Synthesis, characterization and redox behaviour of benzoyldiazenido- and oxorhenium complexes bearing N,N- and S,S-type ligands

Article abstract of DOI:10.1016/j.ica.2009.08.030

The reactions of [ReCl₂{η²-N₂C(O)Ph}(PPh₃ )₂] (1) with 2-aminopyrimidine (H₂Npyrm), 2,2′-bipyridine (bpy) and tetraethylthiuram disulfide (tds), in MeOH upon reflux, lead to the new η¹

Full text of DOI:10.1016/j.ica.2009.08.030

Inorganica Chimica Acta 363 (2010) 1269–1274
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization and redox behaviour of benzoyldiazenido-
and oxorhenium complexes bearing N,N- and S,S-type ligands
Alexander M. Kirillov a, Elisabete C.B.A. Alegria a,b, M. Fátima C. Guedes da Silva a,c, Luísa M.D.R.S. Martins a,b
,
Catarina Sousa b, Armando J.L. Pombeiro a,
*
a Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
b Departamento de Engenharia Química, ISEL, R. Conselheiro Emídio Navarro, 1950-062 Lisbon, Portugal
c Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Campo Grande 376, 1749-024 Lisbon, Portugal
a r t i c l e i n f o
a b s t r a c t
The reactions of [ReCl2{g2-N2C(O)Ph}(PPh3)2] (1) with 2-aminopyrimidine (H2Npyrm), 2,20-bipyridine (bpy)
and tetraethylthiuram disulfide (tds), in MeOH upon reflux, lead to the new
1-(benzoyldiazenido)-
rhenium(III) complexes [ReCl{
1-N2C(O)Ph}(HNpyrm)(PPh3)2] (2) and [ReCl2{ 1-N2C(O)Ph}(bpy)(PPh3)]
(3), and the known oxo(diethyldithiocarbamato)dirhenium(v) complex [Re2O2( -O){Et2NC(S)S}4] (4),
Article history:
Received 20 July 2009
Received in revised form 20 August 2009
Accepted 21 August 2009
Available online 27 August 2009
g
g
g
l
respectively. The Et2NC(S)S ligands in 4 result from S–S bond rupture of tds molecules. The obtained com-
pounds have been characterized by IR, 1H, 31P{1H} and 13C{1H} NMR spectroscopies, FAB+-MS, elemental
and single-crystal X-ray diffraction (for 2 and 4) analyses. Complex 2 represents the first structurally charac-
terized Re compound derived from 2-aminopyrimidine. Besides, the redox behaviour of 2–4 in CH2Cl2
solution has been studied by cyclic voltammetry, and the Lever electrochemical ligand parameter (EL) has
been estimated, for the first time, for HNpyrm. The electrochemical results are discussed in terms of electronic
properties of the Re centres and the ligands.
Dedicated to Professor Jonathan Dilworth
with recognition for his scientific
achievements.
Keywords:
Rhenium
Benzoyldiazenido complexes
Pyrimidine
2,20-Bipyridine
Dithiocarbamate
Electrochemistry
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
N,N- and S,S-type ligands, we report herein the synthesis, full char-
acterization and redox behaviour of three complexes derived from
Rhenium is known to possess a very rich coordination chemis-
try [1–3] that nowadays continues to be a topic of intensive re-
search, mainly due to the variety of applications of Re complexes,
ranging from medicinal chemistry [4–6] and catalysis [2,7–11] to
photophysics [12–14] and materials chemistry [1,15,16]. In partic-
1, upon reactions with 2-aminopyrimidine (H2Npyrm), 2,20-bipyr-
idine (bpy) or tetraethylthiuram disulfide (tds). The choice of these
ligands was governed by their relative simplicity, commercial
availability and recognized applications for the synthesis of biolog-
ically active molecules [31–33].
ular, the benzoylhydrazido complex [ReCl2{g
2-N2C(O)Ph}(PPh3)2]
(1) discovered by Chatt et al. [17,18], has been successfully used
as a versatile starting material for the preparation of various rhe-
nium compounds with significance in the fields of nitrogen fixa-
tion, nuclear–medical research, catalysis and electrochemistry
[19–26].
In pursuit of our general interest on the coordination chemistry
of rhenium [2,9–11,24–30], we have recently obtained from 1 a
series of Re complexes bearing various N- and N,O-donor ligands,
such as aminopolyalcohols, pyridinecarboxylates, scorpionates
and N-heterocycle species [10,24]. Aiming at the extension of these
studies and further exploration of the reactivity of 1 towards other
2. Experimental
2.1. Materials and general procedures
All manipulations and reactions (unless stated otherwise) were
performed under an atmosphere of dinitrogen using standard
vacuum and inert-gas flow techniques. Solvents were purified
by standard procedures and freshly distilled prior to use. All
chemicals were obtained from commercial sources and used as
received. [ReCl2{g
2-N2C(O)Ph}(PPh3)2] (1) was prepared by a pub-
lished method [18]. Infrared spectra were recorded on a Nicolet
Impact 400D or a Perkin–Elmer 1330 spectrophotometers, in
KBr pellets (abbreviations: vs – very strong, s – strong, m – med-
ium). 1H, 31P{1H} and 13C{1H} NMR spectra were recorded on a
* Corresponding author. Fax: +351 21 846 4455.
E-mail address: pombeiro@ist.utl.pt (A.J.L. Pombeiro).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.08.030

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A.M. Kirillov et al. / Inorganica Chimica Acta 363 (2010) 1269–1274
Varian Unity 300 spectrometer at ambient temperature; d values
(15 mL), and the obtained mixture was refluxed for about 2 h.
The obtained greyish purple suspension was filtered off, washed
with MeOH (3 ꢀ 10 mL) and dried in vacuo to yield compound 3
as a purple solid. Yield 42 mg (68%), based on 1. Product 3 is solu-
ble in Me2CO, CH2Cl2, CHCl3 and MeCN. IR (KBr), selected bands,
are in ppm relative to SiMe4 (1H or 13C) or external 85% aqueous
solution of H3PO4
(
31P). Coupling constants are given in Hz;
abbreviations refer to: s – singlet, d – doublet, t – triplet, q –
quartet, m – complex multiplet, br – broad. Positive-ion FAB mass
spectra were obtained on a Trio 2000 spectrometer by bombard-
ing 3-nitrobenzyl alcohol (m-NBA) matrices of the samples with
8 keV (ca. 1.28 ꢀ 1015 J) Xe atoms. Mass calibration for data sys-
tem acquisition was achieved using CsI. The C, H, N, S elemental
analyses were carried out by the Microanalytical Service of the
Instituto Superior Técnico.
The electrochemical experiments were performed on an EG&G
PAR 273A potentiostat/galvanostat connected to a personal com-
puter through a GPIB interface. Cyclic voltammograms (CV) were
obtained using a two-compartment three-electrode cell, at Pt disc
working (d = 1.0 mm) and Pt wire counter electrodes, in 0.2 M
[nBu4N][BF4]/CH2Cl2 solution. Controlled-potential electrolyses
(CPE) were carried out in electrolyte solutions with the above-
mentioned composition, in a three-electrode H-type cell. The
cmꢁ1: 1634 [vs,
and/or
m
(C@O)], 1515 and 1475 [vs,
m(N@N) N2C(O)Ph
m
(N@C) bpy]. 1H (CD2Cl2), d: 9.09 [d, J = 5.6, 2H,
{H(2)bpy}], 8.70 [d, J = 5.5, 2H, {H(5)bpy}], 8.01 [m, 2H, o-CH
{C(O)Ph}], 7.97 [m, 1H, p-CH {N2C(O)Ph}], 7.92 [m, 2H, m-CH
{N2C(O)Ph}], 7.75 [t, J = 7.8, 2H, {H(3)bpy}], 7.48 [t, J = 7.4, 2H,
{H(4)bpy}], 7.35–7.28 [m, 6H, o- or m-CH (PPh3)], 7.25–7.10 [m, 9
H, {(m or o) + p}CH (PPh3)]. 31P{1H} (CD2Cl2), d: ꢁ5.86 [s]. 13C{1H}
(CD2Cl2), d: 167.50 [s, C@O {N2C(O)Ph}], 151.88 [s, C(1) (bpy)],
151.52 [s, C(2) (bpy)], 139.28 [s, C(3) (bpy)], 135.98 [s, Cp
{C(O)Ph}], 134.07 [t, JCP = 5.3, Co (PPh3)], 132.87 [s, Co or Cm
{C(O)Ph}], 132.27 [s, Cm or Co {C(O)Ph}], 130.55 [s, Cp (PPh3)],
129.25 [t, JCP = 8.0, Ci (PPh3)], 128.63 [t, JCP = 4.6, Cm (PPh3)],
127.46 [s, Ci {C(O)Ph}]. 125.53 [s, C(4) (bpy)], 121.40 [s,
C(5) (bpy)]. FAB+-MS: m/z: 809 [M]+, 773 [MꢁCl]+,
640 [MꢁClꢁ{N2C(O)Ph}]+, 484 [ReCl(PPh3)]+. Anal. Calc. for
C35H28Cl2N4OPRe: C, 52.0; H, 3.5; N, 6.9. Found: C, 52.6; H, 4.3;
N, 6.7%.
compartments were separated by
a sintered glass frit and
equipped with platinum gauze working and counter electrodes.
For both CV and CPE experiments, a Luggin capillary connected
to a silver wire pseudo-reference electrode was used to control
the working electrode potential. The CPE experiments were mon-
itored regularly by cyclic voltammetry (CV), thus assuring no sig-
nificant potential drift occurred along the electrolyses. The
oxidation potentials of the complexes were measured by CV
(see above) in the presence of ferrocene as the internal standard,
2.4. Synthesis of [Re2O2(l-O){Et2NC(S)S}4] (4)
A mixture of 1 (73 mg, 0.080 mmol) and tetraethylthiuram
disulfide (71 mg, 0.24 mmol) was refluxed in MeOH (15 mL) under
air for about 6 h. The resulting brown solution was concentrated
under reduced pressure, followed by the addition of Et2O which
led to the precipitation of a brown compound. This was filtered-
off, washed with Et2O (3 ꢀ 10 mL) and dried in vacuo to give com-
pound 4 as a brown solid. Yield 59 mg (72%), based on 1. It is sol-
uble in MeOH, EtOH, CH2Cl2, CHCl3 and H2O. IR (KBr), selected
and the redox potential values are quoted relative to the SCE by
ox
using the [Fe(
g
5-C5H5)2]0/+ (E ¼ 0:55 V versus SCE) redox cou-
1=2
ple in 0.2 M [nBu4N][BF4]/CH2Cl2. [34] The obtained potentials
versus SCE can be converted to the NHE scale by addition of
0.245 V [35,36].
2.2. Synthesis of [ReCl{g
1-N2C(O)Ph}(HNpyrm)(PPh3)2] (2)
bands, cmꢁ1: 1519 [vs,
911 [m, (Re@O), Et2NS2], 672 [m,
m
(C–N), Et2NCS2], 1021 [m,
m(C@S), Et2NS2],
m
m
(Re–O–Re)]. 1H {(CD3)2CO} d:
To a light green suspension of 1 (72 mg, 0.079 mmol) in
methanol (15 mL), an excess of 2-aminopyrimidine (23 mg,
0.238 mmol) was added and the reaction mixture was refluxed
for about 16 h. After cooling, the resulting cloudy solution was fil-
tered off, and the solid was washed with MeOH (3 ꢀ 10 mL) and
dried in vacuo to furnish compound 2 as a green solid. Yield
43 mg (54%), based on 1. Complex 2 is soluble in CH2Cl2 and CHCl3,
but insoluble in MeOH, Me2CO, Et2O and C6H6. IR (KBr), selected
3.72 [q, 8H, CH2], 2.93 [q, 8H, CH2], 1.33 [m, 24H, CH3]. 13C{1H}
{(CD3)2CO} d: 125.27 and 122.26 [s, Et2NCS2], 37.24 [s, CH2],
17.05 and 9.37 [s, CH3]. FAB+-MS: m/z: 1014 [M]+, 818
[MꢁEt2NCS2]+, 515 [MꢁReO{Et2NCS2}2]+. Anal. Calc. for
C20H40N4O3Re2S8: C, 23.7; H, 4.0; N, 5.5, S, 25.3. Found: C, 23.8;
H, 4.5; N, 5.4; S, 25.0%. X-ray quality crystals of complex 4 were
grown by slow evaporation at 5 °C of a (CH3)2CO/CH2Cl2 solution
of 4.
bands, cmꢁ1: 3118 [m,
[vs, (N@N) N2C(O)Ph and/or
m
(NH)], 1589 [vs,
m(C@O)], 1535 and 1489
m
m
(N@C) HNpyrm]. 1H (CD2Cl2), d:
8.56 [d, 1H, HNpyrm], 8.39 [d, 1H, HNpyrm], 7.75 [d, 2H,
3JHH = 8.0, o-CH {C(O)Ph}], 7.54–7.51 [m, 6H, o- or m-CH (PPh3)],
7.36 [m, 1H, p-CH {C(O)Ph}], 7.33 [m, 2H, m-CH {C(O)Ph}], 7.28–
7.26 [m, 9H, {(o- or m-) + p}CH (PPh3)], 6.27 [t, 1H, HNpyrm].
31P{1H} (CD2Cl2), d: 24.23 [s]. 13C{1H} (CD2Cl2), d: 168.20 [s,
C@O], 135.46 [s, Cp {C(O)Ph}], 134.17 [t, JCP = 5.3, Co (PPh3)],
130.27 [s, Co or Cm {C(O)Ph}], 129.33 [s, Cm or Co {C(O)Ph}],
128.44 [s, Cp (PPh3)], 127.32 [t, JCP = 8.0, Ci (PPh3)], 128.23 [t,
JCP = 4.6, Cm (PPh3)], 127.46 [s, Ci {C(O)Ph}]. FAB+-MS:
m/z: 973 [M]+ꢀ, 879 [MꢁHNpyrm]+, 840 [Mꢁ{N2C(O)Ph}]+,
746 [Mꢁ{N2C(O)Ph}ꢁHNpyrm]+ꢀ, 711 [MꢁPPh3]+ꢀ, 578 [Mꢁ
{N2C(O)Ph}ꢁPPh3]+. Anal. Calc. for C47H39ClN5OP2Re: C, 58.0; H,
4.0; N, 7.2. Found: C, 58.3; H, 4.1; N, 7.2%. X-ray quality crystals
of 2 were grown at 5 °C by slow diffusion of diethyl ether into a
dichloromethane solution of 2.
2.5. X-ray structural determinations
The X-ray diffraction data for 2 and 4 were collected using a
Bruker AXS-KAPPA APEX II diffractometer with graphite-mono-
chromated Mo K
a radiation. Data were collected at 150 K using
omega scans of 0.5° per frame, and a full sphere of data was ob-
tained. Cell parameters were retrieved using the Bruker SMART
software and refined using Bruker SAINT on all the observed
reflections. Absorption corrections were applied using SADABS
[37]. Structures were solved by direct methods using the SHELXS
-
97 package [38] and refined with SHELXL-97 [38]. Calculations were
performed using the WinGX System-Version 1.80.03 [39]. All H
atoms were inserted in calculated positions. The obtained 150 K
crystal structure of 4 was previously measured by others at
295 K [40] revealing identical cell parameters. Therefore, the
structure of 4 is not discussed in the current work. For 2, the crys-
tallographic data are summarized in Table 1, and selected bond
lengths and bond angles in Table 2, while the molecular structure
is shown in Fig. 1.
2.3. Synthesis of [ReCl2{g
1-N2C(O)Ph}(bpy)(PPh3)] (3)
An excess of 2,20-bipyridine (37 mg, 0.236 mmol) was added to
a light green suspension of 1 (72 mg, 0.079 mmol) in methanol

A.M. Kirillov et al. / Inorganica Chimica Acta 363 (2010) 1269–1274
1271
Table 1
Crystal data and structure refinement details for compound 2.
2
Empirical formula
Formula weight
T (K)
C47H39ClN5OP2Re
973.45
150(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71069
triclinic
ꢀ
P1
9.4747(5)
13.9780(6)
16.2498(7)
98.099(3)
98.919(4)
92.625(3)
2099.81(17)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
1.540
3.076
l(Mo K
a
) (mmꢁ1
)
Number of reflections
Number of unique data
18 886
7523
Rint.
0.0605
0.0484, 0.1068
0.970
b
Final R1a, wR2 (I P 2
r)
Goodness-of-fit (GOF) on F2
Fig. 1. Crystal structure of 2 with partial atom labeling scheme. Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Re
pink, O red, P orange, N blue, C grey. Inter-molecular hydrogen bond: D–Hꢃ ꢃ ꢃA
[d(Dꢃ ꢃ ꢃA) Å; \(DHA)°]: N12–H12ꢃ ꢃ ꢃN10i [2.969(8) Å, 159.00°]; Symmetry operation
to generate equivalent atoms (i): ꢁx, 1 ꢁ y, ꢁz. (For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this
article.)
P
P
a
R1
=
||Fo| ꢁ |Fc||/ |Fo|.
P
P
2
2 1=2
wR2 ¼ ½ ½wðF2o ꢁ Fc2Þ ꢂ= ½wðF2oÞ ꢂꢂ
.
b
Table 2
Selected bond lengths (Å) and angles (°) for compound 2.
Re1–Cl1
Re1–P1
Re1–P2
Re1–N1
Re1–N11
Re1–N12
N1–N2
N2–C1
O1–C1
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–N1
Cl1–Re1–N11
2.3816(18)
2.4514(18)
2.4547(17)
1.768(6)
2.121(6)
2.126(6)
1.259(8)
1.406(9)
1.221(9)
88.53(6)
85.88(6)
107.7(2)
149.93(15)
Cl1–Re1–N12
P1–Re1–P2
88.41(16)
174.32(7)
87.46(18)
94.60(15)
90.52(15)
93.24(18)
90.76(15)
90.37(15)
102.3(2)
163.7(2)
61.7(2)
carbamato)dirhenium(v) complex [Re2O2(l-O){Et2NC(S)S}4] (4)
P1–Re1–N1
P1–Re1–N11
P1–Re1–N12
P2–Re1–N1
P2–Re1–N11
P2–Re1–N12
N1–Re1–N11
N1–Re1–N12
N11–Re1–N12
Re1–N1–N2
(Scheme 1), as shown by X-ray diffraction analysis which agrees
with that reported by others [40]. In particular, it bears a linear
O@Re–O–Re@O core where the Re atoms adopt an octahedral coor-
dination geometry, filled by four S,S-bidentate dithiocarbamate li-
gands. Compound 4 was previously synthesized by the following
pathways which are different from that we found in this work:
(i) treatment of [ReOCl3(PPh3)2] [40,41] or [Re2O3Cl4(py)]
(py = pyridine) [41] with sodium diethyldithiocarbamate, and (ii)
hydrolysis of [ReOCl{Et2NC(S)S}2] [41]. Hence, herein we provide
a new entry to 4 based on the reaction of the chelate 1 with tds
in air. The possibility of the transformation of 1 to an oxorhe-
nium(V) complex [ReOCl2(OMe)(PPh3)2] with the loss of the
N2C(O)Ph ligand has been previously reported [25].
173.6(5)
3. Results and discussion
All the obtained compounds have been isolated in ca. 62–72%
yields as green (2), purple (3) or brown (4) air-stable solids. They
are soluble and stable (within several days) in some organic sol-
vents, while 4 is also soluble in water. All the complexes have been
characterized by IR, 1H, 31P{1H} and 13C{1H} NMR spectroscopies,
FAB+-MS, elemental and single-crystal X-ray diffraction (for 2 and
4) analyses. Their redox behaviour has been also studied by cyclic
voltammetry.
3.1. Synthesis and spectroscopic characterization
2-benzoylhydrazido chelate [ReCl2{g2
-
The reactions of the
g
N2C(O)Ph}(PPh3)2] (1) with 2-aminopyrimidine (H2Npyrm) and
2,20-bipyridine (bpy) in refluxing methanol give rise to the forma-
tion of the novel
[ReCl{
1-N2C(O)Ph}(HNpyrm)(PPh3)2]
N2C(O)Ph}(bpy)(PPh3)] (3) (Scheme 1). In the formation of 2 and
3, the
2-benzoylhydrazido behaves as a hemilabile ligand with
opening of the chelating ring, leading to a monodentate benzoyl-
diazenido species,
1-N2C(O)Ph, and providing one vacant coordi-
g
1-(benzoyldiazenido)rhenium(III) complexes
g
(2)
and
[ReCl2{g1
-
The IR spectra of 2 and 3 exhibit strong bands with maxima at
g
1589 and 1634 cmꢁ1, respectively, assigned to
m
(C@O) of the
N2C(O)Ph ligand. Two strong bands observed in the 1535–
1475 cmꢁ1 range are attributed to
(N@N) of the organodiazenido
moiety, and (N@C) of either HNpyrm or bpy ligands. In other re-
g
m
nation position. The latter, along with the replacement of either
one ligated Clꢁ or one PPh3, is occupied by the new N,N-type che-
lating ligand. Such reactions involve a formal two-electron reduc-
tion of Re(V) to Re(III) that is believed to result from an intra-
molecular redox process on account of the expected conversion
m
lated Re complexes, such IR bands appear at comparable values
[10,24,25].
The FAB+-MS spectra of the all complexes 2–4 exhibit the
molecular ion [M]+ peaks with the expected isotopic patterns,
while the fragmentation pathways occur by cleavage of the me-
tal–ligand bonds and the degradation of some ligands. Hence, for
2 and 3 the [MꢁPPh3]+, [MꢁPPh3ꢁCl]+, [Mꢁ{N2C(O)Ph}]+ and
[MꢁPPh3ꢁ{N2C(O)Ph}]+ fragments, as well as those derived upon
the loss of HNpyrm and bpy moieties, have been detected. For com-
pound 4, the characteristic [MꢁEt2NCS2]+ and [MꢁReO{Et2NCS2}2]+
fragments have been observed.
of the dihapto benzoylhydrazido(3–) ligand,
the monohapto benzoyldiazenido(1–),
1-N2C(O)Ph.
Aiming at the synthesis of a
1-benzoyldiazenido compound
g
2-N2C(O)Ph, into
g
g
with tetraethylthiuram disulfide (tds), we have attempted a similar
reaction of 1 with tds which, however, resulted in (i) the degrada-
tion of 1 and (ii) the S–S bond rupture in the tds molecules, with
the unexpected formation of the already known oxo(diethyldithio-

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A.M. Kirillov et al. / Inorganica Chimica Acta 363 (2010) 1269–1274
PPh3
N
C
Ph
N
N
H
+
2Npyrm
O
N
Re
Cl
MeOH,
Δ
HN
PPh3
2
PPh3
PPh3
N
Ph
C
N
N
Cl
Cl
N
N
+ bpy
O
Re
Re
C
Ph
Cl
O
MeOH,
N
Δ
Cl
PPh3
3
1
O
Et
Et
S
S
Re
N
N
C
C
C
C
N
N
+ tds
S
S
Et
Et
Et
Et
O
MeOH,
Δ
S
S
Re
S
S
Et
Et
O
4
Scheme 1. Synthesis and molecular formulae of compounds 2, 3 and 4.
The 1H and 13C{1H} NMR spectra of 2 and 3 reveal resonances
(see Section 2) typical for the aromatic protons of the coordinated
PPh3, N2C(O)Ph, HNpyrm and bpy [10,21,22,24,25,28,30]. The ster-
eochemically favoured trans coordination of phosphines in solution
is supported by the single resonance observed at d 24.23 in the
31P{1H} spectrum of 2. In the solid state, the mutually trans orien-
tation of two PPh3 ligands in 2 has been also evidenced by the X-
ray crystal structural analysis (see below).
The monodeprotonated 2-aminopyrimidine ligand is planar and
its binding to the Re1 atom is realized through the amino N12 and
pyrimidine N11 atoms disposed trans to the
chloro ligands, respectively, with the distorted N1–Re1–N12
[163.7(2)°] and Cl1–Re1–N12 [149.93(15)°] angles. The Re1–N11
[2.121(6) Å] and Re1–N12 [2.126(6) Å] bonds are equal, within
g
1-N2C(O)Ph and
3r, resulting in the formation of the chelating four-membered
Re1–N11–C11–N12 ring. The strained character of the latter can
be evidenced by the very restricted bite N11–Re1–N12 angle of
61.7(2)°. The triphenylphosphine ligands are bound almost linearly
[P1–Re1–P2 174.32(7)°] with the average Re–P distance of
2.4531 Å. The molecules of 2 are involved in hydrogen bond inter-
actions, with relevance for those concerning the N12 amine hydro-
gen and the pyrimidine N10 atoms from two adjacent molecules
(Fig. 1). Other bonding parameters in 2 are comparable to those re-
3.2. X-ray crystal structure of [ReCl{g
1-N2C(O)Ph}(HNpyrm)(PPh3)2]
(2)
The molecular structure of 2 (Fig. 1) comprises the hexacoordi-
nated rhenium(III) atom that bears two PPh3 ligands in trans posi-
tion, while the equatorial sites are occupied by the chloro and g1
-
benzoyldiazenido ligands, being trans to the bidentate HNpyrm
moiety. The Cl1–Re1–N11 [149.93(15)°] and N11–Re1–N12
[61.7(2)°] angles (Table 2) represent major deviations from the
octahedral coordination geometry around the Re1 atom. As in the
ported for related
g
1-diazenido Re(III) complexes with different
bidentate N,O-, N,S- and O,O-type ligands, e.g. [ReCl{g1
-
N2C(O)Ph}(L)(PPh3)2] {L = 2-nitrosoacetate [10], 2-iminopropio-
nate [10], 2-picolinate [10], N-(1,3-thiazol-2-yl)benzamide [22],
pyridine-2-thiolate [44] and maltolate [45]}. Besides, complex 2
represents the first structurally characterized Re compound de-
rived from 2-aminopyrimidine [3].
other
g
1-diazenido rhenium complexes [10,22,23,25,42], the Re1–
N1–N2 moiety is linear [173.6(5)° angle], and the Re1–N1
[1.768(6) Å] and N1–N2 [1.259(8) Å] bonds are slightly shorter
than those within the
g
2-N2C(O)Ph ligand in the starting com-
pound 1 [10], being indicative of some increase of the double bond
3.3. Electrochemical studies of 2–4
order character. Taking into consideration a classification of organ-
ohydrazido ligands [43], the
a linear, four-electron donor diazenido(1–) species (a).
g
1-N2C(O)Ph moiety in 2 is typical for
The redox properties of 2–4 have been investigated by cyclic
voltammetry (CV), at a platinum electrode (d = 1 mm) in a 0.2 M
[nBu4N][BF4]/CH2Cl2 solution at 25 °C. The obtained cyclic voltam-
metric data are summarized in Table 3, while a typical example of
a voltammogram is shown for compound 3 in Fig. 2. Hence, the
neutral 18-electron Re(III) complexes 2 and 3, and the Re(V) com-
plex 4, show a first single-electron oxidation process (wave Iox) (as
confirmed by controlled-potential electrolysis). It is reversible for 2
ox
I
and 4 at E1=2 of 0.74 and 0.92 V versus SCE, respectively, and irre-
versible for 3 at IEpox ¼ 0:77 V versus SCE. These waves are assigned
to the ReIII ? ReIV (for 2 and 3) or the ReV ? ReVI (for 4) oxidations,

A.M. Kirillov et al. / Inorganica Chimica Acta 363 (2010) 1269–1274
1273
Table 3
Cyclic voltammetric data for the complexes 1–4.a
IEpox (IEo1x=2) (Iox
)
IIEpox (IIEo1x=2) (IIox
)
IErped (IEr1e=d2) (Ired
)
IIErped (IIE1re=d2) (IIred
)
Complex
1b
2c
3
0.93
(0.74)
0.77
1.42
(0.91)
0.93
1.14
ꢁ0.98
ꢁ1.31
(ꢁ1.45)
ꢁ1.47
(ꢁ1.21)
(ꢁ1.03)
4
(0.92)
a
Values given in V 0.02 relative to SCE (in [nBu4N][BF4]/CH2Cl2, scan rate = 200 mV sꢁ1; for further details, see Section 2); values for reversible waves are given in
brackets; potentials versus SCE can be converted to the NHE by adding 0.245 V.
Given for comparative purposes; a third irreversible oxidation wave is also observed at IIIEpox ¼ 1:80 V.
b
A third irreversible oxidation wave is also observed at IIIEpox ¼ 1:23 V.
c
4
2
parameter EL, see below, of ꢁ1.83 V versus NHE) [29], suggesting
IIox
Iox
that the dithiocarbamate ligands can effectively stabilize the rhe-
nium(VI) oxidized complex.
Due to the lower oxidation state of Re (in 2 and 3) and the pres-
ence of the rich electron donor oxo group (in 4), compounds 2–4
exhibit oxidation potentials that are less anodic in comparison
with the starting Re(V) chelate 1. The latter shows three irrevers-
ible oxidation waves at Eopx of 0.93, 1.42 and 1.80 V versus SCE.
All the Re complexes also exhibit (Table 3) a first reduction
0
-2
-4
-6
-8
Ired
red
wave (Ired), irreversible for 2 at Ep ¼ ꢁ0:98 V and reversible for
I
red
IIred
I
3 and 4, at E1=2 ¼ ꢁ1:21 V and ꢁ1.03 V versus SCE, respectively.
This is followed, at a lower potential, by a second wave (IIred), irre-
versible for 2 and 4, at IIErped ¼ ꢁ1:31 and ꢁ1.47 V versus SCE,
red
II
respectively, but reversible for 3, at
E
¼ ꢁ1:45 V versus SCE.
1=2
The measured first reversible oxidation potential (upon conver-
sion to the NHE scale) for the ReIII ? ReIV oxidation in the complex
[ReCl{g
1-N2C(O)Ph}(HNpyrm)(PPh3)2] (2) was applied to calculate,
-2
-1
0
1
for the first time, the electrochemical Lever EL parameter for the
HNpyrm ligand, by applying the linear relationship (1), valid for
octahedral complexes [35,36]. This equation relates the redox po-
E / V vs. SCE
Fig. 2. Cyclic voltammogram of [ReCl2{
initiated by the anodic sweep, in 0.2 M [nBu4N][BF4]/CH2Cl2, at
electrode and at a scan rate of 0.2 V sꢁ1
g
1-N2C(O)Ph}(bpy)(PPh3)] (3) (1.4 mM),
Pt working
a
tential (V versus NHE) with the sum of the EL values for all the li-
.
P
gands ( EL). EL is a measure of the net electron-donor character of
a ligand (the stronger the latter, the lower is EL). The slope (SM) and
intercept (IM) are parameters dependent on the metal redox cou-
ple, spin state and stereochemistry. Tables of values of these
parameters have been collected [35,36,48,49].
featuring the formation of the respective cationic species, which, in
the cases of 2 and 4, are considerably stable during the time of
the cyclic voltammetry experiment. At a higher potential, a second
oxidation irreversible wave (IIox) is observed at IIEpox of 0.93 and
1.14 V versus SCE for 3 and 4, respectively, thus showing the insta-
bility of the doubly oxidized species. In contrast, wave IIox is
ꢀ
X
ꢁ
E ¼ SM
EL þ IM ðV vs: NHEÞ
ð1Þ
ox
1=2
II
reversible for 2, at
E
¼ 0:91 versus SCE (Table 3). These IIox
waves are assigned to the ReIV ? ReV (for 2 and 3) or the ReVI ? R-
Hence, by using the reported [35] SM and IM values for the Re(III/IV)
redox couple (0.86 and 0.51 V versus NHE, respectively), the known
ligand EL values for PPh3, N2C(O)Ph(1–) and Clꢁ (i.e. 0.39 [36], 0.11
[29] and ꢁ0.24 [36] V versus NHE, respectively), and the IE1ox=2 value
for compound 2 [converted to the NHE scale, i.e. 0.98(5) V versus
NHE], we have estimated the overall electrochemical Lever ligand
parameter for the bidentate HNpyrm ligand as ꢁ0.10 V versus
NHE, i.e. ꢁ0.05 V versus NHE formally averaged for each of the
two-electron donor binding arms.
eVII (for 4) oxidations. In addition,
a
third irreversible
oxidation wave (IIIEpox ¼ 1:23 V versus SCE) is observed for
compound 2.
The similarity of the first oxidation potentials observed for 2
and 3 (Table 3) suggests that the overall electron-donor character
of the HNpyrm + PPh3 pair in 2 is similar to that of the bpy + Clꢁ
pair. The E1=2 potentials observed in 2 and 3 are also compara-
ble to those reported for the related complexes [ReCl2
ox
I
{N2C(O)Ph}(Hpz)(PPh3)2] (Hpz = pyrazole) and [ReCl2 {N2C(O)
Since the EL parameter is a measure of the net electron-donor
ability of a ligand (see above), one can conclude that HNpyrm
(EL = ꢁ0.05 V, averaged for each arm; hereinafter all values are in
V versus NHE) is a much stronger electron-donor than pyrimidine
itself (EL = 0.29 V) [36], bipyrimidime (EL = 0.31 V) [36], 2,2-bipyri-
dine (EL = 0.26 V) [36], pyridine (EL = 0.25 V) [36], indazole
(EL = 0.26 V) [49] and imidazole (EL = 0.12 V) [36]. However, EL of
HNpyrm is comparable to that of 2,4-pentanedionate(1–)
(EL = ꢁ0.08 V) [36] and higher than those of dimethyldithiocarba-
mate(1–) (EL = ꢁ0.12 V), di-2-pyridylaminate(1–) (EL = ꢁ0.16 V),
nitrate (EL = ꢁ0.11 V) [36] or alkynyls (EL = ꢁ0.1 to ꢁ0.7 V) [48].
However, it is worth to mention that the estimated herein EL value
should be considered rather cautiously, since it is derived from the
oxidation potential of only one compound. Further estimates of EL
ox
Ph}(Hpz)2(PPh3)] (IE ¼ 0:73 and 0.68 V versus SCE, respectively)
1=2
[24]. However, other
g
1-diazenido Re(III) compounds with differ-
ent ligands can exhibit rather distinct redox behaviours. For [ReCl2
{N2C(O)Ph}(PMePh2)3], [ReCl{N2C(O)Ph}(NCNEt2)(PMePh2)3] [BF4]
and [ReCl{N2C(O)Ph}{NCNC(NH2)2}(PMePh2)3][BF4] [46], only one
ox
1=2
reversible oxidation wave has been detected with the E
values
in the 1.07–1.48 V versus SCE range. The related phosphine com-
pounds show also higher potentials, i.e. Eopx ¼ 1:24 V versus SCE
for [ReCl2{N2C(O)Ph}(PR3)3] [R3 = (OMe)3 or Ph(OEt)2] [47].
The first oxidation potential of 4 (0.92 V versus SCE) is lower
than those commonly observed for Re(V) species, what can be
associated with the presence of the remarkably strong electron do-
nor oxo ligand (possessing the Lever electrochemical ligand

1274
A.M. Kirillov et al. / Inorganica Chimica Acta 363 (2010) 1269–1274
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The present work has extended the recognized application
[10,19–25] of the versatile
synthesis of novel
1-(benzoyldiazenido)rhenium(III) complexes
with N,N-ligands of the types 2-aminopyrimidine and 2,20-bipyri-
dine. Apart from the opening of the
2-benzoylhydrazido ring,
g
2-benzoylhydrazido chelate 1 to the
g
g
chloride is the only replaced ligand in the reaction of 1 with
H2Npyrm (being displaced by the anionic monodeprotonated form
of the latter, i.e. HNpyrm), whereas the displacement of phosphine
occurs in the similar reaction of 1 with the neutral bpy. It is worth-
while to mention that the reactivity observed herein for H2Npyrm
is comparable to that reported in the reactions of 1 with some N,O-
type ligands, i.e. picolinic, N-hydroxyiminodiacetic and N-hydroxy-
2,20-iminodipropionic acids [10].
Besides, compound 1 widens the group of rhenium precursors
[40,41] for the preparation of the oxo(diethyldithiocarbama-
to)dirhenium(v) complex 4. The hydrosolubility and stability of
this compound, along with the high metal oxidation state, may
be of potential importance in aqueous phase oxidative catalysis.
This is in line with the interest of our laboratory on the preparation
of water-soluble metal complexes [50,51] and their application in
the catalytic functionalization of alkanes [52–55].
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