Reactivity of Copper(I) Complexes Containing Ligands Derived from (1S,3R)-Camphoric Acid with Dioxygen

Article abstract of DOI:10.1002/ejic.202100187

Amine derivatives prepared from camphoric acid were used as ligands for the synthesis of corresponding copper(I) complexes. Their reactivity towards dioxygen was analyzed. The formation of a short-lived bis(μ-oxido)copper complex was spectroscopically observed during the reaction of the copper(I) complex with (1R, 3S)-N¹,N¹,N³,N³-Tetramethyl-1,2,2-trimethylcyclopentane-1,3-diamine as a ligand. Furthermore, a regioselective demethylation of the ligand system was detected. Deuteration of the methyl groups of the ligand allowed crystallization and characterization of the bis(μ-oxido)copper complex. Derivatives of the ligand with pyridine residues caused suppression of the reactivity of the corresponding copper(I) complexes towards dioxygen. Additionally, the ligand system could be modified for intramolecular oxygenation reactions with benzaldehyde that led to the formation of salicylaldehyde, a selective hydroxylation in ortho position.

Full text of DOI:10.1002/ejic.202100187

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Reactivity of Copper(I) Complexes Containing Ligands
Derived from (1S,3R)-Camphoric Acid with Dioxygen
[
a, b]
[b]
[a]
[b]
Fabian Stöhr,
Niclas Kulhanek, Jonathan Becker, Richard Göttlich,* and
[a]
Siegfried Schindler*
Amine derivatives prepared from camphoric acid were used as
ligands for the synthesis of corresponding copper(I) complexes.
Their reactivity towards dioxygen was analyzed. The formation
of a short-lived bis(μ-oxido)copper complex was spectroscopi-
cally observed during the reaction of the copper(I) complex
Deuteration of the methyl groups of the ligand allowed
crystallization and characterization of the bis(μ-oxido)copper
complex. Derivatives of the ligand with pyridine residues
caused suppression of the reactivity of the corresponding
copper(I) complexes towards dioxygen. Additionally, the ligand
system could be modified for intramolecular oxygenation
reactions with benzaldehyde that led to the formation of
salicylaldehyde, a selective hydroxylation in ortho position.
1
1
3
3
with
(1R,
3S)-N ,N ,N ,N -Tetramethyl-1,2,2-trimeth-
ylcyclopentane-1,3-diamine as a ligand. Furthermore, a regiose-
lective demethylation of the ligand system was detected.
Introduction
cleaving the imine after the reaction. With this “click and cleave”
[7]
[6]
method, non-activated, aliphatic and aromatic systems up to
[
17,18]
Copper enzymes are able to activate dioxygen under ambient
conditions and thereby catalyze the oxidation of organic
complex steroid systems
could be hydroxylated via CÀ H
activation. In addition, this method has already been used
successfully as a key step in the synthesis of C-12 hydroxylated
[1]
substrates. Examples include the enzyme tyrosinase, which
[2]
[18]
catalyzes the selective oxidation of tyrosine to dopaquinone
and furthermore methane monooxygenase, which is capable to
oxidize methane selectively to methanol.
steroids in high yields. Moreover, external substrates have
already been successfully oxygenated using these active oxygen
[3]
[8,19]
adduct intermediates.
In order to understand the binding of dioxygen to the
active site in these enzymes, various copper(I) complexes as
model compounds were synthesized and investigated in the
Rigid ligand systems can stabilize dinuclear trans-μ-1,2-
[12,20]
peroxo-dicopper(II) complexes.
Tolman and co-workers
observed an equilibrium between side-on peroxido copper
complexes and bis(μ-oxido)copper complexes applying an
alkylated derivative of the small macrocycle triazacyclononane
[4,5–9]
past.
A wide variety of so called “oxygen adduct” complexes
could thus be detected and in some cases also structurally
[10,11,12–14]
[13]
characterized e.g. bis(μ-oxido)copper complexes.
These
as ligand. Furthermore, Itoh and co-workers could demon-
compounds are usually highly reactive and often lead to
strate for a series of tridentate ligands based on a cyclic diamine
unit that a higher rigidity of these ligand systems led to a
[5–7,15,16,17,18]
intramolecular ligand hydroxylations.
To take advant-
[
21]
age of this reactivity, ligand systems were functionalized with
preferred formation of bis(μ-oxido)copper complexes. In this
context we therefore looked for a system that was as easily
accessible and as rigid as possible, to allow for a possible
crystallization of an oxygen intermediate complex. Based on
previous work ligands derived from camphoric acid should
[6,7,17,18]
substrates to be oxidized.
For this purpose, aldehydes
and ketones are typically bound to ligands via imine condensa-
tions in order to simply release the oxidized substrates by
[22]
satisfy these claims.
Ligand systems containing guanidine residues have been
[
a] F. Stöhr, Dr. J. Becker, Prof. Dr. S. Schindler
Institute for Inorganic and Analytical Chemistry,
Justus-Liebig-University Gießen,
[
23,24,25]
used successfully to stabilize “oxygen adduct” complexes.
Heinrich-Buff-Ring 17, 35392 Gießen, Germany
E-mail: siegfried.schindler@ac.jlug.de
[26]
These include, among others, the ligand TMG tren or ligands
3
https://www.uni-giessen.de/fbz/fb08/Inst/iaac/schindler
b] F. Stöhr, N. Kulhanek, Prof. Dr. R. Göttlich
Institute for Organic Chemistry,
based on 1,3-propanediamine, where corresponding copper(I)
complexes were able to hydroxylate phenolates using
dioxygen. In addition, the guanidine-containing ligands 1 and
[
[24]
Justus-Liebig-University Gießen,
Heinrich-Buff-Ring 17, 35392 Gießen, Germany
E-mail: richard.goettlich@org.chemie.uni-giessen.de
https://www.uni-giessen.de/fbz/fb08/Inst/organische-chemie/AGGoet-
tlich
2 (Figure 1) could be synthesized from camphoric acid.
Copper(I) complexes with these ligands reacted with dioxygen
to form bis(μ-oxido) copper complexes. However, so far they
[
27]
have not been used for oxidation reactions of substrates.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202100187
With this background we decided to adapt other groups
than guanidine residues to the system. For this purpose, the
use of various residual groups (Scheme 1, 3a–3c) was first
investigated to test corresponding copper(I) complexes with
these ligands for possible dioxygen activation. Selective intra-
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[
28]
the conversion of 5 in a Schmidt reaction to diamine 6, which
functions as a common precursor for all further ligands
described herein. Ligand 3a could be obtained in good yields
[29]
applying Eschweiler-Clarke conditions (Scheme 2b). To pre-
pare ligand 3b, diamine 6 was first selectively protected at the
sterically less hindered amine function with benzoyl chloride
[30]
(
Scheme 2c). The subsequent methylation of the free amine
function was carried out again applying Eschweiler-Clarke
[27]
[30]
[31]
Figure 1. Camphor-like ligands used in previous work. Complexation with
Cu(I) and reaction with dioxygen resulting in a bis-(μ-oxido) copper complex.
conditions (Scheme 2d). After deprotection (Scheme 2e), an
imine condensation was carried out with 2-formylpyridine. This
was followed by reduction with NaBH4 and subsequent
reductive methylation (Scheme 2f), which led to ligand 3b.
Ligand 3c could be obtained from diamine 6 by adapting the
reaction conditions of step f (Scheme 2) and by an increase of
the equivalents of the reagents.
With these ligands at hand, their complexation properties in
combination with copper ions were examined. Starting with 3a,
it was first reacted with [Cu(CH CN) ]OTf in a ratio of 1:1 in
3
4
acetone. Crystals could be obtained, which were structurally
analyzed. However, in contrast to the expected copper complex
the protonated triflate salt of 3a was obtained (The crystallo-
graphic data are presented in the Supporting Information). The
protons presumably came from the solvent acetone. Therefore,
DCM was used instead but still it was not possible to obtain/
crystallize a copper complex as a product. A possible reason for
this could be that a complex in a 2:1 ratio of ligand to copper
ion is formed as well and thus leading to a product mixture that
did not allow to obtain a clean product. Problems with
bidentate ligands that tend to form complexes in a ligand to
copper(I) ratio of 1:2 have already been described
Scheme 1. Camphor-like ligands used in this work.
molecular ligand hydroxylation should be achieved afterwards
by further modification of this ligand system (Scheme 1, 4a–
4
c).
Results and Discussion
Synthesis of the Ligands and Characterization of
Corresponding Copper Complexes
[6,10]
previously.
To avoid this problem, one equivalent of PPh was added to
3
Camphoric acid (5) is commercially available and therefore, the
synthesis of the ligand systems 3a–3c (Scheme 2) started with
the complex solution, on the one hand to block a free
coordination site at the copper, and on the other hand to
enforce crystallization. Thus, yellow colored crystals of a copper
(I) complex were obtained in which, as expected, the copper(I)
ion is coordinated in a trigonal planar geometry by PPh and
3
the chelating diamine 3a (Figure 2).
The reaction of ligand 3b with [Cu(CH CN) ]ClO led to the
3
4
4
formation of crystals in which two ligands bind to the copper
center. Interestingly, one ligand chelates via a pyridine and an
amine residue, while a second ligand coordinates to the copper
Scheme 2. (a) NaN
3
, H
2
SO
4
, CHCl
3
, 55°C, 77%. (b) Formic acid, formaldehyde,
reflux, 83%. (c) Benzoyl chloride, EtOH 69%. (d) Formic acid, formaldehyde,
reflux, 83%. (e) HCl reflux, 81%. (f) 1.) 2-Formylpyridine, Na SO , MeOH,
2 4
reflux 2.) NaBH
Formylpyridine, Na
NaCNBH , MeOH 26%.
4
, MeOH 3.) Formaldehyde, NaCNBH
3
, MeOH 72%. (g) 1.) 2-
+
2
SO , MeOH, reflux 2.) NaBH , MeOH 3.) Formaldehyde,
4
4
Figure 2. Molecular Structure of [Cu(3a)(PPh
3
)] . Hydrogen atoms and the
3
triflate anion are omitted for clarity. Ellipsoids are drawn at 50% probability.
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center only via a pyridine residue (Figure 3). The ligand
obviously does not act as tridentate ligand. This could be
[32]
caused by a syn-pentane interaction.
When ligand 3c was reacted with [Cu(CH CN) ]OTf in a 1:1
3
4
ratio a yellow colored oil was obtained. Complexation with CuCl
in THF caused formation of yellow colored and crystalline small
plates, which could be examined using SC-XRD (Figure 4). Here
3
c acts as tetradentate ligand, as has already been described in
4
[33]
À
the literature for other N ligands, however with CuCl2 as an
anion.
Attempting to react the ligand with two equivalents of
[
Cu(CH CN) ]OTf resulted in a disproportionation reaction. After
3 4
filtration (to remove the metallic copper) and evaporating the
solvent under ambient conditions, a blue powder was obtained.
Dissolving the residue in methanol followed by a slow
evaporation, led to blue colored crystals, which turned out to
be the copper(II) complex with 3c as ligand (The crystallo-
graphic data are presented in the Supporting Information).
To investigate the influence of methyl and ethyl groups on
possible ligand hydroxylation, the ligands 4a–4c were synthe-
sized to obtain more detailed information on selective ligand
hydroxylation. Benzaldehyde was selected as a test substrate to
be oxygenated, since previous studies have already been
successful in demonstrating high-conversion hydroxylations
near the maximum of 50% on aromatic systems using copper(I)
and dioxygen with bis(μ-oxido)copper complexes as reactive
Scheme 3. (a) Formic acid, formaldehyde, reflux, 83%. (b) EtI 5 eq., Na
EtOH, reflux 81%. (c) Formaldehyde, NaCNBH , rt, 96%. (d) EtI 10 eq., Na
MeCN, reflux 65%. (e),(g),(i) HCl, reflux, 81–91%. (f),(h),(j) Benzaldehyde,
Na SO , MeOH reflux, 56–81%.
2
CO
3
,
3
2
CO
3
,
2
4
[6,15,34]
intermediates.
The synthesis started from the benzoyl-
protected amine 7 which was initially prepared by slight
+
Figure 5. Molecular Structure of [Cu(4c)(CH
3
CN)] . Hydrogen atoms and
triflate anion are omitted for clarity. Ellipsoids are drawn at 50% probability.
[30]
modifications to the literature. This was followed by different
[
30]
alkylation reactions to receive the alkylated amines 8–10.
[31]
After deprotection with HCl and subsequent imine condensa-
tions the ligands 4a–4c were obtained (Scheme 3).
Single crystals could be obtained from the HCl salts of the
ligand systems 4a and 4b. The crystallographic data are
presented in the Supporting Information. Quite unexpected,
these imines turned out to be quite stable, even under acidic
conditions.
+
Figure 3. Molecular Structure of [Cu(3b)
2
] . Hydrogen atoms and perchlorate
anion are omitted for clarity. Ellipsoids are drawn at 50% probability.
Additionally it was possible to obtain single crystals from
the complex of [Cu(CH CN) ]OTf and 4c. This ligand acts as a
3
4
chelate ligand, and one acetonitrile molecule coordinates to the
copper center (Figure 5).
Reactivity of the Copper(I) Complexes with Dioxygen
Due to the problems with obtaining copper(I) complexes as
+
simple 1:1 (copper ion to ligand ratio) [Cu(L)] solids the
Figure 4. Molecular Structure of [Cu(3c)] [CuCl
omitted for clarity. Ellipsoids are drawn at 50% probability.
2
]. Hydrogen atoms are
reactions with dioxygen were performed by mixing solutions of
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copper(I) salts with the ligand in an equimolar ratio as
described previously.
transient intermediate could be observed spectroscopically,
[
35]
characterized by two significant absorbance maxima near
300 nm (limit of the detector) and 414 nm (Figure 6). Based on
earlier work, this result supports the formation of bis(μ-oxido)
When a solution of ligand 3a and [Cu(CH CN) ]OTf in DCM
3
4
was reacted with dioxygen at À 80°C in a bench top experiment
an immediate color change from a yellow to a very dark brown
colored solution was observed. After warming to room temper-
ature, the solution turned irreversibly to a dark green color.
After decomplexation with aqueous ammonia, demethylation
of the ligand system was indicated by means of ESI-MS. Using
GC-MS, two demethylated species could be detected and the
position of the demethylation could be determined on the basis
of the fragmentation pattern. An approximate ratio of 2:1 and
traces of 12 could be found (Scheme 4).
[6–9,24,27,36]
copper complex
and, furthermore, is in excellent agree-
ment with our previous investigation of related copper(I)
complexes with the monoguanidine ligand 2-[3-(dimeth-
ylamino)propyl]-1,1,3,3-tetramethylguanidine (TMGdmap) and
the related bis(guanidine) 1,3-bis(N,N,N’,N’- tetrameth-
[25]
ylguanidino)propane (btmgp).
The absorbance vs. time trace at 414 nm can be fitted with
À 1
a one exponential function and a rate constant of kobs =0.13 s
could be calculated, in line with our results for the reaction of
+
The two demethylated species 11 and 12 could be
separated as a mixture from ligand 3a by means of column
chromatography and the structures of these compounds were
confirmed by NMR. Conversion to the corresponding HCl salts
of the mixture of the demethylated species yielded crystals
which were structurally examined. It turned out as the demeth-
ylated component 11 in form of an HCl salt (The crystallo-
graphic data are presented in the Supporting Information).
Related dealkylation reactions were reported previously by
Stack and co-workers including the observation of a bis(μ-
dioxygen with the complexes [Cu(TMGdmap)] and [Cu-
+
(btmgp)] . Therefore, no further kinetic measurements were
performed. In a first step a mononuclear superoxido copper
complex is formed that reacts in a fast consecutive step to the
bis(μ-oxido)copper complex according to Scheme 5.
As described in great detail previously the rate limiting step
[25]
is the formation of a superoxido complex. With an excess of
dioxygen a first order rate law (Eq. 1) can be applied.
(
1)
[10]
oxido)copper complex as the reactive intermediate. In order
to clarify whether such an oxygen intermediate leads to the
observed demethylation here as well, the complex solution of
ligand 3a and [Cu(CH CN) ]OTf was examined using low
Detailed kinetic investigations by Stack and co-workers on
similar complexes with cyclohexane derivatives as ligands can
be applied here for a mechanistic explanation and the cleavage
3
4
[10]
temperature stopped-flow techniques. At low temperatures, a
of the methyl groups (Scheme 6).
The bis(μ-oxido)copper
complex 13 leads to intramolecular ligand hydroxylation. The
intermediate hemiaminal 14 is split into formaldehyde and the
amine 11 after aqueous work-up. Based on previous work, this
also explains that the conversion of the reaction to the
[6]
demethylated ligands cannot exceed 50%.
It is well known by us and others, that deuteration of alkyl
[
37]
groups can be used to suppress an attack on these groups.
Deuteration of diamine 6 with deuterated formaldehyde and
Scheme 4. Observed oxidation products after the reaction at À 80°C.
Scheme 5. Formation of the bis(μ oxido)copper complex.
Figure 6. Time-resolved UV/Vis spectra of the reaction of [Cu(3a)]OTf
À 3
À 3
(
c=0.5×10 m) with dioxygen (c=2.15×10 m) in DCM at À 89°C for 35 s.
Scheme 6. Proposed pathway for the demethylation of amine 3a to amine
11. Charges omitted.
The inset shows the absorbance vs time at λ=414 nm.
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deuterated formic acid yielded a D-12 analogue of 3a. Reaction
of the deuterated ligand together with [Cu(CH CN) ]PF and
The reactivity of copper(I) complexes with the ligands 3a–
3c was investigated especially to detect dioxygen adduct
complexes as intermediates. This was important prior to the
investigations with ligands 4a–4c that were chosen for possible
intramolecular hydroxylation reactions because more recently
an alternative radical reaction pathway was observed based on
the formation of a hydroperoxido complex instead of a bis(μ-
3
4
6
dioxygen at À 80°C in DCM yielded brown crystals, which
turned out to be the proposed bis(μ-oxido)copper complex
(
Figure 7).
The distance between the oxygen atoms is 2.218 Å, which
indicates a cleavage of the dioxygen bond. The distance is
[10]
[34]
smaller than in Stack’s bis(μ-oxido)copper complex (2.334 Å),
oxido)copper intermediate.
while the distance between the two copper ions is longer
When ligand 4a was reacted with copper triflate in DCM
with dioxygen (Scheme 7) at room temperature a color change
from a yellow to a green color was observed. After treating the
solution with aqueous ammonia to remove the copper(II) ions
and separating it from the organic phase, the organic residue
was analyzed by means of ESI-MS and NMR. Ligand hydrox-
ylation could be determined, and an NMR analysis showed that
a hydroxylation in the ortho position had occurred. With the
integral ratio of the imine proton signals, a ratio of 92 to 8
could be determined.
The low conversion observed in this reaction could be
caused by the fact that a possible oxygen adduct intermediate
might not be sufficiently stabilized at room temperature.
Therefore, the influence of temperature on the reaction was
investigated. It was observed that the conversion increased
with lower temperatures and approached a maximum of 17%
(Table S1).
(2.851 Å vs. 2.744 Å). However, in both cases the copper atoms
are ligated in nearly square planar fashion.
The observed selectivity in the cleavage of the methyl
groups might be caused by the closer distance between the
protons on the labile methyl groups and the oxygen atoms
(2.108 Å vs. 2.234 Å) which corresponds to observed selectivity
above. The closer distance is presumably directed by the methyl
group carried by the carbon 1R. One possibility for the
hydroxylation mechanism of aliphatic CÀ H bonds is described
as the radical abstraction of hydrogen and subsequent rebind-
[17,18,38]
ing of the oxygen.
This mechanism might apply to our
system, at least with regard to selectivity.
When the tridentate ligand 3b was reacted with
[
Cu(CH CN) ]Otf and dioxygen at À 80°C in DCM with dioxygen
3
4
only an irreversible color change to a dark green color could be
observed. After warming to room temperature and decomplex-
ation with aqueous ammonia, it turned out that only traces of
the ligand system were demethylated and/or hydroxylated by
means of ESI-MS. Isolation of these species was unsuccessful
due to the minimal conversion that could not be detected by
GC-MS. Furthermore, stopped-flow measurements did not show
the formation of a reactive intermediate. Most likely, this is
caused due to the formation of a complex with a 2:1 ratio of
ligand to copper (despite the equimolar premixing), which was
detected in the solid.
Additionally, the reaction was carried out in different
solvents. However, in contrast to previous findings, applying
[6,7]
acetone, acetonitrile or methanol suppressed the hydroxyla-
tion reaction completely. Furthermore, since an influence of the
anions on the formation of oxygen intermediates had been
[39]
described in the literature,
various copper(I) salts were
investigated for this reaction (Table S2). Not surprisingly, no
conversion to a hydroxylated product could be detected when
CuCl was used. The chloride anion coordinates strongly to the
copper ion, competes with the incoming dioxygen and thus
binding of oxygen is suppressed. The highest conversion (28%)
was observed when the weakly coordinating BF4 anion was
used.
More or less expected from the molecular structure of the
copper(I) complex with the ligand 3c, a mixture of this ligand
together with [Cu(CH CN) ]OTf in DCM turned out to be inert
3
4
towards dioxygen. No color change of the yellow colored
solution was observed. This suggests that the complex cannot
activate dioxygen under these conditions, presumably, due to
its steric and electronic properties.
Since the conversion was highest when using
[Cu(CH CN) ]BF , a stopped-flow measurement of the reaction
3
4
4
was carried out. The formation of a band at 392 nm could be
detected (Figure 8). Since it was not possible, to fit the
absorbance vs. time trace at 414 nm with a one exponential
function, we thought the band shows the formation of the
copper(II) complex with the hydroxylated ligand 15. For that we
decided to synthesize the ligand 15 by an imine condensation
reaction with salicylaldehyde. A mixture of this ligand together
2
+
Figure 7. Molecular structure of [Cu
the nearest CÀ H’s to O), the PF anions and solvent molecules are omitted
for clarity. Ellipsoids are drawn at 50% probability.
2 2 2
(3ad12) O ] . Hydrogen atoms (except
6
Scheme 7. First attempt at hydroxylation of ligand 4a. Conversion was
determined using the integral of the imine proton signals.
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with pyridine residues lead to absence of any detectable
oxygen intermediate.
However, it was possible to modify the ligand system in
such a way that an intramolecular ligand hydroxylation on
benzaldehyde in ortho position became accessible and salicy-
laldehyde was obtained. This kind of reactivity could only be
observed for one of our ligands, the twice methylated one. The
introduction of ethyl groups again suppressed this reactivity.
We are currently working on increasing the conversion of these
reactions and furthermore we believe we now have a good
basis for to achieve stereoselective oxygenation reactions of
substrates in the near future.
Experimental Section
Figure 8. Time-resolved UV/Vis spectra of the reaction of 4a and
À 3
À 3
General: Chemicals and solvents were purchased from commercial
sources. The solvents were distilled and, if necessary, dried using
standard procedures. Oxygen free solvents were obtained by
redistillation under argon. Preparation under anaerobic conditions
were carried out in a glovebox (MBraun) under Argon atmosphere.
3 4
[Cu(CH CN) ]Otf (c=2×10 m) with Dioxygen (c=2.15×10 m) in DCM at
À 89°C.
with copper(II) triflate was examined by means of UV/Vis. The
resulting spectra is presented in the Supporting Information
and is in agreement with the final spectrum in the stopped flow
measurement. This suggests that the rate limiting step is the
formation of the reactive intermediate and the consecutive
hydroxylation reaction is much faster. However, it is unclear via
which intermediate the reaction proceeds.
The reaction of dioxygen with the copper complexes with
the ligands 4b and 4c under the same conditions did not show
any oxygenation reactions at all. Most likely substitution of one
1
13
H and C spectra were measured on a Bruker Avance II 400 MHz
1
13
and Bruker Avance III HD 400 MHz spectrometer. The H- and C-
NMR spectra were calibrated against the residual proton and
carbon signals of chloroform (δ=7.26). HRMS(ESI) was measured
with an ESI-MS Bruker Mikro-TOF. Elemental analysis was performed
by a Thermo FlashEA-1112 Series. GC-MS analysis was carried out
using an Agilent Technologies 7820 A GC System coupled with an
Agilent Technologies 5977B MSD.
Stopped-Flow measurements: The copper(I) complex solutions
were prepared in a glove box by adding the ligand solution to the
copper salt solution under stirring and were filled in glass syringes.
Saturated solutions of dioxygen were prepared by bubbling dry
oxygen through dry DCM in a syringe for 10 minutes. The saturated
–
or both – methyl groups by ethyl groups increased the sterical
hinderance to such an extent that no dinuclear bis(μ-oxido)
copper complex can form and therefore no hydroxylation was
observed. Obviously, the alternative reaction pathway through
a hydroperoxido complex mentioned above also did not take
place here.
À 3
[40]
dioxygen concentration in DCM is 4.3×10 m at 25°C.
The
measurements were performed by a commercial HI-TECH SF-61SX2
instrument (TgK Scientific, Bradford-on-Avon, UK) at À 89�1
°
C.
(
1R,3S)-Diamino-1,2,2-trimethylcyclopentane (6): Following the
[28]
literature procedure , (1S,3R)-camphoric acid (9.52 g, 47.5 mmol)
was dissolved in 150 ml chloroform and 25 ml conc. H SO were
2
4
added. NaN (9.02 g, 138.7 mmol) was added to the solution in
Conclusion
3
small portions over three hours. The mixture was heated to 55°C
for 18 h. After cooling to rt, 500 ml H O were added, the aqueous
2
CÀ H activation is a very important area in chemistry, and with
our previous developed clip-and-cleave system we could
demonstrate that facile oxygenation reactions of aldehydes and
ketones are possible by applying simple copper(I) complexes
and dioxygen as the sole oxidant. However, there is still room
for optimization of this reaction and therefore we have been
looking for additional ligand systems that might provide even
better results. In this regard we investigated copper complexes
with ligand systems based on camphor derivatives. We found
that the copper(I) complex of the tetramethylated ligand (1R,
phase was separated and NaOH was added until the aqueous phase
was strongly basic. The aqueous phase was extracted with DCM
(3x300 ml) and the combined organic phases were dried with
MgSO
. After filtration and removing of the solvent, a colorless solid
4
1
was obtained (5.21 g, 36.6 mmol, 77%). H NMR (400 MHz, CDCl ) δ
3
3
1
.02 (dd, J=8.4, 6.3 Hz, 1H), 2.11–1.99 (m, 1H), 1.93 (s, 4H), 1.72–
.62 (m, 2H), 1.41–1.29 (m, 1H), 1.05 (s, 3H), 0.85 (s, 3H), 0.80 (s, 3H).
13
1
C{ H} NMR (101 MHz, CDCl ) δ 61.6, 61.0, 46.4, 38.2, 30.2, 25.6,
3
+
22.5, 16.5. HRMS (ESI): calcd. for C H N [M+H ] 143.1544, found
8
18
2
143.1544. Crystals of the HCl salt, which were structurally charac-
terized, were obtained by adding HCl in Et O (2 m) to 6 dissolved in
2
1
1
3
3
methanol, evaporating of the solvent, followed by dissolving of the
residue in methanol/acetonitrile 1:1 and slow evaporating of the
solvent mixture. The crystallographic data are presented in the
Supporting Information.
3
S)-N ,N ,N ,N -tetramethyl-1,2,2-trimethylcyclopentane-1,3-dia-
mine caused a selective, intramolecular demethylation when
reacted with dioxygen. A stopped-flow analysis of this reaction
showed the formation of a bis(μ-oxido)copper complex as a
reactive intermediate. Following up on this, we were able to
successfully crystallize and structurally characterize the oxygen
intermediate through deuteration of the sensitive methyl
groups. In contrast, functionalization of the ligand framework
1
1
3
3
(
1R,3S)-N ,N ,N ,N -Tetramethyl-1,2,2-trimethylcyclopentane-1,3-
diamine (3a): Diamine 6 (1.092 g, 7.677 mmol) was added to 4 ml
formic acid over a period of 20 min at 0°C. Then 4.5 ml
formaldehyde solution (37wt.%) was added dropwise. The solution
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6
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refluxed for 18 hours. After cooling to rt, the solution was made
(obtained by Scheme 2d or 8) (1.480 g, 5.393 mmol). Then 7.5 ml
water was added. The mixture was refluxed for 48 hours. The
suspension was then made basic with NaOH solution and extracted
with 3x50 ml DCM and 3x50 ml ethyl acetate. The combined
organic phases were dried with sodium sulfate. After filtration and
basic with NaOH solution and extracted with DCM (4×50 ml). The
organic phases were combined and dried with Na SO . After
2
4
filtration and removing of the solvent, the colorless residue was
purified by column chromatography (DCM, MeOH 9:1, 1% NEt3;
silica). The product was obtained as a colorless liquid (1.267 g;
removing of the solvent, the product was obtained as a colorless
1
1
6
1
1
.388 mmol; 83%). H NMR (400 MHz, CDCl ) δ 2.42 (t, J=9.3 Hz,
liquid (741 mg, 4.35 mmol, 81%). H NMR (400 MHz, CDCl ) δ 2.89
3
3
H), 2.28 (s, 6H), 2.23 (s, 6H), 1.90–1.77 (m, 1H), 1.75–1.61 (m, 2H),
(t, J=9.2 Hz, 1H), 2.17 (s, 6H), 2.05 (s, 2H), 1.93 (m, 1H), 1.85–1.71
13
1
.59–1.48 (m, 1H), 1.10 (s, 3H), 0.99 (s, 3H), 0.90 (s, 3H). C{ H} NMR
(m, 1H), 1.54–1.40 (m, 1H), 1.25 (m, 1H), 0.94 (s, 3H), 0.85 (s, 3H),
1
3
1
(
100 MHz, CDCl ) δ 74.8, 67.0, 48.1, 45.8, 40.4, 37.2, 24.7, 21.5, 17.9,
1.5. HRMS (ESI): calcd. for C H N [M+H ] 199.2169, found
0.82 (s, 3H). C{ H} NMR (101 MHz, CDCl ) δ 67.4, 61.2, 46.8, 40.1,
3
3
+
+
1
36.7, 29.0, 22.7, 16.1, 11.3. HRMS (ESI): calcd. for C H N [M+H ]
12
26
2
10 22
2
1
99.2168. C H N : calcd. C 72.66, H 13.21, N 14.12; found C 72.64,
171.1856, found 171.1854.
12
26
2
H 13.24, N 14.05.
1
1
3
3
(
1R,3S)-N ,N ,N -Trimethyl- N -(2-pyridinylmethyl)-1,2,2-trimeth-
1
1
3
3
(
1R,3S)-N ,N ,N ,N -Tetramethyl-1,2,2-trimethylcyclopentane-1,3-
ylcyclopentane-1,3-diamine (3b) The amine (obtained by
:
diamine (d ) (3ad ): The reaction was carried out by upscaling the
Scheme 2e or 3e) (1.920 g, 11.27 mmol) was dissolved in 50 ml
12
12
reaction conditions of the synthesis of 3a. (Diamine 6 (2.012 g,
4.14 mmol), formaldehyde d2 (20 wt%, 20 ml), formic acid d2
5 ml), reaction time 48 h) The product was obtained as a colorless
MeOH. 2-Formylpyridine (1.8 ml, 19 mmol) and Na SO (4 g) were
2
4
1
added and the mixture was refluxed under nitrogen for three days.
(
After cooling to room temperature and filtration, NaBH (701 mg,
4
1
liquid (2.419 g, 11.50 mmol, 81%). H NMR (400 MHz, CDCl ) δ 2.42
18.5 mmol) was added to the solution. After 17 h the solvent was
removed, the residue was made basic with NaOH solution and
extracted with DCM (3x150 ml). The organic phases were combined,
and the solvent was removed. The residue was dissolved in 20 ml
MeOH and 7 ml formaldehyde solution (37wt.%), 100 μL AcOH and
NaCNBH3 (1.212 mg, 19.29 mmol) were added. After 20 h the
solvent was removed and extracted with DCM (3x150 ml). The
organic phases were combined, and the solvent was removed. The
residue was purified by column chromatography (diethyl ether, 2%
3
(
1
t, J=9.3 Hz, 1H), 1.90–1.77 (m, 1H), 1.77–1.60 (m, 2H), 1.60–1.49 (m,
H), 1.10 (s, 3H), 0.99 (s, 3H), 0.90 (s, 3H). C{ H} NMR (101 MHz,
13
1
CDCl ) δ 74.72, 67.23, 48.04, 44.87, 39.54, 37.07, 24.68, 21.55, 17.95,
3
+
1
2
1.76. HRMS (ESI): calcd. for C H D N [M+H ] 211.2922, found
12 14 12 2
11.2923.
N-((1S,3R)-3-Amino-2,2,3-trimethylcyclopentyl)benzamide (Sche-
[
30]
me 2c or 7): Based on a modified synthesis , diamine 6 (1.421 g,
1
0.00 mmol) was placed in 20 ml dry EtOH and cooled to 0°C.
NEt ; silica gel). The product was obtained as a colorless oil (2.224 g;
3
Benzoyl chloride (1.05 ml, 9.11 mmol) in 20 ml dry EtOH was added
dropwise to the solution over 20 min. After slowly warming to rt,
the solution was stirred for 21 h. After removing of the solvent, the
1
8
7
1
1
.074 mmol; 72%). H NMR (400 MHz, CDCl ) δ 8.51 (m, 1H), 7.71–
3
.58 (m, 2H), 7.13 (m, 1H), 3.94 (d, J=15.0 Hz, 1H), 3.67 (d, J=
5.0 Hz, 1H), 2.89 (t, J=9.3 Hz, 1H), 2.31 (s, 3H), 2.20 (s, 6H), 1.88–
.64 (m, 4H), 1.61–1.52 (m, 1H), 1.07 (s, 3H), 0.96 (s, 3H), 0.88 (s, 3H).
solution was made basic with sat. NaHCO solution, extracted with
3
DCM (3x30 ml) and dried with Na SO . The product was obtained as
13
1
2
4
C{ H} NMR (101 MHz, CDCl ) δ 161.5, 149.0, 136.5, 122.5, 121.8,
3
a colorless solid after purification by column chromatography
7
2.7, 66.1, 63.4, 49.0, 42.3, 40.3, 37.2, 24.1, 19.1, 18.2, 11.4. HRMS
1
(
DCM, MeOH 9:1, 1% NEt ; silica) (1.556 g; 6.316 mmol; 69%). H
+
3
(ESI): calcd. for C H N [M+H ] 276.2434, found 276.2434.
17 29 3
NMR (400 MHz, CDCl ) δ 8.74 (d, J=9.2 Hz), 7.83–7.75 (m, 2H), 7.49–
3
C H N : calcd. C 74.13, H 10.61, N 15.26; found C 73.74, H 10.65, N
1
7
29
3
7
.36 (m, 3H), 4.34 (ddd, J=9.6, 7.8, 1.7 Hz, 1H), 2.38–2.21 (m, 1H),
15.04.
1
.94–1.79 (m, 1H), 1.74–1.54 (m, 2H), 1.22 (bs, 2H), 1.16 (s, 3H), 0.96
s, 3H), 0.96 (s, 3H). C{ H} NMR (100 MHz, CDCl ) δ 165.7, 135.5,
13
1
1
3
1
3
(
(1R,3S)-N ,N
-Dimethyl-
N ,N -bis(2-pyridinylmethyl)-1,2,2-
(1.01 g,
3
31.0, 128.5, 127.0, 62.4, 59.8, 47.7, 38.4, 30.0, 26.8, 25.1, 16.9. HRMS
trimethylcyclopentane-1,3-diamine (3c): Diamine
7.10 mmol) was dissolved in 50 ml MeOH. 2-formylpyridine (2.1 ml,
2 mmol) and 4 g Na SO were added and the mixture was refluxed
6
+
15 22 2
2
2
4
N-((1S,3R)-3-Dimethylamino-2,2,3-trimethylcyclopentyl)-benza-
under nitrogen for four days. After cooling to room temperature,
[30]
mide (Scheme 2d or 8): Following the literature procedure , the
the mixture was filtered and NaBH (970 mg, 25.6 mmol) was added
4
benzoyl protected amine (obtained by Scheme 2c or 7) (1.601 g,
to the solution. After 24 h the solvent was removed, made basic
with NaOH solution and extracted with DCM (3x150 ml). The
organic phases were combined and the solvent was removed. The
oily, brown residue was taken up in 20 ml AcOH. 1.6 ml
Formaldehyde solution (37wt.%) and NaCNBH3 (2.664 g,
.500 mmol) was added to 1.5 ml formic acid over a period of
4
2.39 mmol) were added at 0°C. After warming to room temper-
2
4
ature, the solution was made basic with NaOH solution and
extracted with DCM (3x150 ml). The combined organic phases were
dried with Na SO . After filtration and removing of the solvent, the
residue was purified by column chromatography (DCM, MeOH 9:1,
1
% NEt ; silica). The product was obtained as a colorless solid
3
1
2
4
(1.480 g; 5.393 mmol; 83%). H NMR (400 MHz, CDCl ) δ 7.80–7.72
3
residue was purified by column chromatography (diethyl ether, 2%
(
1
1
m, 2H), 7.53–7.38 (m, 3H), 6.48 (d, J=9.7 Hz, 1H), 4.46 (q, J=9.5 Hz,
NEt ; silica). The product was obtained as a colorless oil (648 mg;
3
H), 2.26 (s, 6H), 2.22–2.08 (m, 1H), 2.05–1.88 (m, 1H), 1.72–1.58 (m,
1
1
7
3
1
.84 mmol; 26%). H NMR (400 MHz, CDCl ) δ 8.66–8.36 (m, 2H),
1
3
1
3
H), 1.50–1.35 (m, 1H), 1.06 (s, 3H), 1.04 (s, 3H), 1.03 (s, 3H). C{ H}
.71–7.57 (m, 4H), 7.17–7.06 (m, 2H), 3.97 (d, J=15.0 Hz, 1H), 3.79–
.64 (m, 3H), 2.93 (t, J=9.4 Hz, 1H), 2.34 (s, 3H), 2.15 (s, 3H), 2.00–
NMR (100 MHz, CDCl ) δ 167.1, 135.2, 131.5, 128.7, 126.9, 67.4, 58.0,
3
4
8.1, 40.5, 36.7, 27.4, 23.5, 18.0, 11.7. HRMS (ESI): calcd. for
13
1
.55 (m, 5H), 1.13 (s, 3H), 1.05 (s, 6H). C{ H} NMR (101 MHz, CDCl )
+
3
C H N O [M+H ] 275.2118, found 275.2120. Crystals, which were
1
7
26
2
δ 162.3, 161.4, 149.0, 148.9, 136.6, 136.5, 122.4, 122.0, 121.8, 121.6,
structurally characterized, were obtained by dissolving 8 in DCM
and slow evaporating of the solvent. The crystallographic data are
presented in the Supporting Information.
7
2.6, 66.6, 63.3, 58.8, 49.5, 42.4, 37.2, 24.3, 18.9, 18.5, 14.1. HRMS
+
(ESI): calcd. for C H N [M+H ] 353.2700, found 353.2700.
22 32 4
C H N : calcd. C 74.96, H 9.15, N 15.89; found C 73.63, H 9.01, N
2
2
32
4
1
1
15.50.
(
(
1R,3S)-N ,N -Dimethyl-1,2,2-trimethylcyclopentane-1,3-diamine
[31]
Scheme 2e or Scheme 3e): Following the literature procedure
,
N-((1S,3R)-3-Ethylamino-2,2,3-trimethylcyclopentyl)-benzamide
concentrated HCl (10 ml) was added to the methylated amine
[30]
(
Scheme 3b): Following the literature procedure , amine 7 (1.01 g,
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4
.10 mmol) was dissolved in 20 ml EtOH and Iodoethane (1.3 ml,
6 mmol) and K CO (2.20 g, 16.0 mmol) were added. The mixture
with NaOH solution and extracted with DCM (3x100 ml) and ethyl
acetate (3x100 ml). The combined organic phases were dried with
sodium sulfate. After filtration and removing the solvent, the
1
2
3
was refluxed overnight. After evaporation of the solvent the residue
was dissolved in 50 ml H O and was made basic with sat. NaHCO
product was obtained as a colorless liquid (2.006 mg, 10.88 mmol,
2
3
1
solution. The aqueous phase was extracted three times with 50 ml
DCM and the combined organic phases were dried with Na SO .
91%). H NMR (400 MHz, CDCl ) δ 2.92–2.84 (m, 1H), 2.59–2.44 (m,
3
1H), 2.30–2.17 (m, 1H), 2.15 (s, 3H), 2.00–1.87 (m, 1H), 1.86–1.74 (m,
2
4
After filtering and evaporation, the residue was purified with
1H), 1.69–1.44 (m, 3H), 1.32–1.19 (m, 1H), 1.06–0.93 (m, 6H), 0.89 (s,
1
3
1
column chromatography (diethyl ether, 2% NEt ; silica). The
3H), 0.82 (s, 3H). C{ H} NMR (101 MHz, CDCl ) δ 68.2, 61.1, 47.1,
3
3
product was obtained as colorless solid (912 mg, 3.32 mmol,
45.9, 36.7, 35.7, 29.2, 23.2, 16.3, 14.4, 13.1. HRMS (ESI): calcd. for
1
+
8
1%). H NMR (400 MHz, CDCl ) δ 8.86 (d, J=9.6 Hz, 1H), 7.86–7.72
C H N [M+H ] 185.2012, found 185.2014.
3
11 24
2
(
2
7
(
3
+
m, 2H), 7.49–7.35 (m, 3H), 4.34–4.25 (m, 1H), 2.75–2.48 (m, 2H),
1
1
(
1R,3S)-N ,N -Diethyl-1,2,2-trimethylcyclopentane-1,3-diamine
(Scheme 3i): Concentrated HCl (55 ml) was added to amine 10
2.600 g, 8.600 mmol). Then water (40 ml) was added. The mixture
.38–2.22 (m, 1H), 2.08–1.94 (m, 1H), 1.63–1.49 (m, 2H), 1.15 (t, J=
13 1
.1 Hz, 3H), 1.08 (s, 3H), 0.98 (s, 3H), 0.95 (s, 3H). C{ H} NMR
(
101 MHz, CDCl ) δ 165.5, 135.6, 131.0, 128.5, 127.0, 66.1, 59.5, 48.7,
3
was refluxed for 48 hours. The suspension was then made basic
with NaOH solution and extracted three times with DCM (3x100 ml)
and ethyl acetate (3x100 ml). The combined organic phases were
dried with sodium sulfate. After filtration and removing the solvent,
the product was obtained as a colorless liquid (1.523 g, 7.678 mmol,
9%). H NMR (400 MHz, CDCl ) δ 2.90–2.80 (m, 1H), 2.60–2.42 (m,
6.5, 32.0, 30.2, 25.5, 19.2, 16.8. HRMS (ESI): calcd. for C H N O [M
1
7
26
2
+
H ] 275.2118, found 275.2120. Crystals, which were structurally
characterized, were obtained by dissolving the amine in DCM and
slow evaporating of the solvent. The crystallographic data are
presented in the Supporting Information.
1
8
3
N-((1S,3R)-3-Ethyl,methylamino-2,2,3-trimethylcyclopentyl)-ben-
zamide (9): The monoethylated amine (obtained by Scheme 3b)
4H), 2.01–1.82 (m, 2H), 1.73–1.40 (m, 3H), 1.32–1.21 (m, 1H), 1.04–
0.99 (m, 6H), 0.97 (s, 3H), 0.95 (s, 3H), 0.83 (s, 3H). C{ H} NMR
13 1
(
3.41 g, 12.4 mmol) was dissolved in 70 ml MeCN and 1.2 ml
formaldehyde solution (37 wt.%) was added. After stirring for
0 min., NaCNBH (0.86 g, 13.6 mmol) and 13.6 ml AcOH was added
(101 MHz, CDCl ) δ 60.9, 47.5, 45.0, 35.7, 29.3, 23.2, 16.9, 16.8, 16.6.
3
+
HRMS (ESI): calcd. for C H N [M+H ] 199.2169, found 199.2172.
1
2
26
2
3
Crystals of the HCl salt, which were structurally characterized, were
obtained by slow evaporating of the NMR sample. The crystallo-
graphic data are presented in the Supporting Information.
3
at 0°C. The solution was stirred overnight at rt. H O (150 ml) was
2
added and the solution was made basic with NaOH. The aqueous
phase was extracted with DCM (3x100 ml) and the combined
organic phases were dried with Na SO . After filtration and
1
1
3
(
1R,3S)-N ,N -Dimethyl-N -(phenylidene)-1,2,2-trimethyl-cyclopen-
2
4
tane-1,3-diamine (4a): The deprotected amine (obtained by
Scheme 2e or Scheme 3e) (731 mg, 4.29 mmol) was dissolved in
evaporation of the solvent the product was obtained as colorless
1
solid (3.44 g, 11.9 mmol, 96%). H NMR (400 MHz, CDCl ) δ 7.81–
3
2
5 ml dry MeOH and Benzaldehyde (470 μl, 4.6 mmol) and Na SO4
2
7
1
1
.73 (m, 2H), 7.52–7.39 (m, 3H), 6.89 (d, J=9.7 Hz, 1H), 4.46–4.35 (m,
(2 g) were added. The mixture was refluxed overnight. After cooling
H), 2.74–2.44 (m, 1H), 2.34–2.12 (m, 5H), 2.09–1.93 (m, 1H), 1.72–
13
1
to rt, filtration and evaporation of the solvent, the residue was
purified by column chromatography (diethyl ether, 2.5% NEt3;
.57 (m, 1H), 1.49–1.35 (m, 1H), 1.11–0.94 (m, 12H). C{ H} NMR
(101 MHz, CDCl ) δ 166.9, 135.3, 131.4, 128.7, 127.0, 68.5, 58.3, 48.4,
3
silica). The product was obtained as colorless solid (619 mg,
4
6.4, 36.3, 35.9, 28.0, 24.27, 18.5, 14.4, 13.3. HRMS (ESI): calcd. for
1
+
2.40 mmol, 56%). H NMR (400 MHz, CDCl
) δ 8.19 (s, 1H), 7.79–7.71
3
C H N O [M+H ] 289.2274, found 289.2272. Crystals, which were
1
8
28
2
(
m, 2H), 7.43–7.36 (m, 3H), 3.39 (t, J=9.0 Hz, 1H), 2.28 (s, 6H), 2.18–
structurally characterized, were obtained by dissolving 9 in DCM
and slow evaporating of the solvent. The crystallographic data are
presented in the Supporting Information.
2
.05 (m, 1H), 1.98–1.75 (m, 2H), 1.72–1.62 (m, 1H), 1.12 (s, 3H), 1.01
13 1
(
s, 3H), 0.94 (s, 3H). C{ H} NMR (101 MHz, CDCl ) δ 159.4, 136.8,
3
1
30.5, 128.7, 128.3, 79.3, 67.9, 49.0, 40.5, 38.3, 26.9, 22.9, 18.2, 11.6.
+
N-((1S,3R)-3-Diethylamino-2,2,3-trimethylcyclopentyl)-benzamide
HRMS (ESI): calcd. for C H N [M+H ] 259.2169, found 259.2171.
17 26 2
(
10): Amine 7 (3.26 g, 13.2 mmol) was dissolved in 20 ml dry MeCN
Crystals of the HCl salt, which were structurally characterized, were
obtained by slow evaporating of the NMR sample. The crystallo-
graphic data are presented in the Supporting Information.
and Iodoethane (10.7 ml, 132 mmol) and K CO (18.3 g, 132 mmol)
were added. The mixture was refluxed over four days under N2.
2
3
After cooling to rt, the solvent was evaporated, and 100 ml H O was
2
1
1
3
(
1R,3S)-N -Ethyl-N -methyl-N -(phenylidene)-1,2,2-trimethyl-cyclo-
added. The mixture was made basic with sat. NaHCO solution and
3
pentane-1,3-diamine (4b): The deprotected amine (obtained by
Scheme 3g) (2.01 g, 10.9 mmol) was dissolved in 50 ml dry MeOH
and Benzaldehyde (1.4 ml, 13.1 mmol) and Na SO (5 g) were
added. The mixture was refluxed overnight. After cooling to rt,
filtration and evaporation of the solvent, the residue was purified
by column chromatography (diethyl ether, 2.5% NEt ; silica). The
product was obtained as yellow oil (2.40 g, 8.81 mmol, 81%). H
NMR (400 MHz, CDCl ) δ 8.19 (s, 1H), 7.78–7.72 (m, 2H), 7.42–7.37
(m, 3H), 3.36 (t, J=8.9 Hz, 1H), 2.63–2.47 (m, 5H), 2.34–2.01 (m, 3H),
.95–1.60 (m, 1H), 1.15–0.86 (m, 13H). C{ H} NMR (101 MHz, CDCl )
δ 159.4, 136.8, 130.4, 128.7, 128.3, 79.2, 68.5, 49.1, 46.1, 38.3, 36.0,
6.9, 23.3, 18.3, 14.4, 13.3. HRMS (ESI): calcd. for C H N [M+H ]
73.2325, found 273.2326. C H N : calcd. C 79.36, H 10.36, N 10.28;
extracted with DCM (3x100 ml). After filtration and evaporation of
the solvent the product was obtained as colorless solid after
2
4
column chromatography (diethyl ether, 2% NEt ; silica). (2.60 g,
3
1
8
.60 mmol, 65%). H NMR (400 MHz, CDCl ) δ 7.74–7.67 (m, 2H),
3
7.45–7.26 (m, 4H), 4.31–4.20 (m, 1H), 2.65–2.47 (m, 4H), 2.24–1.99
3
(
(
m, 2H), 1.65–1.51 (m, 1H), 1.46–1.33 (m, 1H), 1.02 (s, 3H), 1.00–0.92
1
13 1
m, 12H). C{ H} NMR (101 MHz, CDCl ) δ 166.7, 135.4, 131.2, 128.5,
3
3
1
1
3
27.0, 69.3, 58.8, 49.1, 46.3, 43.9, 35.4, 28.8, 24.7, 19.1, 17.4, 15.3,
+
1.4. HRMS (ESI): calcd. for C H N O [M+H ] 303.2431, found
19
30
2
13
1
1
3
03.2428. Crystals, which were structurally characterized, were
obtained by dissolving 10 in DCM and slow evaporating of the
solvent. The crystallographic data are presented in the Supporting
Information.
+
2
2
18 28 2
1
8
28
2
found C 79.39, H 10.10, N 10.25. Crystals of the HCl salt, which were
structurally characterized, were obtained by adding HCl in Et O
2
(
2 m) to 4b dissolved in CDCl , evaporating of the solvent, followed
3
Deprotection of (9) and (10)
by dissolving of the residue in methanol/acetonitrile 1:1 and slow
evaporating of the solvent mixture. The crystallographic data are
presented in the Supporting Information.
1
1
(
1R,3S)-N -Ethyl-N -methyl-1,2,2-trimethylcyclopentane-1,3-dia-
mine (Scheme 3g): Concentrated HCl (75 ml) was added to amine 9
3.442 g, 11.93 mmol). Then water (55 ml) was added. The mixture
was refluxed for 48 hours. The suspension was then made basic
(
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�
© 2021 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH
�
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1
1
3
(
1R,3S)-N ,N -Diethyl-N -(phenylidene)-1,2,2-trimethyl-cyclopen-
added a solution of 4c (23.2 mg, 0.08 mmol) in approx. 1 ml DCM.
tane-1,3-diamine (4c): The deprotected amine (obtained by
Scheme 3i) (1.52 g, 7.66 mmol) was dissolved in 50 ml dry MeOH
PPh (21.3 mg, 0.08 mmol) was added. Ether diffusion at À 40°C led
3
to the formation of some yellow colored crystals, which were
structurally characterized. Interestingly PPh does not act as ligand.
and Benzaldehyde (0.93 ml, 9.2 mmol) and Na SO4 (5 g) were
2
3
added. The mixture was refluxed for 48 h. After cooling to rt,
filtration and evaporation of the solvent, the residue was purified
[
Cu (3ad ) O ][PF ] : Under inert gas in a glove box: to a solution
2 12 2 2 6 2
of [Cu(CH CN) ]PF (40.7 mg, 0.11 mmol) in approx. 1 ml DCM was
3
4
6
by column chromatography (diethyl ether, 2.5% NEt ; silica). The
3
1
added a solution of 3ad12 (23.0 mg, 0.11 mmol) in approx. 1 ml
DCM. The glass vessel was placed inside a bigger glass vessel filled
with pentane and was closed with a septum. After cooling to
À 80°C dry oxygen was bubbled through the reaction solution for
one minute and then placed in the refrigerator at À 80°C. Pentane
product was obtained as yellow oil (1.26 g, 4.40 mmol, 57%). H
NMR (400 MHz, CDCl ) δ 8.19 (s, 1H), 7.78–7.72 (m, 2H), 7.42–7.37
3
(
m, 3H), 3.31 (t, J=8.9 Hz, 1H), 2.62–2.49 (m, 4H), 2.21–2.10 (m, 1H),
1
3
1
.94–1.73 (m, 2H), 1.65–1.55 (m, 1H), 1.10–1.01 (m, 12H), 0.92 (s,
13
1
H). C{ H} NMR (101 MHz, CDCl ) δ 159.3, 136.9, 130.4, 128.6,
3
diffusion led to the formation of brown colored crystals after about
a week, which were structurally characterized.
28.3, 79.1, 69.4, 49.4, 45.4, 37.1, 27.0, 23.2, 18.6, 17.2, 16.8. HRMS
+
(
ESI): calcd. for C H N [M+H ] 287.2482, found 287.2483.
19
30
2
C H N : calcd. C 79.66, H 10.56, N 9.78; found C 79.80, H 10.53, N
1
9
30
2
Demethylation of amine 3a: Under inert gas in a glove box: to a
9.60.
solution of [Cu(CH CN) ]OTf (310.0 mg, 0.82 mmol) in approx. 10 ml
3
4
1
1
3
DCM was added a solution of 3a (163.2 mg, 0.82 mmol) in approx.
(
1R,3S)-N ,N -Dimethyl-N -(salicylidene)-1,2,2-trimethyl-cyclopen-
1
0 ml DCM. After cooling to À 80°C dry oxygen was bubbled
tane-1,3-diamine (15): The deprotected amine (obtained by
Scheme 2e or Scheme 3e) (345 mg, 2.03 mmol) was dissolved in
0 ml dry MeOH and Salicylaldehyde (211 μl, 2.03 mmol) and
Na SO (2 g) were added. The mixture was refluxed for 4 days. After
cooling to rt, filtration and evaporation of the solvent, the residue
was purified by column chromatography (diethyl ether; silica). The
product was obtained as yellow solid (322 mg, 1.17 mmol, 58%). H
NMR (400 MHz, CDCl ) δ 13.79 (s, 1H), 8.26 (s, 1H), 7.30 (ddd, J=8.6,
.3, 1.7 Hz, 1H), 7.27–7.23 (m, 1H), 6.96 (d, J=8.3 Hz, 1H), 6.87 (td,
J=7.5, 1.1 Hz, 1H), 3.41 (t, J=9.0 Hz, 1H), 2.28 (s, 6H), 2.18–2.02 (m,
H), 2.00–1.79 (m, 2H), 1.74–1.63 (m, 1H), 1.09 (s, 3H), 1.02 (s, 3H),
.97 (s, 3H). C{ H} NMR (101 MHz, CDCl ) δ 163.7, 161.6, 132.3,
31.3, 118.9, 118.6, 117.2, 78.3, 68.0, 48.5, 40.4, 37.9, 27.3, 22.8, 18.1,
1.8. HRMS (ESI): calcd. for C H N O [M+H ] 275.2118, found
75.2121.
through the reaction solution for 10 minutes. After warming to rt,
conc. aqueous NH (50 ml) was added and extracted with DCM
3
2
(3x50 ml). The combined organic phases were dried with sodium
2
4
sulfate and analyzed by HRMS (ESI) and GC-MS. It turned out that
the system was demethylated (HRMS (ESI): calcd. for C H N [M+
1
1
24
2
+
1
H ] 185.2012, found 185.2013, GC-MS data are available in the
Supporting Information). The two demethylated species 11 and 12
3
could be separated as a mixture from ligand 3a by means of
7
1
column chromatography (DCM, MeOH 9:1, 1% NEt ; silica). ( H-
3
1
3
1
NMR and C{ H}-NMR spectra of the mixture of 11 and 12 with
1
0
1
1
2
13
1
minor impurities are available in the Supporting Information). HCl
3
in Et O (2 m) was added to the mixture. After evaporation of the
2
+
solvent the colorless solid was dissolved in MeOH. Slow evaporation
led to the formation of some colorless crystals, which were
structurally characterized. It turned out as the demethylated
component 11 as HCl salt.
17
26
2
Triflate salt of 3a: Under inert gas in a glove box: to a solution of
Cu(CH CN) ]OTf (75,8 mg, 0.20 mmol) in approx. 1 ml aceton was
added a solution of 3a (39.9 mg, 0.20 mmol) in approx. 1 ml aceton.
Ether diffusion led to the formation of some colorless crystals,
which were structurally characterized.
[
3
4
Hydroxylation of 4a (general procedure): Under inert gas in a
glove box: to a solution of the copper salts (0.03 mmol) in approx.
3
ml solvent was added a solution of 4a (7.8 mg, 0.03 mmol) in
approx. 3 ml solvent. Dry oxygen was passed through the reaction
[
Cu(3a)(PPh )]OTf: Under inert gas in a glove box: to a solution of
solutions for 30 min at various temperatures. After warming to rt,
3
[Cu(CH CN) ]OTf (67.7 mg, 0.18 mmol) in approx. 1 ml DCM was
the reaction was stirred overnight. Then conc. aqueous NH (20 ml)
3
4
3
added a solution of 3a (35.7 mg, 0.18 mmol) in approx. 1 ml DCM.
was added and extracted with DCM (20 ml). The organic phase was
dried with sodium sulfate. After filtration and evaporating of the
solvent the reaction mixture was analyzed by HRMS (ESI) and H-
PPh (47.2 mg, 0.18 mmol) was added. Ether diffusion led to the
3
1
formation of some yellow colored crystals, which were structurally
characterized.
NMR. The conversion was determined by using the integral ratio of
the imine protons (one example is presented in the Supporting
[
Cu(3b) ]ClO : Under inert gas in a glove box: to a solution of
+
2
4
Information). HRMS (ESI) of 15: calcd. for C H N O [M+H ]
1
7
26
2
[Cu(CH CN) ]ClO (34.7 mg, 0.11 mmol) in approx. 1 ml DCM was
3 4 4
275.2118, found 275.2116.
added a solution of 3b (29.2 mg, 0.11 mmol) in approx. 1 ml DCM.
Ether diffusion led to the formation of some colorless crystals,
which were structurally characterized.
Deposition Numbers 2063860 (for triflate salt of 3a), 2063861 (for
[Cu(3a)(PPh )]OTf), 2063862 (for [Cu(3b) ]ClO ), 2063863 (for [Cu-
3
2
4
(
3c)][CuCl ]), 2063864 (for [Cu(3c)(H O)](OTf) ), 2074266 for
2
2
2
[
Cu(3c)][CuCl ]: Under inert gas in a glove box: to a solution of CuCl
2
1
1×2HCl), 2063865 (for [Cu(4c)(CH CN)]OTf), 2063866 (for
3
(
(
7.3 mg, 0.07 mmol) in approx. 1 ml THF was added a solution of 3c
21.9 mg, 0.06 mmol) in approx. 1 ml THF. Pentane diffusion at
[Cu (3ad ) O ][PF ] ), 2063867 (for 6×2HCl), 2063868 (for 8),
2 12 2 2 6 2
2
063869 (for N-((1S,3R)-3-ethylamino-2,2,3-trimethylcyclopentyl)-
À 40°C led to the formation of some yellow colored crystals, which
benzamide), 2063870 (for 9), 2063871 (for 10), 2063872 (for (1R,3S)-
were structurally characterized.
1
1
N ,N -diethyl-1,2,2-trimethylcyclopentane-1,3-diamine×HCl),
063873 (for 4a×HCl), and 2063874 (for 4b×HCl) contain the
2
[
Cu(3c)(H O)]OTf : Under inert gas in a glove box: to a solution of
2 2
supplementary crystallographic data for this paper. These data are
provided free of charge by the joint Cambridge Crystallographic
Data Centre and Fachinformationszentrum Karlsruhe Access Struc-
tures service www.ccdc.cam.ac.uk/structures.
3
c (11.7 mg, 0.03 mmol) in approx. 3 ml DCM was added a solution
of [Cu(CH CN) ]OTf (25.1 mg, 0.07 mmol) in approx. 3 ml DCM,
3
4
which led to a disproportionation reaction. After filtration of the
copper, the blue colored solution was evaporated, and the residue
was dissolved in MeOH. Slow evaporation led to the formation of
some blue colored crystals, which were structurally characterized.
[
Cu(4c)(CH CN)]OTf: Under inert gas in a glove box: to a solution of
3
[Cu(CH CN) ]OTf (30.4 mg, 0.08 mmol) in approx. 1 ml DCM was
3 4
Eur. J. Inorg. Chem. 2021, 1–11
www.eurjic.org
9
�
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�
These are not the final page numbers!

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Accepted manuscript online: April 6, 2021
Eur. J. Inorg. Chem. 2021, 1–11
www.eurjic.org
10
�
© 2021 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH
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These are not the final page numbers!

FULL PAPERS
A bis(μ-oxido) copper complex based
on a derivative of (1S,3R)-camphoric
acid could be structurally character-
ized after deuteration of the ligand.
Modification of the ligand system
allowed to achieve selective hydroxy-
lation of benzaldehyde when
F. Stöhr, N. Kulhanek, Dr. J. Becker,
Prof. Dr. R. Göttlich*, Prof. Dr. S.
Schindler*
1
– 11
Reactivity of Copper(I) Complexes
Containing Ligands Derived from
(1S,3R)-Camphoric Acid with
Dioxygen
reacting the corresponding copper(I)
complex with dioxygen.