Synthesis, characterization, properties and structures of rhenium(II), -(III), and -(V) complexes containing amino acids conjugated with a 2-aminothiazole ligand

Article abstract of DOI:10.1039/b201609p

The one-step reaction of KReO₄ with benzoylhydrazine in the presence of concentrated HCl and PPh₃ afforded [Re^V(NNC(Ph)O)(PPh₃)₂Cl₂]1 which was converted with carbon monoxide into the dinitrogen Re(I) complex [ReN₂(CO)₂(PPh₃)₂Cl]2 in good yield. A new class of ligands, of general formula HLⁿ (n = 1-5), was obtained by conjugation of N-protected amino acids and benzoic acid with 2-aminothiazole. Complex 2 reacted with HLⁿ to give neutral Re(II) chelate complexes [Re(Lⁿ)(CO)(PPh₃)₂Cl]5-9 (n = 1-5), by substitution of N₂ and CO groups. The molecular structure of complex 9 was determined by X-ray diffraction. When reactions between [Re(NNC-(Ph)O)(PPh₃)₂Cl₂]1 and HLⁿ (n = 2, 5) were carried out in different stoichiometric ratios, neutral mono- and di-substituted Re(III) organodiazenido complexes [Re(NNCOPh)(L^2,5)(PPh₃)₂Cl]10, 11 and [Re(NNCOPh)(L⁵)₂-(PPh₃)]12 were obtained. In these complexes the organodiazenido Re-N-N moiety adopts a linear conformation, as has been authenticated by X-ray diffraction analysis for 11 and12. Treatment of Re(I) dinitrogen precursors [ReN₂(P)₄Cl] (P= PMe₂Ph, 3 and PMePh₂,4) with ligands resulted in interesting dinuclear oxo-(μ-oxo)-Re(V) species [Re₂(O)₃(Lⁿ)₂(P)₂] (P = PMe₂Ph, n = 1, 13; n = 2, 14; n = 4, 15. P = PMePh₂, n = 2, 16). Suitable crystals for an X-ray analysis have been obtained for complex 14. The structure represents one of the few cases where, for steric reasons, the Re-O-Re bridging unit is not linear but rather bent. All the compounds have been characterized by elemental analyses, IR and NMR spectroscopy. The Re(II) complexes 5-7 and9 were further characterized by electrochemical measurements.

Full text of DOI:10.1039/b201609p

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Synthesis, characterization, properties and structures of rhenium-
(II), -(III), and -(V) complexes containing amino acids conjugated
with a 2-aminothiazole ligand
Antonio Lazzaro,a Gianni Vertuani,a Paola Bergamini,b Nicoletta Mantovani,b
Andrea Marchi,*b Lorenza Marvelli,b Roberto Rossi,b Valerio Bertolasic and Valeria Ferrettic
a Dipartimento di Scienze Farmaceutiche, Università di Ferrara, via Fossato di Mortara 17-19,
44100 Ferrara, Italy
b Laboratorio di Chimica Inorganica e Nucleare, Dipartimento di Chimica,
Università di Ferrara, via L. Borsari 46, 44100 Ferrara, Italy. E-mail: mha@dns.unife.it
c Centro di Strutturistica Diffrattometrica, Dipartimento di Chimica, Università di Ferrara,
via L. Borsari 46, 44100 Ferrara, Italy
Received 12th February 2002, Accepted 10th May 2002
First published as an Advance Article on the web 14th June 2002
The one-step reaction of KReO4 with benzoylhydrazine in the presence of concentrated HCl and PPh3 afforded
[ReV(NNC(Ph)O)(PPh3)2Cl2] 1 which was converted with carbon monoxide into the dinitrogen Re() complex
[ReN2(CO)2(PPh3)2Cl] 2 in good yield. A new class of ligands, of general formula HLn (n = 1–5), was obtained by
conjugation of N-protected amino acids and benzoic acid with 2-aminothiazole. Complex 2 reacted with HLn to
give neutral Re() chelate complexes [Re(Ln)(CO)(PPh3)2Cl] 5–9 (n = 1–5), by substitution of N2 and CO groups.
The molecular structure of complex 9 was determined by X-ray diffraction. When reactions between [Re(NNC-
(Ph)O)(PPh3)2Cl2] 1 and HLn (n = 2, 5) were carried out in different stoichiometric ratios, neutral mono- and
di-substituted Re() organodiazenido complexes [Re(NNCOPh)(L2,5)(PPh3)2Cl] 10, 11 and [Re(NNCOPh)(L5)2-
(PPh3)] 12 were obtained. In these complexes the organodiazenido Re–N–N moiety adopts a linear conformation,
as has been authenticated by X-ray diffraction analysis for 11 and 12. Treatment of Re() dinitrogen precursors
[ReN2(P)4Cl] (P = PMe2Ph, 3 and PMePh2, 4) with ligands resulted in interesting dinuclear oxo-(µ-oxo)-Re() species
[Re2(O)3(Ln)2(P)2] (P = PMe2Ph, n = 1, 13; n = 2, 14; n = 4, 15. P = PMePh2, n = 2, 16). Suitable crystals for an X-ray
analysis have been obtained for complex 14. The structure represents one of the few cases where, for steric reasons,
the Re–O–Re bridging unit is not linear but rather bent. All the compounds have been characterized by elemental
analyses, IR and NMR spectroscopy. The Re() complexes 5–7 and 9 were further characterized by electrochemical
measurements.
intermediates in the preparation of lower oxidation state
compounds.
Introduction
Research in the chemistry of technetium and rhenium
complexes arises from the use of diagnostic 99mTc and thera-
peutic 186/188Re radiopharmaceuticals in nuclear medicine.
In particular, the success of the 186Re(Sn)HEDP (HEDP =
hydroxyethylenediphosphonic acid) radiopharmaceutical as
a palliative of bone pain,1 has reawakened interest in the
co-ordination chemistry of rhenium in order to develop new
186/188Re radiopharmaceuticals having specificity to be
used for the treatment of cancer.
A recent approach to the development of site specific radio-
pharmaceutical and/or radioimaging agents is to derivatize
a chelate, which binds a radionuclide, with a biomolecule
(bifunctional chelating agent, BFCA approach) whose purpose
is to carry the radionuclide to a specific site. There is con-
siderable interest in the design of new ligands; in particular
derivatized amino acids and peptides have attracted attention
over the past fifteen years and new radiopharmaceuticals have
been applied in nuclear medicine.2
Although analogous technetium and rhenium complexes
exhibit similar physical properties, chemical differences can
result in their biological behavior due to redox potentials of the
central metal. It is well known that rhenium complexes are
more difficult to reduce than the corresponding technetium
compounds. As an example, we can mention a comparative
study in vivo between two cations, [99mTc(DMPE)2Cl2]ϩ and
[
186Re(DMPE)2Cl2]ϩ [DMPE = 1,2-bis(dimethylphosphino)-
ethane] for which it was shown that the reduction occurs only
for the technetium complex, not for the rhenium analogue.4
In contrast, in the ϩ1 oxidation state the similarity in chem-
ical behavior between the two elements is particularly strict.
Useful synthetic procedures have been reported to obtain pre-
cursors of rhenium and technetium in lower oxidation states
and emphasis has been placed on Re() and Tc() chemistry.5
The value of these compounds has been increased recently since
the discovery of a new safe and easy synthetic route to the
complex [M(H2O)3(CO)3]ϩ (M = Re, Tc) which avoids the use of
dangerous CO and therefore allows the preparation of 99mTc()
compounds for radiopharmaceutical applications.6 The chem-
istry of this complex is of great interest due to the high stability
of the fac-[M(CO)3]ϩ core and lability of aquo ligands which
can be easily substituted by a variety of appropriate ligands.6b
An alternative idea has been proposed by Katzenellenbogen
who has bound bioactive molecules to the cyclopentadienyl
Selection of a BFCA is largely determined by the nature and
oxidation state of the metal and its co-ordination chemistry will
determine the geometry and stability of the final complex.
Many stable complexes of Re() and Tc() have been reported
because this high oxidation state is easily accessible by
reduction of the [MO4]Ϫ anions. Some of these complexes
display remarkable bioactivity themselves,3 other are used as
DOI: 10.1039/b201609p
J. Chem. Soc., Dalton Trans., 2002, 2843–2851
This journal is © The Royal Society of Chemistry 2002
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ring obtaining analogues of the organometallic compound
[(Cp)M(CO)3].7 It is worth noticing that organometallic
compounds of Re() could provide valuable alternatives as
radiopharmaceutical species.8
An interesting exception is represented by the synthetic
access to low oxidation states of rhenium reported by Chatt9
based on the use of the chelate Re() complex [Re(NNC-
(Ph)O)(PPh3)2Cl2] 1 as a versatile precursor. It reacts with
neutral monodentate ligands L such as CH3CN, CO and
tertiary phosphines, to give organodiazenido complexes, of
general formula [Re(NNCOPh)(L)(PPh3)2Cl2], through dis-
placement of the weakly coordinated carbonyl oxygen atom of
the chelate ring Re–NNC(Ph)O–.9 Moreover, complex 1, as well
as organodiazenido derivatives, is a good synthon to form Re()
dinitrogen complexes [ReN2(L)2(PPh3)2Cl] (L = CO, tertiary
phosphines).10 A series of Re() and Re() complexes with
nitrogen donor ligands have been prepared giving interesting
compounds for a study of low-valent rhenium co-ordination
chemistry.11a–c Thus, the methodology developed by Chatt9,10
and others11 seems to represent an alternative and facile
synthetic approach to obtain new rhenium complexes in low
oxidation states.
We previously reported on reactions of the Re() and Tc()
carbonyl complexes [M(CO)3(PPh3)2Cl] with 2-aminothiazole
and its derivatives and the chemistry of the corresponding
complexes has been extensively studied.12 More recently we
described the synthesis and characterization of a Re() carbonyl
complex containing a bile acid functionalized with 2-amino-
thiazole ligand as an example of a BFCA.13
Along these lines, we report here the synthesis of a new
class of ligands obtained from conjugation of amino acids with
2-aminothiazole, which is a good moiety for the formation of
rhenium complexes in low oxidation states. Afterwards, we
have investigated the reactivity of these ligands toward the
dinitrogen precursors of Re(), [ReN2(CO)2(PPh3)2Cl] 2 and
[ReN2(P)4Cl] (P = PMe2Ph, 3; PMePh2, 4), and the chelate Re()
complex [Re(NNC(Ph)O)(PPh3)2Cl2] 1.
Scheme 1
latter, in MeOH, can be converted into [ReN2(CO)2(PPh3)2Cl] 2
in good yield when CO is bubbled for 45 minutes into the
reaction mixture.
Complexes of Re(), Re() and Re() were obtained and
authenticated by X-ray crystallography. We also report the
electrochemistry for rhenium() complexes. Furthermore, a
modified one-step procedure for the synthesis of [ReN2(CO)2-
(PPh3)2Cl] 2 is also presented.
Preparation and properties of Re(II) complexes
[Re(Ln)(PPh3)2(CO)Cl] 5–9 (n ؍ 1–5)
Treatment of the dinitrogen complex 2 with the appropriate
ligands, in the presence of a base to facilitate their deproton-
ation, results in the formation of red Re() complexes [Re(Ln)-
(CO)(PPh3)2Cl] 5–9 (n = 1–5) in good yield (Scheme 2).
Results and discussion
Synthesis of HL1–5 ligands
This class of ligands was synthesized by coupling reactions
between the amino group of 2-aminothiazole with the carb-
oxylic group of N-protected amino acids ( configuration) and
benzoic acid or its corresponding benzoyl chloride, following a
general procedure previously reported by us.14 These ligands are
stable in the solid state for several months, and were completely
characterized on the basis of their elemental analysis, melting
point, IR and 1H NMR spectra (see Experimental section).
Preparation of [ReN2(CO)2(PPh3)2Cl] 2
Scheme 2
The original preparation of the complex [ReN2(CO)2(PPh3)2Cl]
2 described by Chatt and co-workers10 is performed by the
treatment of the benzoylhydrazido Re() complex [Re(NNC-
(Ph)O)(PPh3)2Cl2] 1 with a stream of carbon monoxide in a
boiling methanol–benzene mixture. The starting material 1 is
prepared from the oxo-complex [ReO(PPh3)2Cl3].9
In order to provide a more convenient route to synthesize
complexes 1 and 2, we propose a one-pot reaction, starting
from [ReO4]Ϫ (see Scheme 1). The perrhenate salt in CH2Cl2 in
the presence of an excess of PPh3, aqueous HCl, and benzoyl-
hydrazine, promptly gives [Re(NNC(Ph)O)(PPh3)2Cl2] 1; the
The IR spectra confirm the loss of the N2 moiety10,11a,c,d and
exhibit a strong band at around 1830–1845 cmϪ1 assigned to
᎐
ν(C᎐O) vibration; another absorption in the range 1500–1530
᎐
cmϪ1 is typical for a co-ordinated CO amidic group.
1
The very broad signals observed in the H NMR spectra
combined with the absence of resonances in the 31P{1H}NMR
spectra seems to suggest the formation of paramagnetic deriv-
atives. In agreement with our expectations, the solid-state
magnetic moment determined for complexes 5 and 9 was 1.7 µB,
which supports a Re() species. As reported in the literature, the
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d5 low spin electronic configuration is the most probable for
Re() and usually magnetic moment values have been found
in the range 1.5–2.0 µB at room temperature for mono- and
bi-nuclear complexes.15 Moreover, an EPR spectrum of 5
collected at 90 K confirmed the presence of an unpaired
electron on the metal. The spectrum consists of six lines which
are clearly due to the I = 5/2 nucleous of rhenium and it is
characterized by a g value of 2.11 and a line width of 380 G.
In order to contribute to the understanding of the real nature
of complexes 5–7 and 9, we investigated their electrochemical
behavior and found it to be similar for all these derivatives. In
particular, the redox profile is characterized by the presence
of two reversible oxidation processes due to the Re(/)
and Re(/) couples, in the range of ϩ(0.580–0.650) V and
Ϫ(0.700–0.777) V, respectively (see Experimental section).
UV–Vis spectra of 5 and 9 in CH2Cl2 solution were also
recorded. These complexes show intense absorptions at 450 and
500 nm (ε > 2000), respectively, assigned to charge-transfer
bands rather than d–d transitions.
Table 1 Selected bond distances (Å) and angles (Њ) for compound 9
Re1–Cl1
Re1–P1
Re1–P2
Re1–O2
Re1–N2
Re1–C1
2.3891(7)
2.4799(7)
2.4682(7)
2.132(2)
2.087(2)
1.857(3)
O2–C2
N1–C2
N1–C3
N2–C3
O1–C2
1.265(3)
1.328(4)
1.343(4)
1.346(4)
1.172(4)
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–O2
Cl1–Re1–N2
Cl1–Re1–C1
P1–Re1–P2
P1–Re1–O2
P1–Re1–N2
P1–Re1–C1
P2–Re1–O2
P2–Re1–N2
88.75(3)
90.56(3)
84.84(6)
169.13(7)
97.8(1)
177.43(2)
88.34(6)
90.25(7)
93.2(1)
P2–Re1–C1
O2–Re1–N2
O2–Re1–C1
N2–Re1–C1
Re1–O2–C2
Re1–N2–C3
C2–N1–C3
Re1–C1–O1
O2–C2–N1
N1–C3–N2
89.3(1)
84.31(8)
177.0(1)
93.1(1)
130.1(2)
124.082)
122.3(2)
176.8(3)
127.2(2)
132.0(2)
89.13(6)
89.96(7)
Re() intermediate species which is subsequently oxidized to the
final Re() product by protic solvent and/or by rhenium species
in higher oxidation states. In contrast, our reactions were
carried out starting from the Re() dinitrogen complex 2 in
aprotic solvent (benzene) giving Re() as the only observed
oxidation state. Control experiments have shown that the result
of this process is independent of the presence of both oxygen
and water. Therefore, we may presume that 2 undergoes a
metal-to-ligand electron transfer to give CO, N2 and organic
by-product.
On the basis of the spectroscopic measurements together
with analytical data, we may consider these derivatives as Re()
neutral complexes [Re(Ln)(CO)(PPh3)2Cl] (n = 1–5) where a
molecule of deprotonated ligand replaces a carbonyl group and
the N2 molecule in the starting complex 2. This supposed
formulation was unambiguously supported by X-ray crystallo-
graphic analysis of the complex [Re(L5)(CO)(PPh3)2Cl] 9. An
ORTEP drawing is shown in Fig. 1 and selected bond distances
and angles are reported in Table 1.
Reactions of [Re(NNC(Ph)O)(PPh3)2Cl2] 1 and formation of
organodiazenido complexes of Re(III) 10, 11 and 12
We have also investigated alternative pathways to form Re()
or Re() dinitrogen complexes with HLn (n = 2, 5). Reactions
of complex 1 in benzene–methanol with the ligands in
stoichiometric ratios give neutral monosubstituted Re()-
organodiazenido [Re(NNCOPh)(L2,5)(PPh3)2Cl] 10 and 11
complexes, while with two equivalents of HL5 the disubstituted
[Re(NNCOPh)(L5)2(PPh3)] 12, is collected (Scheme 3). Further
reduction from Re() to lower states was not observed even in
protic solvents, which we expected to assist the process!
Fig. 1 An ORTEP view of complex 9 showing thermal ellipsoids at
30% probability.
The more usually encountered mononuclear Re() complexes
contain only halide and phosphine ligands15b,16 although com-
pounds containing different ligands have been reported and
structurally characterized,17 the chemistry of rhenium in this
rather uncommon oxidation state is still relatively unknown.
The complexes here reported are examples of stable mono-
nuclear Re() species which contain a monoanionic bidentate
ligand. The formation of Re() complexes was not completely
unexpected since a few examples have already been reported.11b
Nevertheless, it is possible to notice some substantial differ-
ences compared to our results. In fact, the Re() complexes
previously reported in the literature were obtained from the
Re() precursor 1 and authors have suggested formation of an
Scheme 3
The infrared spectra of these compounds show a strong band
at around 1240 cmϪ1 associated with a vibration of the benzoyl
group; absorptions in the range 1504–1510 cmϪ1 and at 1635
cmϪ1 are assigned to ν(N᎐N) and ν(C᎐O) of the organodiaze-
᎐
᎐
nido moiety, Re–NNC(O)Ph, respectively.9,11c An additional
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Table 2 Selected bond distances (Å) and angles (Њ) for compound 11
Table 3 Selected bond distances (Å) and angles (Њ) for compound 12
Re1–Cl1
Re1–P1
Re1–P2
Re1–O1
Re1–N1
Re1–N3
O1–C4
2.429(2)
2.482(2)
2.467(2)
2.045(4)
2.116(5)
1.744(5)
1.303(7)
O2–C11
N1–C3
N2–C3
N2–C4
N3–N4
N4–C11
1.218(8)
1.330(8)
1.358(8)
1.305(7)
1.284(7)
1.374(8)
Re1–P1
Re1–O1
Re1–O2
Re1–N1
Re1–N3
Re1–N5
O1–C4
2.406(3)
2.021(8)
2.040(7)
2.087(9)
2.134(8)
1.753(8)
1.271(14)
1.280(12)
1.200(15)
N1–C3
N2–C3
N2–C4
N3–C13
N4–C13
N4–C14
N5–N6
N6–C21
1.348(16)
1.397(12)
1.360(14)
1.313(13)
1.372(12)
1.314(12)
1.279(12)
1.485(19)
O2–C14
O3–C21
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–O1
Cl1–Re1–N1
Cl1–Re1–N3
P1–Re1–P2
P1–Re1–O1
P1–Re1–N1
P1–Re1–N3
P2–Re1–O1
P2–Re1–N1
88.64(6)
90.41(6)
82.8(1)
164.7(1)
99.8(2)
179.0(1)
89.2(1)
90.1(1)
94.3(1)
90.9(1)
90.9(1)
P2–Re1–N3
O1–Re1–N1
O1–Re1–N3
N1–Re1–N3
Re1–O1–C4
Re1–N1–C3
C3–N2–C4
Re1–N3–N4
N3–N4–C11
N1–C3–N2
O1–C4–N2
85.6(1)
82.0(2)
175.6(2)
95.5(2)
133.4(4)
124.6(4)
121.0(6)
170.1(5)
119.6(5)
131.2(5)
125.4(6)
P1–Re1–O1
P1–Re1–O2
P1–Re1–N1
P1–Re1–N3
P1–Re1–N5
O1–Re1–O2
O1–Re1–N1
O1–Re1–N3
O1–Re1–N5
O2–Re1–N1
O2–Re1–N3
O2–Re1–N5
N1–Re1–N3
N1–Re1–N5
92.4(2)
91.3(2)
93.2(3)
175.4(2)
86.3(3)
83.5(3)
84.3(3)
83.8(3)
174.8(3)
167.2(3)
85.8(3)
101.6(3)
89.0(3)
90.7(3)
N3–Re1–N5
Re1–O1–C4
Re1–O2–C14
Re1–N1–C3
C3–N2–C4
Re1–N3–C13
C13–N4–C14
Re1–N5–N6
N5–N6–C21
N1–C3–N2
O1–C4–N2
N3–C13–N4
O2–C14–N4
97.7(3)
136.3(8)
129.7(6)
123.6(7)
121.7(9)
121.9(6)
122.3(8)
160.5(8)
119
131
123
131.2(9)
128.2(9)
band at 1722 cmϪ1 in the spectrum of 10 is attributed to
1
ν(C᎐O)carbam.. The H NMR spectra consist of two broad sing-
᎐
lets assigned to –CHN and –CHS thiazole protons; the position
of these signals is upfield shifted in comparison with those of
HLn indicative of a decreased aromaticity of the thiazole upon
co-ordination.12e,f A singlet at δ 4.0 observed in the 31P{1H}-
NMR spectra of 10 and 11 reveals that the two phosphinic
groups are equivalent and in trans position to one another; in
complex 12 the phosphorus signal resonates at lower field
(δ 11.3). Magnetic moment measurements are consistent with
the diamagnetic nature of these compounds. It is known that
complex 1 reacts with neutral ligands such as CH3CN, PF3, py
(L), dipy and terpy (LL) to form diamagnetic organodiazenido
complexes of the type [Re(NNCOPh)(L)(PPh3)2Cl2] or [Re-
(NNCOPh)(LL)(PPh3)Cl2].9,11c The monodentate organodiaze-
nido ligand –NNAr may exhibit linear, singly bent and double
bent conformations and this affects the assignment of the
oxidation state of the central metal ion.18 The crystal structures
of 11 and 12 show a singly bent diazenido moiety and they must
be considered as Re() derivatives according to the assignment
proposed by Chatt et al.9,11c and more recently, also on the basis
of X-ray analyses of some rhenium and technetium organo-
diazenido complexes.19 The diamagnetic properties of all these
Re() species may be attributed to a distortion of octahedral
symmetry resulting from the organodiazenido ligand.9,19 Com-
plexes 11 and 12 possess an octahedral geometry with the
oxygen atom of the ligand trans to the –N2COPh group. The
short Re–N–N bond distances together with the Re–N–N bond
angle suggest significant Re–N multiple bonding and a linear
geometry for the Re–NN fragment. A selected list of bond
distances and angles is given in Tables 2 and 3 and ORTEP
views of 11 and 12 are shown in Figs. 2 and 3, respectively.
Fig. 2 An ORTEP view of complex 11 showing thermal ellipsoids at
30% probability.
out in anhydrous solvents and under a nitrogen stream, as well
as in the absence of base.
Oxidation of Re(I) complexes [ReN2(P)4Cl] (P ؍ PMe2Ph,
PMePh2) to oxo-(ꢀ-oxo)-Re(V) dimers [Re2(O)3(Ln)2(P)2]
(P ؍ PMe2Ph, n ؍ 1, 13; n ؍ 2, 14; n ؍ 4, 15. P ؍ PMePh2,
n ؍ 2, 16)
Ligands HLn are potentially capable of binding through
sulfur or nitrogen atoms of thiazole ring and amidic or carb-
amic groups. FTIR spectra of 13–16 show two stretching bands
The ligands used in the present section are HLn (n = 1, 2, 4).
Wishing to obtain Re() dinitrogen complexes, the two pre-
cursors [ReN2(P)4Cl] (P = PMe2Ph, 3; PMePh2, 4) have been
combined with these ligands (Scheme 4). Reactions were carried
out in boiling benzene, in air and in the presence of NEt3 as
deprotonating agent. Complex 3 reacts very slowly with HLn
(n = 1, 2, 4) and after 30 h a violet solid could be collected. In the
same reaction conditions 4 reacts with HL2 to give the corre-
sponding violet compound after 6 h. This notable difference
in reactivity may be ascribed to the steric hindrance of the
phosphines (PMePh2 > PMe2Ph) affecting the substitution rate.
The reaction of 3 with HL5 afforded the Re() complex
[ReCl3(PMe2Ph)3], also collected when the reaction was carried
in the ranges 910–945 and 894–912 cmϪ1 diagnostic of the Re᎐
᎐
O stretching modes, and a strong absorption at ca. 670 cmϪ1
which may be assigned to Re–O–Re stretching. These values are
comparable with literature data for analogous species.20 Add-
itionally, three strong bands are also found at 1280–1300 cmϪ1
,
1430–1440 cmϪ1 and ca. 1660 cmϪ1, assigned to ν(CS) and
1
ν(CN) of thiazole and ν(CO), respectively. All the H NMR
signals have been attributed to the respective protons (see
Experimental section). In particular, the phosphinic
methyl-proton resonances occur as two doublets at δ 1.5–1.6
and 1.9 (J = 13.6 Hz) while a singlet is observed in the
31P{1H}NMR spectra, suggesting equivalence of the two
phosphines. The methyl groups of the two PMe2Ph ligands are
2846
J. Chem. Soc., Dalton Trans., 2002, 2843–2851

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Table 4 Selected bond distances (Å) and angles (Њ) for compound 14
Re1–O1
Re1–P1
Re1–O3
Re1–N2
Re1–N3
Re1–N4
N1–C3
N2–C3
N2–C4
O4–C4
N3–C5
C4–C5
1.690(7)
2.462(2)
1.925(7)
2.075(7)
2.028(8)
2.280(9)
1.322(13)
1.380(14)
1.376(12)
1.233(12)
1.472(12)
1.511(16)
Re2–O2
Re2–P2
Re2–O3
Re2–N5
Re2–N6
Re2–N1
N4–C23
N5–C23
N5–C24
O7–C24
N6–C25
C24–C25
1.684(7)
2.464(3)
1.897(7)
2.078(9)
2.025(7)
2.282(8)
1.344(14)
1.357(14)
1.375(12)
1.231(13)
1.481(12)
1.519(16)
Re1–O3–Re2
O1–Re1–O3
O1–Re1–P1
O1–Re1–N2
O1–Re1–N3
O1–Re1–N4
P1–Re1–O3
O3–Re1–N2
O3–Re1–N3
O3–Re1–N4
P1–Re1–N2
P1–Re1–N3
P1–Re1–N4
N2–Re1–N3
N2–Re1–N4
N3–Re1–N4
Re1–N4–C23
Re1–N2–C3
Re1–N2–C4
Re1–N3–C5
N1–C3–C2
N2–C4–C5
N3–C5–C4
138.3(4)
O2–Re2–O3
O2–Re2–P2
O2–Re2–N5
O2–Re2–N6
O2–Re2–N1
P2–Re2–O3
O3–Re2–N5
O3–Re2–N6
O3–Re2–N1
P2–Re2–N5
P2–Re2–N6
P2–Re2–N1
N5–Re1–N6
N5–Re1–N1
N6–Re2–N1
Re2–N1–C3
Re2–N5–C23
Re2–N5–C24
Re2–N6–C25
N4–C23–N5
N5–C24–C25
N6–C25–C24
166.7(3)
165.7(3)
86.8(2)
103.8(4)
97.9(4)
82.7(4)
86.4(2)
83.8(3)
95.6(3)
86.4(2)
169.3(3)
99.9(2)
88.3(2)
77.2(3)
94.8(3)
171.9(3)
130.4(6)
124.7(6)
115.2(7)
112.7(6)
122.3(7)
113.3(8)
109.3(8)
86.9(3)
103.5(4)
97.6(4)
83.5(3)
86.6(2)
83.4(3)
95.0(3)
84.7(3)
169.6(3)
100.2(2)
88.7(2)
77.4(3)
93.7(3)
171.1(3)
129.8(6)
123.6(6)
114.8(7)
113.7(5)
122.3(9)
113.9(8)
109.0(7)
Fig. 3 An ORTEP view of complex 12 showing thermal ellipsoids at
30% probability.
ligands were never isolated when oxo- or dioxo-rhenium()
precursors were used.
Scheme 4
The displacement of N2 and/or oxidation of the metal seems
to be governed by the experimental conditions employed as well
as the properties of the HLn ligand itself10b,11d and co-ligands. In
fact, the precursor 2 gives rise to Re() species probably due to
the presence of CO which is able to stabilize low oxidation
states of the metal, while 3 and 4 do not contain suitable
co-ligands.
diastereotopic and different chemical shifts may be expected.21
Also for these compounds, the –CHS and –CHN protons of
the thiazolic ring are shifted upfield.12e,f These spectroscopic
data, and the elemental analyses, are not sufficient to give an
exact formulation for these compounds. Crystals suitable for an
X-ray investigation were obtained for complex 14. The structure
shows a dinuclear species where two octahedral Re()-oxo units
share a µ(O) oxygen, (Fig. 4, Table 4).
Crystal structures
This facile oxidation from Re() to Re() oxo-species by air
was quite unexpected. Oxo-Re() complexes with this class of
ORTEP22 views of complexes 9, 11, 12 and 14 are represented
in Figs. 1, 2, 3 and 4 respectively. Selected bond distances and
angles are given in Tables 1, 2, 3 and 4.
In complex 9, the overall geometry around the central
Re1() atom is distorted octahedral. The principal reason for
the distortion is the small bite angle of the deprotonated
benzoyl-2-aminothiazole [O2–Re1–N2 = 84.31(8)Њ]. In this
ligand the lengthening of the C2–O2 bond to 1.265(3) Å and
the C–N bond distances, which are almost equivalent [C2–N1 =
1.328(4), C3–N1 = 1.343(4) and C3–N2 = 1.346(4) Å], indicate a
delocalization of the double bonds and of the negative charge
throughout the O2᎐C2–N1᎐C3–N2 moiety. The Re1–O2
᎐
᎐
distance of 2.132(2) Å shows an unusual lengthening with
respect to the Re1–N2 of 2.087(2) Å because of the trans
influence exerted by the carbonyl group on the O2 oxygen. The
apical triphenylphosphines are trans to each other and display
Re–P distances of 2.480(1) and 2.468(1) Å, which are typical for
this co-ordination mode.23,24
Compound 11 is a Re() complex and contains, with respect
to complex 9, the benzoyldiazenido ligand (PhC(O)–N᎐N)Ϫ
᎐
instead of the carbonyl group. The organodiazenido induces a
further octahedral distortion evaluated by the widening of the
N3–Re1–X(cis) mean angle of 93.8Њ. The short Re1᎐N3
[1.744(5) Å] and N3–N4 [1.284(7) Å] distances suggest the
᎐
Fig. 4 An ORTEP view of complex 14 showing thermal ellipsoids at
30% probability.
J. Chem. Soc., Dalton Trans., 2002, 2843–2851
2847

View Article Online
presence of two adjacent double bonds on the Re1᎐N3᎐N4–Ar
᎐
᎐
Experimental
unit, an observation confirmed by the linearity of the Re1᎐N3᎐
᎐
᎐
Unless otherwise noted, all chemicals were reagent grade and
used without further purification. The compounds [Re-
(NNC(Ph)O)(PPh3)2Cl2]9 and [ReN2(CO)2(PPh3)2Cl]10b were
prepared following the methodologies herein described as well
as literature methods. [ReN2(P)4Cl]10b (P = PMe2Ph, PMePh2)
and [ReO(PPh3)2Cl3]34 were prepared according to literature
procedures. Protected amino acids, in  configuration, were
purchased from Inalco per la Nova Biochem, Milan, Italy.
Elemental analyses were performed using a Carlo Erba
Instruments model EA 1110 machine; FT-IR spectra were
recorded in the range 4000–200 cmϪ1 on a Nicolet 510 P FT-IR
instrument in KBr, using a Spectra-Tech collector diffuse
reflectance accessory. Electrochemical measurements were
carried out on dichloromethane solutions that contained 0.1 M
tetra-n-butylammonium hexafluorophosphate (TBAH) as
supporting electrolyte. E1/2 values were referenced to a SCE
electrode at room temperature and are uncorrected for junction
potentials. Voltammetric experiments were performed with an
Ecochemie Autolab PGstat 30 apparatus using a glassy carbon
working electrode and a platinum wire auxiliary electrode.
Proton spectra of CDCl3 solutions of the compounds were
examined on a Bruker AM 200 spectrometer with SiMe4 as
internal standard, 31P{1H} NMR on the same instrument with
a 85% H3PO4 solution as external standard. Melting points
were taken on a Reichert-Jung Termovar apparatus and are
uncorrected. Conductivities were obtained at sample con-
centrations of ca. 1 × 10Ϫ4 M in CH2Cl2 solutions at room
temperature with an Amel Model 134 conductivity meter.
Electronic absorption spectra were obtained on a Perkin-Elmer
Lambda 40 spectrophotometer, X-band EPR spectrum of 5 was
recorded with a Bruker 220 SE spectrometer. Magnetic moment
measurements were determined on a magnetic susceptibility
balance, MSB-AUTO, Scherwood Scientific Ltd.
N4 moiety [170.1(5)Њ]. These structural data are in perfect
agreement with those observed in other rhenium organodiaze-
nido complexes.19,25–29 The co-ordinated benzoyl-2-amino-
thiazole ligand shows similar features to those observed in
complex 9, except for the Re1–O1 bond which displays a more
usual distance of 2.045(4) Å which is shorter than Re1–N1 one
of 2.116(5) Å, showing that the organodiazenido unit does not
induce a trans influence.
Compound 12 is an analogous organodiazenido complex of
Re() where the chlorine atom and a triphenylphosphine of
complex 11 are substituted by a second deprotonated benzoyl-
2-aminothiazole molecule. The two chelate rings are almost
mutually orthogonal and their geometrical features are com-
parable to those observed in complexes 9 and 11, except for the
lengthening of the Re1–N3 distance to 2.134(8) Å which is due
to the trans influence of the triphenylphosphine group. Accord-
ingly the Re1–P distance is shortened to 2.406(3) Å owing to
the absence of the other triphenylphosphine in a mutual trans
position. The Re᎐N᎐N–Ar unit displays geometrical param-
᎐
᎐
eters in agreement with those observed in complex 11 [Re1–N5
= 1.753(8), N5–N6 = 1.28(1) Å, Re1–N5–N6 = 160.5(8)Њ] giving
rise to an analogous octahedral distortion estimated by the
N5–Re1–X(cis) mean angle of 94.1Њ.
Compound 14 is a dinuclear complex where two octahedral
Re()-oxo units share a µ(O) oxygen. The basal co-ordination
sites of each Re() atom are occupied by two deprotonated
nitrogens of the ligand and by the neutral nitrogen of the
aminothiazole of a second molecule of ligand. A molecule of
dimethylphenylphosphine completes the basal co-ordination.
Usually, the O᎐Re–O–Re᎐O backbone is linear,20b,30–32 however,
᎐
᎐
this structure represents one of the few cases20a,33 where,
for steric reasons, the Re–O–Re bridging unit is rather bent
[Re1–O3–Re2 = 138.3(4)Њ]. The two Re()-oxo dimers are
related by a two-fold non-crystallographic axis coincident with
Synthesis of ligands
the bisector of the Re1–O3–Re2 angle. Re᎐O multiple bonds of
᎐
1.690(7) and 1.684(7) Å, and Re–µ(O) distances of 1.925(7) and
1.897(7) Å are in agreement with the values found in similar
linear and bent complexes.20a,b,30–33 Since the N2 and N5 atoms
are in a trans position with respect to a dimethylphenylphos-
phine group, the Re1–N2 and Re2–N5 distances, 2.075(7) and
2.078(9) Å, respectively, display a lengthening with respect to
Re1–N3 and Re2–N6, 2.028(8) and 2.025(7) Å. Furthermore,
the Re1–N4 and Re2–N1 bonds, 2.280(9) and 2.282(8) Å,
respectively, show a more significant lengthening because both
the N4 and N1 nitrogens are neutral atoms while N2, N3, N5
and N6 are negatively charged.
The ligands have been obtained following the methodologies
previously described by us.14 When benzoyl chloride was
used instead of its corresponding carboxylic acid, addition of
4-methylmorpholine was required to neutralise the hydro-
chloric acid formed in the coupling reaction.
HL1. (82%), mp 126–128 ЊC. (Found: C, 55.3; H, 4.85; N,
13.65; S, 10.7%. C14H15N3O3S requires C, 55.1; H, 4.95; N,
13.75; S, 10.5%); νmax/cmϪ1 3220 (NH), 1720, 1670 (CO);
δH (CDCl3) 1.5 (3H, d, CαHCH3), 4.7 (1H, m, CαH), 5.1 (2H, m,
CH2Ph), 5.95 (1H, br s, CαHNH ), 7.0 (1H, d, CHN), 7.3 (5H,
m, Ph), 7.55 (1H, d, CHS), 13.4 (1H, br s, NH).
Concluding remarks
HL2. (74%), mp 97–99 ЊC. (Found: C, 62.7; H, 5.1; N, 11.1; S,
8.25%. C20H19N3O3S requires C, 63.0; H, 5.0; N, 11.0; S, 8.4%);
νmax/cmϪ1 3325 (NH), 1720, 1684 (CO); δH (CDCl3) 3.1 (2H, m,
CαHCH2), 4.8 (1H, m, CαH), 5.1 (2H, m, CH2Ph), 5.8 (1H, d,
CαH NH ), 6.95 (1H, d, CHN), 7.0–7.4 (10H, m, Ph), 7.5 (1H, d,
CHS), 12.1 (1H, br s, NH).
We have prepared and characterized new rhenium complexes
containing amino acids functionalized with 2-aminothiazole
(HLn). The reaction of the Re() precursor [ReN2(CO)2-
(PPh3)2Cl] 2 with HLn led to Re() derivatives [Re(Ln)(CO)-
(PPh3)2Cl] 5–9 which represent examples of mononuclear
species containing a monoanionic bidentate ligand. Moreover,
unexpected dimeric oxo-(µ-oxo)-Re() species [Re2(O)3(Ln)2(P)2]
(P = PMe2Ph, n = 1, 13; n = 2, 14; n = 4, 15. P = PMePh2, n = 2,
16) were obtained from reaction of HLn and [ReN2(P)4Cl] (P =
PMe2Ph, PMePh2). As shown by our crystallographic studies,
these oxo-complexes are one of the few cases where, for steric
reasons, the Re–O–Re bridging unit is bent rather than linear.
Interaction of HLn ligands with the Re() complex [Re-
(NNC(Ph)O)(PPh3)2Cl2] 1 gave mono- or di-substituted Re()
organodiazenido compounds of general formulation [Re-
HL3. (76%), mp 147–149 ЊC. (Found: C, 48.5; H, 6.35; N,
15.35; S, 11.5%. C11H17N3O3S requires C, 48.7; H, 6.3; N, 15.5;
S, 11.8%); νmax/cmϪ1 3200–3400 (NH), 1678 (CO); δH (CDCl3)
1.45 (9H, s, CCH3), 1.5 (3H, d, CαHCH3), 4.6 (1H, m, CαH),
5.45 (1H, br s, CαH NH ), 7.05 (1H, d, CHN), 7.6 (1H, d, CHS),
12.25 (1H, br s, NH).
HL4. (50%), mp 124–126 ЊC. (Found: C, 59.0; H, 6.05; N,
11.95; S, 9.5%. C17H21N3O3S requires C, 58.8; H, 6.1; N, 12.1; S,
9.25%); νmax/cmϪ1 3240 (NH), 1707–1665 (CO); δH (CDCl3) 1.4
(9H, s, CCH3), 3.1 (2H, m, CαHCH2), 4.7 (1H, m, CαH), 5.3
(1H, br d, CαH NH ), 7.0 (1H, d, CHN), 7.0–7.3 (5H, m, Ph),
7.6 (1H, d, CHS), 11.8 (1H, br s, NH).
(NNCOPh)(L)(PPh3)2Cl]
or
[Re(NNCOPh)(L)2(PPh3)],
respectively. In conclusion, 2-aminothiazole seems to be a
suitable fragment to form bifunctional chelating agents useful
for preparing rhenium complexes in low oxidation states.
2848
J. Chem. Soc., Dalton Trans., 2002, 2843–2851

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HL5. (75%), mp 152–154 ЊC. (Found: C, 58.7; H, 3.9; N,
13.75; S, 15.55%. C10H8N2OS requires C, 58.8; H, 3.95; N, 13.7;
S, 15.7%); νmax/cmϪ1 3100–3200 (NH), 1677 (CO); δH (CDCl3)
7.0, 7.6, 8.1 (7H, m, CHN, Ph, CHS), 12.9 (1H, s, NH).
3.75; S, 2.85%); νmax/cmϪ1 3430 (NH), 1840 (C᎐O), 1713
᎐
᎐
(CO)carbam., 1530 (CO)amidic., 1495–1437 (CN)thiaz and 1171
(CS)thiaz.
.
[Re(L5)(PPh3)2(CO)Cl] 9. (60%), (Found: C, 57.5; H, 3.9;
Synthesis of [ReN2(CO)2(PPh3)2Cl] 2
N, 2.8; S, 3.0%. C47H37ClN2O2P2ReS requires C, 57.7; H, 3.8;
N, 2.85; S, 3.3%); νmax/cmϪ1 1825 ν(C᎐O), 1524 (CO)
,
To [As(Ph)4][ReO4] (200 mg, 0.32 mmol in CH2Cl2, 10 cm3) was
added conc. HCl (20 cm3) and the reaction mixture kept under
vigorous stirring at room temperature until the organic phase
became orange–red, probably due to the formation of oxo-
pentachlororhenate() anion.35 Benzoylhydrazine (3.2 mmol)
was added and a colour change to pale yellow was observed.
After separation of the two phases, ethanol (2 cm3) and PPh3
(2.5 mmol) were added to the organic solution. The mixture
was gently warmed until it became bright green. This solution
contains the chelate complex [Re(NNC(Ph)O)(PPh3)2Cl2] 1. A
mixture of methanol–benzene (1 : 1, 40 cm3) and PPh3 (2.5
mmol) was added and the reaction mixture was heated under
reflux for 45 min while carbon monoxide was bubbled through
the solution. A pale yellow powder was formed during this
time; it was filtered off and washed with EtOH and Et2O to
eliminate excess PPh3. An aliquot of the product may be
obtained from the concentrated mother solution. The identity
of this product was based on a comparison of its spectroscopic
properties and elemental analysis with those of an authentic
sample.10a Yield > 85% based on starting rhenium salt.
amidic
᎐
᎐
1487 (CN)thiaz. and 1172 (CS)thiaz.. E1/2(Re/ couple) ϩ0.580,
E1/2(Re/ couple) Ϫ0.777 V, scan rate = 100 mV sϪ1. λmax/nm
(CH2Cl2) 500 (ε/dm3 molϪ1 cmϪ1 2080).
Synthesis of Re(III) complexes [Re(NNCOPh)(L2,5)(PPh3)2Cl]
10, 11 and [Re(NNCOPh)(L5)2(PPh3)] 12
The green complex [Re(NNC(Ph)O)(PPh3)2Cl2] 1 (150 mg, 0.16
mmol) and HL2,5 (0.16 mmol) were dissolved in 15 cm3 each of
methanol and benzene, and NEt3 (1 cm3) added. The mixture
was refluxed and stirred for 5 h and it was accomplished by a
colour change from green to brown. The solvent was removed
under vacuum and the resulting brown solid washed with etha-
nol (2 × 2 cm3) and dried with diethyl ether. The same results
were obtained when the reactions were performed in benzene
(30 cm3). Recrystallization from CH2Cl2 gave olive-green
crystals of 10 and 11. Following an identical procedure, the
disubstituted complex 12 could be recovered when the reaction
was carried out with two equivalents of ligand. Yields deter-
mined on the starting rhenium precursor were ≥80% for all the
complexes.
Synthesis of Re(II) complexes [Re(Ln)(PPh3)2(CO)Cl] 5–9
(n ؍ 1–5)
[Re(NNCOPh)(L2)(PPh3)2Cl] 10. (85%), (Found: C, 59.5;
H, 4.15; N, 5.6; S, 2.4%. C63H53ClN5O4P2ReS requires C, 60.05;
H, 4.2; N, 5.55; S, 2.5%); νmax/cmϪ1 1722 (CO)carbam., 1635
A sample of the precursor [ReN2(CO)2(PPh3)2Cl] 2 (100 mg,
0.12 mmol) in CH2Cl2–C6H6 (1 : 2v/v, 40 cm3; alternatively, in
C6H6, 40 cm3) was treated with the appropriate ligand as a solid
in 1 : 2 stoichiometric ratio and NEt3 (1 cm3) added. Within
10 min the yellow solution turned to red; the reaction mixture
was refluxed for 6 h. The volume was reduced to ca. 1 cm3 and
an equal volume of diethyl ether and ethanol was added to
induce precipitation. A red solid was filtered off, washed with
ethanol (2 × 2 cm3) and dried with Et2O. Yields determined on
the starting material ranged from 40% for 7 and 8 to 85% for 5.
As an example, a reaction was carried out with HL5 in
anhydrous benzene with Proton-Sponge [1,8-bis(dimethyl-
amino)naphthalene] as deprotonating agent under a stream of
dinitrogen. The corresponding complex 9 was collected in good
yield (ca. 80%). Recrystallization of 9 from CH2Cl2–EtOH gave
good quality crystals suitable for X-ray analysis.
(CO)benzoyl, 1504 (N᎐N)hydraz and 1235 (benzoyl); δH (CDCl3) 2.3
᎐
(1H, m, CαHCH2), 2.7 (1H, m, CαHCH2), 4.2 (1H, m, CαH), 5.0
(2H, s, CH2Ph), 5.15 (1H, d, NH), 6.1 (1H, d, CHN), 6.8 (1H, d,
CHS), 7.0–7.9 (45H, m, Ph); δP (CDCl3) 4.0 (s).
[Re(NNCOPh)(L5)(PPh3)2Cl] 11. (90%), (Found: C, 58.65;
H, 3.95; N, 5.1; S, 3.0%. C53H42ClN4O2P2ReS requires C, 58.8;
H, 3.9; N, 5.2; S, 2.95%); νmax/cmϪ1 1635 (CO)benzoyl, 1510 (N᎐
᎐
N)hydraz and 1238 (benzoyl); δH (CDCl3) 5.65 (1H, d, CHN), 6.2
(1H, d, CHS), 6.4–7.6 (40H, m, Ph); δP (CDCl3) 4.0 (s).
[Re(NNCOPh)(L5)2(PPh3)] 12. (80%), (Found: C, 54.5; H,
3.45; N, 8.4; S, 6.25%. C45H34N6O3PReS2 requires C, 54.7; H,
3.5; N, 8.5; S, 6.5%); νmax/cmϪ1 1635 (CO)benzoyl, 1505 (N᎐N)
and 1235 (benzoyl); δH (CDCl3) 5.75 (1H, d, CHN), 6.2 (1H, d,
CHS), 6.4–7.6 (40H, m, Ph); δP (CDCl3) 11.3 (s).
᎐
hydraz
[Re(L1)(PPh3)2(CO)Cl] 5. (85%), (Found: C, 56.7; H, 3.95; N,
3.7; S, 2.8%. C51H44ClN3O4P2ReS requires C, 56.8; H, 4.1;
N, 3.9; S, 2.95%); νmax/cmϪ1 3424 (NH), 1836 (C᎐O), 1723
᎐
᎐
(CO)carbam., 1530 (CO)amidic., 1491–1435 (CN)thiaz. and 1171
Synthesis of Re(V) complexes [Re2O3(Ln)2(PMe2Ph)2] 13–15 (n ؍
1, 2, 4) and [Re2O3(L2)2(PMePh2)2] 16
(CS)thiaz.. E1/2(Re/ couple) ϩ0.630, E1/2(Re/ couple) Ϫ0.700
V, scan rate = 200 mV sϪ1. λmax/nm (CH2Cl2) 450 (ε/dm3 molϪ1
cmϪ1 2500).
To a solution of the dinitrogen complex [ReN2(PMe2Ph)4Cl] 3
(100 mg, 0.12 mmol) in CH2Cl2–C6H6 (1 : 2, 40 cm3) ligand as a
solid (0.24 mmol) and NEt3 (1 cm3) were added. The resulting
yellow solution was heated under reflux and stirred for ca. 30 h.
After 15 min a colour change to yellow–brown was observed.
The solvent was removed on a rotary evaporator. The brown
residue was treated with EtOH to separate 14 and 15 as violet
solids. Compound 14 was dried with Et2O, while 15, which is
soluble in diethyl ether, was dried under vacuum. Complex 13
was soluble in ethanol and the solid could be precipitated from
EtOH–H2O solution and dried under vacuum with P2O5.
Suitable crystals of 14 for X-ray determination were grown
from a CH2Cl2–EtOH mixture. For comparison, 16 could be
recovered from precursor 4 following the procedure indicated
before but with a reaction time of 6 h. In the synthesis of 13–15,
a chromatographic analysis showed the formation of a
by-product identified as the Re() complex [Re(PMe2Ph)3Cl3]
which was isolated when the reactions were carried out in
[Re(L2)(PPh3)2(CO)Cl] 6. (65%), (Found: C, 59.6; H, 4.0; N,
3.4; S, 2.6%. C57H48ClN3O4P2ReS requires C, 59.2; H, 4.2;
N, 3.6; S, 2.8%); νmax/cmϪ1 3416 (NH), 1838 (C᎐O), 1723
᎐
᎐
(CO)carbam., 1530 (CO)amidic, 1499–1439 (CN)thiaz., 1173 (CS)thiaz.
and 1092 (PPh3). E1/2(Re/ couple) ϩ0.650, E1/2(Re/ couple)
Ϫ0.730 V, scan rate = 200 mV sϪ1.
[Re(L3)(PPh3)2(CO)Cl] 7. (40%), (Found: C, 55.6; H, 4. 5; N,
4.1; S, 2.9%. C48H46ClN3O4P2ReS requires C, 55.2; H, 4.5; N,
4.0; S 3.05%); νmax/cmϪ1 3434 (NH), 1829 (C᎐O), 1713
᎐
᎐
(CO)carbam.
(CS)thiaz.. E1/2(Re/ couple) ϩ0.600, E1/2(Re/ couple) Ϫ0.750
V, scan rate = 100 mV sϪ1
,
1505 (CO)amidic.
,
1435 (CN)thiaz. and 1171
.
[Re(L4)(PPh3)2(CO)Cl] 8. (40%), (Found: C, 57.8; H, 4.5; N,
3.7; S, 2.9%. C54H50ClN3O4P2ReS requires C, 57.5; H, 4.5; N,
J. Chem. Soc., Dalton Trans., 2002, 2843–2851
2849

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Table 5 Crystal data
Compound
9
11
12
14
Formula
M
System
Space group
a/Å
b/Å
c/Å
α/Њ
C47H37ClN2O2P2ReS
977.44
C53H42ClN4O2P2ReS
1082.56
Monoclinic
P21/n
20.8074(6)
9.9213(2)
23.4766(8)
90
108.775(1)
90
4588.4(2)
4
C45H34N6O3PReS2
988.07
Monoclinic
P21/n
10.4175(6)
21.6210(18)
18.4750(12)
90
98.805(5)
90
4112.0(5)
4
C56H56N6O9P2Re2S2
1445.53
Orthorhombic
P212121
14.9495(3)
17.8488(4)
21.3756(2)
90
90
90
5703.6(2)
4
1.695
Triclinic
¯
P1
9.7671(1)
11.7999(2)
19.8616(3)
76.5863(8)
89.1218(10)
68.3395(9)
2063.17(5)
2
β/Њ
γ/Њ
U/Å3
Z
Dc/g cmϪ3
1.573
1.567
1.596
T /K
293
31.79
293
28.69
293
31.45
293
44.30
µ/cmϪ1
Unique reflections
Rint
Observed reflections [I > 2σ(I )]
R (observed reflections)
wR (all reflections)
11830
0.045
10995
0.0303
10883
0.055
8217
0.0590
6345
0.048
4968
0.0649
0.1435
8629
0.065
7129
0.0469
0.1103
0.0734
0.1209
anhydrous solvents and under a nitrogen stream. Complexes
13–15 were purified on a silica gel column and eluted with ethyl
acetate–hexane (1 : 1v/v).
calculated. Further details of the structure determinations are
given in Table 5.
CCDC reference numbers 179466–179469.
See http://www.rsc.org/suppdata/dt/b2/b201609p/ for crystal-
lographic data in CIF or other electronic format.
[Re2O3(L1)2(PMe2Ph)2] 13. (40%), (Found: C, 41.0; H, 3.8; N,
6.7; S, 5.0%. C44H48N6O9P2S2Re2 requires C, 40.5; H, 3.7; N,
6.4; S, 4.9%); νmax/cmϪ1 1657 (COcarbam
, COamidic), 1437
Acknowledgements
(CN)thiaz., 1287 (CS)thiaz., 945, 912 (Re᎐O) and 671 (Re–O–Re);
᎐
δH (CDCl3) 1.5 (12H, m, PCH3), 1.7 (6H, m, CαHCH3), 4.6 (2H,
m, CαH), 5.1 (4H, d, CH2Ph), 6.2 (2H, br d, CHN), 6.6 (2H, br
d, CHS), 7.2–7.5 (20H, m, Ph); δP (CDCl3) Ϫ19.0 (s).
This work was supported by Italian MURST in the frame of
the project “Pharmacological and Diagnostic Properties
of Metal Complexes” (co-ordinator Prof. G. Natile). We are
grateful to Dr A. Molinari for recording EPR spectra and
Dr A. Prodi for electrochemical measurements. We thank
Mr M. Fratta for technical assistance and elemental analyses
and Mr F. Cecconi, ISSECC CNR, Firenze, Italy, for magnetic
moment measurements.
[Re2O3(L2)2(PMe2Ph)2] 14. (90%), (Found: C, 46.1; H, 3.85;
N, 5.65; S, 4.5%. C56H56N6O9P2Re2S2 requires C, 46.2; H, 3.9;
N, 5.8; S, 4.3%); νmax/cmϪ1 1657 (COcarbam., COamidic), 1437
(CN)thiaz., 1281 (CS)thiaz., 910 (Re᎐O) and 671 (Re–O–Re); δ
᎐
H
(CDCl3) 1.5, 1.9 (12H, 2d, J = 13.6 Hz, PCH3), 3.25 (4H, m,
CαHCH2), 4.0 (2H, m, CαH), 5.3 (4H, 2s, CH2Ph), 6.6 (2H, d,
CHN), 7.1–7.4 (32H, m, Ph, CHS); δP (CDCl3) Ϫ21.0 (s).
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N, 5.3; S, 4.05%); νmax/cmϪ1 1659 (COcarbam., COamidic), 1437
(CN)thiaz., 1287 (CS)thiaz., 937, 894 (Re᎐O) and 695 (Re–O–Re);
᎐
δH (CDCl3) 2.0 (3H, s, PCH3), 2.1 (3H, s, PCH3), 3.1–3.5 (4H,
m, CαHCH2), 4.3 (2H, m, CαH), 5.1 (4H, s, CH2Ph), 6.5 (2H, d,
CHN), 7.0 (2H, d, CHS), 7.1–7.8 (40H, m, Ph); δP (CDCl3)
Ϫ10.0 (s).
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