituted, was reacted with Co3þ or Fe3þ, a
neutral species was generated; however, considerable de-
gradation occurred during chromatography, and a pure
sample, suitable for characterization, was not obtained.
As evidenced by these facts, the size of the R substit-
uents is crucial for the formation of homoleptic bis-
(dipyrromethene) triple-stranded complexes. Only li-
gands with the R position unsubstituted can generate
1
using H NMR, the predominant diastereomers were
the helicates (Figure 3). In the solid state, the bis(meso-
phenyldipyrromethene) Co223 helicate had M-N
bond lengths and N-M-N bond angles quite similar to
those of the β-substituted Co213 helicate.17 The mean
˚
M-N bond length of the Co223 helicate was 1.937 A,
also comparable to those of reported mononuclear
complexes.18 The twist angle of the Co223 helicate is
(18) Bruckner, C.; Zhang, Y. J.; Rettig, S. J.; Dolphin, D. Inorg. Chim.
Acta 1997, 263, 279–286.

Article
Inorganic Chemistry, Vol. 49, No. 24, 2010 11553
stable triple-stranded complexes with octahedral metals:
this is consistent with the observations on mononuclear
complexes.3 Further, the failure of R-free R,R0-linked
bis(dipyrromethene) ligand 7 suggests that the location
of the linker is also critical. In contrast, the length of the
linker seems to have no major effect. It is noteworthy,
however, that the length of the linker is among the most
important ligand features that affect the structure of the
product. According to our previous work,11 when n = 0
or n > 4 (n = number of carbon atoms in a linker), the
ligand may favor the formation of mononuclear or even
triangular complexes.9,11,14
Scheme 2. Interconversion between the pseudo-S and pseudo-C Con-
formations of Bis(dipyrromethene) Ligands
Formation of Helicate versus Mesocate. Since the first
discovery of a triple-stranded mesocate over a decade ago,19
chemists have made significant progress toward under-
standing the formation of helicates versus mesocates.20,21
Particularly, Albrecht and co-workers recognized that li-
gand linkers need to take either an asymmetric “S” or a
symmetric “C” conformation in order to form D3 helicates
or C3h mesocates and proposed an empirical odd-even rule
on the basis of the self-assembly of a series of dicatechol
ligands.22-27 It was suggested that, because of the “zigzag”
arrangement of the alkyl chains, a linker with an odd
number of methylene units leads to the symmetric “C”
structure of the ligand and thus facilitates the formation
of mesocate, while one with an even number of methylene
units makes the ligand take an asymmetic “S” conforma-
tion, which favors the helicate. However, obtaining both a
triple-stranded helicate and mesocate from the same reac-
tion in our study implies that an alkyl-linked ligand, upon
coordination, can take either a pseudo-S or pseudo-C
conformation through bond rotation (Scheme 2). Because
the transition between the pseudo-S or pseudo-C confor-
mers, of the methylene-linked ligands, does not usually
involve much steric strain, these conformers interconvert
rapidly under the reaction conditions. Presumably, even an
ethylene-linked ligand may take a cis pseudo-C conformation
and lead to mesocate. Therefore, the stereochemistry of the
product(s) cannot be simply determined by the conforma-
tional preference of an alkyl linker.
ratio, indicating even the more labile In3þ helicate and
mesocate do not interconvert in solution (see the Sup-
porting Information). We therefore conclude that the
lack of interconversion is common for such triple-
stranded helicates and mesocates.
The fact that a pair of helicate and mesocate does not
interconvert opens a door to improving the diastereos-
electivity by changing the reaction conditions. To achieve
this goal, both the reaction medium and temperature were
varied for the complexation of ligand 2. It turned out that
the product ratio of ligand 2 with a trivalent metal did not
change in various solvents such as chloroform, N,N-di-
methylformamide (DMF), and methanol. However, the
reaction temperature had a significant influence on the
product ratio (Table 1). Surprisingly, decreasing the reac-
tion temperature did not enhance the selectivity as it gen-
erally does. On the contrary, increasing the reaction tem-
perature led to the predominant formation of helicates. It
is noteworthy, however, in cases where a triple-stranded
helicate can convert into the mesocate through either a
dissociative or a nondissociative pathway, that the pro-
duct ratio will eventually be governed by thermodynamic
factors.
Conclusion
In summary, we have established the synthesis of a stable
R-free, β,β0-linked bis(dipyrromethene) ligand. A survey on a
series of bis(dipyrromethene) ligands showed that the size of
the R substituents and the linker location of the bis-
(dipyrromethene) ligands is crucial. Coordinating with either
group 13 or transition metals, R-free, β,β0-linked ligands
generated both the triple-stranded helicate and mesocate.
Although the diastereomers did not interconvert under the
reaction conditions, the diastereoselectivity could be en-
hanced by increasing the reaction temperature. The triple-
stranded bis(dipyrromethene) complexes have strong ab-
sorptions around 500 nm and can be, in principle, widely
modified and exploited as self-assembling functional chro-
mophores in the future.
In our previous study,17 the isolated pair of bis-
(dipyrromethene) helicate and mesocate was found not
to interconvert even upon heating. We suggested that
severe steric overlap of the R hydrogen atoms in either a
Bailar or a Ray-Dutt twist intermediate blocks the non-
dissociative interconversion. The same lack of intercon-
version was also observed for the current helicate/
mesocate mixture in solution using variable-temperature
1H NMR. Take the In223 complexes for example, the
temperature change over a range from room temperature
to 155 °C did not lead to a change of the helicate/mesocate
(19) Albrecht, M.; Kotila, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 2134–
2137.
(20) Piguet, C.; Bernardinelli, G.; Hopfgartner, G. Chem. Rev. 1997, 97,
2005–2062.
(21) Albrecht, M. Chem. Rev. 2001, 101, 3457–3497.
(22) Albrecht, M.; Kotila, S. Chem. Commun. 1996, 2309–2310.
(23) Albrecht, M.; Rottele, H.; Burger, P. Chem.;Eur. J. 1996, 2, 1264–
1268.
(24) Albrecht, M. Chem.;Eur. J. 2000, 6, 3485–3489.
(25) Albrecht, M.; Janser, I.; Houjou, H.; Frohlich, R. Chem.;Eur. J.
2004, 10, 2839–2850.
Experimental Section
Materials and Instrumentation. Starting materials were pur-
chased from commercial suppliers and used without further
purification. Column chromatography was carried out using
silica gel (particle size: 0.040-0.063 mm, 230-400 mesh)
or alumina (particle size: 60-325 mesh, neutral, 6% H2O
added). The mass spectrometry (MS) and high-resolution MS
(HRMS) spectra were measured on Kratos MS50 (electron
impact, EI), Kratos Concept IIHQ (EI), or Bruker Esquire∼LC
(electrospray ionization, ESI) spectrometers. The mass of the
(26) Albrecht, M.; Janser, I.; Houjou, H.; Frohlich, R. Chem. Commun.
2005, 157–165.
(27) Albrecht, M.; Frohlich, R. Bull. Chem. Soc. Jpn. 2007, 797–808.

11554 Inorganic Chemistry, Vol. 49, No. 24, 2010
Zhang and Dolphin
metal complexes was examined using MALDI-TOF in the
presence of DCTB as the matrix on a Bruker Biflex IV instru-
ment. Elemental analysis was performed on a Carlo Erba EA
1108 elemental analyzer. 1H and 13C NMR spectra were re-
corded with Bruker 300 spectrometers, and chemical shifts are
reported in ppm using the residual nondeuterated solvent as the
reference standard. The melting points of crystalline com-
pounds were measured with a Bristoline melting point appara-
tus and are uncorrected. The UV-vis spectra were measured on
a Varian Cary 5000 spectrophotometer. X-ray crystallographic
analyses were carried out on a Bruker X8 APEX diffractometer
with graphite-monochromated Mo KR radiation. Data were
collected and integrated using the Bruker SAINT software
package. The structures were solved by direct methods. All
refinements were performed using the SHELXTL crystallo-
graphic software package of Bruker-AXS.
Figure 5. Compounds 10-12.
added DDQ (0.1 g, 0.44 mmol). The reaction mixture was then
stirred at room temperature for 3 h. After the solvent was removed
under pressure, the product was isolated as a dark-brown solid by
column chromatography. Yield: 0.045 g, 45%. Mp: 166-168 °C.
Rf (silica; ethyl acetate/hexanes, 1:4): 0.59. 1H NMR (300 MHz,
CD2Cl2): δ 12.64 (br s, 2H, NH), 7.69-7.68 (d, J = 1.1 Hz,
2H, pyrrole-H), 7.50-7.44 (m, 10H, Ph-H), 7.38-7.37 (m, 2H,
pyrrole-H), 6.41 (d, J = 1.1 Hz, 2H, pyrrole-H), 6.39-6.37 (dd,
J = 4.0 Hz, J0 = 1.1 Hz, 2H, pyrrole-H), 6.30-6.29 (dd, J = 4.0
Hz, J0 = 2.2 Hz, 2H, pyrrole-H), 3.59 (s, 2H, meso-CH2). 13C
NMR (75 MHz, CD2Cl2): δ 153.9, 146.1, 142.2, 137.9, 136.9,
136.1, 134.7, 131.2, 129.5, 129.3, 128.1, 124.7, 114.1, 25.1. MS (EI):
m/z 452 (Mþ). HRMS (EI). Calcd for C31H24N4 (Mþ): m/z
452.20010. Found: m/z 452.19982.
Preparation of Proligands. The R-free, β,β0-linked proligand
1-H2 2HBr was prepared following our recently reported
3
method.17 R,R0-Linked proligands 6- and 7-H2 2HBr were
3
prepared according to the reported procedures.28,29
4,40-Methylenebis(1H-pyrrole-4,2-diyl)bis(phenylmethanone)
(4). β,β0-Linked 4 was synthesized according to the method used
for β,β0-linked diformyldipyrromethanes.30 2-Benzoylpyrrole 3
(1.7 g, 10 mmol) and dimethoxymethane (5 mmol) were dis-
solved in anhydrous acetonitrile (50 mL). The solution was
cooled to 0 °C and subsequently treated with boron trifluoride
diethyl etherate (10 mmol, 1.0 equiv). The reaction was allowed
to proceed at 0 °C for 1 h before being quenched with NEt3.
After evaporation, the reaction mixture was separated by
column chromatography on silica gel using ethyl acetate/hex-
anes (1:4) as the eluent. 4 was obtained as a white solid. Yield:
0.43 g, 12%. Mp: 211-213 °C. Rf (silica; ethyl acetate/hexanes,
1:2): 0.20. 1H NMR (300 MHz, acetone-d6): δ 10.85 (br s, 2H,
NH), 7.86-7.83 (m, 4H, Ph-H), 7.61-7.46 (m, 6H, Ph-H),
7.12-7.10 (m, 2H, pyrrole-H), 6.76-6.75 (m, 2H, pyrrole-H),
3.76 (s, 2H, meso-CH2). 13C NMR (75 MHz, acetone-d6):
δ 184.5, 140.0, 132.3, 129.6, 129.5, 129.2, 127.0, 124.9, 119.6,
24.9. MS (EI): m/z 354 (Mþ). Elem anal. Calcd for C23H18N2O2:
C, 77.95; H, 5.12; N, 7.90. Found: C, 77.61; H, 5.26; N, 7.76.
Bis{5-[phenyl(1H-pyrrol-2-yl)methyl]-1H-pyrrol-3-yl}meth-
ane (5). 4 (0.10 g, 0.28 mmol) in MeOH (10 mL) was treated with
excess NaBH4 in several portions. Once the starting material
was consumed, the solvent was removed and the organic residue
was taken up in CH2Cl2 and washed with H2O. Removal of
CH2Cl2 provided a colorless liquid, which, subsequently, was
dissolved in pyrrole (50 mL) and treated with trifluoroacetic
acid (0.022 mL, 0.29 mmol) at room temperature. The reaction
was allowed to proceed for 15 min before quenching with
aqueous NaOH. After the reaction mixture was washed, dried,
and separated on silica gel, 5 was obtained as a viscous oil. Yield:
0.11 g, 82%. Rf (silica, CH2Cl2): 0.45. 1H NMR (300 MHz,
acetone-d6): δ 9.60 (br s, 2H, NH), 9.20 (br s, 2H, NH),
7.29-7.15 (m, 10H, Ph-H), 6.68-6.65 (m, 2H, pyrrole-H),
6.45-6.43 (m, 2H, pyrrole-H), 6.00-5.97 (dd, J = 5.9 Hz,
J0 = 2.9 Hz, 2H, pyrrole-H), 5.76-5.67 (m, 2H, pyrrole-H),
5.67-5.66 (t, J = 1.8 Hz, 2H, pyrrole-H), 5.38 (s, 2H, pyrrole-
H), 3.53 (s, 2H, meso-CH2). 13C NMR (75 MHz, CD2Cl2): δ 143.1,
133.2, 133.0, 129.1, 128.8, 127.3, 125.0, 117.7, 115.2, 108.7, 108.4,
107.5, 44.7, 25.4. MS (EI): m/z 456 (Mþ). HRMS (EI). Calcd for
C31H28N4 (Mþ): m/z 456.23140. Found: m/z 456.23116.
General Procedure for the Synthesis of Substituted β,β0-Linked
Proligands 8 and 9. 10 (1 mmol) was dissolved in methanol
(5 mL) and treated with HBr (33% in acetic acid, 1 mL) at room
temperature. After the mixture was stirred for 1 h, 11 (or 12)
(2 mmol) was added. The solution was stirred for another 1 h
before the addition of diethyl ether (50 mL). The proligand was
obtained as a red powder after filtration (Figure 5).
1,3-Bis{5-[(4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene)methyl]-2,
4-dimethyl-1H-pyrrol-3-yl}propane Dihydrobromide (8-H2 2HBr).
3
1
Yield: 83%. H NMR (300 MHz, CDCl3 with a few drops of
CD3OD): δ 6.97 (s, 2H, CH), 2.49 (s, 6H, CH3), 2.45 (s, 6H, CH3),
2.36-2.27 (m, 8H, CH2), 2.17 (s, 6H, CH3), 2.14 (s, 6H, CH3),
1.53-1.42 (m, J = 7.7 Hz, 2H, meso-CH2), 0.98-0.92 (t, J = 7.6
Hz, 6H, CH3). 13C NMR (75 MHz, CDCl3 with a few drops of
CD3OD): δ 154.2, 152.3, 142.3, 141.6, 130.9, 127.7, 126.2, 125.7,
118.7, 29.8, 23.3, 16.9, 13.9, 12.3, 9.8, 9.6. Elem anal. Calcd for
C33H46Br2N4: C, 60.19; H, 7.04; N, 8.51. Found: C, 59.53; H, 7.06;
N, 8.38. HRMS (EI, [M - 2HBr þ H]þ). Calcd for C33H45N4: m/z
497.3644. Found: m/z 497.3650.
1,3-Bis{5-[(3,4-dimethyl-2H-pyrrol-2-ylidene)methyl]-2,4-
dimethyl-1H-pyrrol-3-yl}propane Dihydrobromide (9-H2
-
3
2HBr). Yield: 80%, red solid. 1H NMR (300 MHz, CDCl3 with
a few drops of CD3OD): δ 7.45 (s, 2H, CH), 7.11 (s, 2H, CH),
2.50 (s, 6H, CH3), 2.39-2.33 (t, J = 7.7 Hz, 4H, CH2), 2.18
(s, 6H, CH3), 2.17 (s, 6H, CH3), 1.94 (s, 6H, CH3), 1.52-1.46
(m, 2H, CH2). 13C NMR (75 MHz, CDCl3 with a few drops of
CD3OD): δ 156.4, 143.8, 141.9, 139.4, 129.0, 127.2, 126.7, 124.9,
120.9, 29.5, 23.4, 12.8, 10.0, 9.8, 9.6. HRMS (EI, [M - 2HBr þ
H]þ). Calcd for C29H37N4: m/z 441.3018. Found: m/z 441.3009.
General Procedure for the Synthesis of Triple-Stranded M213
Complexes. The M213 complexes were synthesized at 65 °C
following the method used for the preparation of the Fe213
and Co213 complexes.17 After chromatography, on alumina, the
complexes were isolated as a diastereomeric mixture.
Ga213. Yield: 38%. The helicate/mesocate ratio is approxi-
mately 3:2. Rf (alumina; CH2Cl2/hexanes, 1:1): 0.94. 1H NMR
(300 MHz, CD2Cl2, 25 °C): δ 7.06 (s, helicate-CH and mesocate-
CH), 6.77 (s, helicate-CH and mesocate-CH), 6.33 (s, helicate-
CH and mesocate-CH), 6.23 (s, mesocate-CH), 6.21 (s, helicate-
CH), 3.57 (s, meso-CH2 of the helicate), 3.45-3.40 (d, J = 13.9
Hz, meso-CH2 of the mesocate), 3.28-3.24 (d, J = 14.3 Hz,
meso-CH2 of the mesocate), 2.62-2.55 (q, J = 7.4 Hz, CH2),
2.37-2.21 (m, CH2), 1.17-1.11 (m, CH3), 0.99-0.94 (t, J = 7.7
Hz, CH3). MS (MALDI-TOF): m/z 1371.3 (Mþ). HRMS (EI).
Calcd for C81H91N1269Ga2 ([M þ H]þ): m/z 1369.6001. Found:
m/z 1369.6035.
Bis{5-[phenyl(2H-pyrrol-2-ylidene)methyl]-1H-pyrrol-3-yl}-
methane (2-H2). To a CH2Cl2 solution of 5 (0.1 g, 0.22 mmol) was
(28) Chepelev, L.; Beshara, C.; MacLean, P.; Hatfield, G.; Rand, A.;
Thompson, A.; Wright, J.; Barclay, L. J. Org. Chem. 2006, 71, 22–30.
(29) Sakata, Y.; Nakashima, S.; Goto, Y.; Tatemitsu, H.; Misumi, S.;
Asahi, T.; Hagihara, M.; Nishikawa, S.; Okada, T.; Mataga, N. J. Am.
Chem. Soc. 1989, 111, 8979–8981.
(30) Zhang, Z.; Shin, J. Y.; Dolphin, D. J. Org. Chem. 2008, 73, 9515–
9517.
In213. Yield: 32%. The helicate/mesocate ratio is approxi-
mately 3:2. Rf (alumina; CH2Cl2/hexanes, 1:1): 0.94. 1H NMR

Article
Inorganic Chemistry, Vol. 49, No. 24, 2010 11555
(300 MHz, CD2Cl2, 25 °C): δ 7.06 (s, helicate-CH and mesocate-
CH), 6.86 (s, mesocate-CH), 6.85-6.84 (m, helicate-CH and
mesocate-CH), 6.76 (s, helicate-CH), 6.55 (s, helicate-CH), 6.53
(s, mesocate-CH), 3.66 (s, meso-CH2 of the helicate), 3.53-3.48
(d, J = 14.6 Hz, meso-CH2 of the mesocate), 3.42-3.37 (d, J =
14.6 Hz, meso-CH2 of the mesocate), 2.64-2.57 (q, J = 7.4 Hz,
CH2), 2.43-2.23 (m, CH2), 1.17-1.12 (t, J = 7.5 Hz, CH3),
1.04-0.99 (t, J = 7.7 Hz, CH3). MS (MALDI-TOF): m/z 1460.6
(Mþ). HRMS (EI). Calcd for C81H91N12115In2 ([M þ H]þ): m/z
1461.5567. Found: m/z 1461.5533.
the mesocate), 6.61 (s, pyrrole-H of the mesocate), 6.56-6.54 (dd,
J = 4.0 Hz, J0 = 1.1 Hz, pyrrole-H of the helicate), 6.54-6.52 (dd,
J= 4.0Hz, J0 = 1.5 Hz, pyrrole-H of the mesocate), 6.38 (d, J=1.1
Hz, pyrrole-H of the helicate), 6.33 (d, J = 1.1 Hz, pyrrole-H of the
mesocate), 6.24-6.22 (dd, J = 4.0 Hz, J0 = 1.5 Hz, pyrrole-H of
the helicate), 6.22-6.20 (dd, J = 4.4 Hz, J0 = 1.8 Hz, pyrrole-H of
the mesocate), 3.47 (s, meso-CH2 of the helicate), 3.33-3.29 (dd, J=
14.3 Hz, meso-CH of the mesocate), 3.27-3.23 (dd, J = 14.0 Hz,
meso-CH of the mesocate). MS (MALDI-TOF): m/z 1491.7 (Mþ).
HRMS (ESI). Calcd for C93H67N1269Ga2 ([M þ H]þ): m/z
1489.4123. Found: m/z 1489.4102.
General Procedure for the Synthesis of Triple-Stranded M223
Complexes. The proligand 2-H2 (50 mg, 0.11 mmol) was initially
dissolved in a small amount of chloroform (2 mL) and then
added to refluxing methanol (50 mL) (or DMF when the
reaction was performed at 150 °C: only data of the former are
shown in the following). While heating, Co[(Py)4Cl2]Cl (or
Ga(OAc)3 or InCl3) (0.8 mmol) was added to the solution,
followed by the addition of a few drops of NEt3. The mixture
was stirred and heated at reflux for another 1 h before removal
of the solvent. After chromatography on alumina, the com-
plexes were obtained as diastereomeric mixtures.
In223. Yield: 34%. The helicate/mesocate ratio is approxi-
mately 2:1. Rf (alumina; CH2Cl2/hexanes, 1:1): 0.83. 1H NMR
(300 MHz, CD2Cl2, 25 °C): δ 7.51-7.34 (m, Ph-H of the helicate
and mesocate), 7.20 (d, J = 1.1 Hz, pyrrole-H of the mesocate),
7.06 (s, pyrrole-H of the helicate), 7.03 (d, J = 1.1 Hz, pyrrole-H
of the helicate), 6.84 (s, pyrrole-H of the mesocate), 6.57-
6.55 (dd, J = 4.4 Hz, J0 = 1.1 Hz, pyrrole-H of the helicate),
6.54-6.53 (d, J = 1.1 Hz, pyrrole-H of the mesocate), 6.41-6.40
(d, J = 0.8 Hz, pyrrole-H of the helicate), 6.35-6.34 (d, J = 1.1
Hz, pyrrole-H of the mesocate), 6.31-6.29 (dd, J = 4.0 Hz, J0 =
1.4 Hz, pyrrole-H of the helicate), 6.29-6.27 (dd, J = 4.2 Hz,
J0 = 1.6 Hz, pyrrole-H of the mesocate), 3.52 (s, meso-CH2 of
the helicate), 3.40-3.35 (dd, J = 14.3 Hz, meso-CH of the
mesocate), 3.35-3.28 (dd, J = 14.3 Hz, meso-CH of the
mesocate). MS (MALDI-TOF): m/z 1581.5 (Mþ). HRMS
(ESI). Calcd for C93H67N12115In2 ([M þ H]þ): m/z 1581.3689.
Found: m/z 1581.3739.
Co223. Yield: 9%. The helicate/mesocate ratio is approxi-
mately 3:1. Rf (alumina; CH2Cl2/hexanes, 1:1): 0.83. 1H NMR
(300 MHz, CD2Cl2, 25 °C): δ 7.53-7.39 (m, Ph-H of the helicate
and mesocate), 6.69-6.67 (dd, J = 3.9 Hz, J0 = 2.0 Hz, pyrrole-
H of the helicate), 6.65-6.63 (dd, J = 4.2 Hz, J0 = 1.3 Hz,
pyrrole-H of the mesocate), 6.47 (d, J = 1.4 Hz, pyrrole-H of the
helicate), 6.43 (d, J = 1.5 Hz, pyrrole-H of the mesocate), 6.32
(s, pyrrole-H of the helicate), 6.31-6.29 (dd, J = 3.5 Hz, J0 =
2.0 Hz, pyrrole-H of the helicate), 6.28 (d, J = 1.8 Hz, pyrrole-H
of the mesocate), 6.21 (d, J = 1.5 Hz, pyrrole-H of the helicate),
6.17 (s, pyrrole-H of the mesocate), 6.10 (d, J = 1.8 Hz, pyrrole-
H of the mesocate), 3.44 (s, meso-CH2 of the helicate), 3.26 (s,
meso-CH2 of the mesocate). MS (MALDI-TOF): m/z 1469.6
(Mþ). HRMS (ESI). Calcd for C93H67N1259Co2 ([M þ H]þ): m/z
1469.4241. Found: m/z 1469.4236.
Acknowledgment. This work was supported by the Natural
Sciences and Engineering Research Council of Canada. The
authors thank Dr. Brian O. Patrick in the X-ray crystallography
laboratory of the Department of Chemistry at the University of
British Columbia. We also thank mass spectroscopy labora-
tories of the department.
Ga223. Yield: 71%. The helicate/mesocate ratio is approxi-
mately 2:1. Rf (alumina; CH2Cl2/hexanes, 1:1): 0.83. 1H NMR
(300MHz,CD2Cl2,25°C): δ7.51-7.34 (m, Ph-H of the helicate and
mesocate), 6.80 (s, pyrrole-H of the helicate), 6.74 (d, J = 1.5 Hz,
pyrrole-H of the helicate), 6.70 (d, J = 1.1 Hz, pyrrole-H of
Supporting Information Available: X-ray crystallographic
data in CIF format, NMR spectra, crystal data, and additional
references. This material is available free of charge via the
Internet at http://pubs.acs.org.