Synthesis, structural characterisation and reactivity of new dinuclear monocyclopentadienyl imidoniobium and -tantalum complexes (see abstract)

Article abstract of DOI:10.1002/ejic.200300530

The preparation of a family of dinuclear monocyclopentadienyl imidoniobium and -tantalum complexes was achieved by two different synthetic routes. The diimido complexes [{M(Cp′)Cl₂}₂(μ-1,i-NC ₆H₄N)] [Cp′ = η⁵-C₅H ₄SiMe₃, M = Nb, i = 4 (1); Cp′ = η⁵-C₅H₄SiMe₃, M = Nb, i = 3 (2); Cp′ = η⁵-C₅H₄SiMe₃, M = Nb, i = 2 (3); Cp′ = η⁵-C₅Me₅, M = Nb, i = 4 (4); Cp′ = η⁵-C₅Me₅, M = Nb, i = 3 (5); Cp′ = η⁵-C₅H₄SiMe ₃, M = Ta, i = 4 (6); Cp′ = η⁵-C ₅H₄SiMe₃, M = Ta, i = 3 (7)] were prepared by the reaction of one equivalent of the trichloro precursor [{MCl ₃}₂(μ-1,i-NC₆H₄N)] (M = Nb, Ta, i = 4, 3 or 2) with two equivalents of either C₅H ₄(SiMe₃)₂ or C₅Me ₅-(SiMe₃). Complexes 1-7 can also be prepared by the reaction of two equivalents of [MCp′Cl₄] (Cp′ = η⁵-C₅H₄SiMe₃, M = Nb, Ta; Cp′ = η⁵-C₅Me₅, M = Nb, Ta) with one equivalent of the corresponding aniline compound, N,N,N′,N′- tetrakis(trimethylsilyl)-1,4-, -1,3-, or -1,2-phenylenediamine, respectively. The synthesis of [{Ta(Cp′)Cl₂}₂(μ-1,i-NC ₆H₄N)] [Cp′ = η⁵-C₅Me ₅, i = 4 (8); Cp′ = η⁵-C₅Me ₅, i = 3 (9)] was only successful with the second preparative method. The reaction of 1, 2 and 8 with alkylating reagents gave the corresponding tetraalkyl derivatives, [{M(Cp′)R₂}₂(μ-1-i- NC₆H₄N)] [Cp′ = η⁵-C ₅H₄SiMe₃, M = Nb, R = Me, i = 4 (10); Cp′ = η⁵-C₅H₄SiMe₃, M = Nb, R = CH₂SiMe₃, i = 4 (11); Cp′ = η⁵-C ₅H₄SiMe₃, M = Nb, R = CH₂Ph, i = 4 (12); Cp′ = η⁵-C₅H₄SiMe₃, M = Nb, R = Me, i = 3 (13); Cp′ = η⁵-C₅H ₄SiMe₃, M = Nb, R = CH₂SiMe₃, i = 3 (14); Cp′ = η⁵-C₅H₄SiMe₃, M = Nb, R = CH₂Ph, i = 3 (15); Cp′ = η⁵-C ₅Me₅, M = Ta, R = Me, i = 4 (16); Cp′ = η⁵-C₅Me₅, M = Ta, R = CH ₂SiMe₃, i = 4 (17); Cp′ = η⁵-C ₅Me₅, M = Ta, R = CH₂Ph, i = 4 (18)]. The alkylated complexes with other stoichiometries, [{M(Cp′)(Me)(X)} ₂(μ-1,4-NC₆H₄N)] [Cp = η⁵- C₅H₄SiMe₃, M = Nb, X = Cl (19); Cp = η⁵-C₅H₄SiMe₃, M = Nb, X = NMe₂ (20); Cp = η⁵-C₅Me₅, M = Ta, X = Cl (21)], were also prepared. The molecular structures of complexes 1, 8 and 17 were determined by single-crystal X-ray diffraction studies. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300530

FULL PAPER
Synthesis, Structural Characterisation and Reactivity of New Dinuclear
Monocyclopentadienyl Imidoniobium and -tantalum Complexes ؊
X-ray Crystal Structures of [{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,4-NC6H4N)],
[{Ta(η5-C5Me5)Cl2}2(µ-1,4-NC6H4N)] and [{Ta(η5-C5Me5)(CH2SiMe3)2}2-
(µ-1,4-NC6H4N)]
[b]
[a]
[a]
[a]
´
´
´
˜
Antonio Antinolo, Ivan Dorado, Mariano Fajardo, Andres Garces,
[a]
[c]
[d]
´
´
Isabel Lopez-Solera, Carmen Lopez-Mardomingo, Marek M. Kubicki,
Antonio Otero,*[b] and Sanjiv Prashar[a]
Keywords: Cyclopentadienyl ligands / Half-sandwich complexes / N ligands / Niobium / Tantalum
The preparation of a family of dinuclear monocyclopentadi- 1, 2 and 8 with alkylating reagents gave the corresponding
enyl imidoniobium and -tantalum complexes was achieved
by two different synthetic routes. The diimido complexes
[{M(CpЈ)Cl2}2(µ-1,i-NC6H4N)] [CpЈ = η5-C5H4SiMe3, M = Nb,
i = 4 (1); CpЈ = η5-C5H4SiMe3, M = Nb, i = 3 (2); CpЈ = η5-
C5H4SiMe3, M = Nb, i = 2 (3); CpЈ = η5-C5Me5, M = Nb, i =
4 (4); CpЈ = η5-C5Me5, M = Nb, i = 3 (5); CpЈ = η5-C5H4SiMe3,
M = Ta, i = 4 (6); CpЈ = η5-C5H4SiMe3, M = Ta, i = 3 (7)] were
prepared by the reaction of one equivalent of the trichloro
precursor [{MCl3}2(µ-1,i-NC6H4N)] (M = Nb, Ta, i = 4, 3 or 2)
with two equivalents of either C5H4(SiMe3)2 or C5Me5-
(SiMe3). Complexes 1−7 can also be prepared by the reaction
of two equivalents of [MCpЈCl4] (CpЈ = η5-C5H4SiMe3, M =
tetraalkyl derivatives, [{M(CpЈ)R2}2(µ-1,i-NC6H4N)] [CpЈ =
η5-C5H4SiMe3, M = Nb, R = Me, i = 4 (10); CpЈ = η5-
C5H4SiMe3, M = Nb, R = CH2SiMe3, i = 4 (11); CpЈ = η5-
C5H4SiMe3, M = Nb, R = CH2Ph, i = 4 (12); CpЈ = η5-
C5H4SiMe3, M = Nb, R = Me, i = 3 (13); CpЈ = η5-C5H4SiMe3,
M = Nb, R = CH2SiMe3, i = 3 (14); CpЈ = η5-C5H4SiMe3, M =
Nb, R = CH2Ph, i = 3 (15); CpЈ = η5-C5Me5, M = Ta, R = Me,
i = 4 (16); CpЈ = η5-C5Me5, M = Ta, R = CH2SiMe3, i = 4 (17);
CpЈ = η5-C5Me5, M = Ta, R = CH2Ph, i = 4 (18)]. The alkylated
complexes with other stoichiometries, [{M(CpЈ)(Me)(X)}2(µ-
1,4-NC6H4N)] [Cp = η5-C5H4SiMe3, M = Nb, X = Cl (19);
Cp = η5-C5H4SiMe3, M = Nb, X = NMe2 (20); Cp = η5-C5Me5,
Nb, Ta; CpЈ = η5-C5Me5, M = Nb, Ta) with one equivalent of M = Ta, X = Cl (21)], were also prepared. The molecular
the corresponding aniline compound, N,N,NЈ,NЈ-tetrakis(tri- structures of complexes 1, 8 and 17 were determined by
methylsilyl)-1,4-, -1,3-, or -1,2-phenylenediamine, respect- single-crystal X-ray diffraction studies.
ively. The synthesis of [{Ta(CpЈ)Cl2}2(µ-1,i-NC6H4N)] [CpЈ =
η5-C5Me5, i = 4 (8); CpЈ = η5-C5Me5, i = 3 (9)] was only suc-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
cessful with the second preparative method. The reaction of
Germany, 2004)
Introduction
established imido compounds of the d0 metals niobium and
tantalum are known.[1] For example, half-sandwich imido
compounds of Nb and Ta of general formula M(η5-
C5R5Ј)(NR)X2 are well documented[2] and these are of con-
siderable interest since an ‘‘isolobal’’ relationship between
[M(η5-C5R5Ј)(NR)] (M ϭ group 5 metal) and [M(η5-
C5R5Ј)2] (M ϭ Group 4 metal) fragments has been estab-
lished.[3] In fact, it has been claimed that monocyclopenta-
Imido derivatives of early transition metals have been
widely studied and, in particular, a large number of well-
[a]
´
´
Departamento de Tecnologıa Quımica, Ambiental y de los
Materiales, E.S.C.E.T., Universidad Rey Juan Carlos,
´
28933 Mostoles, Madrid, Spain
Fax: (internat.) ϩ 34-91-488-7068
E-mail: S.Prashar@escet.urjc.es
[b]
´
´
´
´
Departamento de Quımica Inorganica, Organica y Bioquımica,
´
Universidad de Castilla-La Mancha, Facultad de Quımicas, dienyl imido group 5 metal complexes could behave in a simi-
Campus Universitario,
lar manner to metallocenes of group 4 metals in olefin pol-
13071-Ciudad Real, Spain
ymerisation catalytic processes.[2g] However, to date several
Fax: (internat.) ϩ 34-926-295-318
E-mail: Antonio.Otero@uclm.es
species of this type have been used as catalysts without
much success.[4] Two main preparative pathways have been
employed in the synthesis of half-sandwich imido group 5
metal complexes. Firstly, reaction of the appropriate cyclo-
pentadienide reagent with imido-containing [M(NR)Cl3L2]
(M ϭ Nb, Ta) precursors[5] has been employed and, sec-
[c]
´
´
Departamento de Quımica Organica, Campus Universitario,
´
Universidad de Alcala,
´
28871 Alcala de Henares, Madrid, Spain
[d]
`
`
dЈElectrosynthese
Laboratoire
de
Synthese
et
´
´
Organometalliques, CNRS UMR 5632, Faculte des Sciences
´
Gabriel, Universite de Bourgogne,
6 bd Gabriel, 21000 Dijon, France
Eur. J. Inorg. Chem. 2004, 1299Ϫ1310
DOI: 10.1002/ejic.200300530
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A. Otero et al.
FULL PAPER
ondly, the most general method involves the introduction as the silylated compounds C5H4(SiMe3)2 and C5Me5-
of the imido group into precursors containing the cyclopen- (SiMe3). This method has previously been used by Green
tadienyl ligand.[6] On considering the different possible et al.[11] to prepare cyclopentadienyl-imido complexes with
pathways to achieve this transformation, the one that is par- constrained geometry and by Maatta et al.[12] for the prep-
ticularly noteworthy is that in which the imido group is in- aration of imido-containing monocyclopentadienyl va-
corporated by breaking the SiϪN bond of a silylamine or nadium derivatives. However, the trichloro complexes
-amide derivative.[7] The use of this last method, developed [{M(L)2Cl3}2(µ-1,i-NC6H4N)] (L ϭ CH3CN; M ϭ Nb, Ta;
by our research group, gives rise to an interesting series of i ϭ 3, 4), do not react with the silylated cyclopentadienyl
organo-diimido complexes [{Nb(L)2Cl3}2(µ-1,i-NC6H4N)] reagents. This lack of reactivity is probably due to the pres-
(L ϭ CH3CN or tBupy) by reaction of NbCl5 with the ence of two additional ligands (L) in the coordination
appropriate aniline N,N,NЈ,NЈ-tetrakis(trimethylsilyl)-1,4-, sphere which diminishes the acidity of the metal centre
-1,3-, or -1,2-phenylenediamine in the presence of CH3CN making the elimination of the expected SiMe3Cl by-product
or tBupy.[8] As a continuation of our research in this field[9] unfavourable. In order to increase the reactivity of the diim-
we are currently interested in the preparation of half-sand- idoniobium and -tantalum precursors towards the cyclo-
wich diimidoniobium and -tantalum complexes in order to pentadienyl reagents, alternative compounds without donor
synthesise new types of dinuclear complexes in which the ligands were employed, namely [{MCl3}2(µ-1,i-NC6H4N)]
two metal centres are linked by conjugated π-systems. This (M ϭ Nb, Ta), which were prepared from the reaction of
class of diimido complex is rare, particularly with an aryl MCl5 with the appropriate N,N,NЈ,NЈ-tetrakis(trimethylsi-
ligand.[10] The work described in this paper focuses on the lyl)phenylenediamine in CH2Cl2.[8] When these diimido
synthesis and structural characterisation of half-sandwich complexes were reacted with the appropriate silylated cyclo-
imidoniobium and -tantalum complexes, and some aspects pentadienyl reagents in a 1:2 molar ratio in CH2Cl2 at 90 °C
of their reactivity.
(see Exp. Sect.), the cyclopentadienyl-containing dinuclear
species [{M(CpЈ)Cl2}2(µ-1,i-NC6H4N)] [CpЈ
ϭ
η5-
C5H4SiMe3, M ϭ Nb, i ϭ 4 (1); CpЈ ϭ η5-C5H4SiMe3,
M ϭ Nb, i ϭ 3 (2); CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, i ϭ 2
(3); CpЈ ϭ η5-C5Me5, M ϭ Nb, i ϭ 4 (4); CpЈ ϭ η5-C5Me5,
M ϭ Nb, i ϭ 3 (5); CpЈ ϭ η5-C5H4SiMe3, M ϭ Ta, i ϭ 4
(6); CpЈ ϭ η5-C5H4SiMe3, M ϭ Ta, i ϭ 3 (7)] were iso-
Results and Discussion
The preparation of derivatives [{M(CpЈ)Cl2}2(µ-1,i-
NC6H4N)] (CpЈ ϭ η5-C5H4SiMe3, η5-C5Me5; M ϭ Nb, Ta;
i ϭ 3, 4) was initially undertaken by reaction of the appro-
lated (Scheme 1).
A number of reactions did not, however, give the desired
priate complex [{M(L)2Cl3}2(µ-1,i-NC6H4N)] (L
ϭ
CH3CN; M ϭ Nb, Ta; i ϭ 3, 4)[8] with different cyclopen- products. These involved tantalum derivatives formed from
tadienide reagents, namely M(C5H4SiMe3) (M ϭ Li, Na, C5Me5(SiMe3) and the derivatives [{MCl3}2(µ-1,2-
K) or K(C5Me5), in several solvents and under different NC6H4N)] (M ϭ Nb, Ta) formed from the reagents C5Me5-
experimental conditions. However, in all cases an intrac- (SiMe3) and C5H4(SiMe3)2. This procedure has provided a
table mixture of products was obtained. As an alternative useful synthetic route to dinuclear monocyclopentadienyl
method to prepare the aforementioned complexes, we de- imido species of these metals, particularly with the reagent
cided to use milder cyclopentadienyl transfer reagents, such C5H4(SiMe3)2, in high yields (about 80% for the tantalum
Scheme 1
1300
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Eur. J. Inorg. Chem. 2004, 1299Ϫ1310

New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes
FULL PAPER
Scheme 2
complexes and quantitative yields for the niobium com-
plexes). The overall reactions for the tantalum species re-
quire long reaction times of about one week. In order to
improve this, an alternative method was considered to pre-
pare the complexes. This method consisted of the reaction
of the appropriate MCpЈCl4 precursor (CpЈ
ϭ
η5-
C5H4SiMe3, η5-C5Me5; M ϭ Nb, Ta) with the correspond-
ing N,N,NЈ,NЈ-tetrakis(trimethylsilyl)phenylenediamine de-
rivative (Scheme 2).
This synthetic route, which is an adaptation of that pre-
viously described by Gibson et al.[3a] for the preparation
of imido-containing niobium complexes, is an easy way to
prepare cleanly (by elimination of SiMe3Cl) the correspond-
ing diimidoniobium and -tantalum complexes 1Ϫ7 as well
as the new tantalum complexes [{Ta(η5-C5Me5)Cl2}2(µ-1,i-
NC6H4N)] [i ϭ 4 (8), i ϭ 3 (9)] in quantitative yields (see
Exp. Sect.). On using this method the reaction times for the
preparation of tantalum complexes are considerably short-
ened (to about 30 h). In wet solvents the materials evolve
to the appropriate oxo-containing complexes with elimin-
ation of the corresponding diamine.[13] For example, solu-
tions of 8 or 9 in wet CH2Cl2 give rise to the oxo complex
Figure 1. Molecular structure and atom-labelling scheme for
[{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,4-NC6H4N)] (1), with thermal ellip-
soids at 30% probability
1
[{Ta(η5-C5Me5)Cl3}2(µ-O)].[14] Complexes 1Ϫ9, as well as Complexes 1Ϫ9 were analysed by variable-temperature H
other complexes described in this work, were characterised NMR spectroscopy in order to study this proposed dy-
by 1H, 13C NMR and IR spectroscopy (see Exp. Sect.). The namic behaviour. However, even at Ϫ90 °C there was no
1H and 13C NMR spectra of 1Ϫ9 exhibit the characteristic evidence of restricted rotation, probably due to the low en-
signals for both the cyclopentadienyl and phenylene groups. ergy value for the rotation barrier. The IR spectra of each
This observation agrees with a structural situation where a complex contains a band between 1300Ϫ1370 cmϪ1, which
diimidophenylene group bridges two metal atoms, which is characteristic of the terminal imido ligand.[3a] Several vi-
are, in turn, located in the plane formed by this ligand, in brational spectroscopic studies of group 5 imido complexes
a three-legged piano-stool geometry around each metal cen- have been carried out.[15] In order to establish unequivocally
tre (see Scheme 1). Free rotation around the NϪC bond the structural disposition of these complexes, an X-ray mo-
would be expected in solution and, for this reason, although lecular analysis of compounds 1 and 8 was carried out. The
a trans-disposition of both cyclopentadienyl ligands was molecular structures and atomic numbering schemes are
considered in Scheme 1, alternative dispositions corre- shown in Figure 1 and 2, respectively. Selected bond lengths
sponding to other rotamers should also be considered. and angles for 1 and 8 are given in Table 1.
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A. Otero et al.
FULL PAPER
Figure 2. Molecular structure and atom-labelling scheme for [{Ta(η5-C5Me5)Cl2}2(µ-1,4-NC6H4N)] (8), with thermal ellipsoids
at 30% probability
˚
The metal-nitrogen distances lie within the range ex-
Table 1. Selected bond lengths (A) and angles (°) for 1 and 8
pected for a triple bond[3a,16,17] [1.776(8) and 1.783(5) A for
˚
1
8
1 and 8, respectively]. The MϪNϪC1 angles of 161.0(7)°
for 1 and 166.4(5)° for 8 deviate slightly from linear. Such
deviations are normally in the range 12Ϫ15° (see Table 2).
In the case of [Nb(ϭNPh)(η5-C5H4SiMe3)2Cl] extended-
Hückel molecular-orbital calculations established that the
imido bond angles for ‘‘linear imide’’ in this class of com-
plex can vary up to 140° with little effect on the NbϪN
bonding.[18] Therefore we propose that in 1 and 8 the nitro-
gen atom is sp hybridized.
MϪN
1.776(8)
2.343(3)
2.344(3)
2.468(9)
2.47(1)
2.39(1)
2.36(1)
2.42(1)
1.39(1)
1.783(5)
2.325(2)
2.339(2)
2.468(7)
2.478(7)
2.382(7)
2.365(6)
2.382(6)
1.377(7)
MϪCl1
MϪCl2
MϪC4
MϪC5
MϪC6
MϪC7
MϪC8
NϪC1
The cyclopentadienyl group is in a typical[3a] eclipsed fa-
shion with respect to the imido group for both complexes
(see Figure 3a). The slight lengthening of the MϪC4
NϪMϪCl1
NϪMϪCl2
Cl1ϪMϪCl2
MϪNϪC1
101.7(3)
103.5(3)
106.0(1)
161.0(7)
102.3(2)
104.3(2)
105.4(1)
166.4(5)
˚
[2.468(9) and 2.468(7) A for 1 and 8, respectively] and
˚
MϪC5 [2.47(1) and 2.478(7) A for 1 and 8, respectively]
distances with respect to other MϪC ring distances may be
due to the trans influence of the imido group.
The structures of 1 and 8 consist of dinuclear complexes
of niobium and tantalum, respectively. The metal atoms are
The second part of this work involves the study of alky-
bound to the cyclopentadienyl ring in an η5 mode, to two lation reactions of complexes 1, 2 and 8. The reaction of
chlorine atoms and to the nitrogen from the imido group alkylating
reagents,
MeLi,
Me3SiCH2MgCl
or
in a three-legged piano-stool conformation. The cyclopen- Mg(CH2C6H5)2(THF)2, in a 1:4 molar ratio with 1, 2 or 8
tadienyl rings are in a trans disposition with respect to each afforded the per-alkylated complexes, [{M(CpЈ)R2}2(µ-1,i-
other. The metal atom is out of the plane defined by N, C1, NC6H4)] [CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, R ϭ Me, i ϭ 4
C2 and C3 by 0.54(2) and 0.39(1) A for complexes 1 and (10); CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, R ϭ CH2SiMe3, i ϭ
˚
8, respectively.
4 (11); CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, R ϭ CH2Ph, i ϭ 4
Table 2. Selected structural data for imido complexes
˚
MϪN (A)
MϪNϪC (°)
Ref.
[{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,4-NC6H4N)] (1)
[{Ta(η5-C5Me5)Cl2}2(µ-1,4-NC6H4N)] (8)
[{Ta(η5-C5Me5)(CH2SiMe3)2}2(µ-1,4-NC6H4N)] (17)
[Nb(ϭNAr)(η5-C5H5)(NHtBu)Cl][a]
[Nb(ϭNAr)(η5-C5H5)Cl2][a]
1.776(8)
1.783(5)
1.794(5)
1.793
1.761
1.763
1.787
1.780
1.774
1.812
160.9(7)
166.4(5)
167.4(5)
168.5
165.6
166.6
174.6
171.3
169.9
171.4
This work
This work
This work
[17a]
[3a]
[17b]
[17c]
[3a]
[Nb(ϭNAr)(η5-C5H5)Cl2][b]
[Nb(ϭNAr)(η5-C5H5)(η2-NHtBu)(CH2tBu)H][a]
[Ta(ϭNAr)(η5-C5Me5)Cl2][a]
[Ta(ϭNAr)(η5-C5Me5)Cl2][b]
[16]
[Ta(ϭNAr)(η5-C5Me5)(CO){Si(SiMe3)3}H][a]
[Ta(ϭNAr)(η5-C5H5)(PMe3)(SiMe2Cl)H][a]
[17d]
[17e]
1.821
171.8
[a]
[b]
Ar ϭ C6H3iPr2-2,6. Ar ϭ C6H3Me2-2,6.
1302
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New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes
FULL PAPER
Figure 3. View along the ring centroid-metal vector (a) for compound 1, and (b) for compound 17
(12); CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, R ϭ Me, i ϭ 3 (13);
Finally, the reactions of 1 and 8 with the milder alkylat-
CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, R ϭ CH2SiMe3, i ϭ 3 ing agent ZnMe2, in a 1:2 molar ratio yielded the chloro-
(14); CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb, R ϭ CH2Ph, i ϭ 3 methyl complexes [{M(CpЈ)(Me)(Cl)}2(µ-1,4-NC6H4N)]
(15); CpЈ ϭ η5-C5Me5, M ϭ Ta, R ϭ Me, i ϭ 4 (16); CpЈ ϭ [CpЈ ϭ η5-C5H4SiMe3, M ϭ Nb (19); CpЈ ϭ η5-C5Me5,
η5-C5Me5, M ϭ Ta, R ϭ CH2SiMe3, i ϭ 4 (17); CpЈ ϭ η5- M ϭ Ta (21)], while the reaction of 19 with LiNMe2 in a 1:2
C5Me5, M ϭ Ta, R ϭ CH2Ph, i ϭ 4 (18)] (Scheme 3).
molar ratio (see Exp. Sect.) afforded the amido-containing
Scheme 3
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A. Otero et al.
FULL PAPER
1
complex
[{Nb(η5-C5H4SiMe3)(Me)(NMe2)}2(µ-1,4- Scheme 4). The H and 13C NMR spectra of these com-
NC6H4N)] (20).
plexes exhibit two sets of signals in a 1:1 ratio, correspond-
1
The H and 13C NMR spectra for complexes 10Ϫ18 are ing to the presence of both diastereomers (R,R/S,S) and
similar to those found for the parent complexes with re- (R,S) (see Exp. Sect.).
gards to both the cyclopentadienyl and phenylene groups
The IR spectra of complexes 10Ϫ21 show a band at ca.
(see Exp. Sect.). In addition, the spectra also contain the 1300Ϫ1350 cmϪ1, which is characteristic of the terminal
resonances due to the alkyl groups attached to the metal imido ligand.[3a] In accordance with the different spectro-
centre. In these complexes the four alkyl groups are both scopic data described for alkyl-containing complexes, a
chemically and magnetically equivalent and only one set of structural disposition similar to that found for the chloro
signals for these groups is present. For example, one singlet complexes can be expected (see Scheme 3). The X-ray crys-
corresponding to methyl groups for complexes 10, 13 and tal-structure determination for 17 confirmed this situation.
1
16 was observed in the H NMR spectra. Furthermore, in The molecular structure and atomic numbering scheme are
all the complexes the metal atom is a pro-chiral centre and shown in Figure 4. Selected bond lengths and angles for 17
so the protons of the methylene groups (for CH2SiMe3 or are given in Table 3.
CH2Ph) for complexes 11, 12, 14, 15, 17 and 18 are dia-
˚
stereotopic and, therefore, give rise to two doublets of an Table 3. Selected bond lengths (A) and angles (°) for 17
1
AB spin-system in their H NMR spectra (see Exp. Sect.).
MϪN
1.794(5)
2.473(7)
2.533(6)
2.492(7)
2.397(7)
2.428(7)
2.149(6)
2.193(7)
1.377(8)
For 19Ϫ21 the two metal atoms of the binuclear moiety are
chiral centres and the stereoisomer the meso-(R,S) and the
enantiomers rac-(R,R) and -(S,S) are formed (see
MϪC4
MϪC5
MϪC6
MϪC7
MϪC8
MϪC9
MϪC10
NϪC1
NϪMϪC9
NϪMϪC10
C9ϪMϪC10
MϪNϪC1
104.7(3)
100.9(3)
104.0(3)
167.4(5)
The structure of 17 consists of a dinuclear complex where
the metal atoms are bound to the cyclopentadienyl rings in
an η5 mode. In addition, the tantalum atoms are linked to
two methylene groups from CH2SiMe3 and to the nitrogen
atom from the imido group. Complex 17 adopts a three-
legged piano-stool conformation about the metal centres.
The cyclopentadienyl rings are in a trans disposition with
respect to each other. The metal atom is out of the plane
Scheme 4
˚
defined by N, C1, C2 and C3, by 0.36(1) A. The metal-
Figure 4. Molecular structure and atom-labelling scheme for [{Ta(η5-C5Me5)(CH2SiMe3)2}2(µ-1,4-NC6H4N)] (17), with thermal ellipsoids
at 30% probability
1304
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1299Ϫ1310

New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes
FULL PAPER
˚
Method B: CH2Cl2 (60 mL) was added to the corresponding com-
plex [{NbCl3}2(µ-1,i-NC6H4N)] (i ϭ 4, 3 or 2) in a Teflon valve
ampoule. C5H4(SiMe3)2 was added to this green suspension and
the ampoule was placed in an oil bath and heated at 90 °C for 24 h.
The initial green suspension changed to a red solution. The solvent
was removed under vacuum and the solids obtained were identified
as 1, 2 and 3, respectively.
nitrogen distance of 1.794(5) A and the MϪNϪC1 angle of
167.4(5)° lie within the range expected for a triple bond
(see Table 2).[3a,16,17]
The cyclopentadienyl group in 17 is in a staggered dispo-
sition with respect to the imido group (Figure 3b), in con-
trary to the eclipsed disposition observed in 1 and 8 (Fig-
ure 3a). The slight lengthening of the MϪC4 [2.473(7) A]
and MϪC5 [2.533(6) A] distances is probably due to the
˚
˚
Complex 1: From [{NbCl3}2(µ-1,4-NC6H4N)] (0.80 g, 1.59 mmol)
and C5H4(SiMe3)2 (0.74 mL, 3.18 mmol). 1.12 g of a red solid was
trans influence of the imido group.
1
obtained (Yield: 100%). H NMR (300 MHz, CDCl3, 25 °C): δ ϭ
0.26 (s, 18 H, 2 ϫ C5H4SiMe3), 6.60 and 6.75 (2m, each 4 H, 2 ϫ
C5H4), 6.89 (s, 4 H, C6H4) ppm. 13C{1H} NMR (75 MHz, CDCl3,
Conclusions
25 °C): δ ϭ Ϫ0.5 (C5H4SiMe3), 114.7, 122.0 and 125.9 (Cipso
;
C5H4SiMe3) 124.3 and 153.9 (Cipso; C6H4) ppm. IR (CsI/Nujol):
ν˜ ϭ 3090m, 1483s, 1395m, 1370s, 1311vs, 1253vs, 1172s, 1099m,
1074w, 1045s, 1004w, 990m, 903s, 840vs, 764m, 703w, 635w, 530w,
423m, 380s and 330m cmϪ1. C22H30Cl4N2Nb2Si2 (706.3): calcd. C
37.41, H 4.28, N 3.97; found C 37.05, H 4.48, N 4.08.
In this paper we report the synthesis of new dinuclear
monocyclopentadienyl imidoniobium and -tantalum com-
plexes and their reactivity towards different alkylating ag-
ents. The molecular structures of several of these complexes
have been determined by single-crystal X-ray diffraction
studies.
Complex 2: From [{NbCl3}2(µ-1,3-NC6H4N)] (0.71 g, 1.41 mmol)
and C5H4(SiMe3)2 (0.66 mL, 2.82 mmol). 1.0 g of a red solid was
1
obtained (Yield: 100%). H NMR (300 MHz, CDCl3, 25 °C): δ ϭ
0.29 (s, 18 H, 2 ϫ C5H4SiMe3), 6.62 and 6.76 (2m, each 4 H, 2 ϫ
C5H4), 6.62 (1 H), 6.72 (2 H) and 7.13 (1 H) (3m, C6H4) ppm.
13C{1H} NMR (50 MHz, CDCl3, 25 °C): δ ϭ Ϫ0.5 (C5H4SiMe3),
114.4, 122.2 and 126.3 (Cipso; C5H4SiMe3), 118.9, 122.1, 128.3 and
155.6 (Cipso; C6H4) ppm. IR (KBr): ν˜ ϭ 3093m, 2953m, 2598m,
1567s, 1462s, 1410m, 1370m, 1332m, 1306m, 1283m, 1250s, 1170s,
1047s, 1036s, 971w, 903s, 839vs, 780s, 757s, 694s, 680m, 630s, 419w
and 374s cmϪ1. C22H30Cl4N2Nb2Si2 (706.3): calcd. C 37.41, H 4.28,
N 3.97; found C 37.40, H 4.55, N 3.68.
Experimental Section
General Remarks: All reactions were performed using standard
Schlenk-tube techniques under an atmosphere of dry nitrogen. Sol-
vents were distilled from appropriate drying agents and degassed
before use. Literature methods were employed for the synthesis of
the following compounds: N,N,NЈ,NЈ-tetrakis(trimethylsilyl)pheny-
lenediamine,[19]
[Nb(η5-C5H4SiMe3)Cl4],[20]
[{NbCl3}2(µ-1,i-
NC6H4N)] (i ϭ 4, 3 or 2),[8a] C5H4(SiMe3)2,[21] [Ta(η5-C5H4Si-
Me3)Cl4],[22] [{TaCl3}2(µ-1,i-NC6H4N)] (i ϭ 4 or 3),[8b] [Ta(η5-
C5Me5)Cl4],[23] C5Me5(SiMe3),[24] [Nb(η5-C5Me5)Cl4],[25] and
[Mg(CH2Ph)2(THF)2].[25] All commercial products were purchased
from Aldrich and were used without further purification: LiMe,
Mg(CH2SiMe3)Cl, ZnMe2 and LiNMe2. IR spectra were recorded
on a PerkinϪElmer 883 and PerkinϪElmer IR-FT Spectrophoto-
meter 2000. 1H and 13C NMR spectra were recorded on a Gemini-
200 and/or UNITY-300 (Varian) spectrometer. Chemical shifts
were measured relative to residual 1H and 13C resonances for
[D1]chloroform and [D6]benzene as solvents. C, H and N analyses
were carried out with a PerkinϪElmer 240Ϫ13, PerkinϪElmer 240
C and/or Heraeus-CHNϪO-Rapid microanalyzer.
Complex 3: From [{NbCl3}2(µ-1,2-NC6H4N)] (0.77 g, 1.53 mmol)
and C5H4(SiMe3)2 (0.72 mL, 3.06 mmol). 1.08 g of a red solid was
1
obtained (Yield: 100%). H NMR (300 MHz, CDCl3, 25 °C): δ ϭ
0.28 (s, 18 H, 2 ϫ C5H4SiMe3), 6.68 and 6.76 (2m, each 4 H, 2 ϫ
C5H4), 6.93 (m, 4 H, C6H4) ppm. 13C{1H} NMR (75 MHz, CDCl3,
25 °C): δ ϭ Ϫ0.6 (C5H4SiMe3), 114.1, 124.2 and 125.9 (Cipso
;
C5H4SiMe3), 125.5, 126.1, and 150.1 (Cipso; C6H4) ppm. IR (CsI/
Nujol): ν˜ ϭ 3101w, 1577w, 1436m, 1395w, 1371m, 1328m, 1315m,
1253s, 1170m, 1115w, 1048m, 1039w, 987w, 966(md), 933w, 903s,
842vs, 754s, 748s, 632w, 398m, 379s and 336m cmϪ1
.
C22H30Cl4N2Nb2Si2 (706.3): calcd. C 37.41, H 4.28, N 3.97; found
C 36.62, H 4.06, N 4.06.
Preparation of [{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,4-NC6H4N)] (1),
[{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,3-NC6H4N)] (2) and [{Nb(η5-
C5H4SiMe3)Cl2}2(µ-1,2-NC6H4N)] (3). Method A: CH2Cl2 (70 mL)
was added to a mixture of [Nb(η5-C5H4SiMe3)Cl4] and the corre-
sponding N,N,NЈ,NЈ-tetrakis(trimethylsilyl)phenylenediamine in a
Teflon valve ampoule. The ampoule was placed in an oil bath and
heated at 65 °C for 24 h. The solvent was removed under vacuum
and the solids obtained were identified as 1, 2 and 3, respectively.
Preparation of [{Nb(η5-C5Me5)Cl2}2(µ-1,4-NC6H4N)] (4). Method
A: Dichloromethane (60 mL) was added to
a mixture of
[{NbCl3}2(µ-1,4-NC6H4N)] (0.62 g, 1.23 mmol) and C5Me5(SiMe3)
(0.60 mL, 2.47 mmol) in a Teflon valve ampoule. The ampoule was
placed in an oil bath and heated to 90 °C for 24 h. The resulting
solution was allowed to cool down to room temperature, filtered
and the solvent removed under vacuum to give 0.83 g of 4 as a
purple, analytically pure, crystalline solid. (Yield: 100%).
Complex 1: From [Nb(η5-C5H4SiMe3)Cl4] (1.15 g, 3.09 mmol) and
1,4-{(Me3Si)2N}2C6H4 (0.61 g, 1.54 mmol). 1.08 g of a red solid
was obtained (Yield: 100%).
Method B: A Teflon valve NMR tube was charged with a solution
of
[Nb(η5-C5Me5)Cl4]
(15 mg,
0.04 mmol)
and
[1,4-
{(SiMe3)2N}2C6H4] (8 mg, 0.02 mmol) in CDCl3. The mixture was
1
placed in an oil bath, heated to 65 °C and monitored by H NMR
Complex 2: From [Nb(η5-C5H4SiMe3)Cl4] (1.05 g, 2.83 mmol) and
1,3-{(Me3Si)2N}2C6H4 (0.56 g, 1.41 mmol). 1.0 g of a red solid was
obtained (Yield: 100%).
spectroscopy. After 24 h the reaction was complete and gave 4 as
the only product. 1H NMR (300 MHz, CDCl3, 25 °C): δ ϭ 2.07 (s,
30 H, 2 ϫ C5Me5), 6.79 (s, 4 H, C6H4) ppm. 13C{1H} NMR
(75 MHz, CDCl3, 25 °C): δ ϭ 11.8 (C5Me5), 123.9 (C5Me5) 125.1
and 151.1 (Cipso; C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 1476s, 1311s,
1262w, 1094w, 1022m, 1003w, 990w, 840m, 799w, 488w, 393m and
Complex 3: From [Nb(η5-C5H4SiMe3)Cl4] (1.01 g, 2.72 mmol) and
1,2-{(Me3Si)2N}2C6H4 (0.54 g, 1.36 mmol). 0.96 g of a dark brown
solid was obtained (Yield: 100%).
Eur. J. Inorg. Chem. 2004, 1299Ϫ1310
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1305

A. Otero et al.
366m cmϪ1. C26H34Cl4N2Nb2 (702.2): calcd. C 44.47, H 4.88, N C22H30Cl4N2Si2Ta2 (882.4): calcd. C 29.95, H 3.43, N 3.17; found
FULL PAPER
3.99; found C 44.04, H 4.92, N 4.22.
C 29.76, H 3.65, N 3.31.
Preparation of [{Ta(η5-C5Me5)Cl2}2(µ-1,4-NC6H4N)] (8): Dichloro-
methane (40 mL) was added to a mixture of [Ta(η5-C5Me5)Cl4]
(1.72 g, 3.76 mmol) and [1,4-{(SiMe3)2N}2C6H4] (0.75 g,
1.88 mmol) in a Teflon valve ampoule. The ampoule was placed in
an oil bath and heated to 90 °C for 48 h. The resulting solution
was allowed to cool down to room temperature, filtered and the
solvent removed under vacuum to give 2.00 g of 8 as a red, analyti-
cally pure, crystalline solid. (Yield: 100%). An X-ray-quality sample
was obtained from a saturated dichloromethane solution at Ϫ40
°C. 1H NMR (300 MHz, CDCl3, 25 °C): δ ϭ 2.16 (s, 30 H, 2 ϫ
C5Me5), 6.65 (s, 4 H, C6H4) ppm. 13C{1H} NMR (75 MHz, CDCl3,
Preparation of [{Nb(η5-C5Me5)Cl2}2(µ-1,3-NC6H4N)] (5): The syn-
thesis of 5 was carried out in an identical manner to 4.
Method A: [{NbCl3}2(µ-1,3-NC6H4N)] (1.42 g, 2.82 mmol) and
C5Me5(SiMe3) (1.38 mL, 5.63 mmol). 1.98 g of 5 was obtained as
a pink solid (Yield: 100%).
Method B: [Nb(η5-C5Me5)Cl4] (17 mg, 0.046 mmol) and [1,3-
{(SiMe3)2N}2C6H4] (9 mg, 0.023 mmol). (Yield: 100%). 1H NMR
(300 MHz, CDCl3, 25 °C): δ ϭ 2.09 (s, 30 H, 2 ϫ C5Me5), 6.43 (1
H), 6.60 (2 H) and 7.08 (1 H) (3m, C6H4) ppm. 13C{1H} NMR
(75 MHz, CDCl3, 25 °C): δ ϭ 11.9 (C5Me5), 124.0 (C5Me5) 120.2,
122.2, 128.2 and 153.6 (Cipso; C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ
1566s, 1415m, 1338m, 1284s, 1236s, 1149w, 1079w, 1026m, 971w,
897w, 865m, 847w, 791m, 687w, 485w, 469w, 402m and 362s
cmϪ1.C26H34Cl4N2Nb2 (702.2): calcd. C 44.47, H 4.88, N 3.99;
found C 44.21, H 5.06, N 4.07.
25 °C): δ ϭ 11.4 (C5Me5), 121.6 (C5Me5) 125.4 and 150.7 (Cipso
;
C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 1485vs, 1338vs, 1091m, 1028s,
995m and 844s cmϪ1. C26H34Cl4N2Ta2 (878.3): calcd. C 35.56, H
3.90, N 3.19; found C 35.50, H 4.07, N 3.47.
Preparation of [{Ta(η5-C5Me5)Cl2}2(µ-1,3-NC6H4N)] (9): The syn-
thesis of 9 was carried out in an identical manner to 8, from [Ta(η5-
C5Me5)Cl4] (0.81 g, 1.75 mmol) and [1,3-{(SiMe3)2N}2C6H4]
(0.35 g, 0,88 mmol). 0.96 g of 9 was obtained as an orange solid
(Yield: 100%). 1H NMR (300 MHz, CDCl3, 25 °C): δ ϭ 2.18 (s, 30
H, 2 ϫ C5Me5), 6.11 (1 H), 6.28 (2 H) and 7.10 (1 H) (3m, C6H4)
ppm. 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ ϭ 11.5 (C5Me5),
121.8 (C5Me5) 122.4, 122.5, 127.0 and 153.7 (Cipso; C6H4) ppm.
Preparation of [{Ta(η5-C5H4SiMe3)Cl2}2(µ-1,4-NC6H4N)] (6) and
[{Ta(η5-C5H4SiMe3)Cl2}2(µ-1,3-NC6H4N)] (7). Method A: CH2Cl2
(40 mL) was added to a mixture of [Ta(η5-C5H4SiMe3)Cl4] and the
corresponding N,N,NЈ,NЈ-tetrakis(trimethylsilyl)phenylenediamine
in a Teflon valve ampoule. The ampoule was placed in an oil bath
and heated at 70 °C for 16 h. The resulting deep-red solution was
allowed to cool down to room temperature. The solution was fil-
tered and the solvent removed under reduced pressure. The final
products obtained were identified as 6 and 7, respectively.
IR (CsI/Nujol): ν˜ ϭ 1568vs, 1315vs, 1026s, 864m and 351s cmϪ1
.
C26H34Cl4N2Ta2 (878.3): calcd. C 35.56, H 3.90, N 3.19; found C
35.23, H 4.00, N 3.19.
Complex 6: From [Ta(η5-C5H4SiMe3)Cl4] (0.81 g, 1.76 mmol) and
1,4-{(Me3Si)2N}2C6H4 (0.35 g, 0.88 mmol). 0.78 g of a red solid
was obtained (Yield: 100%).
Preparation of [{Nb(η5-C5H4SiMe3)Me2}2(µ-1,4-NC6H4N)] (10)
and [{Nb(η5-C5H4SiMe3)Me2}2 (µ-1,3-NC6H4N)] (13): MeLi was
added at Ϫ78 °C to a suspension of complex 1 or 2 in hexane
(50 mL). The mixture was allowed to warm up to room tempera-
ture and was stirred for 5 h. The solution was filtered and the resi-
due extracted with hexane (2 ϫ 20 mL). The extracts and the solu-
tion were combined and the solvent was removed in vacuo to give
a solid, which was identified as 10 or 13, respectively.
Complex 7: From [Ta(η5-C5H4SiMe3)Cl4] (0.81 g, 1.76 mmol) and
1,3-{(Me3Si)2N}2C6H4 (0.35 g, 0.88 mmol). 0.78 g of a yellow oil
was obtained (Yield: 100%).
Method B: CH2Cl2 (40 mL) was added to the corresponding
[{TaCl3)2(µ-1,i-NC6H4N)] (i ϭ 4 or 3) in a Teflon valve ampoule.
C5H4(SiMe3)2 was added to this red suspension and the ampoule
was placed in an oil bath and heated at 90 °C for 72 h. The resulting
red solution was filtered and the solvent was removed under vac-
uum. The final products were washed several times with hexane at
Ϫ40 °C and identified as 6 and 7, respectively.
Complex 10: From [{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,4-NC6H4N)]
(0.85 g, 1.20 mmol) and MeLi (3.44 mL, 4.81 mmol). 0.70 g of a
brown solid was obtained (Yield: 93%). 1H NMR (300 MHz, C6D6,
25 °C): δ ϭ 0.09 (s, 18 H, 2 ϫ C5H4SiMe3), 0.77 (s, 12 H, 4 ϫ Nb-
Me), 5.91 (m, 8 H, 2 ϫ C5H4), 7.19 (s, 4 H, C6H4) ppm. 13C{1H}
NMR (75 MHz, C6D6, 25 °C): δ ϭ Ϫ0.1 (C5H4SiMe3), 37.8 (Nb-
Me), 113.0, 113.1 and 116.7 (Cipso; C5H4SiMe3) 125.4 and 153.7
(Cipso; C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 1477m, 1407m, 1317m,
1251s, 1174m, 1091w, 1046m, 982w, 904m, 879w, 838vs, 807m,
756m, 695w, 631w, 493w and 422w cmϪ1. C26H42N2Nb2Si2 (624.6):
calcd. C 50.00, H 6.78, N 4.48; found C 50.15, H 6.70, N 4.26.
Complex 6: From [(TaCl3)2(µ-1,4-NC6H4N)] (1.71 g, 2.52 mmol)
and C5H4(SiMe3)2 (1.30 mL, 5.02 mmol). 1.72 g of a red solid was
obtained (Yield: 78%). 1H NMR (300 MHz, CDCl3, 25 °C): δ ϭ
0.25 (s, 18 H, 2 ϫ C5H4SiMe3), 6.59 and 6.71 (2m, each 4 H, 2 ϫ
C5H4), 6.75 (s, 4 H, C6H4) ppm. 13C{1H} NMR (75 MHz, CDCl3,
25 °C): δ ϭ Ϫ0.4 (C5H4SiMe3), 114.3, 120.6 and 123.1 (Cipso
;
Complex 13: From [{Nb(η5-C5H4SiMe3)Cl2}2(µ-1,3-NC6H4N)]
(1.66 g, 2.35 mmol) and MeLi (6.71 mL, 9.40 mmol). 1.35 g of a
brown solid was obtained (Yield: 92%). 1H NMR (300 MHz, C6D6,
25 °C): δ ϭ 0.10 (s, 18 H, 2 ϫ C5H4SiMe3), 0.75 (s, 12 H, 4 ϫ Nb-
Me), 5.89 and 5.93 (2m, each 4 H, 2 ϫ C5H4), 7.02 (3 H) and 7.30
(1 H) (2m, C6H4) ppm. 13C{1H} NMR (50 MHz, C6D6, 25 °C): δ ϭ
C5H4SiMe3) 125.0 and 153.0 (Cipso; C6H4) ppm. IR (CsI/Nujol):
ν˜ ϭ 3090w, 1491s, 1333vs, 1254s, 1172m, 1043m, 905s, 841vs and
413m cmϪ1. C22H30Cl4N2Si2Ta2 (882.4): calcd. C 29.95, H 3.43, N
3.17; found C 29.62, H 3.61, N 3.15.
Complex 7: From [(TaCl3)2(µ-1,3-NC6H4N)] (1.71 g, 2.52 mmol)
and C5H4(SiMe3)2 (1.30 mL, 5.02 mmol). 1.57 g of a yellow oil was
obtained (Yield: 71%). 1H NMR (300 MHz, CDCl3, 25 °C): δ ϭ
0.28 (s, 18 H, 2 ϫ C5H4SiMe3), 6.60 and 6.72 (2m, each 4 H, 2 ϫ
C5H4), 6.26 (1 H), 6.39 (2 H) and 7.17 (1 H) (3m, C6H4) ppm.
13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ ϭ Ϫ0.4 (C5H4SiMe3),
113.9, 120.8 and 123.6 (Cipso; C5H4SiMe3), 121.9, 122.7, 127.1 and
154.9 (Cipso; C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 3098w, 1573vs,
Ϫ0.2 (C5H4SiMe3), 38.1 (Nb-Me), 112.6, 113.2 and 117.4 (Cipso
;
C5H4SiMe3), 121.1, 121.3, 128.0 and 157.4 (Cipso; C6H4) ppm. IR
(CsI/Nujol): ν˜ ϭ 1567s, 1409m, 1338m, 1303m, 1250s, 1174m,
1150m, 1045m, 956w, 904m, 838vs, 780m, 757m, 693w, 632w and
495w cmϪ1. C26H42N2Nb2Si2 (624.6): calcd. C 50.00, H 6.78, N
4.48; found C 50.04, H 7.10, N 4.09.
Preparation
of
[{Nb(η5-C5H4SiMe3)(CH2SiMe3)2}2(µ-1,4-
1470vs, 1320vs, 1252vs, 1171s, 905s, 840vs and 417m cmϪ1
.
NC6H4N)] (11): A slight excess of [Mg(CH2SiMe3)Cl] (4.3 mL,
1306
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 1299Ϫ1310

New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes
FULL PAPER
4.3 mmol) was added, at Ϫ78 °C, to a suspension of complex 1 Complex 15: From 2 (0.75 g, 1.06 mmol) and [Mg(CH2Ph)2(THF)2]
(0.68 g, 0.97 mmol) in hexane (50 mL). The mixture was allowed
to warm up to room temperature and was stirred overnight. The
solution was filtered and the residue extracted with hexane (2 ϫ and 2.11 (2d, JH,H ϭ 8.1 Hz, each 4 H, 4 ϫ CH2Ph), 5.64 and
(0.74 g, 2.12 mmol). 0.85 g was obtained (Yield: 86%). 1H NMR
(300 MHz, C6D6, 25 °C): δ ϭ 0.15 (s, 18 H, 2 ϫ C5H4SiMe3), 1.70
2
20 mL). The extracts and the solution were combined. The re-
sulting orange solution was concentrated to 25 mL. Cooling of this
5.79 (2m, each 4 H, 2 ϫ C5H4), 6.612 (2 H), 6.73 (1 H) and 7.16
(1 H) (3m, C6H4), 6.85Ϫ7.08 (m, 20 H, 4 ϫ CH2Ph) ppm. 13C{1H}
solution to Ϫ40 °C gave compound 11 (0.70 g, 0.77 mmol) as an NMR (75 MHz, C6D6, 25 °C): δ ϭ 0.2 (C5H4SiMe3), 43.6
1
orange crystalline solid. (Yield: 79%). H NMR (300 MHz, C6D6,
(CH2Ph), 111.9, 112.3 and 112.9 (Cipso; C5H4SiMe3) 119.8, 120.7,
128.0 and 157.3 (Cipso; C6H4), 125.5, 129.1, 130.6 and 138.8 (Cipso
25 °C): δ ϭ 0.18 (s, 18 H, 2 ϫ C5H4SiMe3), 0.24 (s, 36 H, 4 ϫ
CH2SiMe3), 0.16 and 1.53 (2d, JH,H ϭ 10.2 Hz, each 4 H, 4 ϫ CH2Ph) ppm. IR (CsI/Nujol): ν˜ ϭ 1592s, 1565s, 1549m, 1513w,
;
2
CH2SiMe3), 5.78 and 6.21 (2m, each 4 H, 2 ϫ C5H4), 7.21 (s, 4
1484s, 1409m, 1367m, 1343m, 1304s, 1290s, 1251s, 1234s, 1207m,
H, C6H4) ppm. 13C{1H} NMR (75 MHz, C6D6, 25 °C): δ ϭ 0.0 1177m, 1159w, 1123w, 1084w, 1043m, 1025m, 995w, 901m, 837vs,
(C5H4SiMe3), 2.8 (CH2SiMe3), 55.0 (CH2SiMe3), 108.0, 115.8 and 820s, 805s, 784w, 758s, 695m, 686m, 633w, 541w, 516w, 499w, 443w
119.6 (Cipso; C5H4SiMe3) 125.1 and 153.6 (Cipso; C6H4) ppm. IR and 430w cmϪ1. C50H58N2Nb2Si2 (929.0): calcd. C 64.64, H 6.29,
(CsI/Nujol): ν˜ ϭ 1478s, 1408w, 1314s, 1241s, 1174m, 1092w, 1048m,
N 3.02; found C 64.69, H 6.85, N 2.88.
1040m, 1003w, 988m, 938s, 901s, 831vs, 814s, 755m, 735m, 701m,
Preparation of [{Ta(η5-C5Me5)Me2}2(µ-1,4-NC6H4N)] (16): A solu-
tion of MeLi (2.28 mmol) diluted in Et2O (10 mL) was added drop-
wise, at Ϫ78 °C, to a suspension of complex 8 (0.5 g, 0.57 mmol)
in hexane (50 mL). The mixture was stirred overnight at room tem-
682m, 632w, 549w, 534w, 468m, 416w and 373w cmϪ1
.
C38H74N2Nb2Si6 (913.3): calcd. C 49.97, H 8.17, N 3.07; found C
50.05, H 8.26, N 3.30.
Preparation
of
[{Nb(η5-C5H4SiMe3)(CH2SiMe3)2}2(µ-1,3- perature. The resulting yellow solution was filtered and the residue
extracted with hexane (2 ϫ 25 mL). The solvent was removed in
NC6H4N)] (14): A slight excess of [Mg(CH2SiMe3)Cl] (5.2 mL,
5.2 mmol) was added, at Ϫ78 °C, to a suspension of complex 2 vacuo to give 0.36 g of a yellow solid, which was identified as com-
(0.83 g, 1.17 mmol) in hexane (50 mL). The mixture was allowed
to warm up to room temperature and was stirred overnight. The
plex 16 (Yield: 80%). 1H NMR (300 MHz, CDCl3, 25 °C): δ ϭ 0.01
(s, 12 H, 4 ϫ Ta-Me), 1.96 (s, 30 H, 2 ϫ C5Me5), 6.68 (s, 4 H,
solution was filtered and the residue extracted with hexane (2 ϫ C6H4) ppm. 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ ϭ 10.7
20 mL). The extracts and the solution were combined. The solvent
was removed and the resulting yellow oil was identified as 14
(0.95 g, 1.04 mmol) (Yield: 89%). 1H NMR (300 MHz, C6D6, 25
(C5Me5), 46.5 (Ta-Me), 115.9 (C5Me5) 125.0 and 151.9 (Cipso
;
C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 1493s, 1332vs, 1086m, 1026m,
1007m, 835s, 804m and 500m cmϪ1. C30H46N2Ta2 (796.6): calcd.
°C): δ ϭ 0.20 (s, 18 H, 2 ϫ C5H4SiMe3), 0.27 (s, 36 H, 4 ϫ C 45.23, H 5.82, N 3.52; found C 44.82, H 5.79, N 3.36.
2
CH2SiMe3), 0.21 and 1.57 (2d, JH,H ϭ 10.5 Hz, each 4 H, 4 ϫ
Preparation of [{Ta(η5-C5Me5)(CH2SiMe3)2}2(µ-1,4-NC6H4N)]
CH2SiMe3), 5.89 and 6.28 (2m, each 4 H, 2 ϫ C5H4), 6.92 (2 H),
(17): A solution of Mg(CH2SiMe3)Cl (2.28 mmol) diluted in Et2O
7.08 (1 H) and 7.16 (1 H) (3m, C6H4) ppm. 13C{1H} NMR
(10 mL) was added dropwise, at Ϫ78 °C, to a suspension of com-
(50 MHz, C6D6, 25 °C): δ ϭ 0.0 (C5H4SiMe3), 2.9 (CH2SiMe3),
plex 8 (0.5 g, 0.57 mmol) in hexane (50 mL). The mixture was
55.2 (CH2SiMe3), 107.8, 115.9 and 120.2 (Cipso; C5H4SiMe3) 120.4,
stirred overnight at room temperature. The resulting yellow solu-
tion was filtered and the residue was extracted with hexane (2 ϫ
120.6, 128.3 and 157.4 (Cipso; C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ
1566s, 1409m, 1336m, 1302s, 1280s, 1246s, 1175m, 1152w, 1045m,
25 mL). The solvent was removed in vacuo to give 0.53 g of a yel-
931s, 905s, 838vs, 754s, 697s, 633w, 572w, 472w and 416w cmϪ1
.
low solid, which was identified as complex 17 (Yield: 86%). 1H
NMR (300 MHz, CDCl3, 25 °C): δ ϭ 0.04 (s, 36 H, 4 ϫ
C38H74N2Nb2Si6 (913.3): calcd. C 49.97, H 8.17, N 3.07; found C
49.41, H 8.18, N 3.24.
2
CH2SiMe3), Ϫ1.14 and 0.21 (2d, JH,H ϭ 11.9 Hz, each 4 H, 4 ϫ
Preparation of [{Nb(η5-C5H4SiMe3)(CH2Ph)2}2(µ-1,4-NC6H4N)]
CH2SiMe3), 1.97 (s, 30 H, 2 ϫ C5Me5), 6.63 (s, 4 H, C6H4) ppm.
(12) and [{Nb(η5-C5H4SiMe3)(CH2Ph)2}2(µ-1,3-NC6H4N)] (15): Di- 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ ϭ 2.8 (CH2SiMe3), 11.1
ethyl ether (60 mL) was added at Ϫ78 °C to a mixture of complex
1 or 2 and [Mg(CH2Ph)2(THF)2]. The mixture was allowed to
warm up to room temperature and was stirred overnight. The solu-
(C5Me5), 58.5 (CH2SiMe3), 115.6 (C5Me5) 125.1 and 151.7 (Cipso
;
C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 1489s, 1332vs, 1241s, 1089m,
1024m, 962m, 850vs and 465m cmϪ1. C42H78N2Si4Ta2 (1085.3):
tion was filtered and the residue was extracted with diethyl ether calcd. C 46.48, H 7.24, N 2.58; found C 46.46, H 7.28, N 2.96.
(2 ϫ 20 mL). The extracts and the solution were combined. The
solvent was removed to give a yellow and a pale yellow solid,
Preparation of [{Ta(η5-C5Me5)(CH2Ph)2}2(µ-1,4-NC6H4N)] (18): A
solution of Mg(CH2Ph)2(THF)2 (0.4 g, 1.14 mmol) diluted in Et2O
respectively, and these were identified as the corresponding com-
(20 mL) was added dropwise, at Ϫ78 °C, to a solution of complex
pounds 12 and 15.
8 (0.5 g, 0.57 mmol) in Et2O (30 mL). The mixture was stirred over-
Complex 12: From 1 (0.75 g, 1.06 mmol) and [Mg(CH2Ph)2(THF)2]
night at room temperature. The solvent was removed in vacuo and
(0.74 g, 2.12 mmol). 0.88 g was obtained (Yield: 90%). 1H NMR the resulting yellow residue was extracted with CH2Cl2 (2 ϫ
(300 MHz, C6D6, 25 °C): δ ϭ 0.11 (s, 18 H, 2 ϫ C5H4SiMe3), 1.55
15 mL). The filtrate was placed in a freezer at Ϫ40 °C to afford
0.44 g of 18, after 16 h, as a yellow crystalline solid. The product
2
and 2.13 (2d, JH,H ϭ 8.1 Hz, each 4 H, 4 ϫ CH2Ph), 5.63 and
5.72 (2m, each 4 H, 2 ϫ C5H4), 6.79 (s, 4 H, C6H4), 6.81Ϫ7.07 (m, contained ca. 0.25 equivalents of residual CH2Cl2 (by 1H NMR
20 H, 4 ϫ CH2Ph) ppm. 13C{1H} NMR (75 MHz, C6D6, 25 °C): spectroscopy and elemental analysis). Yield: 68%. 1H NMR
δ ϭ 0.1 (C5H4SiMe3), 43.4 (CH2Ph), 111.6, 112.5 and 112.2 (Cipso
;
(300 MHz, CDCl3, 25 °C): δ ϭ 1.35 and 2.06 (2d, 2JH,H ϭ 11.3 Hz,
C5H4SiMe3) 124.9 and 153.5 (Cipso; C6H4), 125.4, 129.0, 130.5 and each 4 H, 4 ϫ CH2Ph), 1.94 (s, 30 H, 2 ϫ C5Me5), 6.40 (s, 4 H,
138.9 (Cipso; CH2Ph) ppm. IR (CsI/Nujol): ν˜ ϭ 1594m, 1477s, C6H4), 6.90Ϫ7.10 (m, 20 H, 4 ϫ CH2Ph) ppm. 13C{1H} NMR
1408m, 1314s, 1250s, 1205m, 1176s, 1093m, 1035s, 1004w, 995w, (75 MHz, CDCl3, 25 °C): δ ϭ 11.0 (C5Me5), 67.5 (CH2Ph), 115.3
985m, 920w, 902m, 885w, 835vs, 817vs, 760s, 750s, 696vs, 632w, (C5Me5) 124.7 and 151.2 (Cipso; C6H4), 123.2, 127.9, 129.7 and
537w, 515w, 446w and 428w cmϪ1. C50H58N2Nb2Si2 (929.0): calcd.
C 64.64, H 6.29, N 3.02; found C 65.33, H 6.94, N 2.74.
144.6 (Cipso; CH2Ph) ppm. IR (CsI/Nujol): ν˜ ϭ 1593s, 1483vs,
1332vs, 1200m, 1024m, 835s, 742s and 452m cmϪ1
.
Eur. J. Inorg. Chem. 2004, 1299Ϫ1310
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1307

A. Otero et al.
FULL PAPER
C54H62N2Ta2·0.25CH2Cl2 (1122.2): calcd. C 58.06, H 5.61, N 2.50;
found C 57.84, H 5.73, N 2.88.
5.97 and 6.07 (4m, each 4 H, 4 ϫ C5H4), 6.97 (s, 8 H, 2 ϫ C6H4)
ppm. 13C{1H} NMR (50 MHz, C6D6, 25 °C, two isomers): δ ϭ 0.2
(C5H4SiMe3), 13.7 (Nb-Me), 53.3 (NMe2), 113.2, 113.3, 113.4
113.5 and 113.6 (Cipso; C5H4SiMe3), 124.6 and 153.2 (Cipso; C6H4)
ppm. IR (CsI/Nujol): ν˜ ϭ 1485s, 1419w, 1315s, 1249m, 1178w,
1090w, 1040m, 987w, 962m, 904w, 837vs, 802m, 756w, 632w, 543w,
489w, and 383w cmϪ1. C28H48N4Nb2Si2 (682.7): calcd. C 49.26, H
7.09, N 8.21; found C 48.68, H 6.71, N 7.32.
Preparation of [{Nb(η5-C5H4SiMe3)ClMe}2(µ-1,4-NC6H4N)] (19):
ZnMe2 (1.13 mL, 2.26 mmol) was added at room temperature to a
suspension a complex 1 (1.60 g, 2.26 mmol) in toluene (50 mL).
The mixture was stirred for 12 h. The red solution was filtered and
the residue extracted with toluene (3 ϫ 20 mL). The extracts and
the solution were combined. The solvent was removed to give a
brown solid, which was identified as 19 (1.3 g; yield: 86%). 1H Preparation of [{Ta(η5-C5Me5)ClMe}2(µ-1,4-NC6H4N)] (21): A
NMR (300 MHz, C6D6, 25 °C, two isomers): δ ϭ 0.16 (s, 36 H, 4 solution of ZnMe2 (1.26 mmol, 2  in toluene) was added, at room
ϫ C5H4SiMe3), 1.34 and 1.35 (2s, each 6 H, 4 ϫ Nb-Me), 5.69, temperature, to a suspension of complex 8 (0.55 g, 0.63 mmol) in
5.84, 5.85 and 6.17 (4m, each 4 H, 4 ϫ C5H4), 6.93 (s, 8 H, 2 ϫ toluene (50 mL). The mixture was stirred overnight at room tem-
C6H4) ppm. 13C{1H} NMR (75 MHz, C6D6, 25 °C, two isomers): perature. The resulting yellow solution was filtered and the solvent
δ ϭ Ϫ0.4 (C5H4SiMe3), 38.8 (Nb-Me), 110.5, 110.6, 113.5, 113.6,
was removed in vacuo to give 0.39 g of a yellow solid, which was
1
115.6, 115.7, 116.7 (Cipso) and 116.8 (Cipso; C5H4SiMe3), 124.7 and identified as complex 21 (Yield: 75%). H NMR (300 MHz, C6D6,
154.1 (Cipso; C6H4) ppm. IR (CsI/Nujol): ν˜ ϭ 1595w, 1512w, 1310s, 25 °C, two isomers): δ ϭ 0.82 and 0.83 (2s, each 6 H, 4 ϫ Ta-Me),
1250s, 1171m, 1093m, 1045m, 1004w, 986m, 903m, 837vs, 757s, 1.80 (s, 60 H, 4 ϫ C5Me5), 6.91 (s, 8 H, 2 ϫ C6H4) ppm. 13C{1H}
631m, 523w, 477w, 419m and 377w cmϪ1. C24H36Cl2N2Nb2Si2
(665.5): calcd. C 43.32, H 5.45, N 4.21; found C 43.00, H 5.26,
N 3.93.
NMR (75 MHz, C6D6,, 25 °C, two isomers): δ ϭ 10.8 (C5Me5),
41.2 and 41.3 (Ta-Me), 118.1 (C5Me5) 125.6 and 152.1 (Cipso; C6H4)
ppm. IR (CsI/Nujol): ν˜ ϭ 1491s, 1335vs, 1088m, 1026m, 994m,
837s and 491m cmϪ1. C28H40Cl2N2Ta2 (837.4): calcd. C 40.16, H
4.81, N 3.35; found C 40.05, H 4.68, N 3.16.
Preparation of [{Nb(η5-C5H4SiMe3)(NMe2)Me}2(µ-1,4-NC6H4N)]
(20): Diethyl ether (50 mL) was added at Ϫ78 °C to a mixture of
complex 19 (1.15 g, 1.73 mmol) and an excess of LiNMe2 (0.19 g,
3.80 mmol). The mixture was allowed to warm up to room tem-
perature and was stirred for 12 h. The solution was filtered and the
residue was extracted with diethyl ether (2 ϫ 20 mL). The extracts
and the solution were combined. The solvent was removed and
the residue was extracted with pentane (2 ϫ 30 mL). The resulting
solution was concentrated to dryness to give a dark brown oil,
X-ray Structure Determinations for [{M(Cp)Cl2}2(µ-1,4-NC6H4N)]
[M ؍ Nb, Cp ؍ η5-C5H4SiMe3 (1); M ؍ Ta, Cp ؍ η5-C5Me5 (8)]
and [{M(Cp)(CH2R)2}2(µ-1,4-NC6H4N)] [M ؍ Ta, Cp ؍ η5-C5Me5,
R ؍ SiMe3 (17)]: Intensity data for compounds 1 and 17 were
collected on a Nonius-Mach3 diffractometer equipped with a
˚
graphite monochromator (Mo-Kα radiation, λ ϭ 0.71073 A) using
an ω/2θ scan technique. In the case of 1 the specimen diffracted
which was identified as 7 (1.05 g, Yield: 89%). 1H NMR (300 MHz, only weakly. The final unit-cell parameters were determined from
C6D6, 25 °C, two isomers): δ ϭ 0.16 (s, 36 H, 4 ϫ C5H4SiMe3),
25 well-centred reflections and refined by the least-squares method.
0.72 (s, 12 H, 4 ϫ Nb-Me), 3.28 (br., 24 H, 4 ϫ NMe2), 5.86, 5.92, The space group was determined from the systematic absences and
Table 4. Crystal data and structure refinement for 1, 8 and 17
1
8
17
Formula
Mol. mass
T (K)
C22H30Cl4N2Nb2Si2
706.28
293(2)
C26H34Cl4N2Ta2
878.25
110(1)
C42H78N2Si4Ta2
1085.32
250(2)
Cryst. syst.
Space group
orthorhombic
Pbca
13.331(1)
12.547(1)
17.796(1)
monoclinic
P21/a
13.269(1)
8.5840(1)
13.802(1)
triclinic
P1
9.617(1)
10.547(1)
14.943(1)
75.28(1)
¯
˚
a (A)
˚
b (A)
˚
c (A)
β (deg)
100.33(1)
72.84(1)
65.33(1)
1301.0(2)
1
1.385
4.321
546
3
˚
V (A )
2976.6(4)
4
1.576
1.223
1416
1546.6(2)
2
1.886
7.432
Z
Dc (g cmϪ3
)
µ (mmϪ1
F(000)
)
836
Crystal dimensions (mm)
θ range (deg)
hkl ranges
0.3 ϫ 0.2 ϫ 0.2
2.29 to 27.95
Ϫ17 Յ h Յ 0
0 Յ k Յ 16
0 Յ l Յ 23
3577/142
1.135
R1 ϭ 0.0746
wR2 ϭ 0.1800
0.827/Ϫ0.650
0.40 ϫ 0.18 ϫ 0.15
3.08 to 27.53
Ϫ13 Յ h Յ 17
Ϫ10 Յ k Յ 11
Ϫ17 Յ l Յ 17
3454/154
0.3 ϫ 0.3 ϫ 0.4
2.15 to 28.00
Ϫ12 Յ h Յ 12
Ϫ13 Յ k Յ 13
0 Յ l Յ 19
6505/226
1.129
R1 ϭ 0.0461
wR2 ϭ 0.1508
2.494/Ϫ2.221
Data/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)][a]
1.233
R1 ϭ 0.0345
wR2 ϭ 0.0792
0.850/Ϫ0.881
Ϫ3
˚
Largest diff. peak (e·A
)
[a]
2
2 2
2 2
R1 ϭ Σ(Fo Ϫ Fc)/Σ(Fo); wR2 ϭ {Σ[w(Fo Ϫ Fc ) ]/Σ[w(Fo ) ]}0.5
1308
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1299Ϫ1310

New Dinuclear Monocyclopentadienyl Imidoniobium and -tantalum Complexes
FULL PAPER
´
mez-Sal, A. Martın, P. Royo, Organometallics 1999, 18,
this was vindicated by the success of the subsequent solutions and
refinements. Empirical absorption correction was performed for
compound 17. Intensities for 8 were measured on a Nonius-Kap-
paCCD diffractometer at low temperature and treated with Scal-
pack and DENZO routines.[27] The crystal data and details of data
collection and structure analyses are summarised in Table 4.
All structures were solved by direct methods using the SHELXS
computer program[28] and refined in F2 by a full-matrix least-
squares procedure (SHELXL-97).[29] All non-hydrogen atoms were
refined with anisotropic thermal parameters for all compounds.
The hydrogen atoms were included in calculated positions and were
refined with an overall isotropic temperature factor using a riding
model. Weights were optimised in the final cycles.
CCDC-205739 (for 1), -205740 (for 8) and -205742 (for 17) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (internat.)
ϩ 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
1144Ϫ1150.
See for example: [7a] A. Castro, M. V. Galakhov, M. Gomez, F.
Sanchez, J. Organomet. Chem. 1999, 580, 161Ϫ168.
Gountchev, T. D. Tilley, J. Am. Chem. Soc. 1997, 119,
[7]
´
[7b]
´
T. I.
12831Ϫ12841.
[8] [8a]
´
´
I. Dorado, A. Garces, C. Lopez-Mardomingo, M. Fajardo,
A. Rodrıguez, A. Antin˜olo, A. Otero, J. Chem. Soc., Dalton
Trans. 2000, 2375Ϫ2382.
Mardomingo, M. Fajardo, M. Kubicki, A. Antin˜olo, A. Otero,
Dalton Trans. 2003, 910Ϫ917.
´
[8b]
´ ´
I. Dorado, A. Garces, C. Lopez-
[9]
A. Antin˜olo, M. Fajardo, A. Otero, S. Prashar, Eur. J. Inorg.
Chem. 2003, 17Ϫ28.
[10]
[10a]
See for example:
E. A. Maatta, D. D. Devore, Angew.
Chem. 1988, 100, 583Ϫ585; Angew. Chem. Int. Ed. Engl. 1988,
[10b]
27, 569Ϫ571.
28, 623Ϫ624.
E. A. Maatta, C. Kim, Inorg. Chem. 1989,
R. K. Rosen, R. A. Andresen, N. M. Ed-
[10c]
[10d]
elstein, J. Am. Chem. Soc. 1990, 112, 4588Ϫ4590.
garth, R. L. Mallors, T. Norman, J. Chem. Soc., Chem. Com-
G. Ho-
[10e]
mun. 1993, 1721Ϫ1723.
W. Clegg, R. J. Errington, D. C.
R. Hockless, J. M. Kirk, C. Redshaw, Polyhedron 1992, 11,
[10f]
381Ϫ384.
hedron 1998, 17, 969Ϫ976.
Inorg. Chem. 1992, 31, 953Ϫ956.
D. E. Wheeler, J.-F. Wu, E. A. Maatta, Poly-
[10g]
M. Liangand, E. A. Maatta,
[10h]
G. Hogarth, D. E.
Acknowledgments
We gratefully acknowledge financial support from the Ministerio
Humphry, N. Kaltsoyanis, W.-F. Kim, M. Lee, T. Norman, S.
P. Redmond, J. Chem. Soc., Dalton Trans. 1999, 2705Ϫ2723.
[11] [11a]
D. M. Antonelli, M. L. H. Green, P. Mountford, J. Or-
´
de Ciencia y Tecnologıa, Spain (Grant no. BQU2002-04638-C02-
ganomet. Chem. 1992, 438, C4ϪC8. [11b] P. T. Gomes, M. L. H.
01), the Junta de Comunidades de Castilla-La Mancha (PAC-02-
´
Green, A. M. Martın, P. Mountford, J. Organomet. Chem.
1997, 541, 121Ϫ125.
´
´
´
003), the Direccion General de Investigacion de la Consejerıa de
[12] [12a]
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Received July 31, 2003
Early View Article
Published Online February 10, 2004
1310
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