Metallic carbonyl complexes containing heterocycles nitrogen ligands: Part VI. Re(I), Mn(I), Mo(0), and W(0) compounds with 4′-phenyl-2,2′:6′,2″-terpyridine

Article abstract of DOI:10.1016/S0020-1693(00)00292-9

The synthesis and spectroscopic characterization of new transition metal complexes containing the heterocyclic nitrogen ligand 4′-phenyl-2,2′:6′,2″-terpyridine are reported. Complexes of the [XM(CO)₃(L)] type (M = Re(I), Mn(I), Mo(0), or W(0); X = Br or CO; and L = 4′-phenyl-2,2′:6′,2″-terpyridine) were prepared by photosubstitution or by thermolytic reactions. Aspects of the IR, UV-Vis, proton NMR spectra and electrochemistry of the complexes are discussed. Special attention is given to the fact that the heterocyclic nitrogen ligand ph-tpy acts as a bidentate or terdentate chelate in complexes of this type and shows the fluxionality in the coordination. Correlations between redox potentials and spectroscopic measurements indicate the various interactions of the ligand and the metal center, and allow the evaluation of the metal-ligand back-donation.

Full text of DOI:10.1016/S0020-1693(00)00292-9

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 312 (2001) 7–14
Metallic carbonyl complexes containing heterocycles
nitrogen ligandsꢀ
Part VI. Re(I), Mn(I), Mo(0), and W(0) compounds with
4%-phenyl-2,2%:6%,2¦-terpyridine
Sergio A. Moya a,*, Rube´n Pastene a, Hubert Le Bozec b, Pablo J. Baricelli c,
Alvaro J. Pardey d, Jose´ Gimeno e
a Departamento de Qu´ımica Aplicada, Facultad de Qu´ımica y Biolog´ıa, Uni6ersidad de Santiago de Chile, Santiago, Chile
b UMR 6509, CNRS-Uni6ersite´ de Rennes 1, Organome´talliques et Catalyse, Campus de Beaulieu, 35042 Rennes Cedex, France
c Centro de In6estigaciones Qu´ımicas, Facultad de Ingenier´ıa, Uni6ersidad de Carabobo, Valencia, Venezuela
d Escuela de Qu´ımica, Facultad de Ciencias, Uni6ersidad Central de Venezuela, Caracas, Venezuela
e Departamento de Qu´ımica Orga´nica e Ino´rganica, Instituto de Qu´ımica Organometa´lica ‘Enrique Moles’ (CSIC), Facultad de Qu´ımica,
Uni6ersidad de O6iedo, O6iedo, Spain
Received 27 August 1999; accepted 28 August 2000
Abstract
The synthesis and spectroscopic characterization of new transition metal complexes containing the heterocyclic nitrogen ligand
4%-phenyl-2,2%:6%,2¦-terpyridine are reported. Complexes of the [XM(CO)3(L)] type (M=Re(I), Mn(I), Mo(0), or W(0); X=Br or
CO; and L=4%-phenyl-2,2%:6%,2¦-terpyridine) were prepared by photosubstitution or by thermolytic reactions. Aspects of the IR,
UV–Vis, proton NMR spectra and electrochemistry of the complexes are discussed. Special attention is given to the fact that the
heterocyclic nitrogen ligand ph-tpy acts as a bidentate or terdentate chelate in complexes of this type and shows the fluxionality
in the coordination. Correlations between redox potentials and spectroscopic measurements indicate the various interactions of the
ligand and the metal center, and allow the evaluation of the metal–ligand back-donation. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Metal carbonyl complexes; Rhenium(I); Manganese(I); Molybdenum(0) and Tungsten(0); Heterocyclic nitrogen ligand
ucts of photolysis of tridentate terpyridine transition
metal complexes [4]. Moreover, the remarkable photo-
1. Introduction
physical and photochemical properties of these com-
plexes are especially convenient for studying the
structural modifications of heterocyclic nitrogen ligands
A few examples of transition metal complexes with
2,2%:6%,2¦-terpyridine ligand (tpy) coordinated in a
bidentate arrangement, leaving off one external pyridyl
with the purpose of causing variations on the electronic
ring uncoordinated, are known [2]. If the meridional
properties of these species. Furthermore, systems such
coordination site is available the most current binding
mode of this ligand to metals is the terdentate array [3].
The spectroscopic characterization of this type of
as [XReI(CO)3(L)] type (X=halide and L=2,2%-
bipyridine, 2,2%-biquinoline or their derivatives) have
been found to be efficient catalysts for the reduction of
bidentate species is of interest since they have been
CO2 to CO both photochemically [5] and electrochemi-
postulated to have an important participation as prod-
cally [6]. Only scarce examples with the 4%-phenyl-
2,2%:6%,2¦-terpyridine ligand coordinated to iron(III),
ꢀ For Parts I–V, see Ref. [1].
* Corresponding author. Fax: +56-2-681 2108.
E-mail address: smoya@lauca.usach.cl (S.A. Moya).
ruthenium(II), cobalt(II), and platinum(II) centers are
known [7], therefore we have selected this ligand as a
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00292-9

8
S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
model to continue our previous work. We study here
the reaction of a series of carbonyl transition metal
complexes with the 4%-phenyl-2,2%:6%,2¦-terpyridine lig-
and (Fig. 1) to form [XM(CO)3(ph-tpy)] complexes
where X=Br or CO; ph-tpy=4%-phenyl-2,2%:6%,2¦-ter-
pyridine and M=Re(I), Mn(I), Mo(0), or W(0); and
we report the preparation and the coordination behav-
ior of this heterocyclic nitrogen ligand with different
transition metal centers. Part of this work has been
reported previously [1d,16d,22c].
2.2. Physical measurements
Irradiation reactions were carried out with a 500 W
medium-pressure mercury original Hanau TNN 15/32
lamp that was housed in a glass immersion reactor. The
photolysis were performed under dry nitrogen gas at-
mosphere. All the products of photolysis were handled
in the dark. Infrared (IR) spectra (data in cm−1) were
run on a Bruker IFS-66V Fourier-transform spec-
trophotometer using KBr disk and chloroform solu-
tions in NaCl cells or polyethylene pellets (in the far IR
region, 450–150 cm−1). The electronic absorption spec-
tra were recorded using a Shimadzu UV-160 spec-
trophotometer with different solvents in quartz cells on
solutions ranging from 1×10−5 to 1×10−3 mol
dm−3 at r.t. Proton NMR spectra were recorded on a
Bruker DPX 200 operating at 200.131 MHz and a
Bruker AMWB 300 operating at 300.134 MHz. Vari-
able-temperature proton NMR spectra were recorded
on a Bruker AMWB 300 operating at 300.134 MHz
using the Bruker BVT-2000 variable temperature unit
to control the probe temperature in CD2Cl2 or DMSO-
d6. Homonuclear correlated (COSY) spectra were ob-
tained on a Bruker DPA 200 using the standard Bruker
programs NOEXSY.Au and COSY.Au. Molar conduc-
tivity measurements were determined in anhydrous ace-
tonitrile in 1×10−3 mol dm−3 solutions of the
complexes at 25°C, using a Cole-Palmer 01481 conduc-
tivity meter. Electrochemical data from anhydrous ace-
tonitrile solutions of the complexes containing 0.1 mol
dm−3 of tetrabutylammonium perchlorate (TBAP)
were obtained by cyclic voltammetry using a Bank-
Wenking POS 73 potentiostat with a Gould OS 4100
oscilloscope, and a Graphtec XY WX 4301 recorder. A
three-electrode configuration was used, where the work-
ing electrode was a platinum disk, and the reference
and counter electrodes were an aqueous saturated
calomel and platinum wire, respectively. The test solu-
tion was separated from the reference electrode by a
salt bridge containing a Vycor plug and filled with the
corresponding solvent/supporting electrolyte system. A
sweep rate of 200 mV s−1 was used for all the scans.
2. Experimental
2.1. Materials
All the operations were carried out under purified
nitrogen by standard Schlenk and vacuum-line tech-
niques using freshly distilled, dried and degassed sol-
vents. During the synthesis, the solutions of the
complexes were protected from light. Molybdenum car-
bonyl (Aldrich Chemical Co.), tungsten carbonyl
(Merck), and manganese pentacarbonyl bromide
(Strem) were used without further purification. High
purity BrRe(CO)5 was obtained by treating Re2(CO)10
(Aldrich Chemical Co.) with Br2 solution in cyclohex-
ane at room temperature (r.t) [8]. Bicyclo[2,2,1]hepta-
2,5-diene (NBD) was used as received from Aldrich
Chemical Co. The heterocyclic nitrogen ligand 4%-
phenyl-2,2%:6%,2¦-terpyridine was prepared by modifica-
tion of literature methods [9]. 2-Acetylpyridine (Aldrich
Chemical Co.) and benzaldehyde (Merck) were used as
obtained. The solvents used in synthesis, recrystalliza-
tions, and spectroscopic analyses (Mallinckrodt, grade
HPLC) were treated and distilled prior to use [10].
Anhydrous acetonitrile freshly destilled and dried was
used for the electrochemical studies [11]. Tetrabutylam-
monium perchlorate (TBAP) from Fluka was recrystal-
lized twice from HPLC grade ethyl acetate
(Mallinckrodt) before to be used.
Potentials were reported as E1/2=0.5(Ep +Ep ), where
c
Ep and Ep were the anodic and cathodic peack poten-
c
tiacls, respectively. Ferrocene was used as an internal
standard to compensate the junction potential variabil-
ity among experiments. Elemental analyses were per-
formed by the CNRS analysis laboratory, Villeurbanne
(France).
2.3. Preparations
The ligand 4%-phenyl-2,2%:6%,2¦-terpyridine (ph-tpy)
was prepared by a modified literature method which
consisted on two consecutive condensations as follows.
A mixture of 2-acetylpyridine (8.4 ml, 74 mmol), benz-
Fig. 1. Heterocyclic nitrogen ligand 4%-phenyl-2,2%:6%,2¦-terpyridine
(ph-tpy).

S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
9
aldehyde (3.4 ml, 32 mmol) and NaOH (2.0 g) in water
(25 ml)/ethanol (35 ml) was stirred for 1 h at r.t. The
resulting solution was mixed and stirred with 30 ml of
water to obtain a white precipitate of 1,5-bis-(2-
pyridyl)-3-pentan-dione. The crude reaction product
was filtered, washed extensively with cold ethanol and
air-dried. 1,5-bis-(2-pyridyl)-3-pentan-dione (20.0 g, 6.1
mmol) and ammonium acetate (25 g) were dissolved in
ethanol (25 ml) and the clear solution heated to 70°C
for 2 h. Water (about 20 ml) was slowly added to the
cooled solution to give a yellow precipitate. This was
filtered, washed with cold ethanol and diethyl ether,
and finally dried in vacuum. The 4%-phenyl-2,2%:6%,2¦-ter-
pyridine was obtained as pale yellow crystals on recrys-
tallization from hot ethanol. Yield 60%. IR, wC–O (KBr
disk): 1582, 1564, 1548, 1500, 1467,1389, 796, 680, 620
cm−1. 1H NMR (CDCl3, 200 M Hz) l (ppm): 8.75 (2H,
t, H66¦); 7.97 (2H, d, H55¦); 7.43 (2H, dd, H44¦); 8.81
(2H, dd, H33¦); 8.82 (2H, s, H3%5%); 7.43 (2H, m, Hoo%+p);
8.00 (2H, dd, Hm). Anal. Calc. for C21H15N3: C, 81.53;
H, 4.89; N, 13.58. Found: C, 81.62; H, 4.86; N, 13.08%.
M.p. 203–204 °C.
Calc. for [BrMn(CO)3(C21H15N3)]: C, 54.57; H, 2.86.
Found: C, 54.10; H, 2.46%. Molar conductivity 0.0
V−1 cm2 mol−1. M.p. 250–275°C (d).
2.3.3. Mo(CO)4(ph-tpy) (3)
Mo(CO)6 (1.6 g, 4.0 mmol) was dissolved in tetrahy-
drofuran (35 ml) and a solution of the ph-tpy ligand
(2.5 g, 4.1 mmol) in the same solvent was slowly added.
The resulting solution was refluxed under nitrogen and
stirred for 5 h, then concentrated, and cooled to obtain
a red precipitate. The precipitate was filtered, washed
with diethyl ether/ethanol, recrystallized in acetonitrile/
methylene chloride, and dried in vacuum. Yield 85%.
IR, wC–O (KBr disk): 2027, 1915, 1861, 1840 cm−1
wC–O (CHCl3): 2027, 1916, 1861, 1842 cm−1; wM–C
(polyethylene pellet): 382 cm−1
Anal. Calc. for
;
.
[Mo(CO)4(C21H15N3)]: C, 58.04; H, 2.92. Found:
C, 57.90; H, 3.12%. Molar conductivity 0.0 V−1 cm2
mol−1. M.p. 149°C (d).
2.3.4. W(CO)4(ph-tpy) (4)
A solution of W(CO)6 (703 mg, 2.0 mmol) in tetrahy-
drofuran (70 ml) was irradiated at ambient temperature
in a Pyrex glass tube for 1.5 h. To the solution bicy-
clo[2,2,1]hepta-2,5-diene (NBD) was added to obtain
the W(CO)4(NBD) complex (wC–O (CHCl3): 2003 (s),
1984(s), 1884(m), 1838(s) cm−1). The complex was
collected and dissolved in tetrahydrofuran and a sample
of the ph-tpy ligand (600 mg, 2.0 mmol in 10 ml of
THF) was added. The solution was stirred in the dark
for 3 h at 50°C. The solution was concentrated, and
cooled to obtain the stable W(CO)4(ph-tpy) complex.
Yield 83%; IR, wC–O (KBr disk): 2008, 1990, 1891, 1842
2.3.1. BrRe(CO)3(ph-tpy) (1)
BrRe(CO)5 (326 mg, 1 mmol) was dissolved in hot
heptane and the heterocyclic nitrogen ligand (ph-tpy)
(310 mg, 1 mmol) was slowly added. A yellow color
quickly developed which gradually changed to intense
orange after 1 h. The solution was concentrated, diethyl
ether was added and the mixture was cooled in an
ice-bath to obtain a yellow–orange precipitate. The
solid was filtered, dissolved in the minimum amount of
methylene chloride, and flash precipitated with diethyl
ether. The product was collected, washed with diethyl
ether and boiling ethanol, recrystallized from acetoni-
trile/methylene chloride, and dried in vacuum. Yield
90%; IR, wC–O (KBr disk): 2018, 1909, 1878 cm−1; wC–O
(CHCl3): 2024, 1923, 1905 cm−1; wM–C (polyethylene
pellet): 405 and 187 cm−1. Anal. Calc. for [Br-
Re(CO)3(C21H15N3)]: C, 43.71; H, 2.29. Found: C,
44.10; H, 2.48%. Molar conductivity 5.4 V−1 cm2
mol−1. M.p. 265°C.
cm−1; wC–O (CHCl3): 2006, 1990, 1890, 1842 cm−1
;
wM–C (polyethylene pellet): 393 cm−1. Anal. Calc. for
[W(CO)4(C21H15N3)]: C, 49.94; H, 2.62; N, 7.28.
Found: C, 50.41; H, 2.95; N, 6.71%. Molar conductiv-
ity 0.0 V−1 cm2 mol−1. M.p. \300°C.
2.3.5. W(CO)3(ph-tpy) (5)
W(CO)6 (704 mg, 2.0 mmol) in acetonitrile (80 ml)
was refluxed for 22 h, then a solid sample of ph-tpy
(600 mg, 2.0 mmmol in 20 ml of acetonitrile) was added
and stirred in the dark at r.t. until IR spectroscopy
showed the appearance of the three carbonyl bands for
fac-W(CO)3(ph-tpy) complex (about 3 h). The solvent
was then removed in vacuum and the residue was
crystallized in a mixture of acetonitrile/methylene chlo-
ride. Yield 70%; IR, wC–O (KBr disk): 2007, 1895, 1835
cm−1; wC–O (CHCl3): 2015, 1900, 1817 cm−1; wM–C
(polyethylene pellet): 412 and 179 cm−1. Anal. Calc. for
[W(CO)3(C21H15N3)]: C, 37.70; H, 2.50; N, 6.94.
Found: C, 38.25; H, 3.07; N, 7.34%. Molar conductiv-
ity 0.0 V−1 cm2 mol−1. M.p. \300°C.
2.3.2. BrMn(CO)3(ph-tpy) (2)
To a hot solution of ph-tpy ligand (619 mg, 2.0
mmol) in (30 ml) anhydrous petroleum ether 30–60°C a
hot solution of BrMn(CO)5 (548 mg, 2.0 mmol) in
hexane (40 ml) was slowly added and stirred under
nitrogen atmosphere. The solution was concentrated,
diethyl ether was added and the mixture was cooled
overnight to obtain an orange–brown precipitate. The
solid was collected and purified in a similar procedure
as 1, except ethanol was not used to wash the product.
Yield 75%; IR, wC–O (KBr disk): 2009, 1937, 1912
cm−1; wC–O (CHCl3 solution): 2009, 1993, 1952 cm−1
wM–C (polyethylene pellet): 405 and 191 cm−1. Anal.
;

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S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
3. Results and discussion
complexes, maintain an excess of negative load due to
the competition of d orbitals of metal with the tricoor-
dination of ph-tpy ligand.
3.1. Spectroscopic characterization of new complexes
The well known fluxionality, that complexes contain-
ing terpyridine show, has also been observed for the
prepared complexes. The ambient, high and low tem-
perature proton NMR spectrum of these complexes
give strong support to suggest that the 2,2%:6%,2¦-ter-
pyridine ligand acts as a nitrogen heterocyclic bidentate
ligand in some of the prepared complexes. The
4%-phenyl-2,2%:6%,2¦-terpyridine, and 2,2%:6%,2¦-terpyridine
itself, have all coplanar rings with the nitrogen hetero-
cyclic atoms of the peripheral rings in a trans position
with respect to central pyridyl nitrogen atom. This
structural conformation occurs only in the solid state
for these ligands [17]. However, the complex formation
causes the heterocyclic nitrogen ligand to adopt the
cis:cis configuration and in solution rapid rotation
should occurs. Low and ambient proton NMR experi-
ments provide a strong evidence for the fluxionality
occurring in the prepared complexes.
Full proton NMR chemical shift data for the com-
plexes and the ligand are given in Table 1. Assignment
was based taking in consideration their integration,
multiplicity, coupling constant, and value of their
chemical shifts and 2D-COSY spectroscopy. The ambi-
ent proton NMR spectra show seven groups of signals
for the complexes with chemical shifts and forms simi-
lar to 2,2%:6%,2¦-terpyridine itself. When the ligand bond
to metal as a N,N,N terdentate ligand, the ph-tpy
should be a symmetrical ligand giving a lower number
of signals in the proton NMR spectrum. In spite of the
fact that the ph-tpy is coordinated as a N,N bidentate
ligand provides a proton NMR spectrum with a higher
number of signals being the chemical shifts of the
proton on the uncoordinated side of the terpyridine
very similar to those of the free ligand. The protons on
the uncoordinated pyridyl ring experience rather
smaller positive shifts compared with those protons on
the coordinated pyridyl rings. In order to produce the
coordination with the metal, the 4%-phenyl-2,2%:6%,2¦-ter-
pyridine ligand must modify its conformation from
trans:trans of its heteroatoms to cis:cis. This change in
the ligand conformation is reflected in the chemical
shift of the H3 and H3¦ protons which are shifted to
lower frequencies. On warming, the spectra undergoes
changes, coalescence occurring between the correspond-
ing signals pairs (H6/H6¦; H5/H5¦; H4/H4¦; H3/H3¦;
H3%/H5%). The signals for the spectator protons Ho, Hm
and Hp remain as sharp multiplets at all temperatures.
This behavior indicates, that the terdentate ligand is
fluxional and switches its metal coordination between
different adjacent pairs of its three nitrogen atoms. The
low temperature proton NMR study was carried out at
the temperature range of 297 to 183 K. Basically the
The IR spectra in the 2400–1800 cm−1 region for the
above complexes show the presence of carbonyl stretch-
ing frequencies corresponding to terminal carbonyl
groups bonded to the metal. In addition, IR spectra of
BrRe(CO)3(ph-tpy) and BrMn(CO)3(ph-tpy) complexes
show three strong bands, which correspond to carbonyl
stretching frequencies of CO groups in a cis-conforma-
tion, characteristic of a hexacoordinated octahedral
species with Cs symmetry [12]. Furthermore, IR spectra
of Mo(CO)4(ph-tpy) and W(CO)4(ph-tpy) complexes
exhibit three strong bands and one weak wC–O band,
typically generated by vibrational C26 symmetry [13],
where the heterocyclic nitrogen ligand acts as a biden-
tate chelate with the metal in a cis-conformation.
In contrast, IR spectrum of the W(CO)3(ph-tpy)
complex shows three wC–O strong bands, involving the
ph-tpy ligand in a tridentate chelate bonding [14]. The
solution of W(CO)6 in acetonitrile shows one strong
wC–O band at 1979 cm−1, which is transformed in two
strong bands (wC–O, acetonitrile solution: 1940 and 1797
cm−1) after refluxing for 22 h. The latter IR data is
indicative of the presence of fac-W(CO)3(ph-tpy) spe-
cies [15]. The addition of the heterocyclic nitrogen
ligand to the resulting solution, gives a red-brown
product. The IR spectrum of this product shows three
wC–O bands (2015, 1917, 1900 cm−1). This data pro-
vides consistent support to suppose that ph-tpy is act-
ing as a tridentate ligand in this complex. Besides, no
evidence of bidentate species was observed. These re-
sults are in agreement with the stoichiometry given by
microanalysis and by molar conductivity measurements
for the complexes. The substitution of carbonyl groups
by the heterocyclic nitrogen ligand (ph-tpy) produces a
decrease in carbonyl stretching frequency values of the
complexes with respect to the corresponding precursor
complex
C–O
(DwC–O=wCpr–eOcursor−w
) due to a higher electron
donation from the metal to the remaining ligands car-
bonyl groups. This increase in the metal back-bonding
to vacant p* orbitals of the CO ligand results from the
increase of the electron density at the metal center by
the displacement of carbonyl groups by the heterocyclic
nitrogen ligand which has less p-acceptor, but greater
s-donor character than the carbonyl groups. Greater
electron density supplied by the metal and the other
ligands, can be back-donated into p* orbitals of car-
bonyl and/or halogen ligands which lowers the C–O
bond order and decrease the stretching frequency value
[16]. Table 4 shows that the values DwC1–O decreases in
the
order:
W(CO)3(ph-tpy)\Mo(CO)4(ph-tpy)\
W(CO)4(ph-tpy)\BrRe(CO)3(ph-tpy)\BrMn(CO)3-
(ph-tpy). The metal in the molybdenum and tungsten

S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
11
Table 1
Proton NMR chemical shift selected data for ph-tpy and its rhenium(I), manganese(I), molybdenum(0), and tungsten(0) complexes
Complex (ligand)
Assignments l (ppm) a
H66¦
H33¦
H3%5%
H44¦
H55¦
Hmm%
Hoo%+p
BrRe(CO)3(ph-tpy) b (1)
9.21
8.92
8.42
7.83
8.98
8.00
8.16
7.83
7.61
7.61
8.00
8.00
7.61
7.61
BrMn(CO)3(ph-tpy) b (2)
Mo(CO)4(ph-tpy) c (3)
9.15
7.89
8.69
8.64
8.70
8.15
8.68
8.73
8.26
7.82
8.67
8.66
W(CO)4(ph-tpy) c (4)
8.71
8.67
8.67
8.75
8.75
W(CO)3(ph-tpy) b (5)
8.77
8.75
8.36
8.81
8.71
8.82
(ph-tpy) b
7.43
7.97
7.47
a Referred to SiMe4 (internal) in CDCl3 l=0 ppm; see Fig. 1 for hydrogen labeling.
b Recorded at 300 MHz.
c Recorded at 200 MHz.
spectrum remained the same in all this range of temper-
ature. However an important change was observed in
the spectrum, as can be shown in Fig. 2. Cooling this
complex to approximately 203 K caused changes in the
signals at 9.10 ppm. Initially it broadened or eventually
split into an equal intensity doublet at 198 K to pro-
duce finally a doublet of doublet at 183 K. This should
be attributed to the fact that the pendant pyridyl ring
can become locked at low solution temperature with its
nitrogen heteroatoms either syn or anti with respect to
the formed plane by the coordination of the metal with
the two coordinated nitrogen of the ligand [17d].
The proton NMR spectrum of the W(CO)3(ph-tpy)
complex does not present the same behavior observed
for the rhenium complex, being the signals similar to
those appearing in the spectrum of the ph-tpy free
ligand, but slightly shifted by coordination when the
complex is formed (Table 2).
tricoordination of ph-tpy ligand in the W(CO)3(ph-tpy)
complex that leads to an increase in the back-bonding
effect and therefore the resulting difference in the nega-
tive values of chemical shifts (Table 2). This could
discard tricoordination in complexes 1–4 and confirm
participation of a bidentate chelate mode of ph-tpy
ligand in them, and suggest a tricoordination for the
W(CO)3(ph-tpy) complex.
In addition, molar conductivity measurements [19]
and elemental analysis for the W(CO)3(ph-tpy) complex
clearly indicates that the heterocyclic nitrogen ligand
The signals of protons 6 and 6¦ are deshielded due to
a decrease of the electronic density of the rings while
the donation takes place [18]. This effect is reinforced
by the coordination with metal which results in the
displacement of signals to downfield (positive values of
Dl in all spectra of complexes) [12e]. On the other
hand, the signals of H3 and H3¦ of the external pyridyl
rings and H3% and H5% of the central ring, of the coordi-
nated ph-tpy ligand suffer a displacement to high field
(negative values of Dl) due to protective effect that
causes back donation between the metal and the hetero-
cyclic nitrogen ligand, which is reinforced by anisotropy
of neighboring rings [1]. This effect is strong in
BrRe(CO)3(ph-tpy), BrMn(CO)3(ph-tpy), and W(CO)3-
(ph-tpy) complexes, and weak in Mo(CO)4(ph-tpy) and
W(CO)4(ph-tpy) complexes, because of the participa-
tion of the atom of halogen in complexes 1 and 2 and
Fig. 2. (a) Temperature-depending proton NMR spectra for the
BrRe(CO)3(ph-tpy) complex in the range of 183–297 K. (b) detail of
the signal at 198 K, doublet of doublet starts to be formed.

12
S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
Table 2
bands, along with the analysis of the ligand spectrum
[13,14].
Coordination-induced proton NMR chemical shifts for complexes
Complex
Dl (ppm a)
3.2. Electrochemical properties
H66¦
H33¦
H3%5%
The electrochemical properties of this series of com-
plexes 1–5 were studied. The redox potentials were
determined by cyclic voltammetry and the number of
electrons involved in electronic transfer by coulomme-
try (Table 4). Quasi-reversibility approaches were deter-
mined by the difference of potential between the anodic
peak and the cathodic peak current (DEp), the ratio
between the intensities of anodic and cathodic peaks
(ip /ip ) and the relationship between the current and
BrRe(CO)3(ph-tpy) (1)
BrMn(CO)3(ph-tpy) (2)
Mo(CO)4(ph-tpy) (3)
W(CO)4(ph-tpy) (4)
W(CO)3(ph-tpy) (5)
+0.49
+0.20
−0.34
−0.76
+0.20
−1.17
+0.50
+0.04
−0.44
−0.81
−0.58
−0.91
+0.03
+0.02
0.00
−0.03
0.00
−0.01
+0.05
+0.02
+0.03
+0.02
+0.02
a
c
+0.12
−0.55
−0.03
sweep rate. Relationship between the intensity of aver-
age versus 61/2 was used to determine that the processes
of electron transfer of these complexes were diffusion
controlled. Cyclic voltammograms of these systems in
the range 0.0 to −2.2 V versus Fc+/Fc showed a
reduction wave which could be assigned to a reversible
monoelectronic reduction centered in the heterocyclic
nitrogen ligand (Eq. (1)).1 This agrees well with the fact
that the p* molecular orbital of this ligand is the
a Dl=lcomplex−dfree ligand, referred to SiMe4.
Table 3
Electronic absorption data for [XM(CO)3(ph-tpy)] complexes
Complex
umax (nm) (m (dm3 mol−1 cm−1)) a,b
LUMO level of energy, which is confirmed by similar
BrRe(CO)3(ph-tpy) (1)
BrMn(CO)3(ph-tpy) (2)
Mo(CO)4(ph-tpy) (3)
W(CO)4(ph-tpy) (4)
W(CO)3(ph-tpy) (5)
387(1960), 280(24 200), 260(25 100),
393(1620)/CHCl3
421(2500), 312(21 500), 272(23v600),
425(2730)/CH3OH
454(1480), 275(11 720), 251 (12 520),
472(1100)/ether
553(1190), 272(19 900), 249 (20 620),
545(1720)/CHCl3
red
1/2
values of E
[20]:
−
XM(CO)3(ph-tpy)+e− “[XM(CO)3(ph-tpy )]
(1)
’
All the complexes presented a wave of irreversible
oxidation in the region 0.0 to +1.7 V versus Fc+/Fc.
This wave was assigned to a monoelectronic oxidation
process centered at the metal atom (M(II)/M(I): M=
Re or Mn [6d,10e,21,23c]; M%(I)/M%(0): M%=Mo or W
[22] indicating that there is more electronic density
removed from the Mn(I) than from the Re(I) and that
of Mo(0) than of W(0). Consistent with a greater
extension of d orbitals in the third-row transition
metals of a same group, it ensues that the overlap
between the metal orbitals and the heterocyclic nitrogen
atom orbitals of the polypyridine ligand should be
much larger for the metal in the second or third transi-
tion series. So, in complex 5 in which the heterocyclic
nitrogen ligand ph-tpy is tricoordinated, this type of
interaction is increased by the participation of three
heterocyclic nitrogen atoms, making more difficult the
removal of one electron from the metallic center, and
leading to a more positive oxidation potential [23].
Since the potential of oxidation is a measure of the
electronic density in the metal center and the electronic
process of reduction is centered in the heterocyclic
nitrogen ligand ph-tpy, one could establish correlations
between the displacement to low frequency (DwC–O) of
the band of C–O stretching for the vibration of dis-
559(1950), 276(18 600), 263 (24 120),
571(2100)/CHCl3
a In acetonitrile solutions of 2.5 and 5.0×10−4 mol dm−3
.
b Lowest energy absorption band in different solvents (2.5×10−4
mol dm−3).
should be tricoordinated to the tungsten center. Sup-
port for this conclusion comes also from the IR spectra
analysis (vide supra). Proton NMR spectra of this
complex showed that signals corresponding to protons
of the heterocyclic nitrogen ligand are equivalent. This
behavior is typical of tridentate disposition on the part
of the terpyridyl derivative ligands in these species.
UV–Vis absorption spectra obtained for complexes
in acetonitrile solutions at r.t. (Table 3), showed a
group of very intense bands of high energy and a low
energy absorption band having a low intensity. The
high energy bands would correspond to absorptions
due to intraligand transitions and the lowest energy
band could be assigned to an absorption due to a
charge-transfer from the metal to the heterocyclic nitro-
gen ligand (MLCT). Both proposals are supported by
intensity, position, and solvent dependence of these
1 ip /ip :1, DEp=70–110 mV.
a
c

S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
13
Table 4
Decrease of carbonyl stretching frequencies wCO and electrochemical data for [XM(CO)3(ph-tpy] complexes
a
b
Complex
Dw1
Reduction
Oxidation
red c
1/2
E
ip /ip
Epox,I
Epox,II
c
a
c
c
BrRe(CO)3(ph-tpy) (1)
134
Ep −1.78
1.28
1.11
1.26
1.09
1.37
0.84
(i)
1.05
(i) d
c
Ep −1.68
c
E1/2 −1.73
DEp (100) e
BrMn(CO)3(ph-tpy) (2)
Mo(CO)4(ph-tpy) (3)
W(CO)4(ph-tpy) (4)
W(CO)3(ph-tpy) (5)
(ph-tpy)
130
145
136
147
Ep −1.81
0.62
(i)
c
Ep −1.96
c
E1/2 −1.90
DEp (110)
Ep −1.75
0.75
(i)
c
Ep −1.85
c
E1/2 −1.85
DEp (100)
Ep −1.89
0.87
(i)
c
Ep −1.81
c
E1/2 −1.80
DEp (80)
Ep −1.79
1.07
(i)
c
Ep −1.71
c
E1/2 −1.75
DEp (75)
Ep −2.63
c
Ep −2.47
c
E1/2 −2.55
DEp (160)
(Fc+/Fc)
Ep
Ep
E1/2
DEp
0.41
0.35
0.38
(60)
c
c
a DwC1O=wCpOrecursor−w
(cm−1).
complex
CO
b Redox potentials in V (90.030 V) versus Fc+/Fc, in CH3CN 0.1 mol dm−3 of TBAP, 6=200 mV s−1
c E1r/e2d=0.5(Ep −Ep ), where Ep and Ep , are cathodic and anodic peaks, respectively.
.
c
c
c
c
d Irreversible.
e DEp=Ep −Ep in mV.
c
c
charge energy (way A11) [24] and the absorbance energy
of the band of CTM“heterocyclic nitrogen ligand
(ph-tpy) [16d,21c,25], with the difference between the
oxidation and the reduction potentials of these com-
plexes. The two plots gave relationships of the form:
DwC–O (cm−1)=25.55+43.00 (Eox (V)) with r=0.9505
and Eabs (eV)=10.719+3.068 (Eox (V)) with r=
0.9017.
as a fundamental tool for the design and preparation of
new species with predetermined properties.
5. Supplementary material
Additional IR, proton NMR data, including temper-
ature and 2D-COSY information, and electrochemical
experiments are available upon request.
4. Conclusion
Acknowledgements
The bi- or tricoordination of the heterocyclic nitro-
gen ligand ph-tpy, achieved by synthesis of new com-
plexes, originate important changes in the spectroscopic
and electrochemical characteristics, which can be used
This work was supported by DICYT-USACH,
FONDECYT-Chile, CNRS-CONICYT (France/Chile),
and Agencia Espan˜ola de Cooperacio´n Internacional.

14
S.A. Moya et al. / Inorganica Chimica Acta 312 (2001) 7–14
Am. Chem. Soc. 101 (1979) 7415. (d) W.K. Smother, M.S.
Wrighton, J. Am. Chem. Soc. 105 (1983) 1067. (e) S. Van
Wallendael, R.J. Shaver, D.P. Rillema, B.J. Yoblinski, M.
Stathis, T.F. Guarr, Inorg. Chem. 29 (1990) 1761. (f) R. Sahai,
D.P. Rillema, R. Shaver, S. Van Wallendael, D.C. Jackman, M.
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We also thank MOLYMET-Chile S.A. for generous
gifts of rhenium.
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