Synthesis and characterization of binuclear transition metal-rhenium(VII) complexes with bridging cyanide ligands

Article abstract of DOI:10.1016/S0022-328X(98)00495-1

Reacting transition metal complexes in low oxidation states, containing one or two cyanide ligands, with methyltrioxorhenium(VII) leads to bridged mixed metal compounds in good yields. The Re(VII) core is then surrounded by five or six ligands, respectively. The strength of these CN bridges and thus the stability of the newly generated bimetallic compound strongly depends on the donor strength of the ligands surrounding of the Cr/Mo/W or Fe moiety. The stability of the mixed metal molecules is reflected in the temperature dependent behavior of their ¹⁷O-NMR spectra, in their IR (Re=O) stretching frequencies and force constants, as well as several other spectroscopic data. UV-vis absorption spectra show the appearance of charge transfer bands. In the case of the mixed Mo/Re complexes the ⁹⁵Mo-NMR spectroscopy is also a helpful tool to examine the donor capability of the Mo moiety. The described compounds also show photosensitivity.

Full text of DOI:10.1016/S0022-328X(98)00495-1

Journal of Organometallic Chemistry 560 (1998) 117–124
Synthesis and characterization of binuclear transition
metal–rhenium(VII) complexes with bridging cyanide ligands
Isabel S. Gonc¸alves a,b, Fritz E. Ku¨hn c, Andre´ D. Lopes a, A. Jorge Parola d, Fernando Pina d,
Joa˜o Sotomayor d, Carlos C. Roma˜o a,*
a Instituto de Tecnologia Qu´ımica e Biolo´gica, Quinta do Marqueˆs, Apartado 127, 2780 Oeiras, Portugal
b Departamento de Qu´ımica, Uni6ersidade de A6eiro, Campus de Santiago, 3800 A6eiro, Portugal
c Anorganisch-chemisches Institut der Technischen Uni6ersita¨t Mu¨nchen, Lichtenbergstraße 4, D-85747 Garching bei Mu¨nchen, Germany
d Departamento de Qu´ımica, Faculdade de Cieˆncias e Tecnologia da Uni6ersidade No6a de Lisboa, 2825 Monte de Caparica, Portugal
Received 21 November 1997; received in revised form 27 January 1998
Abstract
Reacting transition metal complexes in low oxidation states, containing one or two cyanide ligands, with methyltrioxorheni-
um(VII) leads to bridged mixed metal compounds in good yields. The Re(VII) core is then surrounded by five or six ligands,
respectively. The strength of these CN bridges and thus the stability of the newly generated bimetallic compound strongly depends
on the donor strength of the ligands surrounding of the Cr/Mo/W or Fe moiety. The stability of the mixed metal molecules is
reflected in the temperature dependent behavior of their 17O-NMR spectra, in their IR (ReꢀO) stretching frequencies and force
constants, as well as several other spectroscopic data. UV–vis absorption spectra show the appearance of charge transfer bands.
In the case of the mixed Mo/Re complexes the 95Mo-NMR spectroscopy is also a helpful tool to examine the donor capability
of the Mo moiety. The described compounds also show photosensitivity. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Cyanide bridges; Re(VII) oxides; Fe/Re binuclear complexes; Mo/Re binuclear complexes
1. Introduction
donors containing cyano ligands. MTO is an ideal
acceptor molecule for investigation with different donor
ligands because it has been shown that the chemical
shift of its oxygen ligands in 17O-NMR spectroscopy is
strongly influenced by the donor capability of the coor-
dinating ligands [3]. These chemical shift changes have
proven to be significantly more sensitive than the
changes in bond length detectable by single crystal
X-ray determination [4]. It is also easily possible to
follow the changes of the electron density around the
Re(VII) core by UV–vis [5] and IR spectroscopy [6]. In
this work we report the preparation and spectroscopic
properties of complexes of general formula Cp(L)2Fe–
CN–Re(CH3)O3 (L=0.5dppe, CO), [(CO)5M–CN–
Bridging cyanides involving linear M–CꢁN–M% ar-
rangements are a prime object of studies of charge
transfer, energy transfer and spin-exchange between the
metal ions. Due to its electronic characteristics, the
bridging cyanide ligand has been the subject of several
recent investigations. Molecules containing metal atoms
linked by one or more cyanide bridges are known [1].
Since it is also well established that methyltrioxorhe-
nium(VII) (MTO) and related complexes readily form
adducts with several organic and organometallic donor
molecules [2], we were tempted to examine the behavior
of this molecule in the presence of organometallic
Re(CH3)O3]−
(M=Cr,
Mo,
W)
and
[CpMo(CO)2(–CN–)2Re(L)O3]K [L=Cl, Br, CH3].
* Corresponding author. Tel.: +351 1 4469751; fax: +351 1
4411277; e-mail: ccr@itqb.unl.pt
The 1H-, 17O-, 95Mo-NMR, IR and UV–vis spectra and
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00495-1

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Table 1
Selected IR (cm−1) and 1H-NMR data (ppm) of mononuclear and binuclear complexes
Compound
l(1H)Cp
l(1H)Me
w(CꢁO)
w(CꢁN)
Cp(dppe)Fe–CN
Cp(dppe)Fe–CN–Re(CH3)O3
Cp(CO)2Fe–CN
Cp(CO)2Fe–CN–Re(CH3)O3
[Cp(CO)2Mo(–CN)2]K
[Cp(CO)2Mo(–CN–)2Re(Cl)O3]K
[Cp(CO)2Mo(–CN–)2Re(Br)O3]K
[Cp(CO)2Mo(–CN–)2Re(CH3)O3]K
CH3ReOa3
4.20
4.24
5.07
5.14
5.32
—
—
—
—
—
2.74
—
2.55
—
—
—
2.05
2.81
—
—
2062
2074
2118
2158
2102b
2122
2122
2109
—
1
2
2056, 2006
2058, 2006
1966, 1883
1981, 1915
1979, 1913
1971, 1892
—
3
4
5
All 1H-NMR spectra were recorded in CH3NO2 at r.t.
a Data taken from refs. [3,6]. b w(CꢁN)asym stretch hidden under w(CꢁO) peaks.
photochemical examinations of selected molecules are
presented and discussed.
tion to MTO by an electron donor. In contrast to the
1H-NMR data, the IR data indicate a stronger coordina-
tion than in most known monodentate organic Lewis
base adducts of MTO. Typical values of ReꢀO force
constants in these cases lie in the range 8.3–8.1 ([4]a, [6]).
In the cases of compounds 1 and 2, the force constants
2. Results and discussion
The addition of the cyanide ligands Cp(dppe)Fe–CN
and Cp(CO)2Fe–CN to MTO in CH2Cl2 immediately
leads to orange solutions from which the heterobinuclear
complexes Cp(dppe)Fe–CN–Re(CH3)O3 (1) and
Cp(CO)2Fe–CN–Re(CH3)O3 (2) are isolated as brown–
yellow solids in good yields (Eq. 1). The compounds are
stable at room temperature (r.t.) but decompose slowly
in the presence of air and moisture. As it is well known
for the decomposition of several organorhenium(VII)
oxide derivatives perrhenates are formed by the water
induced decomposition process [4].
˚
are around 7.5 mdyn/A (see Table 2). As expected, the
stronger electron donor Cp(dppe)Fe–CN leads to a
stronger Fe–CN“Re interaction, resulting in a lower
ReꢀO force constant in 1 when compared with that of
2.
As a consequence of the formation of a Fe–CꢁN“Re
bridge, the w(CꢁN) bands of the complexes Cp(dppe)Fe–
CN–Re(CH3)O3 (1) and Cp(CO)2Fe–CN–Re(CH3)O3
(2) occur at higher wavenumbers than the w(CꢁN) bands
of the non-coordinated iron complexes, Cp(dppe)Fe–
CN and Cp(CO)2Fe–CN (Table 1). However, this shift
is much higher for 2 (40 cm−1) than for 1 (12 cm−1).
The factors that affect bridging w(CꢁN) frequency
shifts have been discussed ([1]l). Besides being expected
for any bridging CN ligand the shift observed in 2 is
typical of M–CN–M% bridges in which the M% fragment
is a Lewis acid. No change in backdonation from the
CpFe(CO)2 moiety to the CN is observed as the w(CꢁO)
vibrations of this fragment remain virtually unchanged
upon complexation. On the contrary, the Cp(dppe)Fe
fragment of the Cp(dppe)Fe–CN ligand, considered as
The 1H-NMR spectra of the compounds 1 and 2 were
recorded in CD3NO2 at r.t. (see Table 1). The Cp protons
of 1 and 2 appear as singlets at l 4.24 and 5.14 ppm,
respectively. In comparison with the uncomplexed Fe
compounds, coordination to MTO leads only to a slight
field shift of ca. 0.1 ppm for the chemical shift of the Cp
protons. The chemical shifts of the methyl protons
appear at higher field then those of uncoordinated MTO
in the same solvent. The shift differences of the CH3-pro-
tons in 1 and 2 are due to the electron donor capability
of the Fe ligand complexes. It has to be noted, however,
that these shift changes are small in comparison to several
organic Lewis bases, e.g. pyridine {l(1H) of the MTO–
CH3 group is 1.68 ppm [3]}.
Table 2
˚
Force constants F(ReꢀO) [mdyn/A] and IR vibrations w(ReꢀO) of
complexes 1–5
Compound
F(ReꢀO) w(ReꢀO)
Cp(dppe)Fe–CN–Re(CH3)O3
Cp(CO)2Fe–CN–Re(CH3)O3
[Cp(CO)2Mo(–CN–)2Re(Cl)O3]K
[Cp(CO)2Mo(–CN–)2Re(Br)O3]K
[Cp(CO)2Mo(–CN–)2Re(CH3)O3]K
1
2
3
4
5
7.50
7.56
7.26
7.18
8.12
955 s, 918 vs
962 s, 920 vs
927 w, 911 vs
926 w, 905 vs
988 m, 950 vs
Selected peaks observed in the IR spectra of these
compounds, recorded in KBr, are given in Table 1. The
ReꢀO stretching vibrations clearly indicate the coordina-

I.S. Gonc¸al6es et al. / Journal of Organometallic Chemistry 560 (1998) 117–124
119
Table 3
and shifts the equilibrium to the right side if the coordi-
nating complex is a stronger donor than the solvent [3].
In the case of compound 1, the 17O-NMR shift changes
from 807 ppm at 75°C to 789 ppm at −40°C. In the case
of complex 2, however, the chemical shift does not
change significantly in the same temperature range. If a
3-fold excess of 17O-labelled MTO is added to a solution
of unlabelled Cp(dppe)Fe–CN–Re(CH3)O3, neither the
signal of uncoordinated MTO [l(17O) 825 ppm] nor the
signal of 1 [l(17O) 801 ppm] can be observed both being
reflected by an averaged signal at ca. 820 ppm. Also,
cooling down or warming up the solution does not
change the chemical shift significantly. When stoichio-
metric amounts of labelled MTO and labelled 1 are
mixed, the 17O-NMR signal appears at 816 ppm. In the
proton NMR spectrum a broad peak between the signal
MTO and the signal of 1 can be observed. The known
signals of both components of the mixture do not show
up. The reason for these observations must be a second
exchange equilibrium, as shown in Eq. 3. Similar equi-
libria are known for organorhenium(VII) oxides coordi-
nated by organic Lewis bases ([3]b).
17O-NMR data of selected M–CN–Re complexes
T (°C)
Chemical shift (ppm)
Half width (Hz)
Cp(dppe)Fe–CN–Re(CH3)O3 in CD3CNa
+75
+25
90
807
801
794
789
96
148
201
480
−40
Cp(dppe)Fe–CN–Re(CH3)O3+excess MTO (1:3) in CD3CNa
+75
+20
−40
821
821
824
52
70
192
Cp(CO)2Fe–CN–Re(CH3)O3 in CD3CNa
+75
+20
−40
825
827
832
35
44
87
[Cp(CO)2Mo(–CN–)2Re(CH3)O3]K in CD3NO2a
+80
+25
−25
819
816
814
50
65
105
[(CO)5Cr–CN–Re(CH3)O3]Li in CD3ODa
−25
+20
797
310
370
724b
[(CO)5Mo–CN–Re(CH3)O3]Na in CD3ODa
−25
+20
830
240
520
809b
[(CO)5W–CN–Re(CH3)O3]Li in CD3ODa
−25
+20
735
230
380
697b
a Chemical shifts of MTO: l(17O)=824 ppm (CD3CN), 819 ppm
(CD3NO2), 861 ppm (CD3OD) [3]. b Partial decomposition starts
already below r.t.
extremely electron rich ([1]c), must provide significant
backdonation to the bridging cyanide, almost overriding
the kinematic shift to higher frequencies ([1]l).
The adducts were also characterised by means of their
electronic absorption spectra, depicted in Fig. 1. In the
case of compound 2, the spectrum of the adduct is
coincident with the sum of the spectra of each compo-
nent, MTO and Cp(CO)2Fe–CN. In the case of com-
pound 1, however, the formation of a low intensity new
absorption band, centered at ca. 500 nm (m=30 M−1
cm−1), can be observed. This band can, in principle,
be attributed to a charge transfer from the donor moi-
ety, Cp(dppe)Fe–CN, to the acceptor, MTO, as
17O-NMR spectroscopy performed in CH3CN also
shows that complex 1 has a stronger Fe–CꢁN“Re
interaction than complex 2 (Table 3). This is especially
evident at low temperature. Usually, weak donor ligands
coordinated to MTO in the solid state are easily replaced
by strong donor solvents, e.g. pyridine, THF or CH3CN
(Eq. 2). Cooling down the solution slows this exchange

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I.S. Gonc¸al6es et al. / Journal of Organometallic Chemistry 560 (1998) 117–124
described for [Fe(CN)6]2− and MTO ([5]c). The obser-
vation of a charge transfer (CT) band in compound 1
and its absence (for u\400 nm) in compound 2 are in
agreement with the IR and 17O-NMR data reported
above, reflecting the stronger electron donor character
of Cp(dppe)Fe–CN in comparison to Cp(CO)2Fe–CN.
In order to improve the interaction of CN bridges
with Re(X)O3 molecules, we considered [Cp(CO)2Mo-
(–CN)2]− as a good ligand because it may act as a
bidentate ligand and bears a negative charge. As a
matter of fact, both its w(CꢁO) and w(CꢁN) stretching
frequencies appear at lower frequencies that those of
Cp(CO)2Fe–CN (Table 1).
ppm in the free Mo precursor compound to −190 ppm
in complex 5. The signal is extremely broad (ca. 4000
Hz). The 17O-NMR data also show only a minor shift
difference from uncoordinated MTO [l(17O)=819
ppm] to compound 5 [l(17O)=814 ppm] in d3-ni-
tromethane at −25°C. Warming the solution leads to
an even smaller shift difference [l(17O)=816 ppm at
r.t.]. These data again emphasize the weak coordination
of the Re(VII) center by the CN functions in this case.
In the 1H-NMR the Re–CH3 signal is shifted from
l(1H)=2.81 (free MTO) to 2.05 ppm spectrum of
complex 5. For an octahedrally-coordinated R–
ReO3 ·L complex the latter chemical shift is still an
indication for a weak coordination. Typical chemical
shifts of the Re–CH3 group with strongly coordinating
organic ligands are ca. 1.5 ppm ([4]a, [6,7]). The differ-
ential UV–vis spectrum of a mixture of CH3ReO3 and
[Cp(CO)2Mo(–CN)2]− in MeOH, both 0.01 M, and the
sum of the spectra of the separated components (0.01
M) shows the tail of a band at uB500 nm, also
indicating that some interaction occurs.
Therefore the complexes [Cp(CO)2Mo(–CN–)2-
Re(X)O3]K, with X=Cl (3), Br, (4) CH3 (5), (Eq. 4)
were prepared. In the case of compounds 3 and 4 the
products precipitate immediately after their formation,
thus shifting the equilibrium completely to the product
side. However, the insolubility of 3 and 4 in all com-
mon organic solvents prevented NMR and UV–vis
studies. The IR spectra of both compounds, recorded in
KBr matrix, indicate a distorted octahedral coordina-
tion of the rhenium center in the solid state, as it was
expected for bidentate coordination of the
[Cp(CO)2Mo(–CN)2]− ligand. The force constants of
the complexes were calculated from the ReꢀO vibration
˚
bands to be 7.26 and 7.18 mdyn/A and are, therefore,
in the same order of magnitude as 2,2%-bipyridine ad-
ducts of organorhenium(VII) oxides and rhenium(VII)
halide oxides (they usually range 7.45–7.30 mdyn/A
([4]a, [6,7]). In the case of the soluble compound 5, the
Mo–CN–Re interaction is significantly weaker. The
95Mo-NMR signal is only shifted 10 ppm, from −200
The IR spectrum of compound 5 also supports our
˚
statement that the Mo–CN–Re interaction is weak.
˚
The ReꢀO force constant is 8.12 mdyn/A, thus only
slightly weaker than in uncoordinated MTO
˚
(F(ReO)=8.31 mdyn/A). The w(CO) IR vibrations also
clearly show the difference between the coordinated Mo
complexes 3 (w(CO)=1981 and 1915 cm−1) and 4
(w(CO)=1979 and 1914 cm−1) and the uncoordinated
precursor compound (w(CO)=1966 and 1884 cm−1).
Coordination to the electron withdrawing Re(VII) cen-
tre causes a weakening of the backdonation to the CO
ligands as judged from the increase of the w(CO) fre-
quencies in 3 and 4 relative to w(CO) in the electron
richer starting material. The back donating effect of the
Mo orbitals to the y*-orbitals is somewhat stronger in
the case of [Cp(CO)2Mo(–CN)2]−, therefore reducing
the total bond order in the carbonyl slightly and weak-
ening the CꢁO bond. In the case of complex 5 this
w(CO) is smaller w(CO)=1971 and 1892 cm−1. This
again supports the already mentioned weaker coordina-
tion of the Re(VII) center by the cyano functions in
complex 5 in comparison to 3 and 4. The electron
withdrawing effect of the Re(VII)O3 moiety is also
mirrored in the w(CꢁN) vibration of the molecules 3–5.
The corresponding signal is shifted from 2103 cm−1 in
the starting material to 2122 cm−1 in the products 3
and 4 and 2109 cm−1 in compound 5.
Fig. 1. UV–vis absorption spectra of the heterobinuclear complexes
Cp(dppe)Fe–CN–Re(CH3)O3 (- -) (1) and Cp(CO)2Fe–CN–
Re(CH3)O3 (—) (2). In the inset: absorption differential absorption
spectrum between
a
methanolic solution 0.01
M
in both
Cp(dppe)Fe–CN and MTO and the sum of the spectra of the
separated components (- -); the same applies for Cp(CO)2Fe–CN and
MTO (—).

I.S. Gonc¸al6es et al. / Journal of Organometallic Chemistry 560 (1998) 117–124
121
turning brown within ca. 5 min if left at r.t. In the
presence of water they turn white under formation of
perrhenates. The proton NMR spectra of the com-
plexes 6–8 show a significantly stronger M–CN“Re
interaction then in compounds 2 and 5. The chemical
shifts of the rhenium bound methyl group are around
1.6 ppm in d4-methanol, compared to 2.0 ppm of free
MTO in methanol (methanol is itself a coordinating
solvent, forming an MTO–methanol adduct in solution
[3]). The 17O-NMR results (see Table 3) and the 95Mo
data (see Table 4) of complex 6 support the statement
concerning the stronger coordination of complexes 6–
8. IR spectra could not be obtained due to the ther-
mal instability of the complexes.
Attempts to carry out photochemical studies in or-
der to obtain the reduced electron acceptor species
{ReO4− or ReO3 ([5]a,b)} and the oxidized donor,
were not successful by the following reasons: (i) in
compounds 1, 2 and 5, selective excitation on the new
CT band is not possible; in addition, they are not
thermally stable and (ii) in compounds 6, 7, and 8,
selective excitation is possible but as in the previous
examples the thermal degradation strongly competes
with the photochemical reaction.
Fig. 2. UV–vis absorption spectra of 0.01 M methanolic solutions of
(1) MTO (. . .), (2) [(CO)5M–CN]Na (- -), (3) MTO+[(CO)5M–
CN]Na (—), and differential spectra between (3) and (2)+(1) (. . .).
M=Mo (A), W (B), Cr (C).
In attempting to get some more soluble binuclear
M–CN–Re(L)O3 complexes, the anions [(CO)5M–
CN]− were reacted with MTO, according to Eq. 5.
Both starting materials, MTO and [(CO)5Mo–CN]Na,
are colorless compounds. Mixing them in THF or
diethyl ether immediately leads to a color change to
yellow, a typical color for Lewis base adducts of
MTO when colorless starting materials (e.g. bipy,
quinuclidine) are used [3]. The appearance of the yel-
low color upon mixing the two compounds was moni-
tored by UV–vis absorption spectroscopy (Fig. 2).
Inspection of this figure clearly shows that the ab-
sorption spectrum of the mixture is not coincident
with the sum of the separated components. This result
is similar to those observed above and suggests that
in this case formation of a charge transfer type ad-
duct between [(CO)5M–CN]− (M=Cr, Mo, W) and
MTO also occurs. The products with the formulae
[(CO)5M–CN–Re(CH3)O3]M% {M=Cr, M%=Li (6),
M=Mo, M%=Na (7), M=W, M%=Li (8)} are or-
ange–yellow, moisture and temperature sensitive,
Table 4
95Mo-NMR data for [(CO)5Mo–CN–Re(CH3)O3]Na (7) and
[(CO)5Mo–CN]Na in CD3ODa
T (°C)
Chemical shift(ppm)
Half width (Hz)
[(CO)5Mo–CN]Na
−25
+25
+60
−1892
−1882
−1875
190
130
190
[(CO)5Mo–CN–Re(CH3)O3]Na
−25
+25
+60
−1874
−1865
−1858
250
190
320
a
Partial decomposition of complex 7 occurs already below r.t.

122
I.S. Gonc¸al6es et al. / Journal of Organometallic Chemistry 560 (1998) 117–124
3. Conclusions
sure Hg lamp by means of an interference filter (P/N
56450 Allied Electro Optics (Italy); umax=435.8 nm).
4.2. Preparation of Cp(dppe)Fe–CN–Re(CH3)O3 (1)
A solution of CH3ReO3 (0.20 g, 0.80 mmol) in
MTO and some inorganic Re(X)O3 derivatives eas-
ily form charge transfer complexes with electron rich
organometallic complexes via CN bridges. Depending
on the number of the donor CN functions pentacoor-
dinated or octahedral Re(VII) complexes are formed,
as can be concluded from the spectroscopic results.
When the cyano ligands are weak donors, the com-
plexes show rapid temperature dependent ligand/sol-
vent exchange. In the case of more strongly donating
organometallic donor complexes the resulting
molecules are more stable against donor ligand ex-
change but not necessarily against temperature. Given
the easy preparation of all complexes described here
our findings open a broad field for the synthesis of
novel mixed metal complexes, which might present
interesting photochemical properties.
CH2Cl2 (5 ml) was treated with
a solution of
Cp(dppe)Fe–CN (0.43 g, 0.80 mmol) in the same sol-
vent. After 15 min the dark yellow solution was con-
centrated to ca.
5
ml and addition of ether
precipitated the product. The mother liquor was
filtered off and the remaining precipitate was washed
with diethyl ether/n-pentane and dried in vacuum.
Yield 0.57 g (90%). Anal. Calc. for C33H32NP2O3FeRe
(794.63): C 49.88, H 4.06, N 1.76. Found: C 50.10, H
4.40, N 1.91%. Selected IR (KBr, w cm−1): 3055 m,
2955 m, 2074 vs (NꢁC), 1463 m, 1435 s, 1096 s, 1011
m, 955 s, [sym (ReꢀO)], 918 vs [asym (ReꢀO)], 744 s,
696 s, 532 s. 1H-NMR (CD3NO2, 300 MHz, r.t., l
ppm): 7.53–7.07 (m, 20H, dppe), 4.24 (s, 5H, Cp),
2.74 (s, 3H, Me), 2.56–2.33 (m, 4H, –CH2). 17O-
NMR (−40°C, CD3CN, l ppm): 789. 31P-NMR
(CH3CN, r.t., l ppm): 102 (s).
4. Experimental section
All preparations and manipulations were performed
with standard Schlenk techniques under an oxygen-
and water-free argon atmosphere. Solvents were dried
by standard procedures THF, Et2O, pentane, and hex-
ane over Na/benzophenone ketyl; acetonitrile and
dichloromethane were distilled after refluxing for sev-
4.3. Preparation of Cp(CO)2Fe–CN–Re(CH3)O3 (2)
A solution of CH3ReO3 (0.20 g, 0.80 mmol) in
CH2Cl2 (5 ml) was treated with
a solution of
eral hours over P2O5. Acetone was distilled over
K2CO3 and kept over 4 A molecular sieves. H-NMR
Cp(CO)2Fe–CN (0.16 g, 0.80 mmol) in the same sol-
vent. After 20 min the orange–yellow solution was
concentrated to ca. 5 ml and addition of ether precip-
itated the product. The mother liquor was filtered off
and the remaining precipitate was washed with diethyl
ether/n-pentane and dried in vacuum. Yield 0.35 g
(98%). Anal. Calc. for C9H8NO5FeRe (452.22): C
23.90, H 1.78, N 3.10. Found: C 23.84, H 1.55, N
3.25%. Selected IR (KBr, w cm−1): 3117 m, 3015 m,
2158 vs (NꢁC), 2058 vs (CꢁO), 2006 vs (CꢁO), 1427
m, 1009 m, 962 s, [sym (ReꢀO)], 920 vs [asym
(ReꢀO)], 870 m, 837 m, 606 s, 563 s. 1H-NMR
(CD3NO2, 300 MHz, r.t., l ppm): 5.14 (s, 5H, Cp),
2.55 (s, 3H, Me). 17O-NMR (−25°C, CD3CN, l
ppm): 832.
1
˚
spectra were obtained with a Bruker CXP 300 and a
Bruker Avance DPX-400 spectrometer. IR spectra
were recorded on a Unican Mattson Mod 7000 FT-
IR spectrophotometer and a Perkin-Elmer FT-IR
spectrometer using KBr pellets as IR matrix. 17O-
NMR spectra were measured at 54.14 MHz on a
JEOL JNM GX-400 and 95Mo-NMR at 26.07 MHz
on a Bruker Avance DPX-400. Elemental analyses
were performed in the Mikroanalytisches Labor of the
TU Mu¨nchen in Garching and by J.P. Lopes at the
ITQB, Oeiras. 17O-marked Re2O7 and CH3ReO3 were
prepared according to the literature [3,8]. CpMo(p3-
C3H5)(CO)2 [9], Cp(dppe)Fe–CN [10], Cp(CO)2Fe–
CN [11], [(CO)5M–CN]− (M=Cr, Mo, W) [12] were
prepared as described previously.
4.4. Preparation of [Cp(CO)2Mo(–CN)2]K
4.1. Photochemical studies
A solution of CpMo(p3-C3H5)(CO)2 (0.20 g, 0.77
mmol) in CH2Cl2 (20 ml) was treated with HBF.4Et2O
(one equivalent). After 10 min excess NCMe was
added (2 ml) and the reaction left for 30 min at r.t.
The mixture was taken to dryness and the solid, [Cp-
Mo(NCMe)2(CO)2]BF4, dissolved in methanol:ethanol
(5:10). Excess of KCN (0.13g, 2.00 mmol) was added
and the mixture vigorously stirred for 6h. The result-
ing orange solution was filtered, evaporated to dry-
ness, extracted with acetone and concentrated. Upon
All solutions were prepared and handled in the
dark. Electronic absorption spectra were run on a
Perkin Elmer lambda 6 UV–vis spectrophotometer.
Irradiation experiments were carried out in PTI in-
strumentation, using a medium pressure Hg lamp
(HBO 100 W) mounted in a lamphouse (Model
A1010) connected to a LPS-220 Lamp Arc Supply.
Light of 436 nm was isolated from the medium pres-

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123
addition of n-pentane an oily residue separated which
was solidified to a yellow microcrystalline power after
scratching and repeated washings with pentane. Yield:
0.19 g (80%). Anal. Calc. for C9H5N2O2KMo (308.19):
C 35.08, H 1.64, N 9.09. Found: C 35.26, H 2.17, N
9.20%. Selected IR (KBr, w cm−1): 3111 m, 2102 s, 1966
vs, 1884 vs, 1695 m, 1423 m, 1092 m, 1014 m, 813 s, 536
methanol (4 ml), were added 1.00 mmol of [(CO)5M–
CN]Li or [(CO)5M–CN]Na, respectively at −20°C. The
formerly colorless solutions turned orange–yellow. After
15 min the solvent was removed at −40°C in oil pump
vacuum and the orange residue was washed with 5 ml
cold n-pentane and dried in oil pump vacuum at −50°C.
Yields: 0.3 g (65%) (6), 0.3 g (57%) (7), 0.43 g (71%) (8).
[(CO)5Cr–CN–Re(CH3)O3]Li: Anal. Calc. for
C7H3NO8LiMoRe (474.25): C 17.73, H 0.64, N 2.95.
1
s. H-NMR (CD3NO2, 300 MHz, r.t., l ppm): 5.32 (s,
5H, Cp). 95Mo-NMR (−25°C, CD3NO2, l ppm):
−200.
1
Found: C 18.16, H 0.68, N 2.89%. H-NMR (CD3OD,
400 MHz, −25°C, l ppm): 1.66 (s, 3H, Me). 17O-NMR
(−25°C, CD3OD, l ppm): 797.
4.5. Preparation of complexes of general formula
[CpMo(CO)2(–CN–)2Re(X)O3]K [X=Cl (3), Br (4)]
[(CO)5Mo–CN–Re(CH3)O3]Na: Anal. Calc. for
C7H3NO8NaMoRe (534.24): C 15.74, H 0.57, N 2.62.
To solutions of Re2O7 (0.5 g, 1.03 mmol) in THF (10
ml), were added 1.03 mmol of Bu4NX. The solution
turned pale yellow. After 5 min, 1.03 mmol of
[Cp(CO)2Mo(–CN)2]K were added and after a few
seconds a yellow–brown precipitate formed. The precip-
itate was washed three times with 10 ml of diethyl ether
and with 10 ml n-pentane. The remaining residue was
dried in oil pump vaccum. Yield: 0.51 g (85%) (3) and
0.50 g (79%) (4).
[Cp(CO)2Mo(–CN–)2Re(Cl)O3]K (3). Anal. Calc. for
C9H5N2O5KMoReCl (577.85): C 18.71, H 0.87, N 4.85.
Found: C 18.95, H 1.01, N 4.79%. Selected IR (KBr, w
cm−1): 2122 m, 1981 s, 1915 s, 927 w, 911 vs, 800 m.
[Cp(CO)2Mo(–CN–)2Re(Br)O3]K (4). Anal. Calc. for
C9H5N2O5KMoReBr (622.30): C 17.37, H 0.81, N 4.50.
Found: C 17.52, H 0.92, N 4.37%. Selected IR (KBr, w
cm−1): 2122 m, 1979 s, 1914 s, 926 w, 905 vs, 798 m.
1
Found: C 15.99, H 0.78, N 2.91%. H-NMR (CD3OD,
400 MHz, −25°C, l ppm): 1.67 (s, 3H, Me). 17O-NMR
(−25°C, CD3OD, l ppm): 830. 95Mo-NMR (−25°C,
CD3OD2, l ppm): −1874.
[(CO)5W–CN–Re(CH3)O3]Li: Anal. Calc. for
C7H3NO8LiWRe (606.10): C 13.87, H 0.50, N 2.31.
1
Found: C 13.61, H 0.62, N 2.54%. H-NMR (CD3OD,
400 MHz, −25°C, l ppm): 1.56 (s, 3H, Me). 17O-NMR
(−25°C, CD3OD, l ppm): 735.
Acknowledgements
This work was supported by PRAXIS XXI, Projects
(2/2.1/QUI/316/94 and 2/2.1/QUI/419/94). The authors
want to thank the DAAD and CRUP (INIDA and
Acc¸o˜es Integradas Programme) and Prof. W.A. Herr-
mann for generous support. I.S. Gonc¸alves (BPD) and
A.D. Lopes (BD) thank PRAXIS XXI for grants, and
F.E. Ku¨hn acknowledges the Alexander von Humboldt
foundation for financial support.
4.6. Preparation of [Cp(CO)2Mo(–CN–)2Re(CH3)O3]K
(5)
To a solution of CH3ReO3 (250 mg, 1.00 mmol) in
diethyl ether (4 ml), were added 1.00 mmol of
[Cp(CO)2Mo(–CN)2]K. The solution turned brown im-
mediately. After 30 min, the solution was cooled to
−30°C and the solvent removed in oil pump vacuum.
Removal of the solvent at r.t. leads to a color change to
black within minutes. The residue was washed with 5 ml
cold n-pentane, then dried again. Yield: 0.5 g (89%).
Anal. Calc. for C10H8N2O5KMoRe (557.34): C 21.55, H
1.45, N 5.03. Found: C 21.67, H 1.54, N 4.97%. Selected
IR (KBr, w cm−1): 2984 m, 2898 m, 2109 m, 1971 s, 1892
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