Synthesis and structural characterization of new mixed-ring indenyl derivatives of molybdenum containing phosphorus ligands

Article abstract of DOI:10.1016/j.jorganchem.2006.12.015

Reaction of NaBH₄ with [IndCpMo(dppe)](BF₄)₂ (1) in acetone yields [IndMo(η⁴-C₅H₆)(dppe)] BF₄ (2) quantitatively. The hydride addition takes place at the external face of the Cp ring. Dissolution of 2 in dichloromethane gives [IndMo(η⁴-C₅H₅-exo-CH₂Cl )(dppe)]BF₄, as confirmed by elemental analysis, IR and ¹H NMR spectroscopy. The similar dication [IndCpMo{P(OMe)₃}₂](BF₄)₂ (4) reacts with NaBH₄, in a solvent dependent manner. In acetonitrile, [IndMo(η⁴-C₅H₆){P(OMe)₃} ₂]BF₄ (5) is obtained and in acetone a P(OMe)₃ ligand is lost resulting in the asymmetric phosphite-hydride, [IndCpMoH{P(OMe)₃}]⁺ (6). The molecular structures of [IndMo(η⁴-C₅H₆){P(OMe)₃} ₂]PF₆ and [IndCpMoH{P(OMe)₃}]PF₆ were characterized by single-crystal X-ray diffraction.

Full text of DOI:10.1016/j.jorganchem.2006.12.015

Journal of Organometallic Chemistry 692 (2007) 1593–1600
www.elsevier.com/locate/jorganchem
Synthesis and structural characterization of new mixed-ring
indenyl derivatives of molybdenum containing phosphorus ligands
a,
a
d
Isabel S. Gonc¸alves , Claudia C.L. Pereira , Carla A. Gamelas b,c, Alan Hazell ,
*
´
b
Carlos C. Romao
˜
a
Department of Chemistry, CICECO, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
b
ˆ
Instituto de Tecnologia Quı´mica e Biolo´gica da Universidade Nova de Lisboa, Quinta do Marques, EAN, Apt. 127, 2781-901 Oeiras, Portugal
c
Escola Superior de Tecnologia, Instituto Polite´cnico de Setu´bal, 2910-761 Setu´bal, Portugal
Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark
d
Received 9 July 2006; received in revised form 14 December 2006; accepted 18 December 2006
Available online 22 December 2006
Abstract
Reaction of NaBH4 with [IndCpMo(dppe)](BF4)2 (1) in acetone yields [IndMo(g4-C5H6)(dppe)]BF4 (2) quantitatively. The hydride
addition takes place at the external face of the Cp ring. Dissolution of 2 in dichloromethane gives [IndMo(g4-C5H5-
exo-CH2Cl)(dppe)]BF4, as confirmed by elemental analysis, IR and 1H NMR spectroscopy. The similar dication [IndCpMo-
{P(OMe)3}2](BF4)2 (4) reacts with NaBH4, in a solvent dependent manner. In acetonitrile, [IndMo(g4-C5H6){P(OMe)3}2]BF4 (5) is
obtained and in acetone a P(OMe)3 ligand is lost resulting in the asymmetric phosphite-hydride, [IndCpMoH{P(OMe)3}]+ (6). The
molecular structures of [IndMo(g4-C5H6){P(OMe)3}2]PF6 and [IndCpMoH{P(OMe)3}]PF6 were characterized by single-crystal X-ray
diffraction.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Molybdenum; Cyclopentadienyl; Indenyl; Hydride; Molybdenocene; Mixed-ring indenyl complexes
1. Introduction
reaction of Cp2MoCl2 with LiAlD4, Dꢁ adds to one of
the rings to give a partially ring-deuterated product [4],
and the reaction of Cp2MoCl(Et) with alkylphosphines
gives CpMo(g4-C5H4Et)Cl(PR3) involving metal-to-ring
migration of the ethyl group [5]. More recently, several
other nucleophiles (Rꢁ) have been shown to react with the
dications [Cp2MoL2]2+ (L = CO, PMe3, L2 = dppe) pro-
ducing the cyclopentadiene complexes [CpMo(g4-C5H5R)-
L2]+ (L2 = dppe, R = H, Me, CH2CN, CH2PPh3, SMe;
L = CO or PMe3, R = H) [6]. Indeed, there are more exam-
ples of the introduction of substituents on Cp ligands in
group 6 metallocenes, in particular tungstenocene deriva-
tives with exocyclic boron [7] or silyl substituents [8] have
been reported but their formation results from a ligand
transfer from the metal to the Cp ring. Also, a route to tung-
stenocene complexes with chiral metal centers was devel-
oped by Cooper following earlier scattered reports on
nucleophilic addition at the Cp rings of Cp2MX2 complexes
A large number of reactions undergone by molybdeno-
nþ
cene complexes of the type ½Cp0 MoL2ꢀ (Cp0 = cyclopen-
2
tadienyl ring, g5-C5R5) do not involve the fragment
Cp02Mo, which is remarkably stable [1]. However, nucleo-
philic addition to cyclopentadienyl ligands bonded to
18-electron organotransition metal cations is generally
accepted to be stereospecific with the nucleophile approach-
ing the uncoordinated face of the cyclopentadienyl ligand to
yield g4-cyclopentadiene complexes [2]. Earlier work has
established that in the case of nucleophilic attack of hydride
ion (Hꢁ) on [Cp2MoL2]n+ (M = Mo, W; L2 = dppe (diphe-
nylphosphinoethane) and other ligands; n = 0, 1, 2), the
reaction center is one of the Cp rings [3]. Similarly, in the
*
Corresponding author. Tel.: +351 234378190; fax: +351 234370084.
E-mail address: igoncalves@dq.ua.pt (I.S. Gonc¸alves).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.12.015

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I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
[9]. Mo¨ise and co-workers reported the ability of metallo-
phosphide anions to undergo a direct Cp substitution on
Cp2MCl2 (M = Mo, W), and explored the influence of steric
and electronic factors on the Cp ring nucleophilic substitu-
tion on other metallocenes (g5-C5H4-tBu)2MCl2 [10].
However, the lack of convenient syntheses for the molybde-
nocene system limited for many years the corresponding
exploration of the ring-substituted molybdenocene chemis-
try. Recent reports of routes to both substituted and unsub-
stituted bis-cyclopentadienyl complexes have changed this
situation and helped the development of this area [11,12].
Investigations in our laboratory have focused on new
methods to prepare bent metallocene complexes of molyb-
denum and tungsten containing substituted cyclopentadie-
nyl ligands and g5-cyclic analogues [13]. The synthetic
approach is based on transformations of the diene
complexes to provide a high yield route to metallocenes
as well as differentially substituted chiral and pro-chiral
metallocene analogues, namely the indenyl congeners [Ind-
CpML2]2+. In this paper, we describe a new and high-yield
route to some novel mixed ring molybdenum cations
containing phosphorus ligands of the general formula
[IndMo(g4-C5H6)L2]+ [L = P(OMe)3, L2 = dppe], including
X-ray crystallographic studies, and also present examples
of their reactivity.
phenyl group and the indenyl C6 ring protons (H5–8) at d
7.42–6.82, a multiplet at d 6.50 ppm (H1/3) and a broad sin-
glet at 5.32 ppm (H2) (see Scheme 2 for numbering). The res-
onances for the g4-cyclopentadiene ligand are typical of the
endo conformation and reveal no evidence of rotamers
involving different orientations of the g4-cyclopentadiene
ligand (invariance with temperature). In most diene com-
plexes of general formula [Cp0Mo(g4-diene)LL0]+ the endo
conformation of the diene is favored in spite of the fluxional
behaviour that many of them present in solution [15]. The
chemical shifts of the g4-diene C5H5(CH2Cl) protons are
very similar to those observed for the endo conformer of
[CpMo{g4-C5H5(R)}(dppe)]PF6 (R = Me, PPh3) [6] and,
therefore, the Hb-c was assigned as the lower field resonance
at d 4.98 ppm, followed by the Ha-d and Hendo resonances at
d 4.23 and 2.85 ppm, respectively. The peak at d 3.49 ppm
was attributed to the chloromethyl group (–CH2Cl) bonded
to the saturated carbon. Also, the presence of –CH2Cl at the
external face of the diene is implied by the absence of the C–
H
exo vibration in the IR spectrum. Single crystal diffraction
data obtained from low quality crystals and not completely
refined is already of sufficient quality to confirm this stereo-
chemistry [15b,15c].
Similar trends are observed for the unsubstituted com-
plex [IndMo(g4-C5H6)(dppe)]BF4 (2) in (CD3)2CO, also
assigned as the endo conformer (bridgehead CH2 cis to
the indenyl ring as in Scheme 1) [14]. However, concerning
the chemical shifts of the methylene protons of the C5H6
ring, Hendo was assigned as the higher field resonance at
d 2.80 ppm and Hexo as the lower field resonance at d
3.29 ppm. As expected, C–Hexo in 2 exhibits a distinct IR
stretching vibration at 2768 cmꢁ1. For both compounds 2
2. Results and discussion
2.1. Preparation of [IndMo{g4-C5H5(R)}(dppe)]BF4
(R = H, CH2Cl) complexes
It was shown previously that Hꢁ adds to the Cp ring of
the dication in [IndCpMo(dppe)](BF4)2 (1) to afford the
diene complex [IndMo(g4-C5H6)(dppe)]BF4 (2) [14]. In
fact, the preparation of pure 2 only occurs if acetone and
diethyl ether are used. While attempting to crystallize 2
by slow diffusion of Et2O into a concentrated CH2Cl2 solu-
tion at room temperature, brown crystals were obtained
(Scheme 1). These crystals were identified as [IndMo{g4-
C5H5(CH2Cl)}(dppe)]BF4 (3) by elemental analysis, FTIR
and 1H NMR spectroscopy. The complex 3 can also be pre-
pared by stirring in a CH2Cl2 solution for 48 h. Both 2 and
3 are quite stable at room temperature and can be handled
in air for short periods of time.
and 3 a typical broad band between 1100 and 1000 cmꢁ1
,
attributed to a m(B–F) absorption, is observed in the IR
spectrum and is indicative of the presence of a tetrafluoro-
borate anion, suggesting a cationic molybdenum complex
as counter-ion.
2.2. Mechanism of formation of [IndMo(g4-C5H5-exo-
CH2Cl)(dppe)]BF4
The observation that the CH2Cl fragment of CH2Cl2
adds exo to the cyclopentadiene ligand of [IndMo(g4-
C5H6)(dppe)]BF4 is consistent with a radical mechanism
on the basis of voltammetric studies and literature findings
as summarized in Scheme 2 [16].
The 1H NMR spectrum of 3 shows the resonances of the
g5-indenyl, a multiplet pointing to the presence of the dppe
Scheme 1.

I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
1595
Scheme 2.
Oxidation of 2, possibly caused by adventitious O2 and/
or light, leads to the loss of HÅ and formation of A which
can be structurally reorganized to the radical cation B.
The structure and spin distribution of this species should
be rather similar to those calculated and measured
experimentally for the isoelectronic radical cations [IndCp-
MoL2]+Å (L = P(OMe)3, P(OH)3, CO) [17]. In these studies,
it was shown that the flexibility of the coordination of the
indenyl was the reason for the stabilization of this rare
example of a molybdenocene complex in the Mo(III) oxi-
dation state which is not observed for the isoelectronic
[Cp2MoL2]n+ analogues. Most of the spin density, as calcu-
lated for the model [IndCpMo{P(OH)3}2]+Å, resides on the
Mo atom and the C atoms of the Cp ring. Therefore, this
initial HÅ abstraction produces the same result as the 1e
reduction of the dication [IndCpMo(dppe)]2+. The results
of the cyclovoltammograms presented in Table 1 entirely
support this interpretation. As expected, the CVs of 1
and its fully reduced Mo(II) derivative are the same con-
firming full chemical reversibility.
dark, the addition of the ÅCCl3 radical to the cyclopentadie-
nyl ligand and the chloride anion to the tungsten atom was
observed and CpW{g4-C5H5(CCl3)}(CO)Cl was formed
[19]. In the present work, the cyclic voltammogram (CV)
of [IndMo(g4-C5H6)(dppe)]BF4 (2) in CH2Cl2 was com-
pared with those obtained for the complexes [Ind-
CpMo(dppe)][BF4]2 (1) and (g3-Ind)CpMo(dppe). Also,
for comparison, the CV of (g3-Ind)CpMo(dppe) in CH2Cl2
was repeated in this work (Table 1).
The CVs of the complexes [IndCpMo(dppe)][BF4]2 (1)
and (g3-Ind)CpMo(dppe) showed the expected similarities
in two distinct quasi-reversible 1-electron reduction steps
for the former and two reversible oxidation waves for
the latter (Fig. 1). For [IndMo(g4-C5H6)(dppe)]BF4 (2),
part of the CV is similar to that of (g3-Ind)CpMo(dppe),
showing that the loss of HÅ takes place on the time scale
of the technique and the radical [IndCpMo(dppe)]+Å B is
being formed. The separation between the waves is
150 mV for [IndCpMo(dppe)](BF4)2 (1) and also 150 mV
for [IndMo(g4-C5H6)(dppe)]BF4 (2). As proposed before
[20] these small potential differences suggest marked sta-
bilization of the final reduction product (g3-Ind)CpMo-
(dppe), by an g5 ! g3 hapticity shift concomitant with
the second reduction, and also supports g5-indenyl liga-
tion in the first reduction product, [(g5-Ind)CpMo-
(dppe)]+ (Scheme 2).
Under these circumstances it becomes clear that the exo
addition of the chloromethyl radical (ÅCH2Cl) to the radical
cation complex [IndCpMo(dppe)]+Å should take place at
the Cp ring where the spin density is higher [17]. This kind
of reaction is not unprecedented [18]. For example, during
the reaction of Cp2W(CO) with CCl4 carried out in the

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I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
Table 1
Cyclic voltammetry data for mixed ring dppe derivatives
Compound
Ep,a
Ep,c
Ep,1/2
Ia/Ic
Ref.
[IndCpMo(dppe)](BF4)2 (1)
[IndMo(g4-C5H6)(dppe)]BF4 (2)
(g3-Ind)CpMo(dppe)
ꢁ0.30; ꢁ0.46
ꢁ0.28; ꢁ0.44
ꢁ0.29; ꢁ0.46
ꢁ0.24; ꢁ0.45
ꢁ0.37; ꢁ0.52
ꢁ0.36; ꢁ0.51
ꢁ0.36; ꢁ0.52
ꢁ0.31; ꢁ0.52
ꢁ0.34; ꢁ0.49
ꢁ0.32; ꢁ0.48
ꢁ0.33; ꢁ0.49
ꢁ0.28; ꢁ0.49
1.0; 0.9
1.0; 0.9
1.0; 0.9
1.0; 0.9
[14]
This work
[14]
This work
The voltammograms for 2 and (g3-Ind)CpMo(dppe) were measured in CH2Cl2, in ca. 1.0 mM solutions, scan rate is 0.2 V sꢁ1 and Ep,1/2 values are the
average of the anodic and cathodic peak potentials. Ep,a, anodic sweep (peak potentials, V). Ep,c, cathodic sweep (peak potentials, V). Ep,a, Ep,c and Ep,1/2
are referenced to SCE.
2.3. Preparation of [IndMo(g4-C5H6){P(OMe)3}2]+ and
[IndCpMoH{P(OMe)3}]+ complexes
Hydride additions also take place with the dication
[IndCpMo{P(OMe)3}2](BF4)2 (4). Complex 4 reacts with
1 equivalent of NaBH4, in acetonitrile, to give the yel-
low complex [IndMo(g4-C5H6){P(OMe)3}2]BF4 (5), as
depicted in Scheme 3. The choice of solvent determines
the course of the reaction and hence when the reaction is
carried out in acetone, complex 5 is not stable and looses
a P(OMe)3 ligand with H migration to molybdenum giv-
ing the asymmetric phosphite-hydride, [IndCpMoH-
{P(OMe)3}]+ (6). Compounds 5–6 are moderately air and
moisture sensitive. However, they are indefinitely stable
under inert atmosphere at room temperature and both
are completely insoluble in n-hexane and diethyl ether.
The diene complex [IndMo(g4-C5H6){P(OMe)3}2]BF4
(5) is not fluxional in CD3CN, as concluded from the invari-
ance of its 1H NMR spectrum with temperature (from
ꢁ30 ꢁC to room temperature). However, in (CD3)2CO com-
plex 5 has a fluxional structure and broadening of the AB
spin system of the methylene protons of the C5H6 ligand
is observed at ꢁ70 ꢁC, comparable with [IndM(g4-C5H6)-
(CO)2]BF4 (M = Mo, W) [13]. Both diene complexes
{[IndM(g4-C5H6)L2]BF4, L = CO, P(OMe)3 (5)} are
sensitive toward CO or P(OMe)3 loss and H migration
and, accordingly, give the corresponding metal-hydride
complexes.
Complex 5 was assigned as the endo conformer (bridge-
head CH2 cis to the indenyl ring as in Scheme 3) by com-
parison of its 1H NMR spectrum with the known
congener [CpMo(g4-C5H6)(dppe)]BF4 [6]. In fact, the
chemical shifts of the methylene protons of the C5H6 ring
are very similar to those observed for [CpMo(g4-C5H6)-
(dppe)]BF4 and, therefore, we assigned the Hendo as the
higher field resonance at d 2.87 ppm and the Hexo as the
lower field resonance at d 4.56 ppm. As expected, Hexo in
5 exhibits a distinct IR stretching vibration at 2764 cmꢁ1
.
A crystal structure determination of [IndMo(g4-C5H6)-
{P(OMe)3}2]PF6 (5) also confirmed the overall molecular
architecture (see below).
For the asymmetric hydride [IndCpMoH{P(OMe)3}]-
PF6 (6) the 1H NMR spectrum in CD2Cl2 shows the typical
pattern for the resonances of the planar g5-indenyl: two
sets of signals for the C6 ring protons (H5–8), two singlets
Fig. 1. Cyclic voltammograms of (a) (g3-Ind)CpMo(dppe) in CH2Cl2;
(b) [IndMo(g4-C5H6)(dppe)]BF4 (2) in CH2Cl2, and (c) [IndCpMo(dppe)]-
(BF4)2 (1) in NCMe, with 0.1 M NBu4PF6, scan rate 0.2 V sꢁ1
.

I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
1597
Scheme 3.
˚
for H1/3 and a broad singlet for H2 (see Scheme 2 for the
numbering). The hydride resonance is observed as a dou-
blet at d ꢁ7.42 ppm with 46 Hz couplings to the phospho-
rus nuclei. An additional resonance due to the phosphite
ligand P(OMe)3 is observed at d 3.62 ppm. The IR spec-
trum of 6 shows one weak m(Mo–H) absorption at
1897 cmꢁ1. Recrystallization from CH2Cl2/Et2O afforded
single crystals suitable for structure determination by X-
ray diffraction (see below).
of 2.303(1) A. The geometry at the molybdenum atom is
presented in Table 2. In both cases the tetrahedra are dis-
torted with the angle involving the two organic ligands
being the largest and that between the remaining ligands
˚
being smallest. The Mo–H distance of 1.57(3) A is short
but within the range found in the Cambridge Crystallo-
graphic Data Base [21], and not significantly shorter than
the value of 1.59(3) A found in the related compound (g -
C5H2Ph4)CpMoH[P(OMe)3] [22]. Mo–Ind and Mo–Cp dis-
4
˚
tances are similar to the values found in related compounds:
5
2.4. Crystal structures of [IndMo(g4-C5H6){P(OMe)3}2]-
PF6 and [IndCpMoH{P(OMe)3}]PF6
Mo-g -Ind = 2.03(3) A, Mo-g4-CpH 2.06(3) A in 5;
˚
˚
5
5
˚
˚
Mo-g -Ind = 1.986(2) A, Mo-g -Cp = 1.966(2) A in 6;
5
˚
Mo-g -Ind = 2.019, 2.044 A in [(Ind)2Mo{P(OMe)3}2]-
5
5
Both complexes are tetrahedral, and in [IndMo(g4-
C5H6){P(OMe)3}2]PF6 (5) the molybdenum atom is bonded
to the 5-membered ring of the indenyl group, the double
bonds of the CpH and to two P(OMe)3 groups (Fig. 2).
Mo–C bond distances to Ind are in the range 2.24(2)–
(PF6)2 [23]; Mo-g -Ind = 2.014 A, Mo-g -Cp = 1.999 A
˚
˚
in [(g5-Ind)CpMo{P-(OMe)3}2](BF4)2 [17]; Mo-g3-Ind =
5
2.069 A,
Mo-g -Cp = 1.998 A
in
[(g3-Ind)CpMo-
˚
˚
{P(OMe)3}2] [17].
˚
˚
2.49(3) A, with a mean value of 2.36(1) A, and those to
3. Conclusions
˚
CpH are in the range 2.28(3)–2.41(2) A with a mean value
of 2.35(1) A. In [IndCpMoH{P(OMe)3}]PF6 (6), the
˚
In summary, we present the preparation of diene mixed
ring complexes of the type [IndMo{g4-C5H5(R)}L2]+
(L2 = dppe or L = P(OMe)3; R = H, CH2Cl), which in
the case of L = P(OMe)3 can be used for the preparation
molybdenum is bonded to the Indenyl and Cp groups, to
one P(OMe)3 group, and to a hydrogen atom (Fig. 3).
Mo–C bond distances to Ind are in the range 2.262(2)–
˚
˚
2.419(2) A, with a mean value of 2.328(1) A, and those to
˚
Cp are in the range 2.282(2)–2.341(2) A with a mean value
Fig. 2. Molecular structure of [IndMo(g4-C5H6){P(OMe)3}2]PF6 (5).
Fig. 3. Molecular structure of [IndCpMoH{P(OMe)3}]PF6 (6).

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I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
Table 2
in a C-2 cell enclosed in a Faraday cage) was used with a
carbon electrode as the working electrode, a 7.5 cm plati-
num wire (BAS MW-1032) with a gold-plated connector
as the counter electrode, and a SSC (BAS MF-2063) as
the reference electrode (exhibiting a potential ca. ꢁ44 mV
relative to a saturated calomel electrode). The ferroce-
nium–ferrocene couple was used as an internal standard:
under the experimental conditions used and for the scan
rate of 0.2 V sꢁ1, E1/2 = 0.46 V and ipa/ipc = 1.00. The elec-
trochemical behaviour of the complexes did not seem to be
affected by the presence of ferrocene and vice versa.
[IndCpMo(dppe)](BF4)2 (1) [14] and [IndCpMo-
{P(OMe)3}2](BF4)2 (4) [17] were obtained as described
previously.
˚
Selected bond distances (A) and angles (ꢁ) for 5 and 6
5
6
Mo1–CpH/Cpa
Mo1–Inda
Mo1–P1
Mo1–P2
2.06(3)
2.03(3)
2.405(8)
2.401(8)
1.966(2)
1.986(2)
2.427(1)
–
Mo1–H20
–
–
–
–
1.57(3)
74.5(9)
H20–Mo1–P1
H20–Mo1–Ind
H20–Mo1–Cp
Ind–Mo1–CpH/Cp
Ind–Mo1–P1
Ind–Mo1–P2
P1–Mo1–CpH/Cp
P2–Mo1–CpH
P1–Mo1–P2
a
106.7(10)
97.7(10)
141.02(9)
107.28(6)
–
108.27(6)
–
–
137.3(8)
111.0(6)
110.1(6)
99.8(6)
99.6(6)
87.8(3)
4.2. Preparation of [IndMo(g4-C5H6)(dppe)]BF4 (2)
Cp and Ind are the centres of the cyclopentadienyl and the 5-ring of the
indenyl group, CpH is the centre of the C4H4 of CpH.
A solution of [IndCpMo(dppe)](BF4)2 (0.30 g, 0.35
mmol) in acetone was treated with NaBH4 (15 mg,
0.40 mmol) and the mixture was stirred for 3 h at room
temperature. The resulting solution was filtered and taken
to dryness to give compound 2 (0.26 g, 96%). Anal. Calc.
for C40H37BF4P2Mo (762.41): C, 63.01; H, 4.89. Found:
C, 63.10; H, 4.86%. Selected IR (KBr, cmꢁ1): 3053 (m),
2971 (m), 2768 (m), 1697 (m), 1435 (m), 1084 (vs), 748
(s), 698 (vs), 523 (vs). 1H NMR [(CD3)2CO, 300 MHz,
25 ꢁC, d ppm]: d 7.79–6.90 (c, 24H, Ph + H5–8); 6.37 (m,
2H, H1/3); 5.61 (s (br), 1H, H2); 5.03 (s (br), 2H, Hb-c of
C5H6); 3.37 (s (br), 2H, Ha-d); 3.29 (d (br), 1H, Hexo);
2.80 (d (br), 1H, Hendo); 2.55 (c, 4H, CH2 of dppe).
of the asymmetric hydride complex, [IndCpMoH-
{P(OMe)3}]PF6 (6). Compound 6 is a mixed-ring indenyl
hydride and, to the best of our knowledge, [Ind-
CpMoH(CO)]+ represents the only previously reported clo-
sely related example [13b], apart from the tungsten
analogue [IndCpWH(CO)]+ [24]. Furthermore, asymmetric
hydrides such as 6 might – in view of the extensive chemis-
try of related bis-cyclopentadienyl hydrides [25] – be inter-
esting starting materials for other asymmetric metallocene
analogues containing halogenated and other ligands, which
may provide a fine modulation of the electronic and stereo-
chemical properties of these modified metallocenes. This
work is also part of our general goal to extend the chemis-
try of mixed ring molybdenum systems and to raise their
level of significance in comparison with those of Cp2Mo
complexes.
4.3. Preparation of [IndMo(g4-C5H5-exo-CH2Cl)(dppe)]
BF4 (3)
A solution of [IndMo(g4-C5H6)(dppe)]BF4 (2) (0.34 g,
0.50 mmol) in dichloromethane (20 ml) was stirred for 2
days. The volume was reduced by half and diethyl ether
added to precipitate a brown solid which was filtered,
washed with ether (2 · 10 ml) and dried in vacuum. Recrys-
tallization from CH2Cl2/Et2O (3:15) gave a brown micro-
crystalline product (0.39 g, 97%). Anal. Calc. for
C41H38BClF4P2Mo (810.88): C, 60.73; H, 4.72; Cl, 4.37;
Mo, 11.83. Found: C, 60.86; H, 4.91; Cl, 4.22; Mo,
11.56%. Selected IR (KBr, cmꢁ1): 3053 (m), 2984 (m),
1483 (m), 1435 (s), 1084 (vs), 748 (s), 698 (vs), 521 (vs).
1H NMR (CD2Cl2, 300 MHz, 25 ꢁC, d ppm): d 7.42–6.82
(c, 24H, Ph + H5–8); 6.50 (m, 2H, H1/3); 5.32 (s (br), 1H,
H2); 4.98 (s (br), 2H, Hb-c of C5H5R); 4.23 (s (br), 2H,
Ha-d of C5H5R); 3.49 (s, 2H, CH2Cl), 2.85 (s (br), 1H,
4. Experimental
4.1. Materials and methods
All preparations and manipulations were carried out
using standard Schlenk techniques under nitrogen. Sol-
vents were dried by standard procedures, distilled under
nitrogen and kept over 4 A molecular sieves (3 A for
NCMe). Starting materials were obtained from commercial
sources and used as received.
Microanalyses were performed at the ITQB (by C.
Almeida). IR spectra were measured on a Mattson 7000
FT-IR spectrometer using KBr pellets. H NMR spectra
were measured on a Bruker AMX-300 spectrometer.
Chemical shifts are quoted in parts per million from TMS.
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 atmo-
sphere throughout the measurements. Tetrabutylammo-
nium hexafluorophosphate (0.1 M) in CH2Cl2 was used
as the supporting electrolyte. A glass cell (BAS MF-1082
˚
˚
1
H
endo); 2.52 (c, 4H, CH2 of dppe).
4.4. Preparation of [IndMo(g4-C5H6){P(OMe)3}2]BF4
(5)
Addition of NaBH4 (14.5 mg, 0.38 mmol) to a solution
of [IndCpMo{P(OMe)3}2](BF4)2 (4) (0.24 g, 0.34 mmol)
in acetonitrile caused an immediate change of colour from

I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
1599
bright orange to dark orange. The solution was filtered and
taken to dryness. Further recrystallization from NCMe/
Et2O gave light brown crystals (0.19 g, 92%). Anal. Calc.
for C20H31BF4O6P2Mo (612.15): C, 39.24; H, 5.10. Found:
C, 39.06; H, 4.93%. Selected IR (KBr, cmꢁ1): 3055 (m),
2840 (m), 2764 (w), 1483 (m), 1435 (s), 1055 (vs), 754 (s),
698 (s). 1H NMR (CD3CN, 300 MHz, ꢁ30 ꢁC, d ppm):
7.53–7.48 (m, 2H, H5–8); 7.41 (d, 2H, H1,2 of C5H6);
7.36–7.33 (m, 2H, H5–8); 5.62 (m, 2H, H1/3); 5.55 (t, 1H,
H2); 4.91 (d, 2H, H3,4 of C5H6); 4.56 (m, 1H, Hexo); 3.68
(t, 18H, P(OMe)3); 2.87 (m, 1H, Hendo).
diethyl ether and hexane. Purification by recrystallization
from dichloromethane/diethyl ether was possible, affording
yellow crystals (0.15 g, 91%). Anal. Calc. for C17H22O3-
P2F6Mo (546.23): C, 37.88; H, 4.06. Found: C, 38.02, H;
3.92%. Selected IR (KBr, cmꢁ1): 3130 (m), 2949 (m),
2846 (w), 1897 (w), 1450 (m), 1262 (w), 1181 (m), 1029
(vs), 839 (vs), 795 (m), 760 (m), 557 (s). 1H NMR (CD2Cl2,
300.13 MHz, r.t., d ppm): 7.82–7.68 (m, 2H, H5–8), 7.46–
7.34 (m, 2H, H5–8), 5.56 (t, 1H, H1/3), 5.49 (t, 1H, H1/3),
5.49 (m, 1H, H2), 4.89 (d, 5H, Cp), 3.62 (d, 9H,
P(OMe)3), ꢁ7.42 (d, 1H, Mo–H).
Metathetical change of [IndMo(g4-C5H6){P(OMe)3}2]+
was done by adding a saturated solution of LiCl to the
dication precursor [IndCpMo{P(OMe)3}2](BF4)2 (4) in
Me2CO, which caused the immediate precipitation of the
yellow complex [IndCpMo{P(OMe)3}2]Cl2. This was
washed with the same solvent and a saturated aqueous
solution of KPF6 was added to afford an orange precipi-
tate, [IndCpMo{P(OMe)3}2](PF6)2 (4a), which was recrys-
tallized from Me2CO/Et2O.
4.6. X-ray crystallography
The structures were determined at 100 K using graphite
monochromatized radiation. Data were collected on an
Apex2 diffractometer [26]. Crystal data and experimental
parameters are presented in Table 3. The data were cor-
rected for Lorentz-polarization effects and for absorption
[27]. The structures were solved by direct methods using
SIR97 [28] and refined by least-squares (on F) using pro-
grams from the KRYSTAL package [29]. Hydrogen atoms
4.5. Preparation of [IndCpMoH{P(OMe)3}]PF6 (6)
˚
were kept fixed in calculated positions with C–H = 0.95 A
Addition of NaBH4 (14.5 mg, 0.38 mmol) to a solution
of [IndCpMo{P(OMe)3}2](PF6)2 (0.28 g, 0.30 mmol) in
Me2CO caused an immediate change of colour from
orange to brown and finally yellow after 2 h of reaction.
The solution was filtered and taken to dryness. The residue
was extracted with CH2Cl2 and washed several times with
and with isotropic displacement factors 20% larger than
Ueq for the atoms to which they were bonded for the
organic ligands. The hydrogen atom bonded to Mo was
located from a difference synthesis and refined isotropi-
cally. Complex 5 diffracted very poorly and yielded so
few significant reflections that only isotropic refinement
Table 3
Crystal data and structure refinement for compounds 5 and 6
5
6
Molecular formula
Empirical formula
Formula weight (g molꢁ1
Temperature (K)
Crystal system
[IndMo(g4-C5H6){P(OMe)3}2]PF6
C20H31F6MoO6P3
670.30
100
Orthorhombic
Pbca
[IndCpMoH{P(OMe)3}]PF6
C17H22F6MoO3P2
546.26
100
Monoclinic
P21/n
11.8537(2)
11.4218(2)
15.6992(3)
110.195(1)
1994.85(6)
4
)
Space group
˚
a (A)
11.216(7)
18.01(1)
24.86(2)
90.0
5023(6)
8
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg mmꢁ1
)
1.773
0.794
1.819
0.888
Absorption coefficient (mmꢁ1
)
F (000)
Radiation k (Mo Ka) (A)
h Range
Reflections collected
Reflections independent
Rint
2720.0
0.71073
2.26–25.23
162577
5093
1096.0
˚
0.71073
1.87–30.83
47170
6545
0.058
0.43
Reflections observed [I > 3rI]
Final R indicesa [I > 3rI]
Refinable parameters
1431
4853
R1 = 0.098, wR1 = 0.115
145
R1 = 0.025, wR1 = 0.032
266
Goodness-of-fit
˚
1.112
0.952
ꢁ0.63(8) to 0.73(8)
ꢁ3
Residual electron density (e A
)
ꢁ3.9(2) to 2.9(2)2.5(2), ꢁ1.6(2)
P
P
P
P
P
R1 = iFoj ꢁ jFci/ jFoj; wR1 ¼ ð jjF oj ꢁ jF cjjÞ = wjF o2j1=2, w ¼ 1=fðð F o2Þ þ B þ ð1 þ AÞF o2Þ ꢁ jF ojg with A = 0.10, B = 10. for 5 and 0.03
2
1=2
2
a
and 0.05 for 6.

1600
I.S. Gonc¸alves et al. / Journal of Organometallic Chemistry 692 (2007) 1593–1600
(b) J.R. Ascenso, C.G. de Azevedo, I.S. Gonc¸alves, E. Herdtweck,
D.S. Moreno, M. Pessanha, C.C. Romao, Organometallics 14
˜
(1995) 3901;
was feasible. Atomic scattering factors were taken from the
International Tables for X-ray Crystallography [30].
(c) I.S. Gonc¸alves, C.C. Romao, J. Organomet. Chem. 486 (1995) 155;
˜
Acknowledgements
´
(d) M.G.B. Drew, V. Felix, I.S. Gonc¸alves, C.C. Romao, B. Royo,
˜
Organometallics 17 (1998) 5782;
(e) M.J. Calhorda, I.S. Gonc¸alves, E. Herdtweck, C.C. Romao, B.
˜
Royo, L.F. Veiros, Organometallics 18 (1999) 3956;
(f) I.S. Gonc¸alves, P. Ribeiro-Claro, C.C. Romao, B. Royo, Z.M.
˜
Tavares, J. Organomet. Chem. 648 (2002) 270.
The authors are grateful to FCT, OE and FEDER for
funding (Project POCI/QUI/56109/2004). CCLP thanks
the FCT for a post-doctoral Grant.
[14] C.A. Gamelas, E. Herdtweck, J.P. Lopes, C.C. Romao, Organomet-
˜
Appendix A. Supplementary data
allics 18 (1999) 506.
´
[15] (a) V. Felix, M.J. Calhorda, M.G.B. Drew, I.S. Gonc¸alves, C.C.
Romao, Inorg. Chim. Acta 276 (1998) 263;
(b) C.A. Gamelas, Ph.D. thesis, Instituto de Tecnologia Quımica e
˜
CCDC 610134, 610135 contains the supplementary crys-
tallographic data for 5 and 6. These data can be obtained
free of charge via http://www.ccdc.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorgan-
chem.2006.12.015.
´
´
Biologica, Universidade Nova de Lisboa, 2000.;
´
(c) V. Felix, personal communication.
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