Metallosupramolecular Architectures Formed with Ferrocene-Linked Bis-Bidentate Ligands: Synthesis, Structures, and Electrochemical Studies

Article abstract of DOI:10.1021/acs.inorgchem.7b02503

The self-assembly of ligands of different geometries with metal ions gives rise to metallosupramolecular architectures of differing structural types. The rotational flexibility of ferrocene allows for conformational diversity, and, as such, self-assembly processes with 1,1′-disubstituted ferrocene ligands could lead to a variety of interesting architectures. Herein, we report a small family of three bis-bidentate 1,1′-disubstituted ferrocene ligands, functionalized with either 2,2′-bipyridine or 2-pyridyl-1,2,3-triazole chelating units. The self-assembly of these ligands with the (usually) four-coordinate, diamagnetic metal ions Cu(I), Ag(I), and Pd(II) was examined using a range of techniques including ¹H and DOSY NMR spectroscopies, high-resolution electrospray ionization mass spectrometry, X-ray crystallography, and density functional theory calculations. Additionally, the electrochemical properties of these redox-active metallosupramolecular assemblies were examined using cyclic voltammetry and differential pulse voltammetry. The copper(I) complexes of the 1,1′-disubstituted ferrocene ligands were found to be coordination polymers, while the silver(I) and palladium(II) complexes formed discrete [1 + 1] or [2 + 2] metallomacrocyclic architectures.

Full text of DOI:10.1021/acs.inorgchem.7b02503

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Metallosupramolecular Architectures Formed with Ferrocene-Linked
Bis-Bidentate Ligands: Synthesis, Structures, and Electrochemical
Studies
James A. Findlay, C. John McAdam, Joshua J. Sutton, Dan Preston, Keith C. Gordon,
and James D. Crowley*
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
S
* Supporting Information
ABSTRACT: The self-assembly of ligands of different geo-
metries with metal ions gives rise to metallosupramolecular
architectures of differing structural types. The rotational
flexibility of ferrocene allows for conformational diversity,
and, as such, self-assembly processes with 1,1′-disubstituted
ferrocene ligands could lead to a variety of interesting
architectures. Herein, we report a small family of three bis-
bidentate 1,1′-disubstituted ferrocene ligands, functionalized
with either 2,2′-bipyridine or 2-pyridyl-1,2,3-triazole chelating
units. The self-assembly of these ligands with the (usually) four-
coordinate, diamagnetic metal ions Cu(I), Ag(I), and Pd(II)
1
was examined using a range of techniques including H and
DOSY NMR spectroscopies, high-resolution electrospray ionization mass spectrometry, X-ray crystallography, and density
functional theory calculations. Additionally, the electrochemical properties of these redox-active metallosupramolecular
assemblies were examined using cyclic voltammetry and differential pulse voltammetry. The copper(I) complexes of the 1,1′-
disubstituted ferrocene ligands were found to be coordination polymers, while the silver(I) and palladium(II) complexes formed
discrete [1 + 1] or [2 + 2] metallomacrocyclic architectures.
functionalized ligands and heterometallic metallosupramolecu-
lar systems.9 Ferrocene can be readily functionalized using a
wide variety of standard organic transformations and will
undergo reversible one-electron redox processes. These proper-
ties have been previously exploited in a range of areas including
the development of electronic,10 bioactive,11 and stimuli-
responsive materials12 and redox sensors.13 While a number
of redox-active metallosupramolecular architectures have been
generated with pendant Fc units,5,14 the self-assembly of
systems that exploit ferrocene as a structural component
remains rare. Presumably, the relative lack of interest in using
1,1′-disubstituted ferrocenes as components for metallosupra-
molecular self-assembly is connected to the rotational flexibility
of ferrocene ligands (Figure 1). The multiple accessible
conformers, arising from the ability of the cyclopentadienyl
(cp) rings to rotate about the sandwiched Fe(II) ion, could
potentially complicate the assembly process.
INTRODUCTION
■
The formation of self-assembled metallosupramolecular
architectures has been studied extensively in the past 30
years.1 The main factors determining the structures of these
architectures are the coordination geometry preference of the
metal ion(s) employed, the denticity of the ligands, and the
length and flexibility of the linking units between binding sites
on the ligands. The combination of a suitable metal ion with a
rigid bridging ligand will reliably generate either macrocyclic or
cage architectures. Conversely, bridging ligands with more
flexibility provide less control on the outcome of the self-
assembly process and can lead to mixtures or coordination
polymers.2 With the design principles required for the
generation of discrete macrocyclic or cage architectures
reasonably well understood, efforts are now focused on the
development of applications for these multimetallic architec-
tures. Indeed, metallosupramolecular systems with interesting
biological,3 photophysical,4 and redox5 properties have been
generated. Recently, as part of the efforts to further enhance the
potential applications of metallosupramolecular architectures,
there has been considerable effort put into the development of
more functionalized ligand systems6 and heterometallic7
complexes. Ferrocene (FcH), a well-known robust 18-electron
organometallic sandwich complex,8 displays several properties
that potentially make it ideal for the development of both
There are a number of reports on the exploitation of 1,1′-
disubstituted ferrocenes featuring monodentate heterocyclic
donor groups for the assembly of both discrete metal-
lomacrocyclic architectures and coordination polymers.15,16
Special Issue: Self-Assembled Cages and Macrocycles
Received: September 29, 2017
© XXXX American Chemical Society
A
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tectures,28 herein we examine the use of a series of 1,1′-
disubstituted ferrocene ligands featuring bidentate N−N metal
binding domains for the generation of discrete metal-
losupramolecular systems and coordination polymers. The
ferrocene ligands feature either two bipy units (L1), two 2-
pyridyl-1,2,3-triazole (pytri) units (L3), or one bipy and one
pytri (L2) (Figure 2). The assemblies generated when the 1,1′-
Figure 1. Cartoon representation of the rotational flexibility of 1,1′-
diaryl-substituted ferrocenes: (top) syn (stacked) conformer;
(bottom) anti (open) conformer.
Of particular relevance, Lindner and co-workers have used 1,1′-
bis(3-pyridylethynyl)ferrocene and 1,1′-bis(4-pyridylethynyl)-
ferrocene to assemble discrete [2 + 2] metallomacrocycles with
Ag(I), Pd(II), and Ni(II) ions.17
However, there are far fewer examples of self-assembly with
1,1′-disubstituted ferrocenes featuring bidentate ligands, where
ferrocene forms an integral segment of the structure, as
opposed to occupying a pendant role. Moutet and co-workers
developed a family of 1,1′-disubstituted ferrocenes featuring
two 2,2′-bipyridine (bipy) binding units linked to the ferrocene
core via either ester or amide linkages. When these were
reacted with Cu(I) ions, both a [1 + 1] metallomacrocycle18
and a [2 + 2] double-stranded metallohelicate19 could be
observed crystallographically. Solution studies20 indicated that
the [1 + 1] metallomacrocycle was thermodynamically
preferred at low concentrations, while the [2 + 2] double-
stranded metallohelicate was the dominant species at high
concentrations.
Figure 2. 1,1′-Disubstituted ferrocene ligands L1−L3 in the folded/
stacked (syn) conformation and the model ligands L4 and L5.
Von Zelewsky and co-workers reported, in 2004, a series of
bis-bidentate 1,1′-disubstituted ferrocene ligands with bipy
binding pockets with appended variations of pinene groups.21,22
Upon combination with Cu(I), Ag(I), and Zn(II) ions, the
ligands all formed [2 + 2] double-stranded metallohelicates,
where the metal ions each adopt a tetrahedral coordination
geometry. The steric bulk of the pinene groups limits the ability
of the ligand bipy groups to undergo significant π−π-stacking
interactions, thus promoting splaying of the binding sites and
formation of the M2L2 metallohelicate architecture. Similar
results have been obtained by Wang et al.,23 despite the use of
more flexible linkers between the cp rings and the bidentate
Schiff-base coordinating domain. In related work, Bera and co-
workers have shown that 1,1′-dinaphthyridylferrocene ligands
will form a variety of metallomacrocyclic complexes that react
with Cu(I) or Zn(II) ions. While the 1,1′-dinaphthyridylferro-
cene is a bis-bidentate ligand, the lone pairs of electrons on the
coordinating N atoms are parallel and thus not at ideal
orientations for chelation of most metal ions. Nonetheless,
interesting solid-state macrocyclic structures were reported
including 1:1, 2:1, and 2:2 metal/ligand (M/L) complexes with
the Cu(I) ions. Also, a M4L4 macrocyclic architecture was
formed upon the addition of 1 equiv of ZnCl2, where the
“arms” of each ligand undergo π−π stacking and the two Cl
ions bound to each Zn(II) ion act similarly to a bidentate
capping unit,24 directing formation of the discrete architecture.
As part of our long-standing interest in the use of ferrocene
ligands for the development of stimuli-responsive molecular
switches25−27 and self-assembled metallosupramolecular archi-
disubstituted ferrocene ligands are treated with the diamagnetic
Cu(I), Ag(I), or Pd(II) ions are examined using a battery of
techniques including H NMR spectroscopy, diffusion-ordered
NMR spectroscopy (DOSY), high-resolution electrospray
ionization mass spectrometry (HR-ESI-MS), X-ray crystallog-
raphy, and density functional theory (DFT) calculations.
Additionally, the electrochemical properties of the metal-
losupramolecular assemblies are examined using cyclic
voltammetry (CV).
1
RESULTS AND DISCUSSION
■
Ligand Synthesis. We have previously reported the
synthesis of L1 as part of our work on stimuli-responsive
molecular actuators.26 The new ligands L2 and L3 were
synthesized using procedures analogous to those used to
generate L1. A Pd(0)-catalyzed Sonogashira cross-coupling29 in
diisopropylamine between either 1,1′-diiodoferrocene30 or 1-
(5-ethynyl-2,2′-bipyridine)-1′-iodoferrocene25,26 and 5-ethynyl-
2-(1-hexyl-1H-1,2,3-triazol-4-yl)pyridine (S2) using microwave
irradiation (200 W, 2 h, 100 °C) provided the ferrocene ligands
in good yield (L2, 74%; L3, 64%; see the Supporting
Information, SI). The model ligands L4 and L5 were generated
using similar procedures (see the SI).
1
The new ligands (L2 and L3) were characterized using H
and 13C NMR and IR spectroscopies, HR-ESI-MS, and
elemental analysis (see the SI). It is well established that 1,1′-
diarylferrocenes adopt a folded/stacked syn conformation in
both solution and the solid state (Figures 1 and 2).31 We
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previously showed, using 1H NMR spectral and X-ray
diffraction evidence, along with DFT calculations, that L1
adopts the syn conformation, in both solution and the solid
state, because of favorable π−π interactions32 between the bipy
and suggesting that the broadening is related to either a
fluxional process or the presence of coordination polymers in
solution (or both).
Fortunately, X-ray analysis of the Cu(I) complex of L3 was
able to be performed on single crystals spawned from the slow
diffusion of diethyl ether into an acetone solution. The
structure obtained revealed that in the solid state the complex
exists as a 1D coordination polymer, [Cun(L3)n](PF6)n (Figure
4), which is consistent with the broad 1H NMR spectra
“arms”.26 The H NMR spectra (Figures 3 and S9) indicate
1
1
Figure 3. Partially stacked H NMR spectra (400 MHz, CD3CN, 298
K) showing 5-ethynyl-2,2′-bipyridine (top), L2 (middle), and S2
(bottom). Upfield shifts are observed for all of the proton signals,
indicating that L2 predominantly forms a π−π-stacked syn
conformation in solution.
Figure 4. Solid-state structure of [Cun(L3)n](PF6)n. Selected bond
lengths (Å): Cu1−N9 = 2.075(9), Cu1−N10 = 1.975(1), Cu1−N15 =
1.984(9), Cu1−N16 = 2.080(8), Cu2−N1 = 2.038(1), Cu2−N2 =
2.025(9), Cu2−N7 = 1.999(1), Cu2−N8 = 2.080(1). Color scheme:
that, like L1, both of the new ligands L2 and L3 prefer a syn
π−π-stacked conformation in solution. The proton signals
associated with the bipy (Hc−i) and pytri (Hl−o) arms of L2 and
L3 were shifted upfield relative to those of the model
compounds 5-ethynyl-2,2′-bipyridine and S2, indicating that
the diarmed ferrocene ligands adopt a stacked (syn)
conformation in solution.
Cu(I) Assemblies. Since the pioneering self-assembly work
of Lehn and co-workers33 with Cu(I) ions and bis(bipy)
ligands, it has been well established that combining Cu(I) ions
with flexible or bent bis-bidentate N−N ligands results in the
formation of double-stranded metallohelicates,34 while more
rigid ligand assemblies form [4 + 4] grid complexes.35 Inspired
by those assemblies and with the knowledge that other
ferrocene-linked bis-bidentate ligands had generated double-
stranded metallohelicates with Cu(I) ions,20,21 we initially
examined the complexation of L1−L3 with [Cu(CH3CN)4]-
(PF6).
The addition of an acetone solution of [Cu(CH3CN)4](PF6)
(1 equiv) to one of the ligands (L1, L2, or L3, 1 equiv)
suspended in acetone at room temperature resulted in the
immediate formation of deep-red (L1 and L2) or dark-orange
(L3) solutions, indicative of complex formation.25,26,36,37 The
solutions of Cu(I) complexes were analyzed using HR-ESI-MS
(performed under pseudo-cold-spray conditions) and, surpris-
ingly, only featured ions corresponding to [CuL]+ and [CuL]2+,
which presumably result from the fragmentation of larger
discrete or polymeric systems (see the SI). 1H NMR analysis of
the Cu(I) complexes in a range of common deuterated solvents
of varying polarity and coordination ability resulted in very
broad spectra in each case. To rule out paramagnetic
broadening due to the presence of a small amount of Cu(II)
(from oxidation) in the samples, the spectra were reacquired in
the presence of 2 equiv of L-sodium ascorbate (a common Cu
reducing agent). Essentially identical broad spectra were
obtained, ruling out oxidation of the Cu ions as the cause
−
C, gray; N, purple; Fe, orange red; Cu, copper. H atoms and PF6
counterions were omitted for clarity.
observed above. The coordination polymer crystallized in the
monoclinic P21/c space group, and the asymmetric unit
contains two ligands and two Cu(I) ions and two
hexafluorophosphate anions. The Cu(I) ion was coordinated
to two pytri units in a tetrahedral fashion (τ4 = 0.68).38 The
Cu−N bond lengths range from 1.984(1) to 2.085(1) Å, similar
to those observed for the related [Cu(Bnpytri)2](PF6) [where
Bnpytri = 1-benzyl-4-(2-pyridyl)-1,2,3-triazole].39 The L3
ligands maintain the syn π−π-stacked conformation upon
complexation, and the Fc units adopted the expected eclipsed
conformation. Torsion angles (τ)15 between the two pytri units
of the 1,1′-disubstituted ferrocene L3, the angle between the
two substituents of each cp ring, and the centroid of the cp
rings, in the two crystallographically independent Fc units were
τ = 6.45° and 14.61°. Disappointingly, X-ray-quality crystals of
the Cu(I) complexes formed from L1 or L2 were not obtained.
However, given that each complex displays similar solution
data, it seems likely that all of the Cu(I) complexes are
coordination polymers (i.e., [Cun(L)n](PF6)n). While [2 + 2]
double-stranded metallohelicates were obtained previously
when related 1,1′-disubstituted ferrocene bis-bidentate ligands
were reacted with Cu(I) ions, the formation of Cu(I)
coordination polymers has been observed with more rigid
bis-bidentate N−N ligands.40 In order for L1−L3 to form [2 +
2] double-stranded metallohelicates with the Cu(I) ion, the
ligands would need to rotate into the anti (open) conformer.
Thus, we presume that coordination polymers are observed
here because of the relative stability of the syn (π−π-stacked)
conformation of the ligands.
Ag(I) Assemblies. Ag(I) ions are commonly used for the
generation of metallosupramolecular architectures.41 However,
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unlike Cu(I), the Ag(I) d10 ion adopts a wider variety of
coordination modes and geometries. With bidentate N−N
ligands, Ag(I) ions often form four-coordinate complexes; both
tetrahedral41 and square-planar42 coordination geometries have
been observed. The plasticity of the Ag(I) coordination sphere
may result in the formation of different metallosupramolecular
architectures with the ferrocene ligands L1−L3. Therefore, we
examined the complexation of the ferrocene ligands with Ag(I)
ions.
The addition of solid AgPF6 (1 equiv) to a solution [2:1 (v/
v) CDCl3/CD3NO2] of one of the ligands (L1, L2, or L3, 1
1
equiv) at room temperature was monitored using H NMR
Figure 5. Solid-state structure of [Ag2(L3)2](PF6)2. Selected bond
lengths (Å): Ag1−N3 = 2.207(3), Ag1−N4 = 2.623(3), Ag1−N5 =
2.560(3), Ag1−N6 = 2.214(3). Selected bond angles (deg): N3−
Ag1−N4 = 69.83(1), N4−Ag1−N6 = 106.21(1), N6−Ag1−N5 =
69.76(1), N5−Ag1−N3 = 114.35(1). Color scheme: C, gray; N,
spectroscopy (400 MHz, 298 K). Unlike the Cu(I) complexes,
the addition of Ag(I) ions to the ligands resulted in sharp well-
defined H NMR spectra. All of the proton resonances were
shifted relative to the respective free ligands, with downfield
shifts of the triazole and α-pyridyl proton signals indicative of
coordination of the Ag(I) ions to the bidentate ligand units
1
−
purple; Fe, orange; Ag, white. PF6 counterions and H atoms were
omitted for clarity.
1
(see Figures S16−S18). H DOSY NMR experiments [500
conformation. The torsion angle (τ) between the two pytri
units of the 1,1′-disubstituted ferrocene L3 is 0.59°.
MHz, 298 K, 2:1 (v/v) CDCl3/CD3NO2] were used to
elucidate the structure of the Ag(I) complexes based on the
diffusion rates. The diffusion coefficients (D; ×10−10 m2 s−1) of
each of the ligands (L1, L2, or L3) and the corresponding
Ag(I) complexes are presented in Table S1. For L1 and L2, the
diffusion coefficients of the Ag(I) complexes (D = 6.40 and
5.84 × 10−10 m2 s−1) were only slightly lower than those of the
corresponding ligands (D = 6.60 and 6.26 × 10−10 m2 s−1),
indicating that the relative sizes of the ligands and complexes
are quite similar, consistent with the formation of [1 + 1]
metallomacrocyclic structures. Conversely, a larger difference in
the diffusion coefficients of L3 (D = 5.55 × 10−10 m2 s−1) and
the corresponding Ag(I) complex (D = 4.72 × 10−10 m2 s−1)
was observed, suggesting the formation of a [2 + 2]
metallomacrocyclic structure in this case (Figure S44). The
HR-ESI-MS spectra (performed under pseudo-cold-spray
conditions) of the complexes formed with L1−L3 each showed
ions consistent with the [Ag(L)]+ formulation. While this was
consistent with the expectation for the L1 and L2 complexes, it
suggests that the Ag(I) [2 + 2] metallomacrocycle of L3 is
fragmenting under the conditions of the experiment (Figures
S14, S16, and S19).
Unfortunately, X-ray-quality crystals of the Ag(I) complexes
formed from L1 or L2 were not obtained. However, given that
each complex displays solution phase data similar to those of
the corresponding Pd(II) complexes (vide infra), it seems likely
that the Ag(I) complexes of L1 and L2 are the smaller
entropically favored [1 + 1] metallomacrocycles. The Ag(I)
ions in the [1 + 1] metallomacrocycles presumably display a
distorted tetrahedral coordination geometry because this
geometry would reduce unfavorable steric clashes between
the α-pyridyl protons of the bipy and pytri units.46 Similar [1 +
1] Ag(I) metallomacrocycles have been generated using
ferrocene-containing bis-bidentate Schiff-base ligands.23
Pd(II) Assemblies. Having observed the square-planar
coordination geometry of the Ag(I) ions in the [Ag2(L3)2]-
(PF6)2 complex, we next examined complexation of the
ferrocene ligands with Pd(II) ions. Pd(II)-based self-assembled
architectures47 have been extensively studied, but they most
commonly feature a single cis-protecting N−N chelating
ligand.24 It is unusual for bis-bidentate N−N ligands to be
used with Pd(II) ions to generate self-assembled architec-
tures,48 although we have recently shown that bis(pytri)
complexes of Pd and Pt can be used to generate metallomacro-
cycles.43
X-ray-quality single crystals of the Ag(I) complex of L3 were
obtained by the vapor diffusion of diethyl ether into a CHCl3/
CH3NO2 (2:1, v/v) solution of the complex. The complex
crystallized in the monoclinic P21/c space group, and the
asymmetric unit contains one ligand, one Ag(I) ion, and one
hexafluorophosphate anion (see the SI). The structure data
confirmed the formation of the expected [2 + 2] metal-
lomacrocycle [Ag2(L3)2](PF6)2 (Figure 5). The Ag(I) ions are
coordinated to two pytri units in a square-planar fashion (τ4 =
0.083).38 The Ag−N bond lengths range from 2.207(3) to
2.623(3) Å with two short and two longer bond distances.
Similar, square-planar coordination modes of Ag(I) pytri
complexes43,44 have been observed, but tetrahedral complexes,
such as [Ag(Bnpytri)2](SbF6),45 have also been identified. The
formation of the square-planar geometry is presumably
stabilized by the presence of π−π (3.665 and 3.989 Å), Ag−
Ag (3.935 Å), and hydrogen-bonding [N2−H28−C28 3.599 Å
(N---H) and 4.269(5) Å (N---HC); N7−H13−C13 3.324 Å
(N---H) and 4.028(5) Å (N---HC)] interactions. The L3
ligands maintain the syn π−π-stacked conformation upon
complexation, and the Fc units adopt the expected eclipsed
The addition of [Pd(CH3CN)4](BF4)2 (either 0.5 or 1
equiv) to an acetonitrile solution of one of the ligands (L1−L3,
1 equiv) resulted in the instant formation of either red or deep-
purple solutions, indicative of complex formation.27,37 Interest-
ingly, the behavior of the bis(bipy) ligand L1 differed from that
of the pytri-containing ligands L2 and L3. The addition of
[Pd(CH3CN)4](BF4)2 (0.5 equiv) to an acetonitrile solution of
L1 (1 equiv) resulted in a broad undefined 1H NMR spectrum
(Figure S31). In contrast, the addition of 1 equiv of
[Pd(CH3CN)4](BF4)2 to an acetonitrile solution of L1 (1
1
equiv) resulted in a clear sharp H NMR spectrum consistent
with complex formation (Figure S31). The HR-ESI-MS
spectrum of the 1:1 Pd(II)/L1 mixture displayed two peaks
at m/z 324.014 and 667.0146, consistent with the [Pd(L1)]2+
and [Pd(L1)(H2O)(H−)]+ ions,49 respectively, suggesting the
formation of complex with a 1:1 M/L stoichiometry (Figure
1
S21). The H DOSY NMR experiment [500 MHz, 298 K, 2:1
(v/v) CDCl3:CDNO2] on the 1:1 L1/Pd mixture indicated
that all proton resonances of the complexes had the same
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diffusion coefficient (D = 5.92 × 10−10 cm2 s−1), suggesting the
clean formation of a single species. The diffusion coefficient of
the 1:1 L1/Pd complex was very similar to those observed for
the Ag(I) complexes of L1 or L2 (D = 6.40 and 5.84 × 10−10
cm2 s−1, respectively), providing further support for the
[Pd(L1)](BF4)2 formulation. The 1:1 M/L stoichiometry was
confirmed unequivocally using X-ray diffraction analysis. Dark-
purple single crystals of [Pd(L1)](BF4)2 were obtained from
the slow diffusion of diethyl ether into an acetonitrile solution
of the Pd complex (Figure 6 and the SI). The complex
1
Figure 7. Partially stacked H NMR spectra (400 MHz, CD3CN, 298
K) of (a) [Pd(L2)2](BF4)4, (b) L2, and (c) [Pd(L2)](BF4)4.
of the 0.5:1 mixture of Pd(II) and L2 was similar to that
observed with L3: downfield shifts of the pytri proton
resonances were observed, indicative of Pd complexation with
the pytri pockets, while upfield shifts for the proton resonances
associated with the bipy units were consistent with a π−π
1
interaction. However, unlike the [Pd(L3)2]2+ complex, the H
Figure 6. Solid-state structure of [Pd(L1)]2+. Selected bond lengths
(Å): Pd1−N1 = 2.065(2), Pd1−N2 = 2.032(2), Pd1−N3 = 2.019(2),
Pd1−N4 = 2.070(2). Selected atom distances (Å): H10−H25 = 2.139,
H1−H34 = 1.789 . Color scheme: C, gray; H, white; N, purple; Fe,
NMR spectrum of the 0.5:1 mixture of Pd(II) and L2
contained two species, the [Pd(L2)2]2+ complex (80−90%)
and a second species that had a broad uninterpretable spectrum
(10−20%) that we presume is a coordination polymer/
oligomer (Figure 7). The HR-ESI-MS data for both mixtures
only displayed intense peaks consistent with [Pd(L)2]2+ ions,
confirming formation of the 1:2 M/L complexes (Figures S25
and S30). The vapor diffusion of diethyl ether into an
acetonitrile solution containing a 0.5:1 mixture of [Pd-
(CH3CN)4](BF4)2 and L2 resulted in deep-purple crystals of
[Pd(L2)2](BF4)2 (Figure 8 and the SI). The complex
−
orange red; Pd, dark cyan. BF4 counterions and the remaining H
atoms were omitted for clarity.
crystallizes in the P1 space group, with two metallocycles and
̅
four BF4− counterions present in the unit cell. While the Fc unit
of L1 still adopts an essentially eclipsed conformation, the bipy
“arms” of the ligands are no longer stacked and have τ = 46.61°.
Each bipy “arm” is coordinated to the Pd(II) ion in a pseudo-
square-planar fashion (τ4 = 0.16). The Pd−N bond lengths
range from 2.019(2) to 2.070(3) Å, similar to those of other
Pd(bipy) complexes.27,37,48 The flexibility of the alkyne linkers,
which are bent away from the normal linear geometry (angles
of 170.20° and 167.13°, respectively), enables the two bipy
“arms” to bind to the Pd ion in a distorted square-planar
arrangement. This arrangement also reduces the steric clash
between the α-pyridyl protons of the adjacent bipy units
(Figure 6).46,48
When either L2 or L3 were combined with 0.5 equiv of
[Pd(CH3CN)4](BF4)2 in acetonitrile, red solutions were
obtained. Conversely, when 1 equiv of [Pd(CH3CN)4](BF4)2
was added to one of the ligands (either L2 or L3, 1 equiv) in
Figure 8. Solid-state structure of [Pd(L2)2]2+. Selected bond lengths
(Å) and angles (deg): Pd1−N3 = 2.076(2), Pd1−N4 = 2.022(2); N3−
Pd1−N4 = 79.58. Color scheme: C, gray; H, white; N, purple; Fe,
1
acetonitrile, deep-purple solutions were obtained. H NMR
−
orange red; Pd, dark cyan. BF4 counterions and the remaining H
spectra confirmed that the complexes that were formed with 0.5
equiv of Pd(II) were different from those obtained with 1 equiv
of the metal ion (Figure 7 and the SI). The 1H NMR spectrum
of the 0.5:1 mixture of Pd(II) and L3 clearly indicated the clean
formation of a single complex (Figure S28). However, two sets
of pytri resonances were observed: one set shifted downfield
from the positions in the “free” L3, and the other set shifted
upfield. This suggested the formation of a [Pd(L3)2]2+-type
complex, where two pytri units are coordinated to a Pd(II) ion
in a head-to-tail fashion and the other pytri units are not
complexed but are involved in strong π−π-stacking interactions
with the planar [Pd(pytri)2]2+ motif.50 The 1H NMR spectrum
atoms were omitted for clarity.
crystallizes in the triclinic P1 space group, with two L2
̅
coordinated in a head-to-tail fashion to a single square-planar
Pd(II) ion. The Pd−N bond lengths (Figure 8) are similar to
those observed for other [Pd(pytri)2]2+ complexes,43,50 and the
Fc units adopt the eclipsed conformation with the bipy and
pytri arms in the syn arrangement (τ = 5.52°). This results in a
bipy−[Pd(pytri)2]2+−bipy triple stack that is stabilized by π−π
interactions [centroid−centroid distances of 3.692 Å (py−tri)
and 3.481 Å (py−py)].
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1
The H NMR spectra (400 MHz, CD3CN, 298 K) of 1:1
(D = 4.72 × 10−10 m2 s−1), suggesting that the solution
contained an isomeric mixture of [Pd2(L3)2](BF4)2 metal-
lomacrocycles. The HR-ESI-MS data were also consistent with
that postulate, with three peaks observed at m/z 398.6106,
537.8092, and 560.4782, which correspond to [Pd2(L3)2]4+,
[Pd2(L3)2(H−)(H2O)]3+, and [Pd2(L3)2(BF4)]3+, respec-
mixtures of Pd(II) ions and one of the ligands (either L2 or
L3) were completely different from those observed at the 0.5:1
ratio (Figures 7 and S33). When L2 was combined with 1 equiv
of [Pd(CH3CN)4](BF4)2, all of the proton resonances of the
ligand were shifted downfield, clearly indicative of complex-
ation. The DOSY experiment confirmed that all of the proton
signals had the same diffusion coefficient (D = 5.55 × 10−10 cm2
s−1), suggesting the clean formation of a single species.
Additionally, the diffusion coefficient observed for the 1:1
L2/Pd(II) mixture was very similar to those of the [Pd(L1)]-
(BF4)2, [Ag(L1)](PF6), and [Ag(L2)](PF6) complexes,
suggesting a [Pd(L2)](BF4)2 formulation. Consistently, the
HR-ESI-MS spectrum displayed a dominant signal at m/z
361.0565 (2+ peak), confirming the presence of the [Pd(L2)]2+
ion in solution (Figure S23). We were unable to generate X-
ray-quality crystals of the [Pd(L2)](BF4)2 complex, but
presumably a combination of entropic and enthalpic (steric
repulsion between the α-pyridyl protons of the adjacent bipy
and pytri units) factors led to formation of the [1 + 1] Pd(II)
metallomacrocycle.
tively.49 Closer inspection of the H NMR spectrum provided
1
further insight into the structures of the two [2 + 2]
metallomacrocycles. One set of proton resonances could be
readily assigned to a highly symmetric system (e.g., the
ferrocene protons were observed as two triplets at 4.78 and
4.64 ppm), which was analogous to the [Ag2(L3)2](PF6)2
compound (this was confirmed via X-ray diffraction vide
infra). The second series of peaks displayed four signals due to
the Fc units (4.91, 4.79, 4.72, and 4.50 ppm), suggesting that
the cp rings of the second metallomacrocycle adopted a
staggered conformation, lowering the symmetry of the system.
Additionally, the peak corresponding to the protons of the
triazole-bound methylene (which is a triplet in the symmetric
species) splits into two overlapping pairs of triplets in the
second species. Finally, the three aromatic signals of the
pyridine moieties are deshielded relative to the other isomer,
indicative of a reduced π−π interaction. The collected 1H NMR
data are consistent with the formation of two isomeric [2 + 2]
metallomacrocycles, one where the Fc units are staggered and
the second displaying eclipsed Fc units.
The 1H NMR spectrum (400 MHz, CD3CN, 298 K) of a 1:1
mixture of [Pd(CH3CN)4](BF4)2 and L3 was completely
different from that of [Pd(L3)2](BF4)2, indicating that two
different Pd(II) complexes were obtained from the different
molar ratios. All of the proton signals of the ligand were shifted
downfield relative to the free L3 in the spectrum of the 1:1
mixture (Figure 9). However, like the 1H NMR spectrum of the
DFT [B3LYP/6-31G(d), CH3CN solvent field] calculations
of the staggered and eclipsed [2 + 2] metallomacrocycles were
carried out to determine the relative energies (Figures 10 and
S64).51 The calculation indicated that the staggered conformer
1
Figure 9. Partially stacked H NMR spectra (400 MHz, CD3CN, 298
K) of (a) L3 and (b) [Pd2(L3)2](BF4)4. Blue dotted lines indicate
peaks corresponding to the major species observed in the solid state,
and red dotted lines indicate the minor, less symmetric species.
[Pd(L3)2](BF4)2 complex, two sets of pytri resonances were
observed (in a 4:3 ratio), with both sets shifted downfield from
the free ligand, suggesting that both were coordinated to Pd(II)
ions. The NMR spectrum could be interpreted in two ways: (1)
either a mixture of [1 + 1] and [2 + 2] Pd(II) metallomacro-
cycles had formed or (2) a mixture of isomeric/rotameric
complexes was obtained. A DOSY experiment [500 MHz, 298
K, 2:1 (v/v) CDCl3/CD3NO2] revealed that all of the signals in
1
the H NMR spectrum were diffusing at the same rate (D =
4.24 × 10−10 cm2 s−1), indicating that the two species had the
same molecular weight and thereby ruling out a mixture of [1 +
1] and [2 + 2] metallomacrocycles. The diffusion coefficient
was similar to that observed for the [Ag2(L3)2](PF6)2 complex
Figure 10. DFT calculations [B3LYP/6-31G(d), CH3CN solvent
field] of the (a) eclipsed and (b) staggered conformers of the
[Pd2(L3)2](BF4)4 complex. The hexyl chains were truncated to methyl
groups for computation expediency.
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was 2.93 kJ mol−1 lower in energy than the eclipsed conformer.
However, the small energy different suggests that both
conformers would be present in solution, consistent with the
Table 1. Formal Electrode Potentials (E°) Exhibited by L1−
L3 and the Corresponding Cu(I), Ag(I), and Pd(II)
Complexes
1
observed H NMR data.
a
E° (V)
X-ray-quality purple crystals of [Pd2(L3)2](BF4)4 were
obtained by the vapor diffusion of diethyl ether into a
concentrated acetonitrile solution of the complex. The
macrocycle crystallizes in the monoclinic P21/n space group,
with one Pd(II) ion, one ligand, and two tetrafluoroborate
counterions in the asymmetric unit (see the SI). Only the
eclipsed conformer of the [2 + 2] metallomacrocycle
[Pd2(L3)2](BF4)4 was observed in the solid state (Figure 11).
species
Fc+/0
0.79
CuII/I
PdI/II
L1
L2
L3
0.78
0.78
b
c
[Cun(L1)n]n+
[Cun(L2)n]n+
[Cun(L3)n]n+
[Pd(L2)2]2+
[Pd(L3)2]2+
[Pd(L1)]2+
[Pd(L2)]2+
[Pd2(L3)2]4+
[Ag(L1)]+
0.88
0.58, −0.01
b
c
0.88
0.48, 0.14
b
b
c
c
0.88
0.56, 0.68, 0.18, 0.50
c
c
c
c
,
,
,
,
d
d
d
d
0.80, 0.87
0.83, 0.89
0.91
−0.28
−0.34
−0.09
−0.20
0.91
0.95
−0.27, 0.02
e
0.85
e
[Ag(L2)]+
[Ag2(L3)2]2+
0.83
e
0.83
a
CV at 100 mV s−1; E° = (Epc + Epa)/2; 0.1 M Bu4NPF6 in CH2Cl2/
nitromethane (2:1, v/v); [Fc*]+/0 = 0.00 V.55 Epa. Epc. Irreversible
b
c
d
reduction. [FcH]+/0 = 0.53 V.56
e
Figure 11. Solid-state structure of [Pd2(L3)2](BF4)2. Selected bond
lengths (Å): Pd1−N1 = 2.074(3), Pd1−N2 = 1.996(3), Pd1−N5 =
2.048(3), Pd1−N6 = 2.014(3). Selected bond angles (deg): N1−
Pd1−N2 = 80.0(1), N2−Pd1−N5 = 98.2(1), N5−Pd1−N6 = 79.7(1),
N6−Pd1−N1 = 102.0(1). Color scheme: C, gray; N, purple; Fe,
−
orange; Pd, dark cyan. BF4 counterions and H atoms were omitted
for clarity.
The Pd(II) ions are coordinated to two pytri units in the
expected “head-to-tail” fashion with a square-planar coordina-
tion geometry (τ4 = 0.02).38 The Pd−N bond lengths range
from 1.996(3) to 2.074(3) Å, similar to those observed in
[Pd(L3)2](BF4)2 and related complexes. The Fc units of the
metallocycle are eclipsed (τ = 12.72°), and the pytri “arms”
exhibit π−π interactions [centroid−centroid distances of 3.519
Å (tri−tri) and 3.789 Å (py−py)]. Additionally, the two Pd(II)
ions are aligned with a Pd−Pd distance of 3.625(6) Å.
Figure 12. Overlayed cyclic voltammograms of 1 mM solutions of L3
and [Pd2(L3)2](BF4)4 recorded at a glassy carbon electrode in
CH2Cl2/nitromethane (2:1, v/v) containing 0.1 M NBu4PF6.
The purple single crystals of [Pd2(L3)2](BF4)4 were
dissolved in CD3CN, and the 1H NMR spectrum was
immediately collected (see the SI). One set of signals consistent
with the presence of the eclipsed conformer observed in the
crystal structure was apparent by the number of signals and the
corresponding integrations. However, a second, smaller, set of
signals consistent with the staggered conformation of
[Pd2(L3)2](BF4)4 was also observed. Subsequent reacquisition
of the ligands with copper, palladium, and silver salts shifts the
ferrocenyl oxidation to the anodic potential. The current
response for the Fc+/0 couple is consistent with the number of
ferrocenyl groups in the molecular formula; thus, the Pd(II) 2:2
M/L macrocycle [Pd2(L3)2]4+ shows twice the peak current of
ligand L3 and simpler [Pd(L1)]2+ and [Pd(L2)]2+ systems.
The electrochemistry of the Cu coordination polymers with
ligands L1 and L2 is complex. Oxidation of the Cu occurs
before the Fc, as observed in similar systems.20,25,26,37,52 There
is significant separation between the anodic and cathodic peaks,
consistent with a change of the coordination environment
between the Cu(I) and Cu(II) states and the likelihood of
nitromethane solvent coordination.53 [Cun(L3)n]n+ displays
even more complex behavior, presumably associated with the
weaker binding ability of the pytri ligands versus the bipy units.
The 0.5:1 Pd(II) complexes [Pd(L2)2]2+ and [Pd(L3)2]2+
showed two poorly resolved ferrocenyl oxidations (ca. 0.80 and
0.87 V for L2 and 0.83 and 0.89 V for L3; Table 1 and Figure
S54), suggesting lability of the metal center or stepwise
1
of the H NMR spectrum over time (CH3CN, 298 K) showed
the system equilibration, finally settling after approximately 40
h at a 4:3 ratio of the staggered and eclipsed conformations
(Figure S33).
Electrochemistry. The electrochemistry of the 3 ligands
(L1−L3) and 11 complexes in a dichloromethane (CH2Cl2)/
nitromethane solution (2:1, v/v) was investigated with CV and
differential pulse voltammetry (DPV) using Bu4NPF6 as the
supporting electrolyte. The results are presented in Table 1 and
Figures 12 and S51−S55. All ligands and complexes exhibited
the predicted reversible Fc+/0 redox couple. In the ligands L1−
L3, E° for this is observed between 0.78 and 0.79 V; i.e.,
exchanging one or two bipy arms with pytri has little effect on
the ferrocenyl/ferrocenium potential. As expected, coordination
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from isolated samples. Chemical shifts are reported in parts per million
and referenced to residual solvent peaks (CDCl3, 1H δ 7.26 ppm, 13C δ
77.16 ppm; CD3CN, 1H δ 1.94, 13C δ 1.32 and 118.26 ppm; CD3NO2,
1H δ 4.30 ppm; n.b. the NMR spectra recorded in a mixture of CDCl3
and CD3NO2 were referenced to the nitromethane residual solvent
peak). Coupling constants (J) are reported in hertz (Hz). Standard
abbreviations indicating the multiplicity used are as follows: m =
multiplet, s = singlet, d = doublet, t = triplet, q = quartet, quin =
quintet, dd = double doublet, dt = double triplet, td = triple doublet.
Other abbreviations include DMF = dimethylformamide, DMSO =
dimethyl sulfoxide, MeOH = methanol, TEA = trimethylamine, THF
= tetrahydrofuran, TMEDA = tetramethylethylenediamine, and RT =
room temperature. IR spectra were recorded on a Bruker ALPHA FT-
IR spectrometer with an attached ALPHA-P measurement module.
Microanalyses were performed at the Campbell Microanalytical
Laboratory at the University of Otago. HR-ESI-MS were collected
on a Bruker micro-TOF-Q spectrometer (pseudo-cold-spray con-
ditions refer to the collection of mass spectra with the temperature of
the ion source at 40 °C, as opposed to the standard 180 °C). UV−vis
absorption spectra were acquired with a PerkinElmer Lambda-950
spectrophotometer. Experimental information for intermediates and
model compounds can be found in the SI.
oxidation. Predictably, the observed oxidation potentials lie
between those of the uncomplexed ligands and the 1:1 species.
In the case of the 1:1 Pd(II) complexes [Pd(L1)]2+ and
[Pd(L2)]2+, an irreversible Pd-based reduction process occurs
with Epc observed at −0.09 and −0.20 V, respectively. Similar
reductions have been observed previously by the authors for
other Pd(II) pytri complexes54 and also for the model
compounds [Pd(L4)2]2+ and [Pd(L5)2]2+ (Figure S55) and
the 0.5:1 Pd(II) complexes [Pd(L2)2]2+ and [Pd(L3)2]2+. In
the case of the 2:2 macrocyclic Pd(II) complex of [Pd2(L3)2]2+,
two resolved quasi-reversible one-electron redox couples are
observed at −0.27 and 0.02 V (Figure 12), assigned to the
sequential reduction of the two Pd metals. The forward and
reverse currents for the Pd redox couples are maintained in
multicycle experiments.
CONCLUSION
■
Three bis-bidentate 1,1′-disubstituted ferrocene ligands,
functionalized with either bipy or pytri chelating units, were
synthesized. The free ligands were found to adopt a syn π−π-
stacked conformation in solution. The coordination chemistry
of these redox-active, conformational flexible, ligands was
examined with the (usually) four-coordinate, diamagnetic metal
ions Cu(I), Ag(I), and Pd(II). The resulting complexes were
Safety Note! While no problems were encountered during the course of
this work, azide compounds are potentially explosive, and appropriate
precautions should be taken when working with them.
Synthesis of L2. 1-(5-yl-Ethynyl-2,2′-bipyridine)-1′-iodoferrocene
(438 mg, 0.89 mmol), 5-ethynyl-2-(1-hexyl-1H-1,2,3-triazol-4-yl)-
pyridine (250 mg, 0.98 mmol), CuI (17.0 mg, 0.090 mmol),
[Pd(CH3CN)2Cl2] (13.9 mg, 0.05 mmol), and [PH(tBu)3](BF4)
(31.1 mg, 0.110 mmol) were combined in degassed (argon)
diisopropylamine (7 mL) and stirred under microwave irradiation
(200 W) at 100 °C for 2 h. The crude reaction mixture was taken up in
CHCl3 (50 mL) and added to ethylenediaminetetraacetic acid
(EDTA)/NH4OH(aq) (0.1 M, 50 mL). The organic layer was
separated and the aqueous phase extracted with CHCl3 (5 × 50 mL).
The combined organic layers were washed with brine (50 mL) and
dried over Na2SO4, and the solvent was removed in vacuo. The residue
was purified by column chromatography (silica gel, gradient CH2Cl2,
CHCl3, and then 9:1 CHCl3/CH3CN) to give the desired product as
1
characterized using a range of techniques including H and
DOSY NMR spectroscopies, HR-ESI-MS, DFT calculations,
and, where possible, X-ray crystallography. The Cu(I)
complexes of the 1,1′-disubstituted ferrocene ligands were
found to be coordination polymers, while the Ag(I) and Pd(II)
complexes formed discrete [1 + 1] or [2 + 2] metal-
lomacrocyclic architectures depending on the ligand architec-
ture. Additionally, the electrochemical properties of these
redox-active metallosupramolecular assemblies were examined
using CV and DPV. All of the complexes displayed reversible
ferrocene-based redox processes, while [Pd2(L3)2](BF4)4
showed unusual quasi-reversible Pd reductions.
1
an orange solid upon the removal of solvent. Yield: 407 mg, 74%. H
NMR (400 MHz, CD3CN): δ 8.53 (d, J = 4.0 Hz, 1H, Hi), 8.45 (dd, J
= 2.2 and 0.8 Hz, 1H, Hc), 8.34 (dd, J = 2.2 and 0.9 Hz, 1H, Hl), 8.18−
8.10 (m, 2H, He and Hf), 7.88 (s, 1H, Ho), 7.77 (dd, J = 8.2 and 0.9
Hz, 1H, Hn), 7.75−7.71 (m, 1H, Hg), 7.66 (dd, J = 8.2 and 2.2 Hz, 1H,
Hd), 7.61 (dd, J = 8.2 and 2.2 Hz, 1H, Hm), 7.30 (ddd, J = 7.5, 4.7, and
1.2 Hz, 1H, Hh), 4.64−4.59 (m, 4H, Hb and Hk), 4.46−4.41 (m, 4H,
Ha and Hj), 4.27 (t, J = 7.3 Hz, 2H, Hp), 1.86 (quin, J = 7.1 Hz, 2H,
Hq), 1.36−1.26 (m, 6H, Hr−t), 0.89 (t, J = 6.8 Hz, 3H, Hu). 13C NMR
(126 MHz, CDCl3): δ 155.6, 154.1, 151.6, 151.4, 149.2, 148.5, 148.0,
138.9, 136.9, 123.7, 122.0, 121.4, 120.9, 120.3, 119.8, 119.5, 91.5, 90.8,
84.3, 84.2, 74.6, 73.1, 73.1, 71.2, 71.1, 67.1, 67.0, 50.6, 31.3, 30.3, 26.3,
22.5, 14.1. IR (ATR, cm−1): ν 2951, 2920, 2854, 2206, 1587, 1433,
1030, 793. HR-ESI-MS (MeOH). Found: m/z 617.2145 ([M + H]+).
Calcd for C37H33N6Fe: m/z 617.2111. UV−vis [CHCl3; λmax, nm (ε, L
mol−1 cm−1)]: 443 (1500), 380 (6000). Anal. Calcd for C37H33N6Fe:
C, 72.08; H, 5.23; N, 13.63. Found: C, 72.03; H, 5.45; N, 13.77.
Synthesis of L3. 1,1′-Diiodoferrocene (782 mg, 1.79 mmol), 5-
bromo-2-(1-hexyl-1H-1,2,3-triazol-4-yl)pyridine (954 mg, 3.75 mmol),
CuI (34 mg, 0.179 mmol), [Pd(CH3CN)2Cl2] (23 mg, 0.089 mmol),
and [PH(tBu)3](BF4) (52 mg, 0.179 mmol) were combined in
degassed (argon) diisopropylamine (15 mL) and stirred under
microwave irradiation (200 W) at 100 °C for 2 h. The crude reaction
mixture was taken up in CH2Cl2 (50 mL) and added to EDTA/
NH4OH(aq) (0.1 M, 100 mL). The organic layer was separated and
the aqueous phase extracted with CH2Cl2 (4 × 50 mL). The combined
organic layers were washed with brine (80 mL) and dried over
Na2SO4, and the solvent was removed in vacuo. The residue was
purified by column chromatography (silica gel, gradient CH2Cl2, and
then 9:1 CH2Cl2/acetone) to give an orange solid upon the removal of
solvent. The product was further purified by precipitation from
The results suggest that, despite the conformational flexibility
of the 1,1′-disubstituted ferrocenes, these ligands can be used to
assemble discrete, redox-active, metallosupramolecular assem-
blies. In the majority of examples herein, the ferrocene ligands
remain in the syn π−π-stacked conformation upon complex
formation. Thus, a careful ligand design may be required in
order to favor the anti conformers and allow the formation of
metallocages and helicates rather than macrocycles and
coordination polymers. Polyferrocene macrocycles57 are
generating considerable interest because of their interesting
redox/electronic properties. The ligands reported here and
related systems could be exploited to generate polyferrocene
macrocycles via self-assembly. Efforts in these directions are
underway.
EXPERIMENTAL SECTION
■
General Procedures. Unless otherwise stated, all reagents were
purchased from commercial sources and used without further
purification. Solvents were laboratory-reagent-grade with the following
exceptions: dry tetrahydrofuran and diethyl ether were obtained by
passing the solvents through an activated alumina column on a
PureSolv solvent purification system (Innovative Technologies, Inc.,
Amesbury, MA). Reactions performed under microwave irradiation
were carried out in a Discover CEM focused microwave synthesis
system. Petrol refers to the fraction of petroleum ether boiling in the
range 40−60 °C. 1H and 13C NMR spectra were recorded on either a
400 MHz Varian 400 MR or a Varian 500 MHz VNMRS
spectrometer. Unless otherwise stated, all NMR spectra were obtained
H
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CH2Cl2 with petroleum ether and collected via filtration. Yield: 792
mg, 64%. H NMR (400 MHz, CD3CN): δ 8.43 (d, J = 1.6 Hz, 2H,
orange precipitate was collected by vacuum filtration, rinsed with
diethyl ether (2 × 5 mL), and dried in vacuo. Yield: 10 mg, 68%. H
1
1
Hc), 8.05 (s, 2H, Hf), 7.73 (dd, J = 8.2 and 0.7 Hz, 1H, He), 7.62 (dd, J
= 8.2 and 2.1 Hz, 2H, Hd), 4.61 (t, J = 1.9 Hz, 4H, Hb), 4.44 (t, J = 1.9
Hz, 4H, Ha), 4.36 (t, J = 7.2 Hz, 4H, Hg), 1.93 (quin, signal obscured
by residual acetonitrile solvent peak, Hh), 1.35−1.29 (m, 12H, Hi−k),
0.90 (t, J = 6.7 Hz, 6H, Hl). 13C NMR (126 MHz, CHCl3): δ 151.6,
148.4, 147.9, 138.8, 122.2, 119.8, 119.5, 90.7, 84.3, 73.1, 71.0, 67.3,
50.7, 31.3, 30.3, 26.3, 22.6, 14.1. IR (ATR, cm−1): ν 3092, 2922, 2855,
2209, 1593, 1437, 1377, 844. HR-ESI-MS (CH2Cl2). Found: m/z
713.2795 ([M + Na]+). Calcd for C40H42FeN8Na: m/z 713.2775.
UV−vis [CHCl3; λmax, nm (ε, L mol−1 cm−1)]: 449 (1500), 381
(5500). Anal. Calcd for C40H42N8Fe·0.3hexane: C, 70.07; H, 6.50; N,
15.64. Found: C, 70.09; H, 6.63; N, 15.79.
NMR [400 MHz, 2:1 (v/v) CDCl3/CD3NO2]: δ 8.90 (d, J = 4.8 Hz,
2H, Hi), 8.37 (d, J = 2.0 Hz, 2H, Hc), 8.29 (d, J = 8.0 Hz, 2H, He),
8.22 (d, J = 8.3 Hz, 2H, Hf), 8.19−8.11 (m, 4H, Hd and Hg), 7.70 (dd,
J = 7.5, 5.0 Hz, 2H, Hh), 4.64 (t, J = 1.8 Hz, 4H, Hb), 4.48 (d, J = 1.8
Hz, 4H, Ha). 13C NMR (complex insufficiently soluble for the
collection of adequate 13C NMR spectra). IR (ATR, cm−1): ν 2211,
1590, 1473, 1434, 1168, 1029, 828, 556. HR-ESI-MS (acetone).
Found: m/z 324.5287 ([M − (PF6)− − e−]2+). Calcd for
C34H22N4FeAg2+: m/z 324.5117. Found: m/z 649.0320 [M −
(PF6)−]+). Calcd for C34H22N4FeAg+: m/z 649.0329. UV−vis
[acetone; λmax, nm (ε, L mol−1 cm−1)]: 495 (2700), 400 (5900).
Anal. Calcd for C34H22N4FeAgPF6·CHCl3: C, 47.94; H, 2.63; N, 6.46.
Found: C, 47.91; H, 2.67; N, 6.23.
Synthesis of [Cu(L1)]n(PF6)n. [Cu(CH3CN)4](PF6) (27.5 mg, 0.074
mmol) was dissolved in ∼1 mL of CHCl3/nitromethane (2:1, v/v)
and added to a solution of L1 (40 mg, 0.074 mmol) in 4 mL of
CHCl3/nitromethane (2:1, v/v), and the mixture was stirred for 1 h.
The solution was filtered through Celite and precipitated via the
addition of diethyl ether. The dark-red precipitate was collected by
filtration and rinsed with diethyl ether (2 × 5 mL), before being dried
Synthesis of [Ag(L2)](PF6). AgPF6 (16.4 mg, 0.0650 mmol) was
dissolved in ∼1 mL of nitromethane and added to a stirring solution of
L2 (40 mg, 0.065 mmol) in CHCl3/nitromethane (10 mL, 2:1, v/v).
The resulting mixture was stirred for 30 min before being filtered
through Celite and precipitated via the addition of diethyl ether. The
orange precipitate was collected by vacuum filtration, rinsed with
1
1
diethyl ether (2 × 5 mL), and dried in vacuo. Yield: 51 mg, 90%. H
in vacuo. Yield: 50 mg, 90%. H NMR spectra (400 MHz) of the
NMR [400 MHz, 2:1 (v/v) CDCl3/CD3NO2]: δ 8.75 (d, J = 5.1 Hz,
1H, Hi), 8.72 (s, 1H, Hc), 8.37 (d, J = 2.0 Hz, 1H, Hl), 8.31 (s, 1H,
Ho), 8.16 (d, J = 8.0 Hz, 1H, Hf), 8.11 (dd, J = 7.6 and 1.7 Hz, 1H,
Hg), 8.07 (d, J = 8.0 Hz, 1H, He), 7.99 (dd, J = 8.4 and 2.1 Hz, 1H,
Hd), 7.89 (dd, J = 8.2 and 2.1 Hz, 1H, Hm), 7.67−7.63 (m, 1H, Hh),
7.61 (d, J = 8.2 Hz, 1H, Hn), 4.63 (dt, J = 4.2 and 1.9 Hz, 4H, Hb and
Hk), 4.51−4.43 (m, 6H, Ha, Hj and Hp), 2.04 (quin, J = 6.8 Hz, 2H,
Hq), 1.49−1.24 (m, 6H, Hr, Hs, and Ht), 0.90 (t, J = 6.9 Hz, 3H, Hu).
13C NMR (complex insufficiently soluble for the collection of adequate
13C NMR spectra). IR (ATR, cm−1): ν 2930, 2860, 2208, 1592, 1471,
1433, 1028, 825, 556. HR-ESI-MS (acetone). Found: m/z 361.5676
([M − (PF6)− − e−]2+). Calcd for C37H32N6FeAg2+: m/z 361.5539.
Found: m/z 723.1197 ([M − (PF6)−]+). Calcd for (C37H32N6FeAg+:
m/z 723.1083. UV−vis [acetone; λmax, nm (ε, L mol−1 cm−1)]: 473
(3100), 397 (6200). Anal. Calcd for C37H32N6PF6FeAg: C, 51.12; H,
3.71; N, 9.67. Found: C, 51.04; H, 3.87; N, 9.94.
material in any of acetone-d6, CD3CN, CD3NO2, or a 2:1 mixture of
CDCl3/CD3NO2 yielded very broad spectra despite sharp solvent
signals. IR (ATR, cm−1): ν 2206, 1593, 1475, 1439, 1169, 1027, 828,
789, 556. HR-ESI-MS (acetone). Found: m/z 302.5346. Calcd for
C34H22FeN4Cu2+: m/z 302.5239. Found: m/z 640.0162. Calcd for
C34H22FeN4Cu·H2O·(H−)+: m/z 640.0617. UV−vis [acetone; λmax
,
nm (ε, L mol−1 cm−1)]: 464 (4300), 432 (4200). Anal. Calcd for
C34H22N4FeCuPF6·0.9CHCl3: C, 48.83; H, 2.96; N, 6.53. Found: C,
48.98; H, 2.75; N, 6.72.
Synthesis of [Cu(L2)]n(PF6)n. [Cu(CH3CN)4]PF6 (24.2 mg, 0.065
mmol) was dissolved in ∼1 mL of CHCl3/nitromethane (2:1, v/v)
and added to a solution of L2 (40 mg, 0.074 mmol) in 4 mL of
CHCl3/nitromethane (2:1, v/v), and the mixture was stirred for 1 h.
The solution was filtered through Celite and precipitated via the
addition of diethyl ether. The dark-red precipitate was collected by
filtration and rinsed with diethyl ether (2 × 5 mL), before being dried
1
in vacuo. Yield: 41 mg, 77%. H NMR spectra (400 MHz) of the
Synthesis of [Ag2(L3)2](PF6)2. AgPF6 (14.6 mg, 0.0580 mmol) was
dissolved in ∼1 mL of nitromethane and added to a stirring solution of
L3 (40 mg, 0.058 mmol) in CHCl3/nitromethane (10 mL, 2:1, v/v).
The resulting mixture was stirred for 30 min before being filtered
through Celite and precipitated via the addition of diethyl ether. The
orange precipitate was collected by vacuum filtration, rinsed with
material in any of acetone-d6, CD3CN, CD3NO2, or a 2:1 mixture of
CDCl3/CD3NO2 yielded very broad spectra despite sharp solvent
signals. IR (ATR, cm−1): ν 2953, 2931, 2861, 2207, 1594, 1476, 1439,
1030, 832, 556. HR-ESI-MS (acetone). Found: m/z 339.5842. Calcd
for C37H32FeN6Cu2+: m/z 339.5661. Found: m/z 679.1472. Calcd for
C37H32FeN6Cu+: m/z 679.1328. UV−vis [acetone; λmax, nm (ε, L
mol−1 cm−1)]: 446 (5400). Anal. Calcd for C37H32N6FeCuPF6·H2O·
0.5CHCl3: C, 49.89; H, 3.85; N, 9.31. Found: C, 49.74; H, 3.93; N,
9.41.
Synthesis of [Cu(L3)]n(PF6)n. [Cu(CH3CN)4]PF6 (27.0 mg, 0.072
mmol) was dissolved in ∼1 mL of CHCl3/nitromethane (2:1, v/v)
and added to a solution of L3 (50 mg, 0.072 mmol) in 4 mL of
CHCl3/nitromethane (2:1, v/v), and the mixture was stirred for 1 h.
The solution was filtered through Celite and precipitated via the
addition of diethyl ether. The bright-orange precipitate was collected
by filtration and rinsed with diethyl ether (2 × 5 mL), before being
dried in vacuo. Yield: 52 mg, 80%. 1H NMR spectra (400 MHz) of the
material in any of acetone-d6, CD3CN, CD3NO2, or a 2:1 mixture of
CDCl3/CD3NO2 yielded very broad spectra despite sharp solvent
signals. IR (ATR, cm−1): ν 2954, 2929, 2859, 2210, 1577, 1433, 1231,
1100, 1030, 839, 824, 556. HR-ESI-MS (acetone). Found: m/z
376.6247. Calcd for C40H42FeN8Cu2+: m/z 376.6083. Found: m/z
753.2268. Calcd for C40H42FeN8Cu+: 753.2172. UV−vis [acetone;
λmax, nm (ε, L mol−1 cm−1)]: 480 (2800), 409 (4800). Anal. Calcd for
C40H42N8FeCuPF6·2H2O: C, 51.37; H, 4.96; N, 11.98. Found: C,
51.15; H, 4.93; N, 12.05.
1
diethyl ether (2 × 5 mL), and dried in vacuo. Yield: 46 mg, 84%. H
NMR [400 MHz, 2:1 (v/v) CDCl3/CD3NO2]: δ 8.55 (d, J = 2.0 Hz,
4H, Hc), 8.35 (s, 4H, Hf), 7.87 (dd, J = 8.2 and 2.0 Hz, 4H, Hd), 7.60
(d, J = 8.2 Hz, 4H, He), 4.61 (t, J = 1.9 Hz, 8H, Hb), 4.52 (t, J = 7.3
Hz, 8H, Ha), 4.45 (t, J = 1.9 Hz, 8H, Hg), 2.03 (quin, J = 7.3 Hz, 8H),
1.45−1.26 (m, 24H, Hi, Hj, and Hk), 0.88 (t, J = 6.9 Hz, 12H, Hl). 13
C
NMR [101 MHz, 2:1 (v/v) CDCl3/CD3NO2]: δ 152.4, 144.3, 144.0,
139.5, 123.1, 121.8, 121.1, 92.6, 83.0, 73.2, 70.4, 66.9, 51.3, 30.8, 29.7,
25.8, 22.1, 13.5. IR (ATR, cm−1): ν 2952, 2929, 2870, 2208, 1435,
1225, 835, 556. HR-ESI-MS (acetone). Found: m/z 398.6097 ([M −
(PF6)− − e−]2+). Calcd for C40H42N8FeAg2+: m/z 398.5961. Found:
m/z 797.2044 ([M − (PF6)−]+). Calcd for (C40H42N8FeAg+: m/z
797.1297. UV−vis [acetone; λmax, nm (ε, L mol−1 cm−1)]: 467 (5000),
390 (11700). Anal. Calcd for C80H84N16P2F12Fe2Ag2: C, 50.92; H,
4.49; N, 11.88. Found: C, 50.74; H, 4.50; N, 11.96.
Synthesis of [Pd(L1)](BF4)2. [Pd(CH3CN)4](BF4)2 (32.8 mg, 0.074
mmol) was dissolved in ∼1 mL of acetonitrile and added to a
suspension of L1 (40.0 mg, 0.074 mmol) in 5 mL of acetonitrile, and
the mixture was stirred at RT for 1 h, giving a deep-purple solution.
The solution was filtered through Celite before precipitation via the
addition of diethyl ether. The dark-purple powder was isolated by
vacuum filtration, rinsed with diethyl ether (3 × 5 mL), and air-dried.
Yield: 43 mg, 79%. 1H NMR [400 MHz, 2:1 (v/v) CDCl3/CD3NO2]:
δ 8.75 (d, J = 5.8 Hz, 2H, Hi), 8.61 (s, 2H, Hc), 8.49−8.40 (m, 4H, Hg
and Hd), 8.37 (d, J = 8.4 Hz, 2H, He or Hf), 8.32 (d, J = 8.4 Hz, 2H, He
or Hf), 7.98 (t, J = 7.0 Hz, 2H, Hh), 4.72 (s, 4H, Hb), 4.60 (s, 4H, Ha).
Synthesis of [Ag(L1)](PF6). AgPF6 (5.66 mg, 0.0180 mmol) was
dissolved in ∼1 mL of nitromethane and added to a stirring solution of
L1 (10 mg, 0.018 mmol) in CHCl3/nitromethane (6 mL, 2:1, v/v).
The resulting mixture was stirred for 30 min before being filtered
through Celite and precipitated via the addition of diethyl ether. The
I
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13C NMR (101 MHz, CD3CN): δ 157.7, 155.5, 154.8, 152.0, 144.1,
142.0, 129.0, 126.5, 125.8, 125.0, 100.5, 82.2, 76.4, 72.5, 65.6. IR
(ATR, cm−1): ν 2201, 2188, 1012, 813, 786, 518. HR-ESI-MS
(acetonitrile). Found: m/z 324.0140 ([M − 2(BF4)−]2+). Calcd for
C34H22FeN4Pd2+: m/z 324.0109. Found: m/z 667.0146 ([M −
2(BF4)−·H2O·H−]+). Calcd for C34H22FeN4Pd·H2O·(H−)+: m/z
667.0407. UV−vis [acetone; λmax, nm (ε, L mol−1 cm−1)]: 512
(5000). Anal. Calcd for C34H22FeN4PdB2F8·H2O: C, 48.59; H, 2.88;
N, 6.67. Found: C, 48.48; H, 2.73; N, 6.96.
= 1.5 Hz, 4H, Hc), 8.77 (s, 4H, Hf), 8.76 (s, 4H, Hf′), 8.54 (dd, J = 8.3
and 1.8 Hz, 4H, Hd′), 8.08 (dd, J = 8.3 and 1.8 Hz, 4H, Hd), 8.04 (dd, J
= 8.2 and 0.6 Hz, 4H, He′), 7.92 (dd, J = 8.3 and 0.6 Hz, 4H, He), 4.91
(dd, J = 2.5 and 1.3 Hz, 4H, Hb′ or Hb1′), 4.83−4.77 (m, 12H, Hb and
Hb′ or Hb1′), 4.75 (t, J = 7.2 Hz, 8H, Hg), 4.72−4.70 (m, 4H, Ha′ or
Ha1′), 4.64 (t, J = 1.9 Hz, 8H, Ha), 4.61 and 4.35 (dt, J = 10.4 and 7.0
Hz, 2H, Hg′), 4.50 (td, J = 2.6 and 1.3 Hz, 4H, Ha′ or Ha1′), 4.57 and
4.31 (dt, J = 10.4 and 7.0 Hz, 2H, Hg′), 2.10−1.97 (m, 16H, Hh and
Hh′), 1.51−1.25 (m, 48H, Hi, Hj, Hk, Hi′, Hj′, and Hk′), 0.90−0.84 (m,
24H, Hl and Hl′). 13C NMR (126 MHz, CD3CN): δ 153.4, 153.4,
148.6, 148.1, 145.3, 144.8, 144.6, 128.6, 128.5, 125.6, 125.4, 124.6,
124.3, 99.7, 97.4, 82.7, 81.7, 74.4, 74.2, 74.0, 73.0, 72.9, 72.7, 72.6,
67.1, 65.2, 55.4, 55.2, 31.7, 30.2, 26.4, 23.2, 14.2. IR (ATR, cm−1): ν
2928, 2870, 2200, 1591, 1433, 1035, 828. HR-ESI-MS (acetonitrile).
Synthesis of [Pd(L2)](BF4)2. [Pd(CH3CN)4](BF4)2 (28.8 mg,
0.0650 mmol) was dissolved in ∼1 mL of acetonitrile and added to
a suspension of L2 (40.0 mg, 0.0650 mmol) in 5 mL of acetonitrile,
and the mixture was stirred at RT for 1 h, giving a deep-purple
solution. The solution was filtered through Celite before precipitation
via the addition of diethyl ether. The dark-purple powder was isolated
by vacuum filtration, rinsed with diethyl ether (3 × 5 mL), and air-
dried. Yield: 45 mg, 86%. 1H NMR (400 MHz, CD3CN): δ 9.41 (dd, J
= 5.8 and 1.3 Hz, 1H, Hi), 8.78 (s, 1H, Ho), 8.71 (s, 2H, Hc, Hl),
8.48−8.39 (m, 2H, Hg and He or Hf), 8.35 (d, J = 1.2 Hz, 2H, Hd and
He or Hf), 8.30 (dd, J = 8.3 and 1.5 Hz, 1H, Hm), 8.12 (d, J = 8.3 Hz,
1H, Hn), 7.89 (ddd, J = 7.5, 5.8, and 1.8 Hz, 1H, Hh), 4.74−4.68 (m,
6H, Hb, Hk, and Hp), 4.62 (t, J = 1.9 Hz, 2H, Ha or Hj), 4.60 (t, J = 1.9
Hz, 2H, Ha or Hj), 2.12−2.07 (m, 2H, Hq), 1.48−1.31 (m, 6H, Hr, Hs,
and Ht), 0.93 (t, J = 7.0 Hz, 3H, Hu). 13C NMR (101 MHz, CD3CN):
δ 157.4, 155.6, 155.5, 154.8, 153.2, 149.0, 146.3, 144.1, 141.8, 141.8,
129.2, 127.4, 126.7, 125.8, 125.1, 125.1, 123.6, 100.9, 99.3, 82.3, 82.1,
76.3, 76.3, 72.4, 72.3, 65.7, 65.5, 54.6, 31.7, 30.2, 26.4, 23.1, 14.2. IR
(ATR, cm−1): ν 2929, 2859, 2201, 1593, 1478, 1443, 1250, 1047,
1025, 847, 520. HR-ESI-MS (acetonitrile). Found: m/z 361.0565 ([M
− 2(BF4)−]2+). Calcd for C37H32FeN6Pd2+: m/z 361.0531. Found: m/
z 741.1004 ([M − 2(BF4)−·H2O·H−]+). Calcd for C37H32FeN6Pd·
H2O·(H−)+: m/z 741.1251. UV−vis [acetone; λmax, nm (ε, L mol−1
cm−1)]: 511 (4200). Anal. Calcd for C37H32FeN6Pd: C, 49.57; H,
3.60; N, 9.37. Found: C, 49.30; H, 3.83; N, 9.62.
Found: m/z 884.2098 ([M
−
2(BF4)−]2+). Calcd for
C80H84N16B2F8Fe2Pd22+: m/z 884.1942. Found: m/z 560.4782 ([M
− 3(BF4)−]3+). Calcd for (C80H84N16BF4Fe2Pd23+: m/z 560.4617.
Found: m/z 398.6106 ([M
−
4(BF4)−]4+). Calcd for
C80H84N16Fe2Pd24+: m/z 398.5954. UV−vis [acetone; λmax, nm (ε, L
mol−1 cm−1)]: 511 (7500). Anal. Calcd for C80H84N16B4F16Fe2Pd2·
H2O: C, 49.04; H, 4.42; N, 11.44. Found: C, 48.79 H, 4.33; N, 11.61.
Synthesis of [Pd(L3)2](BF4)2. [Pd(CH3CN)4](BF4)2 (37.4 mg,
0.084 mmol) was dissolved in ∼1 mL of acetonitrile and added to a
suspension of L3 (116 mg, 0.169 mmol) in acetonitrile, and the
mixture was stirred at RT overnight, giving a deep-red solution. The
solution was filtered through Celite and precipitated via the addition of
diethyl ether. Isolation by filtration gave a dark-red/purple powder,
which was rinsed with diethyl ether (2 × 5 mL) and air-dried before
being dried in vacuo. Yield: 118 mg, 84%. 1H NMR (400 MHz,
CD3CN): δ 8.75 (s, 2H, Hr), 8.37 (d, J = 1.7 Hz, 2H, Ho), 8.29 (dd, J
= 8.2 and 1.8 Hz, 2H, Hp), 8.06 (d, J = 8.2 Hz, 2H, Hq), 7.97 (d, J =
1.7 Hz, 2H, Hc), 7.76 (s, 2H, Hf), 7.45 (d, J = 8.1 Hz, 2H, Hd), 7.17
(dd, J = 8.2 and 2.2 Hz, 2H, He), 4.79−4.72 (m, 8H, Hn and Hs), 4.65
(t, J = 1.9 Hz, 4H, Hb or Hm), 4.59 (t, J = 1.9 Hz, 4H, Hb or Hm), 4.50
(t, J = 1.9 Hz, 4H, Ha), 4.14 (t, J = 7.6 Hz, 4H, Hg), 2.29 (quin, J = 7.4
Hz, 4H, Ht), 1.80−1.70 (m, 4H, Hh), 1.69−1.12 (m, 24H, Hi−k and
Hu−w), 0.99 (t, J = 7.2 Hz, 6H, Hx), 0.78 (t, J = 6.9 Hz, 6H, Hl). 13C
NMR (126 MHz, CD3CN): δ 152.9, 152.9, 152.2, 148.2, 148.2, 145.0,
144.3, 139.3, 127.8, 127.7, 127.7, 124.6, 123.9, 123.5, 97.3, 91.0, 85.1,
82.8, 74.1, 73.6, 72.4, 71.8, 69.3, 66.8, 55.1, 51.2, 32.1, 31.7, 30.7, 30.0,
26.9, 26.8, 23.4, 23.2, 14.4, 14.2. IR (ATR, cm−1): ν 3116, 2926, 2858,
2207, 1591, 1456, 1027, 821. HR-ESI-MS (acetonitrile). Found: m/z
743.2543. Calcd for C80H84N16Fe2Pd2+: m/z 743.2394. UV−vis
[acetone; λmax, nm (ε, L mol−1 cm−1)]: 527 (shoulder, 4000). Anal.
Calcd for C80H84N16B4F16Fe2Pd·H2O: C, 57.22; H, 5.16; N, 13.34.
Found: C, 56.93; H, 5.30; N, 13.38.
Synthesis of [Pd(L2)2](BF4)2. [Pd(CH3CN)4](BF4)2 (30.0 mg,
0.0490 mmol) was dissolved in ∼1 mL of acetonitrile and added to
a suspension of L2 (10.8 mg, 0.0245 mmol) in acetonitrile, and the
mixture was stirred at RT overnight, giving a deep-red solution. The
solution was filtered through Celite and crystallized via the slow
diffusion of diethyl ether into an acetonitrile solution. The dark-red/
purple crystals were isolated by filtration, rinsed with diethyl ether (2
× 5 mL), and air-dried before being dried in vacuo. Yield: 30 mg, 84%.
1H NMR (400 MHz, CD3CN; n.b. because of the presence of multiple
broad signals throughout the spectrum, integration of many of the
sharp signals listed are inferred logically): δ 8.69 (s, 1H, Ho), 8.29 (dd,
J = 8.2 and 1.7 Hz, 1H, Hn), 8.16 (d, J = 1.7 Hz, 1H, Hl), 8.13 (d, J =
5.2 Hz, 1H, Hi), 8.05 (d, J = 8.2 Hz, 1H, Hm), 7.97 (d, J = 2.1 Hz, 1H,
Hc), 7.88 (d, J = 8.3 Hz, 1H, He), 7.82 (d, J = 7.9 Hz, 1H, Hf), 7.42
(td, J = 7.7 and 1.9 Hz, 1H, Hg), 7.22 (dd, J = 8.2 and 2.2 Hz, 1H, Hd),
7.17 (dd, J = 7.0 and 4.6 Hz, 1H, Hh), 4.80 (t, J = 1.8 Hz, 2H, Hk),
4.72−4.65 (m, 4H, Hb and Hp), 4.60 (t, J = 1.9 Hz, 2H, Ha or Hj), 4.51
(t, J = 1.9 Hz, 2H, Ha or Hj), 2.27−2.19 (m, 2H, Hq), 1.69−1.45 (m,
6H, Hr−t), 1.01 (t, J = 7.2 Hz, 3H, Hu). 13C NMR: the broadness of the
1H NMR spectrum precluded the collection of a 13C NMR spectrum.
IR (ATR, cm−1): ν 3112, 2929, 2855, 2206, 1586, 1434, 1031, 800.
HR-ESI-MS (acetonitrile). Found: m/z 669.1686 ([M − 2(BF4)−]2+).
CV Experiments. All CV experiments were performed in solutions
at 20 °C [2:1 (v/v) CH2Cl2/nitromethane] with a concentration of 1
mM of the electroactive analyte and 0.1 M NBu4PF6 as the supporting
electrolyte. For the polymeric Cu(I) complexes, the concentration
refers to the repeat unit. A three-electrode cell was used with Cypress
Systems 1.4-mm-diameter glassy carbon working, Ag/AgCl reference,
and platinum wire auxiliary electrodes. Voltammograms were recorded
with the aid of a Powerlab/4sp computer-controlled potentiostat. The
potentials for all complexes were referenced to the reversible formal
potential (taken as E° = 0.00 V) of the [Fc*]+/0 redox couple of
decamethylferrocene.55 Under the same conditions, E° measured for
[FcH]+/0 was 0.53 V. DPV studies were run as part of our normal
procedure and support (are identical to) E° values obtained using CV
[where E° = (Epc + Epa)/2]. All CV data are displayed in the SI.
Crystallographic Information. X-ray data were collected at 100 K
on an Agilent Technologies Supernova system using Cu Kα radiation
with exposures over 1.0°, and data were treated using the CrysAlisPro58
software. The structure was solved using SHELXS within the X-Seed
package,59 and weighted full-matrix refinement on F2 was carried out
using SHELXL-9760 running within the WinGX package.61 All non-H
atoms were refined anisotropically. H atoms attached to C atoms were
placed in calculated positions and refined using a riding model.
Computational Methods. Computational modeling was carried at
the B3LYP/6-31G(d) level with the LanL2DZ electron core potential
Calcd for C74H64Fe2N12Pd2+: m/z 669.1563. UV−vis [acetone; λmax
,
nm (ε, L mol−1 cm−1)]: 541 (shoulder, 3800). Anal. Calcd for
C74H68N12B2F12Fe2Pd·CH3CN·0.2CHCl3: C, 57.85; H, 4.54; N, 11.51.
Found: C, 57.51, H, 4.25; N, 11.52.
Synthesis of [Pd2(L3)2](BF4)4. [Pd(CH3CN)4](BF4)2 (16.1 mg,
0.0360 mmol) was dissolved in ∼1 mL of acetonitrile and added to a
suspension of L3 (25.0 mg, 0.0360 mmol), and the mixture was stirred
at RT for 1 h, giving a deep-purple solution. The solution was filtered
through Celite before precipitation via the addition of diethyl ether.
The dark-purple powder was isolated by vacuum filtration, rinsed with
1
diethyl ether (3 × 5 mL), and air-dried. Yield: 29 mg, 82%. H NMR
(400 MHz, CD3CN, after equilibrium was established, n.b. all
assignments containing a prime have integration of approximately
3/4 that of the major species): δ 9.09 (d, J = 1.5 Hz, 4H, Hc′), 8.93 (d, J
J
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on the Pd centers in an acetonitrile solvent field, using Gaussian 09.62
After an adjustment factor of 0.975 was applied, a MADS of less than
10 cm−1 for the vibrational frequencies indicates a high level of
agreement between the experimental and computational structures.
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ASSOCIATED CONTENT
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S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02503.
Experimental section, 1H, 13C, and DOSY NMR spectral
information, HR-ESI-MS, UV−vis, X-ray, and electro-
chemical data, DFT calculation details, and calculated
structures (PDF)
DFT-calculated structures (XYZ)
DFT-calculated structures (XYZ)
Accession Codes
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: jcrowley@chemistry.otago.ac.nz.
ORCID
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James D. Crowley: 0000-0002-3364-2267
Author Contributions
The manuscript was written through contributions of all
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Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
J.A.F., D.P., and J.S.S. thank the University of Otago for Ph.D.
scholarships. K.C.G. and J.D.C. thank the MacDiarmid Institute
for Advanced Materials and Nanotechnology for financial
support. The authors acknowledge the contribution of the NeSI
high performance computing facilities to the results of this
research. New Zealand’s national facilities are provided by the
New Zealand eScience Infrastructure and funded jointly by
NeSI’s collaborator institutions and through the Ministry of
Business, Innovation & Employment’s Research Infrastructure
program (https://www.nesi.org.nz). C.J.M. thanks the New
Zealand Ministry of Business, Innovation and Employment
Science Investment Fund (Grant UOOX1206) for financial
support. J.D.C. thanks the Marsden Fund (Grant UOO1124)
and the University of Otago (Division of Sciences Research
Grant) for supporting this work. All of the authors thank the
University of Otago for additional funding.
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DEDICATION
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The manuscript is dedicated to Professor Leonard (Len)
Lindoy on the occasion of his 80th birthday.
K
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