Reactivity Study of Unsymmetrical β-Diketiminato Copper(I) Complexes: Effect of the Chelating Ring

Article abstract of DOI:10.1021/acs.inorgchem.6b02876

β-Diketiminato copper(I) complexes play important roles in bioinspired catalytic chemistry and in applications to the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation. Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the copper(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in order to increase the stability and reactivity of these complexes and to discover new copper(I) binding motifs. Here we describe the synthesis, structural characterization, and reactivity of a series of unsymmetrical N-aryl-N′-alkylpyridyl β-diketiminato copper(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All of the aforementioned unsymmetrical ?-diketiminato copper(I) complexes bind CO reversibly and are stable to disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper(I) complexes are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the N-aryl substituent.

Full text of DOI:10.1021/acs.inorgchem.6b02876

Article
pubs.acs.org/IC
Reactivity Study of Unsymmetrical β‑Diketiminato Copper(I)
Complexes: Effect of the Chelating Ring
Wan-Jung Chuang,†,‡ Sung-Po Hsu,§,∥ Kuldeep Chand,†,‡ Fu-Lun Yu,†,‡ Cheng-Long Tsai,†,‡
Yu-Hsuan Tseng,†,‡ Yuh-Hsiu Lu,†,‡ Jen-Yu Kuo,†,‡ James R. Carey,†,‡,⊥ Hsuan-Ying Chen,†,‡
Hsing-Yin Chen,†,‡ Michael Y. Chiang,†,‡,# and Sodio C. N. Hsu*,†,‡
†Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan
‡Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan
§Department of Physiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei 110, Taiwan
∥Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 110, Taiwan
⊥Department of Applied Chemistry, National University of Kaohsiung, Kaohsiung 804, Taiwan
#Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
S
* Supporting Information
ABSTRACT: β-Diketiminato copper(I) complexes play important roles in bioinspired catalytic chemistry and in applications to
the materials industry. However, it has been observed that these complexes are very susceptible to disproportionation.
Coordinating solvents or Lewis bases are typically used to prevent disproportionation and to block the coordination sites of the
copper(I) center from further decomposition. Here, we incorporate this coordination protection directly into the molecule in
order to increase the stability and reactivity of these complexes and to discover new copper(I) binding motifs. Here we describe
the synthesis, structural characterization, and reactivity of a series of unsymmetrical N-aryl-N′-alkylpyridyl β-diketiminato
copper(I) complexes and discuss the structures and reactivity of these complexes with respect to the length of the pyridyl arm. All
of the aforementioned unsymmetrical ß-diketiminato copper(I) complexes bind CO reversibly and are stable to
disproportionation. The binding ability of CO and the rate of pyridyl ligand decoordination of these copper(I) complexes
are directly related to the competition between the degree of puckering of the chelate system and the steric demands of the N-
aryl substituent.
searchers have reported the synthesis and analyses of N,N′-
alkyl β-diketiminato copper(I) complexes containing Lewis
bases or olefin ligands. These compounds have been reported
to have applications in atomic layer deposition or chemical
vapor deposition.31−37 Indeed, many authors have observed
that these complexes were very susceptible to disproportiona-
tion, probably due to the open coordination site.5,35,38 For the
disproportionation of a β-diketiminato copper(I) complex (see
Scheme 2), the corresponding copper(II) complex and a black
material of copper(0) were reported separately by Ito and
Schaper et al.5,35 It has been found that a coordinating solvent
or Lewis base is required to prevent disproportionation and to
INTRODUCTION
■
During the past several decades, β-diketiminato chelating
ligands have been used throughout coordination chemistry as
sterically crowded spectator ligands that stabilize coordinatively
unsaturated metal centers.1−3 An outline of β-diketiminato
copper(I) complexes and their applications is shown on
Scheme 1. In particular, copper(I) complexes containing
N,N′-aryl-substituted β-diketiminato ligands have been widely
studied.4−9 For example, Tolman and co-workers have
prepared and studied N,N′-aryl β-diketiminato copper com-
plexes that mimic the dioxygen activation of copper-containing
metalloproteins.10−20 Likewise, Warren and co-workers re-
ported a series of N,N′-aryl β-diketiminato copper nitrene and
carbene complexes used for amination reactions and for
catalytic cyclopropanation, respectively.21−30 Recently, re-
Received: November 30, 2016
© XXXX American Chemical Society
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Scheme 1. Structural Illustrations of β-Diketiminato Copper(I) Complexes and Their Applications
ascertained. Third, an increase in stability of β-diketiminato
copper(I) complexes may be realized due to pyridyl arm
chelation. To address these issues, four unsymmetrical N-aryl-
N′-alkyl β-diketiminato ligands bearing pendant pyridyl groups
(Chart 1) and their corresponding copper(I) complexes were
prepared and characterized. The results suggest that pendant
pyridyl arms on the N-aryl-N′-alkyl β-diketiminato ligands may
act as hemilabile Lewis bases protecting the copper(I)
center.46−49 According to IR and NMR studies, the length of
the pyridyl arm influences the binding mode interconversion
and binding ability of carbon monoxide in solution of these
copper(I) complexes. The steric demands of the N-aryl
substituent group play only a minor role in the CO binding
(on/off rate) and solution binding behavior.
Scheme 2. Illustration of the Disproportionation during
Formation of a β-Diketiminato Copper(I) Complex by Itoh’s
Report
block the coordination site of the copper(I) center from further
decomposition. However, what is lacking in the literature is a
thorough study of a systematic ligand set that prevents
copper(I) disproportionation.
On the basis of previous studies of symmetric N,N′-alkyl- or
N,N′-aryl-substituted β-diketiminato copper complexes and our
previous work on biomimetic copper complexes,39−44 we
decided to vary the ligand framework to probe new binding
motifs and reactivity in copper chemistry. β-Diketiminato
copper(I) complexes were synthesized by replacing the
symmetric N,N′-alkyl- or N,N′-aryl-substituted ligands with
unsymmetrical N-aryl-N′-alkyl-substituted ligands.45 The
copper(I) complexes containing unsymmetrical N-aryl-N′-
alkyl β-diketiminato ligands may display different binding
modes in comparison to the N,N′-alkyl or N,N′-aryl analogues.
The preparation of these compounds will allow us to probe
three important issues. First, we can determine how the length
of the pendant pyridyl arm is able to effect the coordination
behavior of these copper(I) complexes. Second, which of the
sterically encumbered substituents that allows binding can be
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Copper(I) Com-
plexes. Several synthetic procedures have been described for
the preparation of copper(I) β-diketiminato complexes having
varying ancillary substituents close to the metal cen-
ter.4,5,21−24,34,35,50,51 It is worth mentioning that the β-
diketiminato copper(I) complexes are very susceptible to
disproportionation. Thus, a coordinating solvent or Lewis base
may be required for synthesis of these complexes.5,35,51 We
chose CuOtBu as a copper(I) source to synthesize the N-aryl-
N′-alkyl β-diketiminato copper(I) complexes. Indeed, CuOtBu
as a copper(I) source was previously reported by Warren et al.
as an economical and soluble starting material for the
preparation of copper(I) complexes.52 Direct reactions of
Chart 1. Representation of the N-Aryl-N′-alkyl β-Diketiminato Ligand Sets
B
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Scheme 3. Synthesis of the N-Aryl-N′-alkyl β-Diketiminato Copper(I) Complexes
CuOtBu with L1H−L4H in hexane at room temperature for 1 h
afforded the corresponding CuL1−CuL4 complexes (Scheme
The geometries and bond parameters of the two
independent molecules of CuL1 in the unit cell are very
similar; thus, only one of the structures is represented in Figure
1
3). All four copper(I) complexes were characterized by H
NMR, 13C NMR, and elemental analysis. The 1H NMR spectra
of CuL1−CuL4 complexes show an upfield shift (e.g. for Py-Hα
7.86 ppm for CuL1) in comparison to the ligand precursor
(8.38 ppm for L1H), indicating that coordination between the
copper(I) ion and pendant pyridyl group is retained in solution.
In order to understand the influence of the pyridyl group as a
chelating arm to prevent disproportionation, we prepared the
two ligands L1PhH and L3PhH (Chart 2), containing a phenyl
1a. The anionic ligand L1 of monomer CuL1 serves as a
−
tridentate ligand for Cu and has a slightly distorted T-shaped
coordination geometry, with a nearly planar five-membered ring
produced by a chelating pyridylmethyl arm. The monomer
CuL2 compound exhibits a nearly planar distorted Y-shaped
coordination geometry. The pyridylethyl arm of CuL2 forms a
six-membered chelate ring with a twist-boat form connecting
the planar six-membered diazapentadienyl (NCCCN) biden-
tate chelate ring with a bridging copper. The anionic ligand of
−
L3 serves as a tridentate ligand in the solid state of monomer
Chart 2. Representation of the Two N-Aryl-N′-alkyl β-
Diketiminato Ligands L1PhH and L3PhH
CuL3 and displays a slightly distorted T-shaped coordination
−
geometry that is similar to the coordination of L1 in CuL1.
The CuL4 monomer also shows a nearly planar distorted Y-
shaped coordination geometry about the copper center. Similar
to the case for CuL2, the CuL4 complex forms a twist-boat-like
pyridylethyl arm chelate ring with an NCCCN bidentate
chelate six-membered ring with a bridging copper.
Interestingly, the two pyridyl ligand bridged dinuclear
cyclometalated Cu(I) complexes Cu2(μ-L1)2 and Cu2(μ-L4)2
are found after recrystallization in a coordinating solvent. Each
of the molecular structures of Cu2(μ-L1)2 and Cu2(μ-L4)2
consists of two β-diketiminato copper subunits (in a three-
coordination environment) bridged by two pyridylalkylamide
linkers. These arrangements result in the formation of 10- and
12-membered metallamacrocycles in Cu2(μ-L1)2 and Cu2(μ-
L4)2 (Figure 1e,f), respectively. Cu2(μ-L1)2 and Cu2(μ-L4)2
exhibit a slightly distorted Y-shaped coordination geometry,
which may be due to the chelated ring strain release to form the
bridging complex.
The copper complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2,
and Cu2(μ-L4)2 all display three-coordinate geometries. The
differences in the molecular structures clearly suggest disparities
due to the effective steric effect imposed by their respective N-
aryl substituents and length of the pyridyl arm supporting the
β-diketiminato ligands. The N-aryl ring is also twisted from
perpendicular with respect to the NCCCN plane in CuL1,
CuL2, CuL3, and CuL4. The N-aryl ring twist angles of 18.17
and 18.46° for CuL1 and 13.65° for CuL2 are much larger than
the 2.21° for CuL3 and 9.21° for CuL4, indicating the steric
influence of the ortho position on the N-aryl substituents. The
Cu−N(py) bond lengths (1.932−1.958 Å) of CuL1, CuL2,
group, to compare with L1H and L3H, containing a pyridyl
group. Replacing the pyridyl arm with a phenyl arm may cause
disproportionation during copper(I) complex formation. In-
deed, direct reactions of CuOtBu with L1PhH or L3PhH in
hexane at room temperature afford disproportionation
products, as indicated by a black material of copper(0) and
an intractable strongly colored product. These observations
suggest that the pyridyl arm of N-aryl-N′-alkyl β-diketiminato
ligands (L1H−L4H) could prevent their corresponding copper-
(I) complexes from disproportionation.
Molecular Structures of N-Aryl-N′-alkyl β-Diketimina-
to Copper(I) Complexes. X-ray-quality crystals of CuL1−
CuL4 complexes were obtained in hexane at −20 °C.
Crystallographic analyses revealed that CuL1, CuL2, CuL3,
and CuL4 complexes are mononuclear. On the other hand,
recrystallization of CuL1 and CuL4 in a coordinating solvent
(CH3CN for CuL1, THF for CuL4; Scheme 3) gives the ligand-
bridged dinuclear cyclometalated copper(I) complexes Cu2(μ-
L1)2 and Cu2(μ-L4)2, respectively. Representations of the
molecular structures of CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2,
and Cu2(μ-L4)2 are shown in Figure 1, with selected bond
distances and angles given in Table 1.
C
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Figure 1. ORTEP drawings of complexes CuL1 (a), CuL2 (b), CuL3 (c), CuL4 (d), Cu2(μ-L1)2 (e), and Cu2(μ-L4)2 (f) (50% ellipsoids; hydrogen
atoms not shown for clarity).
Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and Cu2(μ-L4)2
CuL1
molecule A
molecule B
CuL2
CuL3
CuL4
Cu2(μ-L1)2
Cu2(μ-L4)2
Cu−N(amide(aryl))
Cu−N(amide(alkyl))
Cu−N(py)
1.876(4)
1.987(4)
1.952(4)
1.401(7)
1.421(7)
1.342(6)
1.311(6)
99.92(16)
173.72(16)
84.27(16)
71.83
1.877(4)
1.992(4)
1.949(4)
1.381(6)
1.418(6)
1.353(6)
1.317(6)
100.00(16)
174.14(16)
84.08(16)
71.54
1.8915(19)
2.005(2)
1.932(2)
1.401(3)
1.420(4)
1.332(3)
1.306(3)
98.80(9)
160.82(9)
100.06(9)
76.35
1.876(5)
1.995(6)
1.938(5)
1.406(9)
1.418(9)
1.295(8)
1.335(8)
99.3(2)
175.9(3)
84.5(2)
87.79
1.885(2)
1.997(2)
1.934(2)
1.392(4)
1.422(4)
1.319(3)
1.343(4)
100.85(9)
153.30(10)
101.61(9)
80.42
1.947(11), 1.933(11)
1.994(11), 1.980(11)
1.971(12), 1.956(11)
1.39(2), 1.42(2)
1.44(2), 1.42(2)
1.35(2), 1.34(2)
1.31(2), 1.31(2)
98.8(5), 99.8(5)
140.7(5), 137.2(5)
120.5(5), 123.0(5)
79.23, 86.06,
1.975(3)
1.951(2)
1.958(2)
1.405(5)
1.417(5)
1.327(4)
1.326(4)
98.90(10)
120.18(11)
137.33(10)
89.36
C−C(NCCCN backbone)
C−N(NCCCN backbone)
N(amide)−Cu−N(amide)
N(amide(aryl))−Cu−N(py)
N(amide(alkyl))−Cu−N(py)
a
∠NCCCN(aryl)
a
Angle between the NCCCN backbone plane and N-aryl ring.
D
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1
Figure 2. Variable-temperature H NMR spectra of the CuL1 complex (3.4−5.6 ppm).
CuL3, and CuL4 are similar to reported data for N,N′-aryl-
substituted β-diketiminato copper(I) complexes containing
pyridine or lutidine ligation.23,53 Therefore, the pyridyl arms
of our ligand sets (L1 , L2 , L3 , and L4 ) may act as neutral
donors to the copper ion while the NCCCN backbone serves
as an anionic donor. The bond distances of the NCCCN
backbone for the copper complexes CuL1, CuL2, CuL3, CuL4,
Cu2(μ-L1)2, and Cu2(μ-L4)2 are similar to those of the relatively
well-known deprotonated anionic β-diketiminato li-
gand.5,11,15,17,20,21,23,28,34−37,53
suggest that pyridylalkyl arm bridged dimerization may result
from the coordinating solvent-induced crystallization process.
In order to understand the solution behaviors and to gain
insight into the dynamic processes of CuL1−CuL4, variable-
temperature 1H NMR experiments (VT-1H NMR) were
performed. The VT-1H NMR spectra for CuL1 and CuL3
recorded between 20 and −90 °C in toluene-d8 are similar
(Figures S9 and S11 in the Supporting Information).
Particularly revealing portions of the spectra with assignments
for CuL1 are shown in Figure 2. At 20 °C, a singlet (b1) at 4.96
ppm for the central −CH proton on the NCCCN backbone
and another singlet (d1) at 4.12 ppm for methylene −CH2
protons of the pyridylmethyl arm are observed, suggesting the
presence of a CuL1 species. Upon cooling, the intensity of the
central −CH peak at 4.96 ppm decreases while a new −CH
singlet appears at 4.91 ppm (b1′). Concurrently, the peak due
to the methylene −CH2 protons at 4.12 ppm also decreases in
intensity, while two new doublets appear at vastly different
chemical shifts (5.39 ppm, d1a′; 4.52 ppm, d1b′; J = 12 Hz),
indicating a pattern of diastereotopic methylene −CH2 protons.
The multiplets at 3.57 ppm (j1) attributed to the isopropyl
substituent methine −CH protons also change upon cooling.
−
−
−
−
In general, the pyridylmethyl arms form five-membered
chelate rings with the anionic β-diketiminato moieties. The
chelating L1− and L3− ligands give tridentate three-coordinated
mononuclear compounds CuL1 and CuL3. In addition, the
−
−
pyridylethyl arms of L2 and L4 give stable twist-boat
confirmations for the six-membered chelate ring in monomers
CuL2 and CuL4. Coordinating solvents may force the chelating
pyridylalkyl arm to unchelate, forming the ligand-bridged
dinuclear cyclometalated copper(I) complexes Cu2(μ-L1)2 and
Cu2(μ-L4)2.
NMR Study of Copper(I) Complexes. Due to the
crystallographically observed various binding modes of copper-
(I) complexes, it is important to understand the structure of
copper complexes CuL1, CuL2, CuL3, CuL4, Cu2(μ-L1)2, and
Cu2(μ-L4)2 in solution. Solution NMR studies in acetonitrile-d3
and toluene-d8 at room temperature of complexes Cu2(μ-L1)2
and Cu2(μ-L4)2 show NMR signals and chemical shifts similar
to those for complexes CuL1 and CuL4. On the basis of these
NMR observations and crystallization results described above,
the dinuclear structures are obtained from modestly coordinat-
ing solvents such as MeCN and THF, whereas mononuclear
structures are obtained from alkane solvents. Therefore, we
1
We interpret these changes in the H NMR spectrum upon
cooling to indicate that the monomer CuL1 species is the major
species present at higher temperature and the dimer Cu2(μ-L1)2
is the major species present at lower temperature (Scheme 4).
The Cu2(μ-L1)2 dimer is structurally different from
monomer CuL1 and shows a major change in the chemical
shift difference of the methylene protons (Figure 2). We
estimate the equilibrium constants (Keq = [Cu2(μ-L1)2]/
[CuL1]2) at each temperature by integrating the singlets for
the ligand backbone −CH protons and obtained thermody-
namic parameters from an Arrhenius plot of ln Keq versus 1/T
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the pyridylethyl arm. Lowering of the temperature provokes a
progressive splitting of the two sets of signals (d2 and e2) which
become three sets (d2b, d2a + e2b, and e2a) at −90 °C. This
overlapping behavior suggests that, during cooling, a chelating
pyridylethyl ring flipping fluxional process is taking place in
solution (depicted in Scheme 5). As deduced from the
Scheme 4. Interconversion of CuL1/Cu2(μ-L1)2
Scheme 5. Possible Conformational Changes of the Six-
Membered Metallacycle CuL2
(Figure S13 in the Supporting Information): ΔH° = −14.8
0.5 kJ mol−1 and ΔS° = −57.9 2.3 J mol−1 K−1. The large
chemical shift differences between the methylene signals in
Cu2(μ-L1)2 and the negative entropy value for the equilibrium
with CuL1 are consistent with a dimeric complex bearing a
bridged intermolecular pyridylmethyl arm. For the CuL3/
Cu2(μ-L3)2 system, the interconversion behavior also obtained
from the VT-1H NMR investigation of CuL3 (Figure S11 in the
Supporting Information) is consistent with the thermodynamic
parameters (Figure S14 in the Supporting Information): ΔH° =
−27.9 0.4 kJ mol−1 and ΔS° = −97.7 1.8 J mol−1 K−1. A
similar monomer/tetramer interconversion was reported by
Tolman et al. for copper(I) β-diketiminato compounds with
thioether substituents. However, in this case only the tetramer
was identified in the crystalline state.15
coalescence behavior of the ethylene resonance, both CuL2
and CuL4 have the same ΔG⧧ values (9.8 kcal mol−1) during
the ring flipping fluxional process.54 Similar behaviors have
been described in the literature and have been attributed to the
ring flipping of six-membered rings.55,56
The diffusion-ordered spectroscopy (DOSY) technique is a
powerful tool to obtain molecular parameters such as molecular
weight (MW) and hydrodynamic radii in solution.57−60 An
NMR tube with toluene-d8 solvent was loaded with a given
copper(I) complex and three internal references to examine
their DOSY at room temperature. Diffusion (D) and MW
values of complexes CuL1−CuL4 are given in Table S1 in the
Supporting Information. The diffusion coefficient data of 8.340
× 10−10 m2/s for CuL2 (MW value 426) and 9.980 × 10−10 m2/
s for CuL4 (MW value 403) are consistent with the monomeric
structure (<0.1% error for CuL2 and 5% error for CuL4),
indicating that CuL2 and CuL4 retain their chelating
monomeric structures in toluene solution. On the other
The VT-1H NMR spectra recorded between 20 and −90 °C
in toluene-d8 for CuL2 and CuL4 are also similar (Figures S10
and S12 in the Supporting Information). Particularly revealing
portions of the spectra for CuL2 with assignments are shown in
Figure 3. The 1H NMR spectrum of CuL2 at room temperature
shows a singlet (b2) at 4.82 ppm for the central −CH on the
NCCCN backbone and two sets of signals (d2 and e2) at 2.62
and 3.27 ppm for the diastereotopic ethylene −CH2 protons of
1
Figure 3. Variable-temperature H NMR spectra of the CuL2 complex (2.0−5.4 ppm).
F
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hand, the diffusion coefficient data for CuL1 (MW value 615;
49.3% error for monomer) and CuL3 (MW value 602; 62.7%
error for monomer) from the DOSY experiments gave an
average diffusion coefficient of 9.218 × 10−10 m2/s for CuL1
and 11.05 × 10−10 m2/s for CuL3. Using CuL1 as an example,
the DOSY molecular weight has a 49.3% error for the
monomer, indicating that the structure of CuL1 might not
remain as a single species in solution (e.g. a monomer).
Therefore, a fast interconversion between monomer and dimer
was proposed to fit the average molecular weight. Thus, CuL1
and CuL3 may undergo a fast interconversion between the
monomer and dimer in toluene solution. Indeed, Schalley et al.
have reported a similar phenomenon showing that the average
diffusion coefficient for a trimer/tetramer equilibria in a
metallo-supramolecular self-assembly system suggests fast
interconversion on the DOSY time scale at room temper-
ature.61
Electrochemistry of Copper(I) Complexes. Cyclic
voltammetry experiments were performed on 0.1 M Bu4NPF6
acetonitrile solutions of CuL1−CuL4 complexes at room
temperature. All copper(I) complexes exhibited a reversible
or quasi-reversible wave that is attribute to the Cu(I)/Cu(II)
redox couple. The CV data and values for E1/2 (vs Fc+/Fc) are
given in Figure S27 and Table S5 in the Supporting
Information. The lower potentials of CuL1−CuL4 reflect the
stronger electronic donating ability of unsymmetrical N-aryl-
N′-alkyl β-diketiminato ligands in comparison with potentials
reported for other symmetrical N,N′-aryl β-diketiminato
copper(I) complexes.11 Increased shifts in E1/2 for the longer
pyridyl arm from CuL1 to CuL2 (+237 mV) and CuL3 to CuL4
(+252 mV) are more significant than the decrease in E1/2 shifts
of the aryl substituent from CuL1 to CuL3 (−93 mV) and from
CuL2 to CuL4 (−78 mV), indicating that the chelating pyridyl
arm affects the redox potential of these complexes.
Scheme 6. Reactivity Study of the N-Aryl-N′-alkyl β-
Diketiminato Copper(I) Complexes
copper(I) precursor (8.46 ppm for L1Cu−CO and 7.86 ppm
for CuL1). The 1H NMR spectra indicate that the carbonylation
goes to completion, producing a single product.
Solutions of CuL1−CuL4 in toluene were treated with CO (1
atm). According to the FT-IR spectra, all four complexes
displayed a similar single sharp peak at 2065 cm−1, consistent
with the formation of L1Cu−CO, L2Cu−CO, L3Cu−CO, and
L4Cu−CO. The lower νCO values (see Table 2) also
demonstrate that the N-aryl-N′-alkyl β-diketimines bearing
pendant pyridyl group ligand sets (L1H−L4H) have electron-
donating properties stronger than those of the corresponding
N,N′-aryl β-diketiminato ligands.17,20 The same νCO values for
the LnCuI−CO complexes may be due to the steric changes
having little impact on the electronics of the metal center. In all
cases for the LnCuI−CO complexes, the FT-IR spectral changes
are reversible. The original IR spectrum was regenerated upon
passing dinitrogen gas through the solutions, indicating weak
CO binding behavior. Attempts to isolate L1Cu−CO, L2Cu−
CO, L3Cu−CO, and L4Cu−CO in pure solid form were
unsuccessful. Recrystallization of the LnCuI−CO complexes led
to the corresponding CuLn complexes, which did not exhibit
νCO frequencies in the IR spectrum.
Reaction of Copper(I) Complexes with Dioxygen. The
copper(I) complexes CuL1−CuL4 were oxidized to copper(II)
species, as judged by the development of green-brown colors at
rates dependent on the nature of the solvent. The rates of
oxidation are greater in MeOH than in MeCN. Attempts to
isolate the green-brown species in pure solid form were
unsuccessful. Only the oxidized product of CuL2 was isolated.
Treatment of CuL2 in MeCN with O2 at ambient temperature
rapidly yielded a green-brown solution, from which the
L2Cu(μ-OH)2CuL2 products were isolated as crystalline solids
in modest yields. The products were identified by elemental
analysis and X-ray crystallography (Figure S1 in the Supporting
Information). The structure of L2Cu(μ-OH)2CuL2 features a
separation of 3.073 Å between Cu(II) ions and adopts a
distorted-square-planar geometry with two uncoordinated
pendant pyridyl arms. Similar structural features of planar
bis(hydroxo)dicopper(II) core complexes have been observed
for related β-diketiminato copper(II) complexes.20,21
According to Meyer’s description, “Carbon monoxide binds
to the copper(I) complexes under study to varying degrees. In
fact, there is surprisingly limited literature on the quantitative
study of CO interactions with copper(I) complexes.”,62 and so
it seems that there has not been much kinetic research on the
formation of copper(I)−CO adducts. Indeed, we were not able
to locate quantitative CO binding studies to β-diketiminato
copper(I) complexes in the literature. Only Tolman et al. has
described that β-diketiminato copper(I) complexes bind CO
reversibly and reported qualitative copper(I)−CO adduct νCO
data.17,20 Due to the above reasons, the determination of CO
binding ability for β-diketiminato copper(I) complexes was
undertaken for the CuL1−CuL4 compounds. The approximate
equilibrium constant (KCO) and association (kCO) and
dissociation (k‑CO) rate constants are shown in Table 3.
These constants were calculated according to eqs 1 and 2 on
the basis of monitoring FT-IR spectral changes under excess
CO (1 atm).
Reactivity toward Carbon Monoxide. In order to
understand the chelating ring effect and electron-donating
characteristics of N-aryl-N′-alkyl β-diketiminato ligands on the
copper(I) complexes, we examined the reactions of CuL1−
CuL4 with CO (Scheme 6). Our aim was to prepare a simple
CO adduct and compare their νCO values to those reported for
Cu(I)−CO complexes (Table 2).17,20 All copper(I)−CO
adducts were characterized by 1H NMR and 13C NMR,
which indicated complete loss of pyridyl arm coordination.
Indeed, the uncoordinated pyridyl arm is shifted downfield (in
kCO
[LCuI] + [CO] HooooooooI [LCuI−CO]
N2, k−CO
(1)
kCO
k−CO
KCO
=
(2)
The CO on/off rate is competing with the pyridyl arm
chelating ability. The on rate (kCO) of CO is inversely
proportional and the off rate (k‑CO) of CO is directly
proportional to the length of the pyridyl arm, which may due
1
the H NMR) in comparison to that of the corresponding
G
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Table 2. IR Data for Selected Copper(I)−CO and Copper(I)−CNR Adducts
a
b
entry
compound
νCO
,
cm−1
νCNR
,
cm−1
ref
1
LACu−CO
LBCu−CO
LCCu−CO
2097
2070
2071
2065
2065
2065
2065
17
17
20
2
3
c
4
L1Cu−CO
L2Cu−CO
this work
this work
this work
this work
10
c
5
c
6
L3Cu−CO
c
7
L4Cu-CO
b
b
8
LBCu−CNAr
LCCu−CNAr
LDCu−CNAr
LECu−CNAr
L1Cu−CNAr
2126
2123
2121
2114
2122
2120
2122
2120
9
34
b
10
11
12
13
14
15
24
b
36
b
this work
this work
this work
this work
b
L2Cu--CNAr
b
L3Cu−CNAr
L4Cu--CNAr
b
a
b
c
Free CO: νCO 2143 cm−1. CNAr = 2,6-xylyl isocyanide; νCNR 2119 cm−1. All four CO adducts display the same νCO at 2065 cm−1.
with the formation of isocyanide adducts. The uncoordinated
pyridyl arm H NMR signals for the Py-Hα (e.g. 8.49 ppm for
L1Cu(2,6-CNC6H3Me2)) of the isocyanide adducts are shifted
downfield in comparison to the corresponding copper(I)
precursor (7.86 ppm for CuL1).
X-ray-quality crystals of the four N-aryl-N′-alkylpyridyl β-
diketiminato copper(I) isocyanide complexes L1Cu(2,6-
CNC6H3Me2), L2Cu(2,6-CNC6H3Me2), L3Cu(2,6-
CNC6H3Me2), and L4Cu(2,6-CNC6H3Me2) were obtained
from hexane/toluene solutions. The copper centers of all four
copper(I) isocyanide structures are very similar in geometry.
The ORTEP drawing of L1Cu(2,6-CNC6H3Me2) is repre-
sented in Figure 4, while L2Cu(2,6-CNC6H3Me2), L3Cu(2,6-
Table 3. Kinetic Data and Equilibrium Constants of
Carbonylation and Decarbonylation for N-Aryl-N′-alkyl β-
Diketiminato Copper(I) Complexes
1
compound in toluene
kCO, M−1 s−1
k−CO, 10−3 s−1
KCO, 103 M−1
CuL1/L1Cu−CO
CuL2 /L2Cu−CO
CuL3/L3Cu−CO
CuL4/L4Cu−CO
2.62( 0.16)
0.84( 0.21)
2.18( 0.12)
1.56( 0.23)
0.37( 0.08)
1.35( 0.18)
0.49( 0.11)
2.16( 0.13)
7.08( 0.43)
0.62( 0.16)
4.44( 0.24)
0.72( 0.11)
to the binding thermodynamics of the chelating ring. For
example, the on rate (kCO) of CuL1 being faster than that of
CuL2 suggests that the shorter arm leads to higher affinity for
CO. Therefore, the variation in KCO for the CuL1−CuL4
compounds can be related to the degree of competition
between CO and the pyridyl arm. These results are also
consistent with our VT NMR observations; a one-carbon
pyridyl arm (CuL1 and CuL3) may make CO binding easier in
comparison to the two-carbon pyridyl arm species (CuL2 and
CuL4). Meyer and co-workers measured CO binding for a
series of copper(I) coordination complexes with various pyridyl
chelate ring size tripodal tetradentate ligands. The authors
found that increasing the chelate ring size leads to a lower
affinity for CO.62 Therefore, we suggest that the decrease in
KCO from CuL1 to CuL2 and from CuL3 to CuL4 may also be
due to the increasing chelate ring size of the pyridyl arm. On
the other hand, the steric influence of the N-aryl substituent
plays a minor role in CO binding because of the slight decrease
in KCO from CuL1 to CuL3 and similar KCO values of CuL2 and
CuL4, within experimental error.
Figure 4. ORTEP drawing of L1Cu(2,6-CNC6H3Me2) (50%
ellipsoids; hydrogen atoms not shown for clarity).
Synthesis of Copper(I) Isocyanide Complexes. The
reaction of N-aryl-N′-alkylpyridyl β-diketiminato copper(I)
complexes CuL1−CuL4 with 2,6-xylyl isocyanide (2,6-
CNC6H3Me2) promotes pyridyl arm decoordination and
affords the corresponding isocyanide adducts in high yield
(Scheme 6). All copper(I) isocyanide adducts were charac-
CNC6H3Me2), and L4Cu(2,6-CNC6H3Me2) are shown in
Figures S2−S4 in the Supporting Information. Selected bond
distances and angles for the four isocyanide adducts are given in
Table 4. The copper centers are trigonally coordinated by
isocyanide and two nitrogen donors from the β-diketiminato
ligand. The uncoordinated pyridyl arm is pendant and far away
1
terized by H NMR, 13C{1H} NMR, and elemental analysis.
1
The stretching frequencies νCNR of the products show a single
from the copper center, consistent with the H NMR results.
The C−N and C−C bond distances of the β-diketiminato
sharp peak centered at 2120−2122 cm−1 (Table 2) consistent
H
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Inorganic Chemistry
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Table 4. Selected Bond Lengths (Å) and Angles (deg) for L1Cu(2,6-CNC6H3Me2), L2Cu(2,6-CNC6H3Me2), L3Cu(2,6-
CNC6H3Me2), and L4Cu(2,6-CNC6H3Me2) Complexes
L1Cu(2,6-CNC6H3Me2)
L2Cu(2,6-CNC6H3Me2)
L3Cu(2,6-CNC6H3Me2)
L4Cu(2,6-CNC6H3Me2)
Cu−N(amide(aryl))
Cu−N(amide(alkyl))
Cu−C(isocyanide)
1.937(3)
1.921(3)
1.808(4)
1.403(5)
1.395(5)
1.324(4)
1.317(4)
1.159(4)
98.55(11)
134.93(12)
126.41(13)
176.6(3)
88.05
1.921(6)
1.918(6)
1.805(9)
1.40(1)
1.936(2)
1.933(2)
1.810(3)
1.405(4)
1.400(5)
1.326(4)
1.324(4)
1.156(4)
98.17(10)
133.43(12)
128.34(12)
175.8(3)
77.00
1.932(2)
1.947(2)
1.817(3)
1.417(4)
1.403(5)
1.327(5)
1.329(5)
1.157(4)
98.28(10)
131.06(12)
130.56(12)
175.1(3)
87.83
C−C(NCCCN backbone)
1.389(1)
1.36(1)
C−N(NCCCN backbone)
1.346(8)
1.163(9)
100.4(3)
122.6(4)
136.9(3)
176.6(9)
88.71
CNAr(isocyanide)
N(amide)−Cu−N(amide)
N(amide(aryl))−Cu−C(isocyanide)
N(amide(alkyl))−Cu−C(isocyanide)
CN−C(Ar(isocyanide))
a
∠NCCCN(aryl)
a
Angle between the NCCCN backbone plane and N-aryl ring.
ligand are in agreement with delocalization of the double bonds
(Table 4).24,34−36 The C−N distances (1.156−1.163 Å) and
the C−N−CAr angles of isocyanide (175.1−176.6°) are similar
to those of related β-diketiminato copper isocyanide com-
plexes24,34−36 and that of the free ligand (1.160 Å).63
The electron-donating properties of copper(I) isocyanide
adducts aid in the understanding of the differences between
N,N′-aryl- and N,N′-alkyl-substituted β-diketiminato li-
gands.10,24,34−37 As shown in Table 2, the νCNR stretching
frequencies of the N-aryl-N′-alkyl β-diketiminato copper(I)
isocyanide adducts (2120−2122 cm−1) are smaller than those
of the N′-aryl β-diketiminato copper(I) isocyanide analogues
(2121−2126 cm−1)10,24,34 and larger than those of the N,N′-
alkyl β-diketiminato copper(I) isocyanide complexes (2111−
2114 cm−1).35,36 These results suggest that the electron-
donating trend for this set of β-diketiminato ligands is N,N′-
alkyl-substituted > N-aryl-N′-alkyl-substituted > N,N′-aryl-
substituted ligand.
Synthesis of Copper(I)−PPh3 Complexes. In addition to
understand the reactivity of CuL1−CuL4 discussed above, we
prepared four N-aryl-N′-alkylpyridyl β-diketiminato copper(I)
triphenylphosphine complexes by treatment of their parent
copper(I) complexes CuL1−CuL4 with 1 equiv of PPh3. All
copper(I)−PPh3 adducts were characterized by 1H NMR,
13C{1H} NMR, 31P{1H} NMR, and elemental analysis. X-ray-
quality crystals of the four N-aryl-N′-alkylpyridyl β-diketiminato
copper(I)−PPh3 complexes were grown by layering hexane
onto a toluene solution. Due to the similarity of the four
copper(I) PPh3 adduct structures about the copper center, only
L1Cu(PPh3) is represented in Figure 5; the other structures are
shown in Figures S5−S7 in the Supporting Information for
L2Cu(PPh3), L3Cu(PPh3), and L4Cu(PPh3), respectively. The
copper centers are also trigonally coordinated by one
phosphorus atom and two nitrogen donors of the β-
diketiminato ligand. The uncoordinated pyridyl arm is pendant
and far away from the copper center, which is consistent with
the 1H NMR spectral results. The C−N and C−C bond
distances of the β-diketiminato ligand are in agreement with
delocalization of the NCCCN backbone (Table 5).
Figure 5. ORTEP drawing of L1Cu(PPh3) (50% ellipsoids; hydrogen
atoms not shown for clarity).
geometry of these copper(I) complexes is explained on the
basis of chelation for CuL1−CuL4 or bridged dimerization
binding modes for Cu2(μ-L1)2 and Cu2(μ-L4)2, which is
dependent on their crystallization conditions. Room-temper-
ature NMR investigations indicate that the dicopper complexes
Cu2(μ-L1)2 and Cu2(μ-L4)2 have NMR chemical shifts similar
to those of the monocopper isomer counterparts CuL1 and
CuL4, respectively. The VT-1H NMR and DOSY experiments
indicate that the length of the pyridyl arm governs the solution
behavior of CuL1−CuL4. During temperature changes, CuL1
and CuL3 display monomer/dimer interconversion, presumably
due to the ring strain of the five-membered pyridylmethyl arm.
For longer pyridylethyl arms, CuL2 and CuL4 are fluxional on
the NMR time scale because of the twist-boat puckering chelate
ring system.
It has been observed that β-diketiminato copper(I)
complexes are very susceptible to disproportionation.5,35,38 By
introduction of a hemilabile pyridyl group, disproportionation
was not observed in CuL1−CuL4 complexes, but this did not
prevent oxidization. A reactivity study of the CuL1−CuL4
complexes revealed that the pyridyl arm is decoordinated by
addition of CO, 2,6-CNC6H3Me2, or PPh3. On the basis of our
studies, the electron-donating ability for the three types of β-
diketiminato ligand sets is N,N′-alkyl-substituted > N-aryl-N′-
alkyl-substituted > N,N′-aryl-substituted ligand. The equili-
brium constants for CO adduct formation depend on the
degree of competition provided by the length of the pyridyl
arm (major) and the steric demand of the N-aryl substituent
CONCLUSIONS
■
A series of unsymmetrical N-aryl-N′-alkylpyridyl β-diketiminato
copper(I) complexes were synthesized, and their structures
were characterized using single-crystal X-ray diffraction. The
I
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Table 5. Selected Bond Lengths (Å) and Angles (deg) for L1Cu(PPh3), L2Cu(PPh3), L3Cu(PPh3), and L4Cu(PPh3) Complexes
L1Cu(PPh3)
L2Cu(PPh3)
L3Cu(PPh3)
L4Cu(PPh3)
Cu−N(amide(aryl))
Cu−N(amide(alkyl))
Cu−P
1.943(2)
1.961(2)
2.1706(6)
1.407(3)
1.395(3)
1.331(3)
1.322(3)
93.37(7)
141.31(5)
121.31(5)
85.43
1.949(3)
1.956(3)
2.169(1)
1.409(4)
1.397(5)
1.328(5)
1.318(5)
98.6(1)
1.937(2)
1.952(2)
2.1587(6)
1.399(4)
1.397(4)
1.333(3)
1.329(3)
98.24(8)
136.74(6)
124.98(6)
87.33
1.933(3)
1.948(3)
2.156(1)
1.413(5)
1.382(5)
1.335(5)
1.325(5)
98.6(1)
C−C(NCCCN backbone)
C−N(NCCCN backbone)
N(amide)−Cu−N(amide)
N(amide(aryl))−Cu−P
N(amide(alkyl))−Cu−P
133.47(8)
127.80(8)
89.89
134.99(9)
126.21(9)
77.77
a
∠NCCCN(aryl)
a
Angle between the NCCCN backbone plane and N-aryl ring.
5.11 (s, 1H, backbone-CH), 4.22 (s, 2H, CH2Py), 3.70 (septet, 2H, J =
7.1 Hz, ArCH(CH3)2), 1.97 (s, 3H, backbone-CH3), 1.90 (s, 3H,
backbone-CH3), 1.47 (d, 6H, J = 7.1 Hz, ArCH(CH3)2), 1.31 (d, 6H, J
= 7.1 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 125 MHz, 298 K, δ):
165.14, 161.97, 161.82, 150.81, 150.02, 141.06, 135.78, 124.05, 123.81,
123.27, 122.06, 95.06, 53.15, 28.56, 24.73, 24.62, 23.44, 21.34. Anal.
Calcd for C23H30CuN3: C, 67.04; H, 7.34; N, 10.24. Found: C, 66.99;
H, 7.38; N, 10.28.
(minor). Taken together, these results imply that the pyridyl
arm prevents disproportionation and the length of the arm can
influence the reactivity of β-diketiminato copper(I) complexes.
On the basis of these conclusions, future work will consist of
studying this donor arm ligand set for new copper(I) catalysts
and for the generation of new binding motifs for bioinspired
complexes.
CuL2. Under an inert atmosphere a solution of L2H (1.03 g, 2.96
mmol) in 10 mL of hexane was added to a slurry of CuOtBu (0.40 g,
2.96 mmol) in 15 mL of hexane and stirred for 60 min. This complex
was isolated from hexane to give red crystals of CuL2 (0.98 g, 77%).
1H NMR (toluene-d8, 400 MHz, 293 K, δ): 7.95 (ddd, 1H, J = 5.6, 2.2,
1.2 Hz, Py1), 7.20−7.12 (m, 3H, Ar-H), 6.81 (ddd, 1H, J = 2.2, 7.6, 7.6
Hz, Py3), 6.45 (ddd, 1H, J = 7.6, 1.2, 1.2 Hz, Py4), 6.22 (ddd, 1H, J =
5.6, 7.6, 1.2 Hz, Py2), 4.83 (s, 1H, backbone-CH), 3.65 (septet, 2H, J
= 6.8 Hz, ArCH(CH3)2), 3.28 (dd, J = 4.4, 4.0 Hz, 2H, CH2CH2Py),
2.62 (dd, J = 4.6, 4.0 Hz, 2H, CH2CH2Py), 1.84 (s, 3H, backbone-
CH3), 1.82 (s, 3H, backbone-CH3), 1.37 (d, 6H, J = 6.8 Hz,
ArCH(CH3)2), 1.28 (d, 6H, J = 6.8 Hz, ArCH(CH3)2. 1H NMR
(C6D6, 500 MHz, 298 K, δ): 7.96 (d, 1H, J = 5.5 Hz, Py1), 7.27−7.19
(m, 3H, Ar-H), 6.78 (dd, 1H, J = 7.5, 7.6 Hz, Py3), 6.43 (d, 1H, J = 7.6
Hz, Py4), 6.20 (dd, 1H, J = 5.5, 7.5 Hz, Py2), 4.93 (s, 1H, backbone-
CH), 3.74 (septet, 2H, J = 6.7 Hz, ArCH(CH3)2), 3.30 (dd, J = 4.3, 3.8
Hz, 2H, CH2CH2Py), 2.63 (dd, J = 4.3, 3.8 Hz, 2H, CH2CH2Py), 1.89
(s, 3H, backbone-CH3), 1.88 (s, 3H, backbone-CH3), 1.42 (d, 6H, J =
6.7 Hz, ArCH(CH3)2), 1.31 (d, 6H, J = 6.7 Hz, ArCH(CH3)2).
13C{1H} NMR (C6D6, 125 MHz, 298 K, δ): 163.30, 161.80, 161.59,
150.53, 149.99, 141.19, 137.01, 125.42, 123.86, 123.74, 122.27, 94.26,
47.45, 41.69, 28.47, 24.85, 24.15, 23.58, 21.70. Anal. Calcd for
C24H32CuN3: C, 67.65; H, 7.57; N, 9.86. Found: C, 67.71; H, 7.59; N,
9.78.
EXPERIMENTAL SECTION
■
All manipulations involving N-aryl-N′-alkyl β-diketiminato ligands and
copper(I) complexes were carried out under an atmosphere of purified
dinitrogen in a drybox or using standard Schlenk techniques. Chemical
reagents were purchased from Aldrich Chemical Co. Ltd., Lancaster
Chemicals Ltd., or Fluka Ltd. All reagents were used without further
purification, apart from all solvents, which were dried over Na (Et2O,
THF) or CaH2 (CH2Cl2, CH3CN) and then thoroughly degassed
before use. Pure CuOtBu and N-aryl-N′-alkyl β-diketiminato ligands
L1H−L4H were synthesized following published procedures.45,64−66
Ligands L1PhH and L3PhH were prepared by procedures similar to
those for L1H, which are described in the Supporting Information. IR
spectra were recorded using a Varian FT-IR 640 spectrometer. In situ
FTIR measurements were performed using a Mettler Toledo ReactIR
iC10 system equipped with a HgCdTe (MCT) detector and a 0.625
1
in. SiComp probe. H NMR and 13C NMR spectra were acquired
using a Varian Gemini-200 proton/carbon FT NMR, a 400 MHz
NMR, or a Varian Gemini-500 proton/carbon FT NMR spectrometer.
Elemental analyses were performed using a Heraeus CHN-OS Rapid
Elemental Analyzer. Cyclic voltammetry measurements were taken in
10−4 M MeCN solutions using 0.1 M (Bu4N)(PF6) as supporting
electrolyte and referenced to Fc+/0. A platinum-wire counter electrode,
glassy-carbon working electrode, and Ag/AgCl (MeCN) reference
electrode were used.
CuL3. Under an inert atmosphere a solution of L3H (1.00 g, 3.26
mmol) in 3 mL of hexane was added to a slurry of CuOtBu (0.44 g,
3.26 mmol) in 5 mL of hexane and stirred for 60 min. This complex
was isolated from hexane to give orange crystals of CuL3 (1.07 g,
Preparation of Cu(I) Complexes. The syntheses of CuL1−CuL4
were carried out using similar procedures. A representative example for
the synthesis of CuL1 is given below.
1
88%). H NMR (toluene-d8, 400 MHz, 293 K, δ): 7.81 (br s, 1H,
CuL1. Under an inert atmosphere a solution of L1H (1.00 g, 2.86
mmol) in 15 mL of hexane was added to a slurry of CuOtBu (0.39 g,
2.86 mmol) in 30 mL of hexane, and the mixture was stirred for 60
min. The solvent was removed under vacuum and the residue
extracted with 75 mL of hexane and filtered through a plug of Celite.
The volume was reduced and the solution was placed at −20 °C
overnight, yielding the orange crystalline solid CuL1 (0.95 g, 81%). 1H
NMR (toluene-d8, 400 MHz, 298 K, δ): 7.92 (d, 1H, J = 5.4 Hz, Py1),
7.20−7.12 (m, 3H, Ar-H), 6.76 (dd, 1H, J = 6.3, 7.6 Hz, Py3), 6.43 (d,
1H, J = 7.6 Hz, Py4), 6.29 (dd, 1H, J = 5.4, 6.3 Hz, Py2), 5.01 (s, 1H,
backbone-CH), 4.16 (s, 2H, CH2Py), 3.61 (septet, 2H, J = 6.8 Hz,
ArCH(CH3)2), 1.90 (s, 3H, backbone-CH3), 1.87 (s, 3H, backbone-
CH3), 1.40 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 1.29 (d, 6H, J = 6.8 Hz,
ArCH(CH3)2). 1H NMR (C6D6, 500 MHz, 298 K, δ): 7.86 (d, 1H, J =
5.5 Hz, Py1), 7.26−7.18 (m, 3H, Ar-H), 6.71 (dd, 1H, J = 7.2, 7.7 Hz,
Py3), 6.41 (d, 1H, J = 7.7 Hz, Py4), 6.26 (dd, J = 5.5, 7.2 Hz 1H, Py2),
Py1), 6.89 (s, 2H, Ar-H1,2), 6.76 (d, 1H, J = 7.6 Hz, Py3), 6.45 (d, 1H,
J = 7.6 Hz, Py2), 6.24 (br s, 1H, Py4), 4.98 (s, 1H, backbone-CH),
4.19 (s, 2H, CH2Py), 2.37 (s, 6H, ortho ArCH3), 2.24 (s, 3H, para
ArCH3), 1.90 (s, 3H, backbone-CH3), 1.84 (s, 3H, backbone-CH3). 1H
NMR (C6D6, 400 MHz, 298 K, δ): 7.82 (br s, 1H, Py1), 6.95 (s, 2H,
Ar-H1,2), 6.69 (d, 1H, J = 7.8 Hz, Py3), 6.44 (d, 1H, J = 7.8 Hz, Py2),
6.17 (br s, 1H, Py4), 5.08 (s, 1H, backbone-CH), 4.25 (s, 2H, CH2Py),
2.45 (s, 6H, ortho ArCH3), 2.26 (s, 3H, para ArCH3), 1.96 (s, 3H,
backbone-CH3), 1.92 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6,
100.06 MHz, 298 K, δ): 161.76, 150.92, 135.86, 131.65, 130.98,
129.81, 122.21, 122.09, 95.28, 53.64, 23.86, 21.70, 20.09. Anal. Calcd
for C20H24CuN3: C, 64.93; H, 6.54; N, 11.36. Found: C, 64.14; H,
6.55; N, 11.32.
CuL4. Under an inert atmosphere a solution of L4H (1.05 g, 3.26
mmol) in 2 mL of hexane was added to a slurry of CuOtBu (0.44 g,
J
DOI: 10.1021/acs.inorgchem.6b02876
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3.26 mmol) in 4 mL of hexane and stirred for 60 min. This complex
was isolated from hexane to give red crystals of CuL4 (0.99 g, 79%).
1H NMR (toluene-d8, 400 MHz, 293 K, d): 7.91 (d, 1H, J = 5.6 Hz,
Py1), 6.93 (s, 2H, Ar-H1,2), 6.81 (dd, 1H, J = 8.2, 7.6 Hz, Py3), 6.45
(d, 1H, J = 7.6 Hz, Py4), 6.24 (dd, 1H, J = 5.6, 8.2 Hz, Py2), 4.82 (s,
1H, backbone-CH), 3.29 (dd, 2H, J = 5.0, 4.4 Hz, CH2CH2Py), 2.62
(dd, 2H, J = 5.0, 4.4 Hz, CH2CH2Py), 2.39 (s, 6H, ortho ArCH3), 2.28
(s, 3H, para ArCH3), 1.86 (s, 3H, backbone-CH3), 1.78 (s, 3H,
backbone-CH3). 1H NMR (C6D6, 400 MHz, 298 K, δ): 7.95 (d, 1H, J
= 5.2 Hz, Py1), 7.00 (s, 2H, Ar-H1,2), 6.78 (dd, 1H, J = 8.0, 7.4, Hz,
Py3), 6.42 (d, 1H, J = 7.4 Hz, Py4), 6.19 (dd, 1H, J = 5.2, 8.0 Hz Py2),
4.93 (s, 1H, backbone-CH), 3.30 (dd, 2H, J = 4.8, 4.2 Hz,
CH2CH2Py), 2.62 (dd, 2H, J = 4.8, 4.2 Hz, CH2CH2Py), 2.48 (s,
6H, ortho ArCH3), 2.30 (s, 3H, para ArCH3), 1.90 (s, 3H, backbone-
CH3), 1.87 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100.06
MHz, 298 K, δ): 163.63, 161.83, 161.36, 151.39, 150.15, 137.21,
131.47, 130.91, 129.81, 125.60, 122.54, 94.46, 47.77, 41.85, 23.49,
21.99, 21.73, 20.13. Anal. Calcd for C20H26CuN3: C, 64.93; H, 6.54; N,
11.36. Found: C, 64.14; H, 6.55; N, 11.32. Calcd for C42H52Cu2N6: C,
65.69; H, 6.82; N, 10.94. Found: C, 65.11; H, 6.89; N, 11.01.
H1,2), 6.69 (d, 1H, J = 8.6 Hz, Py4), 6.55 (dd, 1H, J = 6.2, 8.2 Hz,
Py2), 4.76 (s, 1H, backbone-CH), 3.89 (dd, 2H, J = 5.0, 4.6 Hz,
CH2CH2Py), 2.96 (dd, 2H, J = 5.0, 4.6 Hz, CH2CH2Py), 2.21 (s, 6H,
ortho ArCH3), 2.20 (s, 3H, para ArCH3), 1.88 (s, 3H, backbone-CH3),
1.66 (s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100 MHz, 298 K,
d):179.78, 165.79, 162.89, 161.46, 150.83, 150.48, 136.44, 132.7,
130.69, 129.89, 124.44, 121.83, 96.13, 54.92, 42.93, 22.86, 22.47,
21.64, 19.63.
General Procedure for the Preparation of Copper(I) 2,6-
Xylyl Isocyanide Complexes. To the appropriate Cu(I) complex
(typically 0.1 g) in toluene (3 mL) was added an equimolar amount of
2,6-xylyl isocyanide (2,6-CNC6H3Me2) solution in toluene (2 mL).
The resulting yellow-brown solution was stirred for 3 h under an inert
atmosphere. The solution was filtered and concentrated to half of its
original volume, layered with hexane (5 mL), and kept at −20 °C
overnight. Yellow crystals formed after 1 day.
L1Cu(2,6-CNC6H3Me2). Yield: 86%. 1H NMR (C6D6, 400 Hz, 298 K,
δ): 8.49 (d, 1H, J = 5.7 Hz, Py1), 7.55 (dd, 1H, J = 7.4, 7.9 Hz, Py3),
6.5−7.22 (m, 6H, Ar (CN) + Ar-H), 6.28 (dd, 1H, J = 5.7, 7.4 Hz,
Py2), 6.46 (d, 1H, J = 7.9 Hz, Py4), 5.38 (s, 2H, CH2Py), 4.94 (s, 1H,
backbone-CH), 3.57 (septet, 2H, J = 7.8 Hz, ArCH(CH3)2), 2.00 (s,
3H, backbone-CH3), 1.85 (s, 3H, backbone-CH3), 1.69 (s, 6H, ortho
Ar(CH3)2(CN)), 1.35 (d, 6H, J = 7.8 Hz, ArCH(CH3)2), 1.30 (d,
6H, J = 7.8 Hz, ArCH(CH3)2). 13C NMR (C6D6, 100 Hz, 298 K, δ):
166.45, 165.15, 163.28, 153.24, 150.88, 149.86, 141.14, 136.46, 135.46,
128.99, 128.31, 124.42, 123.94, 122.19, 121.77, 96.08, 62.56, 28.79,
25.46, 24.05, 23.89, 21.34, 18.91. Anal. Calcd for C32 H39 N4: C,70.76;
H, 7.23; N, 10.31. Found: C, 70.76; H,7.26 ; N, 10.34.
L2Cu(μ-OH)2CuL2. A solution of L2Cu in MeCN (50 mg in 10 mL)
was oxygenated by bubbling of O2 at ambient temperature for 60 s.
The resulting green-brown solution was layered with 10 mL of toluene
and allowed to stand at −20 °C. Brown single crystals formed after 3
days and were either mounted for analysis by X-ray crystallography or
collected by decanting the mother liquor, washed with cold toluene,
and dried in vacuo (23 mg). Anal. Calcd for C48H66Cu2N6O2: C,
65.06; H, 7.51; N, 9.48. Found: C, 65.09; H, 7.49; N, 9.51.
Reaction of Cu(I) Complexes with CO. General Procedure. A
10 mL Schlenk flask under an inert atmosphere was charged with a 40
mM solution of the desired Cu(I) complex in toluene (5 mL) and
sealed using a septum. Carbon monoxide was bubbled through the
solution at room temperature, at which point the IR spectrum was
recorded. For NMR examination, the desired Cu(I) complex was
dissolved in C6D6 (1.0 mL) in a screw-capped NMR tube. Carbon
monoxide was gently bubbled into the solution for 20 min at ambient
temperature, during which time the color changed from red-orange to
L2Cu(2,6-CNC6H3Me2). Yield: 82%. 1H NMR (C6D6, 400 Hz, 298 K,
δ): 8.48(d, 1H, J = 5.7 Hz, Py1), 6.96−7.19 (m, 6H, Ar(CN) + Ar-
H), 6.68 (dd, 1H, J = 7.6, 7.8 Hz, Py3), 6.60 (d, 1H, J = 7.8 Hz, Py4),
6.53 (dd, 1H, J = 5.7, 7.6 Hz, Py2), 4.89 (s, 1H, backbone-CH), 4.2 (s,
2H, J = 4.5, 3.9 Hz, CH2CH2Py), 3.56 (septet, 2H, J = 6.8 Hz,
ArCH(CH3)2), 3.52 (dd, 2H, J = 4.5, 3.9 Hz, CH2CH2Py), 2.00 (s, 3H,
backbone-CH3), 1.87 (s, 6H, ortho Ar(CH3)2(CN)), 1.84 (s, 3H,
backbone-CH3), 1.33 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 1.28 (d, 6H, J
= 6.8 Hz, ArCH(CH3)2). 13C NMR (C6D6, 100 Hz, 298 K, δ): 165.59,
162.51, 162.04, 154.06, 151.15, 150.40, 141.29, 136.15, 135.81, 129.12,
124.26, 123.99, 123.90, 121.52, 95.77, 55.70, 44.66, 28.72, 25.58,
24.14, 23.83, 22.92, 19.08. Anal. Calcd for C33H41N4: C, 71.13; H,
7.42; N, 10.05. Found: C, 71.11; H, 7.50; N, 10.06.
1
yellow. The CO adducts were immediately characterized by H and
13C{1H} NMR spectroscopy.
1
L1Cu−CO. H NMR (C6D6, 400 MHz, 298 K, δ): 8.46 (d, 1H, J =
5.6 Hz, Py1), 7.11−7.10 (m, 3H, Ar-H), 7.07 (dd, 1H, J = 7.6, 8.0 Hz,
Py3), 7.01 (d, 1H, J = 8.0 Hz, Py4), 6.6 (dd, 1H, J = 5.6, 7.6 Hz, Py2),
4.88 (s, 2H, CH2Py), 4.85 (s, 1H, backbone-CH), 3.3 (septet, 2H, J =
7.3 Hz, ArCH(CH3)2), 1.91 (s, 3H, backbone-CH3), 1.71 (s, 3H,
backbone-CH3), 1.19 (d, 6H, J = 7.3 Hz, ArCH(CH3)2), 1.18 (d, 6H, J
= 7.3 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ):
179.18 (CO), 166.63, 164.09, 163.82, 150.33, 150, 141.16, 136.69,
125.44, 124.21, 122.97, 122.52, 96.43, 61.48, 28.64, 25.25, 23.97,
23.59, 23.05.
L3Cu(2,6-CNC6H3Me2). Yield: 79%. 1H NMR (C6D6, 400 MHz, 298
K, δ): 8.50 (d, 1H, J = 5.9 Hz, Py1), 7.54 (dd, 1H, J = 7.9, 8.1 Hz,
Py3), 7.15 (d, 1H, J = 8.1 Hz, Py4), 6.88 (s, 2H, Ar-H1,2), 6.43−6.65
(m, 4H, Ar(CN) + Py2), 5.42 (s, 2H, CH2Py), 4.95 (s, 1H,
backbone-CH), 2.39 (s, 6H, ortho ArCH3), 2.21 (s, 3H, para ArCH3),
2.03 (s, 3H, backbone- CH3), 1.82 (s, 3H, backbone- CH3), 1.67 (s,
6H, ortho Ar(CH3)2(CN)). 13C NMR (C6D6,100 MHz, 298 K, δ):
166.50, 165.13, 162.92, 153.66, 151.48, 149.88, 136.54, 135.41, 131.80,
130.60, 129.65, 128.22, 122.20, 121.74, 96.07, 62.78, 23.03, 22.73,
21.63, 20.01, 18.87. Anal. Calcd for C29H33CuN4: C, 69.50; H, 6.64; N,
11.18. Found: C, 69.53; H, 6.67; N, 11.16.
1
L2Cu−CO. H NMR (C6D6, 400 MHz, 298 K, δ): 8.46 (d, 1H, J =
5.8 Hz, Py1), 7.13−7.11 (m, 3H, Ar-H) 7.05 (dd, 1H, J = 7.7, 7.8 Hz,
Py3), 6.72 (d, 1H, J = 7.8 Hz, Py4), 6.59 (dd, 1H, J = 5.8, 7.7 Hz,
Py2), 4.78 (s, 1H, backbone-CH), 3.98 (dd, 2H, J = 4.7, 4.1 Hz,
CH2CH2Py), 3.29 (septet, 2H, J = 6.7 Hz, ArCH(CH3)2), 3.04(dd,
2H, J = 4.7, 4.1 Hz, CH2CH2Py), 1.88 (s, 3H, backbone-CH3), 1.69 (s,
3H, backbone-CH3), 1.2 (d, 6H, J = 6.7 Hz, ArCH(CH3)2), 1.18 (d,
6H, J = 6.7 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298
K, δ): 179.98, 166.14, 163.54, 161.21, 150.58, 150.16, 141.24, 136.33,
125.34, 124.26, 124.19, 121.8, 96.41, 55.32, 43.61, 28.62, 25.36, 24.06,
23.61, 22.58.
L4Cu(2,6-CNC6H3Me2). Yield: 86%. 1H NMR (C6D6, 400 MHz, 298
K, δ): 8.47 (d, 1H, J = 6.0 Hz, Py1), 7.09 (dd, 1H, J = 8.0, 8.2 Hz,
Py3), 6.98 (d, 1H, J = 8.2 Hz, Py4), 6.9 (s, 2H, Ar-H1,2), 6.50−6.70
(m, 4H, Ar(CN) + Py2), 4.88 (s, 1H, backbone-CH), 4.22 (dd, 2H,
J = 5.6, 4.6 Hz, CH2CH2Py), 3.49 (dd, 2H, J = 5.6, 4.6 Hz,
CH2CH2Py), 2.37 (s, 6H, ortho ArCH3), 2.23 (s, 3H, para ArCH3),
2.03 (s, 3H, backbone-CH3), 1.84 (s, 3H, backbone-CH3), 1.81 (s, 6H,
ortho Ar(CH3)2(CN)). 13C NMR(C6D6,100 MHz, 298 K, δ):
165.44, 162.16, 162.01, 154.14, 151.68, 150.40, 136.11, 135.63, 131.59,
130.72, 129.56, 128.98, 128.31, 124.08, 121.49, 95.74, 55.83, 44.55,
23.00, 22.89, 21.65, 20.04, 18.99. Anal. Calcd for C30H35CuN4: C,
69.94; H, 6.85; N, 10.88. Found: C, 69.86; H, 6.78; N, 10.90.
General Procedure for the Preparation of Copper(I) PPh3
Complexes. To an appropriate Cu(I) complex (typically 0.1 g) in
toluene (3 mL) was added an equal molar amount PPh3 solution in
toluene (2 mL). The resulting yellow solution was stirred for 1 h
under an inert atmosphere. The solvent was evaporated under vacuum
1
L3Cu−CO. H NMR (C6D6, 400 MHz, 298 K, δ): 8.43 (d, 1H, J =
4.2 Hz, Py1), 7.04 (dd, 1H, J = 7.0, 7.8, Py3), 6.99 (d, 1H, J = 7.8 Hz,
Py4), 6.85 (s, 1H, Ar-H1,2), 6.58 (dd, 1H, J = 4.2, 7.0 Hz, Py2), 4.89
(s, 2H, CH2Py), 4.85 (s, 1H, backbone-CH), 2.19 (s, 6H, ortho
ArCH3), 2.17 (s, 3H, para ArCH3), 1.93 (s, 3H, backbone-CH3), 1.67
(s, 3H, backbone-CH3). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ):
179.87, 166.49, 163.79, 163.65, 150.74, 150.29, 136.72, 132.91, 130.49,
129.89, 122.87, 122.44, 96.37, 61.5, 22.98, 22.77, 21.59, 19.64.
1
L4Cu−CO. H NMR (C6D6, 400 MHz, 298 K, d): 8.40 (d, 1H, J =
6.2 Hz, Py1), 7.02 (dd, 1H, J = 8.2, 8.6 Hz, Py3), 6.89 (s, 2H, Ar-
K
DOI: 10.1021/acs.inorgchem.6b02876
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
and the residue extracted with hexane. The solution was evaporated
again to give yellow product.
The in situ IR spectra were obtained in the 2050−2100 cm−1 range. A
buildup of copper(I)−CO adducts was observed at 2065 cm−1. The
decarbonylation of copper(I)−CO adducts was carried out by
bubbling dry N2 gas through the solution at room temperature.
Using the in situ IR monitoring results and calculated absorbance to
molar concentration, plots of time (seconds) versus [LCuI−CO] were
found to be linear, and the slope afforded the representative kCO and
k−CO values; KCO values could be determined using eqs 1 and 2. On
the basis of previous literature, the concentration of CO was assumed
to be constant under saturation conditions.68
X-ray Crystal Structure Determinations. Single-crystal X-ray
diffraction data were measured on a Bruker Nonius Kappa CCD
diffractometer using Mo Kα radiation (λ = 0.71073 Å). The SMART
program was used for data collection.69 Cell refinement and data
reduction were performed using the SAINT program.70 The structures
were determined using the SHELXTL/PC program71 and refined
using full-matrix least squares. All non-hydrogen atoms were refined
anisotropically, whereas the hydrogen atoms were placed at calculated
positions and included in the final stage of refinements with fixed
parameters. A summary of the relevant crystallographic data for all
copper(I) complexes is provided in Tables S1−S3 in the Supporting
Information.
L1Cu(PPh3). Yield: 96%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.42
(ddd, 1H, J = 5.7, 2.3, 1.3 Py1), 7.32 (d, 1H, J = 5.8, 5.6 Hz, Ar-H2),
7.19 (ddd, 2H, J = 2.3, 7.7, 7.7 Hz, Py3), 7.14 (ddd, 1H, J = 7.7, 1.3,
1.3 Hz, Py4), 7.10- 6.86 (m, 16H, J = 6.8 Hz, PPh3 + Ar-H1,3) 6.65
(ddd, 1H, J = 7.7, 5.7, 1.3 Hz, Py2), 5.16 (s, 2H, CH2Py), 5.09 (s, 1H,
backbone-CH), 3.63 (septet, 2H, J = 6.9 Hz, ArCH(CH3)2), 1.95 (d,
6H, J = 5.5 Hz, backbone-CH3), 1.30 (d, 6H, J = 6.9 Hz,
ArCH(CH3)2), 0.96 (d, 6H, J = 6.9 Hz, ArCH(CH3)2). 13C{1H}
NMR (C6D6, 100 MHz, 298 K, δ): 167.59, 164.53, 163.39, 151.48,
149.94, 141.3, 136.38, 134.44, 130.21, 129.45, 124.49, 124.28, 121.26,
96.72, 62.17, 30.72, 28.93, 24.46, 24.32, 22.71. 31P{1H} NMR (C6D6,
162 MHz, 298 K, δ): 3.24. Anal. Calcd for C41H47CuN3P: C, 73.03; H,
6.73; N, 6.23. Found: C, 72.99; H, 6.76; N, 6.21.
L2Cu(PPh3). Yield: 97%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.37
(d, 1H, J = 5.6 Hz, Py1), 7.29 (m, 6H, PPh3 + Ar-H2), 7.29 (dd, 1H, J
= 7.9, 7.8 Hz, Py3), 7.13 (d, 1H, J = 4.9, 4.4 Hz, Ar-H2), 6.99 (m, 11H,
PPh3 + Ar-H1), 6.57 (dd, 1H, J= 5.6, 7.9 Hz, Py2), 6.31 (d, 1H, J = 7.8
Hz, Py4), 4.96 (s, 1H, backbone-CH), 4.03 (dd, 2H, J = 4.4, 3.7, 5.9
Hz, CH2CH2Py), 3.59 (septet, 2H, J = 6.8 Hz, ArCH(CH3)2), 2.96
(dd, 2H, J = 4.4, 3.7 Hz, CH2CH2Py), 2.1 (s, 3H, backbone-CH3), 1.87
(s, 3H, backbone-CH3), 1.22 (d, 6H, J = 6.8 Hz, ArCH(CH3)2), 0.9 (d,
6H, J = 6.8 Hz, ArCH(CH3)2). 13C{1H} NMR (C6D6, 100 MHz, 298
K, δ): 166.12, 162.59, 161.47, 151.72, 150.14, 141.62, 135.9, 134.65,
130.34, 129.61, 124.45, 124.24, 123.44, 121.35, 96.48, 56.48, 43.20,
28.75, 24.62, 24.43, 22.21. 31P{1H} NMR (C6D6, 162 MHz, 298 K, δ):
2.74. Anal. Calcd for C42H47CuN3P: C, 73.28; H, 6.88; N, 6.10.
Found: C, 73.23; H, 6.90; N, 6.11.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b02876.
L3Cu(PPh3). Yield: 98%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.39
(ddd, 1H, J = 5.8, 2.4, 1.4 Hz, Py1), 7.36 (ddd, 1H, J = 2.4, 7.8, 7.8 Hz,
Py3), 7.08 (ddd, 1H, J = 7.6, 1.4, 1.4 Hz, Py4), 6.98- 6.80 (m, 16H,
PPh3 + Ar-H1,3), 6.60 (ddd, 1H, J = 5.8, 7.8, 1.4 Hz, Py2), 5.17 (s, 2H,
CH2Py), 5.04 (s, 1H, backbone-CH), 2.25 (s, 3H, para ArCH3), 2.2 (s,
6H, ortho ArCH3), 1.95 (s, 3H, backbone-CH3), 1.83 (s, 3H,
backbone-CH3). 13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 167.3,
164.67, 162.89, 151.54, 149.9, 136.48, 134.51, 131.79, 131.02, 130.14,
129.88, 129.35, 121.29, 96.68, 62.3, 23.48, 22.69, 21.71, 19.79. 31P{1H}
NMR (C6D6, 162 MHz, 298 K, δ): 2.92. Anal. Calcd for
C38H39CuN3P: C, 72.19; H, 6.22; N, 6.65. Found: C, 72.17; H,
6.23; N, 6.66.
Additional figures and tables as described in the text
(PDF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail for S.C.N.H.: sodiohsu@kmu.edu.tw.
■
L4Cu(PPh3). Yield: 98%. 1H NMR (C6D6, 400 MHz, 298 K, δ): 8.40
(d, 1H, J = 5.3 Hz, Py1), 7.30 (m, 7H, J = 8.1, 7.5 Hz, PPh3 + Py3),
6.98 (m, 9H, PPh3), 6.76 (s, 2H, Ar-H1,3), 6.58 (dd, 1H, J = 7.5 Hz,
Py4), 6.35 (d, 1H, J = 5.3, 8.1 Hz, Py2), 4.95 (s, 1H, backbone-CH),
4.08 (dd, 2H, J = 4.9, 4.1 Hz, CH2CH2Py), 3.03 (dd, 2H, J = 4.9, 4.1
Hz, CH2CH2Py), 2.24 (s, 3H, para ArCH3), 2.19 (s, 6H, ortho
ArCH3), 2.12 (s, 3H, backbone-CH3), 1.81 (s, 3H, backbone-CH3).
13C{1H} NMR (C6D6, 100 MHz, 298 K, δ): 165.77, 162.05, 161.55,
151.8, 150.17, 135.96, 134.56, 131.61, 131.27, 130.22, 129.83, 129.47,
123.53, 121.37, 96.185, 56.53, 43.74, 23.59, 22.33, 21.73, 19.87.
31P{1H} NMR (C6D6, 162 MHz, 298 K, δ): 2.35. Anal. Calcd for
C39H41CuN3P: C, 72.48; H, 6.39; N, 6.50. Found: C, 72.58; H, 6.43;
N, 6.45.
ORCID
Sodio C. N. Hsu: 0000-0002-2576-7289
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support from the Ministry
of Science and Technology of Taiwan (MOST 102-2113-M-
037-008-MY3; MOST 104-2632-M-037-001), NSYSU-KMU
Joint Research Project (NSYSUKMU 105-P006), and
Kaohsiung Medical University “Aim for the Top University
Grant, Grant No. KMU-TP105PR12”. We thank Mr. Ting-
Shen Kuo, National Taiwan Normal University, for X-ray
structural determinations and Mr. Min-Yuan Hung, Center for
Research Resources and Development of KMU, for use of their
facilities.
Diffusion Ordered Spectroscopy (1H-DOSY) Experiments.
The internal reference method was employed for DOSY experiments
at room temperature according to previous literature procedures.58,67
Three different molecular weight compounds were chosen:
tetramethylsilane (TMS, MW = 88.23), hexamethyldisiloxane
(HMDSO, MW = 162.38), and 1,2-bis(trimethoxysilyl)ethane
(BTMSE, MW = 270.43). These three internal references and CuLn
were placed in an NMR tube, and 0.7 mL of toluene-d8 was added.
After the DOSY experiment was recorded, log D vs log MW values of
the three internal references were plotted (see the Supporting
Information). The molecular weight could then be obtained by a
calibration curve of the D value of the desired complex.
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■
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measurements were taken using a ReactIR spectrophotometer
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