The reaction of salicylhydrazide with [ReOX3(PPh 3)2]. Influence of X on product formation

Article abstract of DOI:10.1016/j.inoche.2011.09.041

The reactions of 2-hydroxybenzhydrazide (salicylhydrazide; Hshz) with trans-[ReOX₃L₂] (X = Cl (a), Br (b); L = PPh₃] in acetonitrile and acetone were studied. With a in acetonitrile, the rhenium(III) complex [ReCl₂(shz)(NCCH₃)L₂] (1), with shz coordinated as a monodentate diazenide, was isolated. However, with b in acetonitrile, the oxorhenium(V) dimer (μ-shd) [ReOBr(OPPh ₃)]₂ (2) was formed. The bridging ligand shd^4- was formed by the condensation of two shz ligands, with the elimination of hydrazine. In acetone, the reaction of Hshz with a produced [ReOCl ₂(sha)L] (3), in which the bidentate Schiff base ligand sha ^- was formed by the condensation of shz with acetone. The spectral and X-ray crystallographic characterization of complexes 1-3 are reported.

Full text of DOI:10.1016/j.inoche.2011.09.041

Inorganic Chemistry Communications 15 (2012) 69–72
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
The reaction of salicylhydrazide with [ReOX3(PPh3)2]. Influence of X on
product formation
⁎
T.I.A. Gerber , N.C. Yumata, R. Betz
Department of Chemistry, Nelson Mandela Metropolitan University, Port Elizabeth 6031, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of 2-hydroxybenzhydrazide (salicylhydrazide; Hshz) with trans-[ReOX3L2] (X=Cl (a), Br (b);
L=PPh3] in acetonitrile and acetone were studied. With a in acetonitrile, the rhenium(III) complex [ReCl2
(shz)(NCCH3)L2] (1), with shz coordinated as a monodentate diazenide, was isolated. However, with b in
acetonitrile, the oxorhenium(V) dimer (μ-shd) [ReOBr(OPPh3)]2 (2) was formed. The bridging ligand shd4−
was formed by the condensation of two shz ligands, with the elimination of hydrazine. In acetone, the reaction
of Hshz with a produced [ReOCl2(sha)L] (3), in which the bidentate Schiff base ligand sha− was formed by the
condensation of shz with acetone. The spectral and X-ray crystallographic characterization of complexes 1–3
are reported.
Received 17 August 2011
Accepted 28 September 2011
Available online 4 October 2011
Keywords:
Rhenium (III)/(V)
Salicylhydrazide
Ligand-bridged dimer
© 2011 Elsevier B.V. All rights reserved.
The potential development of therapeutic radiopharmaceuticals
based on the 186Re and 188Re isotopes has created a lot of interest in
the coordination chemistry of rhenium [1]. One of the ligand systems
investigated for the synthesis of stable rhenium complexes has been
substituted hydrazines, which not only act as ligands, but also as
two-electron reducing agents, in addition to having the functionality
to couple the complex to biologically active molecules [2–4]. For ex-
ample, the reaction of perrhenate with the substituted phenylhydra-
zines RC6H4–NHNH2 (R=OCH3, Cl, CO2CH3) in the presence of PPh3
(L) in acetonitrile led to the isolation of [ReIIICl2(NNC6H4R)(NCCH3)
L2] [3]. Also, with 2-hydrazinopyridine the complex [ReIIICl2(NNpy)
L2] has been prepared with trans-[ReOCl3L2] as starting material,
with NNpy being coordinated as a bidentate diazenido(1-) ligand
[4]. Oxorhenium(V) complexes containing diazenido ligands are rare.
In this account the products of the reactions of salicylhydrazide
(Hshz; Scheme 1) with trans-[ReOX3L2] (X=Cl, Br) in acetonitrile
and acetone are reported. As expected, the reaction of Hshz with
[ReOCl3L2] in acetonitrile led to the isolation of [ReIIICl2(shz)
(NCCH3)L2] (1), with shz coordinated in a monodentate fashion [5].
However, by using [ReOBr3L2] as starting material, the dimeric oxor-
henium(V) complex (μ-shd)[ReOBr(OPPh3)]2 (2) was formed [6].
The bridging ligand shd4− was formed by the condensation of two
shz ligands, with the elimination of a hydrazine fragment (Scheme 1).
In acetone, the reaction of [ReOCl3L2] with Hshz produced [ReOCl2
(sha)L] (3), in which sha (see Scheme 1) is the Schiff base product
of acetone and Hshz [7].
Complexes 1–3 were characterized by FTIR, 1H NMR and single
crystal X-ray diffraction. All the data are consistent with their formu-
lation.
½ReCl2ðshzÞðNCCH3ÞL2ꢀð1Þ
The reaction of the substituted hydrazine Hshz with [ReOCl3L2]
produced complex 1, which is similar to what was isolated previous-
ly. The reaction of perrhenate with phenylhydrazines and triphenyl-
phosphine in acetonitrile in the presence of hydrochloric acid
produced the rhenium(III) product [ReCl2(NNC6H4)(NCCH3)L2] [3].
With [ReOCl3L2] and 2-hydrazinopyridine (H2NNHpy) as reactants
in methanol, the complex [ReIIICl2(NNpy)L2] was formed, in which
NNpy acts as a monoanionic diazenido bidentate chelate [4]. However,
by reacting Na[ReO4] with H2NNHpy.2HCl in methanol, a good yield of
[ReIIICl3(N=NpyH)(HN=Npy)] was obtained [8]. The first bis(diaze-
nido) complex of rhenium(III), [ReCl(N2Ph)2 L2], was synthesized by
the reaction of [ReOCl3L2] with a fourfold molar excess of Me3SiN2Ph
in dichloromethane [9].
The infrared spectrum of 1 displays a strong band at 1504 cm−1
typical of ν(N=N). There are two bands, at 458 and 470 cm−1
,
,
which could be assigned to ν(Re-N). A strong band at 1622 cm−1
[ν(C=O)] confirms that the salicylic oxygen atom O(1) is uncoordi-
nated (see Fig. 1). There are no bands in the 3100–3500 cm−1 region
which could be ascribed to ν(N-H). The 1H NMR spectrum only con-
firms the presence of the two PPh3 molecules (a 30 proton multiplet
in the region 7.45–7.76 ppm), the methyl group of CH3CN (a three-
proton singlet at 2.36 ppm), and the four phenylic protons (as two
one-proton doublets and two triplets in the range 6.73–7.40 ppm).
There are no other signals which can be assigned to NH protons.
⁎
Corresponding author. Tel.: +27 41 5044285; fax: +27 41 5044236.
E-mail address: thomas.gerber@nmmu.ac.za (T.I.A. Gerber).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.09.041

70
T.I.A. Gerber et al. / Inorganic Chemistry Communications 15 (2012) 69–72
O
C
O
The N(1)-N(2) bond is double, with a length of 1.248(3) Å. The O
(1)-C(11) bond is double [1.237(3) Å], and the bonding in the mole-
cule is complemented by a O(2)-H O(1) hydrogen bond.
Me
Me
NH2
C
N
C
N
H
acetone
N
H
ðμ−shdÞ½ReOBrðOPPh3Þꢀ2ð2Þ
OH
OH
Hshz
Hsha
The synthetic procedure for the dimer 2 was exactly the same as
for 1, with the only difference being the use of [ReOBr3L2] as the start-
ing material. Complex 2 was isolated in good yield in air, and no re-
duction of the metal occurred. The coordinated phosphines were
oxidized to the oxides, and the bridging ligand shd was formed by
the elimination–condensation reaction of two Hshz molecules. It is
obvious that this unexpected formation of shd is not metal-induced,
and it would seem that the reaction may be bromide initiated. We
cannot explain this phenomenon in any rational way, and no other
examples of this type could be found in the literature.
-
O
C
Me
Me
N
C
N
OH
O
-
A very strong peak at 990 cm−1 in the infrared spectrum of 2 is as-
cribed to the Re=O stretching vibration. This absorption occurs at a
higher frequency that is normally observed for neutral pseudo-
octahedral monooxorhenium(V) complexes [920–970 cm−1] [12], and
is explained by the coordination of the neutral phosphine oxide oxygen
atom in the position trans to the oxo oxygen, instead of the monoanionic
phenolate oxygen of the salicyl group of the ligand shd. The ν(C=O) and
ν(P=O) signals appear at 1602 and 1121 cm−1 respectively. Two
medium-intensity peaks, at 419 and 439 cm−1, are ascribed to ν(Re-O);
the former to the Re–OPPh3 and the latter to the Re-O(phenolate)
bond. There are no signals in the 3100–3500 cm−1 region which could
be assigned to N–H bonds. The 1H NMR spectrum of 2 illustrates the mag-
netic equivalence of the protons on the two salicylic rings of shd, with
only four signals (two doublets and two triplets) in the aromatic region
6.78–6.94 ppm for the eight protons. The only other signals in the spec-
trum are those of the OPPh3 protons, which appear as a multiplet in the
region 7.18–7.67 ppm.
The structure of 2 (Fig. 2) shows that the shd ligand acts as a bridg-
ing tetranegative bis(tridentate) chelate, bridging two [ReOBr(OPPh3)]
units [13]. The dimeric molecule is centrosymmetric around the N(1)-
N(1i) bond [14]. Each rhenium (V) ion lies in a pseudo-octahedral envi-
ronment, with the neutral O(4) of the OPPh3 molecules coordinated
trans to the oxo oxygen O(3) [O(3)-Re-O(4)=171.3(1)˚], which is un-
usual since in all previous six-coordinate monooxorhenium(V)
sha
O
C
N
N
C
O
O
shd4-
Scheme 1. Structures of the ligands in this study.
Green needles of 1, suitable for X-ray crystallography, were
obtained from the evaporation of the filtered reaction solution [10].
The packing in the unit cell shows discrete, monomeric and neutral
molecular units, with no intermolecular contacts shorter than the
Van der Waal's radii sum. The rhenium(III) ion lies in a distorted oc-
tahedral environment (Fig. 1). The two chlorides are cis [Cl(1)-Re-Cl
(2)=90.43(2)˚] to each other, with the diazenide ligand coordinated
in a position trans [N(1)-Re-Cl(2)=176.14(6)˚] to a chloride [11]. The
two PPh3 ligands are trans to each other, with the coordinated aceto-
nitrile trans to the chloride Cl(1). The Re-N(1) bond length of 1.756
(2) Å is shorter than the average of 1.783(3) Å found in three other
similar rhenium(III) diazenide complexes [3]. The Re-N(1)-N(2)
bond angle is essentially linear [171.7(2)˚], and the angle around N
(2) [N(1)-N(2)-C(11)=119.0(2)˚] is typical of sp2 hybridization.
C91
Cl2
C90
N90
O3
i
Re
P1
P2
P1
i
O4
i
Br1
i
i
Cl1
C16
i
C17
O1
C15
Re1
i
N1
C11
O2
C13
C14
N1
i
i
i
C12
O1
N2
C14
C13
i
N1
i
O2
C12
C11
O4
C15
i
C11
Re1
O1
C17
C16
i
Br1
O2
C12
P1
i
C13
C17
O3
C14
C16
C15
Fig. 1. Molecular structure of [ReCl2(shz)(NCCH3)(PPh3)2] (1). The hydrogen atoms on
Fig. 2. ORTEP view of the structure of (μ-shd)[ReOBr(OPPh3)]2 (2), showing the atom-
O(2) and the phenyl rings have been omitted for clarity.
labeling scheme. Hydrogen atoms have been omitted for clarity.

T.I.A. Gerber et al. / Inorganic Chemistry Communications 15 (2012) 69–72
71
complexes containing a phenolate oxygen, it is always the anionic phe-
nolic oxygen which coordinates at the trans site [15]. The rhenium is
lifted by 0.241(1) Å out of the square plane defined by the equatorial
donor atoms Br(1)O(2)N(1)O(1i), which is the result of the steric repul-
sion between these atoms and the oxo oxygen, with the angles O(3)-
Re-Br(1)=92.5(1)˚, O(3)-Re-O(2)=102.2(2)˚, O(3)-Re-N(1)=102.5
(2)˚ and O(3)-Re-O(1i)=96.1(2)˚. The bite angles of the shd ligand are
O(2)-Re-N(1)=90.3(1)˚ (six-membered ring) and N(1)-Re-O(1i)=
77.8(1)˚. The Re-O(4)-P(1) bond angle [157.9(2)˚] is similar to those
found in other rhenium complexes [16].
The Re=O(3) bond length [1.672(3) Å] occurs at the lower end of
the range [1.667(2)–1.702(2) Å] normally observed for octahedral
monooxorhenium(V) complexes, which is probably due to the coor-
dination of a neutral (and not anionic) oxygen atom at the site trans
to O(3) [15,17]. The Re-O(4) length of 2.117(3) Å differs considerably
from Re-O(anionic) lengths, which normally occur in the narrow
range of 1.96(1)–2.01(1) Å [15,17]. The Re-O(2) and Re-O(1i) bond
lengths of 1.969(3) Å and 2.090(3) Å respectively, intimating that O
(2) is charged and O(1i) is a neutral ketonic oxygen. The Re-N(1)
bond distance of 1.983(3) Å is typical of a rhenium (V)-amide bond.
Rhenium(V)-amido and rhenium(V)-amino bonds usually fall in the
ranges 1.91(1)–2.01(1) and 2.11(1)–2.23(1) Å respectively [18]. Nega-
tive charges are therefore supplied to the oxorhenium(V) core by O(2),
N(1) and Br(1), with O(1) and O(4) coordinated as neutral donor
atoms. The N(1)-N(1i) and N(1)-C(11) bonds are single, with lengths
of 1.428(4) and 1.322(6) Å respectively.
O3
C1
C4
P1
N2
C2
Re1
C3
Cl2
N1
O1
C11
Cl1
O2
C16
C12
C15
C13
C14
Fig. 3. View of the molecular structure of [ReOCl2(sha)(PPh3)] (3). The hydrogen atoms
Multidentate ligand-bridged dimers of oxorhenium (V) are rare in
the literature, and dimers of the ReO3+ core are mainly of the oxo-
bridged type [19]. In fact, the coordination chemistry of dinuclear
and polynuclear oxo complexes have received increased attention re-
cently, since these species exhibit structures, reactions and properties
which are unusual for mononuclear complexes [20].
on the phenyl rings have been omitted for clarity.
and 161.58(7)˚ respectively [24]. The metal is lifted out of the mean
equatorial plane formed by Cl2PN by 0.193(1) Å towards O(3).
The Re=O(3) bond length of 1.680(2) Å is within the expected
range [15,17], and the Re-O(1) length of 2.046(2) Å is typical for a
single bond of this kind [25]. The Re-Cl(1) bond is significantly longer
than the Re-Cl(2) one due to the larger trans effect of P compared to
the imino N(2). The bite angle [O(1)-Re-N(2)] of the chelate is
74.18(9)˚. Charge delocalization over the C(3)-N(2)-N(1)-C(1)-O(1)
part of the ligand is indicated by the bond lengths C(3)-N(2) [1.297
(4) Å] and N(1)-C(1) [1.308(4) Å], which are intermediate between
single and double bonds of this nature [15,18,22]. Also, the C(1)-O
(1) bond length of 1.309(4) Å is slightly longer than that for a ketonic
double bond.
½ReOCl2ðshaÞðPPh3Þꢀð3Þ
This complex was prepared by the same procedure which was
used for 1, except that acetone was used as reaction medium. With
trans-[ReOBr3(PPh3)2] and Hshz in acetone, the product [ReOBr2
(sha)(PPh3)] was isolated and characterized [21]. The coordinated
Schiff base ligand sha− was formed by the condensation of acetone
with Hshz. The synthesis is described by the equation
½ReOCl3L2ꢀ þ Hshz þ Me2CO → ½ReOCl2ðshaÞLꢀ þ H2O þ L þ HCl
Appendix A. Supplementary material
Oxorhenium(V) complexes containing bidentate monoanionic N,
O-donor ligands are common in the literature [12,15,22]. No evidence
of reduction of rhenium(V) was found. Also, although the ligand sha
has the potential to act as a bridging ligand (by using N(1) and O(2)
as donor atoms; Fig. 3), only the monomer 3 was isolated.
Supplementary data for 1 (CCDC 837927), 2 (CCDC 837928) and 3
(CCDC 837929) are available from the CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK on request. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif.
The Re=O(3) stretching frequency of 3 was observed at 984 cm−1
in the infrared spectrum, and a medium–intensity band at 412 cm−1
was assigned to ν[Re-O(1)]. Absorptions at 1593 and 1623 cm−1 are
assigned to the coordinated imine C(3)=N(2) and free imine C(1)=
N(1) respectively. In the 1H NMR spectrum the coordinated sha ligand
is characterized by two three-proton singlets at 2.74 and 2.95 ppm, and
two doublets and two triplets in the aromatic range 6.70–7.25 ppm. The
only other signals are those of the protons of PPh3.
Supplementary data to this article can be found online at doi:10.
1016/j.inoche.2011.09.041.
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filtrate over 3 days yielded green crystals, suitable for X-ray crystallographic

72
T.I.A. Gerber et al. / Inorganic Chemistry Communications 15 (2012) 69–72
studies. The crystals were washed with ethanol and diethyl ether. Yield 76 mg
(65% based on Re), m.p. 176 °C. FTIR (KBr pellet): ν(C=O) 1622 s, ν(C=N)
1606 s, ν(Re-N) 457 m, ν(N=N) 458, 470 m cm−1 1H NMR (ppm, DMSO-d6):
7.45-7.76 (m, 30H), 7.40 (d, 1H), 6.95 (t, 1H), 6.80 (d, 1H), 6.73 (t, 1H), 2.36 (s,
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56 mg (78% based on Re), m.p. 324 °C. FTIR (KBr pellet): ν(C=O) 1602 s,
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.
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.
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[10] Crystallographic data for C45H38Cl2N3O2P2Re (1) : monoclinic; space group P21/c;
a=13.9960(3), b=14.4440(2), c=23.1601(4) Å, β=121.228(1)˚; V=4003.6
(1) Å3; Z=4; Dc =1.612 Mg/m3; μ=3.291 mm−1; data/ restraints/parameters:
9941/0/498; S=1.14; final R indices [IN2σ(I)]: R1=0.0198, wR2=0.0460.
[11] Selected bond lengths (Å) and angles (˚) for 1: Re-Cl(1)=2.4215(6), Re-Cl(2)=2.4293
(6), Re-P(1)=2.4730(6), Re-P(2)=2.4650(7), Re-N(1)=1.756(2), Re-N(90)=2.057
(2), N(1)-N(2)=1.248(3), C(11)-O(1)=1.237(3), C(13)-O(2)=1.332(3); Cl(1)-Re-
Cl(2)=90.43(2), P(1)-Re-P(2)=176.04(2), N(1)-Re-Cl(2)=176.14(6), Cl(1)-Re-N
(90)=169.72(6), Re-N(1)-N(2)=171.7(2), N(1)-N(2)-C(11)=119.0(2), N(2)-C
(11)-C(12)=114.1(2), Cl(1)-Re-P(1)=90.97(2), Cl(1)-Re-P(2)=90.98(2).
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Chemical Society Dalton Transactions (1989) 1405;
P. Mayer, E. Hosten, T.I.A. Gerber, A. Abrahams, Bulletin of the Korean Chemical
Society 30 (2009) 1204.
[21] A mixture of trans-[ReOBr3L2] (100 mg, 103 μmol) and Hshz (33 mg, 214 μmol) in
15 cm3 of acetone was heated under reflux for 5 h. The solution was cooled to
room temperature and filtered to give a dark green solution. The reduction of
the solvent under vacuum to about 3 cm3 gave a green precipitate, which was fil-
tered off and dried. Recrystallization from acetone/ethanol gave green crystals.
Yield 39 mg (46% based on Re), m.p. 127 °C. Anal. Calcd. for C28H26Br2N2O3PRe:
C, 41.24; H, 3.21; N, 3.44%. Found: C, 41.47; H, 3.38; N, 3.29%. FTIR (KBr pellet):
ν(C=N) 1593 s, ν(C-O) 1250 s, ν(Re=O) 981 s, ν(Re-N) 459 m, ν(Re-O)
416 m cm−1 1H NMR (ppm, DMSO-d6): 7.58-7.73 (m, 16H), 7.54 (t, 1H), 7.24
.
(d, 1H), 6.98 (t, 1H), 2.57 (s, 3H), 2.14 (s, 3H).
[22] V. Bertolasi, M. Sacerdoti, G. Gilli, U. Mazzi, Acta Crystallographica Section B 38
(1982) 426;
U. Mazzi, E. Roncari, R. Rossi, V. Bertolasi, O. Traverso, L. Magon, Transition Metal
Chemistry 5 (1980) 289;
A. Skarzynska, W.K. Rybak, T. Glowiak, Polyhedron 20 (2001) 2667.
A. Marchi, A. Duatti, R. Rossi, L. Magon, U. Mazzi, A. Pasquetto, Inorganica Chi-
mica Acta 81 (1984) 15;
[13] Crystallographic data for
C50H38Br2N2O8P2Re2 (2): monoclinic; space group
P21/n; a=14.0740(4), b=10.5020(3), c=16.4620(5) Å, β=104.011(1)˚;
T.I.A. Gerber, D. Luzipo, P. Mayer, Journal of Coordination Chemistry 57 (2004)
1345.
V=2360.8(1) Å3; Z=2; Dc =1.954 Mg/m3; μ=6.940 mm−1; data/restraints/
parameters
wR2=0.0792.
:
5831/0/298; S=1.03; final
R
indices [IN2σ(I)]: R1=0.0310,
[23] Crystallographic data for C28H26Cl2N2O3PRe (3): monoclinic; space group P21/c;
a=9.6460(6), b=18.712(1), c=15.2230(9) Å, β=96.845(2)˚; V=2728.1(3)
[14] Selected bond lengths (Å) and angles (˚) for 2: Re-Br(1)=2.5368(6), Re-O(3)=
1.672(3), Re-O(2)=1.969(3), Re-O(4)=2.117(3), Re-N(1)=1.983(3), Re-O(1i)=
2.090(3), P(1)-O(4)=1.509(3), O(1)-C(11)=1.287(5), O(2)-C(13)=1.348(6), N
(1)-C(11)=1.322(6), N(1)-N(1i)=1.428(4); O(3)-Re-O(4)=171.3(1), N(1)-Re-Br
(1)=164.7(1), O(2)-Re-O(1i)=160.0(1), C(11)-N(1)-N(1i)=113.2(3), Re-N(1)-N
(1i)=115.0(3), N(1)-C(11)-C(12)=118.9(4), Re-O(2)-C(13)=124.4(3), Rei-O(1)-
C(11)=112.7(3).
Å3; Z=4; Dc =1.769 Mg/m3; μ=4.742 mm−1
; data/restraints/parameters:
6504/0/337; S=1.16; final R indices [IN2σ(I)]: R1=0.0276, wR2=0.0615.
[24] Selected bond lengths (Å) and angles (˚) for 3 : Re-O(3)=1.680(2), Re-O(1)=2.046
(2), Re-Cl(1)=2.371(1), Re-Cl(2)=2.3324(9), Re-P(1)=2.4791(9), Re-N(2)=
2.153(3), C(3)-N(2)=1.297(4), C(1)-N(1)=1.308(4), N(1)-N(2)=1.395(4),
C
(1)-O(1)=1.309(4); O(1)-Re-O(3)=162.1(1), O(3)-Re-P(1)=84.1(1), O(3)-Re-
Cl(1)=102.5(1), O(3)-Re-Cl(2)=104.94(8), O(3)-Re-N(2)=93.3(1), C(3)-N(2)-
N(1)=115.2(3), N(2)-N(1)-C(1)=112.4(3), N(1)-C(1)-O(1)=121.7(3).
[25] F.A. Cotton, S.J. Lippard, Inorganic Chemistry 4 (1965) 1621.
[15] J.Y. Kim, Y.J. Ji, H.-J. Ha, H.K. Chae, Bulletin of the Korean Chemical Society 24
(2003) 504;