Synthesis, electrochemistry, and crystal and molecular structures of some molybdenum(0) arene derivatives with fluorinated and phenyl-substituted arene ligands

Article abstract of DOI:10.1016/j.jorganchem.2004.02.038

Compounds of general formula Mo(η⁶-arene) (CO)₃, arene=diphenyl, 1; 1,3,5-triphenylbenzene, 2; C₆H₅F, 3; C₆H₅ CF₃, 4, have been prepared in good yields by reacting fac-Mo(CO)₃(DMF)₃, DMF=N,N-dimethylformamide, with BF₃ · OEt₂ and the appropriate arene. The crystal and molecular structures of 1, 3, and 4, are reported. The dinuclear derivative Mo₂(η⁶:η⁶ -C₆H₅-C₆H₅)(CO)₆, 5, was obtained by thermal reaction of Mo(η⁶-toluene) (CO)₃ with Mo(η⁶-diphenyl)(CO)₃. An electrochemical study has been performed on the new complexes, showing that the dimolybdenum complex undergoes a single two-electron reduction at about the same potential as the corresponding dichromium complex, the molybdenum dianion being less stable than the chromium analogue.

Full text of DOI:10.1016/j.jorganchem.2004.02.038

Journal of Organometallic Chemistry 689 (2004) 2158–2168
www.elsevier.com/locate/jorganchem
Synthesis, electrochemistry, and crystal and molecular structures
of some molybdenum(0) arene derivatives with fluorinated
and phenyl-substituted arene ligands q
a
Sara Antonini , Fausto Calderazzo , Ulli Englert , Emanuela Grigiotti ,
a
b
c
a,
c
Guido Pampaloni *, Piero Zanello
a
Dipartimento di Chimica e Chimica Industriale, Universitꢀa delgi Studi di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
b
Institut fu€r Anorganische Chemie der RWTH Aachen, Professor-Pirlet Strasse 1, D-52074 Aachen, Germany
c
Dipartimento di Chimica, Universitꢀa di Siena, Via Aldo Moro, 53100 Siena, Italy
Received 3 February 2004; accepted 27 February 2004
Abstract
Compounds of general formula Mo(g6-arene)(CO)3, arene ¼ diphenyl, 1; 1,3,5-triphenylbenzene, 2; C6H5F, 3; C6H5CF3, 4, have
been prepared in good yields by reacting fac-Mo(CO)3(DMF)3, DMF ¼ N; N-dimethylformamide, with BF3 ꢀ OEt2 and the ap-
propriate arene. The crystal and molecular structures of 1, 3, and 4, are reported. The dinuclear derivative Mo2(g6:g6-C6H5-
C6H5)(CO)6, 5, was obtained by thermal reaction of Mo(g6-toluene)(CO)3 with Mo(g6-diphenyl)(CO)3. An electrochemical study
has been performed on the new complexes, showing that the dimolybdenum complex undergoes a single two-electron reduction at
about the same potential as the corresponding dichromium complex, the molybdenum dianion being less stable than the chromium
analogue.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Molybdenum; Arene; Electrochemistry; Structures
1. Introduction
Cr(g6-arene)(CO)3 derivatives are known [1b,1c,1d] and
some of them are commercially available. However, the
molybdenum and tungsten congeners are not so com-
mon. This may be due to two reasons: the generally
higher kinetic lability of the zerovalent complexes of 4d
transition metals with respect to the corresponding
complexes of 3d and 5d elements [4]; the formation of
stronger bonds descending a vertical sequence of tran-
sition metals [4b,5], which makes W(CO)6 more stable
and less reactive than the molybdenum analogue in
dissociative processes.
Even less frequent are the dinuclear complexes of
condensed aromatics, those of polyphenyls, and the
complexes of fluoro-substituted aromatics, due to steric
and electronic effects, respectively. In this paper, we re-
port the moderate- to high-yield preparation of g6-arene
tricarbonyl derivatives of molybdenum(0) containing
polyphenyls and fluoro-substituted arenes as ligands,
Several transition metals (e.g. V, Cr, Mo, W, Fe, Co)
form complexes with arenes, those of chromium being
studied in a greater detail [1]. The chromium(0) deriva-
tives of general formula Cr(g6-arene)(CO)3 are readily
prepared by several methods, for example by treating
the commercially available Cr(CO)6 with the appropri-
ate arene as a neat liquid or in a basic solvent such as
dioxane or THF, or by reacting Cr(CO)3L3, L ¼ NH3
[2], a- or c-picoline [3], with an excess arene. As a con-
sequence of these high-yielding processes, a number of
q Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2004.02.038.
* Corresponding author. Tel.: +39-50-2219-219/+39-50-9182-21219;
fax: +39-50-2219-246/+39-50-20237.
E-mail address: pampa@dcci.unipi.it (G. Pampaloni).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.02.038

S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
2159
Table 1
IR carbonyl stretching vibrations of Mo(g6-arene)(CO)3 derivatives in
heptane
and their characterization. Moreover, the redox activity
of the complexes is reported and discussed.
Arene
~tCO (cmꢂ1
)
2. Results and discussion
Diphenyl
1983s, 1915s
1982s, 1914s
1995s, 1926s
2002s, 1937s
1,3,5-Triphenylbenzene
Fluorobenzene
Trifluoromethylbenzene
2.1. Synthesis and characterization
2.1.1. Mononuclear compounds
Our first approach to the synthesis of molybdenum
polyphenyl complexes was based on procedures suc-
cessfully applied to the chromium analogues [6]. How-
ever, we have found that Mo(CO)6 in melting diphenyl
(70 °C) forms a metallic mirror. Alternative procedures
consisting of treating a THF/Bu2O mixture as reaction
medium with the Mo(CO)6/arene system or with the
Lewis base adducts fac-Mo(CO)3(CH3CN)3 [7–13] or
fac-Mo(CO)3(DMF)3 were equally unsuccessful, due to
extensive formation of a metallic mirror.
A synthetic approach different from thermal substi-
tution on Mo(CO)6 was therefore necessary. The arene
derivatives have been obtained by reaction of fac-
Mo(CO)3(DMF)3 with the stoichiometric amount of
BF3 ꢀ Et2O in the presence of excess arene, see Eq. (1).
Mo(CO)3 moiety to escape from the hydrocarbon cage
thus decreasing.
Infrared and NMR spectra were recorded for all the
compounds reported in this paper, see Table 1. The IR
spectra are consistent with a C3v local symmetry of the
{Mo(CO)3} group (two carbonyl stretching vibrations
A1 þ E), with higher wavenumber values for the fluo-
rine-containing aromatic ligands C6H5F and C6H5–
CF3, in agreement with the higher electron-withdrawing
power of the substituent. Noteworthy is the large shift
observed for the stretching vibrations on going from
heptane to toluene [the DtCO is 12 and 19 cmꢂ1 for
~
Mo(g6-C6H5–C6H5)(CO)3]. This large difference has
been already pointed out [18] and suggested to be due to
a preferential solvation by the aromatic medium [19].
The NMR spectra (1H and 13C) show the shift of the
resonances towards high fields with respect to the un-
coordinated arene, as usually observed for neutral arene
derivatives of transition metals [20]. The 1H NMR
spectrum of the 1,3,5-triphenylbenzene derivative is
noteworthy because it is indicative of the coordination
of the polyarene molecule to molybdenum. As a matter
of fact, 1,3,5-triphenylbenzene may give 1:1 arene
complexes by coordination through the central C6H3
ring or through one of the three peripheric phenyl rings,
and examples are known of both coordination types
[21]. Due to the presence of two sets of signals at 7.64–
7.49 and ca. 5.8 ppm with an intensity ratio of 13:5, we
conclude that the Mo(CO)3 fragment is bonded to one
of the external C6H5 rings (A of Scheme 1) rather than
to the central C6H3 ring (B of Scheme 1) for which the
intensity ratio of the resonances should be 15:3. In this
connection it is relevant that the 1:1 thermal reaction
between Cr(CO)6 and 1,3,5-triphenylbenzene affords a
mixture of compounds where the Cr(CO)3 fragment is
fac-MoðCOÞ ðDMFÞ þ 3BF3 ꢀ Et2O þ arene
3
3
! Moðg6-areneÞðCOÞ þ 3BF3 ꢀ DMF þ 3CO
3
ðarene ¼ diphenyl; 1; 3; 5-triphenylbenzene;
C6H5F ½14ꢁ; C6H5CF3Þ
ð1Þ
The methodology based on the Lewis acid BF3 ꢀ Et2O
has been used in the past for the preparation of the
Cr(g6-arene)(CO)3 complexes (arene ¼ bromo- and
iodobenzene) from Cr(CO)3(c-picoline)3 [3], while alkyl-
substituted arene derivatives of molybdenum(0) and
tungsten(0) of general formula M(g6-arene)(CO)3 were
synthesized from fac-M(CO)3(L)3, L ¼ DMF [15], py
[16], pentamethyldiethylenetriamine [17].
Reactions proceed smoothly at room temperature
and give the arene derivatives in satisfactory to good
yields. The compounds form yellow crystals, stable in air
in the solid state for short periods of time. They are
sensitive to light, especially the fluorine-substituted
arene derivatives, which have to be prepared and stored
in the dark.
With the exception of 1,3,5-triphenylbenzene, vide
infra, reaction (1) gives the best yields only in the pres-
ence of excess arene (diphenyl/Mo ¼ 10) or in the arene
as solvent (fluorinated derivatives). Unless an excess was
used, extensive formation of molybdenum metal and
Mo(CO)6 took place. In the preparation of the 1,3,5-
triphenylbenzene derivative 2, an arene/Mo molar ratio
of 1 was used, and no formation of Mo(CO)6 was ob-
served. Probably this is due to the presence of four
possible coordination sites for molybdenum in the tri-
phenylbenzene molecule, the probability of the
Mo(CO)3
Mo(CO)3
(a)
(b)
Scheme 1.

2160
S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
bonded to the external C6H5 ring and to the central
C6H3 ring [21a,21b]. The formation of isomer A is
probably due to the larger atomic radius of molybde-
C13
C12
C25
C14
C26
C11
C24
C21
ꢁ
num (1.36 A), whose coordination to the central ring is
consequently less favourable than in the case of chro-
C15
C23
C22
C16
ꢁ
mium (atomic radius, 1.25 A) [10].
Mo
X-ray structural analyses have been performed on
compounds 2–4, derivatives 3 and 4 being the first ex-
amples of fluoro-substituted molybdenum-tricarbonyl
to be structurally characterised. The three molecular
structures are similar as far as the coordination of mo-
lybdenum is concerned and they belong to the piano-
stool class of compounds, see Fig. 1. Selected bond
distances and angles are reported in Table 2.
The unit cell of Mo(g6-C6H5–C6H5)(CO)3, 1, con-
tains two independent molecules which differ in the
orientation of the phenyl substituent with respect to the
plane of the coordinated ring, the dihedral angles being
28.2(2)° and )30.2(2)°. These values compare well with
those reported for diphenyl complexes of transition
metals such as Ti(g6-C6H5–C6H5)(AlCl4)2 (30.6°) [22],
[K([2.2.2]cryptand)][Ti(g6-C6H5–C6H5)2] (31°) [23],
Mn(g6-C6H5–C6H5)Cp (24.4°) [24], and Ru6C(g6-
C6H5–C6H5)(CO)14 (34.2°) [25]. It is interesting to
observe that the six-membered rings are practically
coplanar in crystalline diphenyl [26].
C3
C1
O1
O3
C2
O2
(a)
C13
C12
O2
O3
C3
C2
C11
F
Mo
C14
C15
C16
C1
O1
(b)
The arene and the carbonyl groups are in a staggered
orientation [28] with the following tilting angles: C21–
centroid–Mo1–C1, )30.3(2) and )30.3(2)° and C41–
centroid–Mo2–C5, )28.5(2)°.
C12
C13
C10
C11
C14
F1
Once the atomic radii of chromium and molybdenum
C15
C16
are taken into consideration, the distances within
6
F3
ꢁ
Mo(g -C6H5–C6H5)(CO)3, [Mo-ring: 2.381(3) A, Mo–
Mo
C1
C
carbonyl: 1.949(4), mean values] are similar to those
observed in Cr2(g6:g6-C6H5–C6H5)(CO)6 [Cr-ring: 2.20
C3
C2
A, Cr–Ccarbonyl: 1.85, mean values] [29], in Cr2(g6:
ꢁ
6
O1
ꢁ
g -C6H5–C6H5)(CO)4(P2Me4) [Cr-ring: 2.207 A, Cr–
O3
6
6
ꢁ
C
C6H5–C6H5)(CO)4[1,2-bis(diphenylphosphino)methane]
carbonyl: 1.818 A, mean values] [30], and in Cr2(g :g -
(c)
O2
ꢁ
ꢁ
Cr-ring carbon atoms: 2.209 A, Cr–Ccarbonyl: 1.815 A,
mean values] [31]. The mean C–C bond distances in the
bonded C6H5 ring are longer than the corresponding
Fig. 1. Molecular structures [27] of: (a) one of the two independent
molecules of Mo(g6-C6H5–C6H5)(CO)3; (b) Mo(g6-C6H5F)(CO)3, as
viewed along the ring centroid–Mo direction; (c) Mo(g6-
C6H5CF3)(CO)3. Ellipsoids are drawn at 50% level.
ꢁ
distances in the uncoordinated one (1.410 vs. 1.380 A,
mean values) and correspond to those observed for
structurally characterized diphenyl derivatives [22–
25,29–31].
the arene–metal bond on increasing the electronegativity
of the substituents) and to the reactivity of the C–X
bond with low-valent transition metals (oxidative addi-
tion followed by decomposition) in the sequence
I > Br > Cl > F. Some derivatives of manganese(I) con-
taining electron-withdrawing substituents on the arene
ring have been recently reported [32].
The fluoro- and the trifluororobenzene derivatives
Mo(g6-C6H5F)(CO)3 and Mo(g6-C6H5CF3)(CO)3 are
the first structurally characterized fluoro-substituted
derivatives of molybdenum(0) and belong to the re-
stricted class of g6-arene derivatives containing electron-
withdrawing substituents. Although the chemistry of
g6-arene complexes is rather well developed [1b], com-
pounds containing electron-withdrawing substituents on
the aromatic ligand are rather rare. This is mainly due to
the instability typical of these compounds (weakening of
The Mo–centroid distance in Mo(g6-C6H5F)(CO)3 is
ꢁ
1.91 A and, as it appears from Fig. 1(b), the carbonyl
groups are almost staggered with respect to the C–F
bond in order to form a dihedral angle F–centroid–Mo–
C3 of )19.85(9)°. The mean value of the C–C bond

S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
2161
Table 2
6
6
6
ꢁ
Bond distances (A) and angles (°) for Mo(g -C6H5-C6H5)(CO)3, Mo(g -C6H5F)(CO)3, and Mo(g -C6H5CF3)(CO)3
Mo(g6-C6H5–C6H5)(CO)3
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
O(1)–C(1)
O(2)–C(2)
O(3)C(3)
1.945(4)
1.957(4)
1.957(4)
1.149(5)
1.143(4)
1.150(5)
1.482(5)
C(1)–Mo(1)–C(2)
C(1)–Mo(1)–C(3)
C(2)–Mo(1)–C(3)
C(1)–Mo(1)–C(11)
C(2)–Mo(1)C(11)
C(3)–Mo(1)–C(11)
85.94(16)
87.01(17)
84.74(15)
92.71(14)
117.55(13)
157.66(14)
C(11)–C(21)
Mo(2)–C(6)
Mo(2)–C(4)
Mo(2)–C(5)
O(4)C(4)
1.952(4)
1.954(4)
1.955(4)
1.152(4)
1.148(5)
1.144(5)
1.490(5)
C(6)–Mo(2)–C(4)
C(6)–Mo(2)–C(5)
C(4)–Mo(2)–C(5)
C(4)–Mo(2)–C(31)
C(5)–Mo(2)–C(31)
C(6)–Mo(2)–C(31)
87.19(17)
87.50(17)
85.56(15)
119.12(14)
94.24(14)
153.69(16)
O(5)–C(5)
O(6)–C(6)
C(31)–C(41)
Mo(g6-C6H5F)(CO)3
Mo–C(2)
Mo–C(3)
1.960(2)
1.962(2)
1.969(2)
2.364(2)
1.146(3)
1.147(2)
1.146(3)
C(2)–Mo–C(3)
C(2)–Mo–C(1)
C(3)–Mo–C(1)
C(2)–Mo–C(11)
C(3)–Mo–C(11)
C(1)–Mo–C(11)
F–C(11)–Mo
88.86(9)
85.96(8)
87.55(9)
149.44(9)
90.74(9)
124.56(9)
127.31(15)
Mo–C(1)
Mo–C(11)
O(1)–C(1)
O(2)–C(2)
O(3)–C(3)
Mo(g6–C6H5CF3)(CO)3
Mo–C(1)
Mo–C(3)
1.961(4)
1.970(5)
1.975(4)
1.146(4)
1.144(5)
1.158(5)
C(1)–Mo–C(3)
C(1)–Mo–C(2)
C(3)–Mo–C(2)
C(1)–Mo–C(11)
C(2)–Mo–C(11)
C(3)–Mo–C(11)
87.51(16)
85.84(15)
87.45(19)
117.39(14)
156.60(14)
95.86(17)
Mo–C(2)
O(1)–C(1)
O(2)–C(2)
O(3)–C(3)
Estimated standard deviations in parentheses refer to the least significant digit.
ꢁ
distances is 1.400 A and the C(11)–F bond distance is
Cr(CO)6 with melted diphenyl [37] or in a THF/Bu2O
mixture [6c]. The structure consists of a diphenyl
ligand bridging two {Cr(CO)3} fragments in a trans
arrangement [29].
ꢁ
1.339(3) A. The C–C and C–F bond distances of the
arene ligand are comparable to those observed in Cr(g6-
C6H5F)(CO)2(SiCl3)2 [C–C, mean value, 1.388 and C–F
ꢁ
bond distance, 1.334(9) A] within the 1:1 co-crystallite
We tried to extend the previously reported synthetic
pathways for the chromium derivatives to the 4d
analogue, but the higher thermal lability of the molyb-
denum derivatives Mo(CO)6 and Mo(g6-C6H5–
C6H5)(CO)3 caused the formation of a metallic mirror in
both cases. Moreover, the reaction sequence reported in
Scheme 2 gave a very low yield (from 1H NMR, see
Section 4) of the dinuclear compound, most of the
molybdenum being present after the reaction as
Mo(CO)6 and starting material.
Cr(g6-C6H5F)(CO)2(SiCl3)2 ꢀ Cr(g6-C6H5F)(CO)(H)2-
(SiCl3)2 [33], and in Cr(g6-C6H5F)(CO)2(SnPh3)2 [C–C
ꢁ
ꢁ
mean value, 1.402 A and C–F bond distance, 1.32(2) A]
[34].
The molecular structure of the trifluoromethyl com-
plex, Mo(g6-C6H5CF3)(CO)3, is similar to that of the
ꢁ
fluoro derivative with a Mo–centroid distance of 1.89 A
and a dihedral angle C(10)–centroid–Mo–C3 (see
Fig. 1(c)) of 29.9(2)° larger than the angle observed in
the fluoro derivative probably due to the higher steric
hindrance of the –CF3 group with respect to the fluoro
substituent. The mean Mo–C and C–C distances (2.342
By taking into consideration the higher lability of the
arene ligand in Mo(g6-C6H5CH3)(CO)3 with respect to
ꢁ
and 1.404 A) are comparable with those observed in
6
6
ꢁ
Cr(g -C6H5CF3)(g -1,4-C6H4Me2) (2.131 and 1.408 A)
BF3 OEt2
6
fac-Mo(CO)3(DMF)3
ꢁ
[35] and in Cr(g -C6H5CF3)2 (2.136 and 1.408 A) [36].
Mo(CO)3 Mo(CO)3
2.1.2. Mo2(g6:g6-C6H5–C6H5)(CO)6
Mo(CO)3
The binuclear chromium derivative Cr2(g6:g6-C6H5–
C6H5)(CO)6 was originally obtained by reacting
Scheme 2.

2162
S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
CO in Mo(CO)6 [1b,38], we decided to react Mo(g6-
C6H5CH3)(CO)3 with Mo(g6-C6H5–C6H5)(CO)3 in
boiling heptane (no reaction occurs at room tempera-
ture), see Eq. (2). The formation of the dinuclear de-
rivative is presumably favoured by its low solubility.
However, a maximum yield of 40% was obtained,
further heating over longer reaction times leading to
particular total decomposition.
the case of M(g6-arene)(CO)3, M ¼ Cr, Mo, W,
arene ¼ estrone-3-methyl ether [45], the electrochemi-
cally oxidized species show the following stability trend:
[Cr(g6-arene)(CO)3]þ ꢃ [Mo(g6-arene)(CO)3]þ > [W-
(g6-arene)(CO)3]þ.
The typical redox behaviour of the mononuclear de-
rivatives in CH2Cl2 solution is reported in Fig. 2(a),
which refers to Mo(g6-C6H5CF3)(CO)3 in the presence
of an equimolar amount of Fe(C5Me5)2 as an internal
standard (starred peaks). The pertinent electrode po-
tentials are compiled in Table 3.
They only exhibit an oxidation process at high po-
tential without any associated return peak even at high
scan rates (up to 5 V sꢂ1), suggesting that the oxidation
is accompanied by fast decomposition; moreover, no
reduction process was detected in the cathodic scan up
to 2.1 V (maximum potential allowed in CH2Cl2). Al-
though the controlled potential coulometry failed to
determine the number of electrons involved in the an-
odic process because of electrode poisoning phenomena
Moðg6-C6H5CH3ÞðCOÞ þ Moðg6-C6H5–C6H5ÞðCOÞ
3
3
! Mo2ðg6:g6-C6H5–C6H5ÞðCOÞ þ C6H5CH3
ð2Þ
6
The
dinuclear
compound
Mo2(g6:g6-C6H5–
C6H5)(CO)6 is stable in air for short periods of time in
the solid state, it is slightly soluble in aliphatic hydro-
carbons and promptly reacts with Lewis bases with
formation of diphenyl. Analytical data, and infrared
and NMR spectra are in agreement with the presence of
two tricarbonyl groups of C3v symmetry, and a diphenyl
ligand. The NMR spectra (1H and 13C) are similar to
that reported by Top and Jouen [6c] for the analogous
chromium derivative. The dinuclear nature of the com-
pound is evidenced by the presence of resonances only in
the region of metal-bonded aromatic groups (5.79, 5.65
and 5.58 ppm) at variance with the starting Mo(g6-
C6H5–C6H5)(CO)3 derivative which has resonances
typical of bonded (6.02, 5.87 and 5.64 ppm) and unco-
ordinated phenyl rings (7.48, 7.43 ppm).
The low solubility of the dinuclear compound has not
allowed the preparation of crystals for X-ray analysis
and therefore we can only suggest that the system may
adopt a trans-configuration of the two Mo(CO)3 frag-
ments as observed in Cr2(g6:g6-C6H5–C6H5)(CO)6.
2.2. Electrochemistry
After the first paper by Dessy [39] on the redox
properties of Cr(g6-C6H6)(CO)3, several papers have
appeared concerning electrochemical studies on Cr(g6-
arene)(CO)3 derivatives. They have been reported
to undergo mono-electronic oxidation to the [Cr(g6-
arene)(CO)3]þ cations [40], whose stability increases
with increasing methyl substitution on the aromatic ring
[41]. As far as reduction is concerned, Cr(g6-are-
ne)(CO)3 derivatives can be bi-electronically reduced to
dianions which are very reactive on the time-scale of
cyclic voltammetry [42]. The presence of condensed
aromatics or polyphenyls as ligands increases the sta-
bility of the anions [43] and [Cr2(g6:g6-C6H5–
C6H5)(CO)6]2ꢂ has been isolated and characterized [44].
Due to the fact that most of the electrochemical
studies have been performed on chromium derivatives,
we decided to investigate the electrochemical behaviour
of our arene molybdenum tricarbonyl derivatives and to
compare them with the chromium analogues. Is it
noteworthy that a paper has appeared reporting that in
Fig. 2. Cyclic voltammograms recorded at a platinum electrode on a
CH2Cl2 solution of: (a) Mo(g6-C6H5CF3)(CO)3 (1.6 ꢄ 10ꢂ3 M) and
Fe(C5Me5)2 (1.7 ꢄ 10ꢂ3 M); (b) Mo2(g6:g6-C6H5–C6H5)(CO)6
(1.4 ꢄ 10ꢂ3 M); inset: scan rate 1.0 V sꢂ1; [NBu4][PF6] (0.2 M) as
supporting electrolyte. Scan rate 0.2 V sꢂ1, unless otherwise specified.

S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
2163
Table 3
Formal electrode potentials (V, vs. SCE), peak current ratios and peak-to-peak separations (mV) for the redox processes in CH2Cl2 solution
ð0=þÞ a;b
00
00
Complex
Ep
E
DEpb
i
pc=ibpa
E
DEpb
i
pa=ibpc
ð0=2þÞ
ð0=2ꢂÞ
Mo(g6-C6H5-C6H5)(CO)3
Mo(g6-C6H5F)(CO)3
+0.96
+0.96
+1.17
+0.91
Mo(g6-C6H5CF3)(CO)3
Mo[g6-C6H5-3,5-C6H3(C6H5)2](CO)3
Mo2(g6:g6-C6H5-C6H5)(CO)6
Cr2(g6:g6-C6H5-C6H5)(CO)6
+0.77
77
0.8
)1.65
140
0.4
)1.65c
a Peak potential value for irreversible processes.
b Measured at 0.2 V sꢂ1
c In THF solution, recalculated from [43c].
.
(see below), we can assume the one-electron nature of
the molybdenum-centred oxidation on the timescale of
the voltammetric experiment. This assumption is based
on the appearance of essentially similar peak heights for
equimolar amounts of the complexes Mo(g6-C6H5-
CF3)(CO)3 and decamethylferrocene which, due to their
substantially identical molecular weights (326.1 and
326.3, respectively), should have similar diffusion coef-
ficients.
A close examination of Table 3 shows that the
oxidation potentials of Mo(g6-C6H5–C6H5)(CO)3,
Mo(g6-C6H5F)(CO)3 and Mo[g6-C6H5–3,5-C6H3-
(C6H5)2]-(CO)3 are similar, suggesting that phenyl and
fluoride substituents have similar effects on the oxida-
tion of the central metal atom. On the other hand, the
presence of the stronger electron-withdrawing CF3
substituent in Mo(g6-C6H5CF3)(CO)3 makes the oxi-
dation more difficult, the oxidation potential shifting to
more positive values.
The electrochemical behaviour of Mo2(g6:g6-C6H5–
C6H5)(CO)6 is reported in Fig. 2(b). At a platinum
electrode it exhibits both an oxidation and a reduction,
with some degree of reversibility. The analysis [46] of the
cyclic voltammograms of the oxidation process, with
scan rates varying from 0.02 to 2.0 V sꢂ1, was compli-
cated by both the reagent diffusion and the adsorption
processes, resulting in an appreciable decrease of the
ipavꢂ1=2 and the ipavꢂ1 functions upon increasing the
scan rate. The adsorption phenomena, which are evident
from the shape of the voltammogram, see inset of
Fig. 2(b), increases the current ratio above unity, a value
of 1.2 being obtained in the voltammogram recorded at
1.0 V sꢂ1. Changing the electrode material to gold or
glassy carbon did not prevent the observed adsorption
effects. Moreover, the formed cation rapidly decom-
poses, as confirmed by the absence of a directly associ-
ated reduction peak at low scan rates (from 0.02 to 0.05
V sꢂ1). Only by operating at high scan rates, the ipc=ipa
ratio has finite values.
process following a reversible electron transfer. As a
matter of fact, a consumption of two electrons per
molecule was evaluated by controlled potential cou-
lometry (Ew ¼ ꢂ1:8 V). Unfortunately, cyclic voltam-
metric tests on the exhaustively reduced solution did not
clarify the nature of the reduction process, due to a se-
ries of oxidation processes in the range from 0.0 V to
+1.5 V (Fig. 3, Supplementary material). This suggests
that the electrochemically-formed reduced species is not
stable under the experimental conditions at variance
with the corresponding chromium derivative which af-
fords the [Cr2(g6:g6-C6H5–C6H5)(CO)6]2ꢂ dianion. The
latter has been independently obtained as the lithium
salt by reduction of Cr2(g6:g6-C6H5–C6H5)(CO)6 with
lithium anthracenide [44].
Comparison of the intensities of the oxidation and of
the reduction peaks within the mononuclear complexes
(Fig. 2(a)) with those of the dinuclear derivative
Mo2(g6:g6-C6H5–C6H5)(CO)6 (Fig. 2(b)) suggests
that the anodic process for the latter compound is bi-
electronic.
We can now compare the redox ability of the mo-
lybdenum complexes reported in this paper with that of
the chromium analogue. First of all, the mononuclear
chromium complexes afford irreversible reductions while
the molybdenum complexes undergo irreversible oxi-
dations. This fact suggests that the region of the
HOMO–LUMO gap of the molybdenum species is
shifted towards less positive (more negative) potentials
with respect to the chromium analogues. As a conse-
quence, access to oxidation processes is favoured
whereas the reduction processes occur at negative po-
tentials and are masked by the solvent discharge. As far
as the dinuclear derivative is concerned, we observe that
the dimolybdenum complex undergoes a single two-
electron reduction at about the same potential as the
dichromium complexes but the electrogenerated dianion
is notably less stable. Moreover, the dimolybdenum
derivative is oxidized giving a short-lived dication at
variance with the dichromium complexes. Finally, we
point out that, similar to the case of the dichromium
complexes, the appearance of a single two-electron
reduction for Mo2(g6:g6-C6H5–C6H5)(CO)6 means that
no phenyl–phenyl interaction (or communication) in-
The analysis of the cyclic voltammograms of the ca-
thodic process with increasing scan rate showed the
current function ipavꢂ1=2 to be constant, whereas the
current ratio ipa=ipc decreases. Such trend is diagnostic
[46] of a relatively slow first-order reversible chemical

2164
S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
volving the two molybdenum centres occurs within the
biphenyl ligand. This is further confirmed by the
appearance of a single two-electron oxidation process.
lution. IR (nujol mull, cmꢂ1): 2276m-w, 2250s, 1909vs,
1779vs. Crystallographic data and details of the struc-
ture refinement are in Table 4. Data were collected at
ꢁ
223 K with the Mo Ka (k ¼ 0:71073 A) radiation on a
Enraf–Nonius-CAD4 diffractometer equipped with a
graphite monochromator. A set of 5683 reflections with
indices ꢂ10 6 h 6 10, 0 6 k 6 16, ꢂ18 6 l 6 17, were
collected with the h=h scan. No absorption correction
was applied before averaging symmetry equivalent data.
The structure was solved by direct methods [49], and the
structure model was completed by Fourier difference
syntheses and refined with full-matrix least-squares on
3. Conclusions
This paper has shown that the thermal reaction is not
a general method for the preparation of arene tricar-
bonyl derivatives of molybdenum from Mo(CO)6, due to
the thermal lability of the products. On the other hand,
the DMF adduct fac-Mo(CO)3(DMF)3 in the presence
of BF3 ꢀ Et2O, has been shown to be a valuable starting
material, leading to polyarene and fluoro derivatives of
general formula Mo(g6-arene)(CO)3. Moreover, we have
prepared the dinuclear compound Mo2(g6:g6-C6H5–
C6H5)(CO)6 through a thermal displacement of co-or-
dinated toluene in Mo(g6-C6H5–CH3)(CO)3 in the
presence of Mo(g6-C6H5–C6H5)(CO)3.
F 2 [50]. Maximum and minimum from a final Fourier
ꢁꢂ3
map were 1.033 and )0.891 e A
.
4.3. Synthesis and characterization of Mo(g6-are-
ne)(CO)3 derivatives (arene ¼ diphenyl; 1,3,5-triphenyl-
benzene; C6H5F; C6H5CF3)
The dimolybdenum complex Mo2(g6:g6-C6H5–
C6H5)(CO)6 undergoes a single two-electron reduction
at about the same potential as the dichromium complex
Cr2(g6:g6-C6H5–C6H5)(CO)6 [44], but the electrogen-
erated dianion is notably less stable than that of the
heavier metal. Moreover, the dimolybdenum compound
gives the corresponding short-lived dication more easily
than the dichromium complexes.
4.3.1. Mo(g6-C6H5–C6H5)(CO)3, 1
A suspension of fac-Mo(CO)3(DMF)3 (2.513 g, 6.3
mmol) and diphenyl (9.7 g, 63 mmol) in Et2O (50 ml)
was slowly added (1.5 h) at room temperature of a so-
lution of BF3 ꢀ OEt2 (2.4 ml, 18.9 mmol) in Et2O (100
ml). After 8 h stirring at room temperature, the yellow
solution was transferred to a sublimation apparatus, the
solvent was removed in vacuo at room temperature, and
the residue was gently warmed at ca. 40 °C/10ꢂ2 mmHg
in order to remove the excess diphenyl. The residue of
the sublimation was dissolved in heptane at 60 °C. By
slow cooling, well shaped crystals of Mo(g6-C6H5–
C6H5)(CO)3 formed which were collected by filtration
and shortly dried in vacuo at room temperature (1.2 g).
Anal. Calc. for C15H10MoO3: C, 53.9; H, 2.9. Found: C,
4. Experimental
4.1. General
Unless otherwise stated, all of the operations were
carried out under an atmosphere of nitrogen. Solvents
were dried by conventional methods prior to use. The
compounds fac-Mo(CO)3(CH3CN)3 [47], fac-Mo(CO)3-
(DMF)3 [15], and Mo(g6-C6H5CH3)(CO)3 [15] were
prepared according to literature.
1
53.9; H, 3.7%. H NMR (CD2Cl2): d 7.48 (3H, m), 7.43
(2H, m), 6.02 (2H, d, 6.6 Hz), 5.87 (1H, t, 6.6 Hz), 5.64
(2H, t, 6.2 Hz). 13C{1H} NMR (CD2Cl2): d 136.6, 129.1,
127.6, 115.3, 95.7, 94.5, 93.6. IR (nujol mull, cmꢂ1):
3083w, 3065w, 1962s, 1872vs-br, 1581w, 1526w, 1494m-
w, 1401w, 1153m, 756m, 692m-f, 617m-f, 589m-f, 505m-
f; (toluene, cmꢂ1): 1971s, 1896s; (cyclohexane, cmꢂ1):
1981s, 1912s; (heptane, cmꢂ1): 1983s, 1915s; (dichlo-
romethane, cmꢂ1): 1970s, 1891s.
IR spectra were recorded on a FT-1725X instrument
on solutions or nujol mulls prepared under rigorous
exclusion of moisture and air. NMR spectra were re-
corded with a Varian Gemini 200 BB spectrometer at
1
200, 50.31 and 188.1 MHz for H, 13C, and 19F reso-
nances, respectively. Chemical shifts are referred to
TMS as external standard for 1H and 13C, and to CFCl3
for 19F. Materials and apparatus for electrochemistry
have been described elsewhere [48]. The values of the
electrochemical potentials are referred to the saturated
calomel electrode (SCE) with the one-electron oxidation
of ferrocene occurring at +0.39 V.
On cooling at ca. )30 °C, the mother liquor gave
additional 0.635 g of Mo(g6-C6H5–C6H5)(CO)3 for a
total yield of 87%.
4.3.2. Mo[g6-C6H5–3,5-C6H3(C6H5)2](CO)3, 2
A suspension of fac-Mo(CO)3(DMF)3 (1.176 g, 2.94
mmol) and 1,3,5-triphenylbenzene (0.902 g, 2.94 mmol)
in Et2O (50 ml) was slowly added (2 h) at room tem-
perature of a solution of BF3 ꢀ OEt2 (1.1 ml, 8.8 mmol)
in Et2O (100 ml). Formation of an oily substance was
observed at the end of the addition. After 3 h stirring at
room temperature, the yellow suspension was filtered
and the solution was dried in vacuo at room tempera-
4.2. fac-Mo(CO)3(CH3CN)3CH3CN: crystal structure
solution and refinement
Crystals of fac-Mo(CO)3(CH3CN)3 ꢀ CH3CN were
obtained by slow cooling of a saturated acetonitrile so-

S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
2165
Table 4
Crystallographic data and details of the structure refinement for fac-Mo(CO)3(CH3CN)3 ꢀ CH3CN, Mo(g6-C6H5–C6H5)(CO)3, Mo(g6-
C6H5F)(CO)3, and Mo(g6-C6H5CF3)(CO)3
Compound
fac-Mo(CO)3(CH3CN)3 ꢀCH3CN
344.2
1
3
4
Formula weight
Crystal system
Space group (No)
334.2
Triclinic
276.1
Monoclinic
P21=c
6.6898(7)
11.169(1)
12.846(1)
326.8
Triclinic
Orthorhombic
Pbcm
ꢂ
ꢂ
P1
P1
ꢁ
a (A)
8.2659(9)
12.672(3)
14.935(4)
6.995(1)
12.615(3)
15.765(3)
70.30(2)
84.16(2)
79.06(2)
1284.9(5)
4
6.786(2)
7.758(3)
11.299(3)
96.77(3)
97.90(3)
108.20(3)
551.5(3)
2
ꢁ
b (A)
ꢁ
c (A)
a (°)
b (°)
c (°)
103.24(3)
3
ꢁ
V (A )
1564.4(6)
4
1.461
934.3(2)
Z
4
1.963
1.394
dcalc (g cmꢂ3
)
1.727
1.020
1.964
1.222
l (cmꢂ1
hmin = max (°)
Reflections unique
)
0.846
2.1–27.0
2.5–27.0
5583 (Rint ¼ 0:0265)
343
2.45–27.44
2135 (Rint ¼ 0:0202)
127
3.08–26.97
2391 (Rint ¼ 0:0521)
154
1769 (Rint ¼ 0:1600)
Variables refined
R indexes [I > 2rðIÞ]
99
R1
wR2
0.0544
0.1015
0.0334
0.0740
0.0246
0.0616
0.0328
0.0665
R indexes (all data)
R1
0.1088
0.1132
1.016
0.0552
0.0801
1.006
0.0278
0.0633
1.097
0.0469
0.0703
1.072
wR2
Goodness-of-fit
P
P
R1 ¼ jjFoj ꢂ jFcjj= Foj.
h
i
1=2
P
P
2
2
wR2 ¼
wðFo2 ꢂ Fc2Þ = wðFo2Þ
.
ture. The residue was dissolved in cyclohexane (150 ml)
and filtered at ca. 70 °C. The volume of the solution was
reduced to 20 ml and heptane (50 ml) was added which
caused the precipitation of the yellow microcrystalline
solid which was recovered by filtration and dried in
vacuo at room temperature affording 0.575 g (40% yield)
of Mo[g6-C6H5–3,5-C6H3(C6H5)2](CO)3. Anal. Calc.
for C27H18MoO3: C, 66.6; H, 3.7. Found: C, 66.5; H,
°C, thus obtaining a solid and a solution. The solution
was stored for 64 h at ca. )30 °C obtaining yellow
crystals (0.139 g) which where collected by filtration,
shortly dried in vacuo at room temperature and identi-
fied as Mo(g6-C6H5F)(CO)3. Anal. Calc. for
C9H5FMoO3: C, 39.2; H, 1.8. Found: C, 38.3; H, 1.8%.
1H NMR (C6D6): d 4.46 (3H, m, 3.6 Hz), 3.81 (2H, m,
3.8 Hz). 13C{1H} NMR (C6D6): d 114.5 (d, 251.5 Hz),
94.5, 87.5, 80.1. 19F NMR (C6D6): d )129. IR (heptane,
cmꢂ1): 1995s, 1926s.
The solid obtained from the filtration was suspended
in heptane (50 ml), gently heated at ca. 60 °C and filtered
when hot. After 14 h at room temperature, the yellow
crystals thus obtained were shown to be identical with
the previous crop analytically and spectroscopically
(NMR). Total yield: 0.466 g, 36%.
1
3.9%. H NMR (CDCl3): d 7.64–7.49 (13H, m), 6.01
(2H, d, 5.8 Hz), 5.82 (2H, t, 6.4 Hz), 5.56 (1H, t, 5.8 Hz).
13C{1H} NMR (CDCl3): d 134.5, 127.3, 126.4, 116.2,
96.8, 93.2, 92.3. IR (Et2O, cmꢂ1): 1973s, 1900s; (hep-
tane, cmꢂ1): 1982s, 1914s; (dichloromethane, cmꢂ1):
1970s, 1891s.
4.3.3. Mo(g6-C6H5F)(CO)3, 3, Mo(g6-C6H5CF3)(CO)3,
4
Mo(g6-C6H5CF3)(CO)3. Yield: 56%. Anal. Calc. for
C10H15F3MoO3: C, 36.8; H, 1.5. Found: C, 36.2; H,
1.9%. 1H NMR (C6D5CD3): d 4.81 (2H, d, 6.6 Hz), 4.37
(1H, t, 6 Hz), 4.20 (2H, t, 6 Hz). 19F NMR (C6D6): d
)61.5. IR (heptane, cmꢂ1): 2002s, 1937s; (cyclohexane/
Et2O, cmꢂ1): 1996s, 1926s.
Only the preparation of Mo(g6-C6H5F)(CO)3 is de-
scribed in detail, the trifluoromethylbenzene derivative
being obtained in a similar way. A suspension of fac-
Mo(CO)3(DMF)3 (1.892 g, 4.74 mmol) and a mixture of
fluorobenzene (15 ml) and cyclohexane (25 ml) was
slowly added (2 h) at room temperature to a solution of
BF3 ꢀ OEt2 (1.8 ml, 14.2 mmol) in Et2O (100 ml). After 2
h stirring at room temperature, a yellow–brown sus-
pension was obtained which was filtered. The solution
was dried in vacuo at room temperature and the residue
was dissolved in heptane (60 ml) and filtered at ca. 40
4.4. Mo(g6-arene)(CO)3 derivatives: crystal structure
solution and refinement
Arene ¼ diphenyl. Crystals of Mo(g6-C6H5–C6H5)-
(CO)3 were obtained by slow cooling of a saturated

2166
S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
heptane solution. Crystallographic data and details of
the structure refinement are in Table 4. Data were
perature for 3 h. The initial solution gave a yellow sus-
pension. The solid was collected by filtration and shortly
dried in vacuo at room temperature (0.302 g, 42% yield) of
Mo2(g6:g6-C6H5C6H5)(CO)6, 5. Anal. Calc. for C18H10-
ꢁ
collected at 223 K with the Mo Ka (k ¼ 0:71073 A)
radiation on a Enraf–Nonius-CAD4 diffractometer
equipped with a graphite monochromator on a crystal
of approximate dimensions 0.30 ꢄ 0.14 ꢄ 0.07 mm3. A
set of 6479 reflections with indices ꢂ8 6 h 6 8, ꢂ16 6
k 6 2, ꢂ20 6 l 6 19, were collected with the x=2h scan
method. A numerical absorption correction (minimum
transition 0.843, maximum transition 0.934) was applied
before averaging symmetry-equivalent data. The struc-
ture was solved by direct methods [49], and the structure
model was completed by Fourier difference syntheses
and refined with full-matrix least-squares on F 2 [50].
1
Mo2O6: C, 42.0; H, 2.5. Found: C, 41.6; H, 2.5%. H
NMR (CDCl3): d ¼ 5:79 (2H, d, 6.0 Hz), 5.65 (2H, t, 6.4
Hz), 5.58 (1H, t, 5.8 Hz). 13C{1H} NMR (CDCl3):
d ¼ 94:6, 93.8, 93.2, 93.0. IR (nujol mull, cmꢂ1): 3100w,
3083w, 1953s, 1870vs-br, 1498w, 1289w, 1150w, 609m-f,
578m-f, 502m-f; (toluene, cmꢂ1): 1969s, 1903s.
An attempt was made to prepare the dinuclear com-
pound by reacting equimolar amounts of fac-
Mo(CO)3(DMF)3 and Mo(g6-C6H5–C6H5)(CO)3 with a
solution of BF3 ꢀ OEt2 in Et2O. After 16 h stirring at
room temperature, an IR spectrum of the solution had
absorptions typical of the starting materials and
Mo(CO)6. On work-up, traces only of the dinuclear
compound Mo2(g6:g6-C6H5C6H5)(CO)6, were detected
Maximum and minimum from a final Fourier map were
ꢁꢂ3
0.459 and )0.556 e A
.
Arene ¼ C6H5F. Crystals of Mo(g6-C6H5F)(CO)3
were obtained by slow cooling of a saturated heptane
solution. Crystallographic data and details of the
structure refinement are in Table 4. Data were collected
1
by H NMR spectrometry.
ꢁ
at 213 K with the Mo Ka radiation (k ¼ 0:71073 A) on a
5. Supplementary material
CCD area detector diffractometer equipped with a
graphite monochromator on a crystal of approximate
dimensions 0.30 ꢄ 0.30 ꢄ 0.20 mm3. A set of 6268 re-
flections with indices ꢂ8 6 h 6 6, ꢂ14 6 k 6 12, ꢂ13 6
l 6 16, were collected with the x-scan method. An
empirical absorption correction (minimum transition
0.6799, maximum transition 0.7679) was applied before
averaging symmetry-equivalent data. The structure was
solved by direct methods [49], and the structure model
was completed by Fourier difference syntheses and re-
fined with full-matrix least-squares on F 2 [50]. Maxi-
Fig. 3. Cyclic voltammogram recorded at a platinum
electrode on a CH2Cl2 solution of Mo2(g6:g6-C6H5–
C6H5)(CO)6 (4.2 ꢄ 10ꢂ3 M) after exhaustive two-
electron reduction at )1.8 V. [NBu4][PF6] (0.2 M) as
supporting electrolyte. Scan rate 0.2 V sꢂ1
.
6. Crystallographic material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre: CCDC No. 223579, Mo(CO)3-
(CH3CN)3 ꢀ CH3CN; CCDC No. 223580, Mo(g6-C6H5–
C6H5)(CO)3; CCDC No. 223581, Mo(g6-C6H5F)(CO)3,
CCDC No. 223582, Mo(g6-C6H5CF3)(CO)3. Copies of
the crystallographic data may be obtained free of charge
from: The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: de-
posit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk).
mum and minimum from a final Fourier map were 0.462
ꢁꢂ3
and )0.379 e A
.
Arene ¼ C6H5CF3. Crystals of Mo(g6-C6H5CF3)-
(CO)3 were obtained by slow cooling of a saturated tol-
uene/heptane solution. Crystallographic data and details
of the structure refinement are in Table 4. Data were
collected at 213 K on a crystal of approximate dimen-
sions 0.39 ꢄ 0.10 ꢄ 0.09 mm3. A set of 3893 reflections
with indices ꢂ8 6 h 6 8, ꢂ9 6 k 6 4, ꢂ14 6 l 6 14, were
collected with the h=2h scan method in the range
3:08 6 h 6 26:97°. A numerical absorption correction
(minimum transition 0.6472, maximum transition
0.8980) was applied before averaging symmetry equiva-
lent data. The structure was solved by direct methods
[49], and the structure model was completed by Fourier
difference syntheses and refined with full-matrix least-
Acknowledgements
The authors wish to thank the Ministero dell’Ist-
ꢀ
ruzione, dell’Universita e della Ricerca (MIUR, Roma),
Programma di Ricerca Scientifica di Notevole Interesse
Nazionale, for financial support. P.Z. gratefully ac-
squares on F 2 [50]. Maximum and minimum from a final
ꢀ
knowledges the financial support by the Universita di
Siena (PAR 2003).
ꢁꢂ3
Fourier map were 0.638 and )0.848 e A
.
4.5. Synthesis of Mo2(g6:g6-C6H5–C6H5)(CO)6, 5
References
A mixture of Mo(g6-C6H5CH3)(CO)3 (0.388 g, 1.45
mmol) and Mo(g6-C6H5–C6H5)(CO)3 (0.486 g, 1.46
mmol) in heptane (55 ml) was heated at the reflux tem-
[1] (a) J.P. Collmann, L.S. Hegedus, J.R. Norton, R.G. Finke,
Principles and Applications of Organotransition Metal Chemistry,
University Science Book, Mill Valley, CA, 1987;

S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
2167
ꢃ
(b) E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.), Comprehen-
sive Organometallic Chemistry, Pergamon Press, New York, 1982,
and 1995;
[20] Some selected references: P. von Rague Schleyer, B. Kiran, D.V.
Simon, T.S. Soresen, J. Am. Chem. Soc. 122 (2000) 510;
V. Graves, J.J. Lagowski, Inorg. Chem. 15 (1976) 577;
idem, J. Organomet. Chem. 120 (1976) 397;
(c) F. Rose-Munch, E. Rose, Eur. J. Inorg. Chem. (2002) 1269;
(d) F. Rose-Munch, E. Rose, Arenetricarbonylchromium com-
plexes: ipso, cine, tele nucleophilic aromatic substitutions, in: D.
Astruc (Ed.), Modern Arene Chemistry; Concepts, Synthesis, and
Applications, Wiley-VCH, Weinheim, 2002, p. 368.
[2] G.A. Moser, M.D. Rausch, Synth. React. Inorg. Metal. Org.
Chem. 4 (1974) 38.
F. Calderazzo, G. Pampaloni, L. Rocchi, U. Englert, Organo-
metallics 13 (1994) 2592;
See also: Ch. Elschenbroich, A. Salzer, Organometallics.
Concise Introduction, second ed., VCH, Weinheim, 1992.
A
€
[21] (a) J. Deberitz, H. Noth, J. Organomet. Chem. 55 (1973) 153;
(b) B. Mailvaganam, B.E. McCarry, B.G. Sayer, R.E. Perrier, R.
Faggiani, M.J. McGlinchey, J. Organomet. Chem. 335 (1987) 213;
(c) B.F.G. Johnson, D.S. Shephard, D. Braga, F. Grepioni, J.
Chem. Soc. Dalton Trans. (1997) 3563;
€
[3] (a) K. Ofele, Chem. Ber. 99 (1966) 1732;
(b) M.D. Rausch, J. Org. Chem. 39 (1974) 1787.
[4] (a) F. Basolo, Polyhedron 9 (1990) 150, and references therein;
(b) F. Calderazzo, G. Pampaloni, J. Organomet. Chem. 500
(1995) 47.
(d) J. Bould, W. Clegg, T.R. Spalding, J.D. Kennedy, Inorg.
Chem. Commun. 2 (1999) 315.
[5] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann,
Advanced Inorganic Chemistry, sixth ed., J. Wiley, New York,
1999.
[22] V. Kupfer, U. Thewalt, Z. Anorg. Allg. Chem. 627 (1423) 2001.
[23] D.V. Blackburn, D. Britton, J.E. Ellis, Angew. Chem. Int. Ed.
Engl. 31 (1992) 1495.
[6] (a) G. Natta, R. Ercoli, F. Calderazzo, Chim. Ind. (Milan) 40
(1958) 287;
[24] M. Herberhold, T. Hofmann, W. Milius, B. Wrackmeyer, J.
Organomet. Chem. 472 (1994) 175.
(b) R. Ercoli, F. Calderazzo, A. Alberola, Chim. Ind. (Milan) 41
(1959) 975;
[25] A.J. Blake, B.F.G. Johnson, D. Reed, D.S. Shepard, J. Chem.
Soc. Dalton Trans. (1995) 843.
[26] G.B. Robertson, Nature 191 (1961) 593.
(c) S. Top, G. Jaouen, J. Organomet. Chem. 182 (1979) 381.
[7] During the preparation of fac-Mo(CO)3(CH3CN)3, large yellow
crystals of fac-Mo(CO)3(CH3CN)3 ꢀ CH3CN were obtained from
the mother liquor. The IR spectrum (Nujol mull) showed
absorptions at 2276(m-w) and 2250(s) cmꢂ1, assigned to Mo-
coordinated and to uncoordinated acetonitrile, respectively [8].
Although the molybdenum system is not isostructural with the
tungsten analogue, fac-W(CO)3(CH3CN)3 [9] due to the presence
of uncoordinated nitrile, the metrical data are similar in the two
[27] A. Spek, Platon, University of Utrecht, Utrecht, The Netherlands,
1996.
[28] (a) E.L. Muetterties, J.R. Bleeke, E.J. Wucherer, T.A. Albright,
Chem. Rev. 82 (1982) 499;
(b) T.A. Albright, Acc. Chem. Res. 15 (1982) 149.
[29] (a) P. Corradini, G. Allegra, J. Am. Chem. Soc. 82 (1960) 2075;
(b) G. Allegra, G. Natta, Atti Accad. Naz. Lincei 31 (1961) 399.
[30] W.E. Geiger, N. Van Order Jr., D.T. Pierce, T.E. Bitterwolf, A.L.
Rheingold, N.D. Chasteen, Organometallics 10 (1991) 2403.
[31] N. Van Order Jr., W.E. Geiger, T.E. Bitterwolf, A.L. Rheingold,
J. Am. Chem. Soc. 109 (1987) 5680.
ꢁ
compounds as the atomic radii of molybdenum (1.36 A) and
ꢁ
tungsten (1.37 A) [10] differ only slightly. The mean M–N and M–
ꢁ
C bond distances are 2.231 and 1.923 A, M ¼ Mo, and 2.208 and
ꢁ
1.932 A, M ¼ W, respectively, and agree with those reported for
[32] (a) A. Auffrant, D. Prim, F. Rose-Munch, E. Rose, J. Vaisser-
mann, Organometallics 20 (2001) 3214;
other acetonitrile carbonyl derivatives of molybdenum(0) such as
ꢁ
Mo(CO)2(maleic aldehyde)(CH3CN)2 [2.206(3) and 1.982(3) A]
[11], Mo(CO)3[bis(2–pyridyl)formamidine]2(CH3CN) [2.255(3)
ꢁ
and 1.932(4) A] [12], and fac-Mo(CO)3[1,1-bis(diphenylphosph-
(b)
A. Auffrant, D. Prim, F. Rose-Munch, E. Rose, S.
Schouteeten, J. Vaissermann, Organometallics 22 (2003) 1898.
[33] B.R. Jagirdar, R. Palmer, K.J. Klabunde, L.J. Radonovich, Inorg.
Chem. 34 (1995) 278.
ꢁ
ino)ferrocene](CH3CN) 0.5 H2O [2.222(2) and 1.958(3) A] [13].
ꢁ
The C–N distance [1.096(15) A] of the lattice acetonitrile is shorter
ꢁ
than those in the Mo-bonded ligand [N(1)–C(3), 1.134 A].
[34] A. Khaleel, K.J. Klabunde, Inorg. Chem. 35 (1996) 3223.
[35] S.B. Larson, C.M. Seymour, J.J. Lagowski, Acta Crystallogr. C43
(1987) 1626.
[8] B.N. Storhof, H.C. Lewis Jr., Coord. Chem. Rev. 23 (1977) 1;
B.L. Ross, J.G. Grasselli, W.M. Ritchey, H.D. Kaesz, Inorg.
Chem. 2 (1963) 1023.
[36] S.B. Larson, C.M. Seymour, J.J. Lagowski, Acta Crystallogr. C43
(1987) 1624.
[9] E.J.M. Hamilton, D.E. Smith, A.J. Welch, Acta Crystallogr.
Section C 43 (1987) 1214.
[37] G. Natta, R. Ercoli, F. Calderazzo, E. Santambrogio, Chim. Ind.
(Milano) 40 (1958) 1003.
[10] J. Emsley, The Elements, Clarendon Press, Oxford, 1989.
[11] C.H. Lai, C.H. Cheng, F.L. Liao, S.L. Wang, Inorg. Chem. 32
(1993) 5658.
[38] (a) E.L. Muetterties, J.R. Bleeke, A.C. Sievert, J. Organomet.
Chem. 178 (1979) 197;
(b) C.D. Hoff, J. Organomet. Chem. 282 (1985) 201.
[39] R.E. Dessy, F.E. Stary, R.B. King, M. Waldrop, J. Am. Chem.
Soc. 88 (1966) 471.
[12] P.Y. Yang, F.C. Chang, M.C. Suen, J.D. Chen, T.C. Keng, J.C.
Wang, J. Organomet. Chem. 596 (2000) 226.
[13] L.C. Song, J.T. Liu, Q.M. Hu, G.F. Wang, P. Zanello, M.
Fontani, Organometallics 19 (2000) 5342.
[40] (a) M.K. Lloyd, J.A. McCleverty, J.A. Condor, E.M. Jones, J.
Chem. Soc. Dalton Trans. (1973) 1768;
[14] W. Strohmeier, Chem. Ber. 94 (1961) 3337.
[15] M. Pasquali, P. Leoni, P. Sabatino, D. Braga, Gazz. Chim. Ital.
122 (1992) 275.
(b) S.P. Gubin, V.S. Khandkarova, J. Organomet. Chem. 22
(1970) 449.
[41] (a) A.D. Hunter, V. Mozol, S.D. Tsai, Organometallics 11 (1992)
2251;
[16] A.N. Nesmeyanov, V.V. Krivikh, V.S. Kaganovich, M.I. Rybins-
kaya, J. Organomet. Chem. 102 (1975) 185.
(b) R.D. Rieke, I. Tucker, S.N. Milligan, D.R. Wright, B.R.
Willeford, L.J. Radonovich, M.W. Eyring, Organometallics 1
(1982) 938.
[17] V. Zanotti, V. Rutar, R.J. Angelici, J. Organomet. Chem. 414
(1991) 177.
[18] (a) C.S. Creaser, M.A. Fey, G.R. Stephenson, Spectrochim. Acta
50A (1994) 1295;
[42] R.E. Dessy, R.B. King, M. Waldrop, J. Am. Chem. Soc. 88 (1966)
5112.
(b) S.F.A. Kettle, I. Paul, Adv. Organomet. Chem. 10 (1972)
199;
[43] (a) R.D. Rieke, J.S. Arney, W.E. Rich, B.R. Willeford Jr., B.S.
Poliner, J. Am. Chem. Soc. 97 (1975) 5951;
(b) W.P. Henry, R.D. Rieke, J. Am. Chem. Soc. 105 (1983) 6314;
(c) S.N. Milligan, R.D. Rieke, Organometallics 2 (1983) 171.
(c) D.A. Brown, F.J. Hughes, J. Chem. Soc. (A) (1968) 1519.
[19] J. Ronayne, D.H. Williams, J. Chem. Soc. (B) (1967) 540.

2168
S. Antonini et al. / Journal of Organometallic Chemistry 689 (2004) 2158–2168
[44] R.D. Rieke, S.N. Milligan, L.D. Schulte, Organometallics 6 (1987)
699.
[48] E. Stulz, J.K.M. Sanders, M. Montalti, L. Prodi, N. Zaccheroni,
F. Fabrizi de Biani, E. Grigiotti, P. Zanello, Inorg. Chem. 41
(2002) 5269.
[45] A.M. Bond, E. Mocellin, C.B. Pascual, Organometallics 6 (1987)
385.
[49] G.M. Sheldrick, SHELXS-97 Program for Crystal Structure
€
[46] P. Zanello, Inorganic Electrochemistry, Theory, Practice and
Application, Royal Society of Chemistry, 2003.
[47] B.L. Ross, J.G. Grasselli, W.M. Richtey, H.D. Kaesz, Inorg.
Chem. 2 (1963) 1023.
Solution, University of Gottingen, Germany, 1997.
[50] G.M. Sheldrick, SHELXL-97 Program for Crystal Struc-
€
ture Refinement, University of Gottingen, Germany,
1997.