The syntheses and electrochemical studies of a ferrocene substituted diiminopyridine ligand and its P, S, Se, and Te complexes

Article abstract of DOI:10.1021/ic300974u

A new reversible, redox active diiminopyridine ligand (1Fc) containing pendant ferrocene functionalities was isolated and fully characterized. The reaction of 1Fc with chalcogen pseudohalides of sulfur, selenium, and tellurium yielded the respective N,N′,N″-chelated chalcogen dications. Phosphorus chemistry proceeded in a related manner but, in this case, by the direct addition of 1Fc with PI₃ to yield the N,N′,N″- chelated P(I) cation. These species represent the first synthesized main group complexes involving a redox active diiminopyridine ligand containing pendant ferrocenes. Electrochemical studies of the free ligand shows a reversible two-electron process. The chelated phosphorus cation, however, displayed three events, the first being a quasi-reversible two-electron process, involving the oxidation at the P(I) center, resulting in a P(III) cation. The subsequent reversible one- and two-electron processes arise from the ligand framework and pendant ferrocenes, respectively.

Full text of DOI:10.1021/ic300974u

Article
pubs.acs.org/IC
The Syntheses and Electrochemical Studies of a Ferrocene
Substituted Diiminopyridine Ligand and Its P, S, Se, and Te
Complexes
Eleanor Magdzinski, Pierangelo Gobbo, Caleb D. Martin, Mark S. Workentin, and Paul J. Ragogna*
Department of Chemistry and The Centre for Advanced Materials and Biomaterials Research (CAMBR), Western University, 1151
Richmond St., London ON, N6A 5B7, Canada
S
* Supporting Information
ABSTRACT: A new reversible, redox active diiminopyridine ligand (1Fc) containing
pendant ferrocene functionalities was isolated and fully characterized. The reaction of
1Fc with chalcogen pseudohalides of sulfur, selenium, and tellurium yielded the
respective N,N′,N″-chelated chalcogen dications. Phosphorus chemistry proceeded in a
related manner but, in this case, by the direct addition of 1Fc with PI3 to yield the
N,N′,N″-chelated P(I) cation. These species represent the first synthesized main group
complexes involving a redox active diiminopyridine ligand containing pendant
ferrocenes. Electrochemical studies of the free ligand shows a reversible two-electron
process. The chelated phosphorus cation, however, displayed three events, the first
being a quasi-reversible two-electron process, involving the oxidation at the P(I) center,
resulting in a P(III) cation. The subsequent reversible one- and two-electron processes
arise from the ligand framework and pendant ferrocenes, respectively.
The synthesis and reactivity of nitrogen-based ligands
containing ferrocene pendant to the ligand framework have
appeared in the literature, but their chemistry largely remains
unexplored. Of the few examples reported, studies have been
limited to metals of the d block. Stephan et al. synthesized
ferrocenyl amidinates of Ti or Zr in order to study these ligands
as possible redox tunable olefin polymerization catalysts (Figure
1, I and II).7 In another report, a bis-ferrocenyl-β-diketiminate
was synthesized and used to prepare Zn complexes that
revealed unusual “non-innocent” reactivity at the β-diketiminate
ligand as opposed to the transition metal center (Figure 1, III
and IV).8 Bildstein et al. has focused their efforts in
synthesizing a ferrocene containing 1,4-diaza-1,3-butadiene
ligand for the preparation of Cr, Mo, and W complexes, with
the intention of producing redox tunable olefin polymerization
catalysts (Figure 1, V).9 Gibson et al. has synthesized a
diiminopyridine (DIMPY) ligand to complex Fe and Co
centers, again with an eye toward effective switchable catalysts
for olefin polymerization (Figure 1, VI).10 Another example by
this group utilizes the bis(iminophenoxide) ligand framework
and modifies it in such a way as to contain ferrocene moieties.
The resulting Ti complex (Figure 1, VII) was used to show that
activity can indeed be varied by redox switching of the
ferrocenyl unit contained within the ligand backbone of a
lactide polymerization catalyst by introduction of a chemical
redox agent.11
INTRODUCTION
■
In the past decade, there has been an interest in synthesizing
monocationic and polycationic main group centered molecules
to study the nature of their structure, bonding, and reactivity.
Although there are a variety of synthetic methods used to
produce these species, nitrogen-based ligands have been the
dominant support for the cations.1,2 Many of the reports have
focused on producing novel complexes using ligands where the
substituents (alkyl or aryl) can be varied within the ligand
framework; however, examples of these common supports that
feature pendant redox active (i.e., ferrocene) fragments are
relatively rare (Figure 1). It is known that transition metal
based complexes containing redox active ligands or ligands
substituted with redox active components have been used in a
diverse array of applications including catalysis, optical
materials, or in the manufacture of biological sensors.3−5 The
appeal of ligands with redox active functional groups stems
from their ability to change the electronic properties of the
central metal without the need for further synthetic
modifications. This occurs by either varying an applied
potential or introducing a chemical redox agent into a reaction,
whereby an oxidation or reduction at ferrocene has the ability
to “turn on” or “turn off” a particular molecule. Imparting redox
active species onto a ligand offers exciting opportunities within
homogeneous transition metal catalysts, as the oxidation of the
redox active substituent induces a higher electrophilicty and,
therefore, a change in reactivity of a catalytically active
transition metal center.6 In many cases, these ligands exhibit
reversible redox processes and therefore enable “switchable”
control of the electronic properties of a central metal.
Recently, the nitrogen-based ligand set, diiminopyridine
(Figure 1, R-DIMPY), has been featured prominently in the
Received: May 10, 2012
Published: July 9, 2012
© 2012 American Chemical Society
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Figure 1. A few known nitrogen-based ligand complexes with ferrocenyl and nonferrocenyl substituents.
isolation of cationic main group species.12−21 Our group has
utilized the N,N′-aryl substituted versions to stabilize low valent
dicationic chalcogen (Figure 1, 1DippS, 1DippSe, 1DippTe,
and 1DmpTe)22 or monocationic phosphorus (Figure 1,
1DippP and 1bDippP)23 centers; however, there are no
reports of utilizing nitrogen-based ligands that feature redox
active substituents in the stabilization of highly novel main
group cations.
In this context, we report the synthesis, characterization, and
electrochemical behavior of a new DIMPY ligand (1Fc),
containing pendant ferrocenyl fragments on the imine nitro-
gens (Scheme 1, A). We have explored its reactivity with main
group metals from groups 15 (P) and 16 (S, Se, Te), and
furthermore, the electrochemistries of these compounds have
been investigated. The electrochemical studies reveal the
possibility of generating the putative tricationic phosphorus
centered species, and under the conditions employed this
indicates that the polycation may be isolable. These results
represent the first inroads into such redox active main group
compounds.
chiometry under an ethanol reflux (Scheme 1, A). A dark red-
purple powder precipitated and was isolated using vacuum
filtration. The solids were washed with cold ethanol and dried,
and a sample of the bulk powder was redissolved in CDCl3.
1
The H NMR spectrum indicated the presence of six distinct
signals: three in the aromatic region, consistent with protons on
the DIMPY framework, and three for the monosubstituted
ferrocene species that appeared to shift downfield relative to the
aminoferrocene starting material (Table 1).
A solution of 1Fc in DCM was stirred with one
stoichiometric equivalent of the appropriate chalcogen
pseudohalide starting material (S(OTf)2, CyDABSeOTf2, and
Dipp2BIANTeOTf2) in the same solvent at room temperature
(Scheme 1, B). In all cases, color changes from orange-red to a
dark blue-green were immediately observed. Normal pentane
and Et2O were used to precipitate out the dark blue-green
solids, which were then dried in vacuo. Proton NMR spectra of
the redissolved solids in CD3CN revealed downfield shifts
(Table 1) for all resonances relative to the free ligand, indicative
of coordination of the ligand to an electron deficient chalcogen
center. These compounds were tentatively assigned as the salts
1FcS, 1FcSe, and 1FcTe. X-ray quality crystals of all
compounds were grown, and subsequent X-ray diffraction
experiments confirmed the identity of the solids, which were
isolated in 65−80% yields.
RESULTS AND DISCUSSION
■
Synthesis. N,N′-Diferrocenyl diiminopyridine (FcDIMPY;
1Fc) was prepared by the condensation reaction between 1-
aminoferrocene and 2,6-pyridinedialdehyde30 in a 2:1 stoi-
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Scheme 1. Synthetic Routes to 1Fc, 1FcS, 1FcSe, 1FcTe, and 1FcP
1
and formation of a single phosphorus peak at δP = 123.99. This
shift corresponds with other reported P(I) DIMPY complexes
previously.23 A solid green-black product was precipitated by
the addition of a combination of n-pentane and Et2O. The
Table 1. H NMR Chemical Shifts (ppm) for 1Fc, 1FcS,
1FcSe, 1FcTe, and 1FcP
compound
1Fc
1FcS
1FcSe
1FcTe
1FcP
δH imine, 2H
δH py-d, 2H
δH py-t, 1H
δH Ha-pt, 2H
δH Hb-pt, 2H
δH Hc-s, 10H
8.81
8.21
7.84
4.71
4.35
4.21
10.07
9.02
8.84
5.52
5.18
4.53
10.14
8.94
8.85
5.55
5.15
4.52
10.32
8.84
8.73
5.55
5.07
4.48
9.52
8.63
7.12
5.52
4.86
4.57
1
corresponding H NMR spectrum of the redissolved solids in
CD2Cl2 showed a diagnostic doublet for the imine protons (δH
= 9.52; 3JPH = 2.8 Hz), indicative of the successful incorporation
of phosphorus into the ligand framework.
On the basis of these multinuclear NMR spectroscopic data,
the compound was tentatively assigned as being the DIMPY
complex of the phosphorus salt 1FcP. For further verification,
suitable crystals for X-ray diffraction were grown, and
subsequent diffraction experiments confirmed the identity of
the compound as 1FcP.
The 1:1 stoichiometric addition of 1Fc with PI3 underwent a
similar color transformation as was observed in the formation
of the chalcogen salts (Scheme 1, C). Approximately 10 min
after the addition of 1Fc to PI3, the reaction mixture was
sampled and analyzed by 31P{1H} NMR spectroscopy, which
showed the disappearance of the signal for free PI3 (δP = 178)
X-Ray Crystallography. The solid-state structure obtained
from X-ray diffraction studies on single crystals of 1Fc
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for 1FcS, 1FcSe, 1FcTe, and 1FcP and their analogues 1DippS,
1DippSe, 1DippTe, and 1DippP
1FcS
1DippS22
1FcSe
1DippSe22
1FcTe
1DippTe22
1FcP
1DippP23
E(1)−N(1)
E(1)−N(2)
E(1)−N(3)
C(1)−N(1)
C(7)−N(3)
N(1)−E(1)−N(2)
N(2)−E(1)−N(3)
1.922(5)
1.709(7)
1.922(5)
1.287(8)
1.287(8)
82.60(17)
82.60(17)
1.9068(17)
1.719(3)
2.068(2)
1.872(2)
2.086(9)
1.291(3)
1.284(3)
79.22(9)
78.43(9)
2.025(9)
1.872(3)
2.230(3)
2.068(3)
2.208(3)
1.286(5)
1.308(5)
73.81(12)
74.42(12)
2.243(4)
2.098(3)
2.241(4)
1.284(6)
1.284(7)
72.77(15)
73.35(16)
2.275(4)
1.725(5)
1.777(4)
1.314(5)
1.314(5)
73.90(11)
88.52(14)
1.877(7)
1.722(6)
1.975(8)
1.303(11)
1.316(11)
81.6(3)
a
a
a
a
a
a
a
1.9068(17)
1.280(3)
2.025(9)
1.275(3)
a
a
1.280(3)
1.275(3)
82.39(6)
78.79(6)
a
a
82.39(6)
78.79(6)
81.1(3)
a
Symmetry arising from the centrosymetric nature of those marked compounds.
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Table 3. X-Ray Details for 1Fe, 1FcS, 1FcSe, 1FcTe, and 1FcP
compound
1Fc
1FcS
1FcSe
1FcTe
1FcP
empirical formula
FW (g/mol)
cryst syst
space group
a (Å)
C31H31Fe2N3O1
573.29
C29H23F6Fe2N3O6S3
831.38
C29H23F6Fe2N3O6S2Se1
878.28
C29H23F6Fe2N3O6S2Te1
926.92
C27H23Fe2I3N3P1
912.85
triclinic
monoclinic
C2/c
triclinic
triclinic
monoclinic
C2/c
P1
̅
P1
P1
̅
̅
11.2926(16)
11.6402(17)
12.1762(17)
68.139(3)
72.717(3)
61.101(3)
1286.9(3)
2
12.970(2)
18.528(3)
13.477(2)
90.000
10.7138(9)
11.5291(9)
13.6160(11)
104.007(2)
94.864(3)
107.862(2)
1530.0(2)
2
10.732(3)
11.537(3)
13.662(4)
103.487(6)
94.198(7)
106.741(6)
1557.2(7)
2
12.0077(10)
17.2096(14)
13.8818(11)
90.000
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
109.608(4)
90.000
99.153(2)
90.000
V (Å3)
3050.8(8)
4
2832.1(4)
4
Z
Dc (mg m−3
)
1.479
1.810
1.906
1.977
2.141
radiation, λ (Å)
0.71073
150(2)
0.71073
150(2)
0.71073
150(2)
0.71073
150(2)
0.71073
150(2)
temp (K)
a
R1[I > 2σI]
0.0604
0.0706
0.0325
0.0407
0.0343
a
wR2(F2)
0.1695
0.1586
0.0792
0.0882
0.0740
a
GOF(S)
1.022
1.102
1.029
1.054
1.085
a
R1(F[I > 2(I)]) = ∑∥|Fo| − |Fc |∥/∑ |Fo|; wR2(F2 [all data]) = [w(Fo2 − Fc2)2]1/2; S(all data) = [w(Fo2 − Fc2)2/(n − p)]1/2 (n = no. of data; p = no.
of parameters varied; w = 1/[2(Fo ) + (aP)2 + bP], where P = (Fo + 2Fc2)/3 and a and b are constants suggested by the refinement program.
2
2
Table 4. Solid-State Structures of 1Fc, 1FcS, 1FcSe, 1FcTe, and 1FcP (Thermal Ellipsoids Drawn to the 50% Probability Level;
Solvates and Hydrogen Atoms Removed for Clarity)
a
Disorder removed for clarity.
confirmed the identity of a diiminopyridine ligand bearing
ferrocene groups on the two nitrogen atoms (Table 4). The
carbon−nitrogen double bonds are indicative of a diimine (C
N; 1.266(6) and 1.267(6)), and the remaining metrical
parameters are consistent with the well-documented diimino-
pyridine framework.
The solid-state structures of the corresponding main group
complexes of 1Fc indicate the presence of the cationic
phosphorus (1FcP) or dicationic chalcogen centers (1FcS,
1FcSe, and 1FcTe) within the N,N′,N″-DIMPY chelate (see
Table 2 for salient bond lengths and angles, Table 3 for X-ray
data, and Table 4 for structures). For all species, the bonding
within the diiminopyridine framework has little deviation from
the previously reported N,N′-diisopropylphenyl (Dipp) deriv-
atives (Figure 1, 1DippS, 1DippSe, 1DippTe, and
1DippP),22,23 demonstrating that the ferrocene groups do
not alter the interaction between the ligand to the main group
center. In contrast to the Dipp derivatives that have bulky aryl
groups oriented perpendicular to the diiminopyridine plane, the
ferrocene substituents in all species are coplanar with respect to
the cyclopentadiene ring bound at the nitrogen and the
diiminopyridine contiguous rings.
In all of the structures, the ferrocene groups are oriented anti
to one another to minimize steric interactions, and as a result,
all of the species have pseudo-C2 symmetry through the E(1)−
N(2)−C(4) axis (1FcS and 1FcP are perfectly C2 symmetric).
Compound 1FcP is disordered at the phosphorus center,
modeled with a 50% occupancy at both sites. In the case of
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1FcS, disorder arises from the presence of the other anti
configuration of the complex. Compounds 1FcS and 1FcP lack
sulfur−oxygen and phosphorus−iodine contacts within the sum
of the van der Waals radii to either the triflate (∑v.d.W. S−O =
3.25 Å) or the triiodide counterion (∑v.d.W. P(1)−I = 5.33 Å,
window, compound 1FcP shows three oxidation peaks (Figure
2, C): Peak I with Ep1/2 at 0.36 V is quasi-reversible and is a
two electron process. Peak II appearing as a shoulder
overlapping with peak III is a reversible one electron process.
Peak III with E° at 0.94 V is a reversible two electron process.
To better understand the electrochemistry of 1FcP, an
analogous phosphorus complex 1DippP, containing two Dipp
substituents and a triiodide anion, was analyzed under identical
experimental conditions. This complex (Figure 2, B) shows two
distinct electrochemical processes. The first is a quasi-reversible
oxidation with Ep1/2 at 0.36 V and involves two electrons, and
the second is a reversible one electron peak with E° at 0.81 V.
These two signals appear when nitrogen atoms of the ligand
coordinate the phosphorus and are likely related to the loss of
two electrons on the P(I) forming a P(III) center during the
first quasi-reversible process and the subsequent reversible
oxidation of the ligand induced by complexation to P in the
second one electron reversible process, as these processes are
not observed in the free ligand. The complete CV of this
compound (figure available in Supporting Information) shows
two other irreversible peaks at 2.00 V and 2.54 V due to the
oxidation of the two Dipp groups, consistent with the observed
electrochemistry for the free ligand (figure available in the
Supporting Information) where no other redox behavior is
observed in the −0.5 to 2.0 V range.
∑
P(1)A−I = 5.49 Å). The closest contacts in 1FcSe and
v.d.W.
1FcTe between the cation and anions lie on the edge of the
sum of the van der Waals radii (1FcSe Se···O = 3.367 Å cf.
∑
v.d.W. Se−O = 3.42 Å; 1FcTe Te···O = 3.068 Å cf. ∑v.d.W. Te−
O = 3.58 Å).24 Despite these distant contacts, all species are
viewed as distinct cation−anion pairs, as there is no elongation
of the related sulfur−oxygen bond in the triflate anion,
indicative of ionic formulations.
Electrochemistry. Compounds 1Fc, 1FcP, 1DippP (with
−
I3 anion), and its free Dipp ligand (Figure 1, 1Dipp) were
characterized by cyclic voltammetry (CV) using 2 mM
solutions in 5 mL of a DCM/0.1 M TBAPF6 electrolyte
solution. The working electrode was a 1 mm platinum disk
electrode. The counter electrode was a platinum wire, and the
reference electrode was a Ag/AgCl electrode. However, the
voltammetric curves were all calibrated to the standard calomel
electrode (SCE) using nitrobenzene as the internal standard.
Compound 1Fc (Figure 2, A) shows a reversible peak with
E° at 0.73 V related to the two ferrocene moieties. The peak
The assignment of the voltammetric peaks I and II (Figure 2,
C) obtained for the complex 1FcP is supported by comparison
with the electrochemical data obtained for the aforementioned
1DippP derivative (Figure 2, B) where the first two oxidations
are related to the coordination of the three nitrogens of the
ligand to phosphorus. Peak III, the two electron reversible peak,
is absent from the CV of 1DippP and results from the
oxidation of the two ferrocene groups present in 1FcP. Relative
to the free ligand (1Fc), this signal is shifted slightly toward
more positive potentials due to a loss in electron density from
the ligand framework as a result of coordinating to the electron
deficient phosphorus center.
The electrochemistry of complexes 1FcS, 1FcSe, and 1FcTe
were also investigated by CV. However, the poor solubility of
these complexes and the reactivity of these chalcogen
complexes with the electrochemistry solvents and electrode
materials made analysis more difficult. These compounds were
found to be slightly soluble in CH3CN/0.05 M TBABF4 as an
electrolyte solution. Their CVs were recorded saturating the
electrolyte solution with analyte. In these cases, the working
electrode was a glassy carbon (GC) disk electrode. These CVs,
available in the Supporting Information, show the same general
features, although broadened and less resolved as the
voltammetric curve obtained for the complex 1FcP, namely
the quasi-reversible oxidation of the chalcogen-ligand followed
by a two electron oxidation of the ferrocene moieties.
CONCLUSIONS
Figure 2. From top to bottom, CV of 1Fc (A), 1DippP (B), and 1FcP
(C) recorded at a Pt electrode in DCM/0.1 M TBAPF6 with an
analyte concentration of 2 mM and at 0.5 V s−1. Experiment carried
out inside of a glovebox at room temperature.
■
Compounds 1FcS, 1FcSe, 1FcTe, and 1FcP represent the first
examples of group 15 and 16 salts utilizing a redox active
DIMPY ligand (1Fc) containing pendant ferrocene function-
alities. Cyclic voltammetric studies of the free ligand display a
reversible two electron process with E° at 0.73 V. A full data
collection for the N,N′,N″-chelated chalcogen complexes
remains somewhat inconclusive, due to the insolubility of
these complexes. An electrochemical investigation of 1FcP was
performed, showing three events: a quasi-reversible two
electron process for the production of a P(III) centered cation
current is indicative of a two electron process, showing that the
two ferrocenes are being oxidized at the same or similar
potential, suggesting little or no electronic interaction between
them, as expected due to poor conjugation within the molecule.
Similar redox behavior has been observed for other N,N′-
diferrocenyl diazabutadiene type ligands.9 In the same potential
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a junction, in an CH3CN/0.1 M TBAPF6 solution. A silver wire was
then immersed in the solution inside the glass tube, and the reference
electrode was left to stabilize its potential for a week prior to use. All
data are reported versus the standard calomel electrode (SCE).
Introducing one molar equivalent of nitrobenzene to the electro-
chemical cell after each experiment allowed for the calibration to be
made. The standard potential (E°) for the reversible reduction of
nitrobenzene to its corresponding radical anion was calibrated toward
ferrocene in a separate experiment. The E° of ferrocene in DCM is
established to be 0.644 V vs SCE.31,32 The E° of nitrobenzene in DCM
was found to be −0.986 V vs SCE. The reversible reduction of
nitrobenzene to its radical anion involves a single electron transfer;
therefore, the intensity of the voltammetric peak was used to
approximate the number of electrons exchanged in the electrochemical
processes of the studied compounds. The counter-electrode was a
platinum wire. All electrochemical measurements were carried out
using the same set of electrodes.
The electrochemical measurements of compounds 1Fc, 1FcS,
1FcSe, 1FcTe, and 1FcP were conducted in an in-house designed and
built glass cell at room temperature. Due to the sensitivity of the
compounds to ambient air, the experiments were performed inside of a
glovebox. The electrochemical characterization of compounds 1Fc and
1FcP were carried out in a 5 mL DCM/0.1 M TBAPF6
(tetrabutylammonium hexafluorophosphate) electrolyte solution con-
taining the appropriate analyte (2 mM) and using the platinum
electrode as a working electrode. The electrochemical characterization
of compounds 1FcS, 1FcSe, and 1FcTe were carried out in a 5 mL
CH3CN/0.05 M TBABF4 (tetrabutylammonium tetrafluoroborate)
electrolyte solution saturated with the analyte. For these measure-
ments, the glassy C was used as the working electrode. For all
measurements, feedback correction was employed to minimize the
ohmnic drop between the reference and working electrode. The
corresponding background curves were then subtracted from the CVs
in order to eliminate the capacitive current contribution.
Synthesis. Iodoferrocene. A 500 mL Schlenk flask equipped with
a large stir bar was charged under a nitrogen atmosphere with
ferrocene (8.00 g, 0.043 mol), tBuOK (0.48 g, 0.0043 mol), and 300
mL of THF. The orange-yellow solution was cooled to −78 °C; some
of the dissolved ferrocene precipitated during this process. Under
rigorous stirring, 1.7 M tBuLi (25 mL, 0.043 mol) in n-hexane was
added dropwise over 1 h. The addition was complete after 20 min, at
which time the cold bath was removed and the reaction mixture was
allowed to warm to room temperature, then stirred for an additional 2
h. The color of the reaction mixture changes from opaque orange to
red-orange to a dark clear red. The reaction mixture was once again
cooled to −78 °C, and under vigorous stirring, I2 (12.00 g, 0.0473
mol) was added in one portion. The cold bath was removed, and the
mixture was allowed to warm to room temperature. Stirring continued
for 12 h. The mixture was then first diluted with 200 mL of Et2O, then
washed with portions of saturated aqueous Na2SO3 (2 × 100 mL) and
H2O (3 × 150 mL) and dried with MgSO4. The solvent was removed
by rotary evaporation to yield the crude product as a yellow-brown oil
(8.62 g, 0.026 mol, 60%), which solidifies upon storing in a freezer
overnight. Spectroscopic properties were in agreement with literature
values.33,34 Unreacted ferrocene was present in the crude product;
however, its presence did not affect onward chemistry and was
therefore used without further purification. The relative 1H signal
ratios (ferrocene/iodoferrocene) were examined in order to determine
the amount of pure iodoferrocene per gram of crude solid to be used
in future transformations.
with Ep1/2 at 0.36 V, a second reversible one electron process
from the ligand framework which overlaps with a third two
electron process from the non-communicating ferrocenes (E° =
0.94 V).
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed under an
inert atmosphere in a nitrogen filled MBraun Labmaster dp glovebox
or using standard Schlenk techniques unless stated otherwise.
Reagents were obtained from commercial sources. All solvents were
dried using an MBraun controlled atmospheres solvent purification
system and stored in Straus flasks under a N2 atmosphere or over 4 Å
molecular sieves in the glovebox. Chloroform-d was dried over calcium
hydride, distilled prior to use, and stored in the glovebox over 4 Å
molecular sieves. Acetonitrile-d3 and CD2Cl2 were purchased from
Cambridge Isotope Laboratories and stored in the glovebox over 3 Å
or 4 Å molecular sieves, respectively. The syntheses of S(OTf)2,
CyDABSeOTf2, Dipp2BIANTeOTf2, copper phthalimide, N-ferrocen-
yl pthalimide, and 2,6-pyridinedialdehyde were prepared via literature
procedures.25−30 Iodoferrocene and aminoferrocene were prepared
using modified literature procedures. Proton, 13C{1H}, 19F{1H}, and
31P{1H} NMR spectroscopic data were collected on a 400 MHz Varian
Inova spectrometer (399.762 MHz for 1H; 100.52 MHz for 13C;
376.15 for 19F; 161.825 MHz for 31P). NMR spectra were recorded at
room temperature, unless otherwise indicated, in CDCl3, CD3CN, or
CD2Cl2, and were referenced using the residual protons of the
deuterated solvents (CHCl3, δH = 7.26; CH3CN, δH = 1.9, 3; DCM, δH
= 5.30), coupling constants are listed in hertz. Carbon-12 NMR
spectra were referenced using carbon signals from the respective
solvent (CHCl3, δC = 77.16(3); CH3CN, δC = 1.32(7), 118.26(1);
DCM, δC = 54.00(5)). Phosphorus-31{1H} and 19F{1H} NMR spectra
were recorded unlocked relative to an external standard (31P{1H}, 85%
H3PO4, δP = 0.00; 19F{1H}, CF3C6H5, δF = −63.9). Single crystal X-ray
diffraction data were collected on a Nonius Kappa-CCD or a Bruker
Apex II-CCD area detector using Mo Kα radiation (λ = 0.71073 Å).
Crystals were selected under Paratone-N oil, mounted on MiTeGen
micromounts or nylon loops, and then immediately placed in a cold
stream of N2. Structures were solved and refined using SHELXTL.
UV/vis absorption spectra were recorded over a range of 235−800 nm
using a Varian Cary 300 spectrometer in either CH2Cl2 (for 1Fc and
1FcP) or CH3CN (for 1FcS, 1FcSe, and 1FcTe). 1FcP was measured
at a concentration of 2.5 × 10−5 M, while all other compounds had a
concentration of 2.0 × 10−5 M. FT-IR spectra were collected on
samples as KBr pellets using a Bruker Tensor 27 spectrometer, with a
resolution of 4 cm−1. Samples for FT-Raman spectroscopy were
packed in capillary tubes and flame-sealed. Data were collected using a
Bruker RFS 100/S spectrometer, with a resolution of 4 cm−1. Melting
and decomposition points were recorded in flame-sealed capillary
tubes using a Gallenkamp Variable Heater. High resolution mass
spectrometry (HRMS) was collected using a Finnigan MAT 8200
instrument. Elemental analyses (C, H, N) were performed by
́
Laboratoire d’Analyze Elem
́
entaire de l′Universite
́
de Montrea
́
l,
́
Montreal, QC, Canada. The electrochemical apparatus employed for
cyclic voltammetry (CV) was an Autolab30 electrochemical work-
station equipped with GPES 4.9 software. The working electrodes
were either a glassy carbon (GC) electrode built from a Tokai GC-20
glassy carbon rod (3 mm diameter) or a platinum electrode built from
a platinum wire (1 mm diameter), a Premion product purchased from
Alfa Aesar. The disk electrode surfaces were prepared by polishing on
silicon carbide papers (500, 1200, 2400, and 4000) and successively
over diamond pastes (1 and 0.25 μm) from Struers. The working
electrodes were stored in ethanol and, before using, were polished with
diamond paste (1 μm), rinsed with dry ethanol, sonicated in dry
ethanol for 5 min, and dried. The previous sequence with ethanol was
then repeated using 0.25 μm diamond paste to start. Electrochemical
activation of the disk electrode surfaces was carried out before each
measurement by multicycling at 0.1 V s−1 in the background solution
until stabilization of the capacitive current. The reference electrode
was a Ag/AgCl, built by filling a glass tube closed at an extremity with
Aminoferrocene. To a 500 mL round-bottom Schlenk flask,
degassed, was added anhydrous ethanol (100 mL) to a slurry of N-
ferrocenyl phthalimide29 (5.99 g, 0.018 mol) and hydrazine
monohydrate (0.873 mL, 0.018 mol). The clear yellow solution was
refluxed under N2 for 2.5 h. The mixture was then cooled to room
temperature. Degassed H2O was added (200 mL), and the product
was extracted with Et2O. The yellow organic layer was dried over
MgSO4 and the supernatant transferred to a Schlenk tube and
evaporated in vacuo to dryness, yielding a bright yellow-orange powder
(2.57 g, 0.012 mol, 68%). Impurities were removed by sublimation
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Inorganic Chemistry
Article
under a dynamic vacuum at 60 °C (coldfinger at −15 °C). The
product was stored under an inert atmosphere of N2. Aminoferrocene
prepared according to the above procedure showed spectroscopic
properties consistent with those previously published.35
anal. calcd for C29H23N3Fe2Te1O6S2F6: C, 37.58; H, 2.50; N, 4.53; S,
6.92. Found: C, 37.08; H, 2.19; N, 4.54; S, 6.31.
1FcP. A mixture of 1Fc (0.150 g, 0.299 mmol) in DCM (3 mL) was
added dropwise to a solution of PI3 (0.123 g, 0.299 mmol) in DCM (3
mL) at room temperature and was allowed to stir for 10 min. The
product was precipitated by the addition of n-pentane (3 × 10 mL)
and Et2O (3 × 10 mL) and dried in vacuo to give a dark green-black
fine powder (0.218 g, 0.239 mmol, 80%). 1H NMR (CD3CN, δ): 9.52
(d, 2H), 8.63 (d, 2H, 3JH−H = 7.8), 8.12 (t, 1H, 3JH−H = 7.8), 5.52 (pt,
4H), 4.86 (pt, 4H), 4.57 (s, 10H). 31P NMR (CD3CN, δ): 123.99.
UV/vis (CH2Cl2): λmax 295.1 nm. FT-IR (cm−1 (ranked intensity)):
3081(7), 1628(14), 1459(15), 1407(8), 1375(10), 1335(4), 1242(11),
1104(6), 1025(3), 1001(13), 934(12), 820(2), 769(5), 708(9),
499(1). FT-Raman (cm−1 (ranked intensity)): 3101(10), 1627(6),
1572(2), 1497(9), 1451(5), 1373(7), 1239(4), 1105(12), 1055(11),
831(15), 641(3), 478(13), 298(8), 163(14), 110(1). Decomposition
point: 228−233 °C. HRMS C27H23N3Fe2P1 calcd (found): 532.03290
(532.03176). Elem. anal. calcd for C27H23N3Fe2P1I3: C, 35.52; H, 2.54;
N, 4.60. Found: C, 35.55; H, 2.43; N, 4.78.
1Fc. Mixtures of aminoferrocene (1.91 g, 9.48 mol), degassed
ethanol (50 mL), and 2,6-pyridinedialdehyde30 (0.636 g, 4.72 mmol)
were refluxed under an inert atmosphere for 12 h with constant
stirring. The product was collected by filtration, washed with cold
ethanol (2 × 50 mL), and dried in vacuo to give a fine dark red-purple
powder (2.10 g, 4.20 mmol, 89%). 1H NMR (CDCl3, δ): 8.81 (s, 2H),
3
3
8.21 (d, 2H, JH−H = 7.6), 7.84 (t, 1H, JH−H = 7.6), 4.71 (pt, 4H,
3JH−H = 2.0), 4.35 (pt, 4H, 3JH−H = 2.0), 4.21 (s, 10H). 13C{1H} NMR
(CDCl3, δ): δ 62.62, 67.02, 68.77, 102.27, 120.66, 136.10, 154.11,
156.37. UV/vis (CH2Cl2): λmax 319.9 nm. FT-IR (cm−1 (ranked
intensity)): 1579(13), 1561(4), 1462(6), 1348(14), 1232(11),
1106(3), 1040(15), 1001(7), 962(8), 927(5), 804(1), 738(12),
523(10), 491(2), 456(9). FT-Raman (cm−1 (ranked intensity)):
1616(1), 1580(2), 1562(7), 1458(4), 1376(12), 1273(5), 1229(3),
1110(8), 990(6), 670(11), 642(14), 585(13), 334(10), 283(9),
162(15). Mp: 223−230 °C. Elem. anal. calcd for C27H23N3Fe2: C,
64.71; H, 4.63; N, 8.38. Found: C, 64.47; H, 4.67; N, 8.34.
ASSOCIATED CONTENT
■
1FcS. A solution of 1Fc (150.0 g, 0.299 mmol) in DCM (3 mL)
was added dropwise to a solution of S(OTf)225 (0.076 g, 0.229 mmol)
in DCM (3 mL) at room temperature. The product was precipitated
by the addition of n-pentane (3 × 10 mL) and Et2O (3 × 10 mL) and
dried in vacuo to give a dark blue-green fine powder (0.133 g, 0.160
mmol, 70%). Single crystals were obtained via vapor diffusion of Et2O
in CH3CN. 1H NMR (CD3CN, δ): δ 10.07 (s, 2H), 9.02 (d, 2H, 3JH−H
= 7.8), 8.85 (t, 1H, 3JH−H = 7.8), 5.52 (pt, 4H), 5.18 (pt, 4H), 4.53 (s,
10H). UV/vis (CH3CN): λmax 260.0 nm. FT-IR (cm−1 (ranked
intensity)): 3071(10), 1617(9), 1573(15), 1553(11), 1515(4),
1403(7), 1266(1), 1227(14), 1179(5), 1027(2), 817(8), 636(3),
574(12), 518(13), 484(6). FT-Raman (cm−1 (ranked intensity)):
1614(9), 1547(3), 1511(1), 1499(11), 1400(2), 1294(13), 1231(5),
1090(8), 1064(15), 1043(14), 628(4), 493(7), 296(3), 332(10),
120(12). Decomposition point: 120−130 °C. HRMS
C28H23N3Fe2S2O3F3 calcd (found): 681.9832 (681.9846).
S
* Supporting Information
1H NMR spectra, CVs, UV−vis for all compounds, and a
crystallographic file in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: pragogna@uwo.ca.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are very grateful to the Natural Sciences and
Engineering Research Council of Canada (NSERC), the
Canada Foundation for Innovation, Ontario Ministry of
Research and Innovation, and UWO for generous financial
support. We also thank J. W. Dube for assistance with X-ray
crystallographic studies.
1FcSe. A solution of 1Fc (0.227 g, 0.453 mmol) in DCM (3 mL)
was added dropwise to a solution of CyDABSeOTf226 (0.266 g, 0.453
mmol). The product was then precipitated by the addition of n-
pentane (3 × 10 mL) and Et2O (3 × 10 mL) and dried in vacuo to give
a dark green-blue powder (0.270 g, 0.308 mmol, 68%). Single crystals
were obtained via vapor diffusion of Et2O in CH3CN. 1H NMR
3
(CD3CN, δ): 10.14 (s, 2H), 8.94 (d, 2H, JH−H = 7.8), 8.85 (t, 1H,
REFERENCES
3JH−H = 7.8), 5.55 (pt, 4H), 5.15 (pt, 4H), 4.52 (s, 10H). UV/vis
(CH3CN): λmax 314.9 nm. FT-IR (cm−1 (ranked intensity)):
3058(13), 1607(10), 1573(12), 1549(9), 1512(3), 1407(7),
1267(1), 1221(15), 1169(6), 1028(4), 820(11), 635(2), 571(14),
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1608(10), 1549(2), 1512(1), 1407(3), 1241(4), 1222(6), 1085(13),
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C, 38.97; H, 2.49; N, 4.76; S, 6.84.
■
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