Tricarbonyl complexes of rhenium(I) with acetylpyridine benzoylhydrazone and related ligands

Article abstract of DOI:10.1002/zaac.200390048

Novel rhenium(I) tricarbonyl complexes have been prepared by reactions of (Et₄N)₂[Re(CO)₃Br₃] with acetylpyridine benzoylhydrazone, Hapbhyd, di(2-pyridyl)ketone benzoylhydrazone, Hpy₂bhyd, bis(2-pyridine)ketone, py₂CO, and pyridinealdehyde terephtalaldehydebishydrazone, pytehyd. The ligands remain protonated when no supporting base is added and the following complexes have been isolated: [Re(CO)₃Br(Hapbhyd)], [Re(CO)₃Br(Hpy₂bhyd-py,hyd)], [Re(CO)₃Br(Hpy₂bhyd-py¹,py²)], [Re(CO)₃Br(py₂CO-N,N)] and [Re(CO)₃Br(pytehyd)]. Addition of triethyl amine results in deprotonation of Hapbhyd and the formation of [Re(CO)₃(OH₂)(apbhyd)], whereas Hpy₂bhyd is hydrolysed and a rhenium complex with the monoanionic bis(2-pyridyl)hydroxymethanolato ligand, {py₂C(OH)O}^-, is formed. The same compound, [Re(CO)₃{py₂C(OH)O}], is obtained when triethyl amine and water are added to a mixture of (Et₄N)₂[Re(CO)₃Br₃] and py₂CO. The air-stable products have been studied by spectroscopic methods and X-ray crystallography.

Full text of DOI:10.1002/zaac.200390048

Tricarbonyl Complexes of Rhenium(I) with Acetylpyridine Benzoylhydrazone
and Related Ligands
Jacqueline Grewea, Adelheid Hagenbacha, Brigitte Stromburga, Roger Albertob, Ezequiel Vazquez-Lopezc and
Ulrich Abrama*
a
Berlin, Institute of Chemistry of the Freie Universität Berlin
b
Zurich/Switzerland, Institute of Inorganic Chemistry of the University
c
Vigo, Galicia/Spain, Department of Inorganic Chemistry of the University
Received November 15th, 2002.
th
˜
Dedicated to Professor Alfonso Castineiras on the Occasion of his 60 Birthday
Abstract. Novel rhenium(I) tricarbonyl complexes have been pre-
pared by reactions of (Et4N)2[Re(CO)3Br3] with acetylpyridine ben-
zoylhydrazone, Hapbhyd, di(2-pyridyl)ketone benzoylhydrazone,
Hpy2bhyd, bis(2-pyridine)ketone, py2CO, and pyridinealdehyde
terephtalaldehydebishydrazone, pytehyd. The ligands remain pro-
tonated when no supporting base is added and the following com-
plexes have been isolated: [Re(CO)3Br(Hapbhyd)], [Re(CO)3-
Br(Hpy2bhyd-py,hyd)], [Re(CO)3Br(Hpy2bhyd-py1,py2)], [Re(CO)3-
Br(py2CO-N,N)] and [Re(CO)3Br(pytehyd)]. Addition of triethyl
amine results in deprotonation of Hapbhyd and the formation of
[Re(CO)3(OH2)(apbhyd)], whereas Hpy2bhyd is hydrolysed and a
rhenium complex with the monoanionic bis(2-pyridyl)hydroxyme-
thanolato ligand, {py2C(OH)O}-, is formed. The same compound,
[Re(CO)3{py2C(OH)O}], is obtained when triethyl amine and water
are added to a mixture of (Et4N)2[Re(CO)3Br3] and py2CO.
The air-stable products have been studied by spectroscopic methods
and X-ray crystallography.
Keywords: Rhenium; Benzoylhydrazones; Carbonyls; Crystal struc-
ture
Tricarbonylkomplexe von Rhenium(I) mit Acetylpyridinbenzoylhydrazon und
verwandten Liganden
Inhaltsübersicht. Durch Reaktionen von (Et4N)2[Re(CO)3Br3] mit
Acetylpyridinbenzoylhydrazon, Hapbhyd, Di(2-pyridyl)ketonben-
zoylhydrazon, Hpy2bhyd, Bis(2-pyridyl)keton, py2CO, und Pyridi-
naldehydterephtalaldehydbishydrazon, pytehyd, wurden neue Rhe-
nium(I)-Tricarbonylkomplexe hergestellt und charakterisiert. Ohne
Zugabe von Hilfsbasen koordinieren die Hydrazone als Neutral-
liganden und es konnten folgende Produkte isoliert werden: [Re-
(CO)3Br(Hapbhyd)], [Re(CO)3Br(Hpy2bhyd-py,hyd)], [Re(CO)3-
Br(Hpy2bhyd-py1,py2)], [Re(CO)3Br(py2CO-N,N)] und [Re(CO)3-
Br(pytehyd)]. Durch die Zugabe von Triethylamin erfolgt eine
Deprotonierung von Hapbhyd, was zur Bildung von [Re(CO)3-
(OH2)(apbhyd)] führt. Eine analoge Reaktion mit Hpy2bhyd führt
zur Hydrolyse des Proliganden und es entsteht ein Rheniumkom-
plex mit dem monoanionischen Bis(2-pyridyl)hydroxymethanolato-
Liganden, {py2C(OH)O}Ϫ. Die gleiche Verbindung, [Re(CO)3-
{py2C(OH)O}], entsteht nach Zugabe von Triethylamin und Was-
ser zu einer Mischung aus (Et4N)2[Re(CO)3Br3] und py2CO.
Die luftstabilen Produkte wurden mit spektroskopischen Methoden
und durch Röntgenkristallstrukturanalysen untersucht.
Introduction
T1/2 ϭ 90.64 h) and 188Re (Emax ϭ 2.1 MeV, T1/2 ϭ 16.98
h) are under discussion for radioimmuno therapy [3].
The co-ordination chemistry of rhenium and technetium at-
tract a considerable interest due to the nuclear medical ap-
plications of the γ- and βϪ-emitting nuclides of the ele-
ments. 99mTc (pure γ-emitter, Eγ ϭ 300 keV, half-life
T1/2 ϭ 6.0 h) is the “working horse” in the diagnostic nu-
clear medicine [1]. More than 80 per cent of the routine
studies in this field are done with this artificial element [2].
The βϪ-emitting rhenium isotopes 186Re (Emax ϭ 1.1 MeV,
A facile approach to carbonyl complexes of the elements
by a normal pressure synthesis [4] opened the door to the
application of low-valent carbonyl compounds for nuclear
medical purposes. The co-ordination behaviour of the
[M(CO)3]ϩ cores (M ϭ Tc, Re) has been studied in numer-
ous papers [4Ϫ6]. Knowledge of preferred co-ordination
sites and donor atom arrangements is important for the de-
signing of new metal-based radiopharmaceuticals indepen-
dent of the preferred labelling concept (direct labelling or
bifunctional approach) [6]. Particularly stable bonds have
been found between the [M(CO)3]ϩ core (M ϭ Re, Tc) and
nitrogen donor ligands of aromatic rings [7] which make
multidentate ligands containing pyridine or imidazole sub-
stituents interesting for further studies.
* Prof. Dr. Ulrich Abram
Institut für Chemie
Fabeckstr. 34Ϫ36
Freie Universität Berlin
D-14195 Berlin
Email: abram@chemie.fu-berlin.de
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 0044Ϫ2313/03/629/303Ϫ311 $ 20.00ϩ.50/0
303

J. Grewe, A. Hagenbach, B. Stromburg, R. Alberto, E. Vazquez-Lopez, U. Abram
In the present paper we report the complex formation of
the rhenium(I) tricarbonyl moiety with acetylpyridine ben-
zoylhydrazone, Hapbhyd, and the related ligands bis(2-pyri-
dyl)ketone benzoylhydrazone, Hpy2bhyd, bis(2-pyridine)ke-
tone, py2CO, and pyridinealdehyde terephtalaldehydebishy-
drazone, pytehyd.
Figure 1 Ellipsoid presentation [21] of [Re(CO)3Br(Hapbhyd)].
Thermal ellipsoids represent 50 per cent probability.
˚
Table 1 Selected bond lengths/A and angles/° for [Re(CO)3-
Results and Discussion
Br(Hapbhyd)] and [Re(CO)3(OH2)(apbhyd)]
The reaction of [Re(CO)3Br3]2Ϫ with Hapbhyd yields differ-
ent products depending on the conditions applied. This is
mainly due to the protonation/deprotonation of the NH
function of the hydrazone ligands. All reactions have been
performed on air in solvents which have not been dried un-
less otherwise stated.
Orange-red crystals of [Re(CO)3Br(Hapbhyd)] are
formed when equimolare amounts of (Et4N)2[Re(CO)3Br3]
and the ligand are dissolved in methanol and heated under
reflux. Increasing the amount of hydrazone ligand does not
yield another product but causes problems during the iso-
lation of a pure compound.
The complex is soluble in organic solvents like CHCl3 or
acetone. Its infrared spectrum shows the typical pattern for
a facial tricarbonyl moiety with bands at 2020, 1895 and
1870 cmϪ1. The position of the benzoyl CϭO band is al-
most the same as in the unco-ordinated hydrazone. A ba-
thochromic shift has been found for the CϭN band, while
the NH band is still present in the spectrum of the complex.
This suggests a co-ordination of the potentially tridentate
Hapbhyd only via the pyridine/hydrazone site without de-
protonation. The spectroscopic results are verified by the
structure analysis of the compound. An ellipsoid represen-
tation of the complex molecule is given in Fig. 1 showing
the rhenium atom in [Re(CO)3Br(Hapbhyd)] in a distorted
octahedral environment. Main distortions from an ideal oc-
tahedron are due to the small bite angle of the 5-membered
chelate ring which is only 73.1°. The Re-N and Re-Br bond
lengths are in the same range as previously observed for
other fac-Re(CO)3 complexes [6]. A summary of selected
bond lengths and angles are summarised in Table 1.
Deprotonation of the Hapbhyd ligand can be achieved
when triethyl amine is added. The reaction with (Et4N)2[Re-
(CO)3Br3] then gives [Re(CO)3(OH2)(apbhyd)]. The water
ligand is taken from the solvent, which has not been dried
for the reactions reported in this paper. Applying dried
methanol decreases the yield of the product. No evidence
was found for the cleavage of the C-N bond to the benzoyl
[Re(CO)3Br(Hapbhyd)]
[Re(CO)3(OH2)(apbhyd)]
Re-C10
Re-C20
Re-C30
Re-Br/O1
Re-N1
Re-N2
C6-C7
1.899(8)
1.907(8)
1.904(8)
2.6183(8)
2.158(5)
2.167(5)
1.475(9)
1.48(1)
1.290(8)
1.403(7)
1.374(9)
1.215(9)
1.89(1)
1.925(8)
1.913(9)
2.175(6)
2.168(6)
2.175(6)
1.44(1)
C7-C8
1.48(1)
C7-N2
N2-N3
N3-C27
C27-O28
1.296(9)
1.394(9)
1.30(1)
1.300(9)
Re-N1-C6
N1-C6-C7
C6-C7-N2
C7-N2-Re
116.8(4)
114.8(6)
114.0(6)
119.6(4)
179.6(2)
92.2(2)
91.2(2)
87.7(1)
82.2(2)
87.8(3)
89.1(3)
95.3(3)
97.5(3)
90.1(3)
170.2(3)
97.4(3)
99.2(3)
170.2(2)
73.1(2)
115.6(5)
116.5(6)
115.7(6)
117.9(5)
174.1(3)
93.1(3)
96.6(3)
82.1(2)
79.4(2)
88.2(4)
89.2(4)
95.9(3)
94.7(3)
88.6(4)
172.3(3)
99.3(3)
98.0(3)
171.3(3)
73.9(2)
Br/O1-Re-C10
Br/O1-Re-C20
Br/O1-Re-C30
Br/O1-Re-N1
Br/O1-Re-N2
C10-Re-C20
C10-Re-C30
C10-Re-N1
C10-Re-N2
C20-Re-C30
C20-Re-N1
C20-Re-N2
C30-Re-N1
C30-Re-N2
N1-Re-N2
group and the formation of benzoic acid as has been ob-
served for a formylpyridine benzoylhydrazone complex of
technetium [6], neither the formation of anionic species or
complexes with co-ordinated methanol ligands instead of
water has been detected. The bonding situation in [Re-
(CO)3(OH2)(apbhyd)] (Fig. 2) is very similar to that in [Re-
(CO)3Br(Hapbhyd)]. Deprotonation of the hydrazone does
not cause significant changes in the bond lengths inside the
chelate rings. The CϭN bond length is only slightly length-
˚
ened by 0.005 A. However, a shortening of the N3-C27
304
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311

Tricarbonyl Complexes of Rhenium(I) with Acetylpyridine Benzoylhydrazone
the carbonyl ligand requires a more flexible ligand system
to realise a three-dentate N,N,O co-ordination as has been
demonstrated for [Re(CO)3(histidinate)] [6] or [Tc(CO)3-
(picac)] (picac- ϭ picolineamine-N-acetato-N-acetic acid)]
[7]. The CϭN double bonds in the hydrazones under study,
however, require a planar co-ordination as has been found
in numerous transition metal complexes.
Three different products have been isolated from reac-
tions of (Et4N)2[Re(CO)3Br3] with Hpy2bhyd. As with
Hapbhyd, the ligand remains protonated when no support-
ing base is added. The second pyridine donor site, however,
allows two different bidentate co-ordination modes using
the nitrogen donor atoms exclusively. The sp2 hybridisation
of the central carbon atom (C7) prevents from a tridentate
N,N,N co-ordination mode and the results with Hapbhyd
described above make a complex formation of the benzoyl
group with the rhenium(I) tricarbonyl core less probable.
No obvious preference of one of the possible donor site
combinations (pyridine/pyridine or pyridine/hydrazone) has
been observed. Products of the composition [Re(CO)-
Br(Hpy2bhyd-py1,py2] and [Re(CO)3Br(Hpy2bhyd-py,hyd)]
are formed parallely when (Et4N)2[Re(CO)3Br3] and
Hpy2bhyd are heated on reflux in methanol without the ad-
dition of a supporting base. The percentage of their forma-
tion approximately agrees with the expected 1:2 ratio. The
two isomers can be separated applying their different solu-
bility. Yellow blocks of [Re(CO)3Br(Hpy2bhyd-py1,py2] de-
posit directly from the reaction mixture upon concentration
whereas the second product can be isolated from the oily
residue which is obtained upon complete removal of the
solvent. Re-dissolution in THF and overlayering with n-
hexane gives orange-red crystals of [Re(CO)3Br(Hpy2bhyd-
py1,hyd] · THF. The infrared spectra of both complexes
show the typical pattern of the fac-[Re(CO)3]ϩ core and
suggest non-co-ordinating benzoyl groups by the presence
of CϭO frequencies at 1680 cm-1 which resembles with the
value of the carbonyl band in Hpy2bhyd. FABϩ mass spec-
tra of both isomers show no significant differences.
Figure 2 Ellipsoid presentation [21] of [Re(CO)3(OH2)(apbhyd)].
Thermal ellipsoids represent 50 per cent probability.
Scheme 1
bond together with the lengthening of the C27-O28 bond is
observed which suggests that the negative charge of the li-
gand is widely delocalised over the benzoyl moiety which
does not contribute to the co-ordination of the metal. A
comparison of the bond length situation in the acetylpyrid-
ine benzoylhydrazone moieties in [Re(CO)3Br(Hapbhyd)]
and [Re(CO)3(OH2)(apbhyd)] is given in Scheme 1. The val-
ues in brackets represent those in the aqua complex. More
bond lengths and angles are summarised in Table 1. An
intramolecular hydrogen bond between O1 and O28 (see
Fig. 2) causes a change in the conformation of the complex
molecule. The crystallographic results are confirmed by the
spectroscopic data. While the IR bands of the CϭO vi-
brations occur at almost the same position, the CϭN band
of the aqua complex is bathochromically shifted which indi-
cates a weakening of the double bond. FABϩ mass spectra
of both complexes show no evidence for the molecular ion
peaks. Preferably the bonds to the BrϪ or the H2O ligands
are cleaved giving evidence for the peaks at m/z ϭ 510. Sub-
sequently the three carbonyl ligands are lost.
The molecular structure of [Re(CO)Br(Hpy2bhyd-
py1,py2] is illustrated in Fig. 3. The co-ordination sphere of
the rhenium atom is a distorted octahedron. Main distor-
tions are due to the restricting geometric parameters of the
chelating ligand. The six-membered chelate ring causes an
N1-Re-N31 angle of 83.1(3)°. The bonding parameters of
the hydrazone unit are almost uninfluenced by the complex
formation. The Re-N bond lengths are 2.217(7) and
˚
2.204(7) A which is somewhat longer than those in the ace-
tylpyridine hydrazone complexes discussed above. This can
be attributed to the different sizes of the chelate rings and
has also been found for the other few examples of rhenium
tricarbonyl complexes with six-membered N,N chelate rings
[8,9]. The angular strain inside the six-membered ring can
clearly be derived from the angles around the carbon atom
C7. The chelate ring is in boat conformation to minimize
the strains (Scheme 2). This, however is restricted by repul-
sions between the bulky hydrazone unit and the pyridine
rings.
The fact that the benzoyl moieties of the Hacpbhyd or
acpbhydϪ ligands do not contribute to the co-ordination of
rhenium is not unexpected and underlines the high tend-
ency of the [Re(CO)3]ϩ core to bind to nitrogen donors and
provides a reactive site in the complexes which can be used
for the coupling of biomolecules. The facial arrangement of
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311
305

J. Grewe, A. Hagenbach, B. Stromburg, R. Alberto, E. Vazquez-Lopez, U. Abram
˚
Table 2 Selected bond lengths/A and angles/° for [Re(CO)3-
Br(Hpy2bhyd-py,hyd)] and [Re(CO)3Br(Hpy2bhyd-py1,py2)]
[Re(CO)3-
[Re(CO)3-
Br(Hpy2bhyd-py,hyd)]*
Br(Hpy2bhyd-py1,py2)]
Re-C10
Re-C20
Re-C30
Re-Br
Re-N1
Re-N2/N31
C6-C7
C7-C36
C7-N2
N2-N3
N3-C27
C27-O28
1.904(9)
1.93(1)
1.92(1)
2.602(1)
2.217(7)
2.204(7)
1.49(1)
1.48(1)
1.30(1)
1.360(9)
1.38(1)
1.22(1)
1.93(1)
1.911(8)
1.90(1)
2.615(1)
2.167(7)
2.197(7)
1.44(1)
1.49(1)
1.29(1)
1.39(1)
1.36(1)
1.20(1)
Re-N1-C6
N1-C6-C7
C6-C7-N2
C7-N2-Re
C6-C7-C36
C7-C36-N31
C36-N31-Re
Br-Re-C10
Br-Re-C20
Br-Re-C30
121.2(5)
116.5(7)
113.5(7)
Ϫ
115.5(6)
116.2(7)
115.4(7)
117.5(5)
121.2(8)
112.8(9)
Ϫ
175.7(3)
92.0(3)
93.9(3)
86.3(2)
81.3(2)
89.4(4)
90.2(5)
91.8(3)
94.5(4)
88.5(7)
172.0(6)
98.4(6)
99.4(4)
171.7(3)
73.7(3)
117.4(7)
118.9(7)
119.2(5)
177.7(3)
88.8(3)
93.9(3)
85.7(2)
86.3(2)
91.3(4)
88.4(4)
94.2(3)
91.3(3)
88.3(4)
174.5(3)
95.8(4)
92.8(3)
175.9(3)
83.1(3)
Figure 3 Ellipsoid presentation [21] of [Re(CO)3Br(Hpy2bhyd-
py1,py2)]. Thermal ellipsoids represent 50 per cent probability.
Br-Re-N1
Br-Re-N2/N31
C10-Re-C20
C10-Re-C30
C10-Re-N1
C10-Re-N2/N31
C20-Re-C30
C20-Re-N1
C20-Re-N2/N31
C30-Re-N1
C30-Re-N2/N31
N1-Re-N2/N31
Scheme 2
˚
Hydrogen bond: N3-H3...O40 (x, 1ϩy, z) d(D-H) 0.81(11) A, d(H...A)
1.97(11) A, d(D...A) 2.764(12) A, <(DHA) 166(10)°
˚
˚
distortions of the octahedral co-ordination sphere by the
influence of the 5-membered chelate ring as has been dis-
cussed previously for [Re(CO)3Br(Hacpybhyd)] and [Re-
(CO)3(OH2)(acpybhyd)]. Selected bond lengths and angles
of
[Re(CO)Br(Hpy2bhyd-py1,hyd]
and
[Re(CO)Br-
(Hpy2bhyd-py1,py2] are compared in Table 2.
In contrast to the reaction of (Et4N)2[Re(CO)3Br3] with
Hapbhyd, where the addition of a supporting base results
in the deprotonation of the hydrazone and the formation
of [Re(CO)3(OH2)(apbhyd)], Hpy2bhyd is hydrolysed upon
addition of Et3N and finally [Re(CO)3{py2C(O)OH}], a
complex with a tridentately bonded bis(2-pyridyl)hydroxy-
methanolato ligand is obtained. The compound can also be
isolated from reactions of (Et4N)2[Re(CO)3Br3] with bis(2-
pyridyl)ketone and Et3N or (in less yields) from the hy-
drolysis of [Re(CO)3Br(Hpy2bhyd-py1,py2)]. This, and the
fact that hydrolysis of neat Hpy2bhyd or py2CO under com-
parable conditions proceeds very slowly and under de-
composition of the products, suggest that the nucleophilic
attack of water is metal-promoted in the cases described
above. The hydrolysis or alcoholysis of py2CO in the pres-
ence of metalions and complex-formation with the resulting
Figure 4 Ellipsoid presentation [21] of [Re(CO)3Br(Hpy2bhyd-py,
hyd)]. Thermal ellipsoids represent 50 per cent probability.
Fig. 4 shows the molecular structure of [Re(CO)-
Br(Hpy2bhyd-py1,hyd]. The compound co-crystallises with
a molecule of solvent THF and a hydrogen bond between
H3 and the oxygen atom of the solvent is established. The
rhenium atom is six-co-ordinate with the same extend of
306
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311

Tricarbonyl Complexes of Rhenium(I) with Acetylpyridine Benzoylhydrazone
Figure 6 Ellipsoid presentation [21] of [Re(CO)3Br(py2CO)]. Ther-
Figure 5 Ellipsoid presentation [21] of [Re(CO)3{py2C(OH)O})].
Thermal ellipsoids represent 50 per cent probability.
mal ellipsoids represent 50 per cent probability. A disorder of 50
per cent occupancy between the Br atom and the carbonyl group
C10/O10 have been omitted for clarity.
diol is not without precedent. Besides numerous multi-
nuclear compounds with bridging [py2C(OH)2]0,
[py2C(OH)O]Ϫ and [py2CO2]2Ϫ units, a number of mononu-
clear complexes has been isolated containing bis(2-pyridyl)-
methanediol as neutral N,N’-bonded ligand [10]. Tridentate
co-ordination of the neutral ligand has been observed for
Cu2ϩ and Ni2ϩ complexes [11], whereas its singly depro-
tonated forms is present in chromium, cobalt, ruthenium
or antimony compounds [12] as well as in the rhenium(V)
complex [ReOCl2{py2C(OH)O}] which has been prepared
from [ReOCl3(Ph3P)2] and py2CO in THF [13]. The forma-
tion of [Re(CO)3{py2C(OH)O}] from the hydrolysis of [Re-
(CO)3Cl(py2CO)] has been studied spectroscopically and an
extended electrochemical report has bee given [14].
The ready metal-promoted hydrolysis of Hpy2bhyd may
be attributed to the angular strain in [Re(CO)3Br-
(Hpy2bhyd)] which is induced by the formation of the non-
planar six-membered chelate ring (Fig. 3) and can also be
seen from the lengthening of the Re-N(pyridine) bond
length. The hybridisation of the carbon atom C7 is changed
to sp3 upon hydrolysis and the resulting bond angles at C7
come close to the tetrahedral angle. A representation of the
structure of [Re(CO)3{py2C(OH)O}] is given in Fig. 5.
Selected bond lengths and angles are summarised in Table
3 and compared with the corresponding values in [Re-
(CO)3Br(py2CO)].
The latter compound is obtained when equivalent
amounts of (Et4N)2[Re(CO)3Br3] and py2CO are heated on
reflux in acetonitrile. Hydrolysis and the formation of
[Re(CO)3{py2C(OH)O}] is only observed when consider-
able amounts of water are added. This is remarkable since
attempts to prepare [ReOCl3{py2CO}] with an intact and
unco-ordinated ketone group failed even when unaerobic
conditions were applied [13a]. [Re(CO)3Br(py2CO)] is an
Figure 7 Ellipsoid presentation [21] of [Re(CO)3Br(pytehyd)]. Ther-
mal ellipsoids represent 50 per cent probability.
air-stable orange-red solid which is readily soluble in polar
organic solvents. The IR frequency of the keto group can
be assigned at 1685 cmϪ1 which is slightly shifted compared
with the value of the unco-ordinated py2CO (1675 cmϪ1).
The FABϩ mass spectrum shows a less intense peak for the
molecular ion at m/z ϭ 534/536 (corresponding to the 1:1
isotopic pattern of 79,81Br) and a fragment peak rep-
resenting [Re(CO)3(py2CO)]ϩ. The solid state structure of
[Re(CO)3Br(py2CO)] is one of the few examples where
py2CO is chelate bonded to a single metal atom. To our
knowledge there are only two other examples, a plati-
num(II) complex with an additional cyclobutanedicarboxyl-
ato ligand [15] and a chlorobridged ruthenium(II) dimer
[16].
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311
307

J. Grewe, A. Hagenbach, B. Stromburg, R. Alberto, E. Vazquez-Lopez, U. Abram
˚
˚
Table
3
Selected bond lengths/A and angles/° for
Table 4 Selected bond lengths/A and angles/° for [Re(CO)3-
[Re(CO)3{py2C(OH)O}] and [Re(CO)3Br(py2CO)]
Br(pytehyd]
[Re(CO)3{py2C(OH)O}]
[Re(CO)3Br(py2CO)]
Re-C10
Re-C20
Re-C30
Re-Br
Re-N1
Re-N2
1.900(7)
1.919(8)
1.909(9)
2.620(1)
2.165(5)
2.195(5)
1.147(8)
1.126(9)
C30-O30
N1-C6
C6-C7
1.125(9)
1.355(8)
1.447(9)
1.276(9)
1.399(7)
1.260(9)
1.46(1)
Re-C10
Re-C20
Re-C30
Re-O71/Br
Re-N1
Re-N11
C7-O71/O7
C7-O72
1.892(7)
1.925(8)
1.923(7)
2.101(4)
2.185(5)
2.180(5)
1.397(7)
1.388(7)
1.85(3)
1.897(8)
Ϫ
2.573(6)
2.201(6)
Ϫ
C7-N2
N2-N3
N3-C27
C27-C21
C10-O10
C20-O20
1.30(2)
Ϫ
C10-Re-C20
C10-Re-C30
C10-Re-Br
C10-Re-N1
C10-Re-N2
C20-Re-C30
C20-Re-Br
C20-Re-N1
C20-Re-N2
C30-Re-Br
C30-Re-N1
C30-Re-N2
Br-Re-N1
87.7(3)
90.5(3)
93.8(3)
94.6(3)
168.6(3)
90.7(4)
91.3(3)
175.5(3)
103.5(3)
175.3(2)
93.2(2)
91.6(2)
84.6(1)
Br-Re-N2
83.8(1)
74.1(2)
1176.3(7)
178.1(8)
179.2(6)
116.8(4)
113.6)6)
119.8(6)
115.5(4)
132.7(4)
114.9(6)
111.1(5)
Ϫ
N1-Re-N2
Re-C10-O10
Re-C20-O20
Re-C30-O30
Re-N1-C6
N1-C6-C7
C6-C7-N2
Re-N2-C7
Re-N2-N3
N2-N3-C27
C7-N2-C3
Re-N1-C6
N1-C6-C7
112.4(4)
111.6(5)
106.2(5)
111.9(4)
170.1(3)
97.9(2)
96.6(2)
75.3(2)
74.5(2)
89.1(3)
90.3(3)
97.5(3)
98.0(3)
91.5(3)
172.9(2)
94.5(2)
91.3(3)
169.8(2)
81.8(2)
121.8(5)
120.1(7)
121.0(9)
Ϫ*
178.9(9)
90.9(3)
Ϫ*
88.0(2)
Ϫ*
89.9(6)
Ϫ*
91.2(6)
Ϫ*
Ϫ*
93.6(3)
176.6(3)
Ϫ*
C6-C7-C16/C6’
C16-N11-Re
O71/Br-Re-C10
O71/Br-Re-C20
O71/Br-Re-C30
O71/Br-Re-N1
O71/Br-Re-N11
C10-Re-C20
C10-Re-C30
C10-Re-N1
C10-Re-N11
C20-Re-C30
C20-Re-N1
C20-Re-N11/N1’
C30-Re-N1
Orange-red crystals of [Re(CO)3Br(pytehyd)] were ob-
tained when equivalent amounts of (Et4N)2[Re(CO)3Br3]
and pytehyd were heated under reflux in ethanol. As with
the ligands described above, chelate formation is obtained
with pytehyd. A 5-membered chelate ring is obtained using
the pyridine and hydrazone donor sites as has been ob-
served for [Re(CO)3Br(Hapbhyd)], [Re(CO)3(OH2)-
(apbhyd)] or [Re(CO)3Br(Hpy2bhyd-py,hyd)]. Thus the en-
vironment is very similar to the situation in these com-
plexes. The molecular structure of [Re(CO)3Br(pytehyd)] is
illustrated in Fig. 7. Selected bond lengths and angles are
summarised in Table 4. The most remarkable feature of the
compound is the presence of the reactive formyl group
which allows further substitution reactions at the co-ordi-
nated ligand. This favours this compound for coupling reac-
tions with biomolecules.
C30-Re-N11
N1-Re-N11/N1’
Ϫ*
83.2(3)
Symmetry operation: (‘) x, 0.5-y, z; * symmetry related atoms
An ellipsoid representation of the structure of [Re-
(CO)3Br(py2CO)] is given in Fig. 6. A summary of selected
bond lengths is contained in Table 3. The co-ordination en-
vironment of the rhenium atom is a distorted octahedron
in which the distortions are due to the limiting bite angle
of the chelate ligand (N1-Re-N1’: 83.2(3)°). As discussed
above for [Re(CO)3Br(Hpy2bhyd-py1,py2)], the Re-N bonds
are slightly longer than the other Re-N(pyridine) bonds.
The six-membered chelate ring is in boat conformation min-
imising the angular strain at the carbon atom C7. This
strain is less than in [Re(CO)3Br(Hpy2bhyd-py1,py2)] as can
be derived from the bond angles around C7. The values of
118.6, 118.6 and 121.0° for [Re(CO)3Br(py2CO)] come
much closer to the ideal value of 120° for an idealised sp2
hybridised atom than the corresponding angles in the hy-
drazone complex: 113.5, 117.4 and 128.7°. This should be
addressed to sterical interactions with the non-co-ordinated
hydrazone substituent and limits the synthetic potential of
the ketone moiety in [Re(CO)3Br(py2CO)] for derivatisation
reactions with biomolecules which should weaken the rhe-
nium ligand bonds and finally lead to solvolysis.
Summary and Conclusions
The rhenium(I) tricarbonyl core readily reacts with acetyl-
pyridine hydrazone and related ligands under formation of
chelate complexes. A summary of the performed reactions
and obtained products is given in Scheme 3. The pyridine
site of the ligands always contributes to the complex forma-
tion whereas the benzoyl moiety remains unco-ordinated.
Deprotonation of Hacpybhyd is achieved when a support-
ing base is added. The same procedure decomposes
Hpy2bhyd under formation of bis(2-pyridine)methanediol
which represents the product of hydrolysis of bis(2-pyri-
dine)ketone. It reacts as mononegative, tridentate chelate
ligand under formation of [Re(CO)3{py2C(OH)O}]. A rhe-
nium complex with intact bis(2-pyridine)ketone, [Re(CO)3-
Br(py2CO)], is obtained from direct reactions between
(Et4N)2[Re(CO)3Br3] and the ketone. This compound is
more resistant against hydrolysis than the complex with the
hydrazone derivative, [Re(CO)3Br(Hpy2bhyd-py,hyd)].
However, the formation of inert complexes with the func-
tionalised hydrazones and hydrazonato ligands described
above encouraged us to attempt reactions with hydrazone
ligands containing additional reactive sites for coupling re-
actions with proteins. Exemplarily the complex formation
of the tricarbonylrhenium(I) core with pyridinealdehyde
terephtalaldehydebishydrazone, pytehyd, is described.
308
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311

Tricarbonyl Complexes of Rhenium(I) with Acetylpyridine Benzoylhydrazone
was added to a solution of (Et4N)2[Re(CO)3Br3] (77 mg, 0.1 mmol)
in 10 ml methanol. After heating for 2 h on reflux the solvent was
removed and the oily residue was re-dissolved in THF. Overlayering
with diethyl ether and standing for some days gave yellow-orange
crystals of [Re(CO)3(OH2)(apbhyd)]. Yield: 39 mg (75%). Elemen-
tal analysis, Found: C, 38.4; H, 3.0; N, 7.8%; Calcd. for
C17H14N3O5Re: C, 38.7; H, 2.7; N, 8.0%.
IR (νmax/cmϪ1 2017, 1900, 1895sh (CϵO), 1670 (CϭO), 1480 (CϭN). FAB؉-
MS m/z (assignment, %B): 510 ([M Ϫ H2O]ϩ, 20), 481 ([Re(CO)2(apbhyd)]ϩ,
10), 454 ([Re(CO)(apbhyd)]ϩ, 10), 426 ([Re(apbhyd)]ϩ, 5). 1H-NMR (ace-
tone): 11.3 s OH (1H), 7.3Ϫ9.1 m phenyl, pyridine (13H), 1.3 s CH3 (3H).
[Re(CO)3Br(Hpy2bhyd-py1,py2)]. (Et4N)2[Re(CO)3Br3] (77 mg,
0.1 mmol) and Hpy2bhyd (30 mg, 0.1 mmol) were dissolved in 20
ml methanol and heated on reflux for 2 h. The resulting orange-
red solution has been reduced in volume to about 5 ml and stored
at about 5 °C for 5 days. During this time yellow blocks of [Re-
(CO)3Br(Hpy2bhyd-py1,py2)] deposited which have been filtered off
and washed with a minimum amount of cooled methanol. Yield:
20 mg (30%). Elemental analysis, Found: C, 38.5; H, 2.0; N, 8.6 %;
Calcd. for C21H14N4O4BrRe: C, 38.6; H, 2.1; N, 8.6%.
IR (νmax/cmϪ1): 2005, 1910, 1895 (CϵO), 1680 (CϭO), 1475 (CϭN). FAB؉-
MS m/z (assignment, %B): 651 ([M]ϩ, 30), 595 ([MϪ2(CO)]ϩ, 25), 546 ([M-
PhCO]ϩ, 25).
Scheme 3
[Re(CO)3Br(Hpy2bhyd-py,hyd)] · THF. This compound has been
isolated from the orange-red filtrate obtained during the prep-
aration of [Re(CO)3Br(Hpy2bhyd-py1,py2)]. The solvent has been
removed in vacuum and the oily liquid has been re-dissolved in
THF. Overlayering with n-hexane gave orange-red crystals of [Re-
(CO)3Br(Hpy2bhyd-py,hyd)] · THF.
Appropriate substitution of the chelating hydrazone li-
gands allows the synthesis of functionalised rhenium com-
plexes which can be used for the coupling of biomolecules
and represent an interesting approach for nuclear medical
labelling experiments. An example has been given with [Re-
(CO)3Br(pytehyd)].
Yield: 42 mg (60%). Elemental analysis, Found: C, 41.2; H, 3.3; N,
7.7 %; Calcd. for C25H22N4O5BrRe: C, 41.4; H, 3.0; N, 7.7%. The
crystals lost solvent upon standing at ambient temperatures for sev-
eral weeks.
Experimental
IR (νmax/cmϪ1): 2005, 1915sh, 1895 (CϵO), 1680 (CϭO), 1475 (CϭN).
FAB؉-MS m/z (assignment, %B): 652 ([M]ϩ, 32), 623 ([M-CO]ϩ, 30), 595
([MϪ2(CO)]ϩ, 25), 546 ([M-PhCO]ϩ, 25).
Hapbhyd has been prepared by heating equivalent amounts of ben-
zoylhydrazone and acetylpyridine (ALDRICH) in refluxing etha-
nol. Pytehyd has been prepared by heating formylpyridine hydra-
zone with terephtalaldehyde in boiling methanol in a 2:1 ratio. The
compounds have been characterised by elemental analysis and
standard spectroscopic methods. Hpy2bhyd and py2CO have been
purchased commercially (ALDRICH). All reactions have been per-
formed on air without special precautions against moisture.
[Re(CO)3Br{py2C(OH)O}]. a) Hpy2bhyd (30 mg, 0.1 mmol) has
been dissolved in 20 ml methanol and 2 ml Et3N has been added.
(Et4N)2[Re(CO)3Br3] (77 mg, 0.1 mmol) has been added and the
resulting solution has been heated on reflux for 2 h. Finally the
volume has been reduced to about 3 ml and yellow crystals de-
posited upon cooling. Yield: 16 mg (35%).
Infrared spectra have been recorded for KBr pellets on a Shimadsu
instrument. Routine FABϩ spectra have been measured with a TSQ
spectrometer (Finnigan) with nitrobenzylalcohol as matrix. A
400MHz JEOL spectrometer has been used for the NMR measure-
ments.
b) (Et4N)2[Re(CO)3Br3] (77 mg, 0.1 mmol) and py2CO (19 mg, 0.1
mmol) have been dissolved in 20 ml acetonitrile. 2 ml Et3N and 0.1
ml H2O have been added. The colour of the solution changed to
yellow upon heating on reflux and
a
yellow solid of
[Re(CO)3Br{py2C(OH)O}] precipitated upon cooling. Yield 30 mg
(65%). Elemental analysis, Found: C, 35.6; H, 1.9; N, 5.9%; Calcd.
for C14H9N2O5Re: C, 35.6; H, 1.9; N, 5.9%.
IR (νmax/cmϪ1): 2008, 1910, 1861 (CϵO), 3048 (OH). FAB؉-MS m/z (assign-
ment, %B): 473 ([MϩH]ϩ, 5), 472 ([M]ϩ, 5), 444 ([M-(CO)]ϩ, 3), 416 ([M-
2CO]ϩ, 3). 1H-NMR: pyridine 7.4 m (1H), 7.8 m (1H), 8.8 m (1H); OH 7.75
s (1H).
[Re(CO)3Br(Hapbhyd)]. (Et4N)2[Re(CO)3Br3] (77 mg, 0.1 mmol)
and Hapbhyd (24 mg, 0.1 mmol) were dissolved in 20 ml methanol
and heated under reflux for 2 h. The solvent was removed in
vacuum and the oily residue was re-dissolved in acetonitrile. This
solution was overlayered with diethyl ether. Slow diffusion of the
ether into the acetonitrile layer gave orange-red crystals of
[Re(CO)3Br(Hapbhyd)]. Yield: 35 mg (55%). Elemental analysis,
Found: C, 34.7; H, 2.5; N, 6.9%; Calcd. for C17H13N3O4BrRe: C,
34.6; H, 2.2; N, 7.1%.
IR (νmax/cmϪ1): 2020, 1895, 1870sh (CϵO), 1675 (CϭO), 1480 (CϭN).
FAB؉-MS m/z (assignment, %B): 510 ([MϪBr]ϩ, 8), 482
([Re(CO)2(apbhyd)]ϩ, 5), 454 ([Re(CO)(apbhyd)]ϩ, 5), 426 ([Re(apbhyd)]ϩ,
7). 1H-NMR (acetone): 10.6 s NH (1H), 7.4-9.2 m phenyl, pyridine (13H),
1.4 CH3 s (3H).
[Re(CO)3Br(py2CO)]. (Et4N)2[Re(CO)3Br3] (77 mg, 0.1 mmol)
and py2CO (19 mg, 0.1 mmol) have been dissolved in 20 ml aceto-
nitrile. The mixture has been heated on reflux for 2 h. Orange-
red crystals of [Re(CO)3Br(py2CO)] deposited upon reducing the
volume of the solvent to about 3 ml and cooling. Yield: 30 mg
(55%). Elemental analysis, Found: C, 31.4; H, 1.6; N, 5.0 %; Calcd.
for C14H8N2O4Re: C, 31.4; H, 1.5; N, 5.2%.
IR (νmax/cmϪ1): 2010, 1915, 1880sh (CϵO), 1685 (CϭO). FAB؉-MS m/z
(assignment, %B): 534/536 ([M]ϩ, 4), 455 ([M-Br]ϩ, 10). 1H-NMR: pyridine
7.9 m (1H), 8.2 m (1H), 8.4 m (1H), 9.3 m (1H).
[Re(CO)3(OH2)(Hapbhyd)]. Hapbhyd (24 ml, 0.1 mmol) was dis-
solved in 20 ml methanol and 0.2 ml Et3N was added. This mixture
Z. Anorg. Allg. Chem. 2003, 629, 303Ϫ311
309

J. Grewe, A. Hagenbach, B. Stromburg, R. Alberto, E. Vazquez-Lopez, U. Abram
Table 5 X-ray structure data collection and refinement parameters
[Re(CO)3Br-
(Hapbhyd)]
[Re(CO)3-
(OH2)(apbhyd)]
[Re(CO)3Br(Hpy2-
bhyd-py1,py2)]
[Re(CO)3Br(Hpy2-
[Re(CO)3-
[Re(CO)3Br-
(py2CO)]
[Re(CO)3Br-
(aptehyd)]b)
bhyd-py,hyd)]THFa) {py2(OH)O}]
Crystal
1 · 1 · 0.2
0.20 · 0.20 · 0.05
0.2 · 0.15 · 0.15
0.20 · 0.10 · 0.10
0.2 · 0.15 · 0.05
0.2 · 0.2 · 0.1
0.60 · 0.15 · 0.02
dimensions (mm3)
Formula
C17H13N3BrO4Re
589.41
C17H14N3O5Re
526.51
C21H14BrN4O4Re
652.47
C25H22BrN4O5Re
724.58
C14H9N2O5Re
471.43
C14H8BrN2O4Re
534.33
C17H11BrN3O4Re
587.40
M (g molϪ1
)
Crystal system
Space group
Unit cell
monoclinic
P21/c
a ϭ 11.777(2) A
b ϭ 11.760(1) A
c ϭ 13.513(2) A
triclinic
P1
monoclinic
P21/c
a ϭ 13.480(1) A
b ϭ 11.248(1) A
c ϭ 14.368(2) A
monoclinic
P21
a ϭ 10.961(3) A
b ϭ 9.791(1) A
c ϭ 12.779(2) A
monoclinic
C2/c
a ϭ 27.569(4) A
b ϭ 7.800(1) A
c ϭ 16.157(3) A
orthorhombic
Pnma
a ϭ 8.253(2) A
b ϭ 13.020(2) A
c ϭ 12.532(2) A
monoclinic
P21/c
a ϭ 7.510(2) A
b ϭ 17.158(2) A
c ϭ 14.059(4) A
¯
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
a ϭ 8.270(2)
b ϭ 9.378(2)
c ϭ 11.722(2)
α ϭ 76.99(2)
β ϭ 87.15(2)
γ ϭ 79.54(3)
870.7(3)
˚
˚
˚
˚
˚
˚
˚
˚
β ϭ 100.78(1)°
β ϭ 104.26(1)
β ϭ 101.40(2)°
β ϭ 125.55(1)
β ϭ 92.56(2)°
3
˚
V (A )
Z
1839.6(4)
4
2.128
20
2111.3(3)
4
2.053
20
1344.4(5)
2
1.790
20
2826.6(8)
8
2.216
Ϫ100
1450.0(5)
4
2.448
20
1809.8(7)
4
2.156
20
2
Dc (g cmϪ3
Measuring
)
2.008
20
temperature (°C)
Scan type
ω scans
ω scans
ω-scans
ω-scans
ω-scans
ω-scans
Linear absorption
8.804
7.012
13.793
6.046
8.623
11.154
8.949
coefficient (mmϪ1
)
Absorption correction DELABS [19]
DELABS [199]
0.3345
ψ scans
0.7810
ψ scans
0.8347
SADABS [20]
0.6006
DELABS [19]
0.300
ψ scans
0.6659
Tmin
0.0412
Tmax
0.2719
0.7206
0.9752
0.9955
0.9077
0.740
0.9040
Measured reflections
Independent
reflections/Rint
Refined parameters
R1 (F)/wR2 (F2)
(I > 2σ(I))
4562
3980/0.0354
5925
5064/0.0566
4536
3584/0.0609
6743
5826/0.0337
16326
4134/0.0649
5197
2150/0.0476
4402
3556/0.0373
287
0.0372/0.0729
291
0.0229/0.0518
282
0.0479/0.1300
313
0.0437/0.0961
235
0.0353/0.0666
127
0.0511/0.1260
279
0.0333/0.0686
GooF
1.053
1.020
1.032
1.043
0.913
1.187
1.063
Programs used
SHELXS97 [17],
SHELXL97 [18],
PLATON,
SHELXS97 [17],
SHELXL97 [18],
PLATON,
SHELXS97 [17],
SHELXL97 [18],
PLATON,
SHELXS97 [17],
SHELXL97 [18],
PLATON,
SHELXS97 [17],
SHELXL97 [18],
PLATON,
SHELXS97 [17],
SHELXL97 [18],
PLATON,
SHELXS97 [17],
SHELXL97 [18],
PLATON,
HELENA [19]
HELENA [19]
HELENA [19]
HELENA [19]
HELENA [19]
HELENA [19]
HELENA [19]
a)
Flack parameter: 0.008(16)
[Re(CO)3Br(pytehyd)]. (Et4N)2[Re(CO)3Br3] (77 mg, 0.1 mmol)
and pytehyd (24 mg, 0.1 mmol) were dissolved in 20 ml methanol
and heated under reflux. The solution turned yellow-orange within
30 min. Orange-red crystals of [Re(CO)3Br(pytehyd)] precipitated
after reducing the solvent to about 2 ml and cooling. Yield: 40 mg
(63%). Elemental analysis, Found: C, 34.5; H, 2.2; N, 7.2%; Calcd.
for C17H11N3O4BrRe: C, 34.6; H, 2.2; N, 7.1%.
regarded during the refinement with an approximate 64/36per cent
occupancy of each site.
Further details of the crystallographic data have been deposited
with the Cambridge Crystallographic Data Centre under the depo-
sition numbers CCDC-195113 (([Re(CO)3Br(Hapbhyd)]), CCDC-
195114 ([Re(CO)3(OH2)(apbhyd)]), CCDC-195115 ([Re(CO)3Br-
(Hpy2bhyd-py,hyd)]), CCDC-195116
([Re(CO)3Br(Hpy2bhyd-
IR (νmax/cmϪ1): 2025, 2000, 1875sh (CϵO), 1695 (CϭO), 1485 (CϭN).
FAB؉-MS m/z (assignment, %B): 508 ([MϪBr]ϩ, 15), 480
([Re(CO)2(pytehyd)]ϩ, 10), 452 ([Re(CO)(pytehyd)]ϩ, 5).
py1,py2)]), CCDC-195117 ([Re(CO)3{py2(OH)O}]), CCDC-195118
([Re(CO)3Br(py2CO)]) and CCDC-195119 ([Re(CO)3Br(aptehyd)]).
Acknowledgements. We thank the Hermann Starck AG (Goslar) for
a
generous gift of rhenium metal and Professor J. Strähle
X-Ray structure determinations
(Tübingen) for the opportunity to collect the X-ray data set of [Re-
(CO)3Br(Hpy2bhyd-py1,py2)].
The intensities for the X-ray determinations were collected on an
automated single crystal diffractometer of the type CAD4 (Enraf-
Nonius) or a SMART CCD (Bruker) with Mo Kα (λ ϭ 0.71073
References
˚
˚
A) or Cu Kα radiation (λ ϭ 1.54184 A). Standard procedures have
been applied for data reduction and absorption correction. Struc-
ture solutions and refinements have been performed with
SHELXS97 and SHELXL97 [17, 18]. More details on data collec-
tion and structure calculation are contained in Table 5.
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310
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