Synthesis and reactivity of mixed-ring indenyl complexes of molybdenocene

Article abstract of DOI:10.1016/j.jorganchem.2005.01.027

The complex [IndCpMo(NCMe)₂][BF₄]₂ provides a suitable entry to the synthesis of IndCpMoBr₂ and IndCpMoMe₂. The latter, also available from IndCpMoX₂ (X = Cl, Br) and MeMgCl, reacts with HCl to give IndCpMoCl(Me) which, in turn reacts with NaSPh to yield IndCpMo(SPh)(Me). Cyclic voltammetry shows that these three alkyl complexes undergo a 1e reversible oxidation to 17 e Mo^V cations. IndCpMoCl(Me) is oxidized by [Cp₂Fe]BF₄ to afford [IndCpMoCl(Me)]BF₄ in 95% yield. Reaction of [IndCpMo(NCMe) ₂][BF₄]₂ with KBPz₄ in CH ₂Cl₂/NMF leads to [IndCpMo(κ²-BPz ₄)]BF₄. Taken together with previous reports these results show that the indenyl ring slows down substitutional chemistry at the Cp′₂Mo(IV) fragment (Cp′ = Cp, Ind) by steric reasons, overshadowing any acceleration due to a possible indenyl effect.

Full text of DOI:10.1016/j.jorganchem.2005.01.027

Journal of Organometallic Chemistry 690 (2005) 1718–1725
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of mixed-ring indenyl complexes
of molybdenocene
a
Isabel S. Gonc¸alves , Carla A. Gamelas , Claudia C.L. Pereira , Carlos C. Roma˜o
b,c
b
b,
*
´
a
Department of Chemistry, CICECO, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
ˆ
b
´ ´
Instituto de Tecnologia Quımica e Biologica da Universidade Nova de Lisboa, Quinta do Marques, EAN, Apt. 127, 2781-901 Oeiras, Portugal
´ ´ ´
Escola Superior de Tecnologia, Instituto Politecnico de Setubal, 2910-761 Setubal, Portugal
c
Received 10 December 2004; accepted 27 January 2005
Available online 22 February 2005
Abstract
The complex [IndCpMo(NCMe)2][BF4]2 provides a suitable entry to the synthesis of IndCpMoBr2 and IndCpMoMe2. The latter,
also available from IndCpMoX2 (X = Cl, Br) and MeMgCl, reacts with HCl to give IndCpMoCl(Me) which, in turn reacts with
NaSPh to yield IndCpMo(SPh)(Me). Cyclic voltammetry shows that these three alkyl complexes undergo a 1e reversible oxidation
to 17 e MoV cations. IndCpMoCl(Me) is oxidized by [Cp2Fe]BF4 to afford [IndCpMoCl(Me)]BF4 in 95% yield. Reaction of [Ind-
CpMo(NCMe)2][BF4]2 with KBPz4 in CH2Cl2/NMF leads to [IndCpMo(j2-BPz4)]BF4. Taken together with previous reports these
results show that the indenyl ring slows down substitutional chemistry at the Cp02MoðIVÞ fragment (Cp0 = Cp, Ind) by steric reasons,
overshadowing any acceleration due to a possible indenyl effect.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Molybdenum; Cyclopentadienyl; Indenyl; Molybdenocene; Mixed-ring indenyl complexes
1. Introduction
complexes (Cp0 = Cp, Ind) [4a,4b]. The very interesting
chemistry of these species was studied in terms of their
redox-induced indenyl-slippage processes leaving behind
the study of many other types of derivatives and reac-
tions of the IndCpMo fragment. Indenyl complexes usu-
ally possess a higher reactivity than their Cp analogues,
due either to their higher ground state energy or to facile
haptotropic rearrangements (the indenyl effect) [5,6]. It
is, therefore, expected that IndCpMo derivatives might
exhibit enhanced reactivity compared with their parent
metallocenes, namely in what concerns insertion chemis-
try or associatively driven reactions. In order to be able
to draw conclusions on this issue, we set out to explore
synthetic routes to the relevant starting complexes from
Molybdenocene derivatives in the oxidation state (IV)
have the general formulae Cp2MoXY, [Cp2MoXL]+ and
[Cp2MoL2]2+, in which X and Y represent r-bonded one
electron ligands (e.g., alkyls, hydrides, thiolates) and L
represents two electron donor ligands (olefins, amines,
phosphines, nitriles, CO, CNR, etc.) [1–3]. In terms of
synthesis, this very well established chemistry derives
from the dihydride Cp2MoH2 and the corresponding
dihalides Cp2MoX2 that are readily prepared from it.
Halide substitution then yields the variety of products
mentioned above.
In contrast, our previously devised method of prepar-
ing the mixed-ring IndCpMo(IV) complexes led us di-
rectly to [IndCp0Mo(CO)2]2+ and (g3-Ind)Cp0Mo(CO)2
the dication [IndCpMo(CO)2]2+
.
Accordingly, we now report on the reactivity of [Ind-
CpMo(CO)2]2+ and on improved routes to some funda-
mental mixed ring complexes like IndCpMoX2,
IndCpMoX(SR) and IndCpMoCl(Me) derivatives. The
*
Corresponding author. Tel.: +351 214469751; fax: +351 4411277.
E-mail address: ccr@itqb.unl.pt (C.C. Roma˜o).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.027

I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 690 (2005) 1718–1725
1719
data gathered on these studies is compared to that of
their Cp2Mo(IV) and Ind2Mo(IV) analogues in order
to ascertain the influence of the indenyl ligand on the
chemistry of molybdenocenes.
attempt to prepare 4 by a totally different methodology,
the reaction of IndMoBr3 with Cpꢀ transfer agents was
devised as a viable alternative (Scheme 1). The readily
available IndMo(g3-C3H5)(CO)2 was protonated with
HBF4 Æ Et2O and then treated with 1 equivalent of
(NBu4)Br3 to give the green complex IndMoBr3(CO)2
(5) in good yield.
2. Results
The IR spectrum shows two strong m(C „ O) absorp-
tions at 2101 and 2072 cmꢀ1. These values are compara-
ble with those for the chloro tungsten analogue
IndWCl3(CO)2 (2065 and 2002 cmꢀ1) [8a]. The 1H
NMR spectrum in (CD3)2CO is compatible with the
g5-coordination mode of the indenyl ligand and the
spectrum presents one multiplet in the aromatic region
at d 7.64–7.42 (H5ꢀ8), a doublet at d 6.25 (H1/3) and a
triplet at d 5.82 ppm for H2. Decarbonylation of 5 in
solution takes place after a short period of time as is
the case with IndMCl3(CO)2 (M = Mo, W), [8]. But, in
contrast to the latter, the product obtained could not
be positively identified as the desired IndMoBr3 and
was not further characterized. This shortcoming pre-
vented the completion of Scheme 1.
2.1. Synthetic studies
Reaction of [IndCpMo(CO)2]2+ with excess P(OMe)3,
under reflux and irradiation, gives the analytically pure
complex [CpMo{P(OMe)3}2(CO)2]BF4 (1), with a Cp
signal at d 5.80 ppm in the 1H NMR spectrum and
two characteristic CO stretching vibrations in the IR,
at 1995 and 1915 cmꢀ1, Eq. (1).
ð1Þ
Reaction of [IndCpMo(NCMe)2]2+ with KBPz4 led
to [IndCpMo(j2-BPz4)]BF4 (6) isolated in good yield.
The indenyl ligand in 6 presents a typical g5 chemical
shift pattern, with a doublet for H1/3 at d 6.69 ppm
and a triplet for H2 at d 6.40 ppm, unequivocally as-
signed and distinguished from the peaks of the BPzꢀ4 li-
gand by irradiation experiments. The triplets at d 6.46
and 6.26 ppm are attributed to H5 and H2 of BPzꢀ4 ,
respectively, because of their multiplicity and integrated
area. The triplet at d 6.46 ppm (H5) is transformed into a
doublet by irradiation of the doublets at d 7.18 or d
7.01 ppm, which are assigned to H4 and H6. Irradiation
of the triplet at d 6.26 ppm (H2) affects the doublets at d
7.63 (H3) and 6.53 (H1) ppm (see also compound 7 in
Scheme 2 for numbering).
The lability of the CO ligands in [IndCpMo(CO)2]2+
is expected on the basis of the values for their CO
stretching vibrations (2129 and 2089 cmꢀ1, Ref. [4b])
indicating very low p-backdonation. It is, therefore, sur-
prising that CO substitution from [IndCpMo(CO)2]2+
by Clꢀ or Brꢀ is not a straightforward process and is
sensitive to the solvents and salts used. This problem
is also shared by the chemistry of [Ind2Mo(CO)2]2+. In
fact, Ind2MoCl2 could be made easily by this process
(using LiCl in CH2Cl2) whereas Ind2MoBr2 was ob-
tained from LiBr in acetone but not in CH2Cl2 [7]. Even
the reported preparation of IndCpMoCl2 (2) from [Ind-
CpMoCl(CO)]BF4 in the presence of LiCl in acetone can
yield some surprises if the starting materials are not
freshly distilled or if the irradiation period is longer than
needed. An IR inspection in the CO stretching region
determines the exact period of time required [4b]. Fol-
lowing this careful method, we were now able to prepare
IndCpMoI2 (3) by refluxing and irradiating [IndCp-
MoI(CO)]BF4 [4a,4b] in the presence of (NBu4)I. How-
ever, the dibromide IndCpMoBr2 (4) resisted synthesis
by this method being finally prepared in 80% yield by
reaction of [IndCpMo(NCMe)2]2+ with 2 equivalents
of (NBu4)Br in acetone, Eq. (2).
Bu4NBr
½IndCpMoðNCMeÞ ꢁ½BF4ꢁ ! IndCpMoBr2 ð4Þ ð2Þ
2
2
Alternatively, we also prepared 3 by reaction of Ind-
CpMo(SPh)2 (prepared from 2 [4b]) with excess MeI, a
process already known in Cp2Mo(IV) chemistry [2].
The dihalide complexes 2–4 are stable to air oxidation
during several weeks and are insoluble in chlorinated
solvents as well as in ether or hexane. They are also
insoluble in water but are hydrolysed slowly. In an
Scheme 1.

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I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 690 (2005) 1718–1725
1
4.44 ppm). In comparison to the H NMR spectrum of
7, the Cp resonance of 8 is slightly shielded whereas
the CH3 resonance is more deshielded.
Reaction of 8 with [Cp2Fe]BF4, at room temperature
in NCMe gives the green paramagnetic cation [IndCp-
MoCl(Me)]BF4 (10) in 95% isolated yield. This reaction
is entirely similar to that reported for Cp2MoCl(Me)
and attests for the chemical stability of the IndCpMo(V)
fragment and its 17 e complexes [10]. These reactions are
summarized in Scheme 2.
2.2. Electrochemical studies
The electrochemical data of complexes IndCpMoMe2
(7), IndCpMoX(Me) [X = Cl (8), SPh (9)] and the cat-
ionic [IndCpMo(j2-BPz4)]BF4 (6) were obtained in
dichloromethane (containing 0.1 M tetrabutylammo-
nium hexafluorophosphate) and are summarized in
Table 1.
The cyclic voltammograms (CV) of complexes 7, 8
and 9 all present one reversible redox couple assigned
to the MoIV/V oxidation (within the solvent limits, ca.
ꢀ1.5 to +1.6 V). The peak separations, DEp for each re-
dox couple ranged from 60 to 80 mV in CH2Cl2, which
at the present experimental conditions are plausibly sug-
gestive of one-electron reversible processes. Replace-
ment of one Cl (in 8) by one CH3 (in 7) makes
oxidation of IndCpMo(IV) to IndCpMo(V) easier by
350 mV: the half wave potentials (E1/2) of 7 and 8 are
ꢀ0.22 and +0.13 V, respectively. For the congeners
Cp2MoMe2 and Cp2MoCl(Me) the similar values of
ꢀ0.27 and +0.12 V (DE1/2 = 390 mV) were found in
the same solvent [10]. The chloro-alkyl derivative 8 re-
acts instantaneously in the electrochemical cell when
the solvent is NCMe (blue to violet solution), as ob-
served for Cp2MoBr(Me) [10].
Scheme 2.
Reaction of 2 or 4 with MeMgCl or MeLi affords
moderate yields of the dimethyl complex IndCpMoMe2
(7). Somewhat surprisingly, 7 can also be obtained from
[IndCpMo(NCMe)2]2+ upon reaction with MeMgCl in
Et2O/THF. 7 is a deep blue complex in contrast to the
1
orange Cp2MoMe2 [9]. Its H NMR spectrum presents
the resonance for the Cp protons (d 3.85 ppm) as well
as for the Ind protons (d 4.76 ppm for the H2 triplet,
4.09 for the H1/3 doublet). The CH3 resonances appear
as a singlet at d 0.33 ppm in C6D6. These values are sig-
nificantly shifted relative to those of Cp2MoMe2 (d
4.20 ppm, Cp; 0.19 ppm, CH3). The EI mass spectrum
presents the molecular ion at m/z 306 as well as two
peaks corresponding to stepwise loss of one and two
CH3 groups.
Reaction of 7 with HCl in Et2O affords a quantitative
yield of blue IndCpMoCl(Me) (8). Being chiral-at-metal
8 presents a complex set of resonances for the indenyl
protons due to the fact that they are now diastereop-
topic. The Cp and CH3 resonances at d 4.72 ppm and
d 0.53 are slightly deshielded relative to those in 7, as
expected.
The relative shifts of the peak potentials reflect the
variations in the overall donor/acceptor abilities of the
ligands and ease of oxidation decreases in the order Ind-
CpMoMe2 > IndCpMoCl(Me) > IndCpMo(SPh)(Me).
Table 1
Electrochemical data in CH2Cl2 at room temperaturea
b
c
Compound
Epa
Epc
E1/2
IndCpMoMe2 (7)
ꢀ0.19
+0.17
+0.20
ꢀ0.69
ꢀ1.01
ꢀ0.90
ꢀ1.16
ꢀ0.26
+0.09
+0.14
ꢀ0.87
ꢀ1.16
ꢀ0.99
ꢀ1.26
ꢀ0.22
+0.13
+0.17
ꢀ0.78
ꢀ1.09
ꢀ0.94
ꢀ1.21
IndCpMoCl(Me) (8)
IndCpMo(SPh)(Me) (9)
[IndCpMo(j2-Bpz4)]BF4 (6)
d
[IndCpMo(H2biim)][BF4]2
a
All the voltammograms were measured in ca. 1.0 mM solutions.
Potentials in V vs. SCE; scan rate is 200 mV sꢀ1 and E1/2 values are the
average of the anodic and cathodic peak potentials.
Reaction of 8 with NaSPh gives IndCpMo(SPh)(Me)
(9) in low yield. Again, this asymmetric compound pre-
sents a complex set of indenyl resonances in its 1H NMR
spectrum (three broad singlets at d 5.55, 5.25 and
b
Epa anodic sweep (peak potentials, Volts).
Epc cathodic sweep (peak potentials, Volts).
[Ref. [6a]] the voltammogram was measured in NCMe.
c
d

I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 690 (2005) 1718–1725
1721
In contrast to the previous complexes, the cationic
complex 6 is electroactive on the cathodic part of the
CV and electrochemically silent on the anodic part of
the same. This means that there is no MoIV/V oxidation.
Instead, it undergoes two consecutive reductions that
are assigned to MoIV/III and MoIII/II, a process that
can be interpreted assuming indenyl g5–g3 slippage
(g5-Ind)CpMo(IV) ! (g-Ind)CpMo(III) and (g-Ind)-
CpMo(III) ! (g3-Ind)CpMo(II). Many similar pro-
cesses have been observed and reported by us and
studied in depth [6]. However, this is the first involving
the reduction of a monocation to a monoanion [(g3-Ind-
CpMo(j3-BPz4)]ꢀ as the final product. We have not at-
tempted to isolate this product chemically but its
identity can be safely assumed even on the basis of the
similarities of the redox potentials to those previously
reported, namely with N-heterocyclic bidentate ligands
such as [IndCpMo(Bipy)][BF4]2 (Epa = ꢀ0.59 V), [Ind-
CpMo(tBu2Bipy)][BF4]2 (Epa = ꢀ0.60 V), and [Ind-
[CpMo(CO)2(dppe)]+ [6a] in a simple parallel to the Hꢀ
and PMe3 addition to one Cp ring in the case of the cor-
responding [Cp2Mo(CO)2]2+ complexes (L = PMe3, 1/2
dppe, CO) [11]. It is, nevertheless surprising that even
the weak nucleophile P(OMe)3 affords similar results.
It is also interesting to note that the indenyl ligand is
more prone to undergo addition of phospine nucleo-
philes than the Cp ring.
In spite of the expected lability of the CO ligands in
[IndCpMo(CO)2]2+ we do not have any reasonable
explanation to account for the erratic reactivity of this
complex with weak nucleophiles like the halides. How-
ever, the possible formation of ring-slipped intermedi-
ates (or transition states) that might decompose in
unexpected ways seemed attractive in view of the estab-
lished observation that such species are induced by
weak, specially p-donor, nucleophiles [12]. In order to
test this hypothesis [IndCpMo(NCMe)2]2+ was reacted
with KBPz4, a multidentate anion that might stabilize
CpMo(H2biim)][BF4]2
(Epa = ꢀ0.90 V)
(H2biim =
a
putative ring-slipped complex like [(g3-In-
bis-imidazole) [6a]. These observations leave the neutral
MoIV biscyanide complex IndCpMo(CN)2 as the only
one in this system where both oxidative MoIV/V and
reductive MoIV/III/II processes are observed [6a,6b]. As
a matter of fact, charge effects seem to prevent cationic
complexes [IndCpMoXL]+ and [IndCpMoL2]2+ from
undergoing oxidation to Mo(V). On the other hand,
among the neutral Cp02MoX2 complexes (Cp0 = Cp,
Ind) the biscyanides are, so far, the only capable of
undergoing reversible reductions, certainly due to the
strong p-acidity of the CN-ligand. Indeed, there is not
much electronic difference, in terms of orbitals, between
the species in the two series of redox cascades [Ind-
CpMo(CO)2]2+/+/0 and [IndCpMo(CN)2]0/ꢀ1/ꢀ2, and
the electrochemical and ESR characterization of both
processes reveals strong similarities [6b].
d)CpMo(j3-BPz4)]+. The formation of 6 indicates that
ligand induced ring-slippage in the [IndCpMoL2]+ com-
plexes to afford [(g3-Ind)CpMoL3]+ adducts (Eq. (3)) is
not a thermodynamically favoured process leading to
isolable species, in contrast to the ready redox induced
ring-slippage undergone by 6 itself as seen in the CV
studies, and by several dicationic complexes [IndCp-
MoL2]2+ to give (g3-Ind)CpMoL2 [6b].
3. Discussion
ð3Þ
Presently [IndCpMo(CO)2]2+ is the only entry for the
synthesis of derivatives of the IndCpMo(IV) fragment.
However, direct CO substitution to give IndCpMX2,
[IndCpMoXL]+ or [IndCpMoL2]2+ complexes is not a
straightforward process due to the high reactivity of
the bis-carbonyl dications. In fact, until now the syn-
thetic use of [IndCpMo(CO)2][BF4]2 has been limited
to the preparation of the nitrile precursors [Ind-
CpMo(NCMe)(CO)][BF4]2 and [IndCpMo(NCMe)2]
[BF4]2 and related isonitrile complexes, both the result
of slow CO substitutions [4b,6a]. The first reactivity
problem posed by [IndCpMo(CO)2]2+ is the unusually
high electrophilicity of its rings. Accordingly, P(OMe)3
adds to the indenyl ligand in [IndCpMo(CO)2]2+ to give
[CpMo{P(OMe)3}2(CO)2]BF4 (1) (Eq. (1)). We had pre-
viously reported that a similar reaction with dppe yields
The fact that indenyl slipped species are not isolated
does not mean that indenyl slippage is absent in the nucle-
ophilic substitution reactions of IndCpMo(IV) com-
plexes. This can only be ascertained by kinetic studies

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I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 690 (2005) 1718–1725
that compare reaction rates of substitution reactions in
similar IndCpMo(IV), Cp2Mo(IV) and Ind2Mo(IV) spe-
cies. However, some conclusions can be already drawn
out of the existing data. The results in Scheme 2 on the
straightforward halide substitution by CHꢀ3 and PhSꢀ
nucleophiles on the IndCpMoX2 complexes, parallel
those established a long time ago for the congener
Cp2MoX2 complexes. However, they strongly contrast
to the total lack of reactivity of Ind2MoX2 towards nucle-
ophiles. In fact Ind2MoMe2 cannot be made from the
parent dichloride and CH3MgCl but can be prepared
from Ind2MoCl2 and the Lewis acidic, Clꢀ abstractor,
AlMe3 [7]. Also, Ind2MoX2 does not react with PhSꢀ
and [HB(CHMeEt)3]ꢀ. All of these reactions readily take
place with Cp2MoX2 and IndCpMoX2 complexes. This
contrast suggests that steric congestion around the metal
in the Ind2MoX2 complexes prevents the nucleophile
from reaching the metal, thereby blocking the reaction.
Space around the metal is more readily available in the
Cp containing complexes, enabling the reaction.
Strange as it may seem for a family of complexes stud-
ied over the last four decades, there is, to the best of our
knowledge, no mechanistic study on the nucleophilic sub-
stitution reactions of Cp2MoX2 complexes. Certainly it is
known to all those working with such compounds that
halide abstracting reagents and polar solvents strongly
favour halide substitution, implying that a dissociative
pathway is favoured over an associative one. This is not
unexpected since the Cp2MoX2 complexes are 18 e species
and the Cp ring is not very prone to undergo the ring-slip-
page rearrangements expected for an associative mecha-
nism. However, the situation might be different for the
indenyl containing analogues since the indenyl ring is
prone to elicit the required haptotropic shifts. In a de-
tailed study of an associative reaction taking place at
the Cp2Mo(IV) fragment (the insertion of acetylenes into
the Mo–H bond of Cp2MoH2) Nakamura and Otsuka,
almost 30 years ago, were led to conclude that a rear-
rangement of the wedge like structure of the molybdeno-
cene to an excited structure with parallel rings plays a
central role in explaining some of the results [13]. They
also noted clear differences brought about by the simple
introduction of one CH3 substituent to the Cp ring. Such
a rearrangement will have obvious energetic changes
upon replacement of Cp by Ind. It follows that for In-
d2Mo(IV) complexes any possible acceleration caused
by the indenyl effect is overshadowed by the steric bulk
of the indenyl ligand which blocks the access of nucleo-
philes to the metal [7].
possibility of accomodating extra electrons provided
by the g5–g3 shift of the indenyl ligand. Again going
from the IndCpMo(IV) to the Ind2Mo(IV) fragment
derivatives does not introduce any substantial difference
in the reductive or ring-slippage behaviour.
4. Conclusions
The synthesis of neutral mixed-ring molybdenocenes
IndCpMoXY from [IndCpMo(CO)2]2+ is limited to the
dihalides and even so unexpectedly unreliable. In con-
trast, the dicationic complex [IndCpMo(NCMe)2][BF4]2
provides feasible routes to IndCpMoX2 by nucleophilic
substitution of the NCMe ligand, free of competition
with nucleophilic attack to the indenyl ring or the CO li-
gand. The chemistry of the IndCpMoX2 and Cp2MoX2
complexes (X = CH3, Cl, SPh) is very similar but bears
some significant differences relative to that of their In-
d2MoX2 congeners. These comparisons suggest that: (i)
the existence of accessible free space around the metal is
a decisive factor in the reaction of Cp02MoX2 metalloc-
enes towards nucleophiles; (ii) contrary to the initial
expectations, indenyl-slippage does not apparently play
an overwhelming role in the activation of the substitu-
tional chemistry of molybdenocenes. The lack of ring-
slippage in the complex [IndCpMo(j2-BPz4)]+ with
dangling ligands well suited to coordinate the metal and
stabilize a ring-slipped complex, gives further support
to this last conclusion.
5. Experimental
5.1. Materials and methods
All experiments were carried out under N2 atmo-
sphere by Schlenk techniques. Solvents were dried by
standard procedures, distilled under nitrogen or argon
˚
and kept over 4 A molecular sieves.
Microanalyses were performed at the ITQB (C. Al-
meida). Infrared spectra were recorded on a Unican
Mattson Mod 7000 FTIR spectrophotometer using
1
KBr pellets and/or in solution. H NMR spectra were
obtained with a Bruker CXP 300 spectrometer.
The electrochemical measurements were performed
with a BAS CV – 50 W – 1000 voltammetric analyser
controlled by BAS/Windows data acquisition software.
The solutions were purged with nitrogen and kept under
an inert atmosphere throughout the measurements.
0.1 M tetrabutylammonium hexafluorophosphate in
CH2Cl2 was used as the supporting electrolyte.
A glass cell (BAS MF-1082 in a C-2 cell enclosed in a
Faraday cage) was used with a carbon electrode as the
working electrode, a 7.5 cm platinum wire (BAS MW-
1032) with a gold-plated connector as the counter
On the other hand the introduction of indenyl ligands
in the molybdenocene structure does not disturb the
electronic properties related to redox behaviour in any
dramatic fashion. The changes recorded so far present
a smooth picture with regard to the Mo(IV)/Mo(V) re-
dox process. Naturally, the reductive behaviour is signif-
icantly changed upon indenyl introduction due to the

I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 690 (2005) 1718–1725
1723
electrode, and a SSC (BAS MF-2063) as the reference
electrode (exhibiting a potential ca. ꢀ44 mV relative to
a saturated calomel electrode). The ferrocenium–ferro-
cene couple was used as an internal standard: under
the experimental conditions used and for the scan rate
of 0.2 V sꢀ1, E1/2 = 0.46 V and ipa/ipc = 1.00. The electro-
chemical behaviour of the complexes did not seem to be
affected by the presence of ferrocene and vice versa.
KBPz4 [14], [IndCpMo(CO)2][BF4]2 [4a], [Ind-
CpMo(NCMe)2][BF4]2 [4a], IndCpMoCl2 [4a] and [Ind-
CpMoI(CO)]BF4 [4a,4b] were prepared as described
previously.
80%. Anal. Found: C, 38.78; H, 2.89. Calc. for
C14H12Br2Mo: C 38.57, H 2.77%. Selected IR (KBr,
cmꢀ1): m 3111 (m), 1604 (w), 1537 (w), 1427 (m), 1337
(w), 1014 (w), 773 (s).
5.5. Preparation of IndMoBr3(CO)2 (5)
A
solution of IndMo(g3-C3H5)(CO)2 (0.34 g,
1.09 mmol) in CH2Cl2 was treated with HBF4. Et2O (1
equivalent). After 10 min, (NBu4)Br3 (0.53 g,
1.09 mmol) was added and the reaction was continued
for 1/2 h at room temperature. The supernatant solution
was filtered and the green precipitate was washed with
CH2Cl2 (3 · 30 ml) to yield the pure compound in 70%
yield. Anal. Found: C, 25.99; H, 1.31. Calc. for
C11H7O2Br3Mo: C, 26.07, H, 1.39%. Selected IR
(KBr, cmꢀ1): m 3100 (w), 3050 (m), 2101 (vs, CO),
5.2. Preparation of [CpMo{P(OMe)3}2(CO)2]BF4 (1)
A suspension of [IndCpMo(CO)2][BF4]2 (0.30 g,
0.59 mmol) in CH2Cl2 was treated with excess
P(OMe)3 (4 ml), refluxed and irradiated with a 60 W
tungsten bulb for 2 h. The resulting yellow solution
was evaporated under vacuum until the only remain-
ing liquid was P(OMe)3. An oil separated upon addi-
tion of Et2O and an orange powder was obtained by
washing it with cold Et2O/EtOH (10/1). Further
recrystallization from EtOH/Et2O afforded the pure
complex 1, in 80% yield. Anal. Found: C, 28.29; H,
3.94. Calc. for C13H23BF4O8P2Mo: C, 28.29, H,
4.20%. Selected IR (KBr, cmꢀ1): m 3050 (m); 2957
(w); 1995 (vs, CO), 1915 (vs, CO); 1483 (m); 1084
(vs, B-F); 795 (s); 725 (m); 605 (m). 1H NMR
[(CD3)CO, 300 MHz, r.t., d ppm]: 5.80 (s (br), 5H,
Cp); 3.88 (t, 18H, P(OMe)3).
1
2072 (vs, CO), 1445 (w), 1069 (m), 756 (w). H NMR
[(CD3)CO, 300 MHz, r.t., d ppm]: 7.64 (m, 2H, H5ꢀ8);
7.42 (m, 2H, H5ꢀ8); 6.25 (d, 2H, H1/3); 5.82 (t, 1H, H
H2).
5.6. Preparation of [IndCpMo(j2-Bpz4)]BF4 (6)
A solution of [IndCpMo(NCMe)2][BF4]2 (0.31 g,
0.58 mmol) in CH2Cl2/NMF (20/1) was treated with
KBPz4 (0.18 g, 0.58 mmol) at room temperature. After
stirring for 7 h the violet solution was filtered and the
CH2Cl2 evaporated under vacuum. Upon addition of
Et2O/EtOH (30/1) and washing with Et2O, a violet pow-
der was obtained. This was recrystallized from EtOH/
Et2O in 85% yield. Anal. Found: C, 48.88; H, 3.33; N,
17.30. Calc. for C26H24B2F4N8Mo: C, 48.64, H, 3.77,
N, 17.45%. Selected IR (KBr, cmꢀ1): m 3109 (m), 1508
(m), 1437 (m), 1397 (s), 1294 (s), 1221 (m), 1084 (vs,
5.3. Preparation of IndCpMoI2 (3)
Method a:
A solution of [IndCpMoI(CO)]BF4
1
(0.34 g, 0.66 mmol) in CH2Cl2 was refluxed and irradi-
ated with a 60 W tungsten bulb for 36 h, in the presence
of (NBu4)I (0.50 g, 1.36 mmol). The supernatant solu-
tion was filtered and the dark brown microcrystalline
precipitate washed with Me2CO and Et2O. Yield, 70%.
Method b: A solution of IndCpMo(SPh)2 (0.33 g,
0.66 mmol) in CH2Cl2 was allowed to react with excess
CH3I (0.08 ml, 1.36 mmol) for 4 h at room temperature.
The supernatant solution was filtered and the dark
brown precipitate washed with Me2CO and Et2O. Yield,
75%. Anal. Found: C, 31.23; H, 2.49. Calc. for
C14H12I2Mo: C, 31.73, H, 2.28%. Selected IR (KBr,
cmꢀ1): m 3098 (m), 1422 (m), 1211 (w), 829 (s), 750 (s).
B-F), 833 (s), 764 (s). H NMR [(CD3)2CO, 300 MHz,
r.t., d ppm]: 7.79 (d, 2H, H3 of BPz4, [3J = 1.5 Hz]);
7.63 (d, 1H, H1 of BPz4, [3J = 1.5 Hz]); 7.55–7.51 (m,
2H, H5ꢀ8); 7.18 (d, 2H, H4 of BPz4, [3J = 3.0 Hz]);
7.15–7.12 (m, 2H, H5ꢀ8); 7.01 (d, 2H, H6 of BPz4,
[3J = 2.1 Hz]); 6.69 (d, 2H, H1/3); 6.53 (d, 1H, H1 of
BPz4, [3J = 2.1 Hz]); 6.46 (t, 2H, H5 of BPz4,
[3J = 2.4 Hz]); 6.40 (t, 1H, H2); 6.26 (t, 2H, H2 of
BPz4, [3J = 3.0 Hz]); 5.69 (s, 5H, Cp).
5.7. Preparation of IndCpMoMe2 (7)
Method a: A suspension of [IndCpMo(NCMe)2]
[BF4]2 (0.3 g, 0.56 mmol) in Et2O was allowed to react
with excess of a 3 M solution of MeMgCl in THF
(0.45 ml, 1.35 mmol) from ꢀ20 ꢁC to room temperature,
for 4 h. The reaction mixture was filtered after addition
of H2O (0.3 ml) and the solution taken to dryness under
vacuum. The residue was extracted with hexane and the
extracts were taken to dryness to afford a blue powder in
40% yield.
5.4. Preparation of IndCpMoBr2 (4)
A suspension of [IndCpMo(NCMe)2][BF4]2 (0.35 g,
0.66 mmol) in Me2CO was allowed to react with
(NBu4)Br (0.44 g, 1.36 mmol) for 12 h at room temper-
ature. The supernatant solution was filtered and the vio-
let precipitate washed with Me2CO and Et2O. Yield,

1724
I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 690 (2005) 1718–1725
Method b: A suspension of IndCpMoBr2 (0.06 g,
under vacuum. The residue was extracted with Et2O
(3 · 20 ml) and the extracts were taken to dryness to af-
ford a green powder in 30% yield. Anal. Found: C,
63.22; H, 5.24. Calc. for C21H20MoS: C, 63.00, H,
5.03%. Selected IR (KBr, cmꢀ1): m 3100 (w), 2965 (w),
1262 (m), 1096 (m), 1022 (m), 926 (m), 901 (m), 824
(s). 1H NMR (CDCl3, 300 MHz, r.t., d ppm): 7.53–
7.24 (m, 9H, Ph + H5ꢀ8); 5.55 (s (br), 1H, H1ꢀ3); 5.25
(s (br), 1H, H1ꢀ3); 4.68 (s, 5H, Cp); 4.44 (s (br), 1H,
H1ꢀ3); 0.64 (s, 3H, CH3).
0.14 mmol) in Et2O was allowed to react with excess
of a 3 M solution of MeMgCl in THF (0.15 ml), from
ꢀ20 ꢁC to room temperature, for 1 h. The reaction mix-
ture was filtered after addition of H2O (0.5 ml) and the
solution taken to dryness under vacuum. The residue
was extracted with hexane and the extracts were taken
to dryness to afford a blue powder in 50% yield.
Method c: A suspension of IndCpMoCl2 (0.24 g,
0.70 mmol) in Et2O was allowed to react with excess
of a 1.6 M solution of MeLi in the same solvent
(0.95 ml), from ꢀ20 ꢁC to room temperature, for 2 h.
The reaction mixture was filtered after addition of
H2O (0.2 ml) and the solution taken to dryness under
vacuum. The residue was extracted with hexane and
the extracts were taken to dryness to afford a blue pow-
der in 40% yield.
Method d: A suspension of IndCpMoCl2 (0.24 g,
0.70 mmol) in Et2O was allowed to react with excess
of a 3 M solution of MeMgCl in THF (0.56 ml,
1.68 mmol), from ꢀ20 ꢁC to room temperature, for
1 h. The reaction mixture was filtered after addition of
H2O (0.1 ml) and the solution taken to dryness under
vacuum. The residue was extracted with hexane (or pen-
tane) and the extracts were taken to dryness to afford a
blue powder in 40% yield. Anal. Found: C, 62.51; H,
5.68. Calc. for C16H18Mo: C, 62.75, H, 5.92%. MS
(EI),(m/z): 306 (M+); 290 (M+ ꢀ CH3); 276
(M+ ꢀ 2CH3). Selected IR (KBr, cmꢀ1): m 3098 (m),
2990 (w), 2895 (w), 1427 (w), 1020 (m), 941 (m), 910
(m), 843 (m), 758 (m), 710 (m). 1H NMR (C6D6,
300 MHz, r.t., d ppm): 6.89–6.81 (m, 4H, H5ꢀ8); 4.76
(t, 1H, H2); 4.09 (d, 2H, H1/3); 3.85 (s, 5H, Cp); 0.33
(s, 6H, CH3).
5.10. Preparation of [IndCpMoCl(Me)]BF4 (10)
A solution of IndCpMoCl(Me) (0.05 g, 0.15 mmol) in
NCMe was treated with [Cp2Fe]BF4 (0.04 g, 0.15 mmol)
at room temperature. There was an immediate change
from blue to green and the reaction mixture was taken
to dryness under vacuum after stirring for 1/2 h. The
green powder was washed with Et2O (3 · 20 ml). Yield,
95%. Anal. Found: C, 43.88; H, 3.78. Calc. for
C15H15BClF4Mo: C, 43.57, H, 3.66%. Selected IR
(KBr, cmꢀ1): m 3100 (m), 2891 (w), 1537 (w), 1441 (m),
1036 (vs, B-F), 858 (s), 768 (s).
Acknowledgements
The authors are grateful to FCT, POCTI and FED-
ER for financial support (including a Ph.D. grant to
C.C.L.P.).
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