Synthesis and reactivity of oxametallacyclic niobium compounds by using α,β-unsaturated carbonyl ligands

Article abstract of DOI:10.1002/ejic.200800060

Reduction of mono(cyclopentadienyl)niobium complexes [NbCp ^RCl₄] [Cp^R = C₅Me₄H (1), C₅H₄SiMe₂Cl (2), C₅H ₄SiMe₃ (3)] with Na/Hg in the presence of methyl methacrylate [MMA, CH₂=C(Me)C(O)OMe (a)], methyl acrylate [MA, CH₂=CHC(O)OMe (b)] and mesityl oxide [MO, CMe₂=CHC(O)Me (c)] afforded the corresponding derivatives [NbCp^RCl₂(LL)] [Cp^R = C₅Me₄H, LL = MMA (1a); Cp^R = C₅H₄SiMe₂Cl, LL = MMA (2a), MA (2b), MO (2c); Cp^R = C₅H₄SiMe₃, LL = MMA (3a), MA (3b)] in variable yields depending on both the cyclopentadienyl and the α,β-unsaturated carbonyl compounds. The reactivity of these complexes was studied toward protic and Lewis acids. Addition of triflic acid TfOH (Tf = CF₃SO₂) to 3b gave the triflate complex [NbCp ^RCl₂{(CH₂)₂C(O)OMe}(OTf)] [Cp ^R = C₅H₄SiMe₃ (4)]. The Lewis acids E(C₆F₅)₃ (E = B, Al) reacted with complexes 2b and 3b to give the three-membered metallacyclic (or η²-enone) compounds [NbCp^RCl₂{η²-CH ₂=CHC(OMe){O· E(C₆F₅)₃}}] [Cp^R = C₅H₄SiMe₂Cl, E = B (5), Al (6); CpR = C₅H₄SiMe₃, E = B (7), Al (8)], which decomposed to the corresponding adducts MA·E(C₆F ₅)₃. The same reaction with the 2a and 3a derivatives only allowed the observation of the corresponding adducts MMA·E(C ₆F₅)₃. Complexes 2a,b and 3a,b reacted with CO with elimination of the acrylate compounds, MA and MMA, respectively, to give the carbonylniobium(III) compounds [NbCp^RCl₂(CO) ₂]₂ [Cp^R = C₅H₄Si-Me ₂Cl (9), C₅H₄SiMe₃ (10)]. Analogous reactions with CNAr showed the elimination of the free MA and MMA compounds. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800060

FULL PAPER
DOI: 10.1002/ejic.200800060
Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using
α,β-Unsaturated Carbonyl Ligands
Rocío A. Arteaga-Müller,[a] Javier Sánchez-Nieves,[a] Pascual Royo,*[a] and
Marta E. G. Mosquera[a][‡]
Dedicated to Prof. Dr. W. Herrmann on the occasion of his 60th birthday
Keywords: Niobium / Cyclopentadienyl ligands / Diene ligands / Metallacycles / Acrylate ligands
Reduction of mono(cyclopentadienyl)niobium complexes
[NbCpRCl4] [CpR
C5Me4H (1), C5H4SiMe2Cl (2),
2b and 3b to give the three-membered metallacyclic (or η2-
enone) compounds
[NbCpRCl2{η2-CH2=CHC(OMe){O·
E(C6F5)3}}] [CpR = C5H4SiMe2Cl, E = B (5), Al (6); CpR
=
C5H4SiMe3 (3)] with Na/Hg in the presence of methyl meth-
acrylate [MMA, CH2=C(Me)C(O)OMe (a)], methyl acrylate
[MA, CH2=CHC(O)OMe (b)] and mesityl oxide [MO,
CMe2=CHC(O)Me (c)] afforded the corresponding deriva-
tives [NbCpRCl2(LL)] [CpR = C5Me4H, LL = MMA (1a); CpR
=
C5H4SiMe3, E = B (7), Al (8)], which decomposed to the corre-
sponding adducts MA·E(C6F5)3. The same reaction with the
2a and 3a derivatives only allowed the observation of the
corresponding adducts MMA·E(C6F5)3. Complexes 2a,b and
3a,b reacted with CO with elimination of the acrylate com-
pounds, MA and MMA, respectively, to give the carbonylni-
obium(III) compounds [NbCpRCl2(CO)2]2 [CpR = C5H4Si-
Me2Cl (9), C5H4SiMe3 (10)]. Analogous reactions with CNAr
showed the elimination of the free MA and MMA com-
pounds.
= C5H4SiMe2Cl, LL = MMA (2a), MA (2b), MO (2c); CpR
=
C5H4SiMe3, LL = MMA (3a), MA (3b)] in variable yields de-
pending on both the cyclopentadienyl and the α,β-unsatu-
rated carbonyl compounds. The reactivity of these complexes
was studied toward protic and Lewis acids. Addition of triflic
acid TfOH (Tf = CF3SO2) to 3b gave the triflate complex
[NbCpRCl2{(CH2)2C(O)OMe}(OTf)] [CpR = C5H4SiMe3 (4)].
The Lewis acids E(C6F5)3 (E = B, Al) reacted with complexes
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
The bonding interaction of a butadiene ligand with a
metal center is clearly dependent on the metal atom and
may be formulated as a system containing a dianionic li-
gand for early high-valent transition metals or as a neutral
ligand for low-valent late transition metals. However, the
stability of the formal oxidation state of the metal atom and
the nature of the ancillary substituents of both the complex
and the diene ligand could play an important role in defin-
ing this interaction. Hence, complexes with this type of li-
gand are better represented with contributions from two
main canonical forms, σ2,π-metallacyclic or π2-butadiene
(Figure 1).[1–5]
Figure 1. σ2,π-Metallacyclic or π2-butadiene form.
Replacement of at least one of the terminal CR2 moieties
by an isolobal fragment such as NR, O, S, etc. induces an
important modification on the butadiene ligand.[6–11] Func-
tionalization with one oxygen atom provides an oxametalla-
cyclic system, which consists of a cyclic enolate ligand. The
study of enolate derivatives has attracted attention because
they have been proposed as the active species for polymeri-
zation of polar monomers.[11–16] Another feature of these
compounds is that coordination of the asymmetric α,β-un-
saturated carbonyl ligands will create two new reactive
points in the molecule at the M–C and M–O bonds.
[a] Departamento de Química Inorgánica, Universidad de Alcalá,
Campus Universitario,
28871 Alcalá de Henares (Madrid), Spain
Fax: 34-91-885-4683
E-mail: pascual.royo@uah.es
We describe herein the synthesis of mono(cyclopentadi-
enyl)niobium compounds by using different α,β-unsatu-
rated carbonyl ligands and their reactivity with Brönsted
[‡] X-ray diffraction studies
Supporting information for this article is available on the
WWW under http://www.eurjic.org/ or from the author.
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R. A. Arteaga-Müller, J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
FULL PAPER
and Lewis acids and with strong π-acceptor ligands such as
CO and CNAr.
The presence of the enolate ligand endows asymmetry to
all of the complexes for which the 1H NMR spectra showed
an ABCD spin system for the cyclopentadienyl ring protons
and methyl groups. The formation of the metallacyclic com-
pounds 1a–3a and 2b and 3b was supported by the low-
Results and Discussion
1
field signals observed in the H NMR spectra for the Nb–
Synthesis of Metallacyclic Compounds
CH2 group, shifted to δ ≈ 1.00 and 1.70 ppm from δ = 5–
6 ppm in the starting free acrylate ligands, and also ob-
served in the 13C NMR spectra shifted to δ ≈ 70 ppm with
respect to the free acrylate compounds (δ ≈ 130 ppm).
Moreover, for the MA complexes 2b and 3b the signal of
the internal C–H proton was observed at δ ≈ 5.0 ppm. The
The reduction of the niobium compound [NbCp*Cl4] in
toluene with Na/Hg amalgam in the presence of MMA has
been reported previously,[7] and we have applied this
method using the α,β-unsaturated carbonyl compounds
CH2=C(Me)C(O)OMe
(MMA),
CH2=CHC(O)OMe
1
coupling constant JC,H for the CH2 group of compounds
(MA), and CMe2=CHC(O)Me (MO) to isolate the new de-
rivatives [NbCpRCl2(LL)] [CpR = C5Me4H, LL = MMA
(1a); CpR = C5H4SiMe2Cl, LL = MMA (2a), MA (2b), MO
(2c); CpR = C5H4SiMe3, LL = MMA (3a), MA (3b)]
(Scheme 1). The whole process can be considered as a re-
duction of the metal center followed by the oxidative coup-
ling of the α,β-unsaturated carbonyl ligand. These com-
pounds were obtained in good yields for the MMA and
MA derivatives, whereas the unique isolated mesityl oxide
MO complex was obtained in rather poor yield, probably
because of the steric hindrance of the terminal Me2C group.
1a–3a showed a slight decrease consistent with the lower s
character of this carbon atom (J ≈ 150 Hz in 1a–3a, J =
159 Hz for free MMA), which was corroborated with the
2
geminal JH,H coupling constant of this group (J ≈ 7 Hz in
1a–3a, J = 2 Hz for free MMA). However, in compounds
1
2b–3b the JC,H coupling constant for the CH2 group re-
1
mained unchanged, although the increase of JC,H for the
internal carbon atom suggested higher s character (J ≈
180 Hz in 2b and 3b, J = 162 Hz for free MMA), consistent
with the metallacyclic disposition of the MA ligands. The
poor yield and the lack of purity of the mesityl oxide com-
pound 2c made its characterization by NMR and IR spec-
troscopy difficult, although its molecular structure was de-
termined by X-ray diffraction studies (vide infra) on a sin-
gle crystal.
The metallacyclic configuration was also supported by
the two absorption bands observed in the IR spectrum at
about 1515 and 750 cm–1 corresponding to ν(C=C) and
ν(Nb–O) bands, respectively.
A
similar low yield was reported for the related
[TaCp*Cl2(MO)] complex which was obtained from a CO/
MO exchange reaction.[17] It is remarkable that reduction
proceeded selectively at the niobium atom even in the case
of the (chlorosilyl)cyclopentadienyl-functionalized deriva-
tives.
X-ray Structure of 1a, 2a, and 2c
The X-ray structures of complexes 1a, 2a, and 2c (Fig-
ure 2, Table 1) were similar to those reported for other re-
lated complexes.[7,11,17] The MMA and MO ligands pre-
sented a supine coordination as expected for the disposition
of the five-membered metallacycle folded through the O–
C(1) vector, with a dihedral angle of about 103°, as in re-
lated oxametallacyclic tantalum compounds.
Scheme 1. (i) Na/Hg, toluene, C(R3)2 = C(R2)C(O)R1.
Figure 2. ORTEP diagram of complexes [NbCpRCl2(LL)] [CpR = C5Me4H, LL = MMA (1a); CpR = C5H4SiMe2Cl, LL = MMA (2a),
MO (2c)]. Hydrogen atoms have been omitted and thermal ellipsoids are shown at the 50% level.
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Oxametallacyclic Nb Compounds by Using α,β-Unsaturated Carbonyl Ligands
Table 1. Selected bond lengths [Å] and angles [°] of complexes 1a, 2a, and 2c.
1a
2a
2c
R3CC(R)=C(OR)R[18]
R2C=C(R)C(O)R[18]
Nb–C(1)
Nb–O(1)
Nb–C(2)
Nb–C(3)
O(1)–C(3)
C(2)–C(3)
C(1)–C(2)
Nb–O(1)–C(3)
Nb–C(1)–C(2)
Nb–LL[a]
2.194(7)
2.058(5)
2.388(7)
2.421(7)
1.309(9)
1.398(10)
1.464(10)
89.1(4)
2.209(4)
2.066(3)
2.364(4)
2.426(4)
1.310(5)
1.406(6)
1.446(6)
89.0(2)
2.319(4)
2.005(3)
2.424(5)
2.378(4)
1.364(5)
1.370(7)
1.463(3)
87.6(2)
1.340
1.360
1.512
1.222
1.475
1.340
78.7(4)
103.14
77.5(2)
102.21
76.0(3)
102.28
[a] Dihedral angle formed by O(1)–Nb–C(1) and O(1)–C(3)–C(2)–C(1) planes.
A comparison of the O–C and C–C bond lengths of the
coordinated MMA and MO ligands in complexes 1a, 2a,
and 2c with the corresponding average bond lengths of vi-
nyl ether and α,β-unsaturated carbonyl compounds
(Table 1)[18] showed that the O–C and the internal C–C
bond values are closer to a vinyl ether disposition (metall-
acycle), mainly for derivatives 1a and 2c, whereas the C(1)–
C(2) bond lengths present values intermediate between
these two situations. These parameter sets for complexes 1a
Scheme 2. Reaction of 3b with HOTf (Tf = CF3SO2).
and 2c are very similar to those observed for related com-
pounds [TaCp*Cl2(MMA)][11] and [TaCpCl2(MO)].[17]
The Nb–O bonds are longer than those found for (alkox-
ido)niobium compounds, although they are in the range ob-
served for five-membered alkoxido-metallacyclic deriva-
tives.[19] The distortion due to the formation of the metall-
acycle makes the Nb–O–C angles (about 88°) clearly more
acute than in alkoxido compounds (over 120°) preventing
the π-bonding contribution in the oxygen–niobium bond.
The Nb–C(terminal) bonds are slightly shorter than in re-
lated (butadiene)mono(cyclopentadienyl) complexes[2] for
compounds 1a and 2a and in the same range for complex
2c, in which the terminal carbon atom supports two methyl
groups. Finally, the Nb–C(internal) bond lengths are also
in the range observed for butadiene[2] and diazabutadiene
derivatives.[20]
atom favors stabilization of complex 4 increasing the elec-
tron count and preventing possible side-reactions due to the
β-hydrogen atoms of the new alkyl chain.[25–29] This pro-
posal was supported by NMR spectroscopy (see below) and
by comparison with the reported analogous tantalum deriv-
ative, which was isolated by transmetalation with a zinc
enolate compound.[29] Complex 4 was unstable in chlori-
nated solvents giving a mixture of unidentifiable com-
pounds. A change of solvent from CD2Cl2 to CDCl3 ac-
celerated this decomposition process. We were unable to re-
produce this reaction on a preparative scale neither in these
solvents nor by employing alternative solvents.
The higher nucleophilicity of alkoxido compared with
methyl and chlorido ligands may justify the preferential
protonolysis of the Nb–O bond. The formation of the five-
membered ring may prevent the π-bonding contribution to
the Nb–O bond due to the close Nb–O–C angle, which
would increase the nucleophilicity of this alkoxido group
Reaction with Triflic Acid HOTf (Tf = CF3SO2)
Complexes 1–3 present three nucleophilic centers that that is sterically less protected with respect to the more lin-
can react with protic acids: the Nb–Cl,[21–24] the Nb–C[24]
and the oxametallacyclic Nb–O[19] bonds. It would be rea-
,
ear M–O–C bond angle in related alkoxido complexes.
Formation of the Cs-symmetric compound 4 was in
sonable to expect that the Nb–C bond should be the most agreement with the AAЈBBЈ pattern observed in the 1H
reactive one toward protonolysis due to its lower bond en- NMR spectrum for the cyclopentadienyl ligand. The new
ergy, the higher energy of the resulting C–H bond, and the alkyl chain bonded to the Nb center was confirmed by the
higher nucleophilic character of the niobium-bonded alkyl 1H NMR spectrum that shows two multiplets at δ = 1.90
carbon atom. However, addition of 1 equiv. of HOTf to the and 3.39 ppm corresponding to the Nb–CH2 group and the
acrylate compound 3b led to the alkyl ester derivative new internal CH2 group. Also, the generation of this new
[NbCpRCl2{(CH2)2C(O)OMe}(OTf)] [CpR = C5H4SiMe3 CH2 group was supported by a 2-D HSQC-NMR experi-
(4)] (Scheme 2).
ment. Finally, the presence of the ester moiety coordinated
This compound was formed by protonolysis of the Nb– to the metal atom was confirmed by a resonance observed
O bond followed by the keto-enol transformation through at δ = 194.8 ppm in the 13C NMR spectrum, which was
proton migration in the generated enol intermediate to give shifted downfield with respect to this carbon signal in or-
complex 4. Coordination of the carbonyl group to the Nb ganic esters (δ ≈ 170 ppm). This formulation was confirmed
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R. A. Arteaga-Müller, J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
FULL PAPER
by comparison with the related tantalum compound NMR spectra. We believe that the metal center was reduced
[TaCp*Cl3{CH2CH2C(O)OMe}], for which the X-ray mo- from NbV to NbIII as a consequence of the loss of the buta-
lecular structure has been reported.[29]
diene ligand and the absence of oxidizing agents. Again, the
The same reaction with compounds 2a, 2b, and 3a and interaction of the Lewis acids with the Nb–O bond rather
related reactions employing HCl as the Brönsted acid led than the Nb–C bond could be attributed to the bent Nb–
to decomposition of the starting materials, whereas none O–C angle.
of these compounds reacted with the related Lewis acids
Complexes 5–8 are best described in terms of contri-
butions from two canonical forms, as a metallacycle–olefin
formulation, consistent with the spectroscopic data that
[Me3O][BF4] and (Me3Si)OTf.[30]
supported
a
metallacyclic NbV complex formulation,
Reaction with the Lewis Acids E(C6F5)3 (E = B, Al)
whereas their instability toward decomposition releasing the
MMA·E(C6F5)3 and MA·E(C6F5)3 adducts corresponds
better with an NbIII metal compound with a coordinated
η2-enone ligand.
The reaction of B(C6F5)3 with butadiene compounds has
been reported to give betaine derivatives by rupture of the
M–C bond.[4,8,31] We have investigated the reactivity of
complexes 2a–b and 3a–b with the Lewis acids E(C6F5)3 (E
= B, Al) with the aim of abstracting the alkyl ligand to
generate a cationic enolate compound, considering that
early transition-metal derivatives of this type have been
used as precursors for the catalytic polymerization of acry-
lates.[12–16] Although the nucleophilicity of the oxygen atom
bonded to the niobium atom could compete with that of
the carbon atom, we have previously observed that alkoxido
complexes of the type [Cp*TaMe3(OR)] reacted with these
Lewis acids E(C6F5)3 at the Ta–C bond.[32] Furthermore,
Mashima and co-workers also reported that reaction of the
MMA complex [TaCp*(DAD)(MMA)] [DAD = N(R)
CH=CHN(R)] with AlMe3 produced the activation of the
Ta–C bond of the coordinated MMA ligand.[11]
Addition of 1 equiv. of E(C6F5)3 (E = B, Al) to com-
pounds 2b and 3b gave the three-membered metallacyclic
compounds [NbCpRCl2{η2-CH2=CHC(OMe){O·E(C6F5)3}}]
[CpR = C5H4SiMe2Cl, E = B (5), Al (6); CpR = C5H4SiMe3,
E = B (7), Al (8)] (Scheme 3). These complexes evolved
slowly at ambient temperature releasing the corresponding
adducts MA·E(C6F5)3. When the same reaction was carried
out with the MMA derivatives 2a and 3a, no intermediates
were observed, only the formation of the respective adducts
MMA·E(C6F5)3 was detected. The rate of this transforma-
tion was faster for the more oxophilic compound Al-
(C6F5)3. Unfortunately, we could not isolate or characterize
the organometallic species in any of these experiments;
broad signals were observed in the MeSi region of the
This type of η2-enone complex with the oxygen atom of
the carbonyl group coordinated to a Lewis acid has been
reported for Pd and Pt, although in the starting compounds
the α,β-unsaturated carbonyl ligand was η2-coordinated
through the terminal C–C double bond.[30,33,34]
The most-striking feature of the 13C NMR spectrum is
the signal observed at δ ≈ 185 ppm for the new carbonyl
group. The 13C NMR spectra showed the resonances due
to the Nb-bonded carbon atoms shifted to low field, corre-
sponding to the formation of a strained three-membered
metallacyclic system,[28,35] with the 1JC,H value observed for
these carbon atoms decreased from ca. 180 Hz [C–C(O)]
and ca. 160 Hz (CH2) to ca 160 Hz and ca. 150 Hz, respec-
tively. The 19F NMR spectra were also in agreement with
the formation of adducts of the type R2CO·E(C6F5)3. The
generation of the carbonyl group was confirmed by the ab-
sorption band observed at 1640 cm–1 in the IR spectra.
Reaction with CO and CNAr (Ar = 2,6-Me2C6H3)
Following on from our study on the chemical behavior
of the oxametallacyclic system, we carried out the reaction
of the starting compounds 2a, 2b, 3a, and 3b with CO and
CNAr, for which the ability to be inserted into σ-M–C
bonds is well documented.[36–40] However, the insertion re-
action was not observed, rather displacement of the coordi-
nated MMA and MA ligands (Scheme 4) gave the carbonyl
derivatives [NbCpRCl2(CO)2]2 [CpR = C5H4SiMe2Cl (9),
CpR = C5H4SiMe3 (10)] for the reaction with CO, although
we could not characterize the corresponding organometallic
species resulting from the reaction with CNAr (Scheme 4).
Scheme 3. Reaction of complexes 2–3 [R = Me (a), H (b)] with
E(C6F5)3 (E = B, Al).
Scheme 4. Reaction of complexes 2–3 [R = Me (a), H (b)] with (i)
CNAr (Ar = 2,6-Me2C6H3), (ii) CO.
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Oxametallacyclic Nb Compounds by Using α,β-Unsaturated Carbonyl Ligands
Therefore, the formally NbV starting compounds 2–3 un- gands LL to the NbIII species generated in situ by reduction
dergo a reductive decoupling to the NbIII derivatives. This of the NbV halides [NbCpRCl4] with Na/Hg. The NMR and
process is the reverse of the procedure used for their synthe- crystallographic data supported the formulation of these
sis. This behavior is a demonstration of the weak Nb–O complexes as alkyl-alkoxido-metallacyclic rather than as
interaction of the coordinated ligands, highlighting the ten- butadiene species.
dency of Nb to reduce its oxidation state in the presence of
The reactivity of these complexes with Brönsted and
strong π-acceptor ligands. This type of complex has been Lewis acids is controlled by the higher nucleophilicity of
previously synthesized by reduction of [NbCpRCl4] in the the oxygen atom compared with that of the metallacyclic
presence of CO.[41–43]
carbon atom, because of the closely bent Nb–O–C angle,
The IR and NMR spectroscopic data for compounds 9– which probably does not allow strong π-bonding of the oxy-
10 were analogous to those reported for related com- gen atom free pairs with the metal atom and also makes
plexes[41–43] and the molecular structure of complex 10 was this oxygen atom easily accessible. However, the different
confirmed by X-ray diffraction studies on an appropriate nature of both types of acid employed showed two different
single crystal (Figure 3).
transformations. Thus, whereas protonation of the Nb–O
bond with TfOH gives an enol intermediate which evolves
to give an alkyl ester derivative, addition of the Lewis acids
E(C6F5)3 (E = B, Al) generated a new three-membered
metallacyclic system by reforming the α,β-unsaturated car-
bonyl ligands which remained coordinated by the terminal
C=C double bond. This interaction was not stable enough,
and their evolution to give the adducts MMA·E(C6F5)3 and
MA·E(C6F5)3 was observed, implying a reduction of the
metal center.
Finally, addition of CO and CNAr produced the re-
ductive decoupling and displacement of the coordinated
α,β-unsaturated carbonyl ligands to give the NbIII com-
plexes demonstrating the important contribution of the bu-
tadiene-like canonical form.
Figure 3. ORTEP diagram of [NbCpRCl2(CO)2]2 [CpR = C5H4Si-
Me2Cl (10)]. Hydrogen atoms have been omitted and thermal ellip-
soids are shown at the 50% level. Selected bond lengths [Å] and
angles [°]: Nb(1)–Cl(1) 2.6266(7), Nb(1)–Cl(3) 2.5103(7), Nb(1)–
C(7) 2.132(2), C(7)–O(7) 1.141(4); Nb(1)–C(6)–O(6) 176.9(2),
Nb(1)–C(7)–O(7) 178.8(2), Nb(1)–Cl(1)–Nb(2) 101.92(2).
Experimental Section
General Considerations: All manipulations were carried out under
argon, and solvents were purified from appropriate drying agents.
NMR spectra were recorded at 400.13 (1H), 376.70 (19F), and
100.60 (13C) MHz with a Bruker AV400 spectrometer. Chemical
shifts (δ) are given in ppm using C6D6 as solvent, unless otherwise
stated. 1H and 13C resonances were measured relative to solvent
peaks considering δ(TMS) = 0 ppm, whereas 19F resonances were
measured relative to external CFCl3. Assignment of resonances was
made from HMQC and HMBC NMR experiments. Elemental
analyses were performed with a Perkin–Elmer 240C spectrometer.
The molecular structure of complex 10 corresponds to a
dimetallic system with both niobium atoms hexacoordinate,
assuming that the cyclopentadienyl ligand occupies only
one coordination position. The carbonyl ligands are located
in equatorial positions, one chlorido ligand in an apical po-
sition trans to the cyclopentadienyl group, and the other
two positions correspond with two bridging chlorido sub-
stituents. The substituents on one metal atom present a
trans disposition with respect to the substituents on the
other niobium atom. The Nb–Cl(bridge) bonds are about
0.1 Å longer than the Nb–Cl(terminal) bonds. The terminal
carbonyl ligands are linear with Nb–C–O bond angles of
176.9(2)° and 178.8(2)°. All these bond lengths and angles
are similar to those reported in the literature.[41–43]
Compounds C5Me4H(SiMe3),[44] [NbCpRCl4] (CpR = C5H4Si-
Me2Cl,[21] C5H4SiMe3[23]), B(C6F5)3
,
and 0.5(toluene)·
[45]
[46]
Al(C6F5)3
were prepared according to literature methods. The
α,β-unsaturated carbonyl compounds C(R3)2=C(R2)C(O)R1 were
purchased from Aldrich, dried with CaH2, distilled under vacuum,
and stored under an inert gas prior to use. HOTf (Tf = CF3SO2)
from Aldrich was used without further purification.
[Nb(η5-C5Me4H)Cl4] (1): C5Me4H(SiMe3) (2.88 g, 14.80 mmol) in
toluene (20 mL) was added to a solution of [NbCl5] (4.0 g,
14.80 mmol) in toluene/CH2Cl2 (100:50 mL). The reaction mixture
was further stirred for 6 h, after which the volume was concentrated
under vacuum to ca. 30 mL. The solution was cooled to –40 °C
overnight yielding 1 as a red solid (2.00 g, 38%). 1H NMR (C6D6):
δ = 1.80 (s, 6 H, C5Me4H), 2.00 (s, 6 H, C5Me4H), 5.69 (s, 1 H,
C5Me4H) ppm. 13C NMR (C6D6): δ = 13.9 (C5Me4H), 16.7
(C5Me4H), 123.8 (CH, C5Me4H), 137.1 (CMe, C5Me4H), 138.5
(CMe, C5Me4H) ppm. C9H13Cl4Nb (355.92): calcd. C 30.37, H
Conclusions
Compounds of the type [NbCpRCl2(LL)] [CpR
=
C5Me4H, LL = MMA (1a); CpR = C5H4SiMe2Cl, LL =
MMA (2a), MA (2b), MO (2c); CpR = C5H4SiMe3, LL =
MMA (3a), MA (3b)] were obtained by reactions based on
the oxidative addition of the α,β-unsaturated carbonyl li- 3.68; found C 29.95, H 3.30.
Eur. J. Inorg. Chem. 2008, 2313–2320
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2317

R. A. Arteaga-Müller, J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
FULL PAPER
[Nb(η5-C5Me4H)Cl2(LL)] [LL = MMA (1a)]: A solution of [Nb(η5-
C5Me4H)Cl4] (1) (1.00 g, 2.81 mmol) and CH2=C(Me)C(O)OMe
(MMA) (0.30 g, 3.0 mmol) in toluene (30 mL) was added to 10%
Na/Hg amalgam (0.130 g, 5.62 mmol), and the mixture was stirred
overnight. The solution was filtered, concentrated to ca. 15 mL and
cooled to –40 °C to yield 1a as green crystals (0.52 g, 48%). 1H
NMR: δ = 0.80 (d, J = 6.3 Hz, 1 H, Nb-CH2), 1.58 (d, J = 6.3 Hz,
1 H, Nb-CH2), 1.76 (s, 3 H, C5Me4H), 1.80 (s, 3 H, C5Me4H), 1.87
(s, 3 H, C5Me4H), 2.05 (s, 3 H, C5Me4H), 2.40 (s, 3 H, CH2-CMe),
3.40 (s, 3 H, OMe), 5.79 (s, 1 H, C5Me4H) ppm. 13C{1H} NMR: δ
= 11.3 (C5Me4H), 13.2 (C5Me4H), 13.4 (C5Me4H), 13.9 (C5Me4H),
15.9 (CH2-CMe), 53.9 (OMe), 72.5 (Nb-CH2), 86.9 (CH2-CMe),
116.1 (C5Me4H), 122.2 (C5Me4H), 122.3 (C5Me4H), 123.6
(C5Me4H), 125.6 (C5Me4H), 160.5 (MeOC) ppm. C14H21Cl2NbO2
(385.13): calcd. C 43.66, H 5.50; found C 43.45, H 5.25.
72.0 (Nb-CH2), 88.3 (CH2-CMe), 118.5 (C5H4), 122.1 (C5H4),
122.2 (C5H4), 124.1 (C5H4), 127.9 (C5H4), 160.8 (MeOC) ppm.
C13H21Cl2NbO2Si (401.20): calcd. C 38.92, H 5.28; found C 38.72,
H 5.20.
[Nb(η5-C5H4SiMe3)Cl2(LL)] [LL = MA (3b)]: The same procedure
described above for 1a was applied by using [Nb(η5-C5H4SiMe3)-
Cl4] (3) (1.00 g, 2.69 mmol) and CH2=C(H)C(O)OMe (MA)
1
(0.24 g, 2.80 mmol) to give 3b as a brown solid (0.89 g, 86%). H
NMR: δ = 0.26 (s, 9 H, SiMe3), 1.09 (m, 1 H, Nb-CH2), 1.97 (m,
1 H, Nb-CH2), 3.35 (s, 3 H, OMe), 5.05 (m, 1 H, CH2-CH), 5.80
(m, 1 H, C5H4), 6.27 (m, 1 H, C5H4), 6.55 (m, 1 H, C5H4), 6.70
(m, 1 H, C5H4) ppm. 13C{1H} NMR: δ = –0.5 (SiMe3), 54.7 (OMe),
68.3 (Nb-CH2), 76.2 (CH2-CH), 119.3 (C5H4), 121.5 (C5H4), 125.3
(C5H4), 125.6 (C5H4), 127.9 (C5H4), 166.0 (MeOC) ppm.
C12H19Cl2NbO2Si (387.18): calcd. C 37.23, H 4.95; found C 37.20,
H 5.00.
[Nb(η5-C5H4SiMe2Cl)Cl2(LL)] [LL = MMA (2a)]: The same pro-
cedure described above for 1a was applied by using [Nb(η5-C5H4Si-
Me2Cl)Cl4] (2) (1.00 g, 2.54 mmol) and CH2=C(Me)C(O)OMe
(MMA) (0.27 g, 2.70 mmol) to give 2a as a brown solid (0.91 g,
85%). 1H NMR: δ = 0.65 (s, 3 H, SiMe2Cl), 0.71 (s, 3 H, SiMe2Cl),
1.15 (d, J = 9.9 Hz, 1 H, Nb-CH2), 1.81 (d, J = 9.9 Hz, 1 H, Nb-
CH2), 2.33 (s, 3 H, CH2-CMe), 3.28 (s, 3 H, OMe), 5.86 (m, 1 H,
C5H4), 6.10 (m, 1 H, C5H4), 6.53 (m, 2 H, C5H4) ppm. 13C{1H}
NMR: δ = 2.3 (SiMe2Cl), 2.5 (SiMe2Cl), 15.8 (CH2-CMe), 54.4
(OMe), 71.9 (Nb-CH2), 88.2 (CH2-CMe), 119.1 (C5H4), 120.3
(C5H4), 121.0 (C5H4), 124.3 (C5H4), 125.6 (C5H4), 161.4 (MeOC)
ppm. C12H18Cl3NbO2Si (421.62): calcd. C 34.18, H 4.30; found C
34.05, H 4.25.
Reaction of 3b with Triflic Acid HOTf (Tf = CF3SO2): A teflon-
valved NMR tube was charged with a solution of [Nb(η5-
C5H4SiMe3)Cl2(LL)] [LL = MA (3b)] (0.015 g, 0.039 mmol) in
CD2Cl2, and HOTf was added (3.43 µL, 0.039 mmol). The reaction
was monitored by NMR spectroscopy, and the formation of
[NbCpRCl2{(CH2)2C(O)OMe}(OTf)] [CpR = C5H4SiMe3 (4)] was
observed as the only product. After 24 h at room temperature,
NMR spectroscopy showed decomposition of 4. 1H NMR
(CD2Cl2): δ = 0.38 (s, 9 H, SiMe3), 1.90 (m, 2 H, Nb-CH2), 3.39
(m, 2 H, CH2CO), 4.21 (s, 3 H, OMe), 6.97 (m, 2 H, C5H4), 7.18
(m, 2 H, C5H4) ppm. 13C{1H} NMR: δ = –0.3 (SiMe3), 40.2
(CH2CO), 57.3 (OMe), 65.6 (Nb-CH2), 117.3 (C5H4), 121.4 (C5H4),
125.5 (C5H4), 194.8 (MeOCO) ppm.
[Nb(η5-C5H4SiMe2Cl)Cl2(LL)] [LL = MA (2b)]: The same pro-
cedure described above for 1a was applied by using [Nb(η5-C5H4Si-
Me2Cl)Cl4] (2) (1.00 g, 2.54 mmol) and CH2=C(H)C(O)OMe (MA)
Reaction of Compounds 2a and 3a with E(C6F5)3 (E = B, Al): Tef-
lon-valved NMR tubes were charged with C6D6 solutions of
1
(0.23 g, 2.70 mmol) to give 2b as a brown solid (0.85 g, 82%). H
[NbCpRCl2(MMA)] [CpR
=
C5H4SiMe2Cl (2a), 0.015 g,
NMR: δ = 0.65 (s, 3 H, SiMe2Cl), 0.70 (s, 3 H, SiMe2Cl), 1.03 (m,
1 H, Nb-CH2), 1.88 (m, 1 H, Nb-CH2), 3.27 (s, 3 H, OMe), 5.00
(m, 1 H, CH2-CH), 5.83 (m, 1 H, C5H4), 6.08 (m, 1 H, C5H4),
6.54 (m, 2 H, C5H4) ppm. 13C{1H} NMR: δ = 1.9 (SiMe2Cl), 2.1
(SiMe2Cl), 54.5 (OMe), 62.6 (Nb-CH2), 76.2 (CH2-CH), 119.0
(C5H4), 121.5 (C5H4), 125.4 (C5H4), 125.6 (C5H4), 137.8 (C5H4),
166.0 (MeOC) ppm. C11H16Cl3NbO2Si (407.59): calcd. C 32.41, H
3.96; found C 32.50, H 4.00.
0.037 mmol; CpR = C5H4SiMe3 (3a), 0.015 g, 0.039 mmol] and
E(C6F5)3 (0.037 mmol for 2a, 0.039 mmol for 3a). The reactions
were monitored by NMR spectroscopy which indicated formation
[15]
of compounds MMA·E(C6F5)3 as the only characterizable com-
pounds.
Reaction of Compounds 2b and 3b with E(C6F5)3 (E = B, Al): Tef-
lon-valved NMR tubes were charged with C6D6 solutions of
[NbCpRCl2(MA)] [CpR = C5H4SiMe2Cl (2b), 0.015 g, 0.036 mmol;
CpR = C5H4SiMe3 (3b), 0.015 g, 0.038 mmol) and E(C6F5)3
(0.036 mmol for 2b, 0.038 mmol for 3b). The reactions were moni-
tored by NMR spectroscopy showing the formation of compounds
[NbCpRCl2{η2-CH2=CHC(OMe){O·E(C6F5)3}}] [CpR = C5H4Si-
Me2Cl, E = B (5), Al (6); CpR = C5H4SiMe3, E = B (7), Al (8)].
After several hours, decomposition of 5–8 and formation of the
adducts MA·E(C6F5)3 as the only characterizable compound were
observed. 5: 1H NMR: δ = 0.33 (s, 3 H, SiMe2Cl), 0.35 (s, 3 H,
SiMe2Cl), 2.29 (m, 1 H, CH2-CH), 2.49 (m, 1 H, Nb-CH2), 2.95
(m, 1 H, Nb-CH2), 3.49 (s, 3 H, OMe), 4.51 (m, 1 H, C5H4), 4.75
(m, 1 H, C5H4), 5.32 (m, 1 H, C5H4), 5.56 (m, 1 H, C5H4) ppm.
13C{1H} NMR: δ = 2.0 (SiMe2Cl), 2.1 (SiMe2Cl), 55.4 (OMe), 55.9
(CH2-CH), 67.6 (Nb-CH2), 119.5 (C5H4), 119.8 (C5H4), 122.1
(C5H4), 122.4 (C5H4), Cipso of C5H4 not observed, 134.9 (C6F5),
[Nb(η5-C5H4SiMe2Cl)Cl2(LL)] [LL = MO (2c)]: The same pro-
cedure described above for 1a was applied by using [Nb(η5-C5H4Si-
Me2Cl)Cl4] (2) (1.00 g, 2.54 mmol) and C(Me)2 = C(H)C(O)Me
(MO) (0.26 g, 2.70 mmol) to give 2c as a brown solid (0.17 g, 16%).
1H NMR: δ = 0.73 (s, 3 H, SiMe2Cl), 0.80 (s, 3 H, SiMe2Cl), 1.11
(s, 3 H, Nb-CMe2), 1.76 (s, 3 H, Nb-CMe2), 2.08 (s, 3 H, MeCO),
5.11 (s, 1 H, CMe2-CH), 5.66 (m, 1 H, C5H4), 5.85 (m, 1 H, C5H4),
6.48 (m, 1 H, C5H4), 6.67 (m, 1 H, C5H4) ppm. C13H20Cl3NbOSi
(419.65): calcd. C 37.21, H 4.80; found C 35.95, H 4.06. Because
of the low yield and solubility of this compound, we could not
obtain pure samples for an adequate 13C NMR spectrum and ele-
mental analysis, although single crystals appropriate for X-ray dif-
fraction studies were isolated.
[Nb(η5-C5H4SiMe3)Cl2(LL)] [LL = MMA (3a)]: The same pro-
cedure described above for 1a was applied by using [Nb(η5-
C5H4SiMe3)Cl4] (3) (1.00 g, 2.69 mmol) and CH2=C(Me)C(O)-
OMe (MMA) (0.28 g, 2.80 mmol) to give 3a as a brown solid
(0.89 g, 83%). 1H NMR: δ = 0.26 (s, 9 H, SiMe3), 1.21 (d, J =
138.8 (C6F5), 146.4 (C6F5), 149.6 (C6F5), 185.2 (MeOCO) ppm. 19
F
NMR: δ = –131.3 (m, 6 F, o-C6F5), –156.4 (m, 3 F, p-C6F5), –162.7
(m, 6 F, m-C F ) ppm. IR (C D ): ν = 1638 [ν(CO)] cm–1. 6: 1H
˜
6
5
6
6
NMR: δ = 0.30 (s, 3 H, SiMe2Cl), 0.35 (s, 3 H, SiMe2Cl), 2.35 (m,
6.6 Hz, 1 H, Nb-CH2), 1.88 (d, J = 6.6 Hz, 1 H, Nb-CH2), 2.36 (s, 1 H, CH2-CH), 2.60 (m, 1 H, Nb-CH2), 2.86 (m, 1 H, Nb-CH2),
3 H, CH2-CMe), 3.36 (s, 3 H, OMe), 5.80 (m, 1 H, C5H4), 6.31 (m, 3.49 (s, 3 H, OMe), 4.61 (m, 1 H, C5H4), 5.10 (m, 1 H, C5H4), 5.34
1 H, C5H4), 6.54 (m, 1 H, C5H4), 6.71 (m, 1 H, C5H4) ppm. (m, 1 H, C5H4), 5.53 (m, 1 H, C5H4) ppm. 13C{1H} NMR: δ = 2.1
13C{1H} NMR: δ = –0.7 (SiMe3), 15.2 (CH2-CMe), 54.7 (OMe),
(SiMe2Cl), 2.2 (SiMe2Cl), 56.2 (OMe), 57.0 (CH2-CH), 65.2 (Nb-
2318
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2313–2320

Oxametallacyclic Nb Compounds by Using α,β-Unsaturated Carbonyl Ligands
CH2), 119.2 (C5H4), 119.5 (C5H4), 121.4 (C5H4), 125.7 (C5H4), SiMe2Cl), 5.05 (m, 4 H, C5H4), 5.81 (m, 4 H, C5H4) ppm. 13C{1H}
Cipso of C5H4 not observed, 135.5 (C6F5), 138.8 (C6F5), 148.9
NMR: δ = –0.7 (SiMe2Cl), 102.7 (C5H4), 108.8 (C5H4), Cipso of
(C6F5), 152.1 (C6F5), 184.2 (MeOCO) ppm. 19F NMR: δ = –123.8
C5H4 not observed, 184.4 (CO) ppm. IR (nujol): ν = 2035, 1960
˜
(m, 6 F, o-C6F5), –153.1 (m, 3 F, p-C6F5), –161.7 (m, 6 F, m-C6F5) [ν(CO)] cm–1. C18H24Cl6Nb2O4Si2 (759.08): calcd. C 28.48, H 3.19;
1
ppm. IR (C D ): ν = 1638 [ν(CO)] cm–1. 7: H NMR: δ = 0.02 (s,
found C 29.48, H 3.00. 10: 1H NMR: δ = 0.01 (s, 18 H, SiMe3),
˜
6
6
9 H, SiMe3), 2.45 (m, 1 H, Nb-CH2), 2.62 (m, 1 H, Nb-CH2), 3.09 5.04 (m, 4 H, C5H4), 5.80 (m, 4 H, C5H4) ppm. 13C{1H} NMR: δ
(m, 1 H, CH2-CH), 3.51 (s, 3 H, OMe), 4.66 (m, 1 H, C5H4), 4.77
= –0.7 (SiMe3), 102.6 (C5H4), 108.7 (C5H4), Cipso of C5H4 not ob-
(m, 1 H, C5H4), 5.43 (m, 1 H, C5H4), 5.48 (m, 1 H, C5H4) ppm. served, 185.0 (CO) ppm. IR (nujol): ν = 2030, 1953 [ν(CO)] cm–1.
˜
13C{1H} NMR: δ = –1.1 (SiMe3), 55.1 (OMe), 56.0 (CH2-CH), 67.1 C20H26Cl4Nb2O4Si2 (714.22): calcd. C 33.66, H 3.67; found C
(Nb-CH2), 116.5 (C5H4), 117.1 (C5H4), 118.6 (C5H4), 119.5 (C5H4), 33.99, H 3.57.
Cipso of C5H4 not observed, 135.7 (C6F5), 139.1 (C6F5), 146.7
Single-Crystal X-ray Structure Determination of Compounds 1a, 2a,
2c, and 10: Suitable yellow single crystals of 1a, 2a, 2c, and 10 for
the X-ray diffraction study were selected (Table 2). The crystals
(C6F5), 149.9 (C6F5), 186.4 (MeOCO) ppm. 19F NMR: δ = –132.3
(m, 6 F, o-C6F5), –156.7 (m, 3 F, p-C6F5), –164.1 (m, 6 F, m-C6F5)
1
ppm. IR (C D ): ν = 1640 [ν(CO)] cm–1. 8: H NMR: δ = 0.01 (s,
˜
6
6
were placed on the top of a glass fiber using perfluoropolyether oil
and cooled to 150 K (1a and 2a) or 200 K (2c and 10). The crystals
were mounted on a Bruker–Nonius Kappa CCD single-crystal dif-
fractometer and the data collected using graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å). Multiscan[47] absorption correc-
tion procedures were applied to the data. The structures were
solved, using the WINGX package,[48] by direct methods
(SHELXS-97)[49] and refined by using full-matrix least squares
against F2 (SHELXL-97). All non-hydrogen atoms were anisotropi-
cally refined. Hydrogen atoms were geometrically placed and left
9 H, SiMe3), 2.45 (m, 1 H, CH2-CH), 2.64 (m, 1 H, Nb-CH2), 2.88
(m, 1 H, Nb-CH2), 3.51 (s, 3 H, OMe), 4.75 (m, 1 H, C5H4), 5.10
(m, 1 H, C5H4), 5.42 (m, 2 H, C5H4) ppm. 13C{1H} NMR: δ =
–1.2 (SiMe3), 56.0 (OMe), 57.3 (CH2-CH), 65.4 (Nb-CH2), 117.2
(C5H4), 117.4 (C5H4), 118.7 (C5H4), 119.5 (C5H4), Cipso of C5H4
not observed, 135.7 (C6F5), 138.9 (C6F5), 148.9 (C6F5), 152.0
(C6F5), 184.9 (MeOCO) ppm. 19F NMR: δ = –120.5 (m, 6 F, o-
C6F5), –153.0 (m, 3 F, p-C6F5), –161.5 (m, 6 F, m-C6F5) ppm. IR
(C D ): ν = 1647 [ν(CO)] cm–1.
˜
6
6
Reaction of Compounds 2–3 with CO: Teflon-valved NMR tubes riding on their parent atoms except for the hydrogen atom on C(2)
were charged with C6D6 solutions of [NbCpRCl2(LL)] [CpR
C5H4SiMe2Cl, LL = MMA (2a), 0.015 g, 0.037 mmol; LL = MA
=
in compound 2c. For 1c two independent molecules were observed
in the asymmetric unit. The crystal measured for 2c showed some
(2b), 0.015 g, 0.036 mmol; CpR = C5H4SiMe3, LL = MMA (3a), twinning and some positional disorder between the chlorine atom
0.015 g, 0.039 mmol; LL = MA (3b), 0.015 g, 0.038 mmol] and then
filled with CO. The reaction was monitored by NMR spectroscopy
showing the immediate formation of compounds [NbCpRCl2-
Cl(3) and one of the methyl groups [C(18)] bonded to the silicon
atom. Full-matrix least-squares refinements were carried out by mi-
2
2 2
nimizing Σw(Fo – Fc ) with the SHELXL-97 weighting scheme
(CO)2]2 [CpR = C5H4SiMe2Cl (9), C5H4SiMe3 (10)] and free MMA and stopped at shift/err Ͻ0.001. The final residual electron density
or MA. The C6D6 solution was layered with hexane (1 mL) to af-
ford crystals of complex 9 or 10. 9: H NMR: δ = 0.00 (s, 12 H,
maps showed no remarkable features. CCDC-674114 (1a), -674115
(2a), -674116 (2c), and -674117 (10) contain the supplementary
1
Table 2. Crystallographic data for 1a, 2a, 2c, and 10.[a]
1a
2a
2c
10
Empirical formula
Formula mass
C14H21Cl2NbO2
385.12
C12H18Cl3NbO2Si
421.61
C13H20Cl3NbOSi
419.64
C20H26Cl4Nb2O4Si2
714.20
Color/habit
Crystal size [mm]
Crystal system
Space group
green/prism
0.31ϫ0.27ϫ0.25
monoclinic
C2/c
green/prism
0.12ϫ0.12ϫ0.05
monoclinic
P21/n
dark green/prism
0.36ϫ0.20ϫ0.16
monoclinic
P21/c
dark orange/prism
0.31ϫ0.20ϫ0.17
triclinic
¯
P1
a [Å]
b [Å]
c [Å]
α [°]
34.914(4)
8.3580(5)
27.070(3)
90
127.220(8)
90
6.6776(10)
22.523(2)
10.8035(11)
90
90.055(8)
90
7.1060(12)
11.471(2)
22.148(3)
90
98.3030(13)
90
6.9633(8)
9.8648(13)
10.6684(17)
80.031(11)
81.956(12)
79.204(8)
704.60(17)
1
β [°]
γ [°]
V [Å3]
6290.4(11)
16
1624.9(3)
4
1786.4(5)
4
Z
T [K]
150(2)
1.627
1.100
150(2)
1.723
1.302
200(2)
1.560
1.180
200(2)
1.683
1.301
Dcalcd. [gcm–3]
µ [mm–1]
F(000)
θ range [°]
3136
3.01–27.50
71593
848
3.59–27.50
19644
3671/0.0761
3102
848
3.55–27.54
29896
4107/0.1047
2613
356
3.10–27.50
13916
3218/0.0260
2721
No. of reflections collected
No. of independent reflections (Rint
No. of observed reflections [I Ͼ 2σ(I)] 4507
)
7206/0.1301
No. of data/restraints/parameters
7206/0/355
3671/0/177
0.0376/0.0700
0.0528/0.0743
1.023
4107/0/176
0.0479/0.0962
0.0991/0.1076
0.987
3218/0/145
0.0295/0.0739
0.0384/0.0770
1.052
R1/wR2 [I Ͼ 2σ(I)][a]
0.0722/0.1222
0.1305/0.1338
1.161
R1/wR2 (all data)[a]
GOF (on F2)[a]
Largest difference peak/hole [eÅ–3]
+0.818/–0.864
+0.568/–0.529
0.563/–0.807
+0.7021/–0.938
[a] R1 = Σ(||Fo| – |Fc||)/Σ|Fo|; wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2; GOF = {Σ[w(Fo – Fc ) ]/(n – p)}1/2
.
2
2 2
2
2 2
Eur. J. Inorg. Chem. 2008, 2313–2320
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2319

R. A. Arteaga-Müller, J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
FULL PAPER
[22]
[23]
J. de la Mata, R. Fandos, M. Gómez, P. Gómez-Sal, S. Martí-
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Acknowledgments
We gratefully acknowledge the Ministerio de Educación y Ciencia
(MEC) (project MAT2007-60997) and the Dirección General de
Universidades e Investigación (DGUI) – Comunidad de Madrid
(programme S-0505/PPQ-0328 COMAL-CM) (Spain) for financial
support. R. A. A.-M. acknowledges MEC for a fellowship.
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Received: January 18, 2008
Published Online: April 4, 2008
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