Reactions of Cu(I)Br with aziridine derivatives. Synthesis, characterization and crystal structures of monomeric, dimeric and hexameric aziridine (= az) complexes of the formal type [CuBr(az)2]n (n = 1, 2) and [CuBr(az)]6

Article abstract of DOI:10.1039/c0dt00320d

The first syntheses of monomeric and oligomeric aziridine complexes of copper(I) are described. Cu(I)Br (1) reacts with a series of different aziridine derivatives (C₂H₃PhNH (2), C₂H ₂Me₂NH (3), C₂H₂Me ₂NC₂H₂Me₂NH₂ (4)) to give the neutral dimeric complex [CuBr(C₂H₃PhNH) ₂]₂ (5) and the ionic hexameric complex [Cu ₆Br₅(C₂H₂Me₂NH) ₆]Br (6) with terminal bound aziridine ligands as well as the neutral monomeric complex [CuBr(C₂H₂Me₂NC ₂H₂Me₂NH₂)] (7) where the dimerized aziridine acts as a N,N′-chelating ligand. After purification, all of the complexes were fully characterized and their IR, ¹H and ¹³C NMR spectra are reported and discussed. The single crystal structure analysis revealed distorted tetrahedral geometry for the copper(i) centres in the complexes 5 and 6 and a trigonal planar structure for complex 7. In the oligomers the copper centres are bridged by two μ₂- (5) or two μ₃- and three μ₄-bromido ligands (6), respectively. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00320d

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Reactions of Cu(I)Br with aziridine derivatives. Synthesis, characterization
and crystal structures of monomeric, dimeric and hexameric aziridine (= az)
complexes of the formal type [CuBr(az)2]n (n = 1, 2) and [CuBr(az)]6†
Roman Bobka, J. Nicolas Roedel, Stefan Wirth and Ingo-Peter Lorenz*
Received 16th April 2010, Accepted 28th July 2010
DOI: 10.1039/c0dt00320d
The first syntheses of monomeric and oligomeric aziridine complexes of copper(I) are described.
Cu(I)Br (1) reacts with a series of different aziridine derivatives (C2H3PhNH (2), C2H2Me2NH (3),
C2H2Me2NC2H2Me2NH2 (4)) to give the neutral dimeric complex [CuBr(C2H3PhNH)2]2 (5) and the
ionic hexameric complex [Cu6Br5(C2H2Me2NH)6]Br (6) with terminal bound aziridine ligands as well as
the neutral monomeric complex [CuBr(C2H2Me2NC2H2Me2NH2)] (7) where the dimerized aziridine
acts as a N,N¢-chelating ligand. After purification, all of the complexes were fully characterized and
their IR, 1H and 13C NMR spectra are reported and discussed. The single crystal structure analysis
revealed distorted tetrahedral geometry for the copper(I) centres in the complexes 5 and 6 and a
trigonal planar structure for complex 7. In the oligomers the copper centres are bridged by two m2- (5)
or two m3- and three m4-bromido ligands (6), respectively.
synthesized the first transition metal aziridine complex [Co(az)6]2+
Introduction
{[Co(CO)4]-}2 by disproportionation reaction of [Co2(CO)8].14 In
Although aziridines are isolobal to oxiranes and thiiranes (C2H4X;
the sixties and seventies the research group of Edwards prepared
X = NH, O, S), the reactivity of aziridines differ considerably from
theirs. While oxiranes and thiiranes act as oxidising agents building
oxo or thio complexes via ethylene elimination,1 the aziridines
usually remain intact as three membered rings and coordinate
via the nitrogen atom. Under specific conditions metal mediated
ring opening reactions are possible. Thus b-aminoacyl complexes,2
azametallacyclobutane complexes3 and cyclic carbene complexes4
have been synthesized. Moreover, metal mediated dimerisation of
two aziridine molecules forming N-(2-aminoalkyl)aziridine N,N¢-
chelate ligands has been also observed.5 The tendency towards
ring-opening of aziridines is mainly a result of Baeyer and Pitzer
ring strain6 which easily lead to nucleophilic attack, especially after
activation by protonation or coordination of the nitrogen.
The versatility of the aziridine motif has resulted in widespread
interest in this small N-heterocycle.7 In organic chemistry aziridine
compounds have a lot of synthetic applications: as catalysts in
asymmetric synthesis,8 synthones in natural product synthesis,9
monomers in macromolecular chemistry10 or target molecules in
organic synthesis.11 Another important reason for the increased
interest in aziridine chemistry is its biological role, whereby in vivo
effects of aziridine derivatives are mostly the result of ring opening
and alkylation reactions. This results in the anti-carcinogenic
activity of natural and synthetic aziridine compounds.12 Biological
studies concerning this issue are currently being undertaken and
will be reported in future work.
some aziridine complexes starting from simple transition metal
salts15 and published the first X-ray structure analysis of an aziri-
dine rhodium complex in 1969.16 To this day a series of publications
on the coordination chemistry of aziridines,17 including reports on
main group metal aziridine complexes followed.18
It is known that copper(I) can build a lot of different forms
of coordination compounds depending on type and size of the
ligand.19 Monomeric complexes20 are noted as well as oligo- and
polymeric complexes with different molecular configurations like
stair polymers or cubane oligomers.21 The copper(I) centres exhibit
a linear, trigonal planar or tetrahedral environment depending
on the coordination numbers (2–4).20,21 In this communication,
the synthesis and characterization of the first aziridine copper(I)
complexes and the formation of different structures regulated by
the steric demand of the aziridine derivatives are reported.
Results and discussion
According to Scheme 1 the complexes 5–7 were obtained by
addition of the congruent aziridine derivatives 2–4 to a suspension
of CuBr (1) in dichloromethane. Depending on the substitution
grade in 2-position at the aziridine ring and the corresponding
approach of the ligand different types of structures were formed.
The reaction of the biggest and additionally chelating ligand 4
which is the formal dimer of 3 leads to the monomeric complex 7,
while the other ligands 2 and 3 yield the oligonuclear complexes 5
and 6. In the dimer 5 the Cu:az stoichiometry is 1 : 2, in contrast to
the hexameric complex 6 with 1 : 1 stoichiometry, because of the
more bulky, in 2-position doubly substituted aziridine 3.
The interest into coordination chemistry of aziridines dates back
to 1956, when Jones et al. reported on an unstable uranium-
aziridine complex.13 Two years later it was Hieber et al. who
All products were obtained as colourless powders in good yields
(85–99%) and are soluble in polar solvents such as acetone or
dichloromethane, but insoluble in non-polar solvents such as
n-pentane. Compounds 5–7 are somewhat air sensitive, but can
be stored some months under an atmosphere of argon.
Department Chemistry and Biochemistry, Ludwig-Maximilians-University
Munich, Butenandtstraße 5–13 (House D), D-81377, Munich, Germany.
E-mail: ipl@cup.uni-muenchen.de; Fax: +49-(0)89-2180-77867
† CCDC reference numbers 771766–771768. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00320d
10142 | Dalton Trans., 2010, 39, 10142–10147
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Fig. 2 Molecular structure of [Cu6(m3-Br)2(m4-Br)3(C2H2Me2NH)6]Br (6).
Hydrogen atoms are omitted for clarity and displacement ellipsoids are
shown at the 30% level.
Scheme 1 Synthesis of the copper(I) aziridine complexes 5–7.
The molecular structures of compounds 5–7 were determined
using single crystal X-ray diffraction. Isothermic diffusion of n-
pentane into solutions of 5, 6 or 7 in dichloromethane resulted
in the formation of X-Ray quality single crystals. Details of the
relevant data collection and refinement are summarised in Table
1. The molecular structures of 5–7 are illustrated in Fig. 1–3, some
selected bond lengths and angles are found in Table 2.
Fig. 3 Molecular structure of [CuBr(C2H2Me2NC2H2Me2NH2)] (7).
Hydrogen atoms are omitted for clarity and displacement ellipsoids are
shown at the 30% level.
are tetrahedrally coordinated by two aziridine and two bromido
ligands (5) and one aziridine and three bromido ligands (6).
Whereas in 5 the two Br-bridges are of m2-type, there are in 6 two of
m3- and three of m4-type. In contrast the monomer 7 shows a trig-
onal planar geometry at the copper centre with one terminal bro-
mido ligand and two different N-atoms of the dimerized aziridine
4 acting as a chelating 1,2-aminoaziridinoethane-N,N¢ ligand.
Complex 5 is a non-centrosymmetric dimer with two unsym-
metrical m2-bromido bridges. The Cu ◊ ◊ ◊ Cu distance is 282 pm
and to long for a Cu–Cu bond. The tetrahedral geometry at the
copper centres is strongly distorted. Especially the angles N–Cu–
N (144.0◦ and 145.2◦) and N–Cu–Br (89.6◦–98.1◦) differ strongly
from the ideal tetrahedron angle. The Cu–N bond lengths (197–
198 pm) in 5 are slightly shortened in comparison to the most
Cu–N bond lengths,22 but a few complexes are known with similar
Cu–N bond lengths.23 The two bond lengths Cu–Br(1) ª 256 pm
lie within the expected range,22 while both Cu–Br(2) ª 276 pm are
Fig. 1 Molecular structure of [Cu(m2-Br)(C2H3PhNH)2]2 (5). Hydrogen
atoms are omitted for clarity and displacement ellipsoids are shown at the
30% level.
All three complexes show different structures; a dimeric for 5,
hexameric for 6 and a monomeric for 7. In 5 and 6 the Cu(I) centres
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Table 1 Crystal data and details of the structure refinement for compounds 5–7
Compound
5
6
7
Formula
FW
T/K
C32H36Br2Cu2N4
763.56
200(2)
C24H54Br6Cu6N6
1287.43
200(2)
0.71073
Hexagonal
P63/m
10.3534(15)
10.3534(15)
21.751(4)
90
90
120
2019.2(6)
2
2.1175(5)
9.064
1248
0.10 ¥ 0.075 ¥ 0.04
3.61 to 27.47
-13 £ h £ 13,
-11 £ k £ 11,
-28 £ l £ 28
6163
C8H18BrCuN2
285.69
200(2)
0.71073
Monoclinic
C2/c
17.6475(9)
16.6004(8)
9.3899(5)
90
120.92(3)
90
2359.9(2)
8
1.6082(4)
5.194
1152
0.12 ¥ 0.10 ¥ 0.03
3.52 to 25.99
-21 £ h £ 21
-20 £ k £ 20
-11 £ l £ 11
7876
˚
Wavelength/A
Crystal system
Space group
0.71073
Triclinic
¯
P1
˚
a/A
9.6189(3)
˚
b/A
10.3653(3)
16.4816(5)
79.42(3)
73.374(3)
89.218(3)
1546.46(8)
2
1.6398(8)
3.987
768
0.25 ¥ 0.16 ¥ 0.08
3.13 to 26.05
-11 £ h £ 11,
-12 £ k £ 12,
-19 £ l £ 20
22371
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
rc/g cm-1
m/mm-1
F(000)
Crystal size/mm
q range/◦
Index range
Reflns collected
Independent reflns
Rint
Completeness to q
Refinement method
Data/restraints/parameters
S on F2
Final R indices [I > 2s(I)]
R indices (all data)
Largest difference peak/hole/e A
CCDC number
6017
0.0218
98.6%
1591
0.0255
99.4%
2303
0.0495
99.2%
Full-matrix least squares on F2
6017/0/361
1.052
Full-matrix least squares on F2
1591/0/68
Full-matrix least squares on F2
2303/0/112
1.038
1.079
R1 = 0.0421, wR2 = 0.0999
R1 = 0.0559, wR2 = 0.1074
1.021 and -0.617
771766
R1 = 0.0252, wR2 = 0.0558
R1 = 0.0327, wR2 = 0.0586
0.516 and -0.589
771767
R1 = 0.0351, wR2 = 0.0823
R1 = 0.0546, wR2 = 0.0900
0.589 and -0.542
771768
-3
˚
considerably longer. The two Cu centres and two bromido bridges
form a distorted tetragonal plane.
In addition, all bond angles (58.8–61.7◦) and bond lengths (146–
151 pm) within the aziridine rings of 5–7 are similar to those
observed in the free aziridine.25
The six copper centres of the centrosymmetric complex 6 form
a trigonal prism and are connected via three m4-bromido bridges
(above the three rectangular surfaces of the prism) and two m3-
bromido bridges (above the two triangular planes of the prism).
The Cu ◊ ◊ ◊ Cu distances are 288 and 313 pm, respectively and there-
fore to long for Cu–Cu interactions. Every copper centre shows
a tetrahedral coordination by one aziridine, one m3-bromido and
two m4-bromido ligands. The angles Br(1)–Cu–Br(13) (101.2◦) and
Br(2)–Cu–N (124.1◦) differ more from the ideal tetrahedral angle
at the copper centres than the others (106.2◦–108.7◦). The bond
lengths Cu–m3-Br (246 pm) are shortened in comparison to those
of Cu–m4-Br (258/261 pm). Anyway all bond lengths lie within
the range of bridging Cu–Br bond lengths.22 The Cu–N bonds of
200 pm in 6 are just a little bit longer than those in complex 5.
In the monomeric complex 7 the copper(I) centre is trigonally
planar coordinated by one bromido ligand and both N-atoms
of the dimerized aziridine ligand 4. Because of the chelate ring
the angle N(1)–Cu(1)–N(2) (83.7◦) is strongly reduced and in
contrary that of N(2)–Cu(1)–Br(1) (153.7◦) is similarly enlarged,
while the angle N(1)–Cu(1)–Br(1) (122.6◦) remains nearly ideal.
The bond Cu(1)–N(1) (220 pm) to the tertiary amine is very long
in comparison to that of Cu(1)–N(2) (198 pm) to the primary
amine. The Cu(1)–Br(1) bond length of 227 pm lies within the
normal range. All above mentioned bond angles and lengths of 7
are comparable to similar complexes.24
The spectroscopic data obtained for the complexes 5–7 are
consistent with the molecular structures determined by X-ray
diffraction. The IR spectra are comparable with those of related
aziridine complexes.26 Compounds 5–7 show the typical absorp-
tion bands for the aziridine N–H stretching vibrations in the range
of 3231 to 3204 cm-1. Likewise the n(CH) vibrations between
3084 and 2872 cm-1 and the fingerprint area (1498-757 cm-1) of
aziridines are observed. Additionally the absorption of the NH2
deformation vibration (1585 cm-1) in the IR spectrum of 7 is
noticed.
In the 1H-NMR spectra of 5–7 broadened signals are observed,
which could be assigned to the obtained structures. All signals,
except for the aromatic signals of 5, are shifted to lower fields with
0.40–2.82 ppm, in comparison to the signals of the free aziridines.27
Due to the broad signals of the ring protons the NH signal of 5
is superposed. For the same reason the signals of the methylene
group of 5 overlap to one signal at 2.58. Both NMR spectra of
the hexameric complex 6 are very simple, the protons generate
three broad signals, the C-atoms only two signals, that of az-Cq
was not detected. In the 1H NMR spectrum of 7 the signal of the
CH2 group within the aziridine ring is partially superposed by the
broad NH2 resonance, only one is observed at 2.17, and all of the
others are shifted to lower field compared to 4. Also in the 13C
NMR spectra of 5–7 all signals are shifted to lower fields about
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0.17–3.32 ppm in comparison to the corresponding signals of the
free aziridines,27 except for the aromatic Cq-signal (27.8 ppm) and
one CH2 signal of 5 (62.3 ppm), which are shifted 8.8 and 3.9 ppm
to higher field.
overnight. The n-hexane phase was subsequently removed by
decantation. After drying in vacuo, oligomeric 6 (375 mg, 85%)
was obtained as a colourless powder (decomposition > 85 ◦C).
Found: C, 23.2; H, 4.2; N, 6.7. Calc. For C24H54Br6Cu6N6: C,
22.4; H, 4.2, N, 6.5%). nmax(KBr)/cm-1 3455w, 3204 s, 2999w,
2960 s, 2926 m, 2872w, 2753w, 1581w, 1461 m, 1447 m, 1385 s,
1336 s, 1276w, 1252w, 1190w, 1118 s, 1059w, 1031w, 961 m, 919
m, 907 m, 769w, 525 m, 426w. dH(399.8 MHz; CD2Cl2) 1.40 (36
H, br s, az–CH3), 1.67 (12 H, br s, az–CH2), 2.49 (6 H, br s, NH).
dC(100.5 MHz; CD2Cl2) 25.9 (az–CH3), 36.9 (az–CH2).
Experimental
Materials and methods
All experiments were performed under a dry argon atmo-
sphere using Schlenk line techniques. 2-phenylaziridine (2),
2,2-dimethylaziridine (3) and N-(2-amino-2-methylpropyl)-2,2-
dimethyl-aziridine (4) were prepared according to the litera-
ture methods.28 Copper(I) bromide was purchased from Fluka.
Dichloromethane was distilled from calcium hydride, and n-
pentane and n-hexane were distilled from sodium. All solvents
Synthesis
of
[Bromido-{N-(2-amino-2-methylpropyl)-2,2-
dimethylaziridine}copper(I)] (7). 125 mg (0.871 mmol) of CuBr
were suspended in 20 mL dichloromethane. After adding one
equivalent of N-(2-amino-2-methylpropyl)-2,2-dimethylaziridine
(4) (132 mg, 0.959 mmol) the clear colourless solution was stirred
for 12 h at room temperature. The solvent was removed in vacuo
and the colourless residue was purified by stirring in dry n-hexane
(20 mL) overnight. The n-hexane phase was subsequently
removed by decantation. After drying in vacuo, the monomeric
complex 7 (233 mg, 94%) was obtained as a colourless powder
(decomposition 69 ◦C). Found: C, 33.5; H, 6.6; N, 9.9. Calc. For
C8H18BrCuN2: C, 33.6; H, 6.35, N, 9.8%). nmax(KBr)/cm-1 3455w,
3271 s, 3228 s, 2999w, 2970 s, 2951 s, 2926 m, 2872 m, 2753w,
1581 m, 1467 m, 1453 m, 1385 s, 1371 s, 1336 s, 1276 m, 1225 m,
1190w, 1153 s, 1118 m, 1059 m, 1015w, 995 m, 916 m, 807 s, 769w,
572w, 525 m, 426w. dH(399.8 MHz; CD2Cl2) 2.57 (d, 2J = 12.2 Hz,
˚
were stored under a dry argon atmosphere over 3 A molecular
sieves. The 1H and 13C NMR spectra were recorded using a
Jeol Eclipse 270 and a Jeol Eclipse 400 instrument operating at
270 MHz (1H), 400 MHz (1H) and 68 MHz (13C), 100 MHz (13C).
The 1H and 13C chemical shifts were determined relative to TMS as
external standard. IR spectra (KBr) were recorded using a Nicolet
520 FT-IR and Perkin Elmer Spectrum One FT-IR spectrometer.
Single crystal X-Ray diffraction data were collected using a Nonius
Kappa CCD diffractometer using graphite-monochromated Mo-
Ka radiation. Single crystal X-ray structure analyses were per-
formed by direct methods using the SHELXS software and refined
by full-matrix least-squares with SHELXL-97.29 Table 1 contains
the crystallographic data and details of the structural refinement
of 5–7. Elemental analysis were performed by the Microanalytical
Laboratory of the Department of Chemistry and Biochemistry,
LMU Munich using a Heraeus Elementar Vario El.
2
1H, CH2), 2.47 (s, br, 2H, NH2), 2.17 (s, 1H, CH2), 2.06 (d, J =
12.4 Hz, 1H, CH2), 1.45 (s, 3H, CH3), 1.25 (s, 6H, CH3), 1.18 (s,
3H, CH3). dC(100.5 MHz; CD2Cl2) 62.3 (CH2), 44.3 (CH2), 38.5
(Cq), 28.5 (CH3), 27.8 (Cq), 27.5 (CH3), 26.6 (CH3), 18.3 (CH3).
Conclusion
Synthesis of Bis[l2-bromido-bis(2-phenylaziridine)copper(I)]
(5). 193 mg (1.35 mmol) of CuBr were suspended in
20 mL dichloromethane. After adding two equivalents of
2-phenylaziridine (2) (314 mL, 2.69 mmol) the clear colourless
solution was stirred for 15 min at room temperature. The solvent
was removed in vacuo and the colourless residue was purified by
stirring in dry n-hexane (20 mL) overnight. The n-hexane phase
was subsequently removed by decantation. After drying in vacuo,
the dimer 5 (507 mg, 99%) was obtained as a colourless powder
(decomposition 82 ◦C). Found: C, 50.3; H, 4.75; N, 7.3. Calc.
For C32H32Br2Cu2N4: C, 47.3; H, 4.45, N, 7.1%). nmax(KBr)/cm-1
3302w, 3231 m, 3084w, 3057w, 3030w, 1604w, 1582w, 1498 m,
1451 m, 1451w, 1395w, 1298w, 1273w, 1262 w, 1238w, 1203w,
1139 m, 1123w, 1106w, 1074w, 1028w, 998w, 986w, 940w, 913w,
871 m, 804w, 757 s, 739 m, 698 s, 580w, 587w, 542w, 532w.
dH(399.8 MHz; CD2Cl2) 2.58 (8 H, br s, az–CH2), 3.38 (4 H, br s,
az–CH), 7.03–7.39 (20 H, m, Ph–CH). dC(100.5 MHz; CD2Cl2)
29.5 (az–CH2), 33.1 (az–CH), 126.7 (Ph–CH), 127.5 (Ph–CH),
128.3 (Ph–CH), 139.8 (Ph–Cq).
Studies on the coordination chemistry of the monodentate ligands
2,2-dimethylaziridine, 2-phenylaziridin and the bidentate ligand
N-(2-amino-2-methylpropyl)-2,2-dimethylaziridine with the d10
transition metal halide CuBr show the preference of common
nitrogen coordination. In dependence on the ligand substituents,
the steric demand of the aziridines and their available binding
sites, the formation of different stoichiometries and geometries is
observed. They strongly vary from trigonal planar (monomer 7),
edge-bridged tetrahedral (dimer 5) to trigonal prismatic (hexamer
6). Compound 5 forms two tetrahedra with a common edge, 6
forms a trigonal prism. In this context this rarely observed trigonal
prismatic geometry with six 2,2-dimethylaziridine ligands and six
Cu(I) cations connected via three m4-bromido bridges above the
rectangular surfaces of the prism and two m3-bromido bridges
above its triangular planes is of particular beauty and interest.
Furthermore the trigonal planar Cu(I) complex 7 with the biden-
tate ligand N-(2-amino-2-methylpropyl)-2,2-dimethylaziridine 4
is formed. The connectivity within the presented complexes
was deduced by single crystal X-ray crystallography and NMR
spectroscopy.
Synthesis of [Bis(l3-bromido)-tris(l4-bromido)-hexakis(2,2-
dimethylaziridine-copper(I))]-bromid (6). 296 mg (2.06 mmol)
of CuBr were suspended in 20 mL dichloromethane. After
adding five equivalents of 2,2-dimethylaziridine (3) (929 mL,
10.3 mmol) the clear colourless solution was stirred for 24 h at
room temperature. The solvent was removed in vacuo and the
colourless residue was purified by stirring in dry n-hexane (20 mL)
Acknowledgements
Financial support by the Ludwig-Maximilians University Munich
is gratefully acknowledged.
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