Syntheses and Reactivity Studies of Square-Planar Diamido-Pyridine Complexes Based on Earth-Abundant First-Row Transition Elements

Article abstract of DOI:10.1021/acs.inorgchem.5b00779

The new square-planar complexes M[NNN](pyridine) (M = Fe (1), Co(2); NNN = 2,6-bis(2,6-diisopropylphenylamidomethyl)pyridine) were synthesized and fully characterized to investigate small molecule activation on this platform and also associated ligand innocence. The equatorial pyridine solvent moiety could not be removed; a new bis-ligand species Co[NNN.H]₂ (3) was synthesized in low yield while attempting to make the base-free derivative. Attempts to prepare the Ni analogue of 1 and 2 instead yielded crystals of a di-imino-pyridine complex Ni[PDI]Cl (4) (PDI = 2,6-bis(2,6-diisopropylphenyliminomethyl)pyridine), following loss of methylene backbone hydrogen atoms. Structural analysis indicates that the PDI ligand is a mono-anionic radical. This susceptibility of the ligand to oxidative dehydrogenation was also shown when the reaction of 2 with 2 equiv of trityl chloride yielded a new complex with an asymmetric imino-amino pyridine ligand Co[NNN′]Cl₂ (5) (NNN′ = 2-(2,6-(diisopropylphenyliminomethyl)-6-(diisopropylphenylamidomethyl)-pyridine) in good yield. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.inorgchem.5b00779

Article
pubs.acs.org/IC
Syntheses and Reactivity Studies of Square-Planar Diamido−Pyridine
Complexes Based on Earth-Abundant First-Row Transition Elements
Owen T. Summerscales,*,† Jamie A. Stull,‡ Brian L. Scott,§ and John C. Gordon*,†
‡
§
†Chemistry Division, Materials Science and Technology Division, and Materials and Physics Applications Division, Los Alamos
National Laboratory, Los Alamos, New Mexico 87545, United States
S
* Supporting Information
ABSTRACT: The new square-planar complexes M[NNN]-
(pyridine) (M = Fe (1), Co(2); NNN = 2,6-bis(2,6-
diisopropylphenylamidomethyl)pyridine) were synthesized and
fully characterized to investigate small molecule activation on
this platform and also associated ligand innocence. The
equatorial pyridine solvent moiety could not be removed; a
new bis-ligand species Co[NNN.H]2 (3) was synthesized in low
yield while attempting to make the base-free derivative.
Attempts to prepare the Ni analogue of 1 and 2 instead yielded
crystals of a di-imino−pyridine complex Ni[PDI]Cl (4) (PDI =
2,6-bis(2,6-diisopropylphenyliminomethyl)pyridine), following
loss of methylene backbone hydrogen atoms. Structural analysis indicates that the PDI ligand is a mono-anionic radical. This
susceptibility of the ligand to oxidative dehydrogenation was also shown when the reaction of 2 with 2 equiv of trityl chloride
yielded a new complex with an asymmetric imino−amino pyridine ligand Co[NNN′]Cl2 (5) (NNN′ = 2-(2,6-
(diisopropylphenyliminomethyl)-6-(diisopropylphenylamidomethyl)-pyridine) in good yield.
Scheme 1. Examples of Active First-Row Transition Metal
Catalysts Supported by Nitrogen Donor Pincer Ligands
INTRODUCTION
■
The replacement of precious metal catalysts with those based
on earth-abundant elements, such as the first-row transition
metals Fe, Co, and Ni, is a prerequisite for the development of
a sustainable chemical industry and also has clear impact on
mitigating industrial costs and environmental impact. Develop-
ment of these catalysts with respect to those based on precious
metals meanwhile has been impeded by their often para-
magnetic nature, which frustrates analysis with NMR
techniques and by their preponderance toward one-electron
reactivity, which demands a subtly different approach in terms
of ligand design and reaction conditions.
Recent research focused on this area has shown remarkable
advances in the performance of these types of catalysts in olefin
polymerizations, hydrogenations, and hydroborations1−10 using
a variety of ligands that promote either metal- or ligand-based
redox chemistry, or via cooperative substrate activation without
redox chemistry. This array of mechanistic facility is possibly
owing to the diminished role of purely metal-based redox in the
first- versus second- and third-row transition elements and
currently highlights our lack of fundamental understanding of
the behavior of these complexes.
Our approach includes using pincer ligands with amide
donors (Scheme 1), in particular, those that can promote a
reactive square-planar geometry with possible bifunctional
behavior. With this in mind, we chose to investigate first-row
transition metal derivatives of the diamino−pyridine ligand,
which has been employed for a relatively limited number of
transition metals (e.g., Ti, Zr, Re, Ru, Pd)11−18 and theoretically
allows for square-planar coordination with a monodentate
coligand, in both neutral (protonated) and dianionic forms.
This ligand is closely related to the successful di-imino−
pyridine ligand, which is well-known to be redox-active, and the
Received: April 8, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00779
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
bis(arylcarboxamido) pyridine ligand, assumed to be redox and
chemically innocent.19−22
bound in a tridenate fashion, with approximately square-planar
geometry at the metal centers and a pyridine bound directly
trans to the pyridine donor of the NNN ligand (Figure 1). The
RESULTS AND DISCUSSION
■
Because of the complications of handling the unstable
[NNN]Li2 salt,23 the aminolysis route to “M[NNN]”-type
complexes was chosen (NNN = 2,6-bis(2,6-diisopropylpheny-
lamido-methyl)pyridine). The reaction between M-
(CH2SiMe3)2(py)2 (M = Fe, Co; py = pyridine)24,25 and
[NNN.H2] yielded the new complexes M[NNN](py) (M = Fe
(1) and Co(2)) as dark purple and red crystalline solids,
respectively, in moderate to good yields (1: 65%, 2: 86% yield;
Scheme 2). 1 and 2 were found to be highly air- and moisture-
Scheme 2. Two Synthetic Routes to Square-Planar
Diamido−Pyridine Complexes 1 and 2
Figure 1. Thermal ellipsoid plot of the structure of one molecule in
unit cell of [22.(C7H8)3]; isopropyl groups and hydrogen atoms
omitted for clarity, except for pincer backbone hydrogens, ellipsoids at
50% probability.
pyridine fragment is rotated toward the plane of the aryl ring of
the adjacent groups of 2,6-di-isopropylphenyl (Dipp), presum-
ably due to attractive forces between the π systems. The
pyridine nitrogen atoms are almost colinear with the metal
center (∠N(py)−M−N(py) = 179.17(10) and 176.71(10) for
1; 179.6(3) and 177.8(3) for 2), whereas there is a slight
distortion from ideal square-planar coordination with the
binding of the amide donors (∠N(amide)−M−N(amide)
N(1) = 164.85(9) and 165.71(10) for 1; 167.4(2) and
168.3(3) for 2). M−N(amide) distances are typical (average
(av) 1.902 Å for 1; 1.865(6) Å for 2). We observe that the
pyridine component of the pincer ligand system is bound
slightly closer than the other pyridine molecule, as expected for
a chelating ligand (e.g., in 2, Co−N(py-NNN) av 1.851(5) and
1.843(6) Å vs Co−N(py) 1.913(6) and 1.912(6) Å).
These are the first reported structures containing a diamido−
pyridine ligand bound to a four-coordinate metal center, and
they show a great deal of similarity to related di-imino−pyridine
ligated species with the exception of the C−C−N angles and
distances (as would be expected).19,20 The methylene protons
were located crystallographically, with angles consistent with
the anticipated sp3 hybridized carbon atoms (av ∠C(o-py)−
C(methylene)−N(amide) 109.8(6)°), and the C(methylene)−
N(amide) and C(o-py)−C(methylene) distances are consistent
with single bonds (av 1.455(9) and 1.491(10) Å, respectively).
To increase reactivity of these species for small-molecule
activation chemistry and catalysis, we attempted to synthesize
base-free complexes of the type M[NNN]. The (nonpincer
ligand) pyridine coligand within 1 and 2 is strongly bound and
could not be removed using typical desolvation procedures
(heat and/or high vacuum), nor could it be readily displaced by
other solvents, for example, tetrahydrofuran (THF). Therefore,
the syntheses of these complexes were attempted in the
absence of coordinating solvents. When CoCl2 was used in the
place of CoCl2(py)4, in the absence of coordinating solvents,
instead of the intended three-coordinate complex, the four-
coordinate bis-ligated species Co[NNN.H]2 (3) was obtained
in 21% yield (Scheme 3). Similar reactions with FeCl2 did not
yield tractable products.
sensitive. Further experimentation revealed that an easier route
could be accessed by the addition of 2 equiv of LiCH2SiMe3 as
a base to “MCl2[NNN.H2](py)x” (formed in situ from
MCl2(py)4 (M = Fe, Co) and [NNN.H2]this material was
not characterized, although the iron compound is known)26
with similar isolated yields of 1 and 2. Reaction with 1 equiv of
LiCH2SiMe3 yielded an equimolar mixture of the doubly
deprotonated complex (1 or 2) and starting material, rather
than a complex of the type MCl[NNN.H].
The 1H NMR spectra (C6D6) of 1 and 2 both show
broadened and shifted resonances, consistent with para-
magnetic metal centers. Magnetic susceptibility measurements
using Evans method yielded μeff = 3.71 μB for 1 and μeff = 1.59
μB for 2 consistent with two unpaired (S = 1) and single
unpaired electron (S = 1/2) configurations, respectively. This
would also be consistent with intermediate-spin d6 and low-spin
d7 metal centers in square-planar geometry, respectively. In the
case of 1, the value μeff = 3.71 μB is between spin-only values of
S = 1 (μspin‑only = 2.83 μB) and S = 2 (μspin‑only = 4.90 μB). This
anomaly has been well-documented for similar Fe(II)
porphyrin and phthalocyanine complexes,27 which share the
same D4h symmetry supported by N donors, and is owing to an
orbitally degenerate triplet (S = 1) ground state (3Eg for
iron(II) phthalocyanine,27b which gives μeff ≈ 3.8 μB at T = 100
to 300 K27a). Recently an unsupported high-spin square-planar
Fe(II) complex was reported by Veige et al.28
Unequivocal structural characterization of these molecules
was obtained via single-crystal X-ray diffraction. 1 and 2 were
Complex 3 displays paramagnetically broadened resonances
1
both found to crystallize in the triclinic space group P1, with
within the H NMR spectrum, and a distinctive N−H stretch
̅
two molecules in the unit cell and three molecules of toluene
solvent. The structures reveal that in both cases the ligands are
was found in the IR spectrum at 3350 cm−1 (in addition to
strong features at 2850−3100 cm−1 that overlap with the
B
DOI: 10.1021/acs.inorgchem.5b00779
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 3. Unexpected Synthesis of Bis-Ligand Complex 3
from CoCl2[NNN.H2]
Scheme 4. Synthesis of Di-Imino−Pyridine Complex 4 from
Diamino−Pyridine Starting Materials
was isolated in a crystalline form, it is not a pure, single
compound. Unfortunately, further attempts to purify this
material failed. The continuous wave (CW) electron para-
magnetic resonance (EPR) spectrum showed two peaks
centered at g = 2.001 and g = 2.216 (see Figure S1 in
Supporting Information); the former is likely an organic radical
impurity, whereas the latter is very similar in appearance to the
feature found for Ni[2,6-{(Dipp)NCMe}2C5H3N]Cl and is
likely attributable to 4.31 This peak was assigned as an indicator
of radical anion character of the di-imino−pyridine ligand.
The crystal structure of 4 was solved in monoclinic space
group P21/n, with one molecule of cocrystallized toluene per Ni
complex. In a manner similar to 1 and 2, the metal center is
four-coordinate with a terdentate ligand; the equatorial chloride
ligand is found to be displaced further out of the Ni-[NNN]
plane compared with the equatorial pyridine ligands in 1 and 2,
leading to a more distorted square-planar geometry. The most
significant structural parameters of 4 are the C(o-py)−
C(methylene)−N(amide) angles and C(methylene)−N-
(amide) distances of the pincer arms, which average 115.6(5)
° and 1.320(7) Å, respectively, and are approximately
consistent with an imine functionality. Close inspection reveals
that the CimNim distances are in fact slightly elongated
compared with the neutral PDI ligandalthough still
significantly shorter than a single bondand further indicate
radical anion character.31
pyridine stretches). The crystal structure of 3 was solved in
triclinic space group P1 and exhibits a distorted tetrahedral
geometry at the four-coordinate Co center. Each ligand is
bound through one amide and one pyridine nitrogen atom, and
the remaining dangling amine arm is found to be protonated
(Figure 2). Bond distances and angles are typical for those
Deprotonation at the backbone methylene center has been
reported for similar phosphine−pyridyl [PNP] and [PN] and
amine−dipyridyl [NNN] pincer ligandsin these cases, the
resulting anionic charge is localized on the pyridine nitrogen
atom rather than the α-carbon.32,33 Complete oxidative
dehydrogenation to an imine, as observed herein, is also well-
known for similar ligand systems and is performed by a base/
oxidant combination.34 In many cases, transition metal centers
function as the oxidant; therefore, we propose that a
component of the product mixture is a reduced Ni species,
perhaps metallic Ni(0).
Figure 2. Thermal ellipsoid plot of the core structure of 3; Dipp
groups omitted for clarity, ellipsoids at 40%.
expected for this type of complex.29 Given the low yield and the
unbalanced reactant stoichiometry, it is evident that 3 cannot
be the sole product of this reaction, but we could not isolate
any other compounds from this reaction; the paramagnetism of
the materials precluded useful NMR studies.
Expanding the chemistry to nickel, following identical
synthetic protocols as used for 1 and 2 did not yield the
expected nickel(II) diamido−pyridine complex. The reaction
Given the outcome of the nickel reaction, we were curious as
to whether the diamino−pyridine ligand in the square-planar
complexes 1 or 2 could be converted into a di-imino−pyridine
fragment with the addition of an external oxidant. The cobalt
complex was chosen for this experiment, and trityl chloride was
chosen as an oxidant as it was speculated that the reaction with
complex 2 could logically yield Co[PDI]Cl2 plus 2 equiv of
Ph3CH. Instead, the reaction gave a new species Co[NNN′]Cl2
(5) (NNN′ = 2-(2,6-(diisopropylphenylimino-methyl)-6-(dii-
sopropylphenylamidomethyl)-pyridine) plus an equivalent of
30
between Ni(CH2SiMe3)2(py)2 and [NNN.H2] gave metallic
Ni (mirror) and uncharacterized decomposition products. The
reaction between “NiCl2(py)x.[NNN.H2]” and 2 equiv of
LiCH2SiMe3 meanwhile gave a mixture of products, including a
di-imino−pyridine species Ni[PDI](Cl) (4), which was
obtained as a component of a homogeneous mixture of dark
purple crystals (Scheme 4; PDI = 2,6-bis(2,6-
diisopropylphenyliminomethyl)pyridine). The mechanism of
the formation of this species is unclear, but it involves
additional loss of two methylene hydrogen atoms, presumably
with a strong driving force toward the formation of a
1
the Gomberg dimer Ph3CC6H5CPh2 as detected by H NMR
spectroscopy (Scheme 5). 5 displays a unique, paramagnetically
1
shifted H NMR spectrum, consistent with the presence of a
Co2+ center.
1
conjugated π system. The H NMR spectrum of this solid
5 contains an oxidatively rearranged, asymmetric imino−
amino−pyridine ligand, which is found to be protonated at the
showed a multitude of peaks, which suggests that although it
C
DOI: 10.1021/acs.inorgchem.5b00779
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
been shown to be susceptible to chemical oxidation: we observe
conversion into a di-imino−pyridine ligand on a Ni center
during a salt metathesis reaction, and into an asymmetric
imino−amino−pyridine on a Co center by additional of trityl
chloride to a well-defined diamido−pyridine complex.
Scheme 5. Synthesis of 5 from 2
Although the conditions reported herein are dramatically
different from those found in catalytic applications,26 this work
shows that catalysts based on the diamido−pyridine ligand may
not be chemically resistant to oxidation under certain
conditions. It would be expected that alkyl substitution at the
methylene linker would prevent oxidation of the C−N bond,
for example, with the use of disubstituted pincer 2,6-bis(2,6-
diisopropylphenylamido-2-isopropyl)pyridine.18
amine nitrogen and is overall charge neutral. This structure was
revealed via X-ray diffraction methods and was solved in
monoclinic space group P21/n. The molecule exhibits a five-
coordinate metal complex as shown in Figure 3. The
EXPERIMENTAL SECTION
■
Unless noted otherwise, all operations were performed under a
purified argon atmosphere in a standard MBraun UniLab drybox or
under an argon atmosphere using high-vacuum and Schlenk
techniques. Anhydrous hydrocarbon solvents were purchased from
Sigma-Aldrich and further dried over activated 4 Å molecular sieves.
Deuterated solvents were purchased from Cambridge Isotope
Laboratory and dried over 4 Å molecular sieves. Unless noted,
chemicals were purchased from commercial sources and used without
further purification. [NNN]H2 ,37 CoCl2 (py)4 ,25 Co-
(CH2SiMe3)2(py)2,25 FeCl2(py)4,24 Fe(CH2SiMe3)2(py)2,24
30
NiCl2(py)4,30 and Ni(CH2SiMe3)2(py)2 were prepared according
to the literature. All NMR spectra were recorded using a Bruker 400
Ultra Shield spectrometer. 1H NMR spectra were referenced to solvent
residual peaks (δ 7.15 ppm for C6D6, δ 1.72 and 3.58 ppm (compound
5) for THF-d8). Infrared spectra were measured as KBr discs using a
PerkinElmer Spectrum Two FTIR spectrometer. Solution magnetic
susceptibilities were calculated using the Evans method.38 Elemental
analyses were performed by Midwest Microlab (Indianapolis, IN) or
UC Berkeley Microanalytical Laboratory. The CW EPR spectra were
collected on a Bruker model E500 (Bruker BioSpin, Billerica, MA)
operating in the X-band microwave frequency range equipped with a
Bruker SHQE resonator. The CW spectra were collected at room
temperature. Spectra were acquired using a modulation amplitude of
10 G, a frequency modulation of 100 kHz, an optimum microwave
power of 1 mW, a conversion time of 163 ms, and a resolution of 1024
points. Minimal background signals were observed for an empty tube.
Preparation of Fe[NNN](py) (1) Method A. A solution of
Fe(CH2SiMe3)2(py)2 was prepared in situ by reaction of FeCl2(py)4
(299 mg, 0.67 mmol) and 2 equiv of LiCH2SiMe3 (127 mg, 1.34
mmol) stirred in cold hexane (−30 °C) and allowed to warm to room
temperature overnight. The solution was filtered, and the solvent was
removed in vacuo. The red oily material was redissolved in cold
toluene (−30 °C), and to this was added 0.9 mol equiv of [NNN]H2
(277 mg, 0.61 mmol) in cold toluene (−30 °C), whereupon the
solution immediately changed to a dark purple color. After the solution
was stirred overnight, the solvent was removed in vacuo, and the
product was recrystallized from a minimal quantity of toluene (ca. 5
mL) at −30 °C. The compound was isolated as a highly crystalline
dark purple solid (234 mg, 0.40 mmol, 65% yield). 1H NMR (C6D6) δ
(ppm) −21.08, −16.27, −11.65, 4.80, 7.44, 16.17, 20.84, 47.83
(broad). μeff (benzene-d6) = 3.74 μB. Anal. Calcd. (%) for C36H46N4Fe
(found) C 73.20 (72.91) H 7.85 (7.95) N 9.49 (9.12).
Figure 3. Thermal ellipsoid plot of the structure of 5; isopropyl groups
and hydrogen atoms of Dipp substituents omitted for clarity, ellipsoids
at 50% probability.
asymmetry of the complex is clearly apparentalthough
equivalent in the parent complex 2, the Co(1)−N(1)
2.299(4) Å and Co(1)−N(3) 2.171(4) Å distances indicate
different donor properties and are longer than the Co−
N(amide) distances found in 2. The N3−C19 distance of
1.281(6) Å and N3−C13−C18 angle of 118.0(4)° are
consistent with an imine functionality, whereas the N1−C13
distance 1.495(5) Å and N1−C13−C14 angle 112.1(4)° are
consistent with an amine/amide. The latter was confirmed as a
protonated amine by crystallographic location of the hydrogen
atom, in conjunction with the longer Co−N1 distance and the
nonplanar geometry at the nitrogen center (i.e., sp3 rather than
sp2 hybridized). IR spectroscopy revealed a distinctive N−H
stretch at 3335 cm−1.
This type of asymmetric imino−amino−pyridine ligand is
known and has been used to stabilize a variety of metal centers
in its neutral form, for example, Mn, Fe, and Co.26,35 These
complexes have been found to be moderately active catalysts
for olefin polymerization. The ligands used in these studies are
typically accessed via 1,2-addition reactions from the di-imino−
pyridine ligand,36 as opposed to the reaction found here, where
oxidation of a bound diamino−pyridine ligand has led to a
rearrangement of a methylene proton.
Method B. A solution of FeCl2(py)4 (387 mg, 0.88 mmol) and
[NNN]H2 (400 mg, 0.88 mmol) was stirred in toluene, producing a
yellow precipitate. After 30 min, the solution was cooled to −30 °C
and 2 equiv of LiCH2SiMe3 (164 mg, 1.76 mmol) in cold toluene
(−30 °C) was added, whereupon the solution immediately changed to
a dark purple color. After the solution was stirred overnight, the
solvent was removed in vacuo, and the product redissolved in a
minimal quantity of toluene (ca. 5 mL) and filtered (diatomaceous
earth). The compound was recrystallized from this solution at −30 °C
and isolated as a highly crystalline dark purple solid (384 mg, 0.65
mmol, 74% yield).
CONCLUSION
■
In summary, we have synthesized two new square-planar
complexes 1 and 2 based on the ostensibly “innocent”
diamido−pyridine ligand. However, this ligand framework has
D
DOI: 10.1021/acs.inorgchem.5b00779
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Preparation of Co[NNN](py) (2) Method A. A solution of
Co(CH2SiMe3)2(py)2 was prepared in situ by reaction of CoCl2(py)4
(300 mg, 0.67 mmol) and 2 equiv of LiCH2SiMe3 (127 mg, 1.34
mmol) stirred in cold hexane (−30 °C) and allowed to warm to room
temperature overnight. The solution was filtered and solvent removed
in vacuo. The green oily material was redissolved in cold toluene (−30
°C) and to this was added 0.9 mol equiv of [NNN]H2 (277 mg, 0.61
mmol) in cold toluene (−30 °C), whereupon the solution immediately
changed to a dark blood red color. After the solution was stirred
overnight, the solvent was removed in vacuo, and the product
recrystallized from a minimal quantity of toluene (ca. 5 mL) at −30
°C. The compound was isolated as a highly crystalline dark red solid
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic data in CIF format and tables of bond
distances for 1, 2, 3, 4 and 5, and the EPR spectrum of 4. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.inorgchem.5b00779.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: jgordon@lanl.gov. (J.C.G.)
*E-mail: osummerscales@lanl.gov. (O.T.S.)
1
(310 mg, 0.52 mmol, 86% yield). H NMR (C6D6) δ (ppm) −4.94,
Notes
0.42, 4.75, 18.37, 19.61 (broad); μeff (benzene-d6) = 1.59 μB. Anal.
Calcd. (%) for C36H46N4Co (found) C 72.82 (72.99) H 7.81 (8.07) N
9.44 (9.26).
The authors declare no competing financial interest.
Method B. A solution of CoCl2(py)4 (392 mg, 0.88 mmol) and
[NNN]H2 (400 mg, 0.88 mmol) was stirred in toluene, producing a
bright blue precipitate. After 30 min, the solution was cooled to −30
°C, and 2 equiv of LiCH2SiMe3 (164 mg, 1.76 mmol) in cold toluene
(−30 °C) was added, whereupon the solution immediately changed to
a dark blood red color. After the solution was stirred overnight, the
solvent was removed in vacuo, and the product was redissolved in a
minimal quantity of toluene (ca. 5 mL) and filtered (diatomaceous
earth). The compound was recrystallized from this solution at −30 °C
and isolated as a highly crystalline dark red solid (381 mg, 0.64 mmol,
73% yield).
Preparation of Co[NNN.H]2 (3). A solution of CoCl2 (85 mg,
0.66 mmol) and [NNN]H2 (300 mg, 0.66 mmol) was stirred in
toluene, producing a bright blue precipitate. After 30 min, the solution
was cooled to −30 °C, and 2 equiv of LiCH2SiMe3 (123 mg, 1.32
mmol) in cold toluene (−30 °C) was added, whereupon the solution
immediately changed to a dark green color. After the solution was
stirred overnight, the solvent was removed in vacuo, and the product
was redissolved in a minimal quantity of hexane (ca. 10 mL) and
filtered (diatomaceous earth). The compound was recrystallized from
this solution at −30 °C and isolated as a highly crystalline dark green
solid (132 mg, 0.14 mmol, 21% yield). 1H NMR (C6D6) δ (ppm) 1.25,
3.54, 4.25 (broad); IR (KBr, selected) 3350 cm−1 (N−H stretch).
Anal. Calcd. (%) for C62H84N6Co (found) C 76.58 (76.62) H 8.71
(8.89) N 8.65 (8.98).
Preparation of Ni[PDI](Cl) (4). A solution of NiCl2(py)4 (146 mg,
0.33 mmol) and [NNN]H2 (150 mg, 0.33 mmol) was stirred in
toluene, producing a cream colored precipitate. After 30 min, the
solution was cooled to −30 °C, and 2 equiv of LiCH2SiMe3 (62 mg,
0.66 mmol) in cold toluene (−30 °C) was added, whereupon the
solution immediately changed to a dark purple color. After the solution
was stirred overnight, the solvent was removed in vacuo, and the
product was redissolved in a minimal quantity of hexane (ca. 5 mL)
and filtered (diatomaceous earth). The compound was recrystallized
from this solution at −30 °C and isolated as an impure crystalline dark
purple solid from which single crystals of the product were obtained
for structural analysis.
ACKNOWLEDGMENTS
■
We would like to thank Laboratory Directed Research and
Development (LDRD) for a Director’s postdoctoral fellowship
(O.T.S.). We are grateful for the use of the Bruker X-ray
diffractometer purchased via the National Science Foundation
CRIF:MU award to Prof. R. Kemp of the Univ. of New Mexico
(CHE04-43580) and Dr. T. J. Boyle at Sandia National
Laboratories for data collection. Los Alamos National
Laboratory is operated by Los Alamos National Security,
LLC, for the National Nuclear Security Administration of the
U.S. Department of Energy under Contract No. DE-
AC5206NA25396.
REFERENCES
■
(1) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428.
(2) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Mastroianni,
S.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. J. Chem.
Soc., Dalton Trans. 2001, 1639.
(3) Obligacion, J. V.; Chirik, P. J. J. Am. Chem. Soc. 2013, 135, 19107.
(4) Tondreau, A. M.; Stieber, S. C. E.; Milsmann, C.; Lobkovsky, E.;
Weyhermueller, T.; Semproni, S. P.; Chirik, P. J. Inorg. Chem. 2013,
52, 635.
(5) Zhang, G.; Hanson, S. K. Org. Lett. 2013, 15, 650.
(6) Zhang, G.; Hanson, S. K. Chem. Commun. 2013, 49, 10151.
(7) Zhang, G.; Vasudevan, K. V.; Scott, B. L.; Hanson, S. K. J. Am.
Chem. Soc. 2013, 135, 8668.
(8) Obligacion, J. V.; Semproni, S. P.; Chirik, P. J. J. Am. Chem. Soc.
2014, 136, 4133.
(9) Russell, S. K.; Hoyt, J. M.; Bart, S. C.; Milsmann, C.; Stieber, S. C.
E.; Semproni, S. P.; DeBeer, S.; Chirik, P. J. Chem. Sci. 2014, 5, 1168.
(10) Semproni, S. P.; Milsmann, C.; Chirik, P. J. J. Am. Chem. Soc.
2014, 136, 9211.
(11) Feng, Y.; Aponte, J.; Houseworth, P. J.; Boyle, P. D.; Ison, E. A.
Inorg. Chem. 2009, 48, 11058.
(12) Lilly, C. P.; Boyle, P. D.; Ison, E. A. Dalton Trans. 2011, 40,
11815.
(13) Arnaiz, A.; Cuevas, J. V.; Garcia-Herbosa, G.; Carbayo, A.;
Casares, J. A.; Gutierrez-Puebla, E. J. Chem. Soc., Dalton Trans. 2002,
2581.
(14) del Rio, I.; Gossage, R. A.; Lutz, M.; Spek, A. L.; van Koten, G.
Inorg. Chim. Acta 1999, 287, 113.
Preparation of Co[NNN′]Cl2 (5). To a solution of 2 (122 mg,
0.21 mmol) in THF, 2 equiv of Ph3CCl was added (115 mg, 0.42
mmol), whereupon the solution immediately changed from red to an
emerald green color. After the solution was stirred overnight, the
solvent was removed in vacuo, and the remaining solid was washed
with hexane to leave the product in an analytically pure form (110 mg,
0.19 mmol, 89% yield). 1H NMR analysis of the yellow hexane
(15) Guer
1996, 15, 5085.
(16) Guerin, F.; McConville, D. H.; Vittal, J. J.; Yap, G. A. P.
́
in, F.; McConville, D. H.; Payne, N. C. Organometallics
́
1
washings after removal of volatiles showed pure Ph3CC6H5CPh2. H
Organometallics 1998, 17, 5172.
NMR (d8-THF) δ (ppm) −31.4, −18.47, −4.44, 4.01, 7.71, 31.9, 34.9,
41.7 (broad); IR (KBr, selected) 3335 cm−1 (N−H stretch). Anal.
Calcd. (%) for C31H43N3CoCl2 (found) C 63.37 (63.79) H 7.38 (7.93)
N 7.15 (7.04).
(17) Scollard, J. D.; McConville, D. H.; Payne, N. C.; Vittal, J. J.
Macromolecules 1996, 29, 5241.
(18) Tay, B.-Y.; Wang, C.; Chia, S.-C.; Stubbs, L. P.; Wong, P.-K.;
van Meurs, M. Organometallics 2011, 30, 6028.
E
DOI: 10.1021/acs.inorgchem.5b00779
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(19) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004,
126, 13794.
(20) Bart, S. C.; Chlopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky,
E.; Neese, F.; Wieghardt, K.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128,
13901.
(21) Boyce, D. W.; Salmon, D. J.; Tolman, W. B. Inorg. Chem. 2014,
53, 5788.
(22) Pirovano, P.; Magherusan, A. M.; McGlynn, C.; Ure, A.; Lynes,
A.; McDonald, A. R. Angew. Chem., Int. Ed. 2014, 53, 5946.
(23) Cruz, C. A.; Emslie, D. J. H.; Harrington, L. E.; Britten, J. F.;
Robertson, C. M. Organometallics 2007, 26, 692.
(24) Campora, J.; Naz, A. M.; Palma, P.; Alvarez, E.; Reyes, M. L.
Organometallics 2005, 24, 4878.
(25) Zhu, D.; Janssen, F. F. B. J.; Budzelaar, P. H. M. Organometallics
2010, 29, 1897.
(26) Britovsek, G. J. P.; Gibson, V. C.; Mastroianni, S.; Oakes, D. C.
H.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Eur. J.
Inorg. Chem. 2001, 2001, 431.
(27) (a) Dale, B. W.; Williams, R. J. P.; Johnson, C. E.; Thorp, T. L. J.
Chem. Phys. 1968, 49, 3441. (b) Kuz’min, M. D.; Savoyant, A.; Hayn,
R. J. Chem. Phys. 2013, 138, 244308. (c) Goff, H.; La Mar, G. N.; Reed,
C. A. J. Am. Chem. Soc. 1977, 99, 3641. (d) Strauss, S. H.; Silver, M. E.;
Long, K. M.; Thompson, R. C.; Hudgens, R. A.; Spartalian, K.; Ibers, J.
A. J. Am. Chem. Soc. 1985, 107, 4207. (e) Da Silva, C.; Bonomo, L.;
Solari, E.; Scopelliti, R.; Floriani, C.; Re, N. Chem. - Eur. J. 2000, 6,
4518. (f) Hu, C.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. Inorg. Chem.
2007, 46, 619.
(28) Pascualini, M. E.; Di Russo, N. V.; Thuijs, A. E.; Ozarowski, A.;
Stoian, S. A.; Abboud, K. A.; Christou, G.; Veige, A. S. Chem. Sci. 2015,
6, 608.
(29) Roecker, L.; Akande, J.; Elam, L. N.; Gauga, I.; Helton, B. W.;
Prewitt, M. C.; Sargeson, A. M.; Swango, J. H.; Willis, A. C.; Xin, T. P.;
Xu, J. Inorg. Chem. 1999, 38, 1269.
(30) Carmona, E.; Gonzalez, F.; Poveda, M. L.; Atwood, J. L.;
Rogers, R. D. J. Chem. Soc., Dalton Trans. 1981, 777.
(31) Manuel, T. D.; Rohde, J.-U. J. Am. Chem. Soc. 2009, 131, 15582.
(32) Murso, A.; Stalke, D. Dalton Trans. 2004, 2563.
(33) Murso, A.; Straka, M.; Kaupp, M.; Bertermann, R.; Stalke, D.
Organometallics 2005, 24, 3576.
(34) Machkour, A.; Mandon, D.; Lachkar, M.; Welter, R. Eur. J. Inorg.
Chem. 2005, 2005, 158.
(35) Gibson, V. C.; McTavish, S.; Redshaw, C.; Solan, G. A.; White,
A. J. P.; Williams, D. J. Dalton Trans. 2003, 221.
(36) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.; White, A. J.
P.; Williams, D. J. Chem. Commun. 1998, 2523.
(37) Guer
15, 5586.
(38) Evans, D. F. J. Chem. Soc. 1959, 2003.
́
in, F.; McConville, D. H.; Vittal, J. J. Organometallics 1996,
F
DOI: 10.1021/acs.inorgchem.5b00779
Inorg. Chem. XXXX, XXX, XXX−XXX