Controlling Ligand Exchange through Macrocyclization

Article abstract of DOI:10.1021/acs.inorgchem.8b00031

Ligand exchange at a sterically hindered palladium center was investigated for six different ligands. The palladium atom was coordinated to a tridentate, NNN pincer bis(amido)pyridine macrocycle to produce a square-planar complex, in which an acetonitrile molecule occupies one of the coordination sites. Kinetic studies showed that ligand exchange at the palladium center proceeds through an associative mechanism and, as a consequence, is impeded by the small size of the metallomacrocycle cavity. The ligand-exchange rate on the palladium center between acetonitrile and six different ligands has been investigated and compared to the exchange rate on the corresponding open form. Our results demonstrate that macrocyclization of ligands is a way to modify the rate of guest exchange in a square-planar metal complex.

Full text of DOI:10.1021/acs.inorgchem.8b00031

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Controlling Ligand Exchange through Macrocyclization
Veronica Carta, S. Hessam M. Mehr, and Mark J. MacLachlan*
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
S
* Supporting Information
ABSTRACT: Ligand exchange at a sterically hindered palladium center
was investigated for six different ligands. The palladium atom was
coordinated to a tridentate, NNN pincer bis(amido)pyridine macrocycle
to produce a square-planar complex, in which an acetonitrile molecule
occupies one of the coordination sites. Kinetic studies showed that ligand
exchange at the palladium center proceeds through an associative
mechanism and, as a consequence, is impeded by the small size of the
metallomacrocycle cavity. The ligand-exchange rate on the palladium
center between acetonitrile and six different ligands has been investigated
and compared to the exchange rate on the corresponding open form.
Our results demonstrate that macrocyclization of ligands is a way to
modify the rate of guest exchange in a square-planar metal complex.
displacement of the unsaturated polymer chain, preventing
chain transfer and favoring olefin insertion.25,26
Here we investigate control of ligand exchange on a
palladium pincer complex by using a supramolecular approach.
A tridentate macrocyclic ligand with a NNN pincer bis(amido)-
pyridine functionality has been prepared (Figure 1a). The
INTRODUCTION
■
Pincer ligands are a class of chelating compounds that bind
strongly to a metal through three coordination sites.1−6 The
tridentate ligand confers high stability to the complex but still
leaves a vacant coordination site, which is usually occupied by a
solvent molecule. Pincer complexes have attracted enormous
attention for catalysis, sensing, and other applications.7−10
Tridentate planar bis(amido)pyridine ligands are pincer
ligands that have been widely exploited in supramolecular
chemistry.11−14 Their ability to coordinate to metals like
palladium(II) and platinum(II) with square-planar geometry
and the potential to modify their structures make them suitable
for forming catenanes,15,16 rotaxanes,15,17 and molecular
machines.18,19 Ligand exchange on the fourth coordination
site of the metal center is also important for several other
applications such as designing receptor systems, catalysts20 and
drugs.
It has been previously reported that bis(amido)pyridine
ligands with bulky side groups can be employed to control
ligand exchange on the fourth coordination site of palladium.
For instance, the incorporation of larger aromatic rings on the
pincer backbone results in a NNN pincer complex of Pd2+ that
has enhanced binding between 2-chloroethyl ethyl sulfide and
the palladium.21 Bulky pincer ligands have been shown to affect
the reactivity of transition-metal pincer complexes,22 and ligand
exchange on the fourth coordination site of the palladium
becomes slower with an increase of the steric hindrance near
the metal center.23 This is related to the ligand-exchange
mechanism on the palladium center, which is usually associative
and is therefore impeded by steric bulk around the metal
center. In catalysis, this concept has been used to convert
palladium(II) complexes from olefin oligomerization catalysts
to polymerization catalysts.24 Coordination of bulky α-diimine
ligands to a palladium (or nickel) catalyst inhibits associative
Figure 1. (a) NNN pincer metallomacrocycle of Pd2+. An acetonitrile
molecule occupies the fourth palladium coordination site. (b) NNN
pincer complex of Pd2+. This complex represents the open form of the
metallomacrocycle.
macrocycle coordinates to a palladium ion to give a rigid pincer
complex with a small cavity; an acetonitrile molecule occupies
the palladium atom’s fourth coordination site. The small size of
the cavity provides steric hindrance and impedes the ligand
exchange between acetonitrile and other bulky ligands. Ligand-
exchange studies were performed with several ligands, and the
rate of exchange on the new metallomacrocycle was compared
with the rate of exchange for its corresponding open form
(Figure 1b).
Received: January 5, 2018
© XXXX American Chemical Society
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Scheme 1. Synthesis of Metallomacrocycle 3
past the acetonitrile molecule coordinated to the metal center,
and the conformation is blocked on one side with respect to the
RESULTS AND DISCUSSION
■
Metallomacrocycle 3: Synthesis and Behavior in
Solution. The NNN pincer bis(amido)pyridine macrocycle 2
was prepared by the route shown in Scheme 1. The ring-closing
(final) step proceeded in 71% yield in high dilution conditions
(2.5 mM). Notably, the macrocycle has C2v symmetry by H
NMR spectroscopy, and the components of the macrocycle are
1
palladium−acetonitrile bond. A H−1H COSY NMR experi-
ment was used to correctly assign the chemical shift of each
hydrogen atom in complex 3 (Figure S5).
A single crystal of 3 suitable for single-crystal X-ray
diffraction (SCXRD) was obtained from slow evaporation of
a solution of 3 in 1:1 acetonitrile/dichloromethane (DCM).
The crystal structure (Figure 3) confirms that the palladium ion
1
fluxional. A crystal structure of compound 2 (Figure 2) also
Figure 2. Solid-state structure of compound 2 as determined by
SCXRD: (a) front view; (b) side view.
shows that the macrocycle appears flexible despite the bridge
between the aryl groups. Metalation of macrocycle 2 with
Pd(OAc)2 at 50 °C afforded a yellow metallomacrocycle 3 in
Figure 3. Solid-state structure of compound 3 as determined by
SCXRD: (a) front view; (b) side view; (c) top view.
1
54% yield. The new compounds were characterized by H and
13C NMR spectroscopy and high-resolution electrospray
ionization mass spectrometry (HRESI-MS).
1
The H NMR signals (in CDCl3) corresponding to the
has square-planar geometry where it is coordinated to the
pyridine, two amidic nitrogen atoms, and acetonitrile. The
metallomacrocycle’s cavity is smallthe distance between the
two aromatic rings is 5.80 Åbut the system is not particularly
strained because substituents are oriented out of the plane of
the pyridine and metal to accommodate the acetonitrile guest
amidic hydrogen atom (7.62 ppm) disappeared upon
coordination to palladium(II) and a new peak corresponding
to the coordinated acetonitrile appeared at 1.50 ppm (excess
free acetonitrile is observed at 2.02 ppm). Notably, the
methylene hydrogen atoms present in macrocycle 2 became
diastereotopic upon Pd2+ coordination, indicating reduction of
the C2v symmetry. This shows that, on the time scale of the
NMR experiment, the ring in compound 3 is unable to skip
1
(Figure 3b). This geometry is consistent with the solution H
NMR data, which showed that the methylene protons are
diastereotopic (Figure S3).
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It has been previously reported that some palladium
bis(amido)pyridine complexes are present in an equilibrium
between a monomeric form and a cyclic hexameric or
tetrameric form.27−29 This equilibrium is facilitated by the
lability of the acetonitrile molecule coordinated to the
palladium, which in solution exchanges with another bis-
(amido)pyridine complex that coordinates through its oxygen
atom to form a cyclic structure. The addition of ligands that
bind the metal center can strongly disrupt this equilibrium,
shifting it toward the monomeric form.
noticeable that the structure has substantial disorder located in
two of the bridging chains and on some phenyl rings. Restraints
on the bond lengths and angles worked well enough to model
the phenyl rings, while for the bridging chains, it was necessary
to split the electron density into two parts and fix the total
occupancy to 1. Despite the complexity of the structure and the
weak diffraction of the crystal, Rint was brought down to 15.3%.
The structure is reliable enough to conclude that the aggregate
formed is a tetrameric macrocycle of macrocycles.
Model Compound for Ligand Exchange. In order to
explore the exchange of ligands at palladium in metallomacro-
cycle 3, we first prepared a model complex, 5, as shown in
Scheme 2. In this complex, the phenyl rings are not tethered
together, and they are instead free to move far apart from each
We anticipated that the macrocyclic structure of 3 would
inhibit aggregation and thereby stabilize the monomeric form
of the compound. However, through a variable-temperature
(VT) 1H NMR spectroscopy experiment (Figure S8), we found
that when metallomacrocycle 3 is heated in chloroform, it
partially converts into a new compound (3*). The species 3* is
stable and does not revert to the monomeric form upon cooling
1
other. Compound 5 was characterized by H and 13C NMR
spectroscopy, HRESI-MS, elemental analysis, and SCXRD.
Comparing the 1H NMR data with compound 3 shows that for
compound 5 the methylene protons are not diastereotopic.
These data are consistent with the average C2v symmetry in
1
of the sample to room temperature. H NMR spectroscopy
indicates that the new product is structurally similar to the
monomer but does not contain acetonitrile. In addition, the
peaks corresponding to the pyridine protons become
asymmetric (Figure S6). Our data suggest that compound 3
ejects acetonitrile to form oligomer 3*.
A single crystal of compound 3* was grown by vapor
diffusion of cyclohexane into a solution of 3* in dichloroethane.
Figure 4a shows the crystal structure of this aggregate; it is a
1
solution. The H NMR spectrum of compound 5 in CD2Cl2
(Figure S13) also shows some broad peaks that are not present
if the spectrum is collected in a coordinating solvent such as
dimethyl sulfoxide (DMSO). In DMSO (Figure S12), the peak
corresponding to coordinated acetonitrile (1.80 ppm in
CD2Cl2) is not present either. This suggests that DMSO
exchanges with acetonitrile, shifting the equilibrium toward a
monomeric complex, while in chloroform, some oligomer is
formed. As with compound 3, heating compound 5 in
chloroform for 48 h at reflux produces a new species 5*,
which is likely to be some higher-order aggregate of compound
5, where the acetonitrile molecule is not coordinating, similar to
the cyclic tetramer 3*. (Unlike in the case of 3*, we have not
been able to isolate and purify 5*, but it behaves similarly to 3*,
leading us to postulate that it is also an aggregate.)
A single crystal of 5 was produced from vapor diffusion of
pentane into a solution of 5 in 1:1 chloroform/acetonitrile. The
SCXRD structure of compound 5 is shown in Figure 5. The
Figure 4. (a) Solid-state molecular structure of compound 3* as
determined by SCXRD. Compound 3* is a macrocycle of macrocycles,
where each monomer is bridged by a carbonyl group to the next
palladium atom, forming a cyclic tetramer. (b) Space-filling model
(based on van der Waals radii) for compound 3*. The color of the
atoms indicates the atomic displacement parameters: blue if they are
small, and red if they are high.
cyclic tetramer where each monomer is bridged to the next
palladium atom through a carbonyl group. As shown in the
space-filling model in Figure 4b, the cavity inside compound 3*
is quite small, with the Pd1−Pd3 distance being 7.878(4) Å and
the Pd2−Pd4 distance being 7.095(3) Å. Figure 4b also shows
the atomic displacement parameters for compound 3*. It is
Figure 5. Solid-state molecular structure of compound 5 as
determined by SCXRD: (a) front view; (b) side view.
Scheme 2. Synthesis of the Open Complex 5
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phenyl groups are both on one side with respect to the
palladium coordination plane, but they are able to skip past the
acetonitrile molecule in solution, as supported by the 1H NMR
data (Figure S13). This is consistent with the crystal structure
recently obtained for compound 5 by Jerome et al., which
presents the same unit cell.
Ligand Exchange Studies: Triphenylphosphine, Pyr-
idine, and (Dimethylamino)pyridine (DMAP). The ligands
selected to investigate the exchange with acetonitrile on the
palladium atom are shown in Figure 6. Triphenylphosphine,
their applicability as catalysts in the Suzuki−Miyaura cross-
coupling reaction.
For pyridine, DMAP, and triphenylphosphine, the bridging
chain on compound 3 does not provide enough steric bulk to
significantly slow the exchange process. In spite of this, NMR
studies show that the bridging chain provides enough steric
hindrance to affect the rotation of pyridine and DMAP around
the N−Pd bond. Specifically, Ho1 and Hm1 (Figure 8a)
Figure 6. Compounds used to investigate ligand exchange: pyridine,
triphenylphosphine, DMAP, quinoline, acridine, and 2,6-lutidine.
pyridine, and DMAP exchange quickly with acetonitrile both in
the metallomacrocycle 3 and in the open complex 5. Following
1
ligand exchange by H NMR spectroscopy, the disappearance
of peaks corresponding to higher-order aggregates (3* and 5*)
is notable. The equilibrium shifts toward the monomeric form
as ligand exchange completes. The metallomacrocycle exchange
1
products were characterized by H and 13C NMR, ESI-MS,
elemental analysis, and SCXRD. Molecular structures of
compounds 5-pyr and 5-PPh3 determined by SCXRD are
shown in Figure 7. Attempts to grow single crystals of
compound 5-dmap suitable for SCXRD were unsuccessful.
From the crystal structures of compounds 5-pyr and 5-PPh3,
it is clear that the two phenyl rings of the pincer ligands do not
move very far from each other upon coordination of pyridine or
triphenylphosphine. We anticipated that these ligands, which
are substantially bulkier than acetonitrile, would lead to a large
splaying of the phenyl rings. In fact, 5-pyr has nearly perfect
square-planar geometry at the Pd2+ center, and the
triphenylphosphine complex 5-PPh3 shows only a small
distortion from square planar (the torsion angle between the
the NNN-Pd plane and the phosphorus atom is 15.78°). This is
in agreement with the crystal structure published by Jerome et
al. for compound 5-PPh3, which presents the same torsion
angle and crystallizes in the same unit cell.30 Jerome et al.
synthesized compounds 5 and 5-PPh3 and similar palladium
complexes with substituents in the ortho positions and studied
Figure 8. (a) Structure of DMAP and pyridine, indicating the protons
on the pyridyl ring. (b) High-temperature 1H NMR studies for
compound 3-dmap. (c) High-temperature 1H NMR studies for
compound 3-pyr. Residual C2HDCl4 in C2D2Cl4 is identified with the
asterisk. The peaks corresponding to the ortho and meta positions
become sharper as the temperature increases, generating two distinct
signals. The signals in blue correspond to the ortho protons, whereas
the red peaks are generated by the protons in the meta position.
experience large differences in chemical shift as a result of the
ring current from Ho2 and Hm2, which, combined with the
intermediate rate of ligand rotation at room temperature, makes
1
them completely invisible in the room temperature H NMR
spectra of compounds 3-pyr and 3-dmap. That said, the ortho
and meta resonances can be detected at 113 °C, where the
rotation of pyridine and DMAP is fast enough for the
resonances to become equivalent (Figure 8). High-temperature
Figure 7. Solid-state molecular structures of (a) compound 5-pyr and (b and c) compound 5-PPh3 as determined by SCXRD.
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1H−1H COSY and NOESY NMR experiments confirmed the
correct assignment of the spectra (Figures S33, S39, and S40).
At low temperature, on the other hand, ligand rotation slows to
the point where four distinct 1H resonances emerge (Figure 9).
Table 1. Free Energies of Activation for Ligand Rotation,
ΔGrot⧧, in kJ/mol and kcal/mol, for 3-pyr and 3-dmap,
a
Obtained from Ab Initio Techniques and VT NMR Data,
Using Either the Eyring Equation or the Coalescence
Temperature
from the Eyring
b
computational calculations
from Tc
plot
⧧
ΔGrot
3-pyr
3-pyr 3-dmap 3-pyr 3-dmap
kJ/mol
46.5
11.1
52
12
48
12
54
13
50
12
kcal/mol
a
The rotation rate constants at different temperatures (used to obtain
the ΔGrot⧧) were calculated using approximations of the Bloch
equation. The uncertainties associated with these values are estimated
to be about 10−15%.31 The B3LYP hybrid functional was used in
b
conjunction with the 6-31+G(d,p) basis set. The LANL2DZ basis set
and LANL2 core potential were used in the case of platinum. All
calculations were carried out using the Gaussian 09 (revision D.01)33
suite of ab initio codes. The solvent and dispersion effects are ignored.
⧧
Experimental values of ΔGrot were calculated using two
different methods: by the Eyring plot or through determination
of the coalescence temperature, Tc.31,32 ΔGrot can also be
⧧
calculated by ab initio methods, obtaining the initial
coordinates from the crystal structure of 3-quin, which was
modified by changing the quinoline ligand to pyridine, with the
assumption that doing so does not significantly perturb the
overall geometry of the molecule. More details regarding the
⧧
computational and experimental determinations of ΔGrot can
be found in the Supporting Information.
Ligand-Exchange Studies: Quinoline, Acridine, and
2,6-Lutidine. We next investigated bulkier ligands (quinoline,
acridine and 2,6-lutidine), which we expected to show marked
differences in the exchange rate between the open complex and
strapped metallomacrocycle. When quinoline was added to the
open complex compound 5, the coordinated acetonitrile was
rapidly exchanged for quinoline, similar to the behavior
observed with pyridine. When quinoline was added to
compound 3, however, exchange was much slower and
completed in 55 min. The crystal structure of compound 3-
quin shows that quinoline coordinates with the phenyl group
pointing away from the cavity in order to reduce any steric
strain (Figure 10). Using the atomic coordinates obtained from
the SCXRD data for 3-quin, we calculated the size of the
complex cavity with the software POVME2.34 This calculation
indicates that the cavity is quite small (26.5 Å3) compared with
the volumes of quinoline, acridine, and 2,6-lutidine reported in
the literature: 123, 166, and 113 Å3, respectively.35,36
Figure 9. (a) Structure of pyridine and DMAP, indicating the protons
on the pyridyl ring. (b) Low-temperature 1H NMR studies for
compound 3-dmap. (c) Low-temperature 1H NMR studies for
compound 3-pyr. Residual CHDCl2 in CD2Cl2 is indicated with the
asterisk. The peaks corresponding to the ortho and meta positions
become sharper as the temperature decreases, generating four distinct
signals. The signals in orange correspond to the hydrogen atoms
pointing inside the cavity, which are significantly shielded by the
macrocycle’s phenyl groups, whereas the green peaks are the hydrogen
atoms pointing away from the cavity.
Acridine and 2,6-lutidine exchange slowly with the
acetonitrile in both compounds 3 and 5. It is possible to
1
follow the exchange process by H NMR spectroscopy. Figure
11 shows the kinetic studies performed on compound 5 during
the exchange of acetonitrile with acridine and 2,6-lutidine.
Ligand exchange with acridine reaches completion after 28 min,
while ligand exchange with the more sterically hindered 2,6-
lutidine is complete after 40 min under the same conditions.
This difference is probably due to the presence of the two
methyl groups on lutidine. Ligand exchange obeys a second-
order kinetic rate law characteristic of an associative reaction
mechanism, where both acetonitrile and the new ligand take
part in the transition state.
The chemical shift difference is especially dramatic between Ho1
and Ho2 (3.30 ppm for 3-dmap and 3.55 ppm for 3-pyr), given
Ho1’s position in the diamagnetic ring current. Low-temper-
1
ature H−1H COSY and HSQC NMR experiments confirmed
the assignment of these protons (Figures S35, S42, and S43).
The free energies of activation for ligand rotation, ΔGrot⧧, for
compounds 3-pyr and 3-dmap are reported in Table 1.
The solid-state molecular structures of the exchanged
products of compound 5 are shown in Figure 12. For these
complexes, the metal center is nearly perfectly square-planar
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Figure 10. Solid-state structure of compound 3-quin as determined by SCXRD: (a) front view; (b) side view; (c) top view.
8 h, after which it reached 70% completion. On the other hand,
the exchange between acetonitrile and 2,6-lutidine on
compound 3 was monitored for 10 h, after which the reaction
was only 50% complete. Assuming that second-order kinetics
holds, extrapolation from a linear fit shows that the time to
reach 90% conversion would be 23 and 80 h for acridine and
2,6-lutidine, respectively. The exchange process is significantly
slower for 2,6-lutidine than for the other two ligands, an effect
attributed to the steric bulk given by the methyl groups.
From the crystal structure of 3-acr (Figure 14), it is possible
to see that the phenyl moieties bend to an almost 90° angle in
order to accommodate the acridine molecule. Different from 5-
acr, the acridine molecule does not stack with the phenyl
moieties of the pincer ligand. Instead, in the crystal packing,
two acridine molecules interact through π−π stacking (distance
between phenyl rings: 3.6 Å), forming dimers (Figure 15).
Therefore, our results clearly show that the ligand exchanges
on compounds 3 and 5 are dramatically different; the rate of
ligand exchange on 5 was 50−120 times faster than that on 3.
Even though the tethering group is far from the metal center,
forming the metallomacrocycle substantially affects the sterics
near the metal center and thus affects the kinetics of ligand
exchange. This can be explained by the formation of a
transition state where both the acetonitrile, which is leaving,
and the new ligand, which is coordinating, are participating. We
think that the small cavity in compound 3 allows the formation
of a five-coordinate transition state. This is because the cavity
does not surround the ligands in the plane of the pincer ligand
but bends away to accommodate bulky guests at the metal
center. This can be noted in the crystal structures of 3, 3-quin,
and 3-acr, where the ligands do not sit inside the cavity, and the
phenyl groups bend up to almost a 90° angle. The kinetic
studies show that the reaction follows a second-order rate law,
in agreement with an associative mechanism with two separate
molecules participating in the transition state. The small size of
the cavity, estimated to be 26.5 Å3, provides steric hindrance,
which slows ligand exchange on the palladium.
Figure 11. Ligand-exchange kinetic study on compound 5, performed
with acridine (blue circles) and 2,6-lutidine (orange triangles). 1/X
corresponds to the inverse of the concentration of compound 5. The
initial concentrations of both 5 and the additional ligand were 0.013
M.
and the phenyl rings are not significantly splayed apart. This
possibly indicates that the open complex can easily
accommodate the new ligands even if the kinetic studies reveal
that this exchange is slow. In all of the complexes shown in
Figure 12, the pincer ligand’s phenyl rings point toward
opposite sides of the palladium−pyridine plane. For compound
5-acr, the distance between the aryl rings of the pincer ligand
and coordinated acridine is 3.6 Å, indicating a weak
intermolecular interaction. In compound 5-lut, the distance
between the methyl hydrogen atoms of 2,6-lutidine and the
pincer ligand’s aromatic rings is 3.0 Å, suggesting a CH−π
interaction. Regarding 5-quin, one of the pincer ligand’s phenyl
moieties stacks with one aromatic ring (the distance between
them is 3.7 Å), while there is no stacking for the other phenyl
moiety.
Figure 13 shows the kinetic study of ligand exchange in
metallomacrocycle 3 with quinoline, acridine, and 2,6-lutidine.
1
The H NMR data fit to a second-order kinetic rate law for
compound 3, at least for conversion of <50%. For quinoline
substitution, ligand exchange on compound 3 is 90% complete
in 55 min. The reaction with acridine was monitored for about
Figure 12. Solid-state molecular structures of (a) 5-quin, (b) 5-acr, and (c) 5-lut as determined by SCXRD.
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Figure 13. Ligand-exchange kinetic study on compound 3, performed with (a) quinoline (red diamonds), (b) acridine (blue circles), and (c) 2,6-
lutidine (orange triangles). (d) Comparison between the exchange with 2,6-lutidine and acridine. 1/X corresponds to the inverse of the
concentration of compound 3. The concentration of the solutions is 0.013 M, and the ratio between compound 3 and the additional ligand is 1:1.
Figure 14. Solid-state structure of compound 3-acr as determined by SCXRD: (a) front view; (b) side view; (c) top view.
1
was calculated by integrating a corresponding H NMR peak,
and each measurement was repeated three times. The values
obtained are reported in Table 2.
Table 2. Equilibrium Constants
a
a
a
compound
Keq(pyr−quin)
Keq(pyr−acr)
Keq(pyr−lut)
3
5
0.79 ( 0.07)
0.95 ( 0.07)
no exchange
no exchange
0.14 ( 0.02)
0.016 ( 0.003)
a
Keq is the equilibrium constant for the reaction 3-pyr + X ⇌ 3-X +
pyr. X = quin, acr, and lut.
Out of the three ligands studied, quinoline is the only ligand
able to exchange with pyridine, but the equilibrium remains
slightly shifted toward 3-pyr. Acridine and 2,6-lutidine are
probably too bulky, and no exchange was observed. In the more
flexible complex 5-pyr, all three ligands can exchange, but there
is a noticeable decrease in the equilibrium constant values as
the bulk of the ligands increases. The constant is close to 1 only
for the equilibrium between 5-quin and 5-pyr, while for
acridine and lutidine, the equilibrium is strongly shifted toward
5-pyr.
Figure 15. Dimers formed by 3-acr due to stacking between the
phenyl rings of two acridines. The distance between the two phenyl
rings is 3.6 Å.
Binding Constant Determination. A measure of the
steric bulk increase of the ligands, going from the smaller
pyridine to the bulkier 2,6-lutidine, can be given by calculating
the equilibrium constants for the exchange of pyridine with
quinoline, acridine, and 2,6-lutidine in both compounds 3-pyr
and 5-pyr. The concentration of each species at equilibrium
CONCLUSION
■
A novel NNN pincer macrocyclic palladium complex and its
corresponding open form have been synthesized. Palladium
forms a square-planar complex when coordinated with the
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50 °C for 2 h, after which the reaction was stirred at room temperature
overnight. The product formed as a yellow precipitate. The solution
was concentrated to 2.5 mL, and the yellow precipitate was isolated by
filtration. The filtrate was left to evaporate and gave a second batch of
product. Yield: 56 mg (0.10 mmol, 54%). Crystals suitable for SCXRD
analysis were grown by slow evaporation of a solution of 3 in 1:1
acetonitrile/ethanol.
NNN pincer macrocycle and an acetonitrile molecule. The
lability of the acetonitrile molecule produces an equilibrium
between the metallomacrocycle and higher-order aggregates; a
tetrameric macrocycle of metallomacrocycles was isolated and
structurally characterized by SCXRD. Ligand exchange on the
palladium between acetonitrile and six different ligands has
been investigated for both the macrocycle and corresponding
open complex. For ligands with little steric bulk, the exchange is
rapid, and there is no significant difference between the
metallomacrocycle and open complex. When the ligands have
more steric bulk, the exchange is substantially slower and,
significantly, the ligands exchange much faster on the open
complex than on the metallomacrocycle. Kinetic studies also
revealed that the ligand-exchange reaction proceeds through an
associative mechanism. As a consequence, more steric crowding
around a metal center inhibits the ligand-exchange process. Our
results demonstrate that forming a macrocycle is a way to
control the rate of ligand exchange at a metal center. We are
now exploiting this phenomenon to further control the
supramolecular chemistry of metallomacrocycles.
1
Data for 3. H NMR (400 MHz, CDCl3): δ 8.12 (t, 1H, J = 7.61
Hz), 7.84 (d, 2H, J = 7.61 Hz), 7.26 (d, 4H, J = 8.22 Hz), 6.84 (d, 4H,
J = 8.68 Hz), 5.75 (br m, 2H), 5.50 (d, 2H, J = 16.50 Hz), 4.93 (dd,
2H, J1 = 14.16 Hz, J2 = 3.88 Hz), 4.62 (d, 2H, J = 13.96 Hz), 3.68 (d,
2H, J = 15.86 Hz), 1.49 (s, 3H). 13C NMR (100 MHz, CDCl3): δ
170.2, 156.7, 153.5, 141.0, 135.3, 128.9, 128.3, 125.0, 115.7, 71.8, 66.1,
64.3, 48.2. HRMS (ESI/TOF-Q). Calcd for C25H22N3O4104Pd [3 −
CH3CN + H+]: m/z 532.0641. Found: m/z 532.0646. UV−vis
[CH2Cl2; λmax, nm (εmax, M−1 cm−1)]: 229 (3.7 × 104), 275 (1.5 × 104,
one shoulder).
Compound 3*. Compound 3 (13.8 mg, 24.0 mmol) was heated in
boiling ethanol (5 mL) until the solvent evaporated, yielding a yellow
1
powder that was pure 3* by H NMR spectroscopy. Yield: 12.5 mg
(0.006 mmol, 98%). Crystals suitable for SCXRD analysis were grown
by vapor diffusion of pentane into a solution of 3* in dichloroethane.
Data for 3*. 1H NMR (300 MHz, CD2Cl2): 7.72 (m, 2H), 7.36 (m,
1H), 7.34 (d, 2H, J = 8.68 Hz), 7.23 (d, 2H, J = 8.68 Hz), 6.94 (d, 2H,
J = 8.68 Hz), 6.52 (d, 2H, J = 8.68 Hz), 5.86 (br m, 2H), 5.77 (dd, 1H,
J1 = 7.61 Hz, J2 = 1.27 Hz), 4.98 (m, 3H), 4.76 (d, 1H, J = 15.30 Hz),
4.64 (d, 1H, J = 15.08 Hz), 4.14 (d, 1H, J = 14.85 Hz), 3.41 (d, 1H, J =
15.76 Hz). 13C NMR (100 MHz, CD2Cl2): δ 171.0, 170.3, 158.3,
157.2, 154.2, 152.6, 140.4, 135.2, 131.9, 130.0, 129.2, 128.4, 128.3,
126.6, 126.0, 116.5, 115.9, 66.4, 66.3, 49.4, 46.9.
EXPERIMENTAL SECTION
■
Methods. SCXRD. SCXRD raw data were collected on a Bruker
APEX DUO diffractometer using graphite-monochromated Mo Kα
radiation (λ = 0.71073) at 90 K and processed using APEX2.37 Most of
the structures were solved using SUPERFLIP38 and refined using full-
matrix least squares on F2 within the CRYSTALS39 suite. Hydrogen
atoms were initially refined with restraints on bond lengths and angles,
after which the positions were used as the basis for a riding model.40
All non-hydrogen atoms were refined anisotropically. In the case of
strongly disordered solvent molecules, PLATON/SQUEEZE41 was
used.
Compound 4. 2,6-Pyridinedicarbonyl dichloride (300.1 mg, 1.47
mmol) was dissolved in 5 mL of THF, and the solution was cooled to
0 °C. Triethylamine (1.13 mL, 8.085 mmol) was added dropwise,
followed by benzylamine (0.35 mL, 3.23 mmol), still dropwise. The
solution was stirred at 0 °C for 30 min and then at room temperature
overnight. The solution was concentrated by rotary evaporation,
extracted with DCM and water (3 × 30 mL), dried over Na2SO4, and
evaporated to give 400 mg (1.16 mmol) of a white crystalline solid that
1
1
VT H NMR Spectroscopy. H NMR spectra were collected on a
Bruker AV-400 inverse probe spectrometer and were calibrated to the
residual protonated solvents at δ 6.00 and 5.32 for 1,1,2,2-
tetrachloroethane-d2, and CD2Cl2, respectively. The concentration of
the solutions was 0.06 M.
1
was pure by H NMR spectroscopy. Yield: 79%.
1
Data for 4. H NMR (400 MHz, CD2Cl2): δ 8.35 (d, 2H, J = 7.61
Hz), 8.17 (br t, 2H), 8.04 (t, 1H, J = 7.61 Hz), 7.30 (m, 10 h), 4.62 (d,
4H, J = 6.34 Hz). 13C NMR (75 MHz, CD2Cl2): δ 164.0, 149.5, 139.6,
139.0, 129.1, 128.1, 127.9, 125.6, 43.8. HRMS (ESI/TOF-Q). Calcd
for C21H20N3O2 [4 + H+]: m/z 346.1556. Found: m/z 346.1563. Elem
anal. Calcd for C21H19N3O2: C, 73.03; H, 5.54; N, 12.17. Found: C,
73.11; H, 5.63; N, 12.13. UV−vis [CH2Cl2; λmax, nm (εmax, M−1
cm−1)]: 229 (2.2 × 104, one shoulder).
Compound 5. Compound 4 (97.5 mg, 0.28 mmol) was stirred with
Pd(OAc)2 (62.9 mg, 0.28 mmol) in 10 mL of acetonitrile at room
temperature overnight.42 The precipitate was filtered, washed with
cold acetonitrile, and recrystallized from a 1:1 mixture of chloroform
and acetonitrile to give 55 mg (0.11 mmol) of yellow crystals. Yield:
40%. Crystals suitable for SCXRD analysis were grown by vapor
diffusion of pentane into a solution of 5 in 1:1 acetonitrile/chloroform.
Data for 5. 1H NMR (400 MHz, (CD3)2SO): δ 8.23 (t, 1H, J = 7.61
Hz), 7.65 (d, 2H, J = 7.61 Hz), 7.36 (d, 4H, J = 7.61 Hz), 7.29 (m,
4H), 7.18 (t, 2H, J = 6.98 Hz), 4.30 (s, 4H), 2.07 (s, 3H). 13C NMR
(75 MHz, CDCl3): δ 170.7, 153.2, 142.0, 141.3, 128.7, 128.3, 127.3,
126.5, 124.0, 50.1, 1.9. HRMS (ESI/TOF-Q). Calcd for
C21H18N3O2104Pd [5 − CH3CN + H+]: m/z 448.0439. Found: m/z
448.0435. Elem anal. Calcd for C23H20N4O2Pd: C, 56.24; H, 4.11; N,
11.41. Found: C, 55.52; H, 4.12; N, 10.97. UV−vis [CH2Cl2; λmax, nm
(εmax, M−1 cm−1)]: 229 (2.4 × 104, one shoulder).
Compound 1. Compound 1 was prepared according to a slightly
modified reported procedure.19 A suspension of 4-hydroxybenzyl-
amine (663.7 mg, 5.39 mmol) in 20 mL of dry THF was cooled to
−78 °C. Triethylamine (0.75 mL, 5.39 mmol) was added to the
suspension. A solution of 2,6-pyridinedicarbonyl dichloride (500 mg,
2.45 mmol) in 20 mL of dry THF was added dropwise over 2 h, while
keeping the reaction flask at −78 °C. The cooling bath was removed,
and the solution was stirred overnight at room temperature. The
reaction mixture was then filtered, and the filtrate was concentrated by
evaporation under reduced pressure to give 560 mg (1.48 mmol) of 1
as an off-white solid. Yield: 61%.
NMR data were consistent with those previously reported.19
Compound 2. Compound 1 (346.6 mg, 0.99 mmol), K2CO3
(1.3712 g, 9.92 mmol), and cis-1,4-dichloro-2-butene (0.1 mL, 1.09
mmol) were heated at reflux in acetonitrile (400 mL) for 120 h. The
solution was cooled and filtered in order to remove K2CO3. The
solvent was removed by rotary evaporation to give 300 mg (0.70
mmol) of an off-white pure solid. Yield: 71%. Crystals suitable for
SCXRD analysis were grown by slow evaporation of a solution of 2 in
chloroform.
1
Data for 2. H NMR (400 MHz, CDCl3): δ 8.38 (d, 2H, J = 7.61
Hz), 8.08 (t, 1H, J = 7.61 Hz), 7.62 (br m, 2H), 7.18 (d, 4H, J = 8.25
Hz), 6.84 (d, 4H, J = 8.25 Hz), 5.90 (t, 2H, J = 3.17 Hz), 4.77 (d, 4H, J
= 3.81 Hz), 4.57 (d, 4H, J = 5.08 Hz). 13C NMR (75 MHz, CDCl3): δ
162.9, 158.0, 148.6, 139.3, 129.4, 129.3, 128.7, 124.9, 115.3, 64.8, 43.3.
HRMS (ESI/TOF-Q). Calcd for C25H24N3O4 [2 + H+]: m/z
Compound 5-PPh3. Compound 5 (30.0 mg, 0.06 mmol) and
triphenylphosphine (15.7 mg, 0.06 mmol) were dissolved in 3 mL of
chloroform, and the resulting solution was stirred for 8 h at room
temperature. The solution was evaporated to give yellow crystals.
Yield: 38.5 mg (0.05 mmol, 90%). Crystals suitable for SCXRD
analysis were grown by vapor diffusion of diethyl ether into a solution
of 5-PPh3 in 1:1 acetonitrile/chloroform.
430.1767. Found: m/z 430.1765. UV−vis [CH2Cl2; λmax, nm (εmax
,
M−1 cm−1)]: 229 (4.8 × 104), 276 (1.5 × 104).
Compound 3. A solution of compound 2 (77 mg, 0.18 mmol) and
Pd(OAc)2 (41.2 mg, 0.18 mmol) in 5 mL of acetonitrile was heated at
H
DOI: 10.1021/acs.inorgchem.8b00031
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
Data for 5-PPh3. H NMR (400 MHz, CD2Cl2): δ 8.16 (t, 1H, J =
UV−vis [CH2Cl2; λmax, nm (εmax, M−1 cm−1)]: 228 (4.9 × 104), 257
(1.3 × 105).
7.61 Hz), 7.88 (d, 2H, J = 7.61 Hz), 7.41 (m, 9H), 7.21 (m, 6H), 7.04
(m, 6H), 6.76 (m, 4H), 3.79 (s, 4H). 13C NMR (75 MHz, CDCl3): δ
173.6, 151.3, 142.1, 141.4, 133.5 (d, J = 11.49 Hz), 131.9 (d, J = 2.30
Hz), 129.3 (d, J = 11.49 Hz), 128.3, 128.1, 126.7, 126.2, 125.4 (d, J =
2.30 Hz), 50.9. HRMS (ESI/TOF-Q). Calcd for C39H33N3O2P104Pd
[5-PPh3 + H+]: m/z: 710.1351. Found: m/z 710.1354. Elem anal.
Calcd for C39H32N3O2P104Pd: C, 65.78; H, 4.49; N, 5.90. Found: C,
64.32; H, 4.39; N, 5.75. UV−vis [CH2Cl2; λmax, nm (εmax, M−1 cm−1)]:
228 (1.1 × 105, two shoulders).
Compound 5-lut. Compound 5 (30.0 mg, 0.06 mmol) and 2,6-
lutidine (7.0 μL, 0.06 mmol) were dissolved in 3 mL of chloroform,
and the resulting solution was stirred for 8 h. The solution was
evaporated to give a yellow solid that was washed with hexanes. Yield:
32.2 mg (0.06 mmol, 97%). Crystals suitable for SCXRD analysis were
grown by vapor diffusion of diethyl ether into a solution of 5-lut in 1:1
acetonitrile/chloroform.
1
Data for 5-lut. H NMR (400 MHz, CD2Cl2): δ 8.11 (t, 1H, J =
Compound 5-pyr. Compound 5 (30.0 mg, 0.06 mmol) and
pyridine (5.0 μL, 0.06 mmol) were dissolved in 3 mL of chloroform,
and the resulting solution was stirred for 30 min. The solution was
evaporated to give a yellow solid, which was washed with hexanes.
Yield: 30.0 mg (0.06 mmol, 95%). Crystals suitable for SCXRD
analysis were grown by vapor diffusion of diethyl ether into a solution
of 5-pyr in 1:1 acetonitrile/chloroform.
7.61 Hz), 7.80 (d, 2H, J = 8.25 Hz), 7.64 (t, 1H, J = 8.25 Hz), 7.10 (t,
2H, J = 6.98 Hz), 7.03 (t, 4H, J = 7.61 Hz), 6.95 (d, 2H, J = 7.61 Hz),
6.59 (d, 4H, J = 6.98 Hz), 4.03 (s, 4H), 2.41 (s, 6H). 13C NMR (75
MHz, CD2Cl2): δ 171.5, 160.7, 153.4, 141.8, 141.2, 139.5, 128.6,
127.9, 126.9, 125.1, 123.4, 49.7, 25.8. HRMS (ESI/TOF-Q). Calcd for
C28H27N4O2104Pd [5-lut + H+]: m/z 555.1174. Found: m/z 555.1176.
Elem anal. Calcd for C26H22N4O2Pd: C, 60.38; H, 4.71; N, 10.06.
1
Data for 5-pyr. H NMR (400 MHz, CD2Cl2): δ 8.11 (t, 1H, J =
Found: C, 59.83; H, 4.62; N, 9.75. UV−vis [CH2Cl2; λmax, nm (εmax
,
7.61 Hz), 7.92 (m, 2H), 7.80 (d, 2H, J = 7.61 Hz), 7.26 (m, 1H), 7.06
(m, 6H), 6.97 (m, 2H), 6.81 (m, 4H), 4.19 (s, 4H). 13C NMR (100
MHz, CD2Cl2): δ 171.3, 153.4, 151.7, 141.8, 141.2, 138.7, 128.5,
127.2, 126.5, 125.7, 125.0, 49.1. HRMS (ESI/TOF-Q). Calcd for
C26H23N4O2104Pd [5-pyr + H+]: m/z 527.0826. Found: m/z 527.0824.
Elem anal. Calcd for C26H22N4O2Pd: C, 59.04; H, 4.19; N, 10.59.
M−1 cm−1)]: 229 (5.7 × 104, one shoulder), 314 (1.1 × 104).
Compound 3-PPh3. Compound 3 (33.2 mg, 0.058 mmol) and
triphenylphosphine (15.2 mg, 0.058 mmol) were dissolved in 5 mL of
DCM, and the resulting solution was stirred for 24 h. The solution was
concentrated under reduced pressure and purified by flash
chromatography with an alumina column [eluent, 1% methanol
(MeOH) in DCM; Rf = 0.22] to give the product as a yellow solid.
Yield: 42.5 mg (0.053 mmol, 92%).
Found: C, 58.76; H, 4.04; N, 10.33. UV−vis [CH2Cl2; λmax, nm (εmax
,
M−1 cm−1)]: 228 (4.1 × 104, two shoulders).
1
Compound 5-dmap. Compound 5 (30.0 mg, 0.06 mmol) and
DMAP (7.3 mg, 0.06 mmol) were dissolved in 3 mL of chloroform,
and the resulting solution was stirred for 30 min. The solution was
evaporated to give a yellow oil. The oil was recrystallized by slow
evaporation from acetone and washed with hexanes to give a yellow
solid. Yield: 16.0 mg (0.03 mmol, 47%).
Data for 3-PPh3. H NMR (400 MHz, CD2Cl2): δ 8.22 (t, 1H, J =
7.61 Hz), 7.96 (d, 2H, J = 6.61 Hz), 7.40 (t, 3H, J = 6.34 Hz), 7.23 (t,
6H, J = 7.61 Hz), 7.06 (m, 6H), 6.82 (d, 4H, J = 8.88 Hz), 6.71 (d, 4H,
J = 8.88 Hz) 5.81 (d, 2H, J = 5.71 Hz), 5.02 (m, 4H), 4.60 (d, 2H, J =
14.59 Hz), 2.54 (d, 2H, J = 15.86 Hz). 13C NMR (100 MHz, CD2Cl2):
δ 173.6, 157.0, 152.2, 141.9, 134.6, 134.5 (d, J = 2.20 Hz), 132.5 (d, J =
9.54 Hz), 131.7 (d, J = 2.20 Hz), 130.4, 129.3 (d, J = 10.27 Hz), 127.6,
125.6, 116.1, 65.5, 48.3. HRMS (ESI/TOF-Q). Calcd for
C43H37N3O4P104Pd [3-PPh3 + H+]: m/z 795.1562. Found:
794.1556. UV−vis [CH2Cl2; λmax, nm (εmax, M−1 cm−1)]: 232 (7.7
× 104, two shoulders).
Data for 5-dmap. 1H NMR (400 MHz, CD2Cl2): δ 8.06 (t, 1H, J =
7.61 Hz), 7.74 (d, 2H, J = 8.25 Hz), 7.52 (d, 2H, J = 7.61 Hz), 7.10
(m, 6H), 6.95 (d, 4H, J = 7.61 Hz), 6.16 (d, 2H, J = 7.61 Hz), 4.19 (s,
4H), 2.99 (s, 6H). 13C NMR (75 MHz, CD2Cl2): δ 171.4, 154.9,
153.6, 150.2, 142.2, 140.9, 128.4, 127.5, 126.4, 124.7, 107.9, 49.3, 39.6.
HRMS (ESI/TOF-Q). Calcd for C28H28N5O2104Pd [5-dmap + H+]:
m/z 570.1283. Found: m/z 570.1276. UV−vis [CH2Cl2; λmax, nm
(εmax, M−1 cm−1)]: 228 (1.6 × 105), 275 (1.8 × 105, one shoulder).
Compound 5-quin. Compound 5 (30.0 mg, 0.06 mmol) and
quinoline (7 μL, 0.06 mmol) were dissolved in 3 mL of chloroform
and stirred for 30 min. The solution was evaporated to give a yellow
solid that was recrystallized from a mixture of DCM and hexanes.
Yield: 19.4 mg (0.03 mmol, 56%). Crystals suitable for SCXRD
analysis were grown by vapor diffusion of hexanes into a solution of 5-
quin in chloroform.
Compound 3-pyr. Compound 3 (33.5 mg, 0.058 mmol) and
pyridine (4.7 μL, 0.058 mmol) were dissolved in 5 mL of DCM, and
the resulting solution was stirred overnight. The solution was
concentrated under reduced pressure and washed with hexanes (5
mL × 3) to give the product as a yellow oil. Yield: 27.5 mg (0.045
mmol, 77%).
1
Data for 3-pyr. H NMR (400 MHz, CD2Cl2, 113 °C): δ 8.14 (t,
1H, J = 8.05 Hz), 7.89 (d, 2H, J = 7.68 Hz), 7.55 (t, 1H, J = 7.68 Hz),
7.16 (br, 1H), 6.95 (d, 4H, J = 8.42 Hz), 6.87 (d, 2H, J = 6.95 Hz),
6.83 (d, 4H, J = 8.78 Hz), 5.91 (t, 2H, J = 1.83 Hz), 5.43 (d, 2H, J =
15.73 Hz), 4.94 (dd, 2H, J1 = 13.90 Hz, J2 = 4.03 Hz), 4.68 (d, 2H, J =
13.54 Hz), 3.06 (d, 2H, J = 15.73 Hz). 13C NMR (100 MHz, CD2Cl2):
δ 171.1, 157.5, 153.8, 141.2, 137.8, 135.8, 130.3, 128.3, 125.1, 124.9,
118.0, 67.5, 47.5. HRMS (ESI/TOF-Q). Calcd for C30H27N4O4105Pd
[3-pyr + H+]: m/z 612.1083. Found: m/z 612.1091. UV−vis [CH2Cl2;
λmax, nm (εmax, M−1 cm−1)]: 231 (1.7 × 104, two shoulders).
Compound 3-dmap. Compound 3 (30 mg, 0.052 mmol) and
DMAP (6.4 mg, 0.052 mmol) were dissolved in 5 mL of chloroform,
and the resulting solution was stirred for 2 h. The solution was
concentrated under reduced pressure and purified by flash
chromatography with an alumina column (eluent, 2% MeOH in
DCM; Rf = 0.35) to give the product as a yellow oil. Yield: 18.4 mg
(0.028 mmol, 54%).
1
Data for 5-quin. H NMR (400 MHz, CD2Cl2): δ 8.97 (d, 1H, J =
8.25 Hz), 8.18 (m, 3H), 7.84 (d, 2H, J = 8.25 Hz), 7.81 (d, 1H, J =
7.61 Hz), 7.62 (m, 2H), 6.97 (m, 1H), 6.84 (m, 6H), 6.47 (d, 4H, J =
8.25 Hz), 4.28 (d, 2H, J = 15.23 Hz), 3.72 (d, 2H, J = 15.23 Hz). 13C
NMR (75 MHz, CD2Cl2): δ 171.2, 153.6, 153.4, 146.2, 141.4, 141.2,
139.2, 131.8, 129.1, 128.4, 128.35, 128.31, 128.0, 126.7, 126.1, 124.9,
121.7, 49.1. HRMS (ESI/TOF-Q). Calcd for C30H25N4O2104Pd [5-
quin + H+]: m/z 577.1018. Found: m/z 577.1021. UV−vis [CH2Cl2;
λmax, nm (εmax, M−1 cm−1)]: 230 (9.1 × 104), 309 (2.1 × 104).
Compound 5-acr. Compound 5 (30.0 mg, 0.06 mmol) and
acridine (11.0 mg, 0.06 mmol) were dissolved in 3 mL of chloroform,
and the resulting solution was stirred for 1 h. The solution was
evaporated to give a yellow solid that was recrystallized from a mixture
of DCM and hexanes. Yield: 20.3 mg (0.03 mmol, 54%). Crystals
suitable for SCXRD analysis were grown by vapor diffusion of hexanes
into a solution of 5-acr in chloroform.
Data for 3-dmap. 1H NMR (400 MHz, CD2Cl2, 113 °C): δ 8.11 (t,
1H, J = 7.92 Hz), 7.87 (d, 2H, J = 7.61 Hz), 7.03 (d, 4H, J = 8.53 Hz),
6.83 (d, 4H, J = 8.53 Hz), 6.67 (d, 2H, J = 5.79 Hz), 5.95 (d, 2H, J =
7.01 Hz), 5.88 (t, 2H, J = 2.44 Hz), 5.42 (d, 2H, J = 15.53 Hz), 4.94
(dd, 2H, J1 = 13.71 Hz, J2 = 4.26 Hz), 4.68 (d, 2H, J = 13.10 Hz), 3.16
(d, 2H, J = 15.53 Hz). 13C NMR (100 MHz, CD2Cl2): δ 171.1, 157.4,
154.1, 154.0, 140.9, 136.1, 130.3, 128.3, 124.9, 117.9, 107.0, 67.5, 47.4,
39.4. HRMS (ESI/TOF-Q). Calcd for C32H32N5O4104Pd [3-dmap +
H+]: m/z 654.1495. Found: m/z 654.1505. UV−vis [CH2Cl2; λmax, nm
(εmax, M−1 cm−1)]: 230 (6.2 × 104), 275 (6.6 × 104, one shoulder).
1
Data for 5-acr. H NMR (400 MHz, CD2Cl2): δ 9.29 (d, 2H, J =
8.88 Hz), 8.90 (s, 1H), 8.19 (t, 1H, J = 7.61 Hz), 7.97 (d, 2H, J = 8.88
Hz), 7.88 (d, 2H, J = 7.61 Hz), 7.67 (m, 2H), 7.54 (t, 2H, J = 7.61
Hz), 6.49 (m, 6H), 6.06 (d, 2H, J = 6.98 Hz), 3.80 (s, 4H). 13C NMR
(75 MHz, CDCl3): δ 171.5, 153.7, 148.4, 141.2, 141.1, 141.0, 133.3,
128.5, 127.8, 126.7, 125.1, 49.3. HRMS (ESI/TOF-Q). Calcd for
C34H27N4O2104Pd [5-acr + H+]: m/z 627.1174. Found: m/z 627.1180.
I
DOI: 10.1021/acs.inorgchem.8b00031
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Compound 3-quin. A solution of compound 3 (32.9 mg, 0.057
mmol) and quinoline (6.8 μL, 0.057 mmol) was stirred in 5 mL of
DCM for 4 days. The solvent was evaporated under reduced pressure
to give a yellow solid that was purified by flash chromatography on
alumina (eluent, 1% MeOH in DCM; Rf = 0.22). The product is a
yellow solid. Yield: 28.1 mg (0.042 mmol, 75%). Crystals suitable for
SCXRD analysis were grown by slow evaporation of a solution of 3-
quin in DCM.
Accession Codes
CCDC 1814556−1814566 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
Data for 3-quin. H NMR (400 MHz, CD2Cl2): δ 9.63 (d, 1H, J =
8.88 Hz), 8.20 (t, 1H, J = 7.61 Hz), 8.00 (d, 1H, J = 8.25 Hz), 7.89 (m,
4H), 7.69 (t, 1H, J = 6.98 Hz), 6.79 (m, 8H), 6.38 (dd, 1H, J1 = 8.25
Hz, J2 = 5.08 Hz), 5.92 (m, 2H), 5.78 (dd, 1H, J1 = 5.08 Hz, J2 = 1.27
Hz), 5.18 (d, 2H, J = 15.23 Hz), 4.95 (dd, 2H, J1 = 13.32 Hz, J2 = 5.08
Hz), 4.67 (d, 2H, J = 14.59 Hz), 2.67 (d, 2H, J = 15.86 Hz), 2.99 (s,
6H). 13C NMR (100 MHz, CD2Cl2): δ 171.2, 157.7, 155.0, 153.9,
146.0, 141.3, 137.9, 136.1, 132.0, 130.4, 129.1, 128.9. 128.4, 128.3,
128.1, 125.2, 121.6, 118.1, 67.7, 47.6. HRMS (ESI/TOF-Q). Calcd for
C34H29N4O4104Pd [3-quin + H+]: m/z 661.1229. Found: m/z
661.1250. UV−vis [CH2Cl2; λmax, nm (εmax, M−1 cm−1)]: 230 (1.5
× 105, two shoulders).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: mmaclach@chem.ubc.ca.
ORCID
Mark J. MacLachlan: 0000-0002-3546-7132
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Compound 3-acr. A solution of compound 3 (32.6 mg, 0.057
mmol) and acridine (10.2 mg, 0.057 mmol) was stirred in 5 mL of
chloroform overnight, after which the solvent was evaporated under
reduced pressure to give a yellow solid. The compound was purified by
flash chromatography using alumina. The initial eluent was DCM.
When all of the acridine was removed, the eluent was changed to 2%
methanol in DCM (Rf = 0.36). Yield: 38.7 mg (0.054 mmol, 95%).
Crystals suitable for SCXRD analysis were grown by slow evaporation
of a solution of 3-acr in DCM in an NMR tube.
This work was supported by an NSERC Discovery grant. We
thank Nicholas White and Brian Patrick for assistance with
solving the X-ray diffraction structures.
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7.61 Hz), 8.03 (td, 1H, J1= 8.25 Hz, J2 = 1.27 Hz), 7.95 (d, 2H, J =
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* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00031.
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Crystallographic data, NMR spectra of new compounds,
2D NMR experiments, VT NMR data, details on X-ray
crystallography, and details of computations (PDF)
J
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