Synthesis and structure of the first neutral octahedral cis-dioxorhenium(V) complex

Article abstract of DOI:10.1016/S0020-1693(01)00655-7

The complex cis-[ReO₂(Hdab)(py)₂] (1) (H₂dab = 1,2-diaminobenzene) has been prepared by reacting trans-[ReO₂(py)₄]I with H₂dab in ethanol. This is the first example of a neutral hexacoordinate rhenium(V) complex with a cis arrangement of the two oxo groups. The compound also provides the first example of a bidentate monoanionic monoimino coordination mode of H₂dab. Crystal data for 1·(H₃dab)I·H₂O: C₂₂H₂₆IN₆O₂Re·H ₂O, triclinic, space group P1?, a = 9.570(2), b = 12.493(3), c = 12.851(3) A?, α = 61.60(3), β = 70.56(3), γ = 78.68(4)°, V = 1273.1(4) A?³ and Z = 2.

Full text of DOI:10.1016/S0020-1693(01)00655-7

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Inorganica Chimica Acta 325 (2001) 215–219
Note
Synthesis and structure of the first neutral octahedral
cis-dioxorhenium(V) complex
Giuliano Bandoli a, Alessandro Dolmella a,*, Thomas I.A. Gerber b,*,
Dibanisile Luzipo b, Jan G.H. du Preez b
a Department of Pharmaceutical Sciences, Uni6ersity of Pado6a, Padua, Italy
b Department of Chemistry, Uni6ersity of Port Elizabeth, Nelson Mandela Metropole, PO Box 1600, Port Elizabeth, South Africa
Received 18 June 2001; accepted 27 August 2001
Abstract
The complex cis-[ReO2(Hdab)(py)2] (1) (H2dab=1,2-diaminobenzene) has been prepared by reacting trans-[ReO2(py)4]I with
H2dab in ethanol. This is the first example of a neutral hexacoordinate rhenium(V) complex with a cis arrangement of the two
oxo groups. The compound also provides the first example of a bidentate monoanionic monoimino coordination mode of H2dab.
(
,
Crystal data for 1·(H3dab)I·H2O: C22H26IN6O2Re·H2O, triclinic, space group P1, a=9.570(2), b=12.493(3), c=12.851(3) A,
3
,
h=61.60(3), i=70.56(3), k=78.68(4)°, V=1273.1(4) A and Z=2. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: cis-Dioxorhenium(V); Crystal structures; 1,2-Diaminobenzene
[6], as well as giving complexes with unusual structural
and chemical properties [7].
1. Introduction
1,2-Diaminobenzene is a highly delocalised, unsatu-
rated, electron-rich molecule, and the different forms in
which it was found in transition metal complexes are
There has recently been a renewed interest in the
coordination chemistry of rhenium [1–3]. This is
mainly due to the potential application of the radioiso-
topes 186Re and 188Re in radiotherapy [1]. Rhenium
complexes also serve as model compounds for the
chemically related technetium compounds which are
widely applied in diagnostic medicine [2,3]. Oxorhe-
nium complexes have recently been shown to have
applications in many catalytic oxidation processes and
to oxygen atom transfer between substrates [4,5].
Our interest is currently focused on the synthesis of
rhenium(V) complexes containing the molecule 1,2-di-
aminobenzene (H2dab) and its derivatives. The reaction
of H2dab with transition metals has been studied exten-
sively, since it leads to complexes in different oxidation
states with reversible oxidation–reduction sequences
The neutral diaminobenzene form (a) has been found
in the platinum(II) complex [Pt(H2dab)I2] [8]. The 1,2-
benzosemiquinone diimine monoanionic form (b) has
been isolated in complexes of the type [MII(dab)2] (M=
Co, Ni, Pd, Pt) [9], while the neutral 1,2-benzoquinone
diimine form (c) was found in [Fe(dab)(CN)4]2− [10].
We have recently discovered the imido form (d) in the
complex [ReV(dab)Cl3(PPh3)2] [11] and the diimide form
* Corresponding authors. Tel.: +27-41-5042 276; fax: +27-41-
5042 573.
E-mail addresses: alessandro.dolmella@unipd.it (A. Dolmella),
chatig@upe.ac.za (T.I.A. Gerber).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00655-7

216
G. Bandoli et al. / Inorganica Chimica Acta 325 (1999) 215–219
(e) in the oxo-free complex [ReV(dab)2Cl(PPh3)] [12]
and in (n-Bu4N)[TcVO(dab)2] [7].
2. Experimental
We have now also discovered the mono-imido form
(f) in the complex cis-[ReVO2(Hdab)(py)2] (1), which
was prepared from the reaction of trans-[ReO2(py)4]I
and H2dab in ethanol. To our knowledge this is the first
example of a neutral hexacoordinate rhenium(V) com-
plex with a cis-dioxo structure. The first example of a
neutral cis-dioxorhenium(V) complex was the trigonal–
bipyramidal [ReO2I(PPh3)2] [13], and the first example
of an octahedral one was the cationic cis-
[ReO2(bipy)(py)2](ClO4) [14].
2.1. Reagents
trans-[ReO2(py)4]I was synthesized by a published
procedure [15]. Solvents were reagent grade, and were
purified and dried before use. All other reagents were
obtained commercially (Aldrich), and their purity was
1
checked by H NMR and melting point.
2.2. Synthesis of cis-[ReO2(Hdab)(py)2] (1)
A
mixture of 100 mg (150 mmol) of trans-
[ReO2(py)4]I and 33 mg (305 mmol) of 1,2-diaminoben-
zene (H2dab) in 15 cm3 of ethanol was stirred at room
temperature (r.t.) for 30 h. The original red–orange
solution gradually turned green, and after the reaction
period a fine dark purple precipitate was collected by
filtration from the dark green solution. The product 1
was washed with cold ethanol, water and acetone, and
dried under vacuum. The slow evaporation of the
mother liquor over a period of 3 days at r.t. gave dark
violet crystals, suitable for X-ray analysis, with the
formulation 1·(H3dab)I·H2O. Yield: 63%, m.p.\
300 °C. Anal. Calc. for C16H17N4O2Re: C, 39.74; H,
3.54; N, 11.59. Found: C, 39.91; H, 3.61; N, 11.34%.
IR(KBr): ws(ReO2) 905; wa(ReO2) 876; w(NH) 3236,
Table 1
Summary of crystal and refinement data
Empirical formula
Color, habit
Formula weight
Crystal system
Space group
C22H26IN6O2Re·H2O
dark violet cuboids
737.60
triclinic
P1
9.570(2)
12.493(3)
12.851(3)
61.60(3)
70.56(3)
78.68(4)
1273.1(4)
2
1.924
50.0
4454
3519
0.048; 0.129
1.062
,
a (A)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
1
3262, 3289 cm−1. H NMR (295 K) ppm: 13.63 (br s,
Dcalc (mg m−3
2qmax (°)
Independent reflections
)
3H, NH), 7.36 (s, 8H, pyH), 6.93 (br s, 6H, pyH,
Hdab). UV–Vis: 668 (9750), 383 (4780).
Observed reflections (I\2|(I))
R1 a; wR2
b
2.3. X-ray data collection, structure solution and
refinement of 1·(H3dab)I·H2O
Goodness-of-fit
Other details of data collection/refinement: Siemens/Nicolet R3m/V
diffractometer; Mo Ka radiation (u=0.71073); T=293 K; highly
oriented graphite monochromator; ꢀ−2q scans; two standard reflec-
tions every 150; refinement by full-matrix least-squares method on F2o;
riding model for H atoms.
The most important details of the crystallographic
work are reported in Table 1. A crystal of the dimen-
sions 0.20×0.20×0.20 mm was used for data collec-
tion. Cell constants and orientation matrices for the
data collection have been obtained from the least-
squares refinement of 50 well-centered reflections with
q]8.0°. The intensities were corrected for Lorentz and
polarization factors as well as for absorption effects.
The latter have been treated empirically (C-scans
method).
a R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ.
b wR2=[ꢁ w(Fo2−Fc2)/2ꢁ w(Fo2)/2]1/2
.
Table 2
,
Selected bond distances (A) and angles (°)
The structure was solved by heavy-atom methods,
completed by difference Fourier syntheses and refined
by full-matrix least-squares procedures based on F2,
using the SHELX suite of programs [16,17]. All the
atoms have been refined anisotropically with the excep-
tion of the hydrogen atoms, which have been described
by means of a riding model. The final difference map
did not show any relevant feature. The minimum and
maximum difference peaks were −1.22 and 1.36 e
Bond lengths
ReꢀO(1)
ReꢀN(1)
ReꢀN(3)
N(5)ꢀC(17)
1.723(7)
2.053(8)
2.163(9)
1.41(1)
ReꢀO(2)
ReꢀN(2)
ReꢀN(4)
N(6)ꢀC(22)
1.716(6)
2.042(9)
2.155(9)
1.48(1)
Bond angles
O(1)ꢀReꢀO(2)
O(1)ꢀReꢀN(2)
O(1)ꢀReꢀN(4)
N(1)ꢀReꢀN(2)
ReꢀN(1)ꢀC(1)
118.2(3)
85.2(3)
87.8(3)
72.7(3)
121.2(6)
O(1)ꢀReꢀN(1)
O(1)ꢀReꢀN(3)
O(2)ꢀReꢀN(2)
N(3)ꢀReꢀN(4)
ReꢀN(2)ꢀC(6)
157.8(3)
88.0(3)
156.6(3)
174.3(3)
121.3(7)
A
−3, respectively. A collection of selected bond dis-
tances and angles for 1 is given in Table 2.
,

G. Bandoli et al. / Inorganica Chimica Acta 325 (1999) 215–219
217
3. Results and discussion
The reaction of trans-[ReO2(py)4]I with 1,2-di-
aminobenzene (H2dab) at room temperature in ethanol
did not result in the expected trans-dioxo complex
[ReO2(H2dab)2]I, but rather yielded the novel neutral
complex cis-[ReO2(Hdab)(py)2] (1). The best yield was
obtained with a 1:2 metal–ligand molar ratio, and the
slow evaporation of the mother liquor of the synthetic
solution led to the crystallization of a compound with
the formulation 1·(H3dab)I·H2O. Heating of the reac-
tion mixture under reflux conditions for 2 h gave a
mixture of products, one of which was 1. Complex 1 is
air stable in the solid state for weeks, and in solution
for at least 8 h. It is soluble in a variety of solvents such
as acetonitrile, acetone, chloroform, water and Me2SO.
It is also diamagnetic; diamagnetism for cis-dioxo d2
species has been explained earlier on the basis of spin–
orbit coupling energetics [19].
Fig. 1. A perspective view of the asymmetric unit of 1·(H3dab)I·H2O
with its numbering scheme. Thermal ellipsoids are drawn at the 50%
probability level.
The presence of the cis-dioxo bonds is confirmed by
two strong peaks at 905 and 876 cm−1 in the infrared
spectrum; the former the symmetric and the latter the
asymmetric stretch. The IR spectrum in acetonitrile was
identical with that obtained in a KBr pellet. In the
NMR spectrum a convergence of the proton resonances
of the aromatic rings is observed, as a consequence of
the delocalization of the p-electron density in the rings.
Single crystals of 1·(H3dab)I·H2O of X-ray quality
were obtained from the slow evaporation of the ethano-
lic mother liquor of the synthetic solution. An ORTEP
[20] perspective view of the asymmetric unit, along with
the atom numbering scheme, is given in Figs. 1 and 2
shows the neutral complex 1. In the asymmetric unit,
together with the monomeric complex, there is an un-
bound molecule of the ligand in its protonated form
H3dab+, which is neutralized by an iodide ion. The
rhenium atom is at the center of a distorted octahedral
environment. The equatorial positions are held by the
nitrogen atoms of the monoanionic Hdab− ligand and
two cis-oxo atoms. The apical positions are occupied
by the nitrogen atoms of the two pyridine ligands. The
data in Table 2 indicate that the largest deviations from
ideality in the equatorial plane are due to the restric-
tions imposed on the ligand Hdab by the formation of
a five-membered ring with the metal; in fact, the
N(1)ꢀReꢀN(2) angle is only 72.7°. The strain originat-
ing from such a distortion may be responsible for the
cis orientation of the two oxygen atoms, which have a
O(1)ꢀReꢀO(2) angle of 118.2°. The Re, N(1), N(2),
Fig. 2. The cis-[ReO2(Hpda)(py)2] neutral complex.
2.4. Physical measurements
The instrumentation used in this study is the same as
reported elsewhere [18]. IR spectra were obtained in
1
,
KBr discs and H NMR spectra were run in d6-DMSO.
O(1) and O(2) atoms are nearly coplanar within 0.03 A.
Electronic spectra were all obtained in acetonitrile, and
data are given as umax with extinction coefficients (in
units M−1 cm−1) in parentheses. Elemental analyses
for carbon, hydrogen and nitrogen were carried out by
the Department of Chemistry at the University of the
Western Cape in Cape Town.
The monoanionic Hdab− ligand is also planar within
the equatorial plane and is nearly orthogonal in respect
of the two pyridine synthons. The mean planes of the
pyridines bound to rhenium through the N(3) and N(4)
atoms define, respectively, angles of 97.1 and 87.5° with
the Hdab− plane. Also, the mean planes passing

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G. Bandoli et al. / Inorganica Chimica Acta 325 (1999) 215–219
Fig. 3. The crystal lattice showing the shortest intermolecular interactions.
through the pyridines define an angle to each other of
only 12.5°, so the two ligands are nearly coplanar. The
deviation from ideality can also be measured by the
dihedral angle between two opposing triangular faces of
the octahedron. The angle between the planes
N(1)ꢀN(3)ꢀO(2) and N(2)ꢀN(4)ꢀO(1) is 11.2° (ideally
0°). All the above indicate that the octahedral environ-
ment is only moderately distorted. The ReꢁOoxo (in
cis-dioxo compounds), Re(V)ꢀNpy, and Re(V)ꢀNamine
bond lengths have been compared with those reported
in the Cambridge Structural Database System [21], and
in all cases they fall within the reported limits, close to
the average values. So no unexpected features have
been found.
atom (Ow) at x, y, z and at −x, 1−y, 1−z. The IꢀOw
,
distances are 3.67 and 3.54 A, respectively. The nitro-
gen atoms of the bonded ligand molecule also define
two contacts. The first is between N(1) and Ow at x, y,
,
z, with a distance of 2.98 A, and the second is between
N(2) and the N(5) again at x, y, z; the bond distance in
,
this case being 2.96 A.
Complex 1 is a rare sample of a neutral cis-dioxo
rhenium(V) complex. For Re(V), as well as for other
transition metals with a d2 electron configuration, the
trans-dioxo arrangement is the most common, and
most of the reported trans-dioxo Re(V) complexes are
positively charged [22]. To the best of our knowledge, 1
is the only known example of a neutral octahedral
cis-dioxo complex, and it also provides the first exam-
ple of the bidentate coordination of H2dab in a
monoanionic monoimino form (see structure (f) in Sec-
tion 1).
With respect to the unbound protonated H3dab+
ion, the only feature that deserves mention is that the
C(17)ꢀN(5) and the C(22)ꢀN(6) bond distances are
,
different. The former measures 1.414 A, while the latter
,
is 1.476 A. This indicates that protonation occurred at
the N(6) atom.
With respect to cell packing (Fig. 3), no really strong
intermolecular interactions have been found, and only a
few contacts are worth mentioning. The iodide anion is
involved in two interactions with the water oxygen
4. Supplementary material
All atomic and thermal parameters and all interactive
angles are available from the authors upon request.

G. Bandoli et al. / Inorganica Chimica Acta 325 (1999) 215–219
219
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