Pentabenzylcyclopentadienyl molybdenum and tungsten hydrides: Syntheses, structures and electrochemistry of [MHCpBz(CO)2(L)] (L = CO, PMe3, PPh3)

Article abstract of DOI:10.1016/j.jorganchem.2010.02.012

Complexes [MHCp^Bz(CO)₂(PR₃)] (R = CH₃, M = Mo (1); M = W (2); R = Ph, M = Mo (3); Cp^Bz = C₅(CH₂Ph)₅) were prepared by thermal decarbonylation of the corresponding [MHC

Full text of DOI:10.1016/j.jorganchem.2010.02.012

Journal of Organometallic Chemistry 695 (2010) 1328–1336
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Pentabenzylcyclopentadienyl molybdenum and tungsten hydrides: Syntheses,
structures and electrochemistry of [MHCpBz(CO)2(L)] (L = CO, PMe3, PPh3)
M. Augusta Antunes a, Sónia Namorado a, Cristina G. de Azevedo a, M. Amélia Lemos b, M. Teresa Duarte a,
José R. Ascenso a, Ana M. Martins a,
*
a Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
b IBB – Institute for Biotechnology and Bioengineering, CEQB, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Complexes [MHCpBz(CO)2(PR3)] (R = CH3, M = Mo (1); M = W (2); R = Ph, M = Mo (3); CpBz = C5(CH2Ph)5)
were prepared by thermal decarbonylation of the corresponding [MHCpBz(CO)3] in the presence of tri-
methyl- or triphenyl-phosphine. In solution the NMR spectra of all compounds show the presence of
cis and trans isomers that interconvert at room temperature. In the solid state the molecular structures
obtained for compounds 1 and 2 correspond to the trans isomers, while for 3 the cis isomer is present.
The electrochemistry of [MoHCpBz(CO)2(PMe3)] (1), [MoHCpBz(CO)3] (5), [WHCpBz(CO)3] (6),
[WCpBz(CO)3]2 (7), and [MCpBz(CO)3(CH3CN)]BF4 (8), is described. The cleavage of M–H bonds takes place
upon oxidation or reduction. Cations [MCpBz(CO)2L(CH3CN)]+ form in solvent-assisted M–H bond break-
ing upon oxidation of [MHCpBz(CO)2L] (L = PMe3, CO). Reduction of [MHCpBz(CO)3] gives [MCpBz(CO)3]ꢀ
and H2. The presence of one PMe3 ligand lowers the reduction potential and precludes the observation
of reduction waves.
Article history:
Received 3 December 2009
Received in revised form 4 February 2010
Accepted 13 February 2010
Available online 20 February 2010
Keywords:
Molybdenum
Tungsten
Hydride
Metallocenes
Cyclic voltammetry
Electrochemistry
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
Bullock and co-workers [22,23], and an extension of this system
to [MoHCpBz(CO)3] (CpBz = C5(CH2Ph)5) as a catalyst precursor for
Transition metal hydrides play an important role in several stoi-
chiometric and catalytic reactions involving the transfer of hydro-
gen to unsaturated organic substrates [1]. The delivery of hydrogen
may occur in the form of a proton, a hydrogen atom or a hydride
ketone hydrogenation was recently made by some of us [18]. The
pentabenzylcyclopentadienyl system is less prone to deactivation
than the cyclopentadienyl derivatives and DFT calculations identi-
fied the active species regeneration (iv and v in Chart 1) as the slow
elementary steps, leading to the conclusion that the best catalytic
performance is related to the high steric bulk created by the CpBz
ligand.
The most common procedure to generate cationic transition
metal hydrides is the one-electron oxidation of 18-electron neutral
complexes. The electron removal is accompanied by a drastic pKa
decrease [24] and therefore the 17-electron species suffer deproto-
nation. The proton may be captured by the medium, namely a base,
the solvent or traces of H2O, or by the neutral hydride that may it-
self be susceptible to protonation, leading to cationic dihydrogen
or dihydride compounds [25–28]. Electrochemical studies of half-
sandwich molybdenum and tungsten complexes have received
considerable attention and it was reported that subsequently to
deprotonation, the 17-electron radicals may be trapped by the sol-
vent and further oxidised or dimerize through radical coupling
[24,29–42].
and methods to obtain free energy values
D
GꢁHþ
;
D
GꢁHꢂ and
D
GꢁHꢀ
for a series of metal hydrides have been described [2–9]. On the
other hand, the kinetic rate constants for hydride or hydrogen
atom transfer were measured using the trityl cation/radical as
acceptors [6,10–12].
The sequential transfer of one proton and one hydride is the ba-
sis of ionic hydrogenation reactions. The procedure was used in
stoichiometric reactions to reduce unsaturated carbon–carbon,
carbon–oxygen and carbon–nitrogen bonds, using strong acids
and a silane or a transition metal hydride as hydride donor re-
agents [13–17]. Yet, in spite of proton transfer has long been iden-
tified as a current reactivity pattern for transition metal hydrides,
using of this reaction in catalytic ionic hydrogenations is a recent
attainment [18–21]. A catalytic hydrogenation cycle for the ionic
hydrogenation of simple ketones to alcohols using as catalysts
[MoHCp(CO)2(PR3)] (R = Me, Ph, Cy) and analogous C2- and C3-
bridged cyclopentadienyl-phosphine complexes was reported by
The work reported now focuses on the syntheses and electro-
chemical study of new pentabenzylcyclopentadienyl molybdenum
and tungsten hydride complexes. It aims the comparison with
analogous cyclopentadienyl complexes described in the literature,
* Corresponding author. Tel.: +351 218419172.
E-mail address: ana.martins@ist.utl.pt (A.M. Martins).
0022-328X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.02.012

M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
1329
trans isomers as the most intense peaks appear at higher wave-
numbers [38]. In solution, however, the proton NMR spectra of
[MHCpBz(CO)2(PR3)] attest for the presence of cis and trans iso-
mers. The proton NMR spectrum of 1 in C6D6 at room temperature
shows two resonances, at d ꢀ5.71 (br) and ꢀ5.49 (s) ppm assign-
able to two different hydride ligands. A variable temperature 1H
NMR study performed in d8-toluene showed that the two reso-
nances appearing at room temperature split in two doublets on
cooling until ꢀ80 °C (Fig. 1). The multiplicity of these signals is
2
due to the coupling with the phosphorus and the values of JPH
,
which are 71.2 and 24.1 Hz, allow their assignment to the cis and
trans isomers respectively. At room temperature the 31P NMR spec-
trum of 1 displays one broad resonance at d 10.9 ppm that splits in
two apparent singlets at d 19.4 (cis) and 17.0 (trans) at ꢀ80 °C. The
proton resonances attributable to the CpBz and the PMe3 ligands
broad when the temperature is lowered but do not resolve until
ꢀ80 °C.
At room temperature the hydride resonance of 2 appears as a
doublet of triplets at d ꢀ7.00 ppm due to the coupling with the
tungsten (1JWH = 24.9 Hz) and the phosphorus (2JPH = 73.6 Hz) nu-
cleus. The PMe3 proton resonance shows as a doublet with
2JPH = 8.8 Hz and the 31P resonance is observed at d ꢀ20.8 ppm
Chart 1.
and assessing the influence of a very bulky cyclopentadienyl ligand
on the compounds reactivity and properties [43,44].
1
as a triplet with JPW = 125.2 Hz. On cooling the solution to
ꢀ80 °C the hydride resonance splits in two at d ꢀ6.52 ppm (d,
2. Results and discussion
2
1
2JPH = 22.6 Hz) and ꢀ6.85 ppm (dt, JPH = 72.7 Hz, JWH = 25.3 Hz).
The values of the coupling constants to the phosphorus allow the
assignment of the high field resonance to the cis isomer and the
other to the trans isomer. At ꢀ80 °C the remaining signals are
still not resolved appearing as broad resonances. The carbonyl
carbon resonances of either 1 or 2 have not been detected
regardless of the temperature. The phosphorus NMR resonance
at d 66.5 ppm in [MoHCpBz(CO)2(PPh3)] (3), confirms the coordi-
nation of phosphine. As described for 1 and 2, the NMR spectra
of 3 show the presence of cis and trans isomers when the tem-
perature is lowered below ꢀ30 °C. At ꢀ50 °C the hydride reso-
2.1. Syntheses and characterisation
2.1.1. [MHCpBz(CO)2(PR3)] complexes
Complexes [MHCpBz(CO)2(PR3)] (R = CH3, M = Mo (1); M = W
(2); R = Ph, M = Mo (3); CpBz = C5(CH2Ph)5) were prepared in tolu-
ene by thermal decarbonylation of the corresponding
[MHCpBz(CO)3] [30] in the presence of trimethyl- or triphenyl-
phosphine. This is a common method for the replacement of one
carbonyl ligand in molybdenum and tungsten half-sandwich tri-
carbonyl complexes that usually gives high product yields. Com-
pounds 1, 2 and 3 were obtained in crystalline forms after work-
up in 75%, 80% and 76% yields, respectively.
nance of cis-[MoHCpBz(CO)2(PPh3)] gives rise to
a doublet
centered at d ꢀ4.52 ppm (2JPH = 71.2 Hz) and that of the trans iso-
mer appears as a doublet at d ꢀ5.35 ppm (2JPH = 20.4 Hz). The
carbonyl carbon resonances are not visible in the 13C NMR spec-
trum at room temperature but at ꢀ50 °C they give rise to one
doublet at d 246.8 ppm (2JPC = 21 Hz) assigned to the CO ligand
The IR carbonyl stretching bands of 1–3 are presented in Table 1
in comparison with values reported for analogous complexes. The
lower mCO values revealed by the IR spectra of 1, 2 and 3 are consis-
tent with the results obtained for other pentabenzylcyclopentadie-
nyl molybdenum and tungsten compounds [30,44] and attest a
more extensive metal–carbonyl back bonding in CpBz complexes
*
in comparison with Cp and Cp analogues.
On the other hand, the observation of only two CO peaks, in-
stead of four, suggests the formation of only one isomer. The IR
patterns observed in KBr are compatible with the presence of the
Table 1
IR carbonyl stretching bands of 1,
complexes.
2
and
3
and values reported for analogous
mCꢃO (cm-1
Compound
)
[MoHCpBz(CO)2(PMe3)], 1
[WHCpBz(CO)2(PMe3)], 2
[MoHCpBz(CO)2(PPh3)], 3
cis-[MoHCp(CO)2(PMe3)] [45]
trans-[MoHCp(CO)2(PMe3)]
1915, 1819
1909, 1809
1932, 1847
1947, 1864
1938, 1864
1938, 1860
1926, 1852
1941, 1855
1933, 1855
1930, 1853
1920,1843
1991, 1876
1940, 1862
1944, 1865
1944, 1865
*
cis-[MoHCp (CO)2(PMe3)] [46]
*
trans-[MoHCp (CO)2(PMe3)]
cis-[WHCp(CO)2(PMe3)] [47]
trans-[WHCp(CO)2(PMe3)]
*
cis-[WHCp (CO)2(PMe3)] [46]
*
trans-[WHCp (CO)2(PMe3)]
cis-[MoHCp(CO)2(PPh3)] [48]
trans-[MoHCp(CO)2(PPh3)] [49]
cis-[WHCp(CO)2(PPh3)] [45]
trans-[WHCp(CO)2(PPh3)]
Fig. 1. A variable temperature 1H NMR spectrum in d8-toluene for 1.

1330
M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
cis to the phosphine and one singlet at d 238.5 ppm due to the
trans CO ligand [22].
The reaction of [MoHCpBz(CO)3] with PCy3 was performed in
toluene under reflux, in experimental conditions similar to those
used for the syntheses of 1–3. The product isolated at the end of
the reaction in 10% yield was identified by X-ray diffraction as
[Mo(CO)4(PCy)2] (4). A tentative explanation for the formation of
4 may involve the reductive elimination of HCpBz from the puta-
tive [MoHCpBz(CO)2(PCy3)], forced by the bulkiness and strong do-
nor properties of the tricyclohexylphosphine ligand, followed by
reaction with CO and PCy3. Indeed, in addition to 4, the proton
NMR spectrum of the reaction crude showed resonances character-
istic of pentabenzilcyclopentadiene.
The molecular structures of complexes 1–4 have been obtained
by single crystal X-ray diffraction. The molecular structure of 4 dis-
plays an octahedral Mo center with trans-PCy3 ligands as reported
before [50] and does not justify further discussion.
Crystals of [MoHCpBz(CO)2(PMe3)] (1), [WHCpBz(CO)2(PMe3)]
(2), and [MoHCpBz(CO)2(PPh3)] (3), were grown from Et2O solu-
tions cooled at ꢀ20 °C. The molecular structures are shown in Figs.
2, 3 and 4 and selected bond lengths and angles are presented in
Table 2.
Fig. 3. ORTEP III diagram of 2, using 50% probability level ellipsoids. Calculated
hydrogen atoms have been omitted for clarity.
The first note to address about the molecular structures ob-
tained is the fact that compounds 1 and 2, presenting the PMe3 li-
gand, correspond to the trans isomers, in spite of NMR spectra have
revealed that the major species in solution are the cis isomers. The
structure of 3 presents the cis isomer co-crystallized with a dieth-
ylether molecule.
In all compounds the metal coordination geometry is a dis-
torted four-legged piano stool with angles within the expected val-
ues (see Table 2) [44,51] and thus, the CpBz(centroid)–M–L(i)
angles are higher than the corresponding L(i)–M–L(i) basal angles.
They also follow the ‘‘angular trans influence” defined by Poli,
which establishes that the two larger (or smaller) CpBz(centroid)–
M–L(i) angles are defined by opposite L(i) basal ligands [52b]. For
all complexes the phenyl rings of four benzyl fragments are direc-
ted opposite to the metal and one is bended towards the metal but
sufficiently far apart to prevent any bonding interaction. To better
characterize the relative conformation of the phenyl rings we pres-
ent in Table 2 the torsion angles of the pending benzyl arms de-
fined as MACðCpBz ringÞACðCH
ACipso. In all compounds the
bridgeÞ
2
phenyl rings bending towards the metal define torsion angles of
47–50, while the others present angles that range from 155 to
177°.
Fig. 4. ORTEP III diagram of 3, using 50% probability level ellipsoids. Calculated
hydrogen atoms have been omitted for clarity.
Compounds 1 and 2 are isostructural. The angles between the
carbonyl and the hydride are narrow than CO–PMe3 angles in
consequence of the high steric bulk of trimethylphosphine. The
distances M(1)–C(6), M(1)–C(7), M(1)–P(1), M(1)–H and M(1)–
CpBz(centroid) are consistent with the values reported for analo-
gous complexes [44,52]. The benzyl substituents point towards
the metal over one of the carbonyl ligands, with torsion angles
C(1)–CpBz(centroid)–Mo(1)–C(6) and C(1)–CpBz(centroid)–W(1)–
C(7) of 23.9(6)° and 28.8 (8)° in 1 and 2, respectively. This arrange-
ment is often observed in [MCpBz(CO)3X] (X = H, Me, Cl, I, OTf,
MCpBz(CO)3) complexes [18,30,44,53].
The structure of [MoHCpBz(CO)2(PPh3)] (3), presents two adja-
cent carbonyl ligands with an angle of 81.15(18)°, comparable to
those observed in [MoHCpBz(CO)3] [30]. The relative positioning
of the benzyl substituents of CpBz in relation to the basal ligands
in 3 differs from the two trimethylphosphine analogues previously
discussed as the benzyl group bending towards the molybdenum
atom is positioned between the two adjacent carbonyl ligands
with torsion angles C(1)–CpBz(centroid)–Mo(1)–C(6) and
Fig. 2. ORTEP III diagram of 1, showing the overall geometry. 50% probability level
ellipsoids were used and calculated hydrogen atoms have been omitted for clarity.

M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
1331
Table 2
1.13 V for 5 and at 0.74 V and 1.15 V for 6, as shown in Fig. 5a
for [MoHCpBz(CO)3]. When the experiment was started in the
cathodic direction no reduction waves are observed in the first
scan within the range of potentials available to the solvent. How-
ever, reversing of the cycle after the first scan led to the appearance
of new oxidation waves at ꢀ0.57 V and ꢀ0.54 V for 5 and 6, respec-
tively. As is shown in Fig. 5b for 5 a subsequent cathodic scan re-
veals a new reduction wave with ErpedðVÞ = ꢀ0.95 V. Controlled
potential coulometry performed at the potential of wave I indicates
that an overall transfer of two electrons takes place. The results de-
scribed above are compatible with the reaction sequence pre-
sented in Scheme 1.
Relevant bond distances (Å) and angles (°) for compounds 1, 2 and 3.
[MHCpBz(CO)2(PMe3)]
[MoHCpBz(CO)2(PPh3)], 3
1(M = Mo)
2(M = W)
M–H(1)
M–CT
1.782(3)
2.023(9)
1.955(3)
1.929(2)
2.4542(6)
1.162(3)
1.174(3)
1.702(19)
2.012(6)
1.878(17)
1.940(16)
2.435(4)
1.809(4)
2.024(4)
1.949(4)
1.958(4)
2.4338(11)
1.173(5)
1.155(5)
M–C(6)
M–C(7)
M–P(1)
C(6)–O(1)
C(7)–O(2)
1.203(16)
1.135(15)
C(6)–M–C(7)
H(1)–M–C(6)
H(1)–M–C(7)
H(1)–M–P(1)
C(6)–M–P(1)
C(7)–M–P(1)
98.51(10)
67.46(13)
65.93(13)
127.6(9)
77.70(7)
82.82(7)
97.2(6)
57.2(9)
73.6(9)
126.7(9)
83.6(4)
77.6(4)
81.15(17)
121.3(14)
62.8(14)
64.6(13)
82.22(12)
102.76(12)
Following an initial oxidation to [MHCpBz(CO)3]+ (M = Mo, 5+;
W, 6+) the acidity of the hydride ligands in 5+ and 6+ is greatly en-
hanced [24] favoring the formation of a 17-electron neutral spe-
cies, [MCpBz(CO)3]. The oxidation of this complex to cationic
species [MCpBz(CO)3]+ justifies the second electron transfer occur-
ring at the first wave potential. The stoichiometric balance of 2 far-
adays per mol revealed by the coulommetry excludes the putative
formation of [MCpBz(CO)3]+ directly from [MHCpBz(CO)3]+ as it
would correspond to a 1:1 metal:electron ratio. The coordination
of acetonitrile to the unsaturated species leads to the solvent sta-
bilized cation [MCpBz(CO)3(CH3CN)]+ that is further oxidized at
wave II to [MCpBz(CO)3(CH3CN)]2+. An alternative explanation
provided by Tilset and co-workers for analogous cyclopentadienyl
CT–M–H(1)
CT–M–C(6)
CT–M–C(7)
CT–M–P(1)
108.9(9)
108.8(9)
126.7(5)
130.2(4)
116.3(12)
122.28(12)
124.53(12)
131.06(7)
125.43(7)
123.57(5)
124.07(17) 127.84(6)
M–C(1)–C(10)–C(11) 47.0(3)
M–C(2)–C(20)–C(21) 162.64(15)
M–C(3)–C(30)–C(31) 176.36(15)
50.8(17)
163.2(8)
177.0(8)
ꢀ47.8(5)
ꢀ174.8(3)
168.33(3)
162.4(3)
M–C(4)–C(40)–C(41) –165.59(15) ꢀ165.8(8)
M–C(5)–C(50)–C(51) –169.60(15) ꢀ170.7(9)
ꢀ155.5(3)
C(1)–CT–M–C(6)
C(1)–CT–M–C(7)
23.9(6)
ꢀ54.5(2)
28.8(8)
47.9(2)
CT–CpBz centroid.
2.5E-01
(a)
II
C(1)–CpBz(centroid)–Mo(1)–C(7) of ꢀ54.5(2)° and 47.9(2)°, respec-
tively. The Mo(1)–H(1) bond length in 3 (1.812(4) Å) is slightly
longer than in 1 (1.782(3) Å). This difference may be a consequence
of the trans effect caused by the PMe3 and CO ligands in complexes
1 and 3, respectively. In comparison with other Mo–H bond lengths
determined by X-ray or neutron diffraction, ranging from
2.0E-01
I
1.5E-01
1.0E-01
5.0E-02
0.0E+00
-5.0E-02
*
1.685(3) Å in [MoCp2H2] to 1.789(7) Å in [MoCp (CO)3H], the
Mo(1)–H(1) distance in
3 is also longer [29,30,54–57]. The
distances between Mo(1)–C(6), Mo(1)–C(7) and Mo(1)–P are in
the ranges usually reported in the literature.
2.2. Electrochemical studies
0
500
1000
1500
Electrochemical results obtained for [MoHCpBz(CO)2(PMe3)] (1),
[MoHCpBz(CO)3] (5), [WHCpBz(CO)3] (6), [WCpBz(CO)3]2 (7), and
[MoCpBz(CO)3(CH3CN)]BF4 (8), using Bu4NPF6 as electrolyte, are
summarized in Table 3.
E (mV)
6.0E-02
4.0E-02
2.0E-02
0.0E+00
-2.0E-02
-4.0E-02
(b)
The cyclic voltamograms of [MHCpBz(CO)3] scanned in the ano-
dic direction reveal two distinct irreversible waves at 0.72 V and
IV
Table 3
Cyclic voltammetry data for 1, 5, 6, 7 and 8.
Eopx
(I)
Eopx
(II)
Eopx
(IV)a
Eopx(VI)
Erped
(III)
Erped(V)
Compound
[MoHCpBz(CO)2(PMe3)], 1
[MoHCpBz(CO)3], 5
[WHCpBz(CO)3], 6
0.26 0.74 0.16b
–
-1.64c
-0.95d
–
–
0.72 1.13
0.74 1.15
–
–
-0.57
-0.54
0.48a
0.55a
–
V
[WCpBz(CO)3]2, 7
0.55 1.24 -1.95 -0.64
–
[MoCpBz(CO)3(CH3CN)]BF4, 1.13
–
–
-0.57
-0.95
–
8
-3500
-2500
-1500
E (mV)
-500
Cyclic voltammetry at 25 °C: V vs. Ferrocene/Ferrocenium couple; all potentials
were evaluated at 200 mVsꢀ1 in CH3CN except for 7 where CH2Cl2 was used.
a
Appears only after cathodic scan.
E
Appears upon scan reverse after I.
b
1/2(red) appears upon scan reverse after II.
Fig. 5. Voltammogram of a solution of 5, in CH3CN/Bu4NPF6 at a vitreous carbon
electrode and a scan rate of 200 mVsꢀ1, run in the anodic (a) and cathodic (b)
directions.
c
d
Appears upon scan reverse after I or IV.

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M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
of an independently prepared sample of [MoCpBz(CO)3(CH3CN)]BF4
(8), which shows an irreversible oxidation wave at the same poten-
tial (see below).
Even though the first cathodic scans of 5 and 6 do not reveal any
reduction waves, the analysis of the results of subsequent cycles
(see below) requires that one postulates the reduction of 5 and 6
to the corresponding 19-electron anions [MHCpBz(CO)3]ꢀ that are
converted to [MCpBz(CO)3]ꢀ. A controlled potential electrolysis
performed at ꢀ1.70 V attested the transfer of one electron and
the formation of H2, identified by mass spectrometry, during the
reduction process. The nonappearance of a well-defined cathodic
wave reveals that the reduction of 5 and 6 occurs through a very
broad wave that spreads over a large range of potentials, character-
istic of a quasi-reversible electrode process that displays a low het-
erogeneous rate constant and a small transfer coefficient (a) [58].
The formation of H2 may result either from an homolytic cleavage
of the M–H bonds after reduction [32] or from a heterolytic process
consisting in the loss of hydride from the19-electron reduced com-
plex to the parent metal hydride. This route is consistent with the
diverse reactivity of metal carbonyl hydrides, for which M–H
bonds may break as a proton, a hydrogen atom or a hydride
[8,9,59–62].
The oxidation process observed at wave IV (Fig. 5b) is related to
the oxidation of [MCpBz(CO)3]ꢀ to the radical [MCpBz(CO)3]. Once
formed, [MCpBz(CO)3] may be oxidized to [MCpBz(CO)3(CH3CN)]+
or dimerize to [MCpBz(CO)3]2. The formation of the two compounds
takes place at wave IV potential. The presence of [MCpBz
(CO)3(CH3CN)]+ is inferred from wave V that is observed upon scan
reverse and assigned to its reduction. A similar reduction was ob-
served in the cyclic voltammogram of 8 that also shows a wave at
ꢀ0.95 V (see below); The formation of the dimers is revealed by
small oxidation waves observed at 0.48 V for 5 and 0.55 V for 6
(wave VI) that are assigned to the oxidation of the respective di-
mers, in conformity with the studies of 7 described below. The lack
of cationic oxidation products for 6 (wave V is absent) denotes that
radical coupling is a preferred route for tungsten. The formation of
[MoCp(CO)3]2 by oxidative coupling, upon controlled-potential
electrolysis of [MoHCp(CO)3] in acetonitrile, was reported by Kochi
as a preferential pathway [37].
Scheme 1.
systems claims the coordination of CH3CN and formation of 19-
electron complexes prior to the oxidation reactions (Scheme 2,
path i). [24,35] Even though this mechanism may not be ruled
out, DFT calculations performed on cationic compounds of general
formula [MoCp0(CO)3(L)]+ (Cp0 = C5H5, C5(CH2Ph)5) have shown
that the stability of CpBz derivatives is lower than that of Cp ana-
logues [18] and one equivalent situation may be envisaged for neu-
tral complexes, shifting the solvent coordination equilibrium
towards [MoCpBz(CO)3]ꢂ (Scheme 2, path ii).
Chemical studies have shown that the protonation of
[MHCp0(CO)3] or [MHCp0(CO)2(PR3)] (Cp0 = C5H5, CpBz; PR3 = PMe3,
PPh3) with strong acids leads to the formation of cationic dihy-
drides that are unstable and, in the presence of neutral 2 electron
donors, give [MCp0(CO)3L]+ or [MCp0(CO)2(PR3)L]+ by H2 replace-
ment [13,18,33]. These results raise an alternative hypothesis
where the starting hydride complexes would behave as possible
proton acceptors from [MHCpBz(CO)3]+. [MH2CpBz(CO)3]+ would
then be an intermediate of the formation of [MCpBz(CO)3(CH3CN)]+
and H2 should concomitantly be formed. The electron balance
resulting from such a process would correspond to a global transfer
of one electron per mol of [MH] that does not fit our experimental
findings. This discrepancy between the electronic balance in chem-
ical and electrochemical experiments has been noted by other
authors (see for instance [24,33]) and has been reconciled by con-
sidering that the mechanisms operating in electrochemical and
chemical conditions are different.
The cyclic voltammograms obtained for [MoHCpBz(CO)2(PMe3)]
(1), in acetonitrile are presented in Fig. 6. The two irreversible ano-
dic waves observed in Fig. 6a resemble those of Fig. 5a and are
likely due to oxidation processes similar to those described for
complexes 5 and 6. The lower potentials corresponding to the oxi-
dation waves of 1 reflect a richer metal centre, as expected upon
replacement of a CO by a PMe3 ligand. A coulometric experiment
carried at the potential of wave I confirmed the transfer of 2-elec-
trons as required for the formation of [MoCpBz(CO)2(P-
Me3)(CH3CN)]+ from 1. This complex was isolated at the end of
the experiment and identified by NMR and IR. The oxidation pro-
cess responsible for the appearance of wave II is thus associated
to the oxidation of [MoCpBz(CO)2(PMe3)(CH3CN)]+ to the dication
[MoCpBz(CO)2(PMe3)(CH3CN)]2+. The transfer of one electron at this
potential was confirmed by a coulometric experiment. When the
voltammetric cycle is reversed immediately after wave I (Fig. 6b),
only one reduction process, involving the exchange of 1 electron,
is observed at ꢀ1.64 V (wave V in Fig. 6b). The reduction taking
place at this potential refers to the formation of [MoCpBz(CO)2(P-
Me3)(CH3CN)] from the parent cation. This compound is a 19-elec-
tron species that readily dissociates CH3CN leading to
[MoCpBz(CO)2(PMe3)]. Further reduction of this radical is not ob-
served possibly because an irreversible reaction takes place origi-
nating species that are not reducible within the potential range
available [30,38].
The definitive assignment of the oxidation process occurring at
wave II was possible by comparison with the cyclic voltammogram
The reduction processes taking place at wave III is reversible
Scheme 2.
and related to the 17-electron dication [MoCpBz(CO)2(PMe3)-

M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
1333
the cationic dimer in [WCpBz(CO)3]+ and [WCpBz(CO)3]. The reac-
tion of the cation with the solvent leads to [WCpBz(CO)3(CH2Cl2)]+
[18] that is further oxidized at wave II to the corresponding dicat-
ionic species. The reduction of 7 also results in breaking of the me-
tal-metal bond with formation of [WCpBz(CO)3]ꢀ and
[WCpBz(CO)3]. The anion is further oxidized at ꢀ0.64 V to
[WCpBz(CO)3]. In accordance with the result described above for
1.5E-01
1.0E-01
5.0E-02
0.0E+00
-5.0E-02
(a)
II
I
6
(wave IV in Scheme 1), [WCpBz(CO)3] is not oxidized to
[WCpBz(CO)3]+ at wave IV potential.
The oxidation of [MoCpBz(CO)3(CH3CN)]BF4 (8), performed in
acetonitrile with Bu4NPF6 as electrolyte, showed an irreversible
oxidation wave at 1.13 V and a reduction wave at ꢀ0.95 V. Upon
III
reduction and scan reverse
a new anodic wave appears at
ꢀ0.57 V. The anodic peak is assigned to the oxidation of 8 to
[MCpBz(CO)3(CH3CN)]2+ and the cathodic wave to the process
[MCpBz(CO)3(CH3CN)]+/[MCpBz(CO)3]ꢀ, which results from a 2-
electron transfer. The wave at ꢀ0.57 V corresponds to the
oxidation of [MCpBz(CO)3]ꢀ. The overall process is sequentially rep-
resented in Scheme 1 at waves V and IV.
The redox potentials obtained for pentabenzylcyclopentadienyl
Mo and W complexes are, in general, consistent with results de-
scribed in the literature for analogous half-sandwich complexes
[24,32–34,36,38,40,41,68,69]. The comparison between the first
oxidation waves of [MCpBz(CO)3X] where X = H or X = WCpBz(CO)3
shows a cathodic shift for the dimer that attests for a higher metal
electron density. The replacement of one CO by PMe3 in
[MCpBz(CO)3H] has a similar outcome. The results corroborate
those based on the CO stretching wavenumbers of the correspond-
ing complexes.
-500
0
500
1000
1500
E (mV)
1.0E-01
5.0E-02
0.0E+00
-5.0E-02
(b)
I
V
3. Concluding remarks
-2000 -1500 -1000 -500
0
500
The results described show that [MHCpBz(CO)2(PR3)] (M = Mo,
W; R = Me, Ph) complexes may readily be prepared by carbonyl
replacement by phosphines, but attempts to obtain the molybde-
num tricyclohexylphosphine derivative led to [Mo(CO)4(PCy3)2]
by elimination of HCpBz. Complexes [MHCpBz(CO)2(PR3)] exist in
solution as a mixture of cis and trans isomers that rapidly intercon-
vert at room temperature. The redox potentials of [MHCpBz(CO)2L]
(L = CO, PMe3) revealed a close analogy with values previously re-
ported for other cyclopentadienyl derivatives, pointing out that the
electronic properties of the pentabenzylcyclopentadienyl ligand do
not differ appreciably. However, the steric bulk of CpBz is likely
responsible for some reactivity differences observed, as the lack
of prior solvent coordination in the oxidation of 17-electron spe-
cies [MCpBz(CO)2L] (L = CO, PMe3). This conclusion is attested by
the similarity of the electrochemical data obtained for 5 (L = CO)
in the presence and in the absence of CH3CN, on one side, and by
the formation of [MCpBz(CO)3]2 during the oxidation processes of
5 and 6, which also reveals that formation of 19-electron species
by CH3CN coordination is disfavored in relation to cyclopentadi-
enyl complexes.
E (mV)
Fig. 6. Voltammogram of a solution of 1, in CH3CN/Bu4NPF6 at a vitreous carbon
electrode and a scan rate of 200 mVs-1, run in the anodic (a) and cathodic (b)
directions.
(CH3CN)]2+ formed at wave II. However, the irreversibility of wave
II implies that a homogeneous chemical process involving this spe-
cies must take place before reduction. The first hypothesis that was
considered to justify this behavior was the reaction between the
[MoCpBz(CO)2(PMe3)(CH3CN)]2+ and the electrolyte anion PF6ꢀ
[63,64]. It is well documented that BFꢀ4 may coordinate to molyb-
denum leading to the formation of zwitterionic complexes
[MoCp0(CO)3(FBF3)] (Cp0 = C5H5, Cp , CpBz) [18] and it has also been
*
reported that fluorine abstraction from PFꢀ6 may be forced by
highly acidic metal centers [65–67]. In order to check this possibil-
ity the cyclic voltammogram of 1 in CH3CN/Bu4NClO4 was carried
out. The result excludes the participation of the anion as the pat-
tern observed is similar regardless of the electrolyte counter-ion.
The cyclic voltammogram of 1 in CH2Cl2/Bu4NPF6 shows that
waves III and V are absent in CH2Cl2, which means that acetonitrile
has a key role in the processes taking place at such potentials. At
the present stage the nature of the process occurring at wave III re-
mains elusive.
4. Experimental section
The electrochemistry of [WCpBz(CO)3]2 (7) [30], was studied in
CH2Cl2 solutions containing Bu4NPF6. Two irreversible anodic
peaks are observed at Epox (I) = 0.55 V and Eopx (II) = 1.24 V. The
reduction takes place through a single cathodic wave at Epred
(III) = ꢀ1.95 V. The species formed in wave III is irreversibly oxi-
dized in a subsequent anodic scan at Eopx (IV) = ꢀ0.64 V. The results
obtained are consistent with the breaking of the dimer and forma-
tion of monomeric ions that participate in subsequent redox pro-
cesses. The electron transfer occurring at Eopx (I) causes the
weakening of the metal–metal bond and leads to the cleavage of
4.1. General procedures
All manipulations were performed under a dry nitrogen atmo-
sphere using standard Schlenk and glovebox techniques. Solvents
were previously dried with 4 Å molecular sieves and distilled un-
der a dry nitrogen atmosphere over CaH2 (dichloromethane),
P2O5 (acetonitrile), or sodium/benzophenone (diethyl ether and
toluene). Toluene-d8, benzene-d6 and acetonitrile-d3 were dried
with 4 Å molecular sieves, degassed and stored under nitrogen. Lit-
erature methods were used to prepare [MoHCpBz(CO)3],

1334
M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
[WHCpBz(CO)3] and [WCpBz(CO)3]2 [30]. PMe3, PPh3 and Ph3CBF4
were used as received from Aldrich and Bu4NPF6 was electrochem-
ical grade.
ppm): 140.8 (i-C6H5), 129.2 (o-C6H5), 128.5 (m-C6H5), 126.4 (p-
1
C6H5), 107.6 (C5Bz5), 33.7 (CH2Ph), 23.4 (d, JPC = 35.0 Hz, PMe3,).
1
31P NMR (toluene-d8, ꢀ80 °C, d, ppm): ꢀ16.9 (t, JWP = 123.5 Hz,
NMR spectra were recorded on Bruker AvanceII 300 or Bruker
AvanceII 400 spectrometers. Chemical shifts for 1H were referenced
to resonances of the residual protonated solvents relative to tetra-
methylsilane, and 13C spectra were referenced to the solvent car-
bon resonance. 31P spectra were referenced to external 80%
H3PO4 (d 0 ppm). 19F spectra were referenced to external CF3COOH
(d ꢀ76.55 ppm). 11B spectra were referenced to external BF3ꢂEt2O
(d 0 ppm). IR spectra were recorded as KBr pellets on a Jasco FT/
IR-4100 spectrophotometer. Elemental analyses were performed
at Laboratório de Análises do I.S.T., Lisbon, Portugal.
PMe3), ꢀ17.6 (t, JWP = 125.2 Hz, PMe3). IR (KBr pellet): mCꢃO
1
1909, 1809 cmꢀ1. Anal. Calc. for C45H45O2PW: C, 64.91; H, 5.45.
Found: C, 64.36; H, 5.60%.
4.4. [MoHCpBz(CO)2(PPh3)] (3)
A solution of [MoHCpBz(CO)3] (0.700 g, 1.0 mmol) in toluene
(25 mL) was treated with PPh3 (0.385, 1.5 mmol). After refluxing
overnight, the reaction mixture was evaporated to dryness, and
the oily product formed was extracted in diethyl ether. The filtered
solution was concentrated and cooled at ꢀ20 °C affording yellow
crystals (0.71 g, 0.76 mmol, yield 76%). 1H NMR (toluene-d8,
25 °C, d, ppm): 7.70–7.66 (m, 6H, m-PPh3), 7.12–7.10 (m, 6H, o-
PPh3), 7.06–7.04 (m, 3H, p-PPh3), 6.86–6.85 (m, 15H, p-C6H5, m-
C6H5), 6.69–6.68 (m, 10H, o-C6H5), 3.72 (s, 10H, CH2Ph), ꢀ4.53 (d,
2JPH = 69.8 Hz, 1H, MoH). 13C NMR (toluene-d8, 25 °C, d, ppm):
140.8 (i-C6H5), 138.7 (i-PPh3), 133.8 (m-PPh3), 129.7 (o-C6H5),
129.8 (p-PPh3), 128.3 (o-PPh3), 128.1 (m-C6H5), 126.4 (p-C6H5),
108.9 (C5Bz5), 33.7 (CH2Ph), 31P NMR (toluene-d8, 25 °C, d,
ppm): 66.5 (s, PPh3). 1H NMR (toluene-d8, -50 °C, d, ppm): 3.74
4.2. [MoHCpBz(CO)2(PMe3)] (1)
A 1 M solution of PMe3 in toluene (1.0 mL, 1.00 mmol) was
added dropwise to
a
solution of [MoHCpBz(CO)3] (0.596 g,
0.86 mmol) (25 mL) in the same solvent. After stirring for 2 h at
80 °C the reaction mixture was evaporated to dryness, and ex-
tracted in diethyl ether. Concentration and cooling to ꢀ20 °C
yielded yellow crystals (0.490 g, 0.65 mmol, yield 76%). 1H NMR
(C6D6, 25 °C, d, ppm): 6.93–6.91 (m, 15H, p-C6H5, m-C6H5), 6.83–
2
2
6.80 (m, 10H, o-C6H5), 3.84 (s, 10H, CH2Ph), 1.10 (d, JPH = 8.6 Hz,
(s, 10H, CH2Ph), ꢀ4.52 (d, JPH = 71.2 Hz, 1H, cis-MoH), ꢀ5.35 (d,
9H, PMe3), ꢀ5.49 (s, 1H, MoH), ꢀ5.71 (br, 1H, MoH). 13C NMR
(C6D6, 25 °C, d, ppm): 140.6 (i-C6H5), 129.2 (o-C6H5), 128.1 (m-
C6H5), 126.1 (p-C6H5), 109.0 (C5Bz5), 33.5 (CH2Ph), 23.0 (br,
PMe3). 31P NMR (C6D6, 25 °C, d, ppm): 10.9 (br, PMe3). 1H NMR (tol-
uene-d8, ꢀ80 °C, d, ppm): 6.95 (br, 15H, p-C6H5, m-C6H5), 6.62 (br,
10H, o-C6H5), 3.82 (br, 10H, CH2Ph), 1.06-1.03 (d, 2JPH = 7.4 Hz, 9H,
2JPH = 20.4 Hz, 1H, trans-MoH). 13C NMR (toluene-d8, ꢀ50 °C, d,
2
ppm): 246.93 (d, JPC = 51.07 Hz, trans-CO), d 238.5 (s, cis-CO), 31P
NMR (toluene-d8, ꢀ50 °C, d, ppm): 72.10 (s, trans-PMe3), 71.99 (s,
cis-PMe3). IR (KBr pellet): mCꢃO 1932, 1847 cmꢀ1. Anal. Calc. for
C60H51O2PMo: C, 77.41; H 5.52. Found: C, 75.33; H 5.51%.
2
PMe3), ꢀ5.26 (d, JPH = 24.1 Hz, 1H, trans-MoH), ꢀ5.57 (d,
4.5. [MoCpBz(CO)3(CH3CN)]BF4 (8)
2JPH = 71.2 Hz, 1H, cis-MoH). 13C NMR (toluene-d8, ꢀ80 °C, d,
ppm): 141.0 (i-C6H5), 129.2 (o-C6H5), 128.1 (m-C6H5), 126.4 (p-
A solution of Ph3CBF4 (0.170 g, 0.5 mmol) in CH3CN (20 mL) was
added dropwise, at ꢀ40 °C, to a solution of [MoHCpBz(CO)3]
(0.345 g, 0.5 mmol) (30 mL) in the same solvent. The mixture was
warmed to room temperature and a red-orange solution was ob-
tained. After stirring for 2 h, the solvent was evaporated under vac-
uum. The red residue was washed with hexanes (2 ꢄ 5 mL) and
dried (0.395 g, 0.48 mmol, yield 96%). 1H NMR (CD3CN, 25 °C, d,
ppm): 7.04–7.02 (m, 15H, p-C6H5, m-C6H5), 6.82–6.80 (m, 10H, o-
C6H5), 3.84(s, 10H, CH2Ph), 2.59(s, 3H, CH3CN). 13C NMR (CD3CN,
d, ppm): 237.5 (CO), 224.2 (CO), 138.8 (i-C6H5), 130.4 (o-C6H5),
128.7 (m-C6H5), 127.9 (p-C6H5), 118.3 (CH3CN), 116.8 (C5Bz5),
32.4 (CH2Ph), 2.1 (CH3CN). 11Br NMR (CD3CN, d, ppm): 3.9 (br,
1
C6H5), 109.1 (C5Bz5), 33.5 (CH2Ph), 22.8 (d, JPC = 31.6 Hz, PMe3,).
31P NMR (toluene-d8, ꢀ80 °C, d, ppm): 19.4 (s, cis-PMe3), 17.0 (s,
trans-PMe3). 1H NMR (toluene-d8, 100 °C, d, ppm): 6.88–6.85 (m,
15H, p-C6H5, m-C6H5), 6.83–6.79 (m, 10H, o-C6H5), 3.83 (s, 10H,
2
CH2Ph), 1.24–1.21 (d, JPH = 8.4 Hz, 9H, PMe3), ꢀ5.54 (d,
2
2JPH = 63.7 Hz, 1H, MoH), ꢀ5.75 (d, JPH = 63.7 Hz, 1H, MoH). 13C
NMR (toluene-d8, 100 °C, d, ppm): 141.3 (i-C6H5), 130.0 (o-C6H5),
128.7 (m-C6H5), 126.7 (p-C6H5), 109.7 (C5Bz5), 34.4 (CH2Ph), 23.7
1
(d, JPC = 29.8 Hz, PMe3). 31P NMR (toluene-d8, - 100 °C, d, ppm):
14.4 (s, PMe3). IR (KBr pellet): mC„O 1915, 1819 cmꢀ1. Anal. Calc.
for C45H45O2PMo: C, 72.57; H, 6.09. Found: C, 72.44; H, 6.32%.
BFꢀ4 ). 19F NMR (CD3CN, d, ppm): ꢀ150.6 (br, BFꢀ). IR (KBr pellet):
4
4.3. [WHCpBz(CO)2(PMe3)] (2)
m
CꢃO 2070, 1993, 1976 cm-1
;
m
CꢃN 2321, 2289 cmꢀ1
;
m
BF4 1054 cmꢀ1
.
A 1 M solution of PMe3 in toluene (1.0 mL, 1.00 mmol) was
added dropwise to
4.6. General procedures for electrochemistry
a
solution of [WHCpBz(CO)3] (0.805 g,
1.03 mmol) (25 mL) in the same solvent. The solution was refluxed
overnight. The solvent was evaporated under vacuum and the res-
idue obtained was extracted in diethyl ether. Removal of the sol-
vent afforded a brown solid that was extracted in Et2O. The
extract was filtered, concentrated and cooled to ꢀ20 °C to afford
yellow crystals (0.685 g, 0.82 mmol, yield 80%). 1H NMR (tolu-
ene-d8, 25 °C, d, ppm): 6.90–6.87 (m, 15H, p-C6H5, m-C6H5), 6.75–
Cyclic voltammetric and controlled potential coulometry mea-
surements were carried out using a Radiometer DEA 101 Digital
Electrochemical Analyser interfaced with an IMT 102 Electrochem-
ical Interface. For cyclic voltammetry measurements a three-elec-
trode cell with a total volume of around 5 mL was used. A
Platinum disc
= 3.0 mm) were used as working electrodes, the counter-elec-
trode was a Pt wire and a silver wire was used as a pseudo-refer-
ence electrode; this electrode was kept in separate
(U = 1.5 mm) or vitreous carbon electrodes
(U
2
6.72 (m, 10H, o-C6H5), 3.83 (s, 10H, CH2Ph), 1.31 (d, JPH = 8.8 Hz,
2
2
9H, PMe3), ꢀ7.00 (dt, JPH = 73.6 Hz, JWH = 24.9 Hz, 1H, WH). 13C
NMR (toluene-d8, 25 °C, d, ppm): 140.8 (i-C6H5), 129.6 (o-C6H5),
128.5 (m-C6H5), 126.5 (p-C6H5), 108.0 (C5Bz5), 34.1 (CH2Ph), 24.4
a
compartment and connected to the main compartment by a Luggin
capillary. The ferrocene/ferrocenium couple was used as internal
standard to measure wave potentials, according to IUPAC recom-
mendations [70].
The controlled potential electrolysis electrochemical cell had a
three compartment design. A large platinum gauze electrode was
employed as working electrode. The pseudo-reference electrode
was similar to the one used for cyclic voltammetry measurements
1
(d, JPC = 34.4 Hz, PMe3). 31P NMR (toluene-d8, 25 °C, d, ppm):
1
ꢀ20.8 (t, JWP = 125.2 Hz, PMe3). 1H NMR (toluene-d8, ꢀ80 °C, d,
ppm): 6.92 (br, 15H, p-C6H5, m-C6H5), 6.58–6.56 (br m, 10H, o-
2
C6H5), 3.83 (br, 10H, CH2Ph), 1.18 (br d, JPH = 8.3 Hz, 9H, PMe3),
2
2
ꢀ6.52 (d, JPH = 22.6 Hz, 1H, trans-WH), ꢀ6.85 (dt, JPH = 72.7 Hz,
1JWH = 25.3 Hz, 1H, cis-WH). 13C NMR (toluene-d8, ꢀ80 °C, d,

M.A. Antunes et al. / Journal of Organometallic Chemistry 695 (2010) 1328–1336
1335
and it was also connected to the main compartment by a Luggin
capillary. The counter electrode was also a platinum gauze elec-
trode and it was kept in a different compartment which was con-
nected to the main compartment by a sintered glass.
Concentrations of electrolyte around 0.2 M were used for cyclic
voltammetry and 0.3 M for electrolysis experiments. Concentra-
tions around 3 ꢄ 10ꢀ3 M (for electrolysis experiments) and around
1.2 ꢄ 10ꢀ3 M (for cyclic voltammetry) were used for the complexes
being studied. All experiments were carried out at 25 °C in the ab-
sence of oxygen. Dry nitrogen was bubbled through the solution in
the cell before all the measurements.
checking the intensity of the following fragments: m/e = 2
(H2), = 18 (H2O), = 28 (N2), = 32 (O2), = 44 (Ar).
4.8. Electrolyses of [MoHCpBz(CO)2(PMe3)]. Identification of
[MoCpBz(CO)2(PMe3)(CH3CN)]PF6
The controlled potential electrolysis of 1 was carried out in
CH3CN/Bu4NPF6. After the end of the experiment the mixture
was evaporated to dryness and the solid obtained was extracted
in CH2Cl2 and filtered. The product was obtained from this solution
upon concentration and addition of Et2O. 1H NMR (C6D6): d 6.86–
6.84 (m, 15H, p-C6H5, m-C6H5), 6.74–6.72 (m, 10H, o-C6H5), 3.64
2
2
(d, JPH = 4 Hz, 10H, CH2Ph), 2.16 (d, JPH = 4 Hz, 3H, CH3CN), 1.48
2
(d, JPH = 8 Hz, 9H, PMe3); 1H NMR (CD3CN): d 7.00–6.97 (m, 15H,
4.7. Electrolyses of [MoHCpBz(CO)3]. Identification of H2
p-C6H5, m-C6H5), 6.74-6.71 (m, 10H, o-C6H5), 3,78 (s, 10H, CH2Ph),
2
1.71 (d, JPH = 9.7 Hz, 9H, PMe3); 13C NMR d: 139.0 (i-C6H5), 129.9
The controlled potential electrolysis of 5 was carried out in
CH3CN/Bu4NPF6. After the end of the experiment, a gas phase anal-
ysis was performed with a mass detector (QMS 200 from Balzers),
(o-C6H5), 129.1 (m-C6H5), 127.4 (p-C6H5), 113.3 (C5Bz5), 33.1
(CH2Ph), 16.3 (d, JPC = 30.3 Hz, P(CH3)3). 31P NMR, d 3.93 (PMe3).
IR m .
CO: 1972, 1894 cmꢀ1
Table 4
4.9. X-ray diffraction experimental determination
Crystal data and structure refinement for 1, 2 and 3.
[MoCpBz(CO)2
(PMe3)H] 1
[WCpBz(CO)2
(PMe3)H] 2
[MoCpBz(CO)2
(PPh3)H] 3
Crystallographic and experimental details of crystal structure
determinations are listed in Table 4. Crystals were selected, cov-
ered with polyfluoroether oil, and mounted on a nylon loop. Data
Formula
Formula
weight
T (K)
Mo C45 H45 O2
744.72
P
W C45 H45 O2
832.63
P
Mo C43 H36 O3
1005.04
was collected using graphite monochromated Mo K
a radiation
(k = 0.71073 Å) on a Bruker AXS-KAPPA APEX II diffractometer
equipped with an Oxford Cryosystems open-flow nitrogen cryo-
stat, at 150 K. Cell parameters were retrieved using Bruker SMART
software and refined using Bruker SAINT on all observed reflections
[71]. Absorption corrections were applied using SADABS [72]. Struc-
ture solution and refinement were performed using direct methods
with the programs SIR97 [73] and SHELXL [74] both included in the
package of programs WINGX-Version 1.70.01 [75]. For compound 2,
the poor diffracting power, prevented the anisotropic refinement
of all the non-hydrogen atoms. This refinement would lead to a
very poor ratio of ‘‘number of refined parameters/number of reflec-
tions” thus preventing a good, stable and reliable refinement. So
only W, P, O and C atoms (of CO and PCH3 groups) were refined
anisotropically. All hydrogen atoms, except the hydrides H atom,
were inserted in idealized positions and allowed to refine riding
in the parent carbon atom. Figures were generated using ORTEP3
[76]. Data was deposited in CCDC under the deposit numbers CCDC
751582, 751583, 751584 for 1, 2 and 3, respectively.
150(2)
0.71073
Crystal system monoclinic
298(2)
0.71073
150(2)
k (Å)
0.71073
triclinic
monoclinic
P21/c
19.888(3)
16.866(2)
11.0510(17)
ꢀ
Space group
a (Å)
b (Å)
c (Å)
P21/c
P1
19.9588(3)
16.8617(5)
11.1062(6)
12.891(2)
14.264(2)
15.030(3)
101.098(7)
105.920(8)
95.604(7)
2574.7(8)
2
a
(°)
b (°)
96.945(2)
97.085(5)
c
(°)
V (Å3)
3710.2(2)
4
1.333
0.433
3678.5(10)
4
1.503
3.221
Z
DCalc. (g cmꢀ3
Absorption
)
1.296
0.333
coefficient
(mmꢀ1
F(0 0 0)
Crystal size
(mm)
)
1552
0.2 ꢄ 0.2 ꢄ 0.2
1680
0.2 ꢄ 0.2 ꢄ 0.2
1052
0.05 ꢄ 0.10 ꢄ 0.20
Crystal
morphology
cube
cube
prism
Colour
yellow
yellow
yellow
h (°)
Limiting
indices
1.03–31.71
ꢀ29 6 h 6 29;
ꢀ24 6 k 6 23;
ꢀ16 6 l 6 16
55443/12353
(0.0581)
1.59–19.87
ꢀ18 6 h 6 18;
ꢀ15 6 k 6 15;
ꢀ10 6 l 6 10
15051/3287
(0.0934)
1.45–26.55
ꢀ16 6 h 6 16;
ꢀ17 6 k 6 17;
ꢀ18 6 l 6 18
40253/10521
(0.0919)
Acknowledgements
The authors are grateful to Fundação para a Ciência e a Tecno-
logia, Portugal, for funding (PPCDT/QUI/55744/2004, PTDC/QUI/
66187/2006 and SFRH/BPD/26745/2006)
Reflections
collected/
unique
(Rint
)
Appendix A. Supplementary material
Completeness
to h
98.1% (h = 31.71°) 97.6% (h = 19.87°) 98.2% (h = 26.55°)
Refinement
method
Data/
restraints/
parameters
full-matrix least-
squares on F2
12353/0/446
full-matrix least-
squares on F2
3287/54/247
full-matrix least-
squares on F2
10521/0/626
CCDC 751582, 751583, 751584 contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2010.02.012.
Goodness of fit 1.074
0.986
1.019
on F2
Final R indices
[I > 2 (I)]
R1 = 0.0473,
R1 = 0.0542,
wR2 = 0.1313
R1 = 0.0852,
wR2 = 0.1450
1.988 e–1.459
R1 = 0.0526,
wR2 = 0.1140
R1 = 0.0949,
wR2 = 0.1478
0.486 e–0.996
r
wR2 = 0.1130
R1 = 0.0774,
wR2 = 0.1296
3.099 e–0.889
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