The Curious Case of a Phenylated Guanidinoquinoline Ligand: Synthesis, Complexes and ATRP Properties of DMEG6phqu

Article abstract of DOI:10.1002/zaac.201800258

In previous studies, copper halide complexes of the guanidinoquinoline (GUAqu) ligands 1,3-dimethyl-N-(quinolin-8-yl)-imidazolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)-guanidine (TMGqu) were successfully implemented in atom transfer radical polymerization (ATRP) and could be further enhanced by introduction of alkyl substituents at C6 position of the quinoline backbone. Herein, the ligand DMEG6phqu is presented. The quinoline backbone of this ligand is equipped with a phenyl substituent at C6 position. This study deals with the influence of the phenyl substituent on solubility and molecular structural properties of DMEG6phqu Cu^I and Cu^II bromide complexes. In contrast to previously reported systems, the Cu^IBr complex of DMEG6phqu crystallizes as a trigonal coordinated monochelate complex. However, NMR and UV/Vis spectroscopic experiments indicate that DMEG6phqu forms a bischelate species in solution. The influence of the substituent on the complex redox potential and ATRP equilibrium constant K_ATRP is discussed. In contrast to expectations, it turned out that copper halide complexes of DMEG6phqu are completely insoluble in the apolar monomer styrene. However, ATRP kinetics were performed in solution and the results are compared to previous studies.

Full text of DOI:10.1002/zaac.201800258

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201800258
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
The Curious Case of a Phenylated Guanidinoquinoline Ligand:
Synthesis, Complexes and ATRP Properties of DMEG6phqu
Thomas Rösener,[a] Konstantin Kröckert,[a] Alexander Hoffmann,[a] and Sonja Herres-Pawlis*[a]
Dedicated to Professor Werner Uhl on the Occasion of his 65th Birthday
Abstract. In previous studies, copper halide complexes of the guanidi-
and CuII bromide complexes. In contrast to previously reported sys-
noquinoline (GUAqu) ligands 1,3-dimethyl-N-(quinolin-8-yl)-imid- tems, the CuIBr complex of DMEG6phqu crystallizes as a trigonal
azolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8- coordinated monochelate complex. However, NMR and UV/Vis spec-
yl)-guanidine (TMGqu) were successfully implemented in atom trans-
troscopic experiments indicate that DMEG6phqu forms a bischelate
fer radical polymerization (ATRP) and could be further enhanced by species in solution. The influence of the substituent on the complex
introduction of alkyl substituents at C6 position of the quinoline back-
bone. Herein, the ligand DMEG6phqu is presented. The quinoline
backbone of this ligand is equipped with a phenyl substituent at C6
redox potential and ATRP equilibrium constant KATRP is discussed. In
contrast to expectations, it turned out that copper halide complexes of
DMEG6phqu are completely insoluble in the apolar monomer styrene.
position. This study deals with the influence of the phenyl substituent However, ATRP kinetics were performed in solution and the results
on solubility and molecular structural properties of DMEG6phqu CuI
are compared to previous studies.
ies of different 4,4Ј-substituted 2,2Ј-bipyridine ligands gained
further insights into the influence of ligand substitution on cat-
alyst activities.[6] Decoration of pyridine based ligands with
electron donating substituents had by far the largest influence
on catalyst activity and thus, the most active ATRP catalyst
Introduction
Atom transfer radical polymerization (ATRP) was invented
by several independent groups in 1995 and rapidly became one
of the most versatile reversible-deactivation radical polymeri-
zation (RDRP) methods.[1] In ATRP transition metal com-
plexes mediate an equilibrium between dormant and active
radical species (Scheme 1). The complex on the left side of the
equilibrium (LxMtn) is often referred to as the activator com-
plex, whereas its counterpart on the other side of the equilib-
rium (LxMtn+1–X) is named deactivator complex. Because of
the ATRP equilibrium, only few active radical species coexist
and thus, chain termination reactions can be effectively sup-
pressed. In the past, a large variety of RDRP techniques based
on ATRP was developed. These allow the application of air-
stable catalyst precursors, the drastic reduction of transition
metal concentration and an even higher controllability.[4]
Amongst other factors, the polymerization rate in ATRP highly
depends on the nature of the chosen catalyst. Catalytic proper-
ties of the transition metal complex can be easily adjusted by
the ligand environment. In copper ATRP a large variety of
different N-donor ligands has been evaluated and structure-
reactivity-relationships were derived. The activity of a copper
complex in ATRP is influenced by the denticity of the ligand,
nature of the N-donor and its electron donating ability.[5] Stud-
features the tetrapodal ligand TMPANMe2 [7]
.
* Prof. Dr. S. Herres-Pawlis
E-Mail: sonja.herres-pawlis@ac.rwth-aachen.de
[a] Institut für Anorganische Chemie
RWTH Aachen University
Scheme 1. The ATRP equilibrium and various DMEGqu-based li-
gands. Ligands marked with an asterisk were already presented in pre-
vious publications.[2,3]
Landoltweg 1
52074 Aachen, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201800258 or from the au-
thor.
In the past, our focus lay on the implementation of guanid-
ine ligands as a new and promising ligand class in ATRP.
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Guanidines represent a class of strong and neutral N-donors
and they have great potential in ATRP. Guanidine ligands al-
ready found broad application in the field of homogeneous ca-
talysis. Recent publications describe the application in the ring
opening polymerization (ROP) of lactide[8] or oxygen acti-
vation.[9] However, only few examples of guanidine complexes
in ATRP are known.[10] In a previous publication we showed
that copper complexes of the bidentate guanidinoquinoline
(GUAqu)
ligands
1,3-dimethyl-N-(quinolin-8-yl)-imid-
azolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quino-
lin-8-yl)-guanidine (TMGqu) successfully can mediate ATRP
reactions (Scheme 1).[2] These ligands also attracted attention
in the fields of copper photochemistry[11] and as entatic state
models for electron transfer proteins.[12,13]
The introduction of alkyl substituents led to better solubility
of the complexes in styrene and thus better control of the poly-
Scheme 2. Synthesis of NO2phan: modified nitration step for the syn-
merization reaction. It is also worth mentioning that alkylated thesis of GUAphqu.
versions of DMEGqu showed almost no differences in elec-
tronic properties in comparison with the parental ligand.[3]
In this publication, the ligand DMEG6phqu is presented.
The quinoline backbone of this ligand is equipped with a
phenyl substituent at C6 position. A synthetic strategy for the
synthesis of C6 phenylated GUA6Phqu ligands is presented.
CuI and CuII bromide complexes of DMEG6phqu were investi-
gated with respect to their structural characteristics, since they
represent activator and deactivator complexes in an ATRP. The
focus of this work lay on solubility of corresponding com-
plexes in the monomer and the influence of the phenyl substit-
uent on electronic and ATRP properties of these complexes.
Results and Discussion
Synthesis of GUA6phqu Ligands
First, attempts were made to synthesize GUA6phqu ligands
Scheme 3. Synthesis of DMEGphqu starting from NO2phan, following
a previously published synthetic strategy.[3]
following a published protocol.[3] With this method, a large
variety of C6 substituted guanidinoquinoline ligands can be
synthesized starting from 4-substituted anilines. For the syn-
thesis of GUA6phqu ligands, 4-aminobiphenyl was used as
starting material. It appeared that 4-aminobiphenyl is insoluble
in various organic solvents rendering the original nitration step
impossible. Hence, the nitration step had to be modified.
Following slightly modified literature protocols,[14–16] the syn-
thesis of 3-nitro-4-aminobiphenyl (NO2phan) could be ac-
complished. An overview of the synthetic steps is shown in
Scheme 2.
DMEG6phqu was purified via recrystallization from aceto-
nitrile. Thus, crystals suitable for X-ray crystallography were
obtained. In Table 1 key structural parameters of DMEG6phqu
as well as of DMEGqu and DMEG6etqu are summarized. Key
bond lengths within the ligand are not significantly altered by
substitution at the C6 position.
In contrast to the previously published synthetic strategy,
the intermediates here had to be isolated. Crude NO2phan was
purified by recrystallization from ethanol, which went hand in
hand with a significant loss of yield but resulted in pure prod-
uct. Consequently, the purification step must be improved with
respect to product yield in follow-up studies.
Subsequently, NO2phan was stepwise reacted to 6-phenyl-
quinolin-8-amine (NH26phqu), following the synthetic strategy
previously published.[3] An overview of the synthetic steps is
shown in Scheme 3.
Table 1. Selected bond lengths /Å and ρ of DMEG6phqu in compari-
son with DMEGqu[19] and DMEG6etqu.[3]
DMEG6phqu
DMEGqu
DMEG6etqu
(Parent ligand)
C8–NGUA
CGUA–NGUA
1.391(2)
1.291(2)
1.380(av)
1.372(2)
1.394(2)
1.283(3)
1.381(av)
1.371(2)
1.384(2)
1.291(2)
1.360(av)
1.364(2)
CGUA–NAmine
C8a–Nqu
Geometrical factor
a)
ρ
0.94
0.93
0.95
The ligand precursor was reacted with DMEG Vilsmeier salt
to provide DMEG6phqu following a common procedure.[17,18]
a) ρ = 2a/(b + c) with a = d(CGUA–NGUA) and b and c = d(CGUA
N
–
amine).[20]
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Copper Halide Complexes of DMEG6phqu
Table 2. Key bond lengths /Å and angles /° of the CuI complex
[Cu(DMEGphqu)Br] and the CuII complex [Cu(DMEGphqu)2Br]Br.
Structural Characterization in Solid State
[Cu(DMEGphqu)Br] [Cu(DMEGphqu)2Br]Br
Bond length
Reaction of DMEG6phqu with anhydrous CuIBr and
CuIIBr2 in acetonitrile resulted in complex solutions of dark
red color.
Cu–Br
2.2641(5)
2.045(2)
–
2.015(2)
-
2.5082(6)
2.075(3)
2.131(3)
1.972(3)
1.980(3)
Cu–NGUA(1)
Cu–NGUA(2)
Cu–Nqu(1)
Cu–Nqu(2)
Bright orange crystals of the monochelate complex
[Cu(DMEG6phqu)Br] were crystallized from the CuI solution.
The central metal is coordinated by one bidentate
DMEG6phqu ligand and an additional bromido ligand in a tri-
gonal planar fashion. In contrast to the CuIBr complex of
DMEG6phqu, analogous complexes of the ligands DMEGqu
and DMEG6etqu could be crystallized as bischelates, where
two bidentate DMEG6Rqu (R = H, et) ligands are coordi-
nated.[2,3] The molecular structure of the complex is depicted
in Figure 1 and key structural parameters are summarized in
Table 2.
Comparing Cu–NGUA and Cu–Nqu bond lengths, it appears
that the former is significantly shortened [2.045(2) Å] and the
latter is significantly prolonged [2.015(2) Å] in comparison
with bischelate DMEG6Rqu (R = H, et) complexes (typically
around 2.10 Å for Cu–NGUA or 1.97 Å for Cu–Nqu). As al-
ready stated in a previous publication,[2] due to the rigid aro-
matic backbone of GUAqu ligands, shortening of Cu–NGUA
Bond angle
N
GUA(1)–Cu–
NGUA(2)
NGUA(1)–Cu–Nqu(1) 82.2(1)
–
115.3(1)
80.8(1)
80.9(1)
134.9(1)
176.0(1)
91.7(1)
NGUA(2)–Cu–Nqu(2)
–
NGUA(1)–Cu–X
Nqu(1)–Cu–Nqu(2)
Nqu(1)–Cu–X
136.6(1)
–
141.2(1)
Geometrical factor
a)
τ5
ρ
-
0.69
1.00
b)
0.99
α – β [21]
a) τ5 =
.
b) ρ = 2a/(b + c) with a = d(CGUA–NGUA) and b and
60
c = d(CGUA–Namine).[20] Average ρ value of both guanidine moieties in
the case of the bischelate complex.
goes hand in hand with elongation of Cu–Nqu and vice versa. mainly determined by the ligand bite angle of 82.2(1)°. Thus,
The exceptional short Cu–NGUA bond length can be drawn
back to the absence of a second coordinating DMEG6phqu
N
GUA(1)–Cu–X and Nqu(1)–Cu–X are found at ca. 140°.
The CuIIBr2 complex consists of two coordinating bidentate
ligand. The ρ value is a measure for the delocalization within ligands and an additional coordinating bromido ligand.
the guanidine moiety.[20] Strong coordination of NGUA is affili- The coordination sphere resembles a distorted trigonal bipyra-
ated with enhanced delocalization of electron density within mid. Considering bond lengths, it can be noticed that
the guanidine moiety. In the complex [Cu(DMEG6phqu)Br], ρ [Cu(DMEG6phqu)2Br]Br does not significantly differ from
is nearly 1 due to the strong coordination of the sole guanidine previously published complexes with the ligands DMEGqu
function. In contrast to that, in bischelate CuI complexes of and DMEG6etqu. ρ and τ5 values of [Cu(DMEG6phqu)2Br]Br
DMEGqu and DMEG6etqu, the ρ value is smaller (typically also resemble those of CuIIBr2 complexes of DMEGqu and
around 0.97). Bond angles within the coordination sphere are DMEG6etqu.
Figure 1. Molecular structures of DMEG6phqu, [Cu(DMEG6phqu)Br], and the complex cation of [Cu(DMEG6phqu)2Br]Br in the solid state.
Key atoms are exemplarily marked. Hydrogen atoms are omitted for clarity.
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Structural Characterization in Solution
cal d–d transition at 945 nm indicates furthermore that the
solution was free of the CuII species [Cu(DMEG6phqu)2Br]Br.
The absorption was followed when titrating a solution of CuIBr
with the ligand. Figure 3 shows the corresponding titration
curve.
It appeared that complex solutions of DMEG6phqu with
CuIBr were of different color than corresponding crystals (dark
red vs. bright orange). This indicates that the complex might
have different structures in solution and solid state. For the
characterization of the CuIBr activator complex in solution,
NMR and mass spectrometry experiments were performed.
Additionally, a UV/Vis titration experiment was conducted.
For the NMR experiment, the complex was generated in situ
by reacting DMEG6phqu with CuIBr in a ratio of 2:1 in
[D3]MeCN. This solution was subjected to NMR spectroscopy
and mass spectrometry. The NMR spectra are depicted in Fig-
ures S13 and S14 (Supporting Information). Within the NMR
timescale, one set of NMR signals could be measured. The
absence of a second set of NMR signals indicates, that a
bischelate complex [Cu(DMEG6phqu)2]Br is formed. Narrow
NMR signals indicate that the solution was free of CuII. To rule
out a possible fast exchange of different CuI species variable
temperature NMR spectroscopy was conducted. Here,
DMEG6phqu and CuIBr were also used in a molar ratio of 2:1.
The VT-NMR spectra are depicted in Figures S15 and S16
(Supporting Information). A temperature range from –40 °C to
+40 °C was investigated. Upon decreasing the temperature, the
peaks associated with the DMEG moieties within the complex
resolve due to the slower motion of these groups. Fast equilib-
ria between different CuI species and free and associated li-
gand could not be proven. In HR mass spectra also the
bischelate complex was found (see data in the Experimental
Section). In an additional experiment, a solution of CuBr in
MeCN was titrated with DMEG6phqu. Formation of
[Cu(DMEG6phqu)2]Br was followed by UV/Vis spectroscopy.
In Figure 2, the UV/Vis spectrum of [Cu(DMEG6phqu)2]Br is
depicted.
Figure 3. Titration of CuIBr (1.8ϫ10–3 mol·L–1 in MeCN) with
DMEG6phqu. Absorption trace at 430 nm.
The absorption at 430 nm increases with addition of ligand.
After addition of two equivalents of ligand the absorption trace
begins to flatten, but however, does not reach its maximum.
With addition of excess ligand, an absorption at 350 nm that
is associated with free ligand, starts to increase. The titration
curve is slightly influenced by this ligand-associated absorp-
tion band. Figure S3 (Supporting Information) shows the UV/
Vis spectrum of [Cu(DMEG6phqu)2]Br after addition of ex-
cess ligand. The titration experiment indicates that
a
bischelate complex is formed. After addition of two equiva-
lents of ligand, all the CuI is coordinated by two ligands and
the absorption trace flattenes.
In the case of the paramagnetic CuII deactivator complex
[Cu(DMEG6phqu)2Br]Br, EPR spectroscopy was used for the
structural characterization of the complex in solution.
EPR spectra of [Cu(DMEG6phqu)2Br]Br were measured
both in solid state and in MeCN at room temperature. Both
spectra show significant broadening (see Figure S1, Support-
ing Information) that is caused by a strong electron delocaliza-
tion between the guanidine donors and the bromido ligand.[22]
Since [Cu(DMEG6phqu)2Br]Br shows low solubility in
MeCN, the solution EPR spectrum appears to be noisy.
Both spectra resemble each other which indicates that
[Cu(DMEG6phqu)2Br]Br exists as a pentacoordinate complex
both in solid state and in solution.
Figure 2.
UV/Vis
spectrum
of
[Cu(DMEG6phqu)2]Br
(1.1ϫ10–3 mol·L–1 in MeCN).
[Cu(DMEG6phqu)2]Br possesses an absorption at ca.
430 nm (ε = 7300 L·mol–1·cm–1) that is associated with a
metal-to-ligand charge transfer (MLCT) which could be also
Electrochemistry
Matyjaszewski et al. found a linear correlation between the
found in bischelate CuI complexes of DMEGqu and redox potential of a complex in solution and its activity in
TMGqu.[12] However, the absorption maximum of DMEGqu ATRP.[23] Since electrochemical properties provide infor-
and TMGqu complexes lies at 445 nm. The absence of a typi- mation about the catalyst activities, cyclic voltammetry was
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Table 3. E1/2 for CuIIBr2 complexes with DMEG6phqu, DMEGqu, DMEG6etqu, and DMEG6buqu[3] (potential vs. Fc/Fc+ and SCE[24]).
Complex
E1/2 vs. Fc/Fc+ /mV
E1/2 vs. SCE /mV
ΔEp /mV
[Cu(DMEG6phqu)2Br]Br
[Cu(DMEGqu)2Br]Br
[Cu(DMEG6etqu)2Br]Br
[Cu(DMEG6buqu)2Br]Br
–480Ϯ5
–480Ϯ5
–465Ϯ5
–480Ϯ5
–80Ϯ5
–80Ϯ5
–65Ϯ5
–80Ϯ5
85Ϯ5
85Ϯ5
80Ϯ5
85Ϯ5
performed in acetonitrile starting from crystalline complex stants of activation kact and deactivation kdeact. Polymerization
[Cu(DMEG6phqu)2Br]Br. All measurements were carried out velocity and control highly depend on KATRP
at room temperature at different scan rates to prove reversible Herein, KATRP was determined by reacting the
behavior of the redox process. E1/2 was determined against the [CuI(DMEG6phqu)2]Br activator complex with an ATRP
.
Fc/Fc+ couple and for better comparability with literature data, initiator
and
following
the
evolution
of
the
recalculated against SCE.[24] Figure 4 shows cyclic voltammo- [CuII(DMEG6phqu)2Br]Br deactivator species via UV/Vis
grams of the [CuI(DMEG6phqu)2Br]/[CuII(DMEG6phqu)2Br]+ spectroscopy (details of the procedure can be found in the
couple at different scan rates.
Experimental Section). The activator complex was generated
in situ by reacting DMEG6phqu with CuIBr in a ratio
of 2/1. As discussed earlier, thus the bischelate complex
[Cu(DMEG6phqu)2]Br is formed.
To follow the formation of the CuII complex, a characteristic
d–d transition band in the area around 900-950 nm was chosen.
The maximum of this absorption lies at 945 nm and the extinc-
tion coefficient ε was determined to 360 L·mol–1·cm–1.
KATRP of [Cu(DMEG6phqu)2]Br was determined at 22 °C
in acetonitrile with ethyl α-bromoisobutyrate (EBrib) as initia-
tor and calculated by the method developed by Matyjaszew-
ski.[25] One exemplary plot of F(Y) vs. time is shown in
Figure S2 (Supporting Information). KATRP values for
[Cu(DMEG6phqu)2]Br and the analogous CuIBr complexes of
DMEGqu, DMEG6etqu, and DMEG6buqu are summarized in
Table 4.
Table 4. KATRP values for [Cu(L)2]Br (L = DMEG6phqu, DMEGqu,
Figure 4. Cyclic voltammograms of the [Cu(DMEG6phqu)2Br]/
[Cu(DMEG6phqu)2Br]+ couple at different scan rates starting from
[Cu(DMEG6phqu)2Br]Br.
DMEG6etqu, and DMEG6buqu).[3]
[Cu(L)2]Br; L =
KATRP (Matyjaszewski)
DMEG6phqu
DMEGqu
DMEG6etqu
DMEG6buqu
7.4Ϯ0.9ϫ10–08
9.0Ϯ0.7ϫ10–08
7.9Ϯ0.1ϫ10–08
7.8Ϯ0.7ϫ10–08
E1/2 values of [Cu(DMEG6phqu)2Br]Br and the CuIIBr2
complexes of DMEG6Rqu (R = H, et, bu) are listed in Table 3.
The introduction of an electron withdrawing phenyl substit-
uent at C6 position of the quinoline backbone of the
DMEG6Rqu ligand does not significantly change the redox
In Figure 5 the logarithmic values of KATRP (calculated via
potential of corresponding complexes. As already demon- the method of Matyjaszewski) are plotted against E1/2 deter-
strated for Cu complexes of alkylated DMEG6Rqu ligands, mined via CV. All values roughly follow the correlation pub-
substitution has almost no effect on the donor properties of lished by Matyjaszewski et al.[23]
this class of ligands. Based on the CV data, it is predicted that
The introduction of a phenyl substituent at C6 position of
[Cu(DMEG6phqu)2]Br resembles complexes of unsubstituted the quinoline backbone has no significant influence on the
DMEGqu and alkylated DMEG6etqu and DMEG6buqu in electronic/donor properties of the resulting ligand. This is also
their activity in ATRP.
expressed in a KATRP that is not significantly altered in com-
parison with other DMEG6Rqu (R = H, et, bu) ligands.
Complexes of the bidentate DMEG6Rqu (R = H, et, bu, or
ph) ligands exhibit redox potentials and values for KATRP com-
parable to complexes of the tridentate ligand PMDETA. It
must be mentioned, that PMDETA forms complexes with three
Atom Transfer Radical Polymerization
Determination of KATRP
KATRP is the central equilibrium constant of the ATRP equi- participating N-donors, whereas DMEG6Rqu forms bischelate
librium (see Scheme 1) and represents the ratio of the rate con- complexes with four participating N-donors.
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Figure 6. Semilogarithmic kinetic plot for a styrene polymerization
in solution (PhCN) mediated by [Cu(DMEG6phqu)2]Br. Conditions:
110 °C; ratio: monomer (styrene)/catalyst/ initiator (EBrib) = 100/1/1.
Figure 5. Correlation of CuII/L redox potentials with KATRP values
(measured with EBrib at 22 °C in MeCN). Black squares: Values pub-
lished by Matyjaszewski et al.[23] Blue circles: Values for DMEG6Rqu
complexes previously published.[3] Green circles: Value for the
DMEG6phqu complex.
Polymerization Kinetics
Although it was expected that [Cu(DMEG6phqu)2]Br
exhibits better solubility in styrene than the parent complex
[Cu(DMEGqu)2]Br, it turned out that the new catalyst was
completely insoluble in styrene, even at elevated temperatures.
Nevertheless, in order to gain information whether
[Cu(DMEG6phqu)2]Br could mediate an ATRP, polymeriza-
tion kinetics were then conducted in solution.
As in earlier studies,[2] polymerizations were performed in
benzonitrile (PhCN) as solvent, since it provides high polarity,
good miscibility with styrene, a high boiling point, and it is
rather non-hazardous. Polymerizations were conducted at
110 °C and with EBrib as initiator. Complexes were generated
in situ in the polymerization mixture (copper salt to ligand
ratio: 1/2; for details about the polymerization, see Experimen-
tal Section). Conversion was measured by 1H-NMR spec-
Figure 7. Mn/PD vs. conversion for styrene polymerizations in solu-
tion (PhCN) mediated by [Cu(DMEG6phqu)2]Br. Conditions: 110 °C;
ratio: monomer (styrene)/catalyst/initiator (EBrib) = 100/1/1.
troscopy, the molecular mass distribution was determined by molar masses could not be precipitated. The first monitored
gel permeation chromatography (GPC). Figure 6 shows a point exhibits a slightly increased Mn, since the polymer sam-
semilogarithmic plot of conversion vs. time. In Figure 7, the ple did not precipitate homogeneously. Mn,GPC finely follows
molar mass development vs. conversion is depicted. Polymeri-
Mn,Theo, indicating a controlled polymerization. The polydis-
zations were performed at least three times and the graphs persity provides information about the molecular mass distri-
show averaged data. By means of kinetic studies, it was al- bution with PD = Mw/Mn. The values of PD are around 1.05–
ready proven that bischelate CuI species exclusively catalyse 1.10 throughout the course of reaction. This indicates a very
the ATRP.[2]
An ATRP proceeds with pseudo-first-order kinetics. The control.
narrow molecular mass distribution and high polymerization
concentration of active radical species is rather low and thus
In a previous study, polymerization kinetics in solution were
termination reactions are effectively suppressed. Under these performed with the parent complex [Cu(DMEGqu)2]Br.[2]
conditions, the concentration of polymerizing chains stays con- Table 5 summarizes kobs of the newly developed catalyst
stant and the polymerization rate only depends on the mono- [Cu(DMEG6phqu)2]Br in comparison with kobs of the parent
mer concentration. Linearity of the semilogarithmic conversion complex.[2] The new catalyst exhibits a lower value for kobs
plot (Figure 6) indicates a controlled polymerization and thus than [Cu(DMEGqu)2]Br. kobs depends on KATRP and although
a controlled ATRP. The Mn/PD vs. conversion plot (Figure 7) KATRP values for both complexes do not significantly differ,
provides additional information about the polymerization.
polymerizations with [Cu(DMEG6phqu)2]Br proceed signifi-
Values for Mn are only available for polymer samples with cantly slower. It must be considered that besides KATRP, kobs
a conversion higher than 20%, since polymers with smaller depends on various factors (solubility of the complexes, rate
Z. Anorg. Allg. Chem. 2018, 1317–1328
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Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
of termination reactions, persistent radical effect). Comparing
Experimental Section
catalyst activities by means of kobs thus is only possible to a
limited extent.[26] However, it can be stated that
[Cu(DMEG6phqu)2]Br is suitable for solution ATRP of styr-
ene and does not largely differ from previous reported systems
by means of polymerization velocity and control.
General: Ligand and complex syntheses were performed under inert
conditions by using Schlenk techniques and a glove box in a nitrogen
atmosphere. Solvents were purified according to the literature and kept
under inert conditions.[27] Chemicals for the synthesis of the ligands
as well as CuIIBr2 for complex syntheses were all purchased from
ABCR, Grüssing, AppliChem, Acros Organics or TCI and were used
as received without further purification. CuIBr and the Vilsmeier salt
N,NЈ-dimethylethylene-chloroformamidinium chloride (DMEG-VS)
were synthesized as described in the literature.[17,28]
Table 5. kobs for [Cu(DMEG6phqu)2]Br and [Cu(DMEGqu)2]Br. Styr-
ene ATRP in PhCN. Conditions: 110 °C. Ratio: M/cat./init. = 100/1/1.
[2]
L = DMEG6phqu
2.5Ϯ0.1ϫ10–05
L = DMEGqu
IR Spectroscopy: ATR IR spectra were measured with a Shimadzu
IRTracer 100 with CsI beamsplitter in combination with a Specac
Quest ATR unit (resolution 2 cm–1).
kobs /s–1
4.2Ϯ0.2ϫ10–05
Mass Spectrometry: EI mass spectra were obtained with a Thermo-
Fisher Scientific Finnigan MAT 95 mass spectrometer. ESI mass spec-
tra were obtained with a ThermoFisher Scientific LTQ Orbitrap XL.
The source voltage was 4.49 kV, the capillary temperature amounted
to 299.54 °C. The tube lens voltage lay between 110 and 130 V.
Conclusions
Within this study the synthesis of the phenyl-substituted
guanidinoquinoline ligand DMEG6phqu was presented. The
nitration step of our synthetic approach to C6 substituted
GUAqu ligands had to be optimized due to poor solubility
of the 4-aminobiphenyl precursor. DMEG6phqu as
well as the complexes [Cu(DMEG6phqu)Br] and
[Cu(DMEG6phqu)2Br]Br could be crystallized and charac-
terized. Structural properties of the DMEG6phqu ligand did
not show significant differences in comparison with known
DMEG6Rqu (R = H, et, bu) ligands.
In contrast to previously published CuIBr complexes of
DMEG6Rqu (R = H, et) ligands, [Cu(DMEG6phqu)Br] crys-
tallized as a trigonal planar monochelate complex. The CuIIBr2
complex on the other hand strongly resembles previously pub-
lished CuII complexes of DMEG6Rqu (R = H or et) ligands.
Since in polymerization catalysis it is of greater interest to
know about the complex structure in solution, NMR, UV/Vis,
and EPR experiments with complex solutions were performed.
Thus, it could be demonstrated that DMEG6phqu forms
a bischelate CuIBr complex in solution. EPR spectra of
[Cu(DMEG6phqu)2Br]Br in solid state as well as in solution
indicate that the CuII complex reveals the same constitution in
both solid state and solution.
Elemental Analysis: Elemental analyses were performed with an Ele-
mentar varioEL or Elementar varioEL cube.
NMR Measurements: 1H- and 13C-NMR spectra were measured with
a Bruker Avance III HD 400 or a Bruker Avance II 400 nuclear mag-
netic resonance spectrometer. Measurements were performed in fully
deuterated solvents. The residual signal of the solvent served as an
internal standard.
EPR Measurements: X-band electron paramagnetic resonance spectra
were measured with a Magnetech Mini Scope MS 400. The EPR setup
included a microwave frequency counter Magnetech FC 400 and the
Resonator Rectangular TE102. Measurements were performed in
Hirschmann micropipettes with a calibrated volume of 50 μL. Details
about the chosen measurement parameters are given at the spectra in
the SI.
Gel Permeation Chromatography: The average molecular masses
and the mass distributions of the obtained polystyrene samples were
determined by gel permeation chromatography (GPC) in THF as mo-
bile phase at a flow rate of 1 mL·min–1. The utilized GPCmax VE-
2001 from Viscotek is a combination of an HPLC pump, two Malvern
Viscotek T columns (porous styrene divinylbenzene copolymer) with
a maximum pore size of 500 and 5000 Å and a refractive index detec-
tor (VE-3580) and a viscometer (Viscotek 270 Dual Detector). Univer-
sal calibration was applied to evaluate the chromatographic results.
With respect to ATRP, the redox potential of the activator/
deactivator couple was determined. Furthermore, KATRP was
measured and polymerization kinetics were performed. Phen-
ylation of the quinoline backbone has no significant influence
on E1/2 and KATRP of the corresponding complexes. Contrary
to our expectations, copper bromide complexes of
DMEG6phqu turned out to be completely insoluble in styrene,
UV/Vis Setup for KATRP Determination: UV/Vis measurements were
performed with an Avantes AvaSpec-ULS2048 CCD-Spectrometer and
an Avantes AvaLight-DH-S-BAL lightsource. The measurements were
done in Hellma QS screwcap-cuvettes with an optical pathlength of
10.00 mm.
even at elevated temperatures. Thus, ATRP kinetics were per- UV/Vis Setup for the Titration Experiment: UV/Vis measurements
were performed with an Agilent Technologies Cary 60 UV/Vis spec-
trophotometer. The spectra were obtained with a quartz glass immer-
sion probe (Helma, 1 mm) connected via a Cary 50 fibre optic coupler.
Measurements were performed in a commercial Schlenk measurement
cell.
formed in solution. [Cu(DMEG6phqu)2]Br mediates in solu-
tion a slower ATRP of styrene as [Cu(DMEGqu)2]Br.
It appeared that electronics of DMEGqu ligands can only
hardly be influenced by backbone substitution. This became
already apparent in alkylated DMEG6Rqu ligands and could
be confirmed with this work. In following studies, the influ-
ence of further electron donating and withdrawing substituents
should be evaluated.
CV Measurements: The measurements were performed at room tem-
perature with a Metrohm Autolab Potentiostat PGSTAT 101 using a
three-electrode arrangement with a Pt disc working electrode (1 mm
Z. Anorg. Allg. Chem. 2018, 1317–1328
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
diameter),
a
Pt wire as counter electrode and an Ag/AgCl
the depository numbers CCDC-1844282 for DMEG6phqu, CCDC-
reference electrode. The measurements were performed in CH3CN / 1844283 for [Cu(DMEG6phqu)Br], and CCDC-1844284 for
0.1 mol·L–1 NBu4PF6 with a sample concentration of 10 mM. Ferro-
cene was added as an internal standard after the measurements of the
sample and all potentials are referenced relative to the Fc/Fc+ couple.
Cyclic voltammograms were measured with 200 mV·s–1, 100 mV·s–1,
50 mV·s–1, and 20 mV·s–1.
[Cu(DMEG6phqu)2Br]Br
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
(Fax:
+44-1223-336-033;
E-Mail:
Synthesis of Ligand Precursor 4-Phenyl-2-nitroaniline (NO2phan):
NO2phan was synthesized according to various modified literature pro-
cedures.[14–16] 4-Phenylaniline (16.9 g, 100 mmol) was suspended in
acetic anhydride (280 mL). The mixture was heated to reflux for
30 min and subsequently cooled to 0 °C. Afterwards, the mixture was
carefully poured into iced water (2 L). Thus, 4-phenylacetamide pre-
cipitated as a colorless solid. The precipitate was washed with gener-
ous amounts of water and dried under high vacuum (1ϫ10–3 mbar)
overnight. 4-Phenylacetamide (20.9 g, 98.9 mmol, 99%) was isolated.
Acetic acid was added to 4-phenylacetamide until it was completely
dissolved (300 mL). Afterwards the solution was heated to 70 °C
whilst stirring and fuming HNO3 (99%, 17.2 mL, ex.) in acetic acid
(17.2 mL) was carefully added via a dropping funnel. The reaction
mixture was heated to 70 °C for 1 h and NO2 formed during the reac-
tion was quenched by leading it through a washing bottle filled with
an aqueous solution of NaOH. The red solution was poured into iced
water (1 L). 4-Phenyl-2-nitroacetamide precipitated as a yellow solid,
which was filtered off, washed with generous amounts of water and
dried under high vacuum (1ϫ10–3 mbar). 4-Phenyl-2-nitroacetamide
(25.0 g, 97.6 mmol, 98%) was isolated. 4-Phenyl-2-nitroacetamide
was dissolved in hot ethanol (125 mL) and an aqueous KOH solution
(25 mL, 50%) was carefully added via a dropping funnel. The reaction
mixture was heated to reflux for additional 20 min and subsequently
cooled to –35 °C. The precipitated red product was recrystallized from
ethanol for purification. Red solid. Yield: 7.3 g (34.1 mmol, 34%). 1H
X-ray Diffraction Analysis: The single crystal diffraction data for
DMEG6phqu, [Cu(DMEG6phqu)Br], and [Cu(DMEG6phqu)2Br]Br
are presented in Table 6. The data were collected with a Bruker D8
goniometer with APEX CCD detector. An Incoatec microsource with
Mo-Kα radiation (λ = 0.71073 Å) was used and temperature control
was achieved with an Oxford Cryostream 700. Crystals were mounted
with grease on glass fibers and data were collected at 100 K in ω-scan
mode. Data were collected with SMART,[29] integrated with SAINT[29]
and corrected for absorption by multi-scan methods with SADABS.[29]
The structure was solved by direct and conventional Fourier methods
and all non-hydrogen atoms were refined anisotropically with full-ma-
trix least-squares based on F2 (XPREP,[30] SHELXS-97,[31] and
ShelXle[32]). Hydrogen atoms were derived from difference Fourier
maps and placed at idealized positions, riding on their parent C atoms,
with isotropic displacement parameters Uiso(H) = 1.2Ueq(C) and
1.5Ueq(C methyl). All methyl groups were allowed to rotate but not to
tip.
In the complex [Cu(DMEG6phqu)2Br]Br it was not possible to model
the two water molecules in an adequate manner, and the data set was
treated with the SQUEEZE routine as implemented in PLATON.[33,34]
4
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. 2 H, CH), 7.35 (m, 1 H, CH), 6.91 (d, JHH = 8.3 Hz, 2 H, CH), 6.12
Copies of the data can be obtained free of charge on quoting (br. s, 2 H, NH2) ppm; in accordance with literature data.[35]
NMR (400 MHz, CDCl3): δ = 8.39 (d, JHH = 2.0 Hz, 1 H, CH), 7.66
(dd, 3JHH = 8.5, 4JHH = 2.3 Hz, 1 H, CH), 7.57 (m, 2 H, CH), 7.45 (m,
3
Table 6. Crystallographic data and parameters of DMEG6phqu, [Cu(DMEG6phqu)Br], and [Cu(DMEG6phqu)2Br]Br.
DMEG6phqu
[Cu(DMEG6phqu)Br]
[Cu(DMEG6phqu)2Br]Br
Empirical formula
Formula mass /g·mol–1
Crystal size /mm
T /K
C20H20N4
316.40
0.18ϫ0.17ϫ0.15
100(2)
C20H20BrCuN4
459.85
0.16ϫ0.14ϫ0.13
100(2)
C40H40Br2CuN8
856.16
0.15ϫ0.14ϫ0.13
100(2)
Crystal system
Space group
a /Å
b /Å
c /Å
monoclinic
C2/c
27.187(8)
7.020(2)
17.428(5)
90
monoclinic
P21/n
12.332(2)
7.7143(12)
19.997(3)
90
monoclinic
P21/c
18.6090(13)
16.2503(11)
13.6624(9)
90
α /°
β /°
104.099(4)
90
3226.0(16)
8
1.303
0.080
105.100(2)
90
1836.8(5)
4
1.663
3.376
105.6270(10)
90
3978.8(5)
4
1.429
2.596
γ /°
V /Å3
Z
ρcalcd. /g·cm–3
μ /mm–1
λ /Å
F(000)
0.71073
1344
0.71073
928
0.71073
1740
hkl range
–35/35, –9/9, –22/22
20693
3857
–17/17, –10/10, –28/28
27155
5431
–24/24, –21/21, –18/18
55291
10006
Reflections collected
Independent reflections
Rint.
0.0466
0.0655
0.0897
No. parameters
R1 [I Ն 2σ(I)]
wR2 (all data)
Goodness-of-fit
Δρfin max/min /e·Å–3
219
0.0432
0.1179
1.048
237
0.0375
0.0987
1.023
464
0.0470
0.1209
1.043
0.378/–0.183
0.838/–0.552
1.003/–1.040
Z. Anorg. Allg. Chem. 2018, 1317–1328
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Journal of Inorganic and General Chemistry
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Synthesis of Ligand Precursor 6-Phenyl-8-nitroquinoline
the catalyst with additional acetonitrile (150 mL), the organic phases
(NO26phqu):
were combined and the solvent removed in vacuo. The crude product
was purified by column chromatography (silica gel, ethyl acetate/hex-
anes: 1/1). Bright yellow solid. Yield: 3.3 g (15.0 mmol, 78%). 1H
3
4
NMR (400 MHz, CDCl3): δ = 8.78 (dd, JHH = 4.1, JHH = 1.6 Hz,
3
4
1 H, CH, 2), 8.11 (dd, JHH = 8.3, JHH = 1.5 Hz, 1 H, CH, 4), 7.71
(m, 2 H, CH, 12), 7.49 (m, 2 H, CH, 13), 7.40 (m, 4 H, CH, 3, 6, 14),
4
7.21 (d, JHH = 1.8 Hz, 1 H, CH, 8), 5.08 (br. s, 2 H, NH2, 1) ppm.
13C NMR (100 MHz, CDCl3): δ = 146.6 (CH, 2), 144.1 (Cq, 9), 141.1
(Cq, 11), 140.1 (Cq, 7), 137.9 (Cq, 10), 136.1 (CH, 4), 128.9 (Cq, 5),
128.7 (CH, 13), 127.4 (CH, 14), 127.3 (CH, 12), 121.7 (CH, 3), 114.2
(CH, 6), 109.6 (CH, 8) ppm. IR (ATR): ν˜ = 3468 [w, ν(N–H)], 3301
[w, ν(N–H)], 3171 [w, ν(N–H)], 3026 [vw, ν(C–Harom)], 1622 (m),
1600 (m), 1586 (m), 1577 (m), 1506 (m), 1491 (m), 1459 (w), 1444
(vw), 1422 (m), 1393 (m), 1377 (m), 1342 (w), 1284 (vw), 1248 (w),
1206 (vw), 1156 (w), 1125 (w), 1077 (w), 1033 (w), 1000 (vw), 983
(vw), 926 (vw), 870 (w), 859 (m), 847 (s), 797 (w), 789 (vs), 762 (vs),
746 (m), 699 (vs), 663 (m), 658 (m), 590 (m), 570 (w), 536 (w), 517
(w), 506 (m), 501 (m), 463 (w), 423 (w), 418 (w), 412 (m), 397 (m),
387 (m), 358 (m), 354 (m), 349 (m), 324 (m), 321 (w), 309 (m), 304
(m), 283 (w), 279 (m), 266 (m), 253 (w) cmϪ1. MS (EI+-HR): m/z
calcd. for C15H12N2 [M]+: 220.0995; found: 220.0996. C15H12N2:
calcd. C 81.79, H 5.49, N 12.72%; found: C 81.84, H 5.42, N 12.65%.
NO2phqu was synthesized according to a modified protocol by
Wielgosz–Collin et al.[36] In a 1 L two-necked flask first NO2phan
(6.7 g, 31.2 mmol, 1.0 equiv.) was dissolved in n-butanol (30 mL). HCl
(conc., 7.5 mL) and p-chloranil (7.7 g, 31.2 mmol, 1.0 equiv.) were
added. The mixture was heated to reflux and within 2 h acrolein (2.5 g,
43.7 mmol, 1.4 Eq) in n-butanol (7.5 mL) was added via a dropping
funnel. With the addition of acrolein the reaction mixture changed its
color from yellow-brownish to black. The mixture was cooled to room
temperature and ZnCl2 (5.1 g, 37.4 mmol, 1.2 equiv.) in THF (65 mL)
was added. Afterwards, the reaction mixture was again heated to reflux
for 1 h, then slowly cooled to 0 °C and stirred at that temperature for
2 h. The solid formed was filtered and put on ice. After neutralizing
with an aqueous solution of NaOH, the mixture was extracted with
dichloromethane (3ϫ200 mL). The combined organic layers were
dried over MgSO4 and the solvent removed in vacuo. The crude prod-
uct was purified by column chromatography (silica gel, 100% dichlo-
romethane Ǟ 98% dichloromethane + 2% methanol). Colorless solid.
Yield: 4.8 g (19.2 mmol, 62%). 1H NMR (400 MHz, CDCl3): δ = 9.07
Synthesis of Ligand N-(6-Phenylquinolin-8-yl)-1,3-dimethylimid-
azolidin-2-imine (DMEG6phqu):
3
4
(dd, JHH = 4.1, JHH = 1.6 Hz, 1 H, CH, 1), 8.32 (m, 2 H, CH, 3, 7),
4
8.20 (d, JHH = 2.0 Hz, 1 H, CH, 5), 7.71 (m, 2 H, CH, 11), 7.59 (dd,
4
3JHH = 8.3, JHH = 4.3 Hz, 1 H, CH, 2), 7.54 (m, 2 H, CH, 12), 7.47
(m, H, CH, 13) ppm. 13C NMR (100 MHz, CDCl3): δ = 152.4 (CH,
1), 148.5 (Cq, 8), 138.7 (Cq, 9), 138.6 (Cq, 6), 138.0 (Cq, 10), 136.3
(CH, 3), 129.3 (CH, Cq, 4, 12), 129.1 (CH, 5), 128.8 (CH, 13), 127.3
(CH, 11), 123.5 (CH, 7), 123.1 (CH, 2), 28.6 (CH2, 10), 15.1 (CH3,
11) ppm. IR (ATR): ν˜ = 3093 [vw, ν(C–Harom)], 3073 [w, ν (C–Harom)],
3055 [w, ν(C–Harom)], 1596 (w), 1578 (w), 1532 [s, ν(N=O)], 1490
(m), 1461 (w), 1441 (w), 1427 (vw), 1402 (w), 1385 (m), 1369 (m),
1356 (s), 1338 (m), 1184 (w), 1132 (w), 1078 (w), 1059 (w), 1024
(w), 1000 (vw), 982 (vw), 969 (w), 945 (vw), 919 (w), 908 (vw), 898
(m), 881 (s), 870 (w), 842 (vw), 799 (m), 796 (m), 774 (s), 758 (s),
748 (vs), 691 (vs), 652 (w), 640 (s), 617 (vw), 575 (m), 535 (w), 527
(w), 500 (m), 447 (m), 410 (vw), 397 (vw), 383 (w), 354 (w), 316
(w), 299 (w), 292 (vw), 283 (w), 278 (w), 273 (w), 266 (m), 253 (m)
cmϪ1. MS (EI+-HR): m/z calcd. for C15H10O2N2 [M]+: 250.0737;
found: 250.0732. C15H10N2O2: calcd. C 71.99, H 4.03, N 11.19%;
found: C 72.32, H 3.98, N 11.00%.
DMEG6phqu was synthesized analogously to the literature using the
amine described above.[37] NH26phqu (3.3 g, 15.0 mmol, 1.0 equiv.)
was weighed into an oven dried two-necked Schlenk flask and dis-
solved in acetonitrile (12.5 mL). After addition of triethylamine (3.0 g,
30.0 mmol, 2.0 equiv.), DMEG Vilsmeier salt (2.8 g, 16.5 mmol,
1.1 equiv.) in MeCN (10 mL) was added via a dropping funnel whilst
stirring within 15 min. The formation of a colorless solid was ob-
served. The reaction mixture was heated to reflux for 3 h and sub-
sequently a solution of NaOH (40 mmol, 2.03 g, 1.0 equiv.) in water
(20 mL) was added. With the addition of the NaOH solution the color-
less solid immediately vanished. After removal of the solvent in vacuo,
an aqueous KOH solution (30 mL, 50%) was added and the mixture
stirred for 2 h. The mixture was extracted with acetonitrile
(3ϫ50 mL). The combined organic layers were stirred over MgSO4
and activated charcoal. After filtration, the solvent was removed in
vacuo. Remaining urea was removed under high vacuum
(1ϫ10–3 mbar) at 100 °C. The ligand was purified by recrystallization
from acetonitrile. Yellow blocky crystals. Yield: 3.8 g (12.0 mmol,
Synthesis of Ligand Precursor 6-Phenyl-8-aminoquinoline
(NH26phqu):
1
3
4
80%). H NMR (400 MHz, CDCl3): δ = 8.80 (dd, JHH = 4.1, JHH
=
1.6 Hz, 1 H, CH, 4), 8.10 (dd, 3JHH = 8.3, 4JHH = 1.8 Hz, 1 H, CH, 6),
4
7.70 (m, 3 H, CH, 5, 14), 7.59 (d, JHH = 2.0 Hz, CH, 8), 7.42 (m,
2 H, CH, 15), 7.33 (m, 2 H, CH, 10, 16), 3.44 (s, 4 H, CH2, 3), 2.69
In an oven dried 500 mL Schlenk-flask first Pd/C (10%Pd basis, 0.5 g,
2.5 mol%) was suspended in MeOH (200 mL). Afterwards, NO26phqu
(s, 6 H, CH2, 2) ppm. 13C NMR (100 MHz, CDCl3): δ = 157.1 (CGUA
,
1), 148.9 (CH, 4), 144.2 (Cq, 11), 142.2 (Cq, 12), 140.5 (Cq, 13), 139.5
(4.8 g, 19.2 mmol, 1 equiv.) was added and the flask was sealed with (Cq, 9), 136.3 (Cq, 6), 129.2 (Cq, 7), 128.8 (CH, 15), 127.5 (CH, 16),
a rubber septum. The flask was flushed with H2 and stirred for 24 h 127.4 (CH, 14), 121.3 (CH, 5), 120.8 (CH, 10), 118.8 (CH, 8), 48.4
at ambient temperature. Afterwards, Pd/C was removed. After washing (CH2, 3), 34.8 (CH3, 2) ppm. IR (ATR): ν˜ = 3040 [w, ν(C–Harom)],
Z. Anorg. Allg. Chem. 2018, 1317–1328
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Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
2936 [w, ν(C–Haliph)], 2860 [w, ν(C–Haliph)], 1616 [vs, ν(C=Ngua)],
1603 [vs, ν(C=Ngua)], 1576 (m), 1559 (m), 1479 (vs), 1442 (m), 1417
(m), 1379 (s), 1339 (w), 1281 (m), 1239 (m), 1231 (m), 1200 (w), 698.2688
1137 (w), 1098 (w), 1076 (w), 1026 (m), 968 (m), 915 (w), 881 (w),
867 (m), 791 (m), 763 (s), 733 (w), 697 (s), 642 (m), 631 (m), 617
(m), 600 (m), 589 (m), 569 (m), 463 (m), 444 (m), 354 (m), 349 (m),
328 (m), 324 (m), 283 (m) cmϪ1. MS (EI+-HR): m/z calcd. for C20H20CuBrN4
C40H40CuN8 [Cu(DMEG6phqu)2]+: 695.2668 (100) [C40H4063CuN8]+,
696.2703 (48) [C3913CH4063CuN8]+, 697.2662 (56) [C40H4065CuN8]+,
(23)
[C3913CH4065CuN8]+,
699.2720
(5)
[C3813C2H4065CuN8]+, 700.2738 (1) [C3713C3H4065CuN8]+; found:
695.2650 (100), 696.2681 (42), 697.2640 (44), 698.2663 (20),
699.2699 (4), 700.2749 (1). Isotopic distribution calcd. for
[Cu(DMEG6phqu)Br]+:
458.0167
(70)
C20H20N4 [M]+: 316.1684; found: 316.1682. C20H20N4: calcd.
C 75.92, H 6.73, N 17.71%; found: C 74.80, H 6.24, N 17.42%.
[C20H2063Cu79BrN4]+, 459.0192 (16) [C1913CH2063Cu79BrN4],
460.0150 (100) [C20H2063Cu81BrN4] and [C20H2065Cu79BrN4],
461.0179 (24) [C1913CH2063Cu81BrN4] and [C1913CH2065Cu79BrN4],
462.0135
(33)
[C20H2065Cu81BrN4],
463.0156
(7)
Synthesis of [Cu(DMEG6phqu)Br]: To
a warm solution of
[C1913CH2065Cu81BrN4], 464.0191 (1) [C1813C2H2065Cu81BrN4];
found: 458.0148 (70), 459.0181 (15), 460.0126 (100), 461.0159 (20),
462.0108 (30), 463.0137 (5), 464.0172 (1).
DMEG6phqu (379.7 mg, 1.2 mmol, 2.4 equiv.) in acetonitrile (10 mL),
CuIBr (71.7 mg, 0.5 mmol, 1.0 equiv.) was added in small portions
whilst stirring. A change of color from pale yellow to dark red was
observed. Diffusion of diethyl ether led to crystals suitable for X-ray
Synthesis of [Cu(DMEG6phqu)2Br]Br: To a warm solution of
DMEG6phqu (379.7 mg, 1.20 mmol, 2.4 equiv.) in 10 mL acetonitrile
CuIIBr2 (111.7 mg, 0.50 mmol, 1.0 equiv.) was added in small portions
whilst stirring. A change of color from pale yellow to dark red was
observed. Diffusion of diethyl ether led to crystals suitable for X-ray
diffraction within one week. Dark red crystals. Yield: 34.4 mg
(0.05 mmol, 10%). IR (ATR): ν˜ = 3043 [vw, ν(C–Harom)], 2946 [vw,
ν(C–Haliph)], 2919 [vw, ν(C–Haliph)], 2887 [w, ν(C–Haliph)], 2871 [vw,
ν(C–Haliph)], 1543 [vs, ν(C=Ngua)], 1490 (s), 1469 (m), 1458 (m), 1414
(s), 1393 (vs), 1374 (m), 1341 (m), 1297 (m), 1245 (m), 1232 (m),
1213 (w), 1140 (vw), 1118 (w), 1088 (w), 1045 (w), 1023 (m), 1003
(w), 973 (m), 939 (vw), 912 (vw), 873 (m), 838 (w), 827 (w), 804
(w), 793 (w), 778 (m), 767 (s), 725 (vw), 706 (w), 694 (m), 665 (m),
654 (w), 625 (w), 618 (w), 610 (w), 601 (w), 576 (w), 571 (w), 553
diffraction within
3 d. Bright orange crystals. Yield: 74.0 mg
(0.1 mmol, 20%). IR (ATR): ν˜ = 3048 [vw, ν(C–Harom)], 2927 [vw,
ν(C–Haliph)], 2886 [vw, ν(C–Haliph)], 2861 [w, ν(C–Haliph)], 1586 (m),
1575 (m), 1554 [vs, ν(C=Ngua)], 1532 [vs, ν(C=Ngua)], 1485 (s), 1475
(s), 1452 (m), 1441 (m), 1412 (vs), 1389 (s), 1371 (m), 1338 (m),
1298 (m), 1285 (m), 1234 (m), 1187 (w), 1176 (w), 1151 (m), 1139
(w), 1113 (w), 1071 (w), 1042 (w), 1021 (m), 998 (w), 984 (w), 973
(m), 932 (w), 920 (w), 886 (w), 872 (m), 856 (s), 814 (w), 800 (m),
787 (s), 768 (s), 719 (m), 702 (vs), 664 (m), 655 (w), 627 (m), 614
(m), 608 (m), 570 (m), 547 (m), 518 (m), 466 (w), 452 (w), 335 (m),
289 (m), 267 (m), 265 (m) cmϪ1.MS (ESI+-HR)[m/z]: Isotopic distri-
bution calcd. for C20H20CuBrN4 [Cu(DMEG6phqu)Br]+: 458.0167
(70) [C20H2063Cu79BrN4]+, 459.0192 (16) [C1913CH2063Cu79BrN4],
460.0150 (100) [C20H2063Cu81BrN4] and [C20H2065Cu79BrN4],
461.0179 (24) [C1913CH2063Cu81BrN4] and [C1913CH2065Cu79BrN4],
(w), 517 (w), 509 (vw), 461 (w), 450 (w), 354 (w), 350 (m) cmϪ1
MS Isotopic distribution calcd. for
(ESI+-HR)[m/z]:
[Cu(DMEG6phqu)2Br]+: 774.1848 (65) [C40H4063Cu79BrN8]+,
.
462.0135
(33)
[C20H2065Cu81BrN4],
463.0156
(7)
[C1913CH2065Cu81BrN4], 464.0191 (1) [C1813C2H2065Cu81BrN4];
found: 458.0148 (70), 459.0181 (15), 460.0126 (100), 461.0159 (20),
462.0108 (30), 463.0137 (5), 464.0172 (1). C20H20BrCuN4: calcd.
C 52.24, H 4.38, N 12.18%; found: C 52.11, H 4.23, N 12.18%.
775.1881
(31)
[C3913CH4063Cu79BrN8]+,
776.1846
(100)
[C40H4063Cu81BrN8]+ and [C40H4065Cu79BrN8]+, 777.1872 (45)
[C3913CH4063Cu81BrN8]+ and [C3913CH4065Cu79BrN8]+, 778.1835 (39)
[C40H4065Cu81BrN8]+, 779.1857 (15) [C3913CH4065Cu81BrN8]+,
780.1887
(3)
[C3813C2H4065Cu81BrN8]+,
781.1900
(1)
Synthesis of [Cu(DMEG6phqu)2]Br:
[C3713C3H4065Cu81BrN8]+; found: 774.1846 (70), 775.1873 (30),
776.1821 (100), 777.1845 (45), 778.1811 (38), 779.1826 (14),
780.1856 (4), 781.1903 (1). Isotopic distribution calcd. for [Cu(D-
MEG6phqu)Br]+: 458.0167 (70) [C20H2063Cu79BrN4]+, 459.0192 (16)
[C1913CH2063Cu79BrN4], 460.0150 (100) [C20H2063Cu81BrN4] and
[C20H2065Cu79BrN4], 461.0179 (24) [C1913CH2063Cu81BrN4] and
[C1913CH2065Cu79BrN4],
463.0156 (7)
[C1913CH2065Cu81BrN4],
462.0135
(33)
[C20H2065Cu81BrN4],
464.0191 (1)
[C1813C2H2065Cu81BrN4]; found: 458.0159 (70), 459.0191 (15),
460.0135 (100), 461.0161 (20), 462.0115 (30), 463.0144 (4), 464.0174
(1). C40H40Br2CuN8: calcd. C 56.12, H 4.71, N 13.09%; found:
C 55.73, H 4.69, N 12.85%.
Polymerization Procedure: Styrene (Acros Organics, 99% stab.),
benzonitrile (PhCN, AlzChem), and the initiator ethyl α-bromoisobu-
tyrate (EBrib, abcr, 98%) were freshly distilled over CaH2. All poly-
merizations were performed with in situ generated catalysts. First, the
copper salt (0.19 mmol, CuIBr: 27 mg) next the ligand (0.38 mmol,
DMEG6phqu: 120 mg) were directly weighed into the polymerization
vessel under inert conditions inside a glovebox. Outside the glove box
the prepared Schlenk tube was connected to a Schlenk line. Styrene
(19 mmol, 2.2 mL), solvent (PhCN, 1.0 mL), and finally the initiator
(0.19 mmol, EBrib: 28 μL) were added with gastight glass syringes.
DMEG6phqu (22.1 mg, 0.070 mmol, 2 equiv.) and CuIBr (5.0 mg,
0.035 mmol, 1 equiv.) were dissolved in [D3]MeCN whilst stirring.
Formation of the complex was affiliated with dark red coloring of the
solution. The solution was subjected to NMR and MS spectroscopy.
1H NMR (400 MHz, CDCl3): δ = 8.59 (dd, 3JHH = 4.5, 4JHH = 1.5 Hz,
3
4
2 H, CH, 4), 8.38 (dd, JHH = 8.3, JHH = 1.5 Hz, 2 H, CH, 6), 7.77
4
(m, 4 H, CH, 14), 7.65 (d, JHH = 1.8 Hz, 2 H, CH, 8), 7.52 (m, 5 H,
CH, 5, 15), 7.43 (m, 2 H, CH, 10, 16), 3.44 (s, 4 H, CH2, 3), 2.69 (s,
6 H, CH2, 2) ppm. 13C NMR (100 MHz, CDCl3): δ = 163.2 (CGUA
,
1), 148.1 (CH, 4), 147.4 (Cq, 12), 141.6 (Cq, 9), 141.1 (Cq, 13), 137.9
(Cq, 6), 131.1 (Cq, 7), 130.0 (CH, 15), 129.0 (CH, 16), 128.4 (CH,
14), 123.8 (CH, 5), 118.0 (CH, 10), 116.6 (CH, 8), 49.1 (CH2, 3), 35.7
(CH3, 2) ppm. MS (ESI+-HR)[m/z]: Isotopic distribution calcd. for
After addition of the initiator, the mixture was heated (110 °C) under
vigorous stirring. The first sample was taken with a glass pipette under
inert conditions after 2.5 min. At this point of time the polymerization
Z. Anorg. Allg. Chem. 2018, 1317–1328
www.zaac.wiley-vch.de 1326
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
[8] a) A. Metz, R. Plothe, B. Glowacki, A. Koszalkowski, M. Scheck-
mixture reached its desired temperature and thus was chosen to be
enbach, A. Beringer, T. Rösener, J. Michaelis de Vasconcellos, R.
Haase, U. Flörke, A. Hoffmann, S. Herres-Pawlis, Eur. J. Inorg.
Chem. 2016, 2016, 4974–4987; b) P. M. Schäfer, M. Fuchs, A.
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starting point of the polymerization. Further samples were taken in
certain time intervals. The samples were mixed with CDCl3 and the
conversion measured by H-NMR spectroscopy. Afterwards the poly-
mer was precipitated in ethanol to remove the copper compound and
residual monomer. The solid, colorless polystyrene was dried over-
night and molecular mass distributions were determined by GPC.
1
KATRP Determination: All measurements were performed in oxygen
free acetonitrile at 22 °C. The acetonitrile was degassed by three
freeze-pump-thaw cycles. Stock solutions of the complexes and the
cuvettes were prepared in a glovebox under inert conditions.
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3867–3869; Angew. Chem. 2006, 118, 3951–3954; e) D. Maiti,
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The stock solutions of the initiator [147 μL (1.00 mmol) EBrib in
10 mL of acetonitrile] and the complexes [0.05 mmol CuIBr (7.2 mg)
and 0.1 mmol ligand (DMEG6phqu: 31.6 mg) in 2 mL of acetonitrile]
were prepared. A screwcap cuvette containing a stirring bar was filled
with 1.5 mL of acetonitrile and tightly sealed with a silicon septum. A
reference spectrum (MeCN) was measured. After addition of 400 μL
catalyst solution the time-dependent UV/Vis measurement was started.
By adding 100 μL of EBrib solution the reaction was initiated and the
formation of the CuII species was followed by UV/Vis spectroscopy.
Supporting Information (see footnote on the first page of this article):
ESR spectra of Cu(II) complexes, plot for KATRP determination, UV/
Vis spectrum of [Cu(DMEG6phqu)2]Br after addition of excess
ligand, NMR spectra of all compounds, VT-NMR spectra of
[Cu(DMEG6phqu)2]Br.
Acknowledgements
Financial support by the Fonds der Chemischen Industrie (Fonds fel-
lowships for T.R.) is gratefully acknowledged.
Keywords: Atom transfer radical polymerization (ATRP);
Copper; Substitution; Guanidine; Quinoline; Molecular struc-
ture
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Received: June 16, 2018
Published online: August 17, 2018
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