Design, synthesis, and structural characterization of a new class of ferrocene-containing heterometallic triple-stranded helicates

Article abstract of DOI:10.1021/om300843r

The new ditopic organoiron ligand, [3,5-bis(1-ferrocenyl-prop-3-enol-1-one) (pyridine)] (H₂L^3,5), has been prepared and the reactions of its dianion (Na₂L^3,5) with M³⁺ ions (M = Ga or In) yield a new class of "3d-np block" heterometallic triple-stranded helicates, M₂(L^3,5)₃, by the self-assembly process. The X-ray structural analysis of the new ligand shows that it is in the enolic form with each enolic carbon bonded to the pyridine ring and each carbonyl carbon connected to a ferrocene moiety; overall, the nonferrocenyl part of the molecule is nearly planar. The M₂(L ^3,5)₃ (M = Ga or In) complexes are helicates with three ligand strands, each of which is twisted into an S-shape, coordinating to two metal ions, each of which is in a distorted octahedral geometry. The new helicates are observed as a racemic mixture in the solid state by single-crystal X-ray analysis, and in solution by NMR, with both the left-handed Λ,Λ-and the right-handed Δ,Δ-isomers present. Variable-temperature ¹H NMR study of the Ga₂(L ^3,5)₃ helicate indicates that the right-handed Δ,Δ-isomer and left-handed Λ,Λ-isomer equilibrate through a heterochiral Λ,Δ-intermediate by a concerted twist motion of one-half of the dinuclear complex through a trigonal prismatic transition state, according to the Bailar twist mechanism. Electrochemical properties of the ligand (H₂L^3,5) and the M₂(L ^3,5)₃ helicates were investigated through cyclic voltammetry, and the results indicate the lack of communication between the ferrocene units, because the separation between any two ferrocene units is greater than the 5-6 A range in both the free ligand and the helicates.

Full text of DOI:10.1021/om300843r

Article
pubs.acs.org/Organometallics
Design, Synthesis, and Structural Characterization of a New Class of
Ferrocene-Containing Heterometallic Triple-Stranded Helicates
Muthukrishna Raja,*,† Ratnasabapathy G. Iyer,† Chengeto Gwengo,† Daniel L. Reger,‡ Perry J. Pellechia,‡
Mark D. Smith,‡ and Andrea E. Pascui‡
†Department of Chemistry, Claflin University, Orangeburg, South Carolina 29115, United States
‡Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208, United States
S
* Supporting Information
ABSTRACT: The new ditopic organoiron ligand, [3,5-bis(1-ferrocenyl-prop-3-enol-1-one)(pyridine)] (H2L3,5), has been
prepared and the reactions of its dianion (Na2L3,5) with M3+ ions (M = Ga or In) yield a new class of “3d-np block”
heterometallic triple-stranded helicates, M2(L3,5)3, by the self-assembly process. The X-ray structural analysis of the new ligand
shows that it is in the enolic form with each enolic carbon bonded to the pyridine ring and each carbonyl carbon connected to a
ferrocene moiety; overall, the nonferrocenyl part of the molecule is nearly planar. The M2(L3,5)3 (M = Ga or In) complexes are
helicates with three ligand strands, each of which is twisted into an S-shape, coordinating to two metal ions, each of which is in a
distorted octahedral geometry. The new helicates are observed as a racemic mixture in the solid state by single-crystal X-ray
analysis, and in solution by NMR, with both the left-handed Λ,Λ- and the right-handed Δ,Δ-isomers present. Variable-
1
temperature H NMR study of the Ga2(L3,5)3 helicate indicates that the right-handed Δ,Δ-isomer and left-handed Λ,Λ-isomer
equilibrate through a heterochiral Λ,Δ-intermediate by a concerted twist motion of one-half of the dinuclear complex through a
trigonal prismatic transition state, according to the Bailar twist mechanism. Electrochemical properties of the ligand (H2L3,5) and
the M2(L3,5)3 helicates were investigated through cyclic voltammetry, and the results indicate the lack of communication between
the ferrocene units, because the separation between any two ferrocene units is greater than the 5−6 Å range in both the free
ligand and the helicates.
Currently, no simple synthetic methodology is available for
the synthesis of triple-stranded helicates with mixed valence
metals and/or different metal centers. Challenges associated
with the synthesis of heterometallic triple-stranded helicates
have been met either by assembling them in a multistep
process5 or by using segmented ligands with a bidentate site
coordinated to the pseudo-octahedral d-block cation and a
tridentate site coordinated to the pseudotricapped trigonal
prismatic lanthanide.6 One possible solution to the challenge of
synthesizing heterometallic triple-stranded helicates is to use
metal-containing ligands as building blocks. Multidentate
ligands built from organometallic moieties will be useful not
only because they influence the shapes of the helicates but also
because of their properties. Use of both metalloligands and
INTRODUCTION
■
Elegant structural motifs ubiquitous in nature from the
microscopic to the macroscopic level, man-made art, and
architectures continue to inspire chemists to design and build
similar synthetic molecules from smaller building blocks by the
self-assembly processes.1 Over the past two decades, numerous
multitopic ligands have been developed and their coordination
chemistry with metal ions has been used to synthesize
aesthetically attractive and functionally useful metal-containing
polyhedra of various shapes ranging from simple grids to
complex catenates and knots.2 The helical architecture has, in
particular, fascinated chemists ever since the discovery of
DNA’s double helix structure. Triple-stranded metallohelicates
are considered simple models for more complex biopolymers,
such as DNA and viruses.3 Building triple-stranded helicates
with one type of metal center has led to a large number of
reports in the literature.4
Received: August 30, 2012
Published: December 28, 2012
© 2012 American Chemical Society
95
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
organometallic ligands in the design and synthesis of helicates is
still in its preliminary stage.7
under a nitrogen atmosphere, and the reaction of 1.5 equiv of
the resulting dianion with M(CF3SO3)3 yields the polynuclear
heterometallic complexes M2(L3,5)3 (M = Ga, 1, 3 or In, 2, 4)
in good yield (Scheme 2). The electrospray mass spectra show
the expected isotopic pattern for the [M2(L3,5)3 + H]+ peaks.
Elemental analyses and NMR spectra also match this
formulation.
Recently, we have communicated the synthesis and structural
characterization of a new organometallic ligand, 1-ferrocenyl-3-
(5-bromopyridyl)-prop-3-enol-1-one (H2L), and a new bimet-
allic 2-D coordination polymer, [Cu(L)2]n, derived from it.8
Results from this study, and the reports detailing the efficacy of
polydiketonates9 in crystal engineering, prompted us to explore
the syntheses and reactions of a new bimetallic ligand, in which
two ferrocene moieties are connected to a pyridine ring
through two-ketoenol linkers. Herein, we describe the synthesis
of a new ditopic organometallic ligand, 3,5-bis(1-ferrocenyl-
prop-3-enol-1-one)(pyridine) (H2L3,5), and its reactions with
gallium(III) and indium(III) to form new polynuclear/
heterobimetallic triple-stranded helicates.
Solid-State Structures. Crystals of H2L3,5 were formed by
layering hexane over a cold CH2Cl2 solution. Figure 1a shows
the two independent molecules in the unit cell. Even though
the β-diketonate fragment is known to be in equilibrium
between keto and enol forms, all analytical data clearly
demonstrate that it is in one of the enolic forms. Each enolic
[C(OH)] carbon in the ligand is bonded to the pyridine ring,
and each carbonyl (CO) carbon is connected to a ferrocene
moiety. The observed bond length for the C−O single bond of
each enolic moiety is 1.31 Å, and the observed bond length for
each CO double bond of the carbonyl moiety is 1.27 Å.
These values are in agreement with reported values for similar
bonds.10 Additional support for the enolic structure is offered
RESULTS AND DISCUSSION
■
Synthesis. The protonated form of a new ditopic
organoiron ligand, [3,5-bis(1-ferrocenyl-prop-3-enol-1-one)-
(pyridine)] (H2L3,5), was synthesized as shown in Scheme 1
1
by both H NMR and 13C NMR. The enolic hydrogen atoms
Scheme 1. Synthesis of Ligand H2L3,5
resonate at 16.53 ppm as a broad peak, and the ene carbon
atoms (−CH) are observed at 94.7 ppm.
The central, nonferrocenyl part of the molecule is nearly
planar. The planar acetylacetone (acac) portions are twisted
only slightly away from the pyridine ring plane; measured
torsion angles are 3.5, −6.2, 2.8 and 5.2°, respectively (Table
1). Given this rigid geometry and the short link between the
two acac groups, the deprotonated ligand is designed to bind
two separate metal centers, the arrangement needed to produce
M2L3 helicates, and given the charge, should form neutral
molecules with metals in the +3 oxidation state.
Single crystals of M2(L3,5)3 suitable for X-ray diffraction
analysis were grown by layering Et2O over a CHCl3 solution. X-
ray diffraction analysis of the gallium(III) and indium(III)
complexes prepared from the NaH preparations reveal that
they are nearly isostructural solids (different solvent of
crystallization) in the rhombohedral space group R3 and
̅
composed of neutral M2(L3,5)3 molecules. Two different views
of the structure of In2(L3,5)3 are shown in Figure 1. The
molecule is a helicate composed of three ligand strands
coordinating to two metal ions, each of which is in a distorted
octahedral geometry. This geometry at the metal centers is
confirmed by the large twist angles, the angles between the two
from diethyl-3,5-pyridinedicarboxylate and acetylferrocene in
good yield (82%). The composition and structure of H2L3,5 was
fully characterized by NMR, MS, elemental analysis, and single-
crystal X-ray diffraction.
Both enolic protons in H2L3,5 are easily deprotonated in
THF using NaH or DBU (see the Supporting Information)
Scheme 2. Synthesis of M2(L3,5)3 [M = Ga or In]
96
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
Figure 1. (a) Structure of two independent moleucles of H2L3,5. (b) Side view of In2(L3,5)3. (c) View of In2(L3,5)3 down the In···In axis. (d) S-shape
of the ligand upon coordination to In. Hydrogen atoms are removed for clarity of the figures.
Table 1. Important Metrics for the Ligand and Metal Complexes
H2L3,5
Ga2(L3,5
)
In2(L3,5
)
Ga2(L3,5)3·[DBU-H][CF3SO3]
In2(L3,5)3·[DBU-H][CF3SO3]
3
3
a
twist angle (deg)
NA
45.32
44.33
39.51
38.58
40.26
36.21
7.53
45.71
42.30
35.81
40.81
39.49
30.68
7.67
52.43
52.43
35.05
42.18
42.18
26.50
7.42
53.46
53.46
32.89
42.84
42.84
22.99
7.49
b
average torsion angle (deg)
4.8
intramolecular M···M distance (Å)
cavity diameter (Å)
NA
NA
16.96
21.89
NA
NA
a
b
Twist angle is defined as the angle between the Cmethine···M···M planes. Torsion angle is defined as the O−C−Cpy−Cpy angle.
Cmethine···M···M planes (Table 1),11 angles emphasized by the
view down the M···M axis (Figure 1c). This arrangement
results in a small central intramolecular void with a maximum
diameter, as measured by the M···M distance, of approximately
7.5 Å (for Ga) and 7.6 Å (for In). These values are similar to
those reported in the literature for neutral M2L3 types of
helicates with analogous organic ligands.12 The structures of the
M2(L3,5)3 molecules from the DBU preparations, which
cocrystallize with one [DBU-H][CF3SO3] per helicate, are
also similar (Table 1).
Δ,Δ configurations or a diastereomeric meso form with a Δ,Λ
configuration. Both complexes crystallize as racemates, with
both the left-handed Λ,Λ- and the right-handed Δ,Δ-isomers
present in the unit cell. Figure 2 shows the two forms. Despite
the short connection between the two acac portions of the
ligands and the near planarity of the protonated ligand, the
helicity of the ligand occurs by ligand distortion upon
coordination. Upon deprotonation and coordination, the
ligands distort into an S-shape (Figure 1d). In this
configuration, the small torsion angle that the acac groups
make with the pyridyl ring in the protonated ligand increases
dramatically (Table 1) in the metal complexes. In all cases, one
Three forms of these molecules containing two trischelate
metal centers can exist, two enantiomeric forms with Λ,Λ or
97
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
currently exploring the plausible use of these cavities in “host−
guest” chemistry.
Variable-Temperature NMR. Compared to the free
1
ligand, both H NMR and 13C NMR spectra show slight shifts
in proton and carbon resonances in the Ga2(L3,5)3 and
In2(L3,5)3 complexes with the largest shifts noted for the 4-
pyridyl carbon and hydrogen atoms and the enolic carbon.
1
However, there were notable differences in the H NMR and
13C NMR spectra of the resonances of the substituted
cyclopentadienyl ring of the metal complexes. In the case of
Ga2(L3,5)3 at 20 °C in deuterated tetrachloroethane (TCE-d2)
solution, one of the two proton singlet resonances of the
cyclopentadienyl ring linked to the acac moiety in the free
ligand splits into two distinct resonances. This spliting (5.03
and 4.97 ppm) is a result of two nonequivalent resonances
corresponding to diastereotopic hydrogens of the substituted
cyclopentadienyl ring in the ligand, likely in the 2,2′-position,
thus confirming the chirality of the molecule in solution. In
toluene, these resonances are split by a larger amount (0.42
ppm) and the 3,3′-position resonance is also slightly split (0.04
ppm). The observation of diastereotopic hydrogen atoms has
been reported previously in somewhat similar gallium helicates
by Raymond and co-workers. They also explained the
observation as evidence for the existence of two enantiomeric
isomers and showed by variable-temperature NMR the
interconversion of two enantiomeric isomers.13
Figure 2. Λ,Λ- (left, red) and Δ,Δ (right, blue)-isomers looking down
the In···In axes. The hydrogen atoms are removed for clarity of the
figure, and the ligand ferrocene molecules are represented by the large
balls.
of the three ligands is less S-shaped, presumably to
accommodate the bulky ferrocene side arms. Interestingly, it
is this S-shaped distortion that allows the octahedral
coordination at the metals; if these torsion angles remained
as small as that in H2L3,5, the metals would be in a nearly
trigonal prismatic arrangement.
In the overall packing of the dinuclear helicates from the
NaH preparations, large “holes” form filled with solvent (Figure
3a). Six molecules with alternating chirality form a circular
arrangement with a center hole approximately 20 Å across.
These rings are organized in stacked layers with the resulting
“columns” close packing with six adjacent columns. It is
interesting to compare this arrangement with that of
(M2(L3,5)3·[DBU-H][CF3SO3]) that was prepared using the
organic base DBU to deprotonate the ligand. From this
preparation, the compound crystallizes in a different space
group, although the helicate molecules are present in essentially
the same racemic configuration. In this form of the molecule,
the dinuclear molecules close pack (Figure 3b) with the one
[DBU-H][CF3SO3] present per dinuclear molecule, demon-
strating the substantial impact of having the [DBU-H]-
[CF3SO3] present during the crystallization procedure.
Variable-temperature 1H NMR studies in TCE-d2 and
toluene were carried out to investigate the possible
interconversion of the two enantiomeric forms of the dinuclear
gallium(III) and indium(III) metallohelicates reported here.
Figure 4 shows the results for compound 1 in TCE-d2.
Although most of the resonances show the normal small
changes in chemical shifts with temperature, the 2,2′-
diastereotopic ferrocene resonances broaden above 40 °C,
pass through a coalescence point around 65 °C, and finally
form a relatively sharp singlet at 5.04 ppm at higher
temperatures. Similar results were obtained in toluene in this
temperature range.
Simulation of the exchanging resonances using DNMR
program as implemented in SpinWorks 3.1.8.214 resulted in the
determination of the corresponding rate constants. The
temperature dependence of the chemical shifts was estimated
from the data collected between −20 and 40 °C, and a
correction for this change was introduced into the simulation of
the spectra used in the variable-temperature analysis. The
One significant difference between the new ferrocene-
containing M2L3 helicates reported here and similar neutral
M2L3 helicates with pure organic ligands is the overall packing
of the dinuclear helicates in a unit cell. Unlike their organic
analogues, the ferrocene-containing helicates pack with large
cavities (diameter ∼ 20 Å) filled with solvent molecules. We are
Figure 3. Overall packing of two forms of In2(L3,5)3: (a) In2(L3,5)3 and (b) In2(L3,5)3·[DBU-H][CF3SO3]. Right-handed (Δ,Δ)-enantiomers are
−
colored shades of blue, left-handed (Λ,Λ) are colored shades of red, DBU-H+ is colored green, and CF3SO3 is colored yellow. Interstitial solvent
and the hydrogen atoms are removed for clarity of the figure.
98
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
cene (Fc*) internal standard and each of the ligand or helicates
dissolved in freshly distilled CH2Cl2 using 0.1 M Bu4NPF6 as
the supporting electrolyte. A summary of the electrochemical
data is presented in Table 2. The ligand and helicates exhibit a
Table 2. Electrochemical Data for the Ligand and Helicates
compound
ferrocene (Fc)
E1/2 (V) ΔEp (V) ipa/ipc
n
0.374
−0.173
0.623
0.553
0.538
0.554
0.547
0.073
0.076
0.118
0.246
0.272
0.156
0.170
0.94
0.95
0.57
0.33
0.35
0.25
0.29
decamethylferrocene (Fc*)
H2L3,5
2.30
5.96
5.89
5.94
6.12
Ga2(L3,5
)
3
In2(L3,5
)
3
Ga2(L3,5)3·[DBU-H][CF3SO3]
In2(L3,5)3 ·[DBU-H][CF3SO3]
1
single quasi-reversible oxidation wave, corresponding to the Fc/
Figure 4. Variable-temperature H NMR (400 MHz) spectra of 1 in
TCE-d2.
Fc+ redox couple, as shown in Figure 5 for H2L3,5, and
activation parameters derived from the Eyring plot at 25 °C are
ΔG⧧ = 16.5(9) kcal mol−1, ΔH⧧ = 12(3) kcal mol−1, and ΔS⧧ =
−13(9) cal mol−1 K−1.
Previously, it was shown that similar dinuclear homohelical
gallium(III) trischelates of the form K6Ga2L3, where L is a
biscatecholamide or bisterephthalamide derivative, isomerize by
a concerted twist motion along the 3-fold axis of one-half of the
dinuclear complex through a trigonal prismatic transition state
according to the Bailar twist mechanism.13 The inversion of the
Λ,Λ- and Δ,Δ-helicates involves the heterochiral Λ,Δ-
intermediate, which is produced by a single twist event at
one metal. The energy of activation for the inversion in this
system was reported as ranging from ΔG⧧ = 17.4−19.1 kcal
mol−1 at 25 °C. The activation parameters for 1 are similar to
the ones measured for K6Ga2L3, indicating that the system
reported here also undergoes a similar intramolecular inversion,
where the Λ,Λ- and Δ,Δ-homochiral helicates interconvert
through a heterochiral Λ,Δ-intermediate. The negative entropy
value and the fact that these parameters are not solvent-
dependent support this intramolecular inversion mechanism.
Spectra recorded below 20 °C show line broadening that we
attribute to increases in the viscosity of the solvent; the impact
of solvent viscosity is larger than one normally observes,
presumably because of the unusually large size of the molecule.
The effect was particularly large in toluene, resulting in
broadening of the resonances that are clearly unrelated to the
Δ,Δ−Λ,Λ inversion. In toluene at −75 °C, the lowest
temperature measured, the data indicate a possible second
dynamic process, where one of the broad resonances starts to
split in two, but further analyses of these resonances was not
possible as toluene freezes at −95 °C.
Figure 5. Cyclic voltammograms of 1 mM solutions (Fc/Fc+) of
H2L3,5 (red), Ga2(L3,5)3·[DBU-H][CF3SO3] (pink), and Ga2(L3,5
)
3
(purple) in CH2Cl2 using 0.1 M Bu4NPF6 as supporting electrolyte
and 1 mM decamethylferrocene (Fc*/Fc*+) as the internal reference.
Scan rate: 50 mV/s.
Ga2(L3,5)3 helicates with or without DBU.15 A comparison of
redox peak current of the internal standard Fc* and H2L3,5 or
helicates gives a reasonable estimate for the number of
electrons (n) being transferred during the redox process, as
shown in Table 2.
The oxidation of ferrocene groups occurs at more positive
potentials compared to ferrocene due to the negative inductive
effects of the acetylacetonate moiety. In comparison with
H2L3,5, the half-wave potentials of helicates are shifted to less
positive potentials by at least 70 mV. The presence of the
neutral [DBU-H][CF3SO3] salt in 3 and 4 does not
significantly influence oxidation potentials of the helicates, a
similar feature noted with NMR, mass spectrometry, and
elemental analysis data.
The single-wave redox signatures observed in these multi-
ferrocene systems are consistent with the absence of electronic
interaction between ferrocene units, a phenomenon commonly
dictated by a separation distance between ferrocene units,
which should ideally be in the 5−6 Å range.16 Single-crystal X-
ray diffraction results indicate the Fe···Fe distance to be greater
than this range in the free ligand (14.48 Å), the coordinated
ligand (13.50 Å for 1 and 13.89 Å for 2), and the Fe atoms on
the same side of the helicate (8.12 Å for 1 and 8.58 Å for 2).
Because of the large intramolecular Fe···Fe distances, ferrocene
units in both the ligand and the helicates undergo concurrent
The indium compound 2 undergoes a similar inversion in
toluene. The 2,2′-ferrocene hydrogen atoms are at the fast
exchange limit at room temperature and broaden as the
temperature is lowered. The limiting low-temperature spectrum
would be below the freezing point of toluene, but from the
observation of a coalescence point at about −45 °C, the ΔG⧧
can be estimated to be about 10 kcal/mol at this temperature.
This value is clearly much smaller than that observed with the
gallium complex 1. This difference is explained by the increase
in the size of the metal ion, which facilitates the Bailar twist
mechanism.
Electrochemistry. Cyclic voltammograms were collected at
a scan rate of 50 mV/s for a 1:1 mixture of decamethylferro-
99
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
redox change and the Fc/Fc+ couple appears at the same
potential. The lack of electronic communication has been
reported for similar meta-substituted arene derivatives function-
alized with ferrocene on the periphery17 and other multi-
ferrocene compounds.18 The quasi-reversibility in these systems
is usually associated with large cathodic−anodic peak
separation (ΔEp) values and is common in systems where
conformational reorganization is required to minimize electro-
mV/s. CH2Cl2 was freshly distilled prior to use. All measurements
were conducted in a Faraday cage connected to a GAMRY Framework
station.
Syntheses. 3,5-Diethyl-pyridinedicarboxylate. This compound
was prepared as previously reported by heating 3,5-pyridinedicarbox-
ylic acid (5.00 g, 29.9 mmol), and H2SO4 (1.5 mL) in ethanol (70 mL)
at reflux for 12 h. Yield: 4.79 g, 72%. mp 47−48 °C. 1H NMR
(CDCl3): δH 9.35 (d, J = 2 Hz, 2H), 8.85 (t, J = 2 Hz, 1H), 4.44 (q, J =
7.2 Hz, 4H), 1.42 (t, J = 7.2 Hz, 6H). 13C NMR (CDCl3): δC 164.6,
154.2, 138.0, 126.3, 61.9, 14.4.
static repulsions during redox processes.19,16 As expected in
a
3,3′-(3,5-Pyridyl)bis(1-ferrocenyl-prop-3-enol-1-one) (H2L3,5). A
solution of acetylferrocene (3.07 g, 13.4 mmol) dissolved in THF
(20 mL) was added dropwise to a suspension of KH (0.898 g, 22.4
mmol) in THF (20 mL). After stirring at room temperature for 1 h, a
solution of the 3,5-diethyl-pyridinedicarboxylate (1.00 g, 4.48 mmol)
in THF (20 mL) was added, and the mixture was stirred at room
temperature for 16 h. Excess KH was neutralized by adding 0.1 M HCl
(50 mL), and the product was extracted with three 50 mL portions of
ethyl acetate, washed with brine solution and water, dried over MgSO4,
and concentrated. The crude product was washed three times with
boiling hexane to remove unreacted acetylferrocene. The final purple
powder obtained was redissolved in a minimum amount of CH2Cl2
and crystallized as purple needles by layering hexane. Yield: 2.15 g,
our multiferrocene systems, the exceptionally large peak
separation (ΔEp ≥ 118 mV) is characteristic of the amount
of intramolecular reorientation required for di- or hexaferroce-
nium cations upon oxidation.
CONCLUSION
■
We have synthesized a new organometallic, ditopic ligand
designed for the formation of triple-stranded helicates and
report here the successful preparation of the first polynuclear
heterometallic triple-stranded helicates that contain both d- and
p-block metals, using a ferrocene-based ketoenolate dianion as
the basic ligand building block and gallium(III) and indium(III)
as the p-block metal. The new helicates form a racemic mixture
in both the solid state and solution of the left-handed Λ,Λ- and
the right-handed Δ,Δ-isomers. Variable-temperature NMR
methods have established that the two enantiomers equilibrate
in solution through a series of single metal Bailar twist
rearrangements. Electrochemical data are consistent with the
absence of electronic interaction between the ferrocene units in
the ligand and both helicates. We note that the methods
reported here can be generally applied to synthesize
polynuclear heterometallic helicates using a variety of organo-
metallic ligands as building blocks. We are actively exploring the
reactions of our new ligands with other transition, lanthanide,
and main-group metal ions. The electrochemistry of helicates
with other electroactive metal ions is being investigated.
1
82%. mp 184−185 °C. H NMR (CDCl3): δH 16.53 (s, 2H), 9.23 (s,
4H), 8.67 (s, 2H), 6.44 (s, 2H), 4.93 (d, J = 2 Hz, 4H), 4.63 (d, J = 2
Hz, 4H), 4.24 (s, 10H). 13C NMR (CDCl3): δC 195.0, 176.5, 150.3,
132.2, 131.2, 94.7, 78.4, 73.0, 70.6, 69.1. Anal. Calcd (Found) for
{[C31H25O4NFe2]4·CH2Cl2}, 61.69 (62.31); H, 4.22 (4.10); N, 2.30
(2.28). EI(+)-MS Calcd (Found) m/z: 587.0483 (587.0494). X-ray
quality crystals were grown by layering hexane over a cold CH2Cl2
solution of H2L3,5. The two phases were allowed to slowly diffuse at 4
°C over 4 days.
General Procedure for the Synthesis of M2(L3,5)3 Complexes.
A solution of H2L3,5 (3 equiv) dissolved in THF (20 mL) was added
to a suspension of NaH (7 equiv) in THF (10 mL), and the mixture
was stirred at room temperature for 30 min. A solution of
M(CF3SO3)3 (2 equiv) dissolved in THF (20 mL) was added, and
the mixture was stirred at room temperature for 16 h. The reaction
mixture was filtered over a pad of Celite, concentrated, washed with
three 50 mL portions of ether, and dried under vacuum to afford a
deep red powder. X-ray quality crystals were grown by layering Et2O
over a saturated CHCl3 solution of each M2(L3,5)3 complex to yield
EXPERIMENTAL SECTION
■
G a 2 ( L 3 , 5
)
3 · ( C H C l 3
)
1 . 4 4 ( C 4 H 1 0 O ) 3 . 2 9
.
,
a n d
General Considerations. All preparations were carried out under
a nitrogen atmosphere using standard Schlenk techniques. Acetylfer-
rocene, ferrocene, decamethylferrocene, tetra-n-butylammonium hexa-
fluorophosphate (Bu4NPF6), 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU), In(CF3SO3)3, KH, NaH, Ga(CF3SO3)3, and 3,5-pyridinedi-
carboxylic acid were purchased from Alfa Aesar and were used without
further purification. Solvents were dried using conventional methods
In2(L3,5)3·(CHCl3)1.44(C4H10O)3.29
Ga2(L3,5)3, 1. Ga2(L3,5)3 was synthesized according to the general
procedure from H2L3,5 (0.400 g, 0.681 mmol), NaH (0.064 g, 1.59
mmol), and Ga(CF3SO3)3 (0.235 g, 0.454 mmol). Yield: 0.328 g, 76%.
1
mp > 260 °C. H NMR (CDCl3): δH 8.85 (br, 3H), 8.80 (br, 6H),
6.17 (s, 6H), 5.10 (br, 6H), 4.90 (br, 6H), 4.54 (br, 12H), 4.21 (s,
30H), 3.47 (q, 4H, −CH2 of ether), 1.20 (t, 6H, CH3 of ether). 13C
NMR (CDCl3): δC 193.3, 181.9, 147.9, 137.6, 136.5, 96.5, 79.8, 72.6,
70.7, 70.1, 69.4, 66.0 (−CH2 of ether), 15.4 (CH3 of ether). Anal.
Calcd (Found) for C97H79O13N3Fe6Ga2: C, 59.16 (58.96); H, 4.04
(3.46); N, 2.13 (2.21). ES(+)-TOF MS Calcd for [Ga2(L3,5)3 + H]+
(Found) m/z: 1896 (1896).
and were freshly distilled prior to use. H and 13C NMR spectra were
1
recorded on a JEOL 300 MHz spectrometer, and chemical shifts were
referenced to solvent resonances at δH 7.25, δC 77.12 for CDCl3.
1
Variable-temperature H spectra were recorded on a Varian Mercury/
VX 400 spectrometer. All chemical shifts are in parts per million and
were referenced to residual undeuterated solvent signals (1H).
Robertson Microlit Laboratories performed all elemental analyses.
Melting points were measured on an MSRS MPA160 DigiMelt
apparatus and are uncorrected. The high-resolution mass spectrum of
the ligand was measured using a VG70SQ mass spectrometer in the EI
mode and mass spectra of the complexes on a MicroMass QTOF
spectrometer, at the University of South Carolina Mass Spectrometry
Center.
Electrochemical activity studies were performed using a GAMRY
PCI 600 potentiostat. Cyclic voltammograms were recorded for
CH2Cl2 solutions containing 1.0 mM analyte, 1.0 mM decamethy-
ferrocene (Fc*) internal standard, and 0.1 M Bu4NPF6 supporting
electrolyte using a three-electrode cell consisting of a platinum
working electrode, a glassy carbon counter electrode, and a Ag/AgCl
reference electrode. Half-wave potentials (E1/2) were calculated from
the average of the cathodic and anodic potentials at a scan rate of 50
In2(L3,5)3, 2. In2(L3,5
) was synthesized according to the general
3
procedure from H2L3,5 (0.200 g, 0.341 mmol), NaH (0.027 g, 1.14
mmol), and In(CF3SO3)3 (0.128 g, 0.227 mmol). Yield: 0.216 g, 95%.
1
mp > 260 °C. H NMR (CDCl3): δH 8.94 (br, 3H), 8.85 (br, 6H),
6.22 (s, 6H), 5.00 (br, 12H), 4.54 (br, 12H), 4.21 (s, 30H). 13C NMR
(CDCl3): δC 195.9, 183.3, 148.2, 137.7, 136.8, 96.9, 80.7, 72.5, 70.8,
69.7. Anal. Calcd (Found) for C94H70O12N3Cl3Fe6In2: C, 53.64
(54.20); H, 3.35 (3.21); N, 2.00 (2.05). ES(+)-TOF MS Calcd for
[In2(L3,5)3] + H]+. (Found) m/z: 1986 (1986).
General Procedure for the Synthesis of [M2(L3,5)3]·[DBU-
H][CF3SO3] Helicates. DBU (6 equiv) was added to a degassed
solution of H2L3,5 (3 equiv) dissolved in THF (20 mL), and the
resultant mixture was stirred at room temperature for 30 min. A
solution of M(CF3SO3)3 (2 equiv) dissolved in THF (20 mL) was
added, and the mixture was stirred at room temperature for 16 h. The
100
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
reaction mixture was filtered over a pad of Celite, and the filtrate was
concentrated to afford a sticky oily residue. The residue was washed
with three 50 mL portions of ether, and dried under vacuum to afford
a deep red sticky solid. The sticky solid was recrystallized over 2 days
in the freezer by layering Et2O over a saturated CH2Cl2 solution. X-ray
quality crystals were grown by layering Et2O over a saturated CHCl3
solution of each [M2(L3,5)3]·[DBU-H][CF3SO3] helicate to yield
[Ga2(L3,5)3]·[DBU-H][CF3SO3]·CHCl3 and [In2(L3,5)3]·[DBU-H]-
[CF3SO3]·CHCl3.
[Ga2(L3,5)3]·[DBU-H][CF3SO3], 3. [Ga2(L3,5)3]·[DBU-H][CF3SO3]
was synthesized according to the general procedure described above
from H2L3,5 (0.200 g, 0.341 mmol), DBU (0.1 mL, 0.682 mmol), and
Ga(CF3SO3)3 (0.118 g, 0.227 mmol). Yield: 0.172 g, 68%. mp > 260
°C. 1H NMR (CDCl3): δH 9.76 (br, 1H), 8.84 (br, 3H), 8.80 (br, 6H),
6.20 (s, 6H), 5.10 (br, 6H), 4.90 (br, 6H), 4.53 (br, 12H), 4.21 (s,
30H), 3.48 (m, 4H), 2.80 (br, 2H), 2.07 (br, 2H), 1.79−1.64 (m,
10H), 1.20 (t, 3H). 13C NMR (CDCl3): δC 193.3, 181.9, 166.6, 147.9,
137.6, 136.5, 96.5, 79.9, 72.5, 70.7, 70.1, 69.3, 66.0 (−CH2 of ether),
54.8, 48.9, 38.4,, 33.0, 31.1, 29.1, 26.8, 23.9, 19.5, 15.4 (CH3 of ether).
Anal. Calcd (Found) for C104H87O15N5SCl3F3Fe6Ga2: C, 53.91
(52.38); H, 3.78 (4.05); N, 3.02 (3.76). ES(+)-TOF MS Calcd for
[Ga2(L3,5)3] + H]+ (Found) m/z: 1896 (1896).
[In2(L3,5)3]·[DBU-H][CF3SO3], 4. [In2(L3,5)3]·[DBU-H][CF3SO3]
was synthesized according to the above general procedure from
H2L3,5 (0.200 g, 0.341 mmol), DBU (0.1 mL, 0.682 mmol), and
In(CF3SO3)3 (0.128 g, 0.227 mmol). Yield: 0.205 g, 82%. mp > 260
°C. 1H NMR (CDCl3): δH 9.48 (br, 1H), 8.94 (br, 3H), 8.85 (br, 6H),
6.22 (s, 6H), 5.00 (br, 12H), 4.54 (br, 12H), 4.21 (s, 30H), 3.48 (m,
4H), 2.78 (br, 2H), 2.06 (br, 2H), 1.78−1.72 (m, 10H). 13C NMR
(CDCl3): δC 195.8, 183.3, 166.7, 148.2, 137.7, 136.7, 96.8, 80.7, 72.5,
70.8, 69.7, 61.4, 54.8, 48.9, 38.4, 33.0, 29.1, 26.8, 23.9, 19.5. Anal.
Calcd (Found) for C104H87O15N5SCl3F3Fe6In2: C, 51.90 (51.41); H,
3.64 (3.66); N, 2.91 (3.50). ES(+)-TOF MS Calcd for [In2(L3,5)3] +
H]+. (Found) m/z: 1986 (1986).
Crystallographic Studies. X-ray diffraction intensity data for the
ligand, H2L3,5·(CH2Cl2)0.5, was measured on a Bruker Apex II DUO
diffractometer using Cu Kα radiation (λ = 1.54 Å) at 100 K on a red
crystal with approximate dimensions of 0.030 mm × 0.041 mm ×
0.191 mm. Details of the data collection are given in Table 3. A total of
1985 frames were collected. The frames were integrated with the
Bruker SAINT+ software package using a narrow-frame algorithm.
Because of the thin needle morphology and weak diffracting power of
the available crystals, no reflections were observed above a 2θmax value
of ca. 44° (Cu radiation). Data were truncated at this value. Data were
corrected for absorption effects using the multiscan method
(SADABS). The ratio of minimum to maximum apparent transmission
was 0.747. The data were integrated using a tetragonal unit cell. The
structure was solved and refined using the Bruker SHELXTL20
Software Package, using the space group P42, with Z = 8. PLATON
indicated that the space group was correct with no additional
symmetry. The asymmetric unit consists of two crystallographically
independent, but chemically similar, molecules of H2L3,5, and a region
of disordered dichloromethane. The dichloromethane species are
disordered around a 2-fold axis of rotation and were refined with two
independent positions with a total site occupancy of 0.5. Disordered
atoms were refined with a common isotropic displacement parameter,
with the aid of C−Cl and Cl−Cl distance restraints. All atoms of the
H2L3,5 molecules were refined anisotropically. Some anisotropic
displacement parameters were restrained to approximate a spherical
electron density distribution using SHELX ISOR instructions. This
was necessary to prevent unacceptably oblate and prolate displacement
parameters and is a direct result of the weak diffraction data.
Reasonable positions for all four enolic protons were located in
difference maps. These were refined freely, resulting in normal atomic
positions and parameters. The C−O bond distances are intermediate
between enolic/carbonyl forms and are consistent with similar bonds.
All other hydrogen atoms were placed in geometrically idealized
positions and refined as riding atoms. At convergence, the absolute
structure (Flack) parameter was 0.038(15). The largest peak in the
101
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
final difference electron density synthesis was 0.45 e−/Å3, located near
Cl(3) of the disordered dichloromethane molecules.
large displacement parameters, indicating positional uncertainty and
was refined without hydrogen atoms. Between pyridyl nitrogen atoms
N2 and N3, the species were modeled as a mixture of chloroform and
ether with site occupancies of 0.783(4)/0.217(4), respectively, which
were constrained to sum to unity. The cavity between N1 and N2 was
also modeled as a chloroform/ether mixture with respective
occupancies of 0.438(6)/0.51(1); no hydrogen atoms were included
for these atoms. Another region of non-negligible electron density
occupies channels along the c axis at (0,0,z) and symmetry-equivalent
positions. No good disorder model could be found for the atoms in
this region. They were accounted for using the Squeeze technique in
PLATON. Squeeze calculated a solvent-accessible void volume of
5883.2 Å3 (11.6% of the total unit cell volume), amounting to 2403
electrons per unit cell. The contribution of the atoms in this region
was removed from the structure factor calculations. The reported F.W.,
d(calc), and F(000) were calculated from refined species only. The
largest residual electron density peak of 1.20 e−/Å3 in the final
difference map is located 0.98 Å from In2.
The Ga and In complexes were measured on a Bruker SMART
APEX CCD-based diffractometer (Mo Kα radiation, λ = 0.71073 Å).
Raw area detector data frame processing was performed with the
SAINT+ and SADABS programs. Final unit cell parameters were
determined by least-squares refinement of large sets of strong
reflections taken from each data set. Direct methods structure
solution, difference Fourier calculations, and full-matrix least-squares
refinement against F2 were performed with SHELXS/L as
implemented in OLEX2. Non-hydrogen atoms were refined with
anisotropic displacement parameters, the exception being disordered
species. The hydrogen atoms were placed in geometrically idealized
positions and included as riding atoms. Details of the data collection
are given in Table 3.
The compounds Ga2(L3,5)3·(CHCl3)2.13(1)(C4H10O)1.56(1) and
In2(L3,5)3·(CHCl3)1.44(1)(C4H10O)3.29(1) crystallize in the trigonal
system. The pattern of systematic absences in the intensity data
indicated an R-centered lattice, but were inconsistent with a c-glide
The compound [Ga2(L3,5)3]·[DBU-H][CF3SO3]·CHCl3 crystallizes
in the monoclinic system. The space group C2/c was confirmed by the
pattern of systematic absences in the intensity data and by the
successful solution and refinement of the structure. The asymmetric
unit consists of half of one Ga2(L3,5)3 complex, which resides on a
crystallographic 2-fold axis of rotation oriented perpendicular to the
Ga−Ga vector, one DBUH cation, one triflate anion, and a disordered
chloroform molecule. The ligand of the gallium complex that contains
N2 is bisected by the C2 axis, and therefore, only half of this ligand is
present per asymmetric unit. Atom N2 and C17 are located on the 2-
fold. The C2 axis generates one “N2” ligand per complete complex.
Atoms of the second independent ligand (containing N1) are on
general positions, generating two ligands per symmetry-expanded
gallium complex. The chloroform occupies two symmetry-independ-
ent sites within the asymmetric unit. Both sites are further disordered
about a C2 axis of rotation, and therefore, only half of one CHCl3 is
present per asymmetric unit. The independent sites have occupancy
values of C61/C62 = 0.313(4)/0.187(4), which were constrained to
sum to 0.5. The C2 axis generates four CHCl3 sites per gallium
complex. Twelve C−Cl and Cl−Cl distance restraints were used to
model the chloroform disorder, and atoms of the two independent
sites were assigned common isotropic displacement parameters.
The compound [In2(L3,5)3]·[DBU-H][CF3SO3]·CHCl3 crystallizes
in the monoclinic system. The space group C2/c was confirmed by the
pattern of systematic absences in the intensity data and by the
successful solution and refinement of the structure. The asymmetric
unit consists of half of one In2(L3,5)3 complex, which resides on a
crystallographic 2-fold axis of rotation oriented perpendicular to the
In−In vector, one DBUH and triflate cation−anion pair, and a
disordered chloroform molecule. The ligand of the gallium complex
that contains N2 is bisected by the C2 axis, and therefore, only half of
this ligand is present per asymmetric unit. The C2 axis generates one
“N2” ligand per complete complex. The other ligand (containing N1)
is on a general position, generating two ligands per symmetry-
expanded gallium complex. The chloroform occupies two symmetry-
independent sites in the asymmetric unit. Both sites are further
disordered about a C2 axis of rotation, and therefore, only half of one
CHCl3 is present per asymmetric unit. The independent sites have
occupancy values of C61/C62 = 0.248(8)/0.252(8), which were
constrained to sum to 0.5. The C2 axis of rotation generates four
CHCl3 sites per gallium complex. Twelve C−Cl and Cl−Cl distance
restraints were used to model the chloroform disorder, and the two
independent sites were each assigned a common isotropic displace-
ment parameter.
symmetry element, leaving the space groups R3, R3, R32, R3m, and
̅
R3m. The correct space group was eventually determined to be the
̅
centrosymmetric group R3 (No. 148). The two compounds are
̅
essentially isostructural, but with a different disordered solvent content
and distribution. The asymmetric unit consists of one complete
M2(C31H23NO4Fe2)3 (M = Ga, In) complex and several independent
regions of disordered solvent species.
For the Ga compound, three solvent volumes near the gallium
complex could be satisfactorily modeled; another region was too
heavily disordered for identification. The identifiable disorder areas
were modeled as chloroform molecules, diethylether molecules, or a
mixture of both on the same site. In general, the disordered atoms in a
particular volume were refined with a common isotropic displacement
parameter, and with distance restraints to maintain chemically
reasonable geometries. In total, 67 restraints were used to assist in
modeling the disorder. There is a fully ordered chloroform molecule
(Cl1−Cl3) occupying the cavity between pyridyl rings with nitrogen
atoms N2 and N3. The cavity between pyridyl ring nitrogen atoms N1
and N2 was modeled as containing two partially occupied ether
molecules (O102 and O103, populations 67.6% and 32.4%,
respectively) along with two partially occupied chloroform molecules
(Cl7−Cl9 and Cl10−Cl12, populations 32.4% and 36.3%, respec-
tively). Between pyridyl rings N1 and N3, the disorder was modeled as
a mixture of chloroform (Cl4−Cl6) and ether (O101) with site
occupancies of 0.444(4)/0.556(4), respectively, which were con-
strained to sum to unity. Another region of non-negligible electron
density occupies channels along the c axis at (0,0,z) and symmetry-
equivalent positions. No good disorder model could be found for the
atoms in this region. They were accounted for using the Squeeze
technique in PLATON. Squeeze calculated a solvent-accessible void
volume of 9122.1 Å3 (17.7% of the total unit cell volume), amounting
to 4345 electrons per unit cell. The contribution of the atoms in this
region was removed from the structure factor calculations. The
reported F.W., d(calc), and F(000) were calculated from refined
species only. The largest residual electron density peak of 0.99 e−/Å3
in the final difference map is located in the modeled disordered region,
1.02 Å from C114.
For the In compound, five solvent volumes near the indium
complex could be satisfactorily modeled; another region was too
heavily disordered for identification. The known disorder areas were
modeled as chloroform molecules, diethylether molecules, or a mixture
of both on the same site. In general, the disordered atoms in a
particular volume were refined with a common isotropic displacement
parameter, and with distance restraints to maintain chemically
reasonable geometries. In total, 62 restraints were used to assist in
modeling the disorder. Near pyridyl nitrogen atom N2, a chloroform
molecule was modeled as occupying three distinct orientations with a
total site occupancy summing to 0.79(1). The cavity between pyridyl
nitrogen atoms N1 and N3 is filled by a fully occupied ether molecule
(O101). Another fully occupied ether (O102) is located between
pyridyl nitrogen N2 and ferrocene group Fe4; this ether displayed
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic files in CIF format for the structural
determinations and mass spectrometry data, NMR data, and
cyclic voltammograms for the In2(L3,5)3 helicates. This material
is available free of charge via the Internet at http://pubs.acs.org.
102
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103

Organometallics
Article
(c) Clegg, J. K.; Jolliffe, K. A.; Lindoy, L. F.; Meehan, G. V. Pol. J.
Chem. 2008, 82, 1131.
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
(10) (a) Dudek, M.; Clegg, J. K.; Glasson, C. R. K.; Kelly, N.; Gloe,
K.; Gloe, K.; Kelling, A.; Buschmann, H.-J.; Jolliffe, K. A.; Lindoy, L.
F.; Meehan, G. V. Cryst. Growth Des. 2011, 11, 1697. (b) Burrows, A.
D.; Mahon, M. F.; Renouf, C. L.; Richardson, C.; Warren, A. J.;
Warren, J. E. Dalton Trans. 2012, 41, 4153.
(11) Grillo, V. A.; Seddon, E. J.; Grant, C. M.; Aromi, G.; Bollinger, J.
C.; Folting, K.; Christou, G. Chem. Commun. 1997, 1561.
(12) (a) Saalfrank, R. W.; Seitz, V.; Heinemann, F. W.; Gobel, C.;
Herbst-Irmer, R. J. Chem. Soc., Dalton Trans. 2001, 599. (b) Saalfrank,
R. W.; Seitz, V.; Caulder, D. L.; Raymond, K. N.; Teichert, M.; Stalke,
D. E. J. Inorg. Chem. 1998, 1313. (c) Saalfrank, R. W.; Dresel, A.; seitz,
V.; Trummer, S.; Hampel, F.; Teichert, M.; Stalke, D.; Stadler, C.;
Daub, J.; Schunemann, V.; Trautwein, A. X. Chem.Eur. J. 1997, 3,
2058.
ACKNOWLEDGMENTS
■
The authors acknowledge with thanks the financial support of
the Army Research Office Grant number 59402-59042-CH-
REP.
REFERENCES
■
(1) (a) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev.
2011, 111, 6810−6918. (b) Steed, J. W.; Turner, D. R.; Wallace, K. J.
Core Concepts in Supramolecular Chemistry and Nanochemistry; John
Wiley & Sons: West Sussex, U.K., 2007. (c) Steed, J. W.; Atwood, J. L.
Supramolecular Chemistry, 2nd ed.; John Wiley & Sons: West Sussex,
U.K., 2009.
(2) (a) Xuan, W.; Zhu, C.; Liu, Y.; Cui, Y. Chem. Soc. Rev. 2012, 41,
1677. (b) Friscic, T. Chem. Soc. Rev. 2012, 41, 3493. (c) Kaifer, A.;
́
Gomez-Kaifer, M. Supramolecular Electrochemistry; Wiley-VCH Verlag
(13) (a) Meyer, M.; Kersting, B.; Powers, R. E.; Raymond, K. N.
Inorg. Chem. 1997, 36, 5179. (b) Kersting, B.; Meyer, M.; Powers, R.
E.; Raymond, K. N. J. Am. Chem. Soc. 1996, 118, 7221. (c) Kersting,
B.; Telford, J. R.; Meyer, M.; Raymond, K. N. J. Am. Chem. Soc. 1996,
118, 5712.
GmbH: Weinheim, Germany, 2007; p 164. (d) Prikhod’ko, A. I.;
Sauvage, J. P. J. Am. Chem. Soc. 2009, 131, 6794. (e) Fenlon, E. E. Eur.
J. Org. Chem. 2008, 5023. (f) Pradeep, C. P.; Cronin, L. Annu. Rep.
Prog. Chem., Sect. A: Inorg. Chem. 2007, 103, 287. (g) Fujita, M. In
Molecular Catenanes, Rotaxanes and Knots; Sauvage, J. P., Dietrich-
Buchecker, C., Eds.; Wiley-VCH Verlag GmbH: Weinheim, Germany,
2007; p 57. (h) Movsisyan, L. D.; Kondratuk, D. V.; Franz, M.;
Thompson, A. L.; Tykwinski, R. R.; Anderson, H. L. Org. Lett. 2012,
14, 3424. (i) Ackermann, D.; Jester, S. S.; Famulok, M. Angew. Chem.
2012, 51, 6771. (j) Choudhary, U.; Northrop, B. H. Org. Lett. 2012,
14, 2082. (k) Beves, J. E.; Blight, B. A.; Campbell, C. J.; Leigh, D. A.;
McBurney, R. T. Angew. Chem., Int. Ed. 2011, 50, 9260.
(14) Marat, K. SPINWORKS 3, v.3.1.8.2, University of Manitoba,
2011. This freeware can be downloaded from ftp://davinci.chem.
umanitoba.ca/pub/marat/SpinWorks/.
(15) Cyclic voltammograms for the In2(L3,5
) helicates with or
3
without DBU is provided in the Supporting Information.
(16) Solntsev, P. V.; Dudkin, S. V.; Sabin, J. R.; Nemykin, K. N.
Organometallics 2011, 30, 3037.
(17) (a) Diallo, A. K.; Absalon, C.; Ruiz, J.; Astruc, D. J. Am. Chem.
Soc. 2011, 133, 629. (b) Funk, H.; Long, N. J.; Martin, A. J.;
Opromolla, G.; White, A. J. P.; Williams, D. J.; Zanello, P.
Organometallics 1997, 16, 2646.
(18) (a) Dulatas, L. T.; Brown, S. N.; Ojomo, E.; Noll, B. C.; Cavo,
M. J.; Holt, P. B.; Wopper, M. M. Inorg. Chem. 2009, 48, 10789.
(b) Chen, L.-J.; Li, Q.-J.; He, J.; Tan, H.; Abliz, Z.; Yang, H.-B. J. Org.
Chem. 2012, 17, 1148.
(19) Auger, A.; Swarts, J. C. Organometallics 2007, 26, 102.
(20) SHELXTL; Bruker Analytical X-ray Systems: Madison, WI,
2003.
(3) Lindsey, J. S. New J. Chem. 1991, 15, 153.
(4) (a) Cui, F.; Li, S.; Jia, C.; Mathieson, J. S.; Cronin, L.; Yang, X.-J.;
Wu, B. Inorg. Chem. 2012, 51, 179. (b) Kundu, N.; Abtab, S. M.;
Kundu, S.; Endo, A.; Teat, S. J.; Chaudhury, M. Inorg. Chem. 2012, 51,
2652. (c) Zhang, Z.; Chen, Y.; Dolphin, D. Dalton Trans. 2012, 41,
4751. (d) Lin, S. Y.; Xu, G. F.; Zhao, L.; Guo, Y. N.; Guo, Y.; Tang, J.
Dalton Trans. 2011, 40, 8213. (e) Gancheff, J. S. Spectrochim. Acta, Part
A 2011, 78, 1037. (f) Albrecht, M.; Latorre, I.; Mehmeti, G.; Hengst,
K.; Oppel Iris, M. Dalton Trans. 2011, 40, 12067. (g) Zhu, X.; He, C.;
Dong, D.; Liu, Y.; Duan, C. Dalton Trans. 2010, 39, 10051.
(h) Vicente, J.; Gil-Rubio, J.; Barquero, N.; Camara, V.; Masciocchi,
N. Chem. Commun. 2010, 1053. (i) Zhang, Z.; Dolphin, D. Inorg.
Chem. 2010, 49, 11550. (j) Zhang, Z.; Dolphin, D. Chem. Commun.
2009, 6931.
(5) Fletcher, N. C.; Brown, R. T.; Doherty, A. P. Inorg. Chem. 2006,
45, 6132.
(6) (a) Riis-Johannessen, T.; Bernardinelli, G.; Filinchuk, Y.; Clifford,
S.; Dalla Favera, N.; Piguet, C. Inorg. Chem. 2009, 48, 5512. (b) Riis-
Johannessen, T.; Dalla Favera, N.; Todorova, T. K.; Huber, S. M.;
Gagliardi, L.; Piguet, C. Eur. J. Chem. 2009, 15, 12702. (c) Dalla-
Favera, N.; Hamacek, J.; Borkovec, M.; Jeannerat, D.; Ercolani, G.;
Piguet, C. Inorg. Chem. 2007, 46, 9312.
(7) (a) Fang, C.-J.; Duan, C.-Y.; Mo, H.; He, C.; Meng, Q.-J.; Liu, Y.-
J.; Mei, Y.-H.; Wang, Z.-M. Organometallics 2001, 20, 2525. (b) Fang,
C.-J.; Duan, C.-Y.; He, C.; Meng, Q.-J. Chem. Commun. 2000, 1187.
(c) Quinodoz, B.; Labat, G.; Stoeckli-Evans, H.; von Zelewsky, A.
Inorg. Chem. 2004, 43, 7994. (d) Quinodoz, B.; Stoeckli-Evans, H.; von
Zelewsky, A. Mendeleev Commun. 2003, 146. (e) Mugridge, J. S.;
Fiedler, D.; Raymond, K. N. J. Coord. Chem. 2010, 63, 2779.
(f) Constable, E. C.; Martinez-Manez, R.; Cargill Thompson, A. M.
W.; Walker, J. V. J. Chem. Soc., Dalton Trans. 1994, 185. (g) Li, M. X.;
Bai, Y.; Zhang, B. G.; Duan, C. Y.; Xu, J.; Meng, Q. J. Inorg. Chem.
2005, 44, 5459.
(8) Gwengo, C.; Iyer, R.; Raja, M. Cryst. Growth Des. 2012, 12, 49.
(9) (a) Aromi, G.; Gamez, P.; Reedijk, J. Coord. Chem. Rev. 2008,
252, 964. (b) Saalfrank, R. W.; Spitzlei, C.; Scheurer, A.; Maid, H.;
Heinemann, F. W.; Hampel, F. Chem.Eur. J. 2008, 14, 1472.
103
dx.doi.org/10.1021/om300843r | Organometallics 2013, 32, 95−103