Fac versus mer coordination for a tridentate diethylene glycloiate ligand in tantalum complexes: A combined experimental and theoretical study

Article abstract of DOI:10.1021/om060254e

A series of new tantalum-digol (digol = diethylene glycolate) complexes TaCp*Cl₂(K³-digol) (1), TaCp*Me ₂(κ³-digol) (2), TaCp*ClMe(κ³-digol) (3), and TaCp*Me(OTf) (κ³-digol) (OTf = triflate) (4) have been synthesized. Treatment of 2 with 1 equiv of H₂OB(C₆F₅) ₃ enabled the synthesis of a tantalumoxo borane-stabilized complex, TaCp*{O·B(C₆F₅)₃}(κ:3-digol) (5). Insertion processes into the methyl groups of complexes 2, 3, and 4 were not observed upon reaction with CO or isocyanides. In contrast, complex 4 reacted slowly with 1 equiv of xylylisocyanide (xylyl = 2,6-dimethylphenyl) to yield the dicationic aminocarbene complex [TaCp*{C(Me)NH(xylyl)}(OH ₂)(κ³-digol)][OTf]₂ (6). All products were characterized by NMR spectroscopy and elemental analysis. The single-crystal structures of 1, 5, and 6 were determined. The molecular structures of 1, 2, 3, and 6 were also determined by means of DFT-based methods.

Full text of DOI:10.1021/om060254e

3336
Organometallics 2006, 25, 3336-3344
fac versus mer Coordination for a Tridentate Diethylene Glyclolate
Ligand in Tantalum Complexes: A Combined Experimental and
Theoretical Study
Carles Bo,| Rosa Fandos,† Marta Feliz,| Carolina Herna´ndez,† Antonio Otero,*,‡
Ana Rodr´ıguez,§ Mar´ıa Jose´ Ruiz,† and Ce´sar Pastor
Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Ciencias del Medio Ambiente,
UniVersidad de Castilla-La Mancha, AVenida Carlos III, s/n 45071 Toledo, Spain, Departamento de
Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Facultad de Qu´ımicas, UniVersidad de Castilla-La Mancha,
Campus de Ciudad Real, 13071 Ciudad Real, Spain, Departamento de Qu´ımica Inorga´nica, Orga´nica y
Bioqu´ımica, ETS Ingenieros Industriales, UniVersidad de Castilla-La Mancha, AVenida Camilo Jose´ Cela,
3, 13071 Ciudad Real, Spain, Institute of Chemical Research of Catalonia (ICIQ), AVenida Pa¨ısos
Catalans 16, 43007 Tarragona, Spain, Departament de Qu´ımica F´ısica i Inorga`nica, UniVersitat RoVira i
Virgili, AVenida Marcel.l´ı Domingo s/n, 43007 Tarragona, Spain, and SerVicio Interdepartamental de
Apoyo a la InVestigacio´n, Facultad de Ciencias, UniVersidad Auto´noma de Madrid, Spain
ReceiVed March 21, 2006
A series of new tantalum-digol (digol ) diethylene glycolate) complexes TaCp*Cl2(κ3-digol) (1),
TaCp*Me2(κ3-digol) (2), TaCp*ClMe(κ3-digol) (3), and TaCp*Me(OTf)(κ3-digol) (OTf ) triflate) (4)
have been synthesized. Treatment of 2 with 1 equiv of H2O‚B(C6F5)3 enabled the synthesis of a tantalum-
oxo borane-stabilized complex, TaCp*{O‚B(C6F5)3}(κ3-digol) (5). Insertion processes into the methyl
groups of complexes 2, 3, and 4 were not observed upon reaction with CO or isocyanides. In contrast,
complex 4 reacted slowly with 1 equiv of xylylisocyanide (xylyl ) 2,6-dimethylphenyl) to yield the
dicationic aminocarbene complex [TaCp*{C(Me)NH(xylyl)}(OH2)(κ3-digol)][OTf]2 (6). All products were
characterized by NMR spectroscopy and elemental analysis. The single-crystal structures of 1, 5, and 6
were determined. The molecular structures of 1, 2, 3, and 6 were also determined by means of DFT-
based methods.
ligands have become the focus of a great deal of attention as
ancillary ligand frameworks for group 4 and 5 metal centers.7
In recent years we have developed studies based on the synthesis
of several families of cyclopentadienyl-containing early transi-
tion metal complexes with different types of assisted ligands,
namely, pyrimidine alkoxide8 and pyridyl alkoxide.9 We are
currently interested in studying the reactivity of monocyclo-
pentadienyltantalum derivatives toward diethylene glycol (digol-
H2).10 This ligand can perfectly surround metals, as three
coordination sites are available: an alcoholate double function
for charge neutralization and an oxygen-donor function to
compensate the electronic demands of the metal ion. Surpris-
ingly, the chemistry of poly(ethylene glycol) complexes is
relatively unexplored; some compounds with lanthanides,11
Introduction
Organometallic oxides1 and alkoxides2 play an important role
in numerous catalytic processes3 and also serve as molecular
models for catalyst-substrate surface interactions.4 It is equally
significant that some of the earliest and best known organic-
inorganic representatives, with extraordinary implications in the
development of multifunctional materials, are certainly derived
from these kinds of complexes.5
All of these interesting properties derive from the extreme
versatility of alkoxide ligands, since appropriate substitution
patterns allow for significant modification of the steric and
electronic requirements.6 More recently, chelating alkoxide
* To whom correspondence should be addressed. E-mail:
antonio.otero@uclm.es.
(6) (a) Rothwell, I. P. Acc. Chem. Res. 1988, 21, 153. (b) Rothwell, I.
P. Chem. Commun. 1997, 1331.
(7) (a) Tshuva, E. Y.; Groysman, S.; Goldberg, I.; Kol, M. Organome-
tallics 2002, 21, 662. (b) Tshuva, E. Y.; Goldberg, I.; Kol, M. J. Am. Chem.
Soc. 2000, 122, 10706. (c) Shao, P.; Gendron, R. A. L.; Berg, D. J.; Bushnell,
G. W. Organometallics 2000, 19, 509.
(8) Antin˜olo, A.; Carrillo-Hermosilla, F.; Corrochano, A. E.; Fandos,
R.; Ferna´ndez-Baeza, J.; Rodr´ıguez, A. M.; Ruiz, M. J.; Otero, A.
Organometallics 1999, 18, 5219.
(9) Fandos, R.; Herna´ndez, C.; Otero, A.; Rodr´ıguez, A. M.; Ruiz, M.
J.; Terreros, P. J. Chem. Soc., Dalton Trans. 2000, 2990.
(10) Abbreviations used: diethylene glycol ) digol-H2, diethylene
glycolate ) digol.
(11) (a) Hirashima, Y.; Shiokawa, J. Chem. Lett. 1979, 463. (b)
Hirashima, Y.; Tsutsui, T.; Shiokawa, J. Chem. Lett. 1981, 1501. (c)
Hirashima, Y.; Tsutsui, T.; Shiokawa, J. Chem. Lett. 1982, 1405. (d)
Hirashima, Y.; Kanetsuki, K.; Shiokawa, J.; Tanaka, N. Bull. Chem. Soc.
Jpn. 1981, 54, 1567. (e) Hirashima, Y.; Kanetsuki, K.; Yonezu, I.;
Kamakura, K.; Shiokawa, J. Bull. Chem. Soc. Jpn. 1983, 56, 738. (f) Rogers,
R. D.; Voss, E. J.; Etzenhouser, R. D. Inorg. Chem. 1988, 27, 533.
† Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-
La Mancha.
‡ Facultad de Qu´ımicas, Universidad de Castilla-La Mancha.
§ ETS Ingenieros Industriales, Universidad de Castilla-La Mancha.
| Institute of Chemical Research of Catalonia (ICIQ) and Universitat
Rovira i Virgili.
Universidad Auto´noma de Madrid.
(1) Roesky, H. W.; Haiduc, I.; Hosmane, N. S. Chem. ReV. 2003, 103,
2579.
(2) Bradley, D. C.; Mehrotra, R. C.; Singh, A.; Rothwell, I. P. Alkoxo
and Aryloxo DeriVatiVes of Metals; Academic Press: London, 2001.
(3) Sobota, P. Coord. Chem. ReV. 2004, 248, 1047.
(4) (a) Basset, J.-M.; Gates, B. C.; Candy, J. P.; Choplin, A.; Leconte,
M.; Quignard, F.; Santini, C. Surface Organometallic Chemistry: Molecular
Approaches to Surface Catalysis; Kluwer: Dordrecht, The Netherlands,
1988. (b) Coperet, C.; Chabanas, M.; Saint-Arroman, R. P.; Basset, J. M.
Angew. Chem., Int. Ed. 2003, 42, 156.
(5) Sanchez, C.; Soler-Illia, G. J. de A. A.; Ribot, F.; Lalot, T.; Mayer,
C. R.; Cabuil, V. Chem. Mater. 2001, 13, 3061.
10.1021/om060254e CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/07/2006

fac Vs mer Coordination for a Tridentate Diethylene Glyclolate
Organometallics, Vol. 25, No. 14, 2006 3337
Table 1. Selected Bond Distances (Å) and Angles (deg) for
TaCp*Cl2(K3-digol) Isomers
mer
fac
X-raya
calc
calc
Cp
Cp*
Cp
Cp*
1-mer
1-mer*
1-fac
1-fac*
Ta(1)-Cl(1)
2.457 (3)
2.488 (3)
1.950 (7)
2.212 (3)
1.934 (6)
2.467 (4)
147.9 (3)
73.7 (3)
74.2 (3)
84.9 (2)
87.2 (2)
75.3 (18)
2.473
2.525
1.953
2.257
1.955
2.487
147.5
73.8
73.9
88.0
87.5
76.2
2.483
2.514
1.962
2.282
1.969
2.518
147.1
73.4
73.7
86.8
86.8
74.4
2.462
2.455
1.973
2.383
1.966
2.487
96.9
71.5
71.5
149.9
84.0
80.4
2.469
2.460
1.982
2.467
1.981
2.508
98.2
69.6
70.7
149.4
83.4
82.4
Ta(1)-Cl(2)
Ta(1)-O(1)
Ta(1)-O(2)
Ta(1)-O(3)
Ta(1)-C(Cp)b
O(3)-Ta(1)-O(1)
O(3)-Ta(1)-O(2)
O(1)-Ta(1)-O(2)
O(3)-Ta(1)-Cl(1)
O(1)-Ta(1)-Cl(1)
O(2)-Ta(1)-Cl(1)
Figure 1. ORTEP drawing of compound 1 with thermal ellipsoids
shown at 30% probability.
Scheme 1
a X-ray specifications for TaCp*Cl2(κ3-digol) (1). b Average Ta-C
distances.
Scheme 2
alkali and alkaline-earth metals,12 and yttrium and titanium13
have been reported, but to the best of our knowledge, only one
organometallic complex of titanium containing this type of
ligand has been described.14
We report here the synthesis, characterization, and theoretical
studies of some monocyclopentadienyltantalum complexes
containing the tridentate diethylene glycolate ligand. An inter-
esting insertion reaction is also reported along with the formation
of an aminocarbene dicationic complex.
through the three oxygen atoms, two of which are located in
the equatorial plane, trans to one another, and the central one
occupying the position trans to the Cp* group. The coordination
around the metal is best described as a pseudo-octahedral
geometry, with the tantalum atom 0.557(1) Å out of the plane
defined by the atoms Cl(1), Cl(2), O(1), and O(3). The Ta(1)-
O(1) and Ta(1)-O(3) bond distances [1.950(7) and 1.934(6)
Å, respectively] are within the normal range for tantalum
alkoxide complexes.15 The Ta(1)-O(2) bond length [2.212(6)
Å] is longer and is comparable to that found previously by our
group for similar ligands [2.375(6) Å].16
Another general way to achieve the synthesis of alkoxide
derivatives of early transition metals is the reaction of metal
alkyl complexes with alcohols to yield the corresponding alkanes
and the alkoxide complexes. A likely mechanism for the
protonolysis of the carbon-metal bond requires initial donation
of an oxygen lone pair to the metal center.17 This methodology
has proven useful in the synthesis of alkyl/alkoxide tantalum
complexes. For example, the tantalum complex TaCp*Me4
reacts with diethylene glycol in a 1:1 ratio to render complex
2, which was isolated in 53% yield (see Scheme 2).
Results and Discussion
The tantalum complex TaCp*Cl4 reacts with digol-Li2 to yield
complex 1, which was isolated in good yield (70%) as a pale
yellow solid (Scheme 1). This complex is air sensitive, rather
soluble in THF and toluene, but sparingly soluble in pentane
and Et2O.
Complex 1 was characterized by the usual analytical and
spectroscopic techniques. The 1H NMR spectrum exhibits
resonances at 2.21 (s), 3.63 (t), and 4.59 (t) ppm, and these are
attributed to the Cp* ligand and the methylene protons of the
dialkoxide ligand, respectively. The ratio of the integrals is
consistent with the proposed stoichiometry. The multiplicity and
number of methylene proton signals indicate a trans disposition
of the chloride ligands and the coordination of the dialkoxide
through the three oxygen atoms, with the central one in a trans
disposition with respect to the Cp* ligand (see Scheme 1). The
13C NMR spectrum is also consistent with the proposed
structure.
Complex 2 is air sensitive, rather soluble in THF and toluene,
but sparingly soluble in pentane and Et2O. This complex was
1
characterized by H and 13C NMR and IR spectroscopy.
1
The H NMR spectrum shows singlet signals at -0.03 and
This structure was also confirmed by an X-ray diffraction
study. An ORTEP drawing of 1 is shown in Figure 1, and some
selected bond distances and angles are given in Table 1. The
crystal consists of discrete molecules separated by van der Waals
distances. The tantalum atom is bonded to the cyclopentadienyl
ring in a η5-mode. The digol ligand is bonded to the metal center
1.91 ppm, which are assigned to the methyl groups bonded to
the tantalum center and to the Cp* ligand, respectively. The
methylene protons give rise to three multiplet signals centered
at 2.85, 3.66, and 4.09 ppm. This situation is in contrast with
the two triplets observed in complex 1, where the two oxygen
atoms were covalently bonded to the metal and the two chloro
(12) (a) Sieger, H.; Vogtle, F. Tetrahedron Lett. 1978, 30, 2709. (b)
Singh, T. P.; Reinhardt, R.; Poonia, N. S. Inorg. Nucl. Chem. Lett. 1980,
16, 293. (c) Ohmoto, H.; Kai, Y.; Yasuoka, N.; Kasai, N.; Yanagida S.;
Okahara, M. Bull. Chem. Soc. Jpn. 1979, 52, 1209.
(13) Sobota, P.; Utko, J.; Sztajnowska, K.; Jerzykiewicz, L. B. New J.
Chem. 1998, 851.
(15) De Castro, I.; Galakhov, M. V.; Go´mez, M.; Go´mez-Sal, P.; Mart´ın,
A.; Royo, P. J. Organomet. Chem. 1996, 514, 51.
(16) Fandos, R.; Herna´ndez, C.; Lo´pez-Solera, I.; Otero, A.; Rodr´ıguez,
A. M.; Ruiz, M. J.; Terreros, P. Organometallics 2000, 19, 5318.
(17) Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-
Zirconium and Hafmium Compounds; Ellis Horwood Limited; Halsted
Press: New York, 1986.
(14) Yi-Yeol, L.; Jin-Heong, Y. (Samsung General Chemicals Co., Ltd.,
S. Korea) Eur. Pat. Appl. EP964004, 1999.

3338 Organometallics, Vol. 25, No. 14, 2006
Bo et al.
Table 2. Relative Energy (kcal‚mol-1) of the fac and mer
Scheme 3
Isomers of 1, 2, and 3 for Cp and Cp* Ligandsa
Efac - Emer
1
2
3
Cp
Cp*
9.9
8.2
-0.5
-1.8
7.3
6.7
a A positive value indicates preference for the mer isomer.
Scheme 4
the most stable by 2.4 kcal‚mol-1 and was therefore selected
to evaluate the mer/fac relative stability.
The relative stabilities of the fac and mer isomers of
compounds 1, 2, and 3 are shown in Table 2 for Cp and Cp*
ligands. In all cases, the difference in energy agrees with the
mer/fac selectivity described above. The thermodynamically
most stable isomer (mer for 1 and 3, and fac for 2) matches
that obtained experimentally. The trend arising from Table 2
indicates that the preference for the mer coordination mode is
reduced as the number of chloride ligands decreases. This
preference is ultimately reversed in 2. It is worth noting that
the preference for mer is enhanced when a Cp ligand, rather
than a Cp*, is present. In 1 and 3 the energy differences between
the two isomers are large enough to account for the experimental
observation. Similar ∆E values for the mer and fac isomers of
the related compound V(O)(oda)(H2O)2 [oda ) O(CH2COO-)2]
have been reported.19 However, in complex 2 the energy
difference between the two isomers is quite small, less than 2
kcal‚mol-1, but the trend is in the right direction. Other cases
reported in the literature show a similar type of behavior. For
instance, Galindo and co-workers also found a small energy
difference between the fac and mer isomers of the Ni(oda)-
(H2O)3 derivative.20 In a study on different systems, Harvey et
al.21 comprehensively explained the cis/trans preference in
[PtX2(PR3)2] (X ) Cl, Br, I, Me; R ) H, F, Ph, Me) complexes.
In that case, the cis/trans preference was determined by a range
of effects that depended on X, R, and, to a great extent, the
solvent. Those authors used a similar DFT methodology and
found, for R ) Me and in the gas phase, a preference of 6
kcal‚mol-1 for trans when X ) Cl and of 2 kcal‚mol-1 for cis
when X ) Me. These results are almost reproduced by the
values for compounds 1 and 2 in Table 2. In the present case,
the stability of the fac isomer in 2 is probably driven by the
preference of the strong sigma donor methyl ligands to bind
trans to weaker ones.
A detailed analysis of the computed geometries of the isomers
of 1, 2, and 3 shows that the Ta-Cl bond distances are longer
than the Ta-Me bonds and the Ta-Cp distances do not change
considerably. The Ta-O2(ether) length increases with the
number of methyl groups, in the order Cl > ClMe > Me2, and
in all cases the Ta-O2(ether) distances are longer than the
remaining Ta-O1 and Ta-O3. However, in all cases the
existence of a Ta-O2(ether) bond is confirmed by the presence
of a bond critical point. Calculated geometrical parameters show
that the mer 1, 2, and 3 isomers have shorter Ta-O2(ether)
distances than the fac compounds. In accordance with this, the
mer isomers present a slightly higher electron density (0.06 e-)
than the fac derivatives (0.04 e-) at the bond critical point.
The reactivity of TaCp*Me2(κ3-digol) (2) with protonating
reagents and unsaturated molecules was studied. Reaction with
ligands were arranged in a trans fashion. Bearing this arrange-
ment in mind, we propose that complex 2 is a monomer with
the digol ligand bonded to the metal center in a fac18 fashion in
which the three oxygen atoms are bonded to the metal center
and the two methyl groups are in a cis disposition (see Scheme
2).
The differences in the coordination modes of the digol ligand
in 1 and 2 encouraged us to assess the preparation of a trans-
dimethyl complex by methylation of compound 1. As we
envisaged, reaction of 1 with 2 equiv of MeLi in pentane gave
only the cis dimethyl complex 2, which was isolated in 63%
yield (Scheme 3). Evidence for the formation of the trans
complex was not found.
The use of other methylating agents such MeMgCl or MeMgI
gave the cis complex 2 and TaCp*Me4 as the only identifiable
compounds in the reaction mixture.
Finally, reaction of 2 equiv of MeMgBr with complex 1 gave
the monomethylated complex 3. When this reaction was repeated
with only 1 equiv of MeMgBr, the same result was achieved
and 3 was isolated in 46% yield as a pale yellow solid (Scheme
4).
This compound is soluble in toluene, THF, and acetonitrile
1
but is sparingly soluble in pentane. The H NMR spectrum
shows two singlets at 0.11 and 2.07 ppm, and these are assigned
to the methyl groups bonded to the tantalum atom and to the
cyclopentadienyl ligand, respectively. Four multiplets are
observed centered at 3.17, 4.17, 4.39, and 4.54, and these
correspond to the nonequivalent protons of the digol ligand. In
addition, the 13C{1H} NMR spectrum shows two signals at 72.4
and 74.1 ppm for the methylene carbons, which is consistent
with a mer disposition of the oxygen atoms (see Scheme 4).
In complexes 1, 3, and 4 (see below) the digol ligand adopts
the mer disposition, but in 2 it coordinates in the fac manner.
A visual inspection of the X-ray structures suggests that the
preference for coordination in the fac or mer arrangement was
not determined by steric effects. In an effort to gain insight into
this issue, the structures of the fac and mer isomers of 1, 2, and
3 were determined at a DFT level (see Computational Details
and Supporting Information) considering both the Cp* ligands
as used in the experiments and simple Cp ligands. Selected
geometrical parameters for the computed structures of compound
1 are collected in Table 1. The agreement between X-ray
measurements and computed values is fairly good. All metal-
ligand bond distances are, however, slightly overestimated. In
the case of compound 3, the digol ligand can adopt two different
conformations, 3-mer and 3-mer-is, as shown in the Supporting
Information. At the present level of theory, the 3-mer isomer is
(19) del Rio, D.; Galindo, A.; Vicente, R.; Mealli, C.; Ienco, A.; Masi,
D. J. Chem. Soc., Dalton Trans. 2003, 1813.
(20) Grirrane, A.; Pastor, A.; Ienco, A.; Mealli, C.; Galindo, A. J. Chem.
Soc., Dalton Trans. 2002, 3771.
(21) Harvey, J. N.; Heslop, K. M.; Orpen, G. A.; Pringle, P. G. Chem.
Commun. 2003, 278.
(18) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750.

fac Vs mer Coordination for a Tridentate Diethylene Glyclolate
Organometallics, Vol. 25, No. 14, 2006 3339
Table 3. Bond Lengths (Å) and Angles (deg) for 5
Ta(1)-O(1)
Ta(1)-O(2)
Ta(1)-O(3)
Ta(1)-O(4)
O(1)-B(1)
O(2)-C(1)
O(3)-C(4)
O(4)-C(3)
O(4)-C(2)
1.828(2)
1.946(2)
1.952(3)
2.313(2)
1.498(5)
1.421(5)
1.424(5)
1.444(5)
1.449(5)
B(1)-O(1)-Ta(1)
O(1)-Ta(1)-O(2)
O(1)-Ta(1)-O(3)
O(2)-Ta(1)-O(3)
O(1)-Ta(1)-O(4)
O(2)-Ta(1)-O(1)
O(3)-Ta(1)-O(4)
174.0(2)
107.25(11)
102.21(11)
130.41(11)
87.78(10)
70.90(10)
71.37(10)
Table 4. 19F NMR Data in C6D6 at Room Temperature for
Fluorine-Containing Compounds
compound
ortho
para
meta
B(C6F5)3
-129.7
-135.4
-133.7
-142.6
-156.4
-159.7
-160.6
-163.9
-165.6
H2O‚B(C6F5)3
TaCp*{O‚B(C6F5)3}(κ3-digol) (5)
Figure 2. ORTEP drawing of compound 5 with thermal ellipsoids
shown at 30% probability.
Scheme 7
Scheme 5
and even longer than those found in the compounds [TaCp*Cl-
(O){η2-C(Me)dNR}] [1.731(7) Å]25 and [TaCp2*H(O)] [1.73-
(2) Å].26 This value for the Ta-O bond length is a consequence
of the coordination of the oxygen atom to the borane ligand
and is within the range of values found in complexes with Ta-
O-Ta bridges [1.82-2.10 Å]. The O-B bond distance of
1.498(5) Å is shorter than that found for H2O‚B(C6F5)3 [1.5769-
(14) Å]27 but within the range observed for neutral oxo-borane
compounds [1.496-1.591 Å].28 The Ta-O-B angle deviates
slightly from linearity [174.0(2)°], probably due to the steric
requirements of the Cp* and B(C6F5)3 ligands.
All of the spectroscopic data for compound 5 are in agreement
with the structure described, but the 19F NMR spectrum probably
provides the most conclusive evidence. This spectrum shows
resonances broadly similar to those of B(C6F5)3, but the para-
fluorine has shifted slightly upfield as in H2O‚B(C6F5)3 (see
Table 4). This resonance is the most sensitive of the aromatic
fluorine shifts and is a good indicator of tetracoordination of
the boron atom.29
Scheme 6
triflic acid occurs in a rather selective way to yield, through
protonolysis of one tantalum-methyl bond, the corresponding
alkyl complex 4 (Scheme 5).
This compound is soluble in toluene, THF, and acetonitrile
but sparingly soluble in pentane, with this latter observation in
agreement with its proposed neutral character. The NMR spectra
show that, at room temperature, the methylene groups in the
dialkoxide ligand are inequivalent and their signals appear in
the 13C spectrum at 71.9 and 74.5 ppm; this confirms the mer
1
disposition of the digol ligand (see Scheme 5). The H NMR
Insertion processes into the methyl groups of complexes 2,
3, and 4 were not observed upon reaction with CO or
isocyanides, probably because the central oxygen atom in the
digol ligand blocks the initial coordination of these molecules
and prevents reactivity.
spectrum shows singlet signals at -0.21 and 1.86 ppm, and
these are attributed to the methyl groups bonded to the metal
center and to the Cp* ligand, respectively, while the methylene
groups give rise to several multiplets centered at 3.29, 3.85,
4.15, and 4.89 ppm.
In contrast, complex 4 reacts slowly at room temperature (5
days) with 1 equiv of xylylisocyanide to yield the dicationic
aminocarbene complex 6 (Scheme 7), probably by initial
displacement of the triflate ligand by the isocyanide and
subsequent protonation of the generated cationic iminoacyl
(Scheme 8). Complex 6 was isolated as a colorless crystalline
We also studied the reaction of 2 with the water adduct H2O‚
B(C6F5)3, which proved to be a useful oxo transfer reagent22
and gave complex 5 in good yield (Scheme 6).
The molecular structure of compound 5 was determined by
X-ray diffraction studies (Figure 2, Table 3). In this complex a
tantalum oxo-borane adduct was formed. A related oxo-
niobocene-borane adduct was previously reported by some of
us.23 The most notable feature of this compound, a Ta-O bond
distance of 1.828(2) Å, is comparable to that in the reported
mononuclear complex [TaCp*Cl2{O‚B(C6F5)3}], 1.784(2) Å,24
(25) Go´mez, M.; Go´mez-Sal, P.; Jime´nez, G.; Mart´ın, A.; Royo, P.;
Sa´nchez-Nieves, J. Organometallics 1996, 15, 3579.
(26) Parkin, G.; Asselt, A. V.; Leahy, D. J.; Whinnery, L.; Hua, N. G.;
Quan, R. W.; Henling, L. M.; Schaefer, W. P.; Santarsiero, B. D.; Bercaw,
J. E. Inorg. Chem. 1992, 31, 82.
(27) Danopoulos, A. A.; Galsworthy, J. R.; Green, M. L. H.; Cafferkey,
S.; Doerrer, L. H.; Hursthouse, M. B. Chem. Commun. 1998, 2529.
(28) (a) Barrado, G.; Doerrer, L.; Green, M. L. H.; Leech, M. A. J. Chem.
Soc., Dalton Trans. 1999, 1061. (b) Sarsfield, M. J.; Helliwell, M. J. Am.
Chem. Soc. 2004, 126, 1036.
(29) Doerrer, L. H.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 1999,
4325.
(22) Neculai, D.; Roesky, H. W.; Neculai, A. M.; Magull, J.; Walfort,
B.; Stalke, D. Angew. Chem., Int. Ed. 2002, 41, 4294.
(23) Antin˜olo, A.; Carrillo-Hermosilla, F.; del Hierro, I.; Otero, A.;
Fajardo, M.; Mugnier, Y. Organometallics 1997, 16, 4161.
(24) Sa´nchez-Nieves, J.; Frutos, L. M.; Royo, P.; Castan˜o, O.; Herdtweck,
E. Organometallics 2005, 24, 2004.

3340 Organometallics, Vol. 25, No. 14, 2006
Bo et al.
Scheme 8
clarity. The pentamethylcyclopentadienyl ring is bound to the
Ta atom in an almost symmetric η5-fashion with the distance
between the metal and the centroid of the ring being 2.135(9)
Å. The Ta atom is also bound to four oxygen atoms, with the
Ta-O lengths ranging between 1.901(7) and 2.209(7) Å. Three
oxygen atoms belong to a mer-κ3-digol ligand. The coordination
around Ta is completed by the carbenic C(5) atom from the
aminocarbene ligand. The complex can be described as pseudo-
octahedral, with the Ta atom displaced by 0.420(3) Å from the
equatorial plane containing the atoms O(1), O(3), O(4), and C(5).
The Ta-OH2 distance of 2.194(8) Å is shorter than Ta-
O(2) [2.209(7) Å] and similar to that found in the literature for
TaCp*(OH2)(p-tert-butylcalix[4]arene) [2.188(3) Å].31 The Ta-
(1)C(5)N(1)C(7) moiety of the aminocarbene ligand is almost
planar and is perpendicular to the phenyl ring [dihedral angle
87.2(8)°]; the bond distances are N(1)-C(5) [1.330(14) Å],
N(1)-C(7) [1.467(15) Å], C(5)-C(6) [1.501(16) Å], and C(5)-
Ta(1) [2.240(13) Å], and these are comparable to those found
in other tantalum complexes with this type of ligand.30
The X-ray structure of 6 was taken as the starting point for
a geometry optimization at the DFT level, adding the two
undetected aquo hydrogen atoms and one proton attached to
the nitrogen atom. The optimized bond distances and angles
are generally overestimated in comparison with the experimental
values. All of the Ta-O distances, including the Ta-OH2
distance, are 0.03 Å longer than the values obtained in the X-ray
study. Consequently, the nature of the aquo ligand is confirmed.
The Ta-C(5) distance differs by only 0.05 Å in comparison to
the experimental value and is characteristic of the aminocarbene
ligand.
Moreover, the location of the N-bound hydrogen atom, which
lies in the same plane as Ta(1)C(5)N(1)C(6), clearly indicates
the aminocarbene nature of the ligand. Analysis of the electronic
structure of this isolated moiety (see Supporting Information)
clearly reveals a Fischer-type carbene; the difference in energy
(computed at the same level as above) between the singlet and
the triplet states favors the most stable singlet by 31.2
kcal‚mol-1, a value quite close to that reported recently for
related (alkyl)(amino)carbenes.32 The bonding mechanism be-
tween the aminocarbene and the metal fragment consists of
donation from the carbene lone pair to an empty tantalum d
orbital of appropriate symmetry. Metal-to-carbene π back-
donation, even though orbitals of appropriate symmetry can
interact effectively, does not contribute to bonding because of
the lack of metal electrons.
solid and was characterized by the usual analytical and
spectroscopic techniques as well as by X-ray diffraction.
The mechanism of this transformation, i.e., methyl insertion
into the xylylisocyanide (XylylNC)-Ta bond in [TaCp*(digol)-
(XylylNC)(Me)]+ (7) to give [TaCp*(digol)η2-(C,N)-(C(Me)-
NXylyl)]+ (8), as shown in Scheme 8, was investigated by
means of DFT calculations using Cp ligands instead of Cp*
and PhNC instead of XylylNC. We considered that the geometry
of the active [TaCp(digol)(PhNC)(Me)]+ (7′) intermediate
corresponds to the fac isomer since the methyl insertion reaction
is favored with the cis disposition of the two ligands. Molecular
structures for 7′, 8′, and the corresponding transition state TS7′-8′
are displayed in Figure 3. Methyl insertion is thus energetically
favorable, with the difference in energy between the [TaCp-
(digol)(PhNC)(Me)]+ and [TaCp(digol)η2-(C,N)-(C(Me)NPh)]+
being -26.2 kcal‚mol-1. The energy barrier to reach the
transition state from 7′ amounts to only 11.8 kcal‚mol-1, a value
that fully justifies the formation of 8′. Characteristic interatomic
distances are also given in Figure 3. The value of the angle
Me-Ta-C decreases from 71° to 47° and the Me-C distance
decreases to 1.862 Å in TS7′-8′, thus confirming the success of
the insertion reaction. In the product 8′, the CdN distance (1.292
Å) is characteristic of a double bond and the Me-C distance
(1.485 Å) corresponds to a single C-C bond. The distance
between the Ta atom and the C atom of the PhNC moiety
decreased from 2.245 Å in the intermediate to 2.098 Å in the
TS, whereas the Ta-Me distance increased from 2.262 to 2.494
Å.
Complex 6 is air stable in solution for several days and does
not react with additional isocyanide; it is insoluble in toluene
and pentane but is soluble in acetonitrile and THF, as one would
expect given its cationic nature.
Conclusions
The work described here concerned the synthesis of several
monocyclopentadienyl complexes of tantalum with an assisted
dialkoxide ligand, which exhibits a tridentate fac or mer
coordination depending on the nature of the methyl- and chloro-
substituents present in the molecule. DFT-based studies indicate
that the preference for the mer coordination mode is reduced
as the number of chloride ligands decreases, a finding in full
agreement with experimental observations. A comparative
theoretical study between Cp and Cp* derivatives indicates that
the fac/mer selectivity is enhanced when the former ligand is
used. Optimized metal-ligand bond distances are slightly
overestimated, especially for the Cp* geometries. The Ta-
O(ether) distance is longer than the Ta-O distances, and it
NMR data are in full agreement with the presence of an
aminocarbene ligand in this complex, with the amino proton
observed at 10.7 ppm in the 1H NMR spectrum as a broad signal
and the carbene carbon signal at 267.1 ppm in the 13C NMR
spectrum.30 In addition, characteristic ν(N-H) and ν(O-H)
absorptions were found at ∼3200 cm-1 in the IR spectrum. The
bound H2O molecule of 6 gives rise to a broad resonance at
1
2.45 ppm in the H NMR spectrum and was further revealed
by the solid-state structure determined crystallographically. An
ORTEP drawing of 6 is shown in Figure 4, and some selected
bond distances and angles are summarized in Table 5.
The crystal is formed by the cationic unit and two inequivalent
triflate anions. In Figure 4 the anions have been omitted for
(31) Acho, J. A.; Doerrer, L. H.; Lippard, S. J. Inorg. Chem. 1995, 34,
2542.
(30) Galakov, M. V.; Go´mez, M.; Jime´nez, G.; Royo, P.; Pellinghelli,
M. A.; Tiripichio, A. Organometallics 1995, 14, 1901.
(32) Canac, Y.; Conejero, S.; Donnadieu, B.; Schoeller, W. W.; Bertrand,
G. J. Am. Chem. Soc. 2005, 127, 7312.

fac Vs mer Coordination for a Tridentate Diethylene Glyclolate
Organometallics, Vol. 25, No. 14, 2006 3341
Figure 3. Molecular structures of 7′, TS7′-8′, and 8′ and relative energies. Selected distances in Å, angles in deg. The imaginary harmonic
frequency for the TS is 410 cm-1
.
Figure 4. ORTEP drawing, with thermal ellipsoids shown at 30% probability, and molecular structure determined by DFT for 6.
Table 5. Selected Bond Distances (Å) and Angles (deg) for
Compound 6a
instead of the expected neutral insertion compound. This reaction
probably occurred by displacement of the triflate ligand. The
mechanism of this transformation was determined by DFT
calculations as well as the complete geometry of 6. The
computed geometry of 6 agrees well with X-ray structural
parameters, confirming the nature of the aquo and aminocarbene
ligands. The electronic study of 6 enabled the identification of
this ligand as a Fischer-type carbene, and the bonding mecha-
nism involves donation of the carbene lone pair to an empty
Ta(V) d orbital.
X-ray
calc
Ta(1)-O(1)
1.898(6)
2.209(6)
1.920(6)
2.176(8)
2.24(1)
1.942
2.256
1.957
2.362
2.269
1.316
1.467
145.8
154.8
127.6
121.5
121.4
Ta(1)-O(2)
Ta(1)-O(3)
Ta(1)-O(4)
Ta(1)-C(5)
N(1)-C(5)
1.31(1)
1.47(1)
N(1)-C(7)
O(1)-Ta(1)-O(3)
O(4)-Ta(1)-C(5)
C(5)-N(1)-C(7)
N(1)-C(5)-Ta(1)
C(6)-C(5)-Ta(1)
147.2(3)
153.1(3)
127.0(9)
123.5(7)
121.7(7)
Finally, a novel example showing the efficiency of H2O‚
B(C6F5)3 as an oxo-transfer reagent has been found. It is
important to note the potential role that the digol ligand, and
other similar compounds, can play in modulating the structure
and reactivity of early transition metal complexes. Further
studies are currently being carried out.
a X-ray specifications for [TaCp*{C(Me)NH(xylyl)}(OH2)(κ3-digo-
l)][OTf]2 (6).
becomes longer in the methylated compound 3. The existence
of a Ta-O(ether) bond is supported by the characterization of
the Ta-O(ether) bond critical point in the electronic density
distribution.
Experimental Section
The reactivity of all of the methyl complexes with unsaturated
molecules such as carbon monoxide or isocyanides was also
studied. It was found that the central oxygen atom in the digol
ligand probably blocks the initial coordination of these molecules
and prevents reactivity. Only compound 4 reacted with xylyl-
isocyanide, yielding a dicationic aminocarbene complex (6)
General Remarks. All compounds were prepared and handled
with rigorous exclusion of air and moisture under a nitrogen
atmosphere by using standard vacuum line and Schlenk techniques.
All solvents were dried and distilled under nitrogen.
The following reagents were prepared by literature procedures:

3342 Organometallics, Vol. 25, No. 14, 2006
Bo et al.
33
TaCp*Cl4 and TaCp*Me4.34 The commercially available com-
TaCp*Me(OTf)(K3-digol) (4). To a solution of complex 2 (0.385
g, 0.85 mmol) in toluene (10 mL) was added triflic acid (78 µL,
0.85 mmol). The mixture was stirred for 30 min, the solvent was
removed under vacuum, and the residue was washed with pentane
(5 mL) to yield a white solid (0.208 g, 42%), which was
pounds Cp*H, LiMe, MeMgBr, xylylisocyanide, tert-butylisocya-
nide, triflic acid, H2O‚B(C6F5)3, and diethylene glycol were used
as received from Aldrich.
Elemental analyses were performed with a Perkin-Elmer 2400
microanalyzer. IR spectra were recorded in the region 4000-400
cm-1 with a Nicolet Magna-IR 550 spectrophotometer as Nujol
mulls using PET cells. 1H, 19F, and 13C NMR spectra were obtained
on a 200 MHz Mercury Varian Fourier transform spectrometer.
Trace amounts of protonated solvents were used as references, and
chemical shifts are reported in units of parts per million relative to
SiMe4.
1
characterized as 4. H NMR (C6D6): δ -0.18 (s, 3 H, CH3-Ta),
1.87 (s, 15 H, Cp*), 3.29 (m, 2 H, CH2O), 3.85 (m, 2 H, CH2O),
4.15 (m, 2 H, CH2O), 4.89 (m, 2 H, CH2O). 13C{1H} NMR
(C6D6): δ 11.0 (Cp*), 38.4 (CH3-Ta), 71.9 (CH2O), 74.5 (CH2O),
122.5 (Cp*), 124.1 (CF3). Anal. Calcd for C16H26F3O6STa
(584.38): C, 32.88; H, 4.48. Found: C, 32.73; H, 4.48.
TaCp*{O‚B(C6F5)3}(K3-digol) (5). To a solution of complex 2
(0.29 g, 0.64 mmol) in toluene (5 mL) was added H2O‚B(C6F5)3
(0.34 g, 0.64 mmol). The mixture was stirred for 4 h, the solvent
was removed under vacuum, and the residue was dissolved in
diethyl ether (5 mL). Slow diffusion of pentane into this solution
gave a white microcrystalline solid (0.46 g, 75%), which was
characterized as 5. Crystals of complex 5 suitable for X-ray
diffraction were obtained by recrystallization from diethyl ether/
TaCp*Cl2(K3-digol) (1). To a solution of diethylene glycol (0.2
mL, 2.17 mmol) in diethyl ether (30 mL) at -78 °C was added
nBuLi (1.6 M in hexane solution) (2.7 mL, 4.34 mmol). The mixture
was allowed to reach room temperature and stirred for 15 min.
The solution was cooled to -78 °C, and Cp*TaCl4 (0.993 g, 2.17
mmol) was added. The mixture was allowed to reach room
temperature and stirred for 3 h. The solvent was removed under
vacuum, the residue was extracted with toluene, and after filtration,
the toluene was evaporated and the yellow oil washed with cold
pentane to afford a pale yellow solid (0.752 g, 70%), which was
characterized as 1. Crystals of complex 1 that were suitable for
X-ray diffraction were obtained by crystallization from toluene/
pentane. IR (Nujol/PET) ν (cm-1): 1109 (s), 1092 (s), 1029 (s),
927 (m), 545 (s). 1H NMR (C6D6): δ 2.21 (s, 15 H, Cp*), 3.63 (t,
J ) 5.67 Hz, 4 H, CH2O), 4.59 (t, J ) 5.67 Hz, 4 H, CH2O). 13C-
{1H} NMR (C6D6): δ 12.1 (Cp*), 73.2 (CH2O), 74.3 (CH2O), 125.1
(Cp*). Anal. Calcd for C14H23Cl2O3Ta (491.18): C, 34.23; H, 4.72.
Found: C, 34.22; H, 4.73.
1
pentane. H NMR (C6D6): δ 1.59 (s, 15 H, Cp*), 2.11 (m, 2 H,
CH2O), 2.96 (m, 2 H, CH2O), 3.76 (m, 2 H, CH2O), 4.05 (m, 2 H,
CH2O). 13C{1H} NMR (C6D6): δ 9.9 (Cp*), 69.9 (CH2O), 73.3
(CH2O), 123.6 (Cp*). 19F NMR (C6D6): δ -133.7 (m, ortho),
-159.7 (t, para), -165.6 (m, meta). Anal. Calcd for C32H23BF15O4-
Ta (948.26): C, 40.53; H, 2.44. Found: C, 40.51; H, 2.72.
[TaCp*{C(Me)NH(xylyl)}(OH2)(K3-digol)][OTf]2 (6). To a
solution of complex 4 (0.246 g, 0.42 mmol) in toluene (3 mL) was
added xylylisocyanide (0.055 g, 0.42 mmol). The mixture was
stirred for 5 days, the solvent was evaporated to dryness, and the
mixture was extracted with acetonitrile (2 mL). Removal of the
solvent under vacuum and washing with diethyl ether (2 mL) gave
6 (0.114 g, 31%). Crystals of complex 6 suitable for X-ray
diffraction were obtained by crystallization from acetonitrile/diethyl
TaCp*Me2(K3-digol) (2). This compound can be synthesized
using either of the following methods.
(A) A solution of diethylene glycol (0.075 g, 0.71 mmol) in THF
(1 mL) was added to a solution of Cp*TaMe4 (0.268 g, 0.71 mmol)
in pentane at -78 °C. The mixture was allowed to reach room
temperature and stirred for 3 h. The solvent was evaporated to
dryness, and the resulting oily solid was washed with cold pentane
(2 × 2 mL). The compound was dried to give an oily yellow solid
(0.166 g, 53%), which was characterized as 2. IR (Nujol/PET) ν
(cm-1): 1445 (m), 1372 (m), 1138 (s) 1090 (vs), 1033 (s), 920
(m), 907 (m), 516 (m) 474 (m). 1H NMR (C6D6): δ -0.03 (s, 6 H,
CH3-Ta), 1.91 (s, 15 H, Cp*), 2.85 (m, 2 H, CH2O), 3.66 (m, 2
H, CH2O), 4.09 (m, 4 H, CH2O). 13C{1H} NMR (C6D6): δ 11.1
(Cp*), 40.5 (CH3-Ta), 66.6 (CH2O), 73.27 (CH2O), 117.5 (Cp*).
Anal. Calcd for C19H29O3Ta (450.35): C, 42.67; H, 6.49. Found:
C, 41.41; H, 5.71.
1
ether. H NMR (CD3CN): δ 2.23 (s, 3 H, CH3-CN), 2.32 (s, 15
H, Cp*), 2.37 (s, 6 H, CH3-xylyl), 2.45 (br, H2O), 4.2-5.1 (mc,
br, 8 H, CH2O), 7.28-7.42 (m, 3 H, xylyl), 10.65 (br, NH). 19F
NMR (CD3CN): δ -79.77. 13C{1H} NMR (CD3CN): δ 11.1 (Cp*),
11.4 (CH3-xylyl), 14.9 (CH3-CN), 74.3 (CH2O), 76.3 (CH2O),
117.6 (Cp*), 124.3 (CF3), 127.4 (ar), 130.0 (ar), 133.4 (ipso-CH3),
136.5 (ipso-CN), 267.1 (CN). Anal. Calcd for C26H38F6NO10S2Ta
(882.64): C, 35.58; H, 4.23; N, 1.59. Found: C, 35.41; H, 4.08;
N, 1.85.
Computational Details
(B) To a solution of complex 1 (0.176 g, 0.36 mmol) in pentane
(10 mL) was added MeLi (1.6 M in diethyl ether) (0.45 mL, 7.15
mmol). The mixture was stirred for 2 h, the solvent was removed
under vacuum, and the residue was extracted with toluene (2 mL).
The sample was dried to give an oily yellow solid (0.103 g, 63%),
which was characterized as 2.
TaCp*MeCl(K3-digol) (3). To a solution of complex 1 (0.269
g, 0.55 mmol) in diethyl ether (10 mL) was added MeMgBr (3 M
in diethyl ether) (0.20 mL, 0.55 mmol). The mixture was stirred
for 30 min, the solvent was removed under vacuum, and the residue
was washed with pentane (5 mL) to yield a pale yellow solid (0.163
g, 46%), which was characterized as 3‚MgBrCl‚1/2Et2O. 1H NMR
(C6D6): δ 0.11 (s, 3H, CH3-Ta), 2.07 (s, 15 H, Cp*), 3.17 (m, 2
H, CH2O), 4.17 (m, 2 H, CH2O), 4.39 (m, 2 H, CH2O), 4.54 (m, 2
H, CH2O). 13C{1H} NMR (C6D6): δ 12.0 (Cp*), 41.2 (CH3-Ta),
72.4 (CH2O), 74.1 (CH2O), 121.8 (Cp*). Anal. Calcd for C15H26-
BrCl2MgO3Ta‚1/2(C4H10O) (647.49): C, 31.51; H, 4.83. Found:
C, 31.83; H, 4.98.
All DFT calculations were carried out using the Amsterdam
Density Functional (ADF2004.01) program developed by Baerends
et al.35 and vectorized by Ravenek.36 The numerical integration
scheme applied for the calculations was developed by te Velde et
al.37 The geometry optimization procedure was based on the method
reported by Versluis and Ziegler.38 The BP86 functional described
as a combination between local VWN exchange-correlation
potential with nonlocal Becke’s exchange correction39 and Perdew’s
correlation correction were used.40 Relativistic corrections were
introduced by scalar-relativistic zero-order regular approximation
(35) (a) Baerends, E. J.; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.
(b) Baerends, E. J.; Ros, P. Chem. Phys. 1973, 2, 52.
(36) Ravenek, W. In Algorithms and Applications on Vector and Parallel
Computers; te Riele, H. J. J., Deckker, T. J., van de Horst, H. A., Eds.;
Elsevier: Amsterdam, The Netherlands, 1987.
(37) (a) Boerrigter, P. M.; te Velde, G.; Baerends, E. J. Int. J. Quantum
Chem. 1988, 33, 87. (b) te Velde, G.; Baerends, E. J. J. Comput. Chem.
1992, 99, 84.
(33) Burt, R. J.; Chatt, J.; Leigh, G. J.; Teuben, J. H.; Westerhof A. J.
Organomet. Chem. 1977, 129, C33.
(34) Sanner, R. D.; Carter, S. T.; Burton, W. J. J. Organomet. Chem.
1982, 240, 157.
(38) Versluis, L.; Ziegler, T. J. Chem. Phys. 1988, 88, 322.
(39) Becke, A. D. Phys. ReV. A 1988, 38, 3098.
(40) Perdew, J. P. Phys. ReV. B 1986, 34, 7406. Perdew, J. P. Phys.
ReV. B 1986, 33, 8822.

fac Vs mer Coordination for a Tridentate Diethylene Glyclolate
Organometallics, Vol. 25, No. 14, 2006 3343
Table 6. Crystal Data and Structure Refinement for 1, 5, and 6
1
5
6
empirical formula
fw
C14H23Cl2O3Ta
491.17
C32H23BF15O4Ta
948.26
C24H38NO4Ta‚2CF3SO3
883.64
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
290(2)
0.71073
100(2)
290(2)
0.71073
1.54178
triclinic
P1h
monoclinic
P21/n
10.060(2)
12.410(1)
13.713(5)
monoclinic
P21/n
10.414(2)
25.139(4)
12.841(7)
9.4230(1)
11.2053(1)
16.6550(1)
75.192(1)
73.809(1)
78.027(1)
1615.06(2)
2
b (Å)
c (Å)
R (deg)
â (deg)
105.13(2)
94.36(3)
ø (deg)
volume (Å3)
Z
1652.6(7)
4
1.974
6.978
3352(2)
4
1.751
3.489
1760
density(calcd) (g/cm3)
1.950
7.445
920
abs coeff (mm-1
F(000)
)
952
cryst size (mm3)
0.22 × 0.20 × 0.20
2.25 to 28.04
-13 e h e 12
0 e k e 16
0 e l e 18
4101
3946 [R(int) ) 0.0265]
3946/0/186
1.004
0.18 × 0.14 × 0.08
0.20 × 0.10 × 0.10
θ range for data collection (deg)
index ranges
2.83 to 62.73
2.12 to 27.96
-10 e h e 10
-12 e k e 11
-19 e l e 17
9766
4814 [R(int) ) 0.0302]
4814/0/570
-13 e h e 13
0 e k e 33
0 e l e 16
no. of reflns collected
indep reflns
8392
8055 [R(int) ) 0.0619]
8055/99/457
0.998
no. of data/restraints/params
goodness-of-fit on F2
1.038
final R indices [I > 2σ(I)]
largest diff peak and hole (e‚Å-3
R1 ) 0.0231, wR2 ) 0.0474
0.760 and -0.822
R1 ) 0.0261, wR2 ) 0.0657
0.989 and -0.490
R1 ) 0.0606, wR2 ) 0.1160
1.272 and -1.386
)
(ZORA).41 A triple-ú plus two polarization basis set was used for
tantalum atoms and a plus one polarization function for the other
atoms. For non-hydrogen atoms a relativistic frozen-core potential
was used, including 4d for tantalum, 2p for chlorine, and 1s for
carbon and oxygen. A numerical integration parameter of 5.0 was
employed in optimization and single-point calculations. Geometry
convergence criteria were raised 1 order of magnitude to 10-3
hartree‚Å-1. Symmetry constraints were not used. The topological
analysis of the electron density function was carried out using the
Xaim program package.42
empirical absorption corrections (SADABS43) to be applied using
multiple measurements of symmetry-equivalent reflections (ratio
of minimum to maximum apparent transmission: 0.7013). The unit
cell parameters were calculated and refined from the full data set.
The raw intensity data frames were integrated with the SAINT44
program, which also applied corrections for Lorentz and polarization
effects.
For all three compounds, the software package SHELXTL45
version 6.10 was used for space group determination, structure
solution, and refinement. The structure was solved by direct methods
(SHELXS-97),46 completed with difference Fourier syntheses, and
refined with full-matrix least-squares using SHELXL-9747 minimiz-
ing w(Fo2 - Fc2)2. Weighted R factors (Rw) and all goodness of fit
S are based on F2; conventional R factors (R) are based on F. All
non-hydrogen atoms were refined with anisotropic displacement
parameters. All scattering factors and anomalous dispersions factors
are contained in the SHELXTL 6.10 program library. The hydrogen
atom positions were calculated geometrically and were allowed to
ride on their parent carbon atoms with fixed isotropic U, except
H100 and H101 for 6, which were located in the difference Fourier
map and subsequently fixed.
X-ray Data Collection, Structure Determination, and Refine-
ment of Complexes 1, 5, and 6. The crystallographic data and
experimental details about the data collection and structure refine-
ment are listed in Table 6. The crystals of compounds 1 and 6
were selected and mounted on a fine glass fibber with epoxy
cement. The data collections were performed at 25 °C on a Nonius-
Mach3 diffractometer equipped with a graphite-monochromated
radiation source (λ ) 0.71073 Å) using a ω/2θ scan technique to
a maximum value of 56°. Unit cell dimensions were obtained by a
least-squares fit of the 2θ values of 25 high-order reflections by
using the Mach3 centering routines. Data were corrected in the usual
fashion for Lorentz and polarization effects, and a semiempirical
absorption correction was not necessary.
Acknowledgment. Some of us (R.F., C.H., A.O., A.R.,
M.J.R.) gratefully acknowledge financial support from the
Ministerio de Educacio´n y Ciencia, Spain (Grant No. BQU2002-
04638-CO2-02) and the Junta de Comunidades de Castilla-La
Mancha (Grant Nos. PAC-02-003 and GC-02-010). C.B. and
M.F. are indebted to the ICIQ Foundation for financial support.
A single crystal of 5 was mounted on a glass fiber and transferred
to a Bruker SMART 6K CCD area-detector three-circle diffracto-
meter with a MAC Science rotating anode (Cu KR radiation, λ )
1.54178 Å) generator equipped with Goebel mirrors at settings of
50 kV and 100 mA. X-ray data were collected at 100 K, with a
combination of six runs at different æ and 2θ angles, 3600 frames.
The data were collected using 0.3° wide ω scans (1 s/frame at 2θ
) 40° and 2 s/frame at 2θ ) 100°), with a crystal-to-detector
distance of 4.0 cm. The substantial redundancy in data allows
(43) Sheldrick, G. M. SADABS Version 2.03, A Program for Empirical
Absorption Correction; Universita¨t Go¨ttingen, 1997-2001.
(44) SAINT+ NT Ver. 6.04, SAX Area-Detector Integration Program;
Bruker AXS: Madison, WI, 1997-2001.
(45) Bruker AXS SHELXTL Version 6.10, Structure Determination
Package; Bruker AXS: Madison, WI, 2000.
(46) Sheldrick, G. M. SHELXS-97, Program for Structure Solution: Acta
Crystallogr. Sect. A 1990, 46, 467.
(47) (a) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen, 1997. (b) SMART V. 5.625, Area-Detector
Software Package; Bruker AXS: Madison, WI, 1997-2001.
(41) (a) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys.
1993, 99, 4597. (b) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem.
Phys. 1994, 101, 9783. (c) van Lenthe E.; Ehlers, A.; Baerends, E. J. J.
Chem. Phys. 1999, 110, 8943.
(42) Ortiz Alba, J. C.; Bo, C. Xaim-1.0; Universitat Rovira I Virgili:
Tarragona, Spain. http://www.quimica.urv.es/XAIM.

3344 Organometallics, Vol. 25, No. 14, 2006
Bo et al.
of 2 and 3, selected geometrical parameters, interaction diagram
of molecular orbitals of 6, and CIF files for 1, 5, and 6. This material
is available free of charge via the Internet at http://pubs.acs.org.
M.F. thanks the Torres Quevedo program of the Ministerio de
Educacio´n y Ciencia, Spain.
Supporting Information Available: Cartesian coordinates (in
Å) of the structures considered in this study, molecular structures
OM060254E