Versatile Heteroleptic Cu(I) Complexes Based on Quino(xa)-line-Triazole Ligands: from Visible-Light Absorption and Cooperativity to Luminescence and Photoredox Catalysis

Article abstract of DOI:10.1002/ejic.202100653

Four new heteroleptic Cu(I) complexes based on 1, 2, 3-triazolyl-quinoline or quinoxaline and a chelating diphosphine were prepared and fully characterised. The mononuclear derivatives absorb in the visible region, up to 600 nm, while the dinuclear complex has a long-tail absorption up to 800 nm, showing an additional electronic state corroborated by theoretical calculations. Although a methylene group between the triazole and the quino(xa)line moiety increases the bite angle and decreases the luminescence in solution, all complexes emit brightly in the solid-state. Their redox properties in the excited state were determined, proving their ability in serving as photoredox catalysts in atom transfer radical addition successfully.

Full text of DOI:10.1002/ejic.202100653

European Journal of Inorganic Chemistry
Accepted Article
Title: Versatile heteroleptic Cu(I) complexes based on quino(xa)line-
triazole ligands. From visible-light absorption and cooperativity to
luminescence and photoredox catalysis.
Authors: Cecilia Bruschi, Xin Gui, Nasrin Salaeh-arae, Tobia Barchi,
Olaf Fuhr, Sergei Lebedkin, Wim Klopper, and Claudia
Bizzarri
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202100653
Link to VoR: https://doi.org/10.1002/ejic.202100653
01/2020

10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
Versatile heteroleptic Cu(I) complexes based on quino(xa)line-
triazole ligands. From visible-light absorption and cooperativity to
luminescence and photoredox catalysis.
Cecilia Bruschi,[a] Xin Gui,[b] Nasrin Salaeh-arae,[a] Tobia Barchi,[a] Olaf Fuhr,[c, d] Sergei Lebedkin,[c]
Wim Klopper,[b] Claudia Bizzarri*[a]
[a]
C. Bruschi, N. Salaeh-arae, T. Barchi, Dr. C. Bizzarri
Institute of Organic Chemistry,
Karlsruhe Institute of Technology
Fritz-Haber-Weg 6,
76137 Karlsruhe (Germany)
E-mail: bizzarri@kit.edu
Website: https://www.ioc.kit.edu/bizzarri/english/index.php
Dr. X. Gui, Prof. Dr. W. Klopper
Institute of Physical Chemistry–Theoretical Chemistry
Karlsruhe Institute of Technology (KIT),
Fritz-Haber-Weg 2, 76131 Karlsruhe (Germany)
Dr. O. Fuhr, Dr. S. Lebedkin
Institute of Nanotechnology
Karlsruhe Institute of Technology
Hermann-von-Helmholtz Platz 1, 76344Eggenstein-Leopoldshafen (Germany)
Dr. O. Fuhr
[b]
[c]
[d]
Karlsruhe Nano MicroFacility (KNMF)
Karlsruhe Institute of Technology
Hermann-von Helmholtz-Platz 1, 76344Eggenstein-Leopoldshafen (Germany)
Supporting information for this article is given via a link at the end of the document
Abstract: Four new heteroleptic Cu(I) complexes based on 1,2,3-
triazolyl-quinoline or quinoxaline and a chelating diphosphine were
prepared and fully characterised. The mononuclear derivatives
absorb in the visible region, up to 600 nm, while the dinuclear complex
has a long-tail absorption up to 800 nm, showing an additional
electronic state corroborated by theoretical calculations. Although a
methylene group between the triazole and the quino(xa)line moiety
increases the bite angle and decreases the luminescence in solution,
all complexes emit brightly in the solid-state. Their redox properties in
the excited state were determined, proving their ability in serving as
photoredox catalysts in atom transfer radical addition successfully.
which are remarkably well-performing, but cannot be considered
sustainable in the long term and for widespread use. Therefore,
envisioning a global use of such new technologies, we need to
shift our attention to other metals that are earth-abundant.[4]
Copper is one of the most promising alternatives.[5] This earth-
abundant metal has a d10 electronic configuration in its oxidative
state +1. Non-radiative metal-centred (MC) transitions are
consequently forbidden, while Cu(I) complexes exhibit metal-to-
ligand charge-transfer (MLCT) transitions, often absorbing at low
energy, in the visible region. Since the late 1970s, thanks to the
work of McMillin on the room temperature luminescent Cu(I)–
bis(1,10-phenanthrolines),[6] these complexes have attracted the
interest of many researchers and have been exploited in different
application fields, such as optoelectronics,[7] photovoltaics[8] or
photoredox catalysis.[9] Although the development of Cu(I)
coordination complexes has started over forty years, they have a
vast potential that is still uncovered. They have much shorter
excited state lifetimes than Ru(II) or Ir(III) complexes. Heteroleptic
Cu(I) complexes made of diimine (N^N) and chelating phosphine
(P^P) with bulky substituents are appealing. Their sterical
hindrance is known to reduce the possible Jahn-Teller distortion
that affects Cu(I) complexes in their excited state,[10] avoiding
possible non-radiative pathways responsible for low emission
quantum yield and short-living lifetime. Our scientific target is to
develop new Cu(I) complexes that can absorb visible light and find
applications as photosensitisers and photoredox catalysts. With
this in mind, we look for alternative ligands that can replace the
ubiquitous 1,10-phenanthroline. Thus, in this work, new copper
complexes have been synthesised with quino(xa)line-based
Introduction
Nowadays, the need for clean energy is increasing in the face of
an economy that cannot rely on fossil fuels anymore, a limited and
non-renewable resource responsible for global damages such as
the greenhouse effect. For this reason, many efforts are made for
finding new alternative energy systems.[1] Among them, the
cleanest and the most easily accessible one is sunlight. Nature
can exploit and store this source by converting water and CO2 into
organic compounds such as glucose. Many strategies focus on
developing coordination metal complexes to increase
[2]
sustainability in solar energy conversion
and optoelectronic
applications.[3] The majority of these transition metal complexes
are based on expensive ruthenium, iridium or other rare metals,
1
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10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
ligands, expecting an increased absorbance towards long
wavelengths (> 400 nm). The synthesis of these ligands is
straightforward and does not need the use of Pd catalysts as in
our previously reported ligands.[11] Furthermore, the quinoxaline
heterocycle allows the coordination of a second Cu(I) nucleus, so
that a dinuclear complex could be obtained and the cooperativity
between these two metal centres was investigated. The chelating
phosphine was the bulky bis [(2-diphenylphosphino)phenyl] ether
(DPEPhos) for all complexes
reported herein. Full
electrochemical and photophysical characterisations were
performed and their results are supported by theoretical
calculations. Finally, these complexes were tested as photoredox
catalysts in the atom transfer radical addition (ATRA).[12]
Scheme 1. (Left) Synthetic procedures for the monochelating ligands 5, 6, 7 and dichelating ligand 8. (i) NH4Cl; (ii) NBS; benzoylperoxide; (iii) NaN3;
ethynylbenzene; CuSO4·5H2O; sodium ascorbate; Na2CO3. (Right) Synthetic procedures for the mononuclear complexes 1, 2, 3 and dinuclear complex 4.
(Cu(CH3CN)4BF4) and a chelating diphosphine (DPEPhos) at
room temperature, under inert atmosphere and in dry solvent
Results and Discussion
(dichloromethane, DCM) (see Scheme 1, right side). The
mononuclear complexes 1-3 and the dinuclear complex 4 were
isolated after removing the solvent under reduced pressure.
The mononuclear complexes formed good quality crystals by slow
diffusion of cyclohexane, in which the complexes are not soluble,
into their concentrated solutions in dichloromethane. Although we
purified complex 4 via the same method, the crystals obtained
were not good for X-ray diffraction. The X-ray crystal structures of
1-3 are shown in Figure 1. All structures belong to the triclinic
system with the P1 space group. The three compounds show
similar distances between the metal center and the coordinative
nitrogen atoms, with a smaller length between Cu and the triazole
(1: 2.087 Å, 2: 2.095 Å, 3: 2.059 Å) than between Cu and the
quino(xa)line (1: 2.129 Å, 2: 2.117 Å, 3: 2.139 Å). The distances
between Cu and the two P atoms also show similarity (1: 2.2487
Å 2: 2.2991 Å 3: 2.273 Å for Cu-P1 and 1: 2.3107 Å 2: 2.2555 Å 3:
2.2627 Å for Cu-P2). Moreover, the three complexes show similar
angles N2-Cu-N4 (1: 91.1°, 2: 89.79°, 3: 90.6°) and P1-Cu-P2 (1:
110.59°, 2: 111.72°, 3: 113.37°). The bite angles values suggest
a pseudo-tetrahedral geometry for all described compounds.
Complex 1 presents a weak interaction (Figure S9.1) between the
phenyl group of the triazole (at position 4) and a phenyl group
bound to P2 with an angle between the two rings planes of 11.80°
and a distance between the two rings centroids of 4.122 Å.
Complex 2 shows a weaker interaction involving the same units
(Figure S9.2, angle between the two planes: 31.44°, distance
between the two centroids: 4.580 Å). Differently from the two
previous cases, complex 3 has a π-π stacking interaction
between one phenyl group bound to P2 of the DPEPhos and the
six-member ring containing the heteroatoms of the quinoxaline
moiety of the diimine ligand (see rings E’ and A in Figure S9.3,
Synthesis and X-Ray structures
The diimine ligands presented herein are shown in Scheme 1
together with the respective synthetic steps. These ligands
possess the same chelating binding mode: dative bonds from the
N atom in position 2 of the 1,2,3-triazole and from the N atom in
position 1' of the quinoxalyl (for ligand 5, 7 and 8) or quinolyl (for
ligand 6) substituent. They can be synthesised in few steps,
without the need of expensive catalysts or harsh conditions. The
first step is the synthesis of brominated derivatives of
quino(xa)lines. The monobrominated (9) and its corresponding
dibrominated (12) precursors were obtained with high yield
through a condensation reaction involving ammonium chloride as
catalyst.[13] This reaction was fast (ca. 30 min) and showed an
evident stepwise change of colours, from yellow to red and finally
to greyish. Differently, the monobrominated precursor 10 was
obtained with a modified procedure[14] of a radical bromination
reaction, using N-bromosuccinimide as bromine donor and
benzoylperoxide as initiator, directly on quinaldine (2-methyl-
quinoline). The monobrominated precursor 11 was synthesised
adopting both procedures used for other ligands, namely, the
condensation reaction followed by the radical bromination. Then,
all the bromoderivatives underwent a nucleophile substitution by
sodium azide and, in a one-pot reaction, cyclisation with
ethynylbenzene via a Cu alkyne-azide cycloaddition (CuAAC).[15]
For the dichelating ligand 12 a double number of equivalents of
NaN3 and ethynylbenzene was necessary.
The so-obtained ligands needed no further purification and were
used for the synthesis of Cu(I) complexes . As known from
literature,[16] heteroleptic Cu(I) complexes are formed upon
addition of the diimine ligands to a solution of a Cu(I) precursor
2
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10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
angle between the two planes: 6.35°, distance between the two
centroids: 3.595 Å). Indeed, in complex 3, the phenyl group of the
triazole is interacting not with the phenyl group of the DPEPhos,
as in complexes 1 and 2, but with the phenyl group of the ligand
7 (in position 3' of the quinoxaline moiety) of the next Cu(I)
complex (see G and C rings in Figure S9.5, angles between the
two planes: 17.68°, distance between the two centroids: 3.818 Å).
Complex 3 is the only complex in this study showing such packing
in the solid state.
Figure 1. ORTEP drawings of molecular structures of 1-3 in the solid state.
All four new complexes have a good stability in dichloromethane
solvent. Indeed, for each complex the 1H-NMR spectra in CD2Cl2
remained identical even after a week (Figure S3.1-S3.4). On the
contrary, these compounds are not stable in coordinative polar
solvents such as acetonitrile (ACN), methanol, or N,N-
dimethylformamide (DMF). This instability is attributed to
nm are dominated by spin allowed transitions centred on the
diimine ligands and on the DPEPhos.
1
decoordination. In fact, the H-NMR spectra of the NˆN ligands
and their corresponding complexes are superimposable in ACN,
excluding the extra peaks due to DPEPhos in the complex
solution (Figure S3.9-S3.16). This lability is correlated to the
increased flexibility of NˆN, due to the presence of the methylene
spacer between the quino(xa)line and triazole units, affecting the
easiness of ligand exchange. Therefore, a comparison was done
for the bond lengths and bite angles between complexes 1-4 and
previously published Cu-complexes with a related structure
R1[11b] and R2[11a] (cf. Figure 2). In the latter the methylene spacer
is absent and they are stable in coordinative polar solvents.
Although complexes 1-3 show negligible difference in bond
lengths (Δ < 0.06 Å), more significant differences are associated
with the N^N bite angels N2-Cu-N4 (ca. 10°) in respect to R1[11b]
and R2[11a] (Table 1).
Figure 2. Structures of copper(I) complexes R1[11b] (left) and R2[11a] (middle) in
comparison to 1-3 (right).
The highest absorption peak at ca. 240 nm is attributed to the NˆN
ligands, it has a molar absorption coefficient ɛ = (4-7)·104 M-1cm-
1
in 5-8 and ɛ = (6-11)·104 M-1cm-1 in 1-4. The absorption at
around 280 nm is nearly absent in the NˆN ligands spectra and,
for this reason, can be assigned to a ligand centred transition 1LC
on the phosphine ligands. At ca. 320 nm, the absorption can be
assigned to a 1LC transition on the quin(ox)aline moiety, since the
spectra of the NˆN ligands also show a similar feature. As a further
proof, this value is nearly equal for the monochelating ligand 5
and its corresponding dichelating ligand 8, in which only one
quinoxaline unit is present. Finally, the absorption spectra of the
complexes show a low intensity band starting from the near-UV
and extending into the visible region (see insert in Figure 3),
which can be assigned to the population of a metal to ligand
charge transfer state, 1MLCT. In particular, this MLCT is a
transition that goes from the metal core to the quinoxaline unit for
complexes 1, 3 and 4, and to the quinoline unit for complex 2. This
attribution is corroborated by the theoretical calculations (vide
infra). The presence of one more electron-donating N atom in the
quinoxaline mojety causes a bathochromic shift of the MLCT of 1
(λabs: 425 nm) in respect to 2 (λabs: 376 nm), which shows basically
Table 1. Selected bond lengths and bond angles for 1, 2, 3 and R1[11b] and
R2.[11a]
Cu-N2
Bond
length
(Å)
Cu-N4
Bond
length
(Å)
Cu-P1
Bond
length
(Å)
Cu-P2
Bond
length
(Å)
N2-Cu-N4
Bond angle
(°)
P1-Cu-P2
Bond
angle
(°)
1
2.087
2.095
2.059
2.038
2.069
2.129
2.2487
2.2991
2.273
2.3107
2.2555
2.2627
2.2742
2.249
91.1
110.59
111.72
113.37
114.59
116.21
2
2.117
2.139
2.095
2.093
89.79
90.6
3
[17]
R1
R2
2.2168
2.249
79.93
79.8
[11a]
the same absorption of the quinoline-based complex R2[11a]
.
Complex 3 has a larger bathochromic shift at ca. 435 nm. This is
due to the presence of the phenyl substituent in 3 compared to
the methyl substituent in complex 1.
Photophysical characterisation
UV-Vis absorption spectra were recorded for compounds 1-4
(Figure 3) and their corresponding ligands 5-8 (Figure S5.1) in
DCM solutions. The absorption bands in the UV region below 350
3
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10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
excited-state lifetimes of complexes 1 (49 ns) and of 3 (43 ns) are
one order of magnitude lower compared to the lifetime of 2 (528
ns). However, since the quantum yield of 3 is only about three
times lower compared to the one of 2, this implies that both the
radiative (kr) and non-radiative constants (knr) of the quinoxaline
based complex 3 are higher compared to the quinoline based
1.2x105
1
2
3
4
1x105
2500
8x104
2000
complex 2. The PL lifetimes of 1-3 are short when compared to
[11a]
1500
the complex R2
(τ = 2.25 µs). This is especially surprising for
6x104
[11a]
complex 2, which shows almost the same emission as R2
.
1000
Therefore, this is a further evidence that the methylene spacer
between the quinoline and triazole units is responsible for more
efficient non-radiative deactivation pathways in solution for 2 , as
compared to R2[11a. Excitation spectra of 1-3 complexes were also
recorded and they fit nicely with the corresponding absorption
spectra.
4x104
500
0
400
500
600
700
800
2x104
0
300
400
500
600
700
800
Wavelenght (nm)
1.2
1
2
Figure 3. Absorption spectra recorded for complexes 1, 2, 3,
4
in
3
4
1
0.8
0.6
0.4
0.2
0
dichloromethane solutions (Inset: zoom-in of the near-UV-vis region).
Interestingly, in the absorption spectrum of the dinuclear complex
4, the 1MLCT transition shows a red shift (at 440 nm), compared
to its corresponding mononuclear complex 1, and a weak new
band, centred at around 600 nm. These results were confirmed
by theoretical calculations and could be related to a cooperative
effect between the two metal centres. To the best of our
knowledge, this is one of the few cases of heteroleptic copper(I)
complexes[18] where two copper centres share the same N^N
ligand and consequently the same lowest unoccupied energy
level, (LUMO), centred in this case on the quinoxaline unit.
Differently, most of the published dinuclear copper complexes
show two separated coordinated copper units, each with its own
LUMO level, communicating through a bridge unit, e.g. amine
based ligand [11a, 16] or phosphine based ligand.[19] [17, 20]
400
500
600
700
800
Wavelenght (nm)
The stability of all complexes in dichloromethane, as already
verified by 1H-NMR spectra, was checked with absorbance
spectra recorded at different times. The absorbance spectra of all
complexes do not show any change after a week and they do not
show any new peak (Figure S3.5-S3.8), which could have been
attributed to the absorption of an in situ formed homoleptic
complex [Cu(NˆN)2]+.
The emission spectra for 1-3 were recorded under inert
atmosphere (Ar) in dichloromethane at room temperature (Figure
4). While no emission of the dinuclear complex 4 was detectable
at room temperature, the spectra of 1-3 present broad and
structureless profile, as it is typical for MLCT transition. Moreover,
the photoluminescence (PL) is quenched in air-equilibrated
solutions, suggesting an involvement of the triplet excited state,
undergoing a triplet-triplet annihilation process with molecular
oxygen.
Figure 4. Emission (solid curves) and excitation (dotted curves) spectra of 1, 2,
3 recorded at room temperature (298 K) in Ar-saturated dichloromethane
solutions. Dashed curves: emission spectra of 1-4 recorded in
a
dichloromethane rigid matrix at 77 K .
Emission spectra of all complexes were recorded also in a
dichloromethane rigid matrix at 77 K (dashed curves, Figure 4).
The mononuclear complexes show a maximum emission that has
a hypsochromic shift compared to the emission spectra recorded
at room temperature, attributed to a rigidochromic effect,
confirming the contribution of a MLCT to the emissive state at
room temperature. The emission spectra of the mononuclear
complex 1, 3 and of the dinulcear complex 4 are broad and
structureless even at 77 K. On the other hand, the emission profile
of 2 suggests a more structured shape, which indeed is
manifested in solid state (Figure 5). The emission maxima of 1-3
The emission maxima are observed at ca. 741, 643 and 670 nm
for 1, 2 and 3, respectively. Interestingly, the emission of 3 is blue-
shifted compared to 1, despite its red-shifted MLCT absorption
at 77 K maintain the same order as at room temperature (λmax
:
649 nm, 543 nm, 632 nm for 1, 2 and 3 respectively). At 77 K even
the dinuclear complex 4 emits (λmax : 671 nm). Comparing its
emission to that of the corresponding mononuclear complex 1, the
maximum wavelength is red-shifted, confirming the presence of
an additional excited state.All photophysical properties are
summarised in Table 2.
1
band. This result suggests that a lower stabilisation of the excited
state occurs for 3 in respect to 1, since a higher stericall hindrance
is caused by the phenyl substituent in position 3' of the
quinoxaline moiety in complex 3, in comparison to the methyl
group in complex 1. This may have a significant role in contrasting
the Jahn-Teller effect,[21] typical for Cu(I) complexes in their
excited state.[22] Emission quantum yields are up to 1% in solution
at room temperature for the three emitting complexes. The
4
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10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
Table 2. Photophysical properties of the complexes 1-4 in solution (DCM) and in solid state.
Solution
Solid state
298 K
τ [b]
77 K
298 K
5 K
PLQY[a]
<0.001
0.01
PLQY[c]
PLQY[c]
0.70
λabs
λem
kr
(s-1
knr
(s-1
λem
λem
τ [d]
λem
τ [d]
Sample
(nm)
(nm)
(ns)
)
)
(nm)
(nm)
(ms)
(nm)
(ms)
0.20 (65%)
1.43 (55%)
0.40 (45%)
1
2
425
376
741
643
49
/
/
649
543
580
540
0.43
0.31
557
0.055 (35%)
528
1.89·104
1.88∙106
0.95
0.36 (72%)
496,
530,
560
1.63 (72%)
0.52 (28%)
0.072 (28%)
0.026 (52%)
0.33 (61%)
0.14 (39%)
3
4
435
670
n.d.
0.004
n.d.
43
9.30∙104
2.32∙107
632
672
600
737
0.16
621
742
0.70
0.0093 (48%)
0.012[e]
440,
600
45·10-6(65%)
250·10-6(35%)
0.81·10-3(70%)
6.9·10-3(30%)[e]
n.d.
/
/
0.0038
[a] PLQY values in the solution were estimated using Ru(bpy)3Cl2 in aerated water solution as reference (PLQY=0.040)[23] [24]
.[b] Lifetimes in solution a room
,
temperature were recorded with a time correlated single photon counting and with Nanoled as excitation source (λexc = 368 nm). [c] PLQY values in the solid state
were measured at 298 K using an integrating sphere and estimated at 5 K from the temperature-dependent emission spectra. [d] Lifetimes in the solid state were
recorded by connecting a photomultiplier to a fast oscilloscope and using a nitrogen laser (~2 nsec, ~5 µJ per pulse) for pulsed excitation at 337 nm. Indicated
lifetimes with relative weights in percent correspond to biexponential decay traces [e] This value was measured at 7 K.
.
In contrast to their weak PL in solution, 1-3 display bright emission
in the solid state with quantum yields of 43, 31 and 16%,
respectively, determined at room temperature using an
integrating sphere and excitation at 350 nm. In line with the
observation of practically absent PL of the dinuclear complex 4 in
solution, only very weak phosphorescence at ca. 737 nm was
detected for the solid compound (Figure 5). Its efficiency was
estimated as 0.38% at room temperature. By cooling 1-4 down to
5 K, the PL efficiency approaches, respectively, 70, 95, 70 and
1.2%, as estimated from the temperature-dependence emission
spectra (Figure 5). Such high efficiency may be attributed to rigid
molecular structures in the solid state and the absence of (co-
crystallized) solvent molecules in the coordination sphere.
Another distinct feature of the solid-state emission of 1-3 is its
significant blue shift compared to the DCM solutions, with the
maxima at about 580, 540 and 600 nm at 295 K. The onsets of
absorption in the excitation (PLE) spectra correspond, however,
to those in solution. Noteworthy, the emission spectra of 3 is red-
shifted compared to the one of 1, while at room temperature their
emission maxima are inverted. This behavior could be correlated
to the packing observed in the X-ray crystal structure of 3.
Note that the solid-state absorption/ PLE spectra are expected to
overemphasise the intensity of weak MLCT bands due to high
optical thickness and non-validity of the Beer-Lambert law for
polycrystalline sample preparations such as used in this work.
The PL decay occurs for solid complexes 1-3 on the time scale of
structured emission spectra, whereas the emission of 1 and 3
remains nearly structureless (Figure 5).
Figure 5. Emission (PL) and excitation (PLE) spectra of solid (polycrystalline)
complexes 1-4 in the temperature range of 5-295 K. The spectra were excited/
recorded at 350/560, 350/540, 400/620 nm and 450/800 nm, respectively.
a
few milliseconds - hundreds of microseconds at low
temperatures and moderately accelerates at 295 K, roughly
correlating with the decrease of the PL intensity (Figure S5.3).
Such long lifetimes clearly indicate that the emission is
phosphorescence, supporting the above conclusions derived
from the PL properties of 1-3 in solution. At low temperatures, in
particular below ~100 K, complex 2 shows vibronically well-
This difference might relate to the different patterns of π-π
stacking interaction in solid 1-3 (with the less pronounced one in
case of 2), as discussed above. Complex 3 is the only one
showing a bathochromic shift at lower temperatures, indicating for
5
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10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
this complex the possibility of a TADF behaviour.[25] Non-radiative
relaxation is thus strongly dominating in 4. Correspondingly, the
PL decay is relatively fast, with an effective lifetime of ca. 4 s at
7 K (Figure S5.3).
Table 3. Reduction and oxidation potentials of copper complexes 1-4 in DCM[a]
Sample
Eox [V]
Ered [V]
Eox* [V] [b]
Ered* [V] [b]
Electrochemical characterisation
1
2
3
4
0.88
0.75
0.90
0.89
-2.30
-1.37
-2.27
-1.99
n.d.
-0.05
0.62
0.72
n.d.
Cyclic voltammetry (CV) of compounds 1-4 was performed in Ar-
-2.40
saturated
DCM
solutions
using
tetrabutylammonium
hexafluorophosphate (TBAPF6) as supporting electrolyte. All the
CV herein presented are reported vs. ferrocene (Fc/Fc+), used as
an internal standard[26] (Figure 6). For comparison, the CV of the
diimine ligands 5-8 was measured (Figures S6.1-S6.4). Because
of reduced solubility in DCM of ligands 6 and 8, their CV were
measured in DMF. All complexes show an irreversible oxidation
process that is assigned to the CuI/CuII oxidation. These oxidation
potentials are at ca. 0.95 V for 1, 3 and dinuclear complex 4, while
the oxidation of 2 occurs ca. 150 mV earlier and it is quasi
reversible. Moreover, when observing the current associated with
the oxidation process of 4, this is ca. the double of the current
-2.17, -2.50
-1.30, -1.73,
-2.00
[a] Obtained by cyclic voltammetry, at scan rate 100 mV s-1, using ferrocene as
internal reference. [b] Redox values for the excited states were calculated using
the following equations: Eox*= Eox-E00; Ered*= Ered+E00 where the E00 values were
estimated (2.25 V for 1, 3.02 V for 2, 2.89 V for 3) as described in literature. [28]
[29]
,
Quantum chemical calculations
associated
with
the mononuclear
complexes,
equal
concentrations used. This is an indication that the two Cu(I)
centres oxidise simultaneously under these conditions.
Compounds 1 and 2 show irreversible reduction at ca. -2.1 V,
while 3 displays additional, also irreversible, reduction processes
at -2.0 V and -2.2 V. The dinuclear complex 4 show three
reduction processes, which occur at higher potential compared to
the corresponding mononuclear complex 1 (-1.30 V, -1.73 V, -2.0
V). All the reduction processes could be attributed to the diimine
ligands, although the reduction processes in 1-4 occur at ca. 200
mV higher potential than in their corresponding ligands.
The ground-state (S0) geometries of the mononuclear complexes
1-3 (Table 4) were optimised at PBE0-D3(BJ) level of theory
starting from the obtained X-ray diffraction structures. The S0
geometry of the binuclear complex 4 was built and optimised
based on the structure of 1 (Table 4).
To further investigate the photophysical properties of the
heteroleptic copper(I) complexes, quantum chemical calculations
utilising the GW approximation and Bethe–Salpeter equation
(GW/BSE) were performed at both one component (1c, scalar-
relativistic) and quasirelativistic two-component (2c, including
spin–orbit coupling) levels.
Table 4. Calculated bond lengths and bond angles for 1-4.
Bond
length
(Å)
Bond
lenght
(Å)
Bond
length
(Å)
Bond
length
(Å)
Bond
angle
Bond
angle
(deg)
P1-Cu-
P2
(deg)
Cu-N2
Cu-N4
Cu-P1
Cu-P2
N2-Cu-N4
1
2
3
4
2.130
2.132
2.105
2.117
2.135
2.126
2.126
2.142
2.257
2.256
2.254
2.256
2.316
2.312
2.314
2.316
93.6
92.9
93.4
90.0
114.4
114.3
114.4
115.8
At the optimised S0 geometry, the calculated absorption spectra
(Figure S7.1) agree well with the experimental results. The MLCT
absorption bands are occurring with relative maxima at 438 nm
for 1, 397 nm for 2, 447 nm for 3, 431 and 645 nm for 4, which fit
nicely with the experimental values, with a slight red-shifted up to
0.18 eV. A natural transition orbital (NTO) analysis confirms the
MLCT character of the transitions in the visible region (Figure
S7.2). The first absorption band of all four complexes corresponds
to charge transfer from the copper atom to the
quinoline/quinoxaline moiety of the diimine ligand, while the
triazole moiety is not involved. For complex 2, less delocalisation
of π electrons on the quinoline ring can be seen from the particle
NTO compared to quinoxaline, which leads to higher energy
Figure 6. CV of 1-4 recorded at room temperature in Ar-saturated
dichloromethane solutions (0.2 M TBAPF6) at scan rate 100 mV s-1 and reported
versus Fc/Fc+.
In order to use these compounds in photoredox catalysis, it is
important to evaluate their redox potentials in the excited (triplet)
state Eox (PS*+) and Ered (PS*-). These parameterswere calculated
by estimating the E00 value, which is the energy difference
between the zero vibrational levels of the excited and ground
states.[27] The estimation adopted equations found in literature,[28]
[29]. The reduction and oxidation potentials of complexes 1-4 in
their ground and excited states are listed in Table 3.
6
This article is protected by copyright. All rights reserved.

10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
∗
levels of quinoline π orbitals, and hence the absorption is shifted
the di-nuclear complex 4 (2.5%). Surprisingly, even though the
photophysical and oxidation properties of 4 are less promising for
a photocatalytic application as compared to 1, the product yield is
similar in these reaction conditions (ca. 40%). Since the Cu(I)
complex 2 was the one giving the best results, it was tested in
another ATRA reaction using iodoform CHI3 as the organic halide.
In this case, the yield obtained was modest (28%). However, it is
still the double value of the yield obtained without the catalyst
(Table 5, entry 7). Furthermore, complex 2 gave better results
under blue light irradiation also in comparsion to the frequently
used iridium(III) or ruthenium(II) photoredox catalysts (reported
maximum yield of 15%).[30h] The inferior photocatalytic results for
copper complexes 1 and 3 in respect to 2 could be explained
considering the much lower lifetime and the lower oxidation
reduction of the excited state of the former compounds. Both
factors play an important role for the efficiency of a photocatalytic
reaction.
to higher energy. Besides the lowest absorption band at 645 nm,
the dinuclear species 4 exhibits one further MLCT transition at
431 nm compared to the monomers (Figure 7). This arises from
the electron coupling between the two copper centers.
Table 5. Visible light induced ATRA reactions with 2 as photoredox catalyst.
Entry
Catalyst
Organic halide
λ (nm)
Yield[a] (%)
Figure 7. Dominating occupied (blue/yellow) and virtual (red/white) natural
transition orbitals (NTOs, iso-value: ±0.04ꢀ0−3/2) of the MLCT excitation of 4
calculated at PBE0 evGW-BSE/def2-TZVP level. Phenyl groups of DPEPhos
and all hydrogen atoms are omitted for clarity.
1[b]
2[b]
3[b]
4[b]
5[d]
6[d]
7[d]
2
CBr4
CBr4
CBr4
CBr4
CHI3
CHI3
CHI3
420
420
no
86%
80[c]
/
2
2
Photocatalytic ATRA reaction
no
2
420
420
no
21
28
/
Once the new complexes reported here were characterised
photophysically and electrochemically, their performance as
photoredox catalysts was tested. The reaction selected was the
atom-transfer radical addition (ATRA, Scheme 2). This process ,
as far as we know, has already been proved in several studies to
be successfully catalysed by homoleptic-copper complexes[30]
but only once by heteroleptic-copper complexes[31]. Photocatalytic
tests were carried out by irradiating for 20 h with a 420 nm lamp
a dichloromethane solution containing styrene and carbon
tetrabromide, with a catalytic amount of the heteroleptic copper
complexes (5% for 1-2 and 1% for 3). The best performing
photoredox catalyst in this work was complex 2 (Table 5).
2
no
420
14
[a] The yield was estimated using dodecane anhydrous as internal reference.[b]
Styrene (1 equiv), CBr4 (1 equiv), 2 (5%), irradiation at 420 nm for 20 h in
dichloromethane dry (1.5 mL). [c]The yield is calculated for the product isolated
by flash chromatography. [d] Styrene (2 equiv), CHI3 (1 equiv), 2 (5%),
irradiation at 420 nm for 20 h in dichloromethane dry (1.5 mL).
Conclusion
We presented three mononuclear and one dinuclear Cu(I)
complexes based on derivatives of quino(xa)lyl-1,2-3-triazole as
diimine ligand and DPEPhos as chelating diphosphine. Their
electronic and photophysical properties were fully characterised
in solution and in solid state. Thanks to the bis-diimine ligand, the
dinuclear complex shows additional electronic states, suggesting
a communication between the two metal centres. Although the
four complexes show modest or no emission in solution, their
luminescence properties in solid state are promising for
optoelectronic applications, with a Φ up to 40% at room
temperature. Nevertheless, for photocatalysis, it is not always
needed a high luminescent complex in solution. Indeed, we tested
their activity as photoredox catalysts in a blue-light driven ATRA
reaction with styrene as starting material and tetrabromomethane
or iodoform as organic halide. The yields obtained with one
mononuclear complex (2) are only slightly lower than those
reported in the literature for other homoleptic Cu(I) complexes.
The promising results of this work motivate further optimisation of
Scheme 2. ATRA reaction with styrene and organic halide (CBr4, or CHI3) at
25°C for 20 h.
In fact, when 2 was used, the desired ATRA product was
obtained with a high yield of 86% (Table 5, entry 1). Differently,
copper complexes 1 and 3 did not show catalytic activity in the
above-mentioned conditions, leading to the same low amount of
product as obtained for the reaction carried out without the
catalyst (entry 4). The product was not observed, when the
reaction was performed in the dark. Then, photocatalytic tests
were performed in a biphasic system with an aqueous solution of
ascorbic acid (1M), as sacrificial electron donor, for complexes 1-
3 (1% of photocatalyst). In these conditions, we could obtain an
almost three times higher yield compared to the reaction carried
out in the absence of the catalyst, although lower than 50% (Table
S8.1). The same reaction was repeated, using a higher amount of
photocatalyst, 5% for the mononuclear complex 1 and 2.5 % for
7
This article is protected by copyright. All rights reserved.

10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
for two days. A solution of NH4OH (10%) was subsequently added for the
quenching. The organic product was extracted three times with
dichloromethane, then it was washed with water and brine, dried over
Na2SO4 and filtered. Lastly, the solvent was removed under reduced
the electronic and photophysical properties of Cu(I) complexes,
which is a challenge that has to be overcome to pursue a more
sustainable chemistry.
pressure.
5: White powder. 179 mg (Yield: 71%) 1H-NMR (400 MHz, CD2Cl2) δ 8.04
– 8.00 (m, 2H), 7.96 (s, 1H), 7.84 – 7.80 (m, 2H), 7.75 (dddd, J = 16.6, 8.4,
7.0, 1.7 Hz, 2H), 7.44 – 7.39 (m, 2H), 7.35 – 7.30 (m, 1H), 5.93 (s, 2H),
2.81 (s, 3H).13C-NMR (126 MHz, CDCl3) δ [ppm] = 152.78 (Cq), 148.22
(Cq), 142.10 (Cq), 140.75 (Cq), 130.73 (+, CArH), 130.38 (Cq), 129.67 (+,
CArH), 129.10 (Cq), 128.85 (+, CArH), 128.58 (Cq), 128.30 (+, CArH), 125.75
(+, CArH), 54.06 (–, CH2), 22.48 (+, CH3). HRMS m/z (C18H15N5): 301.1327
(calc); 301.1326 (found).
Experimental Section
Synthesis
Synthesis of 2-(bromomethyl)-3-methylquinoxaline (9): Bromobutane-
2,3-dione (0.279 g, 1.85 mmol, 1.00 equiv) was dissolved in 5 mL MeOH,
followed by ammonium chloride (49 mg, 0.93 mmol, 0.50 equiv) and 1,2-
phenylendiamine (0.200 g, 1.85 mmol, 1.00 equiv). The reaction mixture
was stirred at room temperature for 30 minutes. Then water was added
and the organic products were extracted with dichloromethane (3 times).
The organic phase collected was washed with brine, dried over Na2SO4,
and filtered. The solvent was removed under vacuum. The product was
used without any further purification for the next step, since the 1H-NMR
analysis revealed the product was clean. The product was a light brown
solid. 328 mg. (Yield:75%) 1H-NMR (400 MHz, CDCl3) δ [ppm] = 8.06 –
8.00 (m, 2H), 7.77 – 7.70 (m, 2H), 4.76 (s, 2H),2.89 (s, 3H). 13C-NMR (126
MHz, CDCl3) δ [ppm] = 153.24 (Cq), 150.98 (Cq), 142.09 (Cq), 140.95 (Cq),
130.58 (+, CArH), 129.61 (+, CArH), 129.14 (+, CArH), 128.53 (+, CArH),
31.94 (–, CH2), 22.57 (+, CH3).
6: White powder. 130 mg (Yield: 55%) 1H-NMR (300 MHz, CD2Cl2) δ 8.30
(s, 1H), 8.22 – 8.09 (m, 2H), 7.99 (d, J = 7.8 Hz, 1H), 7.88 – 7.74 (m, 2H),
7.72 – 7.56 (m, 2H), 7.33 (d, J = 8.5 Hz, 2H), 7.09 (d, J = 7.7 Hz, 1H), 5.93
(s, 2H). 13C-NMR (126 MHz, CDCl3) δ [ppm] = 154.78 (Cq), 148.58 (Cq),
147.80 (Cq), 137.96 (+, CArH), 130.58 (Cq), 130.40 (+, CArH), 129.33 (+,
CArH), 128.97 (+, CArH), 128.37 (+, CArH), 127.88 (+, CArH), 127.73 (Cq),
127.35 (+, CArH), 125.87 (+, CArH), 120.34 (+, CArH), 119.82 (+, CArH),
56.63 (–, CH2). HRMS m/z (C18H14N4): 286.1218 (calc); 286.1218 (found).
7: Greenish powder. 204 mg (Yield: 46%) 1H NMR (400 MHz, CD2Cl2) δ
8.14 (dd, J = 8.2, 1.6 Hz, 1H), 8.11 – 8.07 (m, 1H), 7.92 (s, 1H), 7.87 –
7.76 (m, 4H), 7.67 (dd, J = 6.7, 3.0 Hz, 2H), 7.59 (q, J = 3.2, 2.6 Hz, 3H),
7.42 (t, J = 7.5 Hz, 2H), 7.33 (t, J = 7.4 Hz, 1H), 5.92 (s, 2H).13C-NMR (126
MHz, CDCl3) δ [ppm] = 154.15 (Cq), 147.57 (Cq), 141.94 (Cq), 141.20 (Cq),
137.43 (Cq), 131.12 (+, CArH), 130.77 (Cq), 130.58 (+, CArH), 129.83 (+,
CArH), 129.51 (+, CArH), 129.28 (Cq), 129.21 (+, CArH), 129.18 (+, CArH),
128.96 (+, CArH), 128.28 (+, CArH), 125.87 (+, CArH), 53.67 (–, CH2).HRMS
m/z (C23H17N5): 363.1484 (calc); 363.1483 (found).
Synthesis of 2-(bromomethyl)quinoline (10): According to a modified
procedure,[14] 2-methyl-quinoline (0.500 g, 3.49 mmol, 1.00 equiv) was
reacted with N-bromsuccinimide (1.236 g, 6.98 mmol, 2.00 equiv.) and
benzoylperoxide (0.339 g, 1.39 mmol, 0.40 equiv.) in acetonitrile under
argon atmosphere. The reaction mixture was left under stirring, at 90 °C
for 25 h. Water was afterwards added for the quenching and the product
was extracted successively with dichloromethane (3 times), dried over
Na2SO4, and filtered. The solvent was removed under reduced pressure.
The crude product was purified by silica gel chromatographic column using
the Cy:EtOA=(95:5) as eluent. 105 mg (Yield: 13%) 1H-NMR (300 MHz,
CDCl3) δ [ppm] = 8.20 (t, J = 8.8 Hz, 1H), 8.07 (dq, J = 8.5, 1.0 Hz, 1H),
7.86 – 7.78 (m, 1H), 7.74 (ddt, J = 8.4, 6.9, 1.5 Hz, 1H), 7.63 – 7.52 (m,
2H), 4.72 (s, 2H).
Synthesis of the dichelating ligand 8: According to a modified procedure,
the dibrominated starting ligand 12 (0.270 g, 0.88 mmol, 1.00 equiv) was
dissolved into a 25 mL solution of ethanol and water (7:3) and 2 mL
acetonitrile. Then the other reactants were added in the following order:
sodium azide (0.137 g, 2.10 mmol, 2.40 equiv.), sodium ascorbate (0.198
g, 1.00 mmol, 1.14 equiv.), copper sulfate pentahydrate (0.091 g, 0.37
mmol, 0.42 equiv.), sodium carbonate (0.087 g, 1.06 mmol, 1.20 eq),
ethynylbenzene (0.179 mg, 1.75 mmol, 2.00 equiv.). Please, be careful
and use protective equipment when using NaN3, as it can be explosive.
The reaction mixture was left under stirring for two days. Then a NH4OH
(10%) solution was added for quenching the reaction and the organic
product was extracted with dichloromethane (3 times). The organic phase
collected was washed with brine, dried over Na2SO4, filtered. The product
is a brown solid. 203 mg (Yield: 52%) 1H-NMR (400 MHz, CD2Cl2) δ 8.08
(dt, J = 7.0, 3.5 Hz, 2H), 8.04 (s, 2H), 7.83 (dd, J = 9.4, 7.2 Hz, 6H), 7.42
(t, J = 7.5 Hz, 4H), 7.33 (t, J = 7.0 Hz, 2H), 6.12 (s, 4H). 13C-NMR (126
MHz, CDCl3) δ [ppm] = 148.47 (Cq), 148.21 (Cq), 141.87 (Cq), 131.48 (+,
CArH), 130.33 (Cq), 129.36 (+, CArH), 129.01 (+, CArH), 128.52 (+, CArH),
125.91 (+, CArH), 120.76 (+, CArH), 53.52 (–, CH2).HRMS m/z (C26H21N8)
445.1889 (calc); 445.1888 (found).
Synthesis of 2-methyl-3-phenylquinoxaline (13): 2-methyl-3-
phenylquinoxaline was synthesised from phenyl-1,2-propanedione and
1,2-phenylendiamine using the same procedure adopted for 2-
(bromomethyl)-3-methylchinoxaline (9). In this case the crude product was
further purified by silica gel chromatographic column using
Cy:EtOA=(95:5) as eluent. 2.416 g (Yield: 78%). 1H-NMR (300 MHz,
CDCl3) δ [ppm] = 8.17 – 8.09 (m, 1H), 8.09 – 8.01 (m, 1H), 7.79 – 7.69
(m, 2H), 7.69 – 7.61 (m, 2H), 7.57 – 7.44 (m, 3H), 2.78 (s, 3H).
Synthesis of 2-(bromomethyl)-3-phenylquinoxaline (11):
2-methyl-3-phenylquinoxaline was reacted with N-bromsuccinimide and
benzoylperoxide following the same procedure as used for 2-
(bromomethyl)quinoline (10) in order to get the desired product 11. 337 mg
(Yield: 30%) 1H-NMR (300 MHz, CDCl3) δ [ppm] = 8.18 – 8.11 (m, 2H),
7.83 – 7.74 (m, 4H), 7.59 – 7.52 (m, 3H), 4.76 (s, 2H).
General procedure for the synthesis of the mononuclear complexes
1, 2, 3: According to literature,[16] Cu(ACN)4BF4 (1.00 equiv) and DPEPhos
(1.00 equiv) were dissolved in dry dichloromethane in a Schlenk flask
under argon atmosphere.. After 30 minutes, the desired monochelating
ligand 5-7 (1.00 equiv) was added. The reaction mixture was left under
stirring for four hours. Then the solvent was removed under reduced
pressure. The crude product was dissolved in a minimum amount of
dichloromethane and crystallized by a slow diffusion of cyclohexane.
Synthesis of 2,3-bis(bromomethyl)quinoxaline (12):
2,3-bis(bromomethyl)quinoxaline was synthetized using the same
procedure adopted for 2-(bromomethyl)-3-methylchinoxaline, using 1,4-
dibromobutane-2,3-dione as starting material. The product was used
without any further purification for the next step, since the 1H-NMR analysis
revealed the product was clean. The product was a lightly brown solid. 203
mg (Yield: 97 %) 1H-NMR (300 MHz, CDCl3) δ [ppm] = 8.15 – 8.02 (m,
2H), 7.85 – 7.76 (m, 2H), 4.93 (s, 4H). 13C NMR (126 MHz, CDCl3) δ [ppm]
= 151.01 (Cq), 141.72 (Cq), 131.12 (+, CArH), 129.20 (+, CArH), 30.63 (–,
CH2).
1: Yellow powder. 500 mg (Yield: 88%) 1H NMR (400 MHz, CD2Cl2) δ 8.54
(s, 1H), 8.05 (d, J = 8.5 Hz, 1H), 7.99 (dd, J = 8.6, 1.3 Hz, 1H), 7.60 (ddd,
J = 8.4, 6.9, 1.4 Hz, 1H), 7.47 – 7.42 (m, 2H), 7.32 (td, J = 7.8, 1.7 Hz, 2H),
7.25 (dtd, J = 6.2, 5.0, 2.0 Hz, 7H), 7.17 – 6.89 (m, 21H), 6.75 (dtd, J = 8.1,
4.2, 1.6 Hz, 2H), 6.01 (s, 2H), 3.00 (s, 3H). 13C NMR (101 MHz, CD2Cl2) δ
157.98, 157.92, 157.86, 154.23, 148.70, 147.80, 140.00, 134.57, 133.85,
133.77, 133.70, 132.47, 131.67, 130.72, 130.63, 130.55, 130.37, 129.82,
129.45, 129.20, 129.16, 129.11, 129.05, 126.24, 125.54, 124.38, 123.84,
General procedure for the synthesis of the monochelating ligands 5,
6, 7: According to a modified procedure,[32] the monobrominated starting
ligand 9-11 (1.00 equiv) was dissolved into a solution of ethanol and water
(7:3). Then the other reactants were added in the following order: sodium
azide (1.20 equiv), sodium ascorbate (0.562 equiv.), copper sulfate
pentahydrate (0.204 equiv), sodium carbonate (0.084 mg, 1.01 mmol,
0.591 equiv), ethynylbenzene (0.175 g, 1.71 mmol, 1.00 equiv). Please,
be careful and use protective equipment when using NaN3, as it can be
explosive. The reaction mixture was left under stirring at room temperature
120.35, 51.98, 23.42. 31P-NMR (162 MHz, CD2Cl2) δ -13.99. HRMS (ESI)
+
-
902.2232 (z=1) (C54H43Cu1N5O1P2 +). Calcd for C54H43Cu1N5O1P2 BF4 .
Elemental analysis: [C54H43BCu1F4N5O1P2 ]·CH2Cl2 : C = 61.44, H = 4.22,
N = 6.51 (calc.); C = 61.35, H = 4.15, N = 6.57 (found).
2: Brown powder. 322 mg (Yield: 83%) 1H NMR (400 MHz, CD2Cl2) δ 8.51
(s, 1H), 8.47 (d, J = 8.4 Hz, 1H), 8.25 (d, J = 8.6 Hz, 1H), 8.06 (d, J = 8.4
8
This article is protected by copyright. All rights reserved.

10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
Hz, 1H), 7.85 (dd, J = 8.3, 1.4 Hz, 1H), 7.42 – 7.23 (m, 9H), 7.23 – 6.97
(m, 23H), 6.72 (dtd, J = 7.8, 4.0, 1.6 Hz, 2H), 6.66 (s, 1H), 5.94 (s, 2H).
13C NMR (101 MHz, CD2Cl2) δ 157.90, 157.85, 157.79, 154.33, 148.40,
147.51, 140.55, 134.47, 133.93, 132.17, 131.36, 131.19, 131.02, 130.31,
130.27, 129.78, 129.49, 128.95, 128.89, 128.85, 128.82, 128.75, 128.30,
128.25, 125.99, 125.48, 125.43, 125.40, 125.38, 125.34, 125.20, 123.60,
123.12, 120.42, 54.90.31P-NMR (162 MHz, CD2Cl2) δ -13.96. HRMS (ESI)
Fachinformationszentrum Karlsruhe Access Structures service supplied
these data free of charge. Single-crystal X-ray diffraction data were
recorded at low temperature on a STADI VARI diffractometer with
monochromated Ga Ka (l=1.34143 Å) or Mo Kα (λ=0.71073) radiation.
Adopting Olex2[40], the ShelXT[41] structure solution program using Intrinsic
Phasing wad selected for determining the structure and the ShelXL[42]
refinement package using Least Squares minimisation was selected for
refining the structure. Anisotropic temperature factors for all non-hydrogen
atoms were adopted for the refinement; hydrogen atoms were computed
on idealised positions.
+
-
887.2124 (z=1) (C54H42Cu1N4O1P2 +). Calcd for C54H42Cu1N4O1P2 BF4 .
Elemental analysis (C54H42BCu1F4N4O1P2 )·H2O : C = 65.30 H = 4.47, N =
5.64 (calc.); C = 65.75, H = 4.37, N = 5.77 (found).
3: Orange powder. 493 mg (Yield: 92 %) 1H NMR (400 MHz, CD2Cl2) δ
8.11 (s, 3H), 7.79 – 7.41 (m, 8H), 7.41 – 7.20 (m, 11H), 7.20 – 6.96 (m,
19H), 6.77 (dq, J = 8.0, 4.2 Hz, 2H), 5.86 (s, 2H). 13C NMR (101 MHz,
CD2Cl2) δ 158.09, 148.71, 134.66, 133.67, 132.71, 132.24, 130.85, 129.52,
129.35, 129.24, 126.38, 125.64, 120.34, 54.24 31P NMR (162 MHz,
CD2Cl2) δ -14.51. HRMS (ESI) 964.2390 (z=1) (C59H45Cu1N5O1P2 +). Calcd
Photoredox catalysis: The experiments were conducted in
a
Photoreactor from Luzchem (Model: LZC-ICH2). Blue-LED lamps were
used at a wavelength of 420 nm. Photon flux was calculated by
K3Fe(C2O4)3 actinometry[43], and it has a value of 4.13 10-8 E s-1, equivalent
to 2.48 1016 photons/s.
+
-
for
C59H45Cu1N5O1P2
BF4 .
Elemental
analysis
General procedure for ATRA reaction with CBr4: A solution of styrene
(170 μL, 1.5 mmol, 1 equiv.), CBr4 (494 mg, 1.5 mmol, 1 equiv) and of the
desired complex 2 (73 mg, 0.075 mmol, 5%) in 1.5 mL of dry CH2Cl2,
deaerated by bubbling a stream of nitrogen through it for about 10 minutes,
was irradiated with a 420 nm LED for 20 h under stirring, placing the
sample at a distance of ca. 3 cm from the light source. Then the solvent
was removed under reduced pressure. The yield was estimated from the
1H-NMR analysis using dry dodecane as an internal standard. Quantum
yield was calculated considering the total number of photons irradiating the
reaction vessel for 20 h, and it is 43 %.
(C54H42BCu1F4N4O1P2 )·H2O · CH2CL2 : C = 62.38 H = 4.28, N = 6.06
(calc.); C = 62.68, H = 4.20, N = 6.08 (found).
Synthesis of the dinuclear complex 4: According to literature,[16]
(Cu(CH3CN)4)BF4 (0.133 g, 0.42 mmol, 2.00 equiv) was reacted with
DPEPhos (0.192 g, 0.42 mmol, 2.00 equiv) in 25 mL of dry CH2Cl2 at room
temperature for 30 min, under argon atmosphere. The desired dichelating
ligand 8 (93 mg, 0.21 mmol, 1 equiv) was subsequently added to the
reaction mixture that was left under stirring over night. Then the solvent
was removed under reduced pressure. The crude product was dissolved
in a minimum amount of dichloromethane and precipitated by a slow
diffusion of cyclohexane. The product was a red powder. 162 mg. (Yield:
42%). 1H NMR (400 MHz, CD2Cl2) δ 8.56 (s, 2H), 7.90 – 7.82 (m, 2H), 7.49
(dt, J = 7.1, 1.4 Hz, 4H), 7.36 – 7.06 (m, 52H), 7.01 (t, J = 7.4 Hz, 8H), 6.79
General procedure for ATRA reaction with CHI3: A solution of styrene
(57 μL, 0.5 mmol, 2 equiv.), CHI3 (98 mg, 0.25 mmol, 1 equiv) and of the
desired complex 2 (12 mg, 0.0125 mmol, 5%) in 1.5 mL of dry CH2Cl2,
deaerated by bubbling a stream of nitrogen through for about 10 minutes,
was irradiated with a 420 nm LED for 20 h under stirring, placing the
sample at a distance of ca. 3 cm from the light source. Then the solvent
was removed under reduced pressure. The yield was estimated from the
1H-NMR analysis using dry dodecane as an internal standard.
– 6.71 (m, 4H), 6.26 (s, 4H).13C NMR (101 MHz, CH2Cl2) δ 157.94, 148.89,
147.64, 141.43, 134.68, 133.87, 133.79, 133.71, 132.62, 131.73, 130.86,
130.34, 130.16, 129.98, 129.53, 129.34, 129.28, 129.23, 126.57, 125.56,
124.63, 120.32,52.30.31P NMR (162 MHz, CD2Cl2) δ -14.78. HRMS (ESI)
-
1733,37
(z=1)
(C98H76Cu2N8O2P42+BF4 ).
Calcd
for
analysis:
-
(C98H76Cu2N8O2P42+·2BF4 ).
Elemental
[C98H76B2Cu2F8N8O2P4 ]·H2O : C = 63.96, H = 4.27, N = 6.09 (calc.); C =
63.83, H = 4.53, N = 6.28 (found).
Acknowledgements
Electrochemical and photophysical experimental details are reported
in the electronic supplementary information.
Financial support by the DFG-funded transregional collaborative
research center SFB/TRR 88 Cooperative Effects in Homo and
Heterometallic Complexes (3MET)" is gratefully acknowledged
(projects B9, C1 and C7). CB, NSA, TB and C. Bizzarri thank Prof.
Bräse for giving access to his laboratories and fruitful discussion.
Computational details
All quantum-chemical calculations were performed with the TURBOMOLE
program package [33]. The resolution-of-the-identity (RI) approximation
was used for all two-electron integrals. The equilibrium geometries were
optimised at the PBE0-D3(BJ) level of theory [34], and the electronic
excitations were calculated at the CD-evGW(10)/BSE level of theory
(eigenvalue-only self-consistent GW (evGW) [35] employing contour
deformation (CD) [36] for the highest 10 occupied and lowest 10 unoccupied
orbitals, followed by the Bethe–Salpeter equation (BSE) [37] approach). For
non- and scalar-relativistic one-component (1c) calculations, the def2-
TZVP basis set was taken for Cu, P, N and C atoms in triazole and
quinoline/quinoxaline moieties, and the def2-SV(P) basis set [38] was taken
Keywords: ATRA • Cooperativity • Dinuclear Cu(I) Complex •
Heteroleptic Cu(I) Complexes • Visible-Light Absorption
for the rest of the atoms. For quasirelativistic two-component (2c)
[39]
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was
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European Journal of Inorganic Chemistry
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10.1002/ejic.202100653
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
A broad spectrum of properties for these new heteroleptic Cu(I) complexes shows their versatility in diverse application fields. Their
luminescence in solid state reaches a Φ up to 40% at r.t. and they show photoredox activity in a visible-light driven ATRA reaction.
Furthermore, cooperative effect in the dinuclear complex was observed in electronic absorption and confirmed by theoretical
calculations.
11
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