Linkage isomerism in transition-metal complexes of mixed (arylcarboxamido)(arylimino)pyridine ligands

Article abstract of DOI:10.1021/ic500638z

The synthesis of a series of asymmetric mixed 2,6-disubstituted (arylcarboxamido)(arylimino)pyridine ligands and their coordination chemistry toward a series of divalent first-row transition metals (Cu, Co, and Zn) have been explored. Complexes featuring both anionic N,N,N″-carboxamido and neutral O,N,N-carboxamide coordination have been prepared and characterized by X-ray crystallography, cyclic voltammetry, and UV-visible and EPR spectroscopy. Specifically, ^RLM(X) (M = Cu; X = Cl^-, OAc^-) and ^RL(H)MX₂ (M = Cu, Co, Zn; X = Cl^-, SbF ₆^-) complexes that feature N,N,N″- or O,N,N-coordination are presented. Base-induced linkage isomerization from O,N,N-carboxamide to N,N,N″-carboxamido coordination is also confirmed by multiple forms of spectroscopy.

Full text of DOI:10.1021/ic500638z

Article
pubs.acs.org/IC
Open Access on 05/12/2015
Linkage Isomerism in Transition-Metal Complexes of Mixed
(Arylcarboxamido)(arylimino)pyridine Ligands
David W. Boyce, Debra J. Salmon, and William B. Tolman*
Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis,
Minnesota 55455, United States
S
* Supporting Information
ABSTRACT: The synthesis of a series of asymmetric mixed 2,6-
disubstituted (arylcarboxamido)(arylimino)pyridine ligands and their
coordination chemistry toward a series of divalent first-row transition
metals (Cu, Co, and Zn) have been explored. Complexes featuring both
anionic N,N′,N″-carboxamido and neutral O,N,N′-carboxamide coordina-
tion have been prepared and characterized by X-ray crystallography, cyclic
voltammetry, and UV−visible and EPR spectroscopy. Specifically, RLM(X)
R
(M = Cu; X = Cl−, OAc−) and L(H)MX2 (M = Cu, Co, Zn; X = Cl−,
−
SbF6 ) complexes that feature N,N′,N″- or O,N,N′-coordination are
presented. Base-induced linkage isomerization from O,N,N′-carboxamide
to N,N′,N″-carboxamido coordination is also confirmed by multiple forms
of spectroscopy.
INTRODUCTION
■
In their doubly deprotonated form, bis(arylcarboxamido)-
pyridines 1 have been used as ligands to support nickel and
copper complexes that exhibit novel properties. A unique
anionic copper(II)−superoxide complex supported by 12− (R =
iPr) acts as a nucleophile, in contrast to other such species
supported by neutral N-donor ligands.1,2 Monoanionic nickel-
(II)− and copper(II)−hydroxide complexes supported by 12−
(R = iPr or Me) undergo CO2 fixation reactions at
exceptionally high rates3 and react with CH3CN in an
unprecedented manner to yield cyanomethide complexes,
[(12−)M(CH2CN)]− (R = Me, M = Ni or Cu).4 In addition,
one-electron oxidation of the copper(II)−hydroxide complexes
yields thermally unstable Cu(III) species that rapidly oxidize
dihydroanthracene via hydrogen atom abstraction (HAT).4,5
Among the various factors that underlie these unique
observations, the dianionic nature and strong electron-donating
properties of the supporting ligand 12− would appear to be key.
As part of ongoing studies of these various influences, we asked:
What would be the consequences of decreasing the negative
charge of the supporting ligand while keeping the steric
properties approximately constant?
As a first step toward addressing this question experimentally,
we targeted ligands 2a−2c for synthesis and study of their
coordination chemistry. These ligands may be viewed as a
hybrid of the aforementioned 1 and bis(arylimino)pyridines
like 3, which have been widely studied,6 including with Cu(II).7
Ligand 2b has been reported, but only as a product of an
oxidation of a reduced Ni(II) complex of 3.8 A direct large-scale
synthesis was not described, and 2a and 2c are new. Alkyl-
substituted analogues 4, which, in deprotonated form, would be
expected to be more basic than monoanionic versions 2a−2c,
have been used to prepare Ni(II), Pd(II), and Fe(II) catalysts
(e.g., for olefin polymerizations).9 Ligands 510 and 611 are
noteworthy relatives of 2a−2c, insofar as they contain similar
tridentate, mer, monoanionic N-donor sets.
Received: March 19, 2014
Published: May 12, 2014
© 2014 American Chemical Society
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Herein, we report reproducible, large-scale synthetic routes
to 2a−2c and the results of explorations of their ability to
complex to divalent metal ions, with an emphasis on Cu(II).
We found that metalations in the absence of base result in
complexes that exhibit carboxamide O,N,N′-coordination and
that subsequent treatment of these compounds with base
induces isomerization to carboxamido N,N′,N″-coordination.
The structural and spectroscopic characterization of the
complexes provides a foundation for future studies of
biomimetic and/or catalytic reactivity.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Ligands and
R
N,N′,N″-Bound Complexes LCuX (X = Cl−, OAc−). The
report of iPr2L(H) (2b)8 sparked our interest in
arylcarboxamido(arylimino)pyridine ligands and motivated the
development of a large-scale synthesis that could be modified to
enable access to a series of related ligands with variable aryl
substitution. We found that treatment of 6-acetylpicolinic acid
with oxalyl chloride, followed by the desired aniline in the
presence of NEt3, yielded ketocarboxamide precursors 7
(Scheme 1). Addition of 7a or 7b to a preformed mixture of
Scheme 1
Figure 1. Representations of the X-ray crystal structures of (a)
iPrMeL(H) (2c), (b) iPr2LCuCl (8b), (c) Me2LCuCl (8a), and (d)
iPr2LCuOAc (9b), showing all non-hydrogen atoms as 50% thermal
ellipsoids. See Table 1 for selected interatomic distances and angles.
R
TiCl4 and the second aniline provided L(H) (2a−2c) in a
all of the X-ray structures, each of which shows a tetragonal
geometry for the Cu(II) ion. Disparate Cu−N bond distances
within each complex are seen, with the trend Cu−N(pyridyl) <
Cu−N(amide) < Cu−N(imine) reflected by the average
distances of 1.927, 1.980, and 2.100 Å, respectively. The
observation of the shortest Cu−N bond for the pyridyl group is
consistent with previously reported structures of complexes of
bis(arylcarboxamido)pyridine or diiminopyridine ligands 1 and
3.12 Apparently, as a result of decreased steric bulk of its
methyl-substituted aryl groups, the X-ray structure of Me2LCuCl
(8a) is composed of polymeric repeating units resulting from
axial coordination of the carboxamide carbonyl of one
“monomer” to the copper center of a neighboring unit (8a;
Cu1−O1′1 = 2.345(3) Å) (Figure 1c). Similar axial
coordination, albeit intramolecular and involving an acetate
ligand O atom, is observed in iPr2LCuOAc (9b; Cu1−O2 =
2.369(2) Å; Figure 1d) and iPrMeLCuOAc (9c; Cu1−O3 =
2.456(3) Å; Figure S6b, Supporting Information).
total yield of up to 47%. The indicated formulations for 7a,7b
and 2a−2c were supported by H and 13C NMR spectroscopy
1
and, in the case of iPrMeL(H) (2c), X-ray crystallography. In the
X-ray crystal structure of 2c, the amide, pyridine, and imine
moieties are coplanar, but with the imine donor facing away
from the putative metal ion binding pocket (Figure 1a and
Table 1).
Treatment of RL(H) (2a−2c) with sodium methoxide in the
presence of CuCl2 yielded complexes RLCuCl (8a−8c)
(Scheme 2). Related complexes RLCuOAc (9b,9c) were
synthesized by refluxing iPr2L(H) (2b) or iPrMeL(H) (2c),
respectively, with Cu(OAc)2·H2O in MeCN. The formulations
of all of these compounds are supported by UV−vis and EPR
spectroscopy, ESI mass spectrometry, and X-ray crystallo-
graphic data (8a, 8b, and 9b in Figure 1; 8c and 9c in Figure
S2, Supporting Information). Similar N,N′,N″-coordination of
their arylcarboxamido(arylimino)pyridine ligands is apparent in
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a
Table 1. Selected Interatomic Distances (Å) and Angles (deg) for the Indicated X-ray Crystal Structures
iPrMeL(H) (2c)
Me2LCuCl (8a)
N(1)−C(1)
O(1)−C(1)
C(2)−N(3)
1.344(3)
1.223(3)
1.260(3)
O(1)−C(1)−N(1)
124.0(3)
114.2(2)
126.6(2)
122.6(2)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−Cl(1)
Cu(1)−O(1)′
2.005(3)
1.934(3)
2.130(3)
2.2092(10)
2.345(3)
N(2)−Cu(1)−N(1)
N(2)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−Cl(1)
N(1)−Cu(1)−Cl(1)
N(3)−Cu(1)−Cl(1)
80.18(12)
77.58(11)
154.56(11)
172.53(9)
102.41(9)
98.25(8)
N(1)−C(1)−C(3)
N(3)−C(2)−C(8)
C(2)−N(3)−C(21)
iPr2LCuCl (8b)
iPrMeLCuCl (8c)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−Cl(1)
1.960(3)
1.939(2)
2.098(3)
2.1923(9)
N(2)−Cu(1)−N(1)
N(2)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−Cl(1)
N(1)−Cu(1)−Cl(1)
N(3)−Cu(1)−Cl(1)
81.68(10)
77.43(10)
159.01(10)
175.40(8)
102.31(8)
98.65(8)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−Cl(1)
1.962(3)
1.926(3)
2.070(3)
2.1755(10)
N(2)−Cu(1)−N(1)
N(2)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−Cl(1)
N(1)−Cu(1)−Cl(1)
N(3)−Cu(1)−Cl(1)
81.14(12)
77.92(12)
158.74(12)
173.84(9)
102.66(9)
98.52(9)
iPr2LCuOAc (9b)
iPrMeLCuOAc (9c)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−O(2)
Cu(1)−O(3)
1.999(3)
1.913(3)
2.127(3)
2.369(2)
1.921(2)
N(2)−Cu(1)−O(3)
N(2)−Cu(1)−N(1)
O(3)−Cu(1)−N(1)
N(2)−Cu(1)−N(3)
O(3)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−O(2)
O(3)−Cu(1)−O(2)
174.69(10)
81.39(11)
103.75(10)
78.02(10)
97.06(10)
157.92(10)
117.31(10
60.32(9)
Cu(1)−N(1)
Cu(1)−N(2)
Cu(1)−N(3)
Cu(1)−O(2)
Cu(1)−O(3)
1.974(2)
1.923(2)
2.075(2)
1.932(2)
2.456(3)
N(2)−Cu(1)−O(2)
N(2)−Cu(1)−N(1)
O(2)−Cu(1)−N(1)
N(2)−Cu(1)−N(3)
O(2)−Cu(1)−N(3)
N(1)−Cu(1)−N(3)
N(2)−Cu(1)−O(3)
O(2)−Cu(1)−O(3)
167.88(11)
81.31(9)
103.56(10)
78.15(9)
96.17(10)
159.32(9)
134.20(11)
55.70(11)
[
iPr2L(H)Cu(MeCN)][(SbF6)2] (10)
[
iPrMeL(H)Cu(H2O)THF][(SbF6)2] (12)
Cu(1)−O(1)
Cu(1)−N(3)
Cu(1)−N(4)
Cu(1)−N(2)
1.9910(16)
N(2)−Cu(1)−O(1)
N(4)−Cu(1)−N(3)
O(1)−Cu(1)−N(3)
N(2)−Cu(1)−N(4)
N(4)−Cu(1)−O(1)
N(2)−Cu(1)−N(3)
81.21(7)
97.95(8)
161.66(7)
177.88(9)
100.36(8)
80.50(8)
Cu(1)−O(1)
Cu(1)−N(2)
Cu(1)−O(2)
Cu(1)−N(3)
Cu(1)−O(3)
2.044(2)
1.912(2)
1.914(2)
2.067(2)
2.235(2)
N(2)−Cu(1)−O(1)
N(2)−Cu(1)−O(2)
O(2)−Cu(1)−O(1)
N(2)−Cu(1)−N(3)
O(2)−Cu(1)−N(3)
O(1)−Cu(1)−N(3)
N(2)−Cu(1)−O(3)
O(2)−Cu(1)−O(3)
O(1)−Cu(1)−O(3)
N(3)−Cu(1)−O(3)
79.79(9)
165.24(10)
95.64(9)
79.62(10)
104.13(10)
159.39(9)
99.11(9)
94.92(9)
90.39(8)
93.62(9)
2.0223(19)
1.921(2)
1.8938(19)
iPrMeL(H)CoCl2 (14)
iPrMeL(H)ZnCl2 (15)
Co(1)−O(1)
Co(1)−Cl(1)
Co(1)−N(2)
Co(1)−Cl(2)
Co(1)−N(3)
2.2533(17)
2.2579(8)
2.0537(18)
2.2517(8)
2.2115(19)
N(2)−Co(1)−N(3)
N(2)−Co(1)−Cl(2)
N(3)−Co(1)−Cl(2)
N(2)−Co(1)−O(1)
N(3)−Co(1)−O(1)
Cl(2)−Co(1)−O(1)
N(2)−Co(1)−Cl(1)
N(3)−Co(1)−Cl(1)
Cl(2)−Co(1)−Cl(1)
O(1)−Co(1)−Cl(1)
75.77(7)
120.24(6)
105.85(5)
74.15(7)
149.65(6)
92.76(5)
122.63(6)
100.99(5)
115.67(3)
91.83(5)
Zn(1)−O(1)
Zn(1)−N(2)
Zn(1)−Cl(1)
Zn(1)−Cl(2)
Zn(1)−N(3)
2.2501(18)
2.074(2)
N(2)−Zn(1)−Cl(1)
N(2)−Zn(1)−Cl(2)
Cl(2)−Zn(1)−Cl(1)
N(2)−Zn(1)−O(1)
Cl(2)−Zn(1)−O(1)
Cl(1)−Zn(1)−O(1)
N(2)−Zn(1)−N(3)
Cl(2)−Zn(1)−N(3)
Cl(1)−Zn(1)−N(3)
O(1)−Zn(1)−N(3)
116.92(7)
124.35(7)
118.26(4)
74.05(7)
95.44(6)
94.00(6)
74.19(8)
97.74(6)
105.26(6)
147.73(7)
2.2304(9)
2.2260(8)
2.288(2)
a
Estimated standard deviations are indicated in parentheses. Full lists of atomic coordinates and bond distances are available in the CIFs (Supporting
Information).
R
X-band EPR spectra of solutions of LCuCl (8a−8c) and
RLCuOAc (9b,9c) in CH2Cl2/toluene (1:1 v/v) at 2−30 K
exhibit rhombically distorted axial signals with resolved N-
superhyperfine coupling (8a, 8b in Figure 2; 8c, 9b, 9c, in
Figure S3, Supporting Information). Parameters from spectral
simulations are listed in Table 2 (entries 1−5). These
parameters compare favorably to those obtained for Cu(II)
complexes of bis(arylcarboxamido)pyridine ligand 1, as
illustrated by entries 6 and 7.1,4 From the combined data, it
appears that a gz value of ∼2.2, a large A∥(Cu) ∼ 195 × 10−4
cm−1, and well-resolved N-superhyperfine features are
signatures of N,N′,N″-coordination of the supporting ligand.
The only exception to this generalization is the smaller A∥(Cu)
value and lesser-resolved N-superhyperfine coupling for 8a.
With the data in hand, we can only speculate that the outlier
properties of 8a result from the reduced steric bulk of the aryl
groups in this complex, perhaps enabling axial ligand
interactions with the copper center (as seen in its X-ray
structure) that perturb the EPR spectrum.
Cyclic voltammetry was performed on complexes iPr2LCuCl
(8b) and iPr2LCuOAc (9b) to investigate the effect of the
asymmetric ligand environment on the oxidation potential of
neutral iPr2LCuX (X = Cl−, OAc−) complexes in comparison to
previously studied anionic [(1)CuX−] (R = iPr, X = Cl−)
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Scheme 2
Figure 3. Cyclic voltammograms of [(1)CuCl]− (black trace) and
iPr2LCuCl (8b) (red trace) all performed in acetone (0.1 M Bu4NPF6).
Figure 4. EPR spectra (black) and simulations (gray) of (a)
iPrMeLCuOAc (9c) and (b) [iPrMeL(H)Cu(MeCN)2][(SbF6)2] (11).
Parameters derived from the simulations are listed in Table 2.
Figure 2. EPR spectra (black) and simulations (gray) of (a) Me2LCuCl
(8a) and (b) iPr2LCuCl (8b). Parameters derived from the simulations
are listed in Table 2.
500 mV s−1 resulted in an irreversible oxidative wave (Figure
S5b, Supporting Information). The observed ∼0.5 V larger
oxidation potentials for iPr2LCuCl (8b) and iPr2LCuOAc (9b)
relative to analogues supported by 1 support the hypothesis
that installing the neutral imine donor into the ligand
framework significantly raises the oxidation potential of
N,N′,N″-copper(II) complexes.
compounds. A reversible oxidative wave was observed for
iPr2LCuCl (8b) upon scanning anodically with E1/2 = 0.760 V vs
Fc/Fc+ and ΔEp = 62 mV (50 mV s−1, 0.1 M Bu4NPF6 in
acetone, Figure 3, red trace). In comparison to the analogous
[(1)CuCl]− (R = iPr; E1/2 = 0.296 V vs Fc/Fc+) complex, the
oxidation potential of iPr2LCuCl (8b) is larger by almost 0.5 V
(Figure 3). Data for iPr2LCuOAc (9b) under identical
conditions (0.1 M Bu4NPF6 in acetone) demonstrated a
slightly lower oxidation potential of E1/2 = 0.708 V vs Fc/Fc+
using scan rates of greater than 1000 mV s−1; scan rates below
Synthesis and Characterization of O,N,N′-Bound
Complexes [RL(H)Cu(S)n][SbF6]2 (S = Solvent) and iPrMeL-
(H)MCl2 (M = Co, Cu, Zn). In the absence of coordinating
halides, a variety of solvent-labile cationic copper(II) complexes
a
Table 2. EPR Parameters Derived from Simulations of Experimental X-Band Spectra
entry
compound
gx
gy
gz
A∥(Cu)
A(Nav)
A(Cl)
ref
b
1
2
Me2LCuCl (8a)
iPr2LCuCl (8b)
iPrMeLCuCl (8c)
iPr2LCuOAc (9b)
iPrMeLCuOAc (9c)
2.08
2.05
2.23
2.20
2.185
2.21
2.20
2.190
2.189
2.27
2.27
2.27
2.14
165
196
197
190
194
199
193
165
165
155
12.5
15
12.5
15
b
b
b
b
2.065
2.06
2.09
3
2.045
2.072
2.055
2.064
2.055
2.07
15
15
4
2.037
2.07
15
5
15
6
(12−)Cu(CH3CN) (R = iPr)
(12−)Cu(MeOH) (R = Me)
2.027
2.028
2.06
15.6
15
1
7
4
b
8
[
[
[
iPr2L(H)Cu(MeCN)][(SbF6)2] (10)
iPrMeL(H)Cu(MeCN)2][(SbF6)2] (11)
iPrMeL(H)Cu(H2O)(THF)][(SbF6)2] (12)
b
b
b
9
2.06
2.07
10
11
2.03
2.11
iPrMeL(H)CuCl2 (13)
2.14
2.14
a
b
Measured in frozen solution at 2−30 K; units of A are in 10−4 cm−1. See the Experimental Section or indicated references for details. This work.
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with bound solvent ligands were prepared by treatment of
iPr2L(H) (2b) or iPrMeL(H) (2c) with [Cu(MeCN)5](SbF6)2
(Scheme 3). X-ray crystal structures of the complexes
Scheme 3
[
iPr2L(H)Cu(MeCN)][(SbF6)2] (10, Figure 5b) and [iPrMeL-
(H)Cu(OH2)(THF)][(SbF6)2] (12, Figure 5c) revealed
tetragonal copper ion geometries with O,N,N′-ligation at
typical Cu−O,N distances (Table 1). Metal−ligand bond
distances (Table 1) are generally longer than those in the
N,N′,N″-coordinated complexes, as expected for the differences
in the protonation state of the ligands (neutral charge for
O,N,N′- vs anionic for N,N′,N″-coordination). Longer axial
interactions with counterions (10, Cu−F = 2.662(2) and
2.712(2) Å; 12, Cu−F = 2.719(2) Å) and/or solvent molecules
(12, Cu−O(THF) = 2.235(2) Å) are also present. Also, in 12,
two THF solvate molecules form hydrogen bonds to the bound
water molecule, with H(water)−O(THF) distances of 1.788(9)
and 1.802(11) Å, respectively.
Consideration of the EPR spectra for complexes 10−12
reveals notable differences compared to the spectra for 8 and 9,
which enable N,N′,N″- and O,N,N′-coordination to be
distinguished (Table 2 and Figure S3, Supporting Information).
Notably, the complexes with O,N,N′-coordination display
larger gz (∼2.3 vs 2.2), decreased rhombicity (gx ∼ gy), and
smaller A∥(Cu) values (160 vs ∼190 × 10−4 cm−1). In addition,
N-superhyperfine coupling is not observed for any of the
O,N,N′-copper(II) complexes. These differences are illustrated
in Figure 4, in which data and simulations for iPrMeLCuOAc
(9c) and [iPrMeL(H)Cu(MeCN)2][(SbF6)2] (11) are directly
compared.
Figure 5. Representations of the X-ray crystal structures of (a)
iPrMeL(H)ZnCl2 (15), (b) [iPr2L(H)Cu(MeCN)][(SbF6)2] (10), and
−
(c) [iPrMeL(H)CuOH2(THF)](SbF6)2 (12) (omitting one SbF6 and
showing two additional THF solvate molecules), with all non-
hydrogen atoms shown as 50% thermal ellipsoids and the hydrogen
atoms attached to the amide N atoms and the H2O molecule as
spheres. See Table 1 for selected interatomic distances and angles.
Additional complexes exhibiting O,N,N′-coordination in-
cluded iPrMeL(H)MCl2 (M = Cu, Co, Zn), which were
generated through the combination of divalent metal ions
with iPrMeL(H) (2c) in the absence of added base (Scheme 3).
For example, treatment of iPrMeL(H) (2c) with MCl2 (M = Cu,
Co, Zn) yielded the neutral complexes 13−15. These
complexes were characterized by UV−visible spectroscopy,
ESI-MS, elemental analysis, and, in the cases of 14 (M = Co)
and 15 (M = Zn), by X-ray crystallography. The X-ray
structures of 14 and 15 are essentially isostructural, with five-
coordinate geometries illustrating O,N,N′-binding of the
protonated forms of the arylcarboxamido(arylimino)pyridine
ligand (15 in Figure 5a; 14 in Figure S6c, Supporting
Information). Coordination geometries intermediate between
square-pyramidal and trigonal-bipyramidal are indicated by τ
values of 0.566 (14) and 0.491 (15).13 Consistent with the
solvent-labile cationic copper(II) metal−ligand bond distances,
those in 14 and 15 are elongated relative to those in the
N,N′,N″-coordinated complexes (Table 1). In both structures,
solvent molecules in the crystal lattice propagate hydrogen-
bonding networks through intermolecular interactions with the
amide proton of the bound ligand iPrMeL(H) (2c). In the
absence of suitable crystals for structure determination by X-ray
diffraction, the formulation of 13 (M = Cu) is supported by
CHN analysis results and the presence of a peak envelope for
[
iPrMeL(H)CuCl]+ in the ESI mass spectrum, which is
consistent with the [iPrMeL(H)MCl]+ peaks observed for 14
and 15.
O,N,N′-Carboxamide to N,N′,N″-Carboxamido Link-
age Isomerization. As described above, O,N,N′-bound
complexes of L(H) or N,N′,N″-bound complexes of L− may
be accessed by performing the syntheses in the absence or
presence of base. In addition, we have been able to demonstrate
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or in a Vacuum Atmospheres inert atmosphere glovebox, unless
otherwise stated. Cu(MeCN)5(SbF6)2 was synthesized according to
published procedures.15 2,6-dibromopyridine was recrystallized from
benzene/n-heptane and dried prior to use. The synthesis of 6-
acetylpyridine-2-carboxylic acid was performed according to the
literature,16 with slight modifications (see the Supporting Information
for details).
that addition of base can induce conversion of the former to the
latter type. Such a linkage isomerization reaction was identified
by monitoring reactions of iPrMeL(H)CuCl2 (13) with NEt3 by
EPR and UV−vis spectroscopy (Figures S7 and S8, Supporting
Information). Preparation and analysis of a uniform series of
independent frozen solution (1:1, MeCN/toluene) samples of
iPrMeL(H)CuCl2 (13) after reaction with increasing amounts of
NEt3 (ranging from 0 to 2 equiv of NEt3) by EPR spectroscopy
allowed the reaction to be monitored incrementally. Interest-
ingly, the EPR spectra of iPrMeL(H)CuCl2 (13) exhibit an
isotropic signal, which does not vary upon preparation in
various solvents and analysis under a range of temperatures (2−
30 K). While this signal deviates from the previously observed
spectral features for the O,N,N′- and N,N′,N″-coordinated
copper(II) series of compounds, related isotropic EPR signals
have been reported for similar neutral N,N,N-coordinated CuX2
Physical Methods. UV−vis spectra were recorded with an
HP8453 (190−1100 nm) diode array spectrophotometer. Elemental
analyses were performed by Complete Analysis Laboratories, Inc.
(Parsippany, NJ) and Robertson Microlit Laboratory (Ledgewood,
NJ). EPR spectra were recorded with a Bruker Continuous Wave
EleXsys E500 spectrometer at either 2 or 30 K. EPR simulations were
performed by using Bruker SimFonia software (version 1.25). NMR
spectra were recorded on either Varian VI-300 or VXR 300
1
spectrometers at room temperature. Chemical shifts (δ) for H and
13C NMR spectra were referenced to residual protium in the
deuterated solvent (1H) or the characteristic solvent resonances of
the solvent nuclei (13C). ESI-MS were recorded with a Bruker
BIOTOF II instrument in positive ion mode. Cyclic voltammetry was
performed in a three-electrode cell with a Ag/Ag+ reference electrode,
a platinum auxiliary electrode, and a glassy carbon working electrode
and analyzed with BASi Epsilon software. Tetrabutylammonium
hexafluorophosphate (Bu4NPF6) was used as the supporting electro-
lyte. X-ray crystallography data collections and structure solutions were
conducted by using either Siemens SMART or Bruker APEX II CCD
instruments and the current SHELXTL suite of programs.17
(X = Cl−, ClO4 , SCN−, NO3 ) complexes.14 Upon reaction of
iPrMeL(H)CuCl2 (13) with NEt3, the isotropic EPR signal
diminishes in intensity as features consistent with the axial
signal of iPrMeLCuCl (8c) appear. This axial signal displays g
and A∥(Cu) values in agreement with the EPR spectra of
independently synthesized iPrMeLCuCl (8c).
−
−
Consistent with this result, the progressive addition of
increasing amounts of NEt3 to a solution of iPrMeL(H)CuCl2
(13) results in a color change from orange to dark green, which
is characteristic of iPrMeLCuCl (8c). The absorption features for
the latter reached maximum intensity upon addition of ∼1
equiv of NEt3. Also, single crystals isolated from THF solutions
of iPrMeL(H)CuCl2 (13) after reaction with NEt3 were
determined to be isostructural to those obtained from
independently synthesized iPrMeLCuCl (8c) by X-ray diffraction
analysis.
6-Acetyl-N-(2,6-diisopropylphenyl)picolinamide (7a). 6-Ace-
tyl-2-pyridinecarboxylic acid (1.69 g, 10.3 mmol) was dissolved in
toluene (100 mL), treated with oxalyl chloride (1.39 mL, 16.5 mmol),
and refluxed 16 h under N2. The solvent was removed in vacuo after
cooling the mixture to room temperature. The resulting brown solid
and 2,6-diisopropyl aniline hydrochloride salt (1.1 equiv, 2.4 g, 11.3
mmol) were dissolved in THF (75 mL) and cooled to 0 °C under N2.
Triethylamine (2.5 equiv, 3.6 mL, 25.7 mmol) was then added via
syringe, resulting in the immediate formation of a white precipitate.
After stirring for 15 min at 0 °C, the reaction mixture was warmed to
room temperature and subsequently brought to reflux for 2 h. After
cooling to room temperature, the reaction mixture was filtered and the
resulting brown filtrate was concentrated by rotary evaporation. The
resulting residue was then washed with hexanes to yield a brown solid
and isolated via filtration. The brown solid was then dissolved in a
10:90% EtOAc:pentane solution and passed through charcoal.
Evaporation of the resulting filtrate yielded a white solid (2.46 g,
74%). 1H NMR (300 MHz, CD2Cl2): δH 9.35 (br s, 1H, NH), 8.43 (d,
1H, J = 8.4 Hz, Py H), 8.23 (d, 1H, J = 7.5 Hz, Py H), 8.10 (t, 1H, J =
7.8 Hz, Py H), 7.37 (t, 1H, J = 7.6 Hz, Ar H), 7.26 (d, 2H, J = 7.2 Hz,
Ar H), 3.14 (m, 2H, Ar CH(CH3)2), 2.77 (s, 3H, C(O)CH3), 1.22 (d,
12 H, J = 6.9 Hz, Ar CH(CH3)2). 13C NMR (300 MHz, CD2Cl2): δC
23.9, 26.1, 29.5, 124.1, 124.6, 126.3, 128.9, 131.9, 139.5, 146.9, 149.7,
152.6, 163.4, 199.0. Anal. Calcd for C20H24N2O2: C 74.04, H 7.46, N
8.64. Found: C 73.96, H 7.29, N 8.55.
CONCLUSIONS
■
In conclusion, we have developed a modular synthesis for the
preparation of arylcarboxamido(arylimino)pyridine ligands and
demonstrated their abilities to coordinate a variety of metal(II)
ions (Cu, Co, and Zn). Synthetic procedures for preparation of
complexes featuring anionic N,N′,N″-carboxamido or neutral
O,N,N′-carboxamide ligation, as well as demonstration of
linkage isomerization from O,N,N′- to N,N′,N″-coordination,
have been established within these novel ligand frameworks.
Extensive spectroscopic and structural characterization of a
variety of metal(II) complexes in various coordination
environments has provided an insight into how the asymmetric
carboxamido(arylimino)pyridine framework influences the
properties of these novel complexes. Ongoing investigations
are focused on further establishing how these ligands support
metal complexes in higher oxidation states and their potential
reactivity.
6-Acetyl-N-(2,6-dimethylphenyl)picolinamide (7b). 7b was
synthesized following the identical procedure as was used for 7a,
except with the substitution of 2,6-dimethylaniline for 2,6-diisopropyl
1
aniline (1.92 g, 70%). H NMR (300 MHz, CD2Cl2): δH 9.43 (br s,
1H, NH); 8.44 (d, 1H, J = 7.5 Hz, Py H), 8.22 (d, 1H, J = 7.8 Hz, Py
H), 8.10 (t, 1H, J = 7.8 Hz, Py H), 7.17 (br s, 3H, Ar H), 2.78 (s, 3H,
C(O)CH3), 2.31 (s, 6H, Ar CH(CH3)2). 13C NMR (300 MHz,
CD2Cl2): δC 18.8, 26.1, 124.5, 126.2, 127.8, 128.7, 134.5, 136.0, 139.4,
149.8, 152.6, 162.1, 199.0. Anal. Calcd for C16H16N2O2: C 71.62, H
6.01, N 10.44. Found: C 71.71, H 6.01, N 10.40.
EXPERIMENTAL SECTION
■
General. All solvents and reagents were obtained from commercial
sources and used as received unless otherwise stated. The solvents
tetrahydrofuran (THF), diethyl ether (Et2O), toluene, pentane, and
dichloromethane were passed through solvent purification columns
(Glass Contour, Laguna, CA). Dichloromethane and acetonitrile were
dried over CaH2 and then distilled under vacuum prior to use. THF
was dried over sodium/benzophenone prior to use. Acetone was dried
over activated 3 Å molecular sieves and distilled under vacuum prior to
use. Purified solvents were stored in a nitrogen-filled glovebox over
either activated 3 Å molecular sieves or CaH2 and filtered through a
0.45 μm PTFE syringe filter immediately before use. All complexes
were prepared under dry nitrogen using standard Schlenk techniques
Me2L(H) (2a). 2a was synthesized following the identical procedure
as was used for 2b, except starting from 7b instead of 7a (1.43 g, 48%).
1H NMR (300 MHz, CD2Cl2): δH 9.50 (br s, 1H, NH), 8.62 (d, 1H, J
= 7.8 Hz, Py H), 8.35 (d, 1H, J = 6.6 Hz, Py H), 8.07 (t, 1H, J = 7.8
Hz, Py H), 7.16−6.92 (m, 6H, Ar H), 2.31 (s, 6H, Ar CH(CH3)2, N-
arylcarboxamide), 2.23 (s, 3H, NCCH3), 2.04 (s, 6H, Ar
CH(CH3)2, N-arylimine). 13C NMR (300 MHz, CD2Cl2): δC 16.8,
18.2, 18.9, 123.7, 124.0, 124.4, 125.8, 127.7, 128.4, 128.6, 136.0, 138.7,
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155.5, 176.7. Anal. Calcd for C24H25N3O: C 77.60, H 6.78, N 11.31.
Found: C 77.49, H 6.69, N 11.40
°C. MS (ESI+, CH3OH): m/z = 548.24 [8c + Na+]+. UV−vis
(CH2Cl2) λmax (ε, M−1 cm−1): 435 (1976); 660 (346) nm. EPR [9.64
GHz, CH2Cl2/toluene (1:1), 2 K]: gx = 2.060, gy = 2.045, gz = 2.185;
A∥(Cu): 197 × 10−4 cm−1; A(N): 15 × 10−4 cm−1, A(Cl): 15 × 10−4
cm−1. Anal. Calcd for C28H32ClCuN3O: C 63.99, H 6.14, N 8.00.
Found: C 63.85, H 6.04, N 7.94.
iPr2L(H) (2b). A solution of 2,6-diisopropylaniline (3.7 mL, 19.8
mmol) was dissolved in 100 mL of toluene and cooled to 0 °C under
N2. TiCl4 (0.36 mL, 3.3 mmol) was added via syringe, and the
resulting cloudy brown solution was stirred for 2 h. After warming the
solution to room temperature, a solution of 7a (2.14 g, 6.6 mmol) in
40 mL of toluene was added to the reaction. The reaction mixture was
then refluxed for 16 h. After cooling to room temperature, Et2O (100
mL) was added and the reaction mixture was stirred for 15 min. The
reaction mixture was then filtered through Celite, and the brown-
yellow filtrate was concentrated via rotary evaporation. The resulting
brown-yellow solid was purified by column chromatography on silica
gel (EtOAc/pentane (1:10); Rf = 0.36) to yield a yellow solid (2.02 g,
63%). The 1H NMR and high-resolution ESI-MS of 2b are previously
iPr2LCuOAc (9b). A suspension of 2b (100 mg, 0.21 mmol) and
Cu(OAc)2·H2O (45 mg, 0.23 mmol) in 50 mL of MeCN was heated
to reflux for 2 h, resulting in a dark green solution. Upon cooling to
room temperature, the reaction was stirred with MgSO4 for 30 min.
The reaction mixture was then filtered, and the solvent was removed
via rotary evaporation to yield a dark green solid (0.0964 g, 77%).
Single crystals suitable for X-ray diffraction were obtained from
diffusion of pentane into a concentrated CH2Cl2 solution at −20 °C.
MS (ESI+, CH3OH): m/z = 545.21 [9b − OAc−]+. UV−vis (CH2Cl2)
λmax (ε, M−1 cm−1): 385 (1972); 655 (275) nm. EPR [9.64 GHz,
DCM/toluene (1:1), 30 K]: gx = 2.0375, gy = 2.0725, gz = 2.2100;
A∥(Cu): 190 × 10−4 cm−1, A(N): 15 × 10−4 cm−1. Anal. Calcd for
C34H43CuN3O3: C 67.47, H 7.16, N 6.94. Found: C 67.43, H 7.17, N
6.85.
reported3 and correlate well with the current data. H NMR (300
1
MHz, CD2Cl2): δH 9.45 (br s, 1H, NH), 8.61 (d, 1H, J = 7.8 Hz, Py
H), 8.36 (d, 1H, J = 7.5 Hz, Py H), 8.08 (t, 1H, J = 7.8 Hz, Py H),
7.39−7.08 (m, 6H, Ar H), 3.17 (m, 2H, Ar CH(CH3)2, N-
arylcarboxamide), 2.76 (m, 2H, Ar CH(CH3)2, N-arylimine), 2.26
(s, 3H, NCCH3), 1.24−1.14 (m, 24 H, Ar CH(CH3)2). 13C NMR
(300 MHz, CD2Cl2): δC 17.5, 23.1, 23.5, 23.9, 28.9, 29.5, 30.3, 123.6,
124.1, 124.1, 124.4, 124.5, 128.8, 132.1, 136.2, 138.8, 146.7, 146.9,
149.3, 155.5, 163.9, 166.4. Anal. Calcd for C32H41N3O: C 79.46, H
8.54, N 8.69. Found: C 79.42, H 8.66, N 8.51.
iPrMeLCuOAc (9c). 9c was synthesized as for 9b, except using 2c
instead of 2b. Single crystals suitable for X-ray diffraction were
obtained from diffusion of pentane into a concentrated CH2Cl2
solution at −20 °C (0.103 g, 80%). MS (ESI+, CH3OH): m/z =
489.13 [9c − OAc−]+. UV−vis (acetone) λmax (ε, M−1 cm−1): 375
(1860); 645 (343) nm. EPR [9.64 GHz, CH2Cl2/toluene (1:1), 2 K]:
gx = 2.070, gy = 2.055, gz = 2.200; A∥(Cu): 194 × 10−4 cm−1, A(N): 15
× 10−4 cm−1. Anal. Calcd for C30H35CuN3O3: C 65.61, H 6.42, N 7.65.
Found: C 65.49, H 6.41, N 7.54.
iPrMeL(H) (2c). 2c was synthesized following the identical procedure
as was used for 2b, except using 2,6-dimethylaniline instead of 2,6-
diisopropylaniline (1.81 g, 64%). Single crystals suitable for X-ray
diffraction were obtained from slow evaporation of a concentrated
CH2Cl2 solution at room temperature. 1H NMR (300 MHz, CD2Cl2):
δH 9.45 (br s, 1H, NH), 8.63 (d, 1H, J = 7.8 Hz, Py H), 8.36 (d, 1H, J
= 7.5, Py H), 8.08 (t, 1H, J = 7.8 Hz, Py H), 7.39−6.93 (m, 6H, Ar H),
3.17 (m, 2H, Ar CH(CH3)2), 2.23 (s, 3H, NCCH3), 2.05 (s, 6H, Ar
CH(CH3)2, N-arylimine), 1.24 (d, 12H, J = 6.9 Hz, Ar CH(CH3)2, N-
arylcarboxamide).13C NMR (300 MHz, CD2Cl2): δC 16.8, 18.2, 23.9,
29.5, 123.7, 124.1, 124.1, 124.5, 125.8, 128.4, 128.8, 132.1, 138.7,
146.9, 149.1, 149.3, 155.5, 163.9, 166.5. Anal. Calcd for C28H33N3O: C
78.65, H 7.78, N 9.83. Found: C 78.59, H 7.80, N 9.79.
[
iPr2L(H)Cu(MeCN)][(SbF6)2] (10). Cu(MeCN)5(SbF6)2 (81 mg,
0.10 mmol) and 2b (50 mg, 0.11 mmol) were combined in 4 mL of
THF. After stirring for 30 min, pentane (10 mL) was added. A green
solid precipitated and was isolated by vacuum filtration. The resulting
green powder was washed with pentane (3 × 10 mL) and dried under
vacuum for 1 h (0.767 g, 70%). Single crystals suitable for X-ray
diffraction were obtained from diffusion of pentane into a
concentrated CH2Cl2 solution at −30 °C. MS (ESI+, CH3OH): m/
z = 545.23 [iPr2LCu+]+. UV−vis (CH2Cl2) λmax (ε, M−1 cm−1): 428
(1864); 665 (463) nm. EPR [9.64 GHz, CH2Cl2/toluene (1:1), 30 K]:
gx = 2.06, gy = 2.07, gz = 2.27; A∥(Cu): 165 × 10−4 cm−1. Anal. Calcd
Me2LCuCl (8a). 8a was synthesized analogously to 8b and 8c, except
using 2a instead of 2b and the reaction time was shortened to 30 min
(longer times resulted in lower yields) (0.111 g, 76%). Single crystals
suitable for X-ray diffraction were obtained from diffusion of Et2O into
a concentrated MeCN solution at −20 °C. MS (ESI+, CH3OH): m/z
= 490.64 [8a + Na+]+. UV−vis (CH2Cl2) λmax (ε, M−1 cm−1): 435
(1964); 655 (348) nm. EPR [9.64 GHz, THF/toluene (1:1), 2 K]: gx
= 2.08, gy = 2.05, gz = 2.23; A∥(Cu): 165 × 10−4 cm−1; A(N): 12.5 ×
10−4 cm−1; A(Cl): 12.5 × 10−4 cm−1. Unfortunately, repeated attempts
to obtain satisfactory CHN analysis were unsuccessful.
for C32H41N3OCuSb2F12 (
iPr2L(H)Cu; the MeCN ligand was lost
upon drying of the crystals under vacuum prior to analysis): C 37.73,
H 4.06, N 4.12. Found: C 37.43, H 4.26, N 4.76.
[
iPrMeL(H)Cu(MeCN)2][(SbF6)2] (11). 11 was synthesized following
the procedure as was used for 10 except 2c was used in place of 2b
(0.0890 g, 73%). MS (ESI+, CH3OH): m/z = 489.18 [iPrMeLCu+]+.
UV−vis (CH2Cl2) λmax (ε, M−1 cm−1): 415 (1060); 690 (215) nm.
EPR [9.64 GHz, CH2Cl2/toluene (1:1), 30 K]: gx = 2.06, gy = 2.07, gz
= 2.27; A∥(Cu): 165 × 10−4 cm−1. Anal. Calcd for C32H39N5O-
CuSb2F12: C 36.79, H 3.76, N 6.70. Found: C 36.73, H 3.81, N 6.44.
iPr2LCuCl (8b). Anhydrous CuCl2 (0.0353 g, 0.263 mmol) and 2b
(0.1156 g, 0.239 mmol) were placed in a 100 mL round-bottom flask
and dissolved in 20 mL of THF, forming a golden brown solution.
Sodium methoxide (0.5 M in MeOH, 0.57 mL, 0.287 mmol) was
added, causing the solution to turn dark green with a light-colored
precipitate. After stirring for 16 h, the reaction was filtered and the
solvent was removed via rotary evaporation. The resulting green
residue was dissolved in CH2Cl2 (10 mL) and filtered to remove any
insoluble material. Pentane (50 mL) was then added, and the mixture
was placed in a −20 °C freezer for several hours. The resulting green
solid was isolated by vacuum filtration (0.101 g, 73%). Single crystals
suitable for X-ray diffraction were obtained from diffusion of pentane
into a concentrated CH2Cl2 solution at −20 °C. MS (ESI+, CH3OH):
m/z = 581.16 [8b + Na+]+. UV−vis (CH2Cl2) λmax (ε, M−1 cm−1): 440
(1785); 675 (260) nm. EPR [9.64 GHz, CH2Cl2/toluene (1:1), 2 K]:
gx = 2.065, gy = 2.090, gz = 2.200; A∥(Cu): 196 × 10−4 cm−1; A(N): 15
× 10−4 cm−1; A(Cl): 15 × 10−4 cm−1. Anal. Calcd for C32H40ClCu-
N3O: C 66.07, H 6.93, N 7.22. Found: C 65.98, H 6.89, N 7.13.
iPrMeLCuCl (8c). 8c was synthesized following an identical
procedure as was used for 8b, except using 2c instead of 2b (0.0989
g, 70%). Single crystals suitable for X-ray diffraction were obtained
from diffusion of pentane into a concentrated CH2Cl2 solution at −20
[
iPrMeL(H)Cu(H2O)THF][(SbF6)2] (12). Cu(MeCN)5(SbF6)2 (93
mg, 0.12 mmol) and 2c (57 mg, 0.12 mmol) were combined in 4
mL of THF in a glovebox. After stirring for 30 min, the reaction was
removed from the glovebox and 10 mL of wet solvent (THF) was
added to the reaction mixture. The reaction was allowed to continue
stirring for 1 h, after which the solvent was removed. The resulting
green residue was taken up in 5 mL of THF, and pentane (100 mL)
was added to the flask. A green solid resulted after several hours of
storage at −20 °C. The solid was isolated via vacuum filtration and
washed with pentane (3 × 10 mL). Single crystals suitable for X-ray
diffraction were obtained from diffusion of pentane into a
concentrated CH2Cl2 solution at −20 °C (0.0884 g, 63%). MS (ESI
+, CH3OH): m/z = 489.21 [iPrMeLCu+]+. UV−vis (CH2Cl2) λmax (ε,
M−1 cm−1): 410 (2395); 695 (375) nm. ESI-MS: m/z 489.22
[iPrMeLCu+]+. EPR [9.64 GHz, THF/toluene (1:1), 30 K]: gx = 2.03,
gy = 2.11, gz = 2.27; A∥(Cu): 155 × 10−4 cm−1. Anal. Calcd for
C32H43CuF12N3O3Sb2: C 36.51, H 4.12, N 3.99. Found: C 36.60, H
4.29, N 3.76.
iPrMeL(H)CuCl2 (13). Anhydrous CuCl2 (16 mg, 0.12 mmol) and 2c
(50 mg, 0.12 mmol) were combined in 4 mL of MeCN. The solution
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was stirred at room temperature for 30 min, resulting in an orange-
brown solution. Et2O (12 mL) was added to the solution, which was
then cooled to −30 °C. The resulting orange-brown solid was
collected by vacuum filtration, washed with pentane (3 × 10 mL), and
dried under vacuum for 1 h (0.0624 g, 95%). MS (ESI+, CH3OH): m/
z = 525.27 [13 − Cl−]+. UV−vis (MeCN) λmax (ε, M−1 cm−1):
400(sh) (726); 450 (700); 890 (94) nm. EPR [9.64 GHz, MeCN/
toluene (1:1), 30 K]: gx,y,z = 2.14. Anal. Calcd for C28H33Cl2N3OCu: C
59.84, H 5.92, N 7.48. Found: C 59.71, H 5.82, N 7.46.
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A.; McDonald, A. R. Angew. Chem., Int. Ed. 2014, DOI: 10.1002/
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4701. (b) Huang, D.; Makhlynets, O. V.; Tan, L. L.; Lee, S. C.; Rybak-
Akimova, E. V.; Holm, R. H. Inorg. Chem. 2011, 50, 10070−10081.
(c) Huang, D.; Makhlynets, O. V.; Tan, L. L.; Lee, S. C.; Rybak-
Akimova, E. V.; Holm, R. H. Proc. Natl. Acad. Sci. U.S.A. 2011, 108,
1222−1227. (d) Zhang, X.; Huang, D.; Chen, Y.-S.; Holm, R. H. Inorg.
Chem. 2012, 51, 11017−11029.
(4) Tehranchi, J.; Donoghue, P. J.; Cramer, C. J.; Tolman, W. B. Eur.
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(5) Donoghue, P. J.; Tehranchi, J.; Cramer, C. J.; Sarangi, R.;
Solomon, E. I.; Tolman, W. B. J. Am. Chem. Soc. 2011, 133, 17602−
17605.
iPrMeL(H)CoCl2 (14). CoCl2 (16 mg, 0.12 mmol) and 2c (53 mg,
0.12 mmol) were stirred in 10 mL of a 1:1 acetone/MeCN mixture to
yield a bright green solution. After stirring for 2 h, the reaction mixture
was filtered and the filtrate was concentrated to approximately 2 mL
total volume. Et2O (10 mL) was added to the solution, which was then
cooled to −30 °C. The resulting green powder was collected by
vacuum filtration, washed with pentane (3 × 10 mL), and dried under
vacuum for 1 h (0.0463 g, 71%). Single crystals suitable for X-ray
diffraction were obtained from diffusion of Et2O into a concentrated
MeCN solution at −30 °C. MS (ESI+, CH3CN): m/z = 521.06 [14 −
Cl−]+. UV−vis (MeCN) λmax (ε, M−1 cm−1): 590 (230); 685 (303)
nm. Anal. Calcd for C28H33Cl2N3OCo: C 60.33, H 5.97, N 7.54.
Found: C 60.18, H 5.87, N 7.45.
(6) Selected recent examples: (a) Bowman, A. C.; Milsmann, C.; Bill,
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́
Stieber, S. C. E.; Sylvester, K. T.; Fernandez, I.; Lobkovsky, E.;
Semproni, S. P.; Bill, E.; Wieghardt, K.; DeBeer, S.; Chirik, P. J. J. Am.
Chem. Soc. 2012, 134, 17125−17137. (c) Darmon, J. M.; Turner, Z. R.;
Lobkovsky, E.; Chirik, P. J. Organometallics 2012, 31, 2275−2285.
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M.; Cruse, R. W.; Nye, S. A.; Boyer, J. L.; Delis, J. G. P.; Chirik, P. J.
ACS Catal. 2012, 2, 2169−2172. (e) Stieber, S. C. E.; Milsmann, C.;
Hoyt, J. M.; Turner, Z. R.; Finkelstein, K. D.; Wieghardt, K.; DeBeer,
S.; Chirik, P. J. Inorg. Chem. 2012, 51, 3770−3785. (f) Tondreau, A.
M.; Atienza, C. C. H.; Darmon, J. M.; Milsmann, C.; Hoyt, H. M.;
Weller, K. J.; Nye, S. A.; Lewis, K. M.; Boyer, J.; Delis, J. G. P.;
Lobkovsky, E.; Chirik, P. J. Organometallics 2012, 31, 4886−4893.
(g) Tondreau, A. M.; Stieber, S. C. E.; Milsmann, C.; Lobkovsky, E.;
iPrMeL(H)ZnCl2 (15). ZnCl2 (16 mg, 0.12 mmol) and 2c (50 mg,
0.12 mmol) were dissolved in 4 mL of THF. After stirring for 15 min,
a light colored precipitate formed in the solution. The solid was
collected by vacuum filtration, washed with pentane (3 × 10 mL), and
dried under vacuum for 1 h (0.0488 g, 74%). Single crystals suitable
for X-ray diffraction were obtained from diffusion of Et2O into a
concentrated MeCN solution at −30 °C. 1H NMR (300 MHz,
(CD3)2SO): δH 10.18 (br s, 1H, NH); 8.55 (d, 1H, J = 7.5 Hz, Py H),
8.24−8.18 (m, 2H, Py H), 7.36−6.90 (m, 6H, Ar H), 3.11 (m, 2H, Ar
CH(CH3)2), 2.94 (s, 3H, NCCH3), 1.99 (s, 6H, Ar CH(CH3)2, N-
arylimine), 1.15 (d, 12H, J = 6.6 Hz, Ar CH(CH3)2, N-
arylcarboxamide). MS (ESI+, CH3CN): m/z = 526.17 [15 − Cl−]+.
Anal. Calcd for C28H33Cl2N3OZn: C 59.64, H 5.90, N 7.45. Found: C
59.58, H 5.78, N 7.35.
Weyhermuller, T.; Semproni, S. P.; Chirik, P. J. Inorg. Chem. 2012, 52,
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135, 4862−4877.
ASSOCIATED CONTENT
■
S
* Supporting Information
(7) (a) Fan, R.-Q.; Wang, P.; Yang, Y.-L.; Zhang, Y.-J.; Yin, Y.-B.;
Hasi, W. Polyhedron 2010, 29, 2862−2866. (b) Le Gall, B.; Conan, F.;
Cosquer, N.; Kerbaol, J.-M.; Sala-Pala, J.; Kubicki, M. M.; Vigier, E.;
Selected spectroscopic and ESI-MS data (PDF) and X-ray data
(CIF). This material is available free of charge via the Internet
at http://pubs.acs.org.
Gomez-Garcia, C. J.; Molinie, P. Inorg. Chim. Acta 2005, 358, 2513−
́
2522. (c) Le Gall, B.; Conan, F.; Cosquer, N.; Kerbaol, J.-M.; Kubicki,
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300−308.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: wtolman@umn.edu.
(8) Manuel, T. D.; Rohde, J.-U. J. Am. Chem. Soc. 2009, 131, 15582−
15583.
(9) (a) Zhang, W.; Wang, Y.; Yu, J.; Redshaw, C.; Hao, X.; Sun, W.-
H. Dalton Trans. 2011, 40, 12856−12865. (b) Shen, M.; Sun, W.-H.
Appl. Organomet. Chem. 2009, 23, 51−54. (c) Shen, M.; Hao, P.; Sun,
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Notes
The authors declare no competing financial interest.
(10) Cabell, L. A.; Best, M. D.; Lavigne, J. J.; Schneider, S. E.;
Perreault, D. M.; Monahan, M.-K.; Anslyn, E. V. J. Chem. Soc., Perkin
Trans. 2 2001, 315−323.
ACKNOWLEDGMENTS
■
We thank the National Institutes of Health for financial support
of this research (R37GM47365 to W.B. T.). The authors thank
Benjamin D. Neisen and Gereon M. Yee for assistance in
collecting EPR spectra, Dr. Patrick J. Donoghue for synthesis
and cyclic voltammetry characterization of [NBu4][(1)CuCl],
and Dr. Victor G. Young, Jr., for assistance with X-ray
crystallography. Some experiments reported in this paper
were performed at the Biophysical Spectroscopy Center in the
University of Minnesota Department of Biochemistry, Molec-
ular Biology, and Biophysics.
(11) Scott, J.; Vidyaratne, I.; Korobkov, I.; Gambarotta, S.; Budzelaar,
P. H. M. Inorg. Chem. 2008, 47, 896−911.
(12) Wang, D.; Lindeman, S. V.; Fiedler, A. T. Eur. J. Inorg. Chem.
2013, 4473−4484 and references therein.
(13) Addison, A. W.; Rao, T. N.; Reedjik, J.; van Rijn, J.; Verschoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.
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