2H-azirines as ligands: structural characterization of the first neutral and cationic (η5-C5Me5)Rh(III) 2H-azirine complexes

Article abstract of DOI:10.1002/zaac.200800098

The synthesis and structural characterization of two azirine rhodium(III) complexes are described. The stabilization, N-coordination and phenylgroup π-stacking of the highly reactive and strained 3-phenyl-2H-azirine by transition metal coordination is observed. The reaction of the dimeric complex [(η⁵-C₅Me₅)RhCl₂]₂ with 3-phenyl-2H-azirine (az) in CH₂Cl₂ at room temperature in a 1:2 molar ratio afforded the neutral mono-azirine complex [(η⁵-C₅Me₅)RhCl₂(az)]. The subsequent reaction of [(η⁵-C₅Me₅)RhCl ₂]₂ with six equivalents of az and 4 equivalents of AgOTf yielded the cationic tris-azirine complex [(η⁵-C ₅Me₅)Rh(az)₃](OTf)₂. After purification, all complexes have been fully characterized. The molecular structures of the novel rhodium(III) complexes exhibit slightly distorted octahedral coordination geometries around the metal atoms.

Full text of DOI:10.1002/zaac.200800098

DOI: 10.1002/zaac.200800098
2H-Azirines as Ligands: Structural Characterization of the First Neutral and
Cationic (η5-C5Me5)Rh(iii) 2H-Azirine Complexes
J. Nicolas Roedel and Ingo-Peter Lorenz*
München, Ludwig-Maximilians University, Department of Chemistry and Biochemistry
Received March 12th, 2008.
Dedicated to Professor H.-P. Boehm on the Occasion of his 80th Birthday
Abstract. The synthesis and structural characterization of two
azirine rhodium(iii) complexes are described. The stabilization, N-
coordination and phenylgroup π-stacking of the highly reactive and
strained 3-phenyl-2H-azirine by transition metal coordination is
observed. The reaction of the dimeric complex [(η5-C5Me5)RhCl2]2
with 3-phenyl-2H-azirine (az) in CH2Cl2 at room temperature in a
1:2 molar ratio afforded the neutral mono-azirine complex [(η5-
C5Me5)RhCl2(az)]. The subsequent reaction of [(η5-C5Me5)RhCl2]2
with six equivalents of az and 4 equivalents of AgOTf yielded the
cationic tris-azirine complex [(η5-C5Me5)Rh(az)3](OTf)2. After
purification, all complexes have been fully characterized. The mo-
lecular structures of the novel rhodium(iii) complexes exhibit
slightly distorted octahedral coordination geometries around the
metal atoms.
Keywords: Rhodium; Azirine; π-stacking; X-ray crystallography
Introduction
have been reported, for example the rearrangement of 2H-
and 3H-azirines to indoles catalyzed by [Rh(CO)2Cl]2 and
[Rh2(OCOCF3)4] or the reaction of two azirines to yield
pyrazine or pyrrole derivatives catalyzed by [Mo(CO)6] and
[Fe2(CO)9] [7, 12Ϫ19].
2H-Azirines have attracted considerable interest from the
synthetic, mechanistic and theoretical point of view, es-
pecially because of their versatile reactivity [1Ϫ3]. This is in
contrast to 1H-azirines which are only known as transient
intermediates representing a cyclic conjugated anti-aro-
matic system with four π-electrons. The reason for the in-
creased reactivity of 2H-azirines is mainly due to high ring
strain energy. Sordo et al. calculated ring strain energies of
46.7 kcal/mol at the B3LYP/6-31G* level of theory for 3,4-
dihydro-1aH-azirine-2,3-c-pyrrol-2-one [4]. The forced de-
formation of bond angles in this unsatured three membered
ring system is the main reason for the ring strain, which
was first taken into consideration by A. von Baeyer in his
strain theory [5].
2H-Azirines as versatile starting materials in organic syn-
thesis can react as nucleophiles, electrophiles and dieno-
philes or dipolarophiles in cyclo addition reactions [6Ϫ8].
Interestingly, all three bonds of the azirine ring can be
cleaved depending on the experimental conditions used [1].
Moreover, this highly strained imines are suitable precur-
sors in the synthesis of an impressive number of hetero-
cycles [6, 7, 9Ϫ11]. In this context transition metal cata-
lyzed ring expansion or rearrangement reactions of azirines
Concerning the coordination chemistry of azirines, to the
best of our knowledge only two X-ray structure analyses of
ZnBr2 and PdCl2 azirine complexes have been reported [1,
20Ϫ22]. The authors discussed the surprising effect of stabi-
lization by coordination. The azirine N atoms coordinate to
the lewis acidic transition metal centres which results in the
typical tetrahedral coordination geometry for the zinc(ii)
complex and a square planare geometry with a trans
arrangement of the azirine ligands for the palladium(ii)
complex. Inspired by our recent results on the aziridine co-
ordination chemistry of manganese(i), cobalt(ii), nickel(ii),
copper(ii), rhenium(i), ruthenium(ii) and palladium(ii)
[23Ϫ26], we chose to study the coordination chemistry of
2H-azirines as a barely investigated class of highly strained
ligands. At the beginning we chose to study the reactivity of
2H-azirines towards the dimeric rhodium(iii) complex [(η5-
C5Me5)RhCl2]2. In this communication we report the syn-
thesis and structural characterization of two 2H-azirine
rhodium(iii) complexes and the stabilization of the highly
reactive 3-phenyl-2H-azirine in the coordination sphere of
the (η5-C5Me5)Rh(iii) cation.
Results and Discussions
* Prof. Dr. I.-P. Lorenz
Department Chemie und Biochemie
Ludwig-Maximilians-Universität München
Butenandtstraße 5Ϫ13 (Haus D)
D-81377 München, Germany
Fax: ϩ49-(0)89-2180-77867
Synthesis
Scheme 1 and 2 illustrate the reaction of [(η5-C5Me5)-
RhCl2]2 with 2 equivalents az (2) yielding [(η5-C5Me5)-
RhCl2(az)] (3) and with 6 equivalents of az in the presence
E-mail: ipl@cup.uni-muenchen.de
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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J. N. Roedel, I.-P. Lorenz
of 4 equivalents of AgOTf yielding [(η5-C5Me5)Rh(az)3]-
(OTf)2 (4), respectively. Further synthetic details are given
in the experimental section. Both compounds are sensitive
to moisture and protic solvents and are soluble in polar
solvents such as dichloromethane and insoluble in nonpolar
solvents such as n-hexane. The molecular structures of 3
and 4 are illustrated in Figures 2 and 3 together with selec-
ted bond lengths and angles.
Scheme 1 Reaction of [(η5-C5Me5)RhCl2]2 (1) with 3-phenyl-2H-
azirine (2) yielding [(η5-C5Me5)RhCl2(az)] (3).
Fig. 1 1H NMR signals of the three CH2 az groups of 4 at r. t.
(A) and 55 °C (B).
Scheme 2 Reaction of [(η5-C5Me5)RhCl2]2 (1) with AgOTf and 3-
phenyl-2H-azirine (2) yielding [(η5-C5Me5)Rh(az)3](OTf)2 (4).
Spectroscopy
1
The H NMR spectra of 3 and 4 show the expected azirine
signals shifted to lower field due to deshielding caused by
transition metal coordination. A good indication for the N-
coordination of az to RhIII is the chemical shift of the CH2
1
ring signal. The H signals of 3 and 4 are slightly shifted to
lower field in comparison to the signals observed for 2. For
example, the CH2 ring proton signals are observed at
1.88 ppm (3) and 2.68 and 2.41 ppm (4), respectively, com-
pared to 1.75 ppm for 2. Likewise in the 13C NMR spectra
the tendency of signal shift to lower field, compared to the
corresponding signals of the free azirine, is observed [27].
The intramolecular π-stacking interaction of the phenyl
groups of two az ligands of 4, which is found later on in
Fig. 2 Molecular structure of [(η5-C5Me5)RhCl2(az)] (3). The
thermal ellipsoids are drawn at the 30 % probability level. Hydro-
gen atoms are omitted for clarity.
1
the solid state, can be observed in solution by H NMR
˚
Selected bond lengths/A and angles/°: Rh(1)ϪN(1) 2.103(3), Rh(1)ϪC(9)
spectroscopic measurements at r. t. and 55 °C (in CDCl3),
respectively. At r. t. the CH2 signals of two az ligands are
observed at 2.68 ppm and that of the third at 2.41 ppm in
2:1 ratio (A in Fig. 1). Heating up this solution to 55 °C
delivers only one corresponding broad signal for all three
az ligands at 2.44 ppm (B in Fig. 1). Obviously, the intra-
molecular π-stacking is lost at higher temperatures. After
cooling this solution to 30 °C both signals again appear,
now at 2.72 and 2.43 ppm.
2.145(3), Rh(1)ϪC(10) 2.160(3), Rh(1)ϪC(11) 2.129(3), Rh(1)ϪC(12)
2.149(3), Rh(1)ϪC(13) 2.156(3), Rh(1)ϪCl(1) 2.421(10), Rh(1)ϪCl(2)
2.390(9), N(1)ϪC(1) 1.526(4), N(1)ϪC(2) 1.255(4), C(1)ϪC(2) 1.456(4),
N(1)ϪRh(1)ϪCl(1) 87.22(7), N(1)ϪRh(1)ϪCl(2) 87.72(7), Cl(1)ϪRh(1)Ϫ
Cl(2) 90.94(3), C(2)ϪC(1)ϪN(1) 49.72(18), C(2)ϪN(1)ϪC(1) 62.2(2),
N(1)ϪC(2)ϪC(1) 68.0(2).
Mass spectrometric investigations in the FABϩ mode of
complex 3 revealed fragmentation peaks for the cleavage of
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2H-Azirines as Ligands
the az ligand (MϩϪaz), and the subsequent separation of
chlorido ligands (MϪazϪn Cl) (n ϭ 1, 2). In the FABϩ
spectra of the tris-azirine complex 4 the peak for the intact
cation [(η5-C5Me5)Rh(az)3]2ϩ was not detected. The
fragmentation pattern resulting from the successive
cleavage of the azirine ligands and the coordination of
one triflato group with peaks for (MϪn azϪOTf) to
[(η5-C5Me5)Rh(az)3Ϫn 2ϩ (n ϭ 1, 2, 3) or (MϪn azϪ2 OTf)
]
(n ϭ 1, 2) were observed, respectively.
The IR spectra of the complexes 3 and 4 show sharp
absorption bands for the azirine CϭN stretching vibrations
at 1769 cmϪ1 (3) and 1765 cmϪ1 (4). A shift of 29 cmϪ1 (3)
and 25 cmϪ1 (4) to higher wavenumbers compared to ν(Cϭ
N) ϭ 1740 cmϪ1 of az is detected [21]. In addition, the typi-
cal σ- and δ-ring vibrations of az, the C5Me5 ligand and
OTf anions in the fingerprint region were observed. The
stretching and deformation vibrations of the CF3 and SO3
groups in compound 4 are dectected at 1031 cmϪ1 (σ),
637 cmϪ1 (δ) (SO3) and 1266 cmϪ1 (σ), 769 cmϪ1 (δ) (CF3)
[28, 29]. As expected, the ν(C-H) absorptions of 3 and 4
Fig. 3 Molecular structure of [(η5-C5Me5)Rh(az)3](OTf)2 (4). The
thermal ellipsoids are drawn at the 30 % probability level. Hydro-
gen atoms, one dichloromethane molecule and two triflate anions
are omitted for clarity.
were observed between 2907 cmϪ1 and 3086 cmϪ1
.
˚
Selected bond lengths/A and angles/°: Rh(1)ϪN(1) 2.108(3), Rh(1)ϪN(2)
Crystal Structure Analysis
2.089(3), Rh(1)ϪN(3) 2.107(3), Rh(1)ϪC(25) 2.146(4), Rh(1)ϪC(26)
2.157(3), Rh(1)ϪC(27) 2.161(3), Rh(1)ϪC(28) 2.145(3), Rh(1)ϪC(29)
2.175(4), N(1)ϪC(1) 1.535(5), N(1)ϪC(2) 1.258(5), C(1)ϪC(2) 1.465(5),
N(2)ϪRh(1)ϪN(1) 84.25(11), N(2)ϪRh(1)ϪN(3) 89.00(11), N(3)ϪRh(1)Ϫ
N(1) 87.17(11), C(2)ϪN(1)ϪC(1) 62.3(3), C(2)ϪC(1)ϪN(1) 49.5(2),
N(1)ϪC(2)ϪC(1) 68.1(3).
The molecular structures of the compounds 3 and 4 have
been determined by single crystal X-ray diffraction analysis.
Single crystals were obtained by isothermic diffusion of n-
pentane into the dichloromethane solutions of 3 or 4,
respectively. The X-ray structure analysis of 3 and 4 re-
vealed the formation of octahedral coordination. The RhIII
centres are coordinated besides the η5-C5Me5 ligand by the
nitrogen atom of one az and two chlorido ligands in com-
plex 3 and by the N atoms of three az ligands in 4, both
presenting a slightly distorted octahedral coordination.
All of the RhϪligand bond lengths in 3 lie within the
expected ranges and are comparable to those in similar
the corresponding Rh(1)ϪN(1) bond in complex 3.
˚
Rh(1)ϪN(2) with 2.089 A, however, is a little bit shortened.
The CϭN, CϪN, CϪC bond lengths in all three az ligands
are almost equal to each other and slightly enlarged com-
pared to bond distances observed in the free 2H-azirine
[31]. The angles between the planes of the azirines and the
phenyl rings of 4 show the values 5.26°, 11.57° to 22.51°.
For one az ligand in compound 4 an almost coplanar ring
arrangement of 4.86° is observed, whereas the other two az
ligands exhibit much larger distortion angles of 11.57° and
22.51° due to steric reasons. In addition in compound 4 the
intramolecular plane to plane π-stacking between the phe-
nyl moieties of two az ligands is observed as it has been
˚
complexes [20], for example 2.103 A for Rh(1)ϪN(1). The
CϭN, CϪN, CϪC bond lengths in the az ligand are slightly
enlarged compared to bond distances observed in uncoordi-
nated 2H-azirines using single crystal X-ray diffraction. The
az ligand is almost coplanar and exhibits an angle between
the azirine ring plane and the phenyl ring plane of 4.86°.
Moreover in compound 3 an intermolecular plane to plane
π-stacking between the η5-C5Me5 ligand and the phenyl
ring of the az ligand is observed. The distance between the
1
already demonstrated by H NMR spectra. The distance
˚
between the centroids of both aromatic moieties is 4.023 A
and an angle of 7.92° between the planes of the the two
phenyl rings is formed.
˚
centroids of both aromatic systems is measured at 4.039 A
and a distortion angle of 7.92° between the planes of the
η5-C5Me5 ligand and the phenyl ring is formed [30].
Experimental Part
The structure of compound 4 shows that the Rh3ϩ ion is
bonded to the η5-C5Me5 ligand and to the three az ligands
and is best described as a slightly distorted octahedron. The
solid state structure of compound 4 also shows two triflato
anions for each twofold cationic [(η5-C5Me5)Rh(az)3]2ϩ
fragment. All of the RhϪC bond distances in 4 are within
the expected range [26]. It is noteworthy that the RhϪN
General Methods and Materials:
All manipulations were performed under a dry argon atmosphere
using Schlenk line techniques. Dichlormethane was distilled from
CaH2, n-pentane and n-hexane were distilled from sodium. All sol-
˚
vents were stored under dry argon atmospheres and over 3 A mo-
lecular sieves (dichlormethane) respectively or sodium pieces (n-
pentane, n-hexane). The 1H, 13C and 19F NMR spectra were re-
corded using a Jeol Eclipse 270 and a Jeol Eclipse 400 instrument
bond lengths in
Rh(1)ϪN(3) with 2.108 A and 2.107 A are almost equal to
4 differ slightly. Rh(1)ϪN(1) and
˚
˚
Z. Anorg. Allg. Chem. 2008, 1485Ϫ1489
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1487

J. N. Roedel, I.-P. Lorenz
mosphere [33, 34]. Additionally az was cooled to Ϫ32 °C due to
the thermic instability at r.t. (Caution: 3-phenyl-2H-azirine is
highly irritant).
Table 1 Crystal data and details of the structure refinement for
compounds 3 and 4.
Compound
3
4
The novel azirine transition metal complexes 3 and 4 have been
prepared as follows. Complex 3 was synthesized by solving one
equivalent of 1 in dry dichloromethane and the direct addition of
two equivalents of az (2). The reaction mixture was stirred at r.t.
for 45 min. After removal of the solvent in vacuo the residue was
purified by washing the solid with dry n-hexane (20 mL). The or-
ange solid was dried in vacuo. The red crystalline product was ob-
tained after recrystallization from a dichloromethane / n-pentane
solution.
Formula
FW
Temperature /K
Wavelength /A
C18H22Cl2NRh
426.19
200(2)
0.71073
monoclinic
P21/c
8.5382(17)
14.524(3)
14.574(3)
104.86(3)
1746.9(6)
4
1.6205(6)
1.279
864
0.15 x 0.08 x 0.01
3.16 to 27.48
Ϫ11ՅhՅ11,
Ϫ18ՅkՅ18,
Ϫ18ՅlՅ18
7611
3997
0.0343
99.8 %
C37H38Cl2F6N3O6RhS2
972.65
200(2)
0.71073
monoclinic
P21/c
12.116(2)
17.612(4)
20.178(4)
103.34(3)
4189.8(14)
4
1.5420(5)
0.709
1976
0.20 x 0.16 x 0.04
3.20 to 26.00
Ϫ14ՅhՅ14,
Ϫ21ՅkՅ21,
Ϫ24ՅlՅ24
15979
8197
0.0254
99.7 %
˚
Crystal system
Space group
˚
a /A
˚
b /A
˚
c /A
β /°
3
˚
V /A
Complex 4 was synthesized by reacting [η5-(C5Me5)RhCl2]2 (1) with
four equivalents of silver(i)triflate. After 3 hours of stirring at ambi-
ent temperature the precipitated AgCl was removed by centrifug-
ation and decantation of the solution. Subsequently 6 equivalents
of 3-phenyl-2H-azirine (2) were added and again the solution was
stirred for 15 min at r.t. resulting in the formation of the tris-azirine
complex 4. After removal of the solvent in vacuo the brownish
residue was purified by stirring in dry n-hexane (10 mL) for 12
hours at ambient temperature. The n-hexane phase was then
removed by decantation and the brownish red solid was dried in
vacuo.
Z
ρcalc. /g cmϪ1
μ /mmϪ1
F(000)
Crystal size /mm
θ range /°
Index Range
Reflns collected
Independent reflns
Rint
Completeness to θ
Refinement method
Full-matrix least
Full-matrix least
squares on F2
8197 / 0 / 520
1.040
squares on F2
[(η5-C5Me5)RhCl2(az)] (3):
Data / restraints / parameters 3997 / 0 / 196
S on F2
1.061
Final R indices [I>2 σ (I)]
R1 ϭ 0.0331,
wR2 ϭ 0.0693
R1 ϭ 0.0540,
wR2 ϭ 0.0770
R1 ϭ 0.0443,
wR2 ϭ 0.1154
R1 ϭ 0.0612,
wR2 ϭ 0.1268
1.258 and Ϫ0.975 e.A
677718
Reagents: 129 mg (0.194 mmol) 1, 114 mg (0.971 mmol) 2. Yield
37 % (31 mg, 0.072 mmol); red crystals; decomposition > 170 °C;
C18H22Cl2NRh (426.19); C 51.28 (calc. 50.73); H 5.05 (5.20); N,
3.67 (3.29) %.
IR (KBr, cmϪ1): 3086 w, 3042 w, 2970 w, 2907 w, 1769 s, 1598 w, 1579 w,
1464 m, 1451 m, 1376 w, 1360 w, 1341 w, 1327 w, 1307 w, 1275 w, 1184 w,
1161 w, 1129 w, 1084 w, 1021 m, 927 w, 837 w, 796 w, 765 s, 733 w, 693 m,
686 s, 617 w, 546 w, 532 w cmϪ1. MS (FAB-pos): m/z ϭ 426 (Mϩ, 8 %), 391
(Mϩ Ϫ Cl, 100 %), 273 (MϩϪazϪCl, 92 %), 237 (MϩϪazϪ2 Cl, 66 %). 1H
NMR (270 MHz, CDCl3): δ ϭ 8.03 (dd, 3J ϭ 7.6 Hz, 4J ϭ 1.6 Hz, 2 H, Ph-
az), 7.63-7.51 (m, 3 H, Ph-az), 1.88 (s, 2 H, CH2-az), 1.61 (s, br, 15 H, Me-
C5Me5) ppm. 13C {1H} NMR (68 MHz, CD2Cl2): δ ϭ 165.7 (Cq-CϭN),
133.5 (CH-az), 130.6 (Cq-az), 129.2 (CH-az), 94.3 (br, Cq-C5Me5), 19.5
(CH2-az), 9.5 (CH3-C5Me5) ppm.
R indices (all data)
Ϫ3
Ϫ3
˚
˚
Largest difference peak/hole 0.675 and Ϫ0.530 e.A
CCDC number 677717
operating at 270 MHz (1H), 400 MHz (1H), 68 MHz (13C),
100 MHz (13C) and 376 MHz (19F). All chemical shifts are given
in ppm relative to TMS (1H, 13C). Mass spectra were measured
using a JEOL Mstation JMS 700 in the FABϩ mode (NBA matrix).
Multi-isotope containing fragments refer to the isotope with the
highest abundance. Infrared spectra were recorded with a Nicolet
520 FT-IR and Perkin Elmer Spectrum One FT-IR spectrometer
in the 4000 Ϫ 400 cmϪ1 range. Single crystal X-ray diffraction data
were collected on a Nonius Kappa CCD using graphite-monochro-
mated Mo-Kα radiation. Single crystal X-ray structure analyses
were performed using direct methods using the SHELXS software
and refined by full-matrix least-squares with SHELXL-97 [32].
Table 1 contains the crystallographic data and details of the
[(η5-C5Me5)Rh(az)3](OTf)2 (4):
Reagents: 131 mg (0.212 mmol) 1, 150 mg (1.280 mmol) 2, 223 mg
(0.868 mmol) AgOTf. Yield 84 % (158 mg, 0.178 mmol); brownish
red powder; decomposition
> 113 °C; C36H36F6N3O6RhS2
(887.71): C 48.80 (calc. 48.71); H 3.95 (4.09); N 4.69 (4.73).
IR (KBr, cmϪ1): 3067 w, 1765 m, 1596 w, 1491 w, 1452 w, 1378 w, 1266 vs,
1224 w, 1161 m, 1132 w, 1074 w, 1031 s, 1000 w, 833 w, 769 w, 689 w, 637 s,
573 w, 548 w, 518 w cmϪ1. MS (FAB-pos): m/z ϭ 621 (MϩϪOTfϪaz, 18 %),
504 (MϩϪOTfϪ2 az, 100 %), 472 (MϩϪ2 OTfϪaz, 34 %), 387
(MϩϪOTfϪ3 az, 89 %), 355 (MϩϪ2 OTfϪ2 az, 73 %). 1H NMR (400 MHz,
CD2Cl2): δ 7.83 (d, 3J ϭ 7.4 Hz, 2 H, Ph-az), 7.74-7.45 (m, 13 H, Ph-az),
2.68 (s, 4 H, CH2-az), 2.41 (s, 2 H, CH2-az), 1.87 (s, br, 7 H, Me-C5Me5),
1.79 (s, br, 8 H, Me-C5Me5) ppm. 13C {1H} NMR (100 MHz, CD2Cl2): δ ϭ
171.1 (Cq-CϭN), 169.4 (Cq-CϭN), 136.8 (CH-az), 136.3 (CH-az), 131.6
(CH-az), 130.6 (CH-az), 130.1 (CH-az), 129.7 (CH-az), 129.3 (CH-az), 129.2
(CH-az), 129.0 (CH-az), 122.2 (q, 1JC,F ϭ 320 Hz, CF3), 121.3 (Cq-az), 120.8
(Cq-az), 21.4 (CH2-az), 21.3 (CH2-az), 9.5 (CH3-C5Me5) ppm. 19F {13C}
NMR (376 MHz, CD2Cl2): δ ϭ Ϫ79.3 (s, CF3-OTf) ppm.
structural refinement of
3 and 4. The CCDC numbers of
compounds 3 and 4 contain the supplementary crystallographic
data for this paper. This data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Elemental analysis were per-
formed by the Microanalytical Laboratory of the Department of
Chemistry and Biochemistry, LMU Munich using a Heraeus Ele-
mentar Vario El. Uncorrected melting points were obtained using
a Büchi Melting Point B-540 device.
General method for the synthesis of [(η5-C5Me5)-
RhCl2(az)] (3) and [(η5-C5Me5)Rh(az)3](OTf)2 (4)
Conclusion
3-phenyl-2H-azirine (az) (2) and [η5-(C5Me5)RhCl2]2 (1) were pre-
Two 2H-3-phenylazirine complexes of Rh(iii) have been pre-
pared according to literature methods and stored in dry argon at-
pared and isolated. Of note, these complexes are the first
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Z. Anorg. Allg. Chem. 2008, 1485Ϫ1489

2H-Azirines as Ligands
[15] H. Alper, J. E. Prickett, S. Wollowitz, J. Am. Chem. Soc. 1977,
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[18] H. Alper, F. Urso, D. J. Smith, J. Am. Chem. Soc. 1983, 105,
6737Ϫ6738.
fully characterized organometallic 2H-azirine complexes. A
remarkable stabilization of the highly strained and reactive
ligand is observed by coordination. The connectivity within
both complexes was deduced by single crystal X-ray crystal-
lography and NMR spectroscopy. The coordination chemis-
try of further 2H-azirine ligands to other transition metal
complexes is under investigation.
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