Alkyl alkyne mono((trimethylsilyl)cyclopentadienyl) niobium complexes. Synthesis and chemical behavior in insertion processes (see abstract)

Article abstract of DOI:10.1021/om010521a

The alkyl alkyne mono((trimethylsilyl)cyclopentadienyl) niobium complexes were investigated. The compounds were characterized by infrared spectrophotometry, NMR spectroscopy and elemental analysis. The molecular structures of the complexes were determined

Full text of DOI:10.1021/om010521a

Organometallics 2002, 21, 293-304
293
Alk yl Alk yn e Mon o((tr im eth ylsilyl)cyclop en ta d ien yl)
Niobiu m Com p lexes. Syn th esis a n d Ch em ica l Beh a vior
in In ser tion P r ocesses. X-r a y Cr ysta l Str u ctu r es of
[NbCp ′(CH2SiMe3)2(Me3SiCCSiMe3)] a n d
[NbCp ′(NAr ){η4-CH(SiMe3)C(SiMe3)C(CH2SiMe3)dCH(SiMe3)}],
(Cp ′ ) η5-C5H4SiMe3, Ar ) 2,6-Me2C6H3). DF T Stu d ies of
th e Mod el Com p lexes [Nb(η5-C5H5)R2(HCCH)]
(R ) Cl, Me)
Agust´ın Galindo,† Manuel Go´mez,*,‡ Pilar Go´mez-Sal,‡ Avelino Mart´ın,‡
Diego del R´ıo,† and Fernando Sa´nchez‡
Departamento de Quı´mica Inorga´nica, Universidad de Alcala´ de Henares,
Campus Universitario, E-28871 Alcala´ de Henares, Spain, and Departamento de
Quı´mica Inorga´nica, Universidad de Sevilla, Aptdo. 553, E-41071 Sevilla, Spain
Received J une 14, 2001
The dichloro niobium complex [NbCp′Cl2(R′CCR′)] (Cp′ ) η5-C5H4SiMe3; R′ ) SiMe3; 1)
can be obtained by reduction of NbCp′Cl4 with excess of aluminum in the presence of 1
equiv of bis(trimethylsilyl)acetylene. The dialkyl derivatives [NbCp′R2(R′CCR′)] (Cp′ ) η5-
C5H4SiMe3; R′ ) SiMe3; R ) Me (2), CH2SiMe3 (3), CH2CMe3 (4), CH2C6H5 (5)) were obtained
by treating 1 with the stoichiometric amounts of the appropriate alkylating reagents.
Reactions of the dialkyl alkyne complexes [NbCp′R2(R′CCR′)] (2-5) with 1 equiv of 2,6-
Me2C6H3NC in C6D6 resulted in migration of only one of the two alkyl groups to give the
alkyl alkyne η2-iminoacyl complexes [NbCp′R{η2-C(R)dNAr}(R′CCR′)] (Cp′ ) η5-C5H4SiMe3;
R′ ) SiMe3; Ar ) 2,6-Me2C6H3; R ) Me (6), CH2SiMe3 (7), CH2CMe3 (8)). However, when
hexane solutions of the dialkylated complexes 2 and 3 were treated with 1 equiv of isocyanide
at 40-50 °C (2) and 80 °C (3), respectively, the imido niobacyclopent-3-ene [NbCp′(NAr)-
{η4-CH(SiMe3)C(SiMe3)dC(Me)CH2}] (9) and the imido niobacyclopropane(vinyl) [NbCp′-
(NAr){η4-CH(SiMe3)C(SiMe3)C(CH2SiMe3)dCH(SiMe3)}] (10) (Cp′ ) η5-C5H4SiMe3; Ar ) 2,6-
Me2C6H3) can be isolated, probably via azaniobacyclopropane intermediates. In the case of
the dialkylated complex 4 the reaction with 1 equiv of isocyanide at room temperature gives
initially the alkyne neopentyl η2-iminoacyl complex 8, which is slowly transformed into the
imido niobacyclohept-2-ene [NbCp′(NAr){η2-CH2CMe2CH2CH(CH2CMe3)C(SiMe3)dC(SiMe3)}]
(Cp′ ) η5-C5H4SiMe3; Ar ) 2,6-Me2C6H3; 11), but the intermediate species were not observed.
1
All the new compounds have been characterized by IR spectrophotometry, H and 13C{1H}
NMR spectroscopy, and elemental analyses. The molecular structures of the complexes 3
and 10 have been determined by X-ray diffraction analyses. DFT calculations have been
carried out on the model complexes [Nb(η5-C5H5)R2(HCCH)] (R ) Cl, Me). The theoretical
studies rationalize the disposition of the alkyne ligand in complex 3.
In tr od u ction
formation of a metallacyclic imine, which may subse-
quently rearrange7 or dimerize.8 Furthermore, it has
been reported that in the reaction between alkyne
tantalum(III) derivatives and nitriles, the azatantala-
cyclopentene complexes formed may participate in an
intermolecular tautomerization process to enamines.5c
Alkyne niobium and tantalum(III) complexes are known
as very efficient catalysts for the oligomerization and
polimerization of internal alkynes.3 The catalytic process
can be explained by alkylidene9 and alkenyl10 pathways.
Early transition metal complex1 promoted coupling
of unsaturated organic substrates constitutes a powerful
strategy for C-C bond formation in organic synthesis2
and catalytic polymerization.3 In particular, niobium
and tantalum alkyne complexes have provided conve-
nient routes to carbonylic derivatives4 and nitrile5
coupling reactions via metallacyclic intermediates.6
Therefore, if the organic substrate is a nitrile, the
resulting products can be vicinal diamines5a and poly-
functionalized aromatic compounds,5b via the initial
In the literature, a great deal of alkyne niobium and
tantalum complexes containing halo,11 aryloxide,5c cyclo-
pentadienyl,12 and hydridotris(pyrazolyl)borate13 type
groups can be found, the number of alkyl mono(cyclo-
pentadienyl) derivatives being scarce. In this paper, we
* To whom correspondence should be addressed. Fax: 34-91-885 46
83. E-mail: manuel.gomez@uah.es.
† Universidad de Sevilla.
‡ Universidad de Alcala´ de Henares.
10.1021/om010521a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 12/15/2001

294 Organometallics, Vol. 21, No. 2, 2002
Galindo et al.
Sch em e 1a
report new alkyl alkyne (trimethylsilyl)cyclopentadienyl
niobium complexes and the insertion and intramolecular
rearrangement processes observed in the reactions with
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a
Reagents and conditions: (i) Al excess, HgCl2, C2(SiMe3)2,
THF, 12 h, room temperature; (ii) 2 equiv of MgClR (R ) Me
(2), CH2SiMe3 (3), CH2C6H5 (5)) or LiCH2CMe3 (4), hexane,
12 h, -78 °C to room temperature.
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J . C. J . Am. Chem. Soc. 1989, 111, 4486.
2,6-Me2C6H3NC. All compounds were fully character-
ized, and in addition, some of the complexes were
studied by X-ray diffraction methods. In particular, the
molecular structure of the complex [NbCp′(CH2Si-
Me3)2(Me3SiCCSiMe3)] (Cp′ ) η5-C5H4SiMe3; 3), shows
an almost perpendicular conformation of the alkyne
ligand with respect to the Cp′ plane. The relative
orientation of an alkyne ligand with respect to [MCp-
L2]14 (Cp ) η5-C5H5) or [MTpL2]13e,f (Tp ) hydridotris-
(pyrazolyl)borate) type fragments has been analyzed in
several papers for different combinations of electronic
configurations, metals, and L ligands.15 We report
herein a DFT study of the model complexes [Nb(η5-
C5H5)R2(HCCH)] (R ) Cl, Me) that serves to rationalize
the disposition of the alkyne ligand and other structural
parameters on these types of compounds.
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1414.
Resu lts a n d Discu ssion
Syn th esis of Dich lor o a n d Dia lk yl Alk yn e De-
r iva tives. [NbCp′Cl2(Me3SiCCSiMe3)] (Cp′ ) η5-C5H4-
SiMe3; 1) was synthesized in high yield by reaction of
NbCp′Cl4 with an excess of aluminum powder and
mercury(II) chloride in the presence of 1 equiv of C2-
(SiMe3)2 (see Scheme 1). When n-hexane solutions of 1
were treated with stoichiometric amounts of the alky-
lating reagents MgClR (R ) Me, CH2SiMe3, CH2Ph) or
LiCH2CMe3 under rigorously anhydrous conditions at
room temperature, suspensions were obtained from
which the dialkyl alkyne complexes [NbCp′R2(Me3-
SiCCSiMe3)] (Cp′ ) η5-C5H4SiMe3; R ) Me (2), CH2-
SiMe3 (3), CH2Ph (4), CH2CMe3 (5)) could be isolated
in good yields. Complexes 1-5 were found to be air- and
moisture-sensitive and soluble in hexane, THF, and
aromatic solvents.
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3199. (d) Kwon, D.; Curtis, M. D. Organometallics 1990, 9, 1. (e) Curtis,
M. D.; Real, J .; Hirpo, W.; Butler, W. M. Organometallics 1990, 9, 66.
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1992, 237. (g) Siemeling, U.; Gibson, V. C. J . Organomet. Chem. 1992,
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Pellinghelli, M. A.; Tiripicchio, A. Organometallics 1994, 13, 462. (i)
Hirpo, W.; Curtis, M. D. Organometallics 1994, 13, 2706. (j) Chan, M.
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1977, 16, 536. (b) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D.
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R.; Faller, J . W. J . Am. Chem. Soc. 1979, 101, 592.
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Alkyl Alkyne Cyclopentadienyl Niobium Complexes
Organometallics, Vol. 21, No. 2, 2002 295
The spectroscopic properties of the complexes 1-5 are
basically similar to those reported for metallacyclopro-
pene derivatives,12a,16 in which the alkyne ligand acts
as a 4e donor. The IR spectra of all the complexes show
the characteristic absorptions for the (trimethylsilyl)-
cyclopentadienyl (νj(C-H) at ca. 837 cm-1 17
ring and
)
for the trimethylsilyl substituent (νjδs(CH3) at ca. 1246
cm-1).17,18 Furthermore, the absorption band observed
at ca. 1582 cm-1 and assigned to the stretching vibration
νj(CdC) is consistent with the hybridization change of
the carbon atoms in the alkyne ligand,16,19 while the
corresponding Nb-C band17,20 in the dialkyl derivatives
is located at ca. 480 cm-1. The NMR spectroscopic data
are in agreement with the structures proposed in
1
Scheme 1. The H NMR spectrum of complex 2 shows a
singlet for the trimethylsilyl substituents of the alkyne
ligand; however, complexes 3-5 show a broad signal for
1
the same groups in the H NMR spectrum. This fact is
consistent with the free rotation of the alkyne ligand
in complex 2 and the slow rotation of the alkyne ligand
in complexes 3-5 due to the bulkier alkyl substituent.
Moreover, when a CDCl3 solution of compound 3 is
cooled from 303 to 223 K, the alkyne trimethylsilyl
substituents signal broadens and, at 223 K, splits into
two signals. The kinetic parameters of this process
F igu r e 1. ORTEP drawing of compound 3. Thermal
ellipsoids are shown at the 50% level.
(log A ) 14.2 ( 0.33; Ea ) 14.6 ( 0.4 kcal mol-1
;
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 3
∆Hq ) 14.0 ( 0.4 kcal mol-1; ∆Sq ) 4.7 ( 1.4 eu;
∆Gq(298 K) ) 12.6 kcal mol-1) calculated on the basis
of the DNMR data21a,b show that this transformation is
an intramolecular pseudorotation process similar to
those reported for other mono(cyclopentadienyl) com-
plexes with a four-legged piano-stool structure.21c The
13C{1H} NMR spectra show only one signal for the
trimethylsilyl substituents of the alkyne ligand, which
is broad in the case of complex 4. The alkyl groups
directly bonded to the niobium atom are also equivalent,
but in the complexes 3-5 the diasterotopic R-CH2
protons of such groups appear as an AB spin system.
The 13C{1H} NMR spectra show broad signals for all
carbon atoms directly bonded to the metal center due
to the quadrupole moment interaction21d with the 93Nb
nucleus. Chemical shifts of the acetylenic carbon atoms,
at ca. δ 244, are in agreement with a four-electron-donor
Nb(1)-C(41)
Nb(1)-C(21)
Si(2)-C(21)
Si(4)-C(41)
C(41)-C(51)
2.087(6)
2.193(6)
1.834(6)
1.856(6)
1.323(7)
Nb(1)-C(51)
Nb(1)-C(31)
Si(3)-C(31)
Si(5)-C(51)
2.092(5)
2.198(5)
1.841(6)
1.888(5)
C(41)-Nb(1)-C(51)
36.9(2) C(41)-Nb(1)-C(21)
90.5(2)
89.2(2)
C(51)-Nb(1)-C(21) 111.2(2) C(41)-Nb(1)-C(31)
C(51)-Nb(1)-C(31) 110.7(2) C(21)-Nb(1)-C(31) 106.6(2)
Si(2)-C(21)-Nb(1)
C(51)-C(41)-Si(4)
Si(4)-C(41)-Nb(1)
C(41)-C(51)-Nb(1)
129.8(3) Si(3)-C(31)-Nb(1)
139.7(5) C(51)-C(41)-Nb(1)
148.4(3) C(41)-C(51)-Si(5)
71.3(3) Si(5)-C(51)-Nb(1)
129.0(3)
71.7(4)
140.7(5)
147.9(3)
the (trimethylsilyl)cyclopentadienyl ring, whereas the
13C{1H} NMR spectra show three carbon resonances for
the same group, in accordance with Cs symmetry.
The molecular structure of compound 3 is shown in
Figure 1. Selected bond distances and angles are
presented in Table 1. The complex 3 can be described
as a monomer with a typical three-legged piano-stool
environment for the niobium atom if we assume that
the centroid of the alkyne ligand is occupying a single
coordination site. The most relevant aspects of the
structure are the perpendicular disposition of the alkyne
ligand with respect to the Cp′ ring and the plane formed
by the alkyl substituents at the niobium center; the
angles formed by the Si4-C41-C51-Si5 plane with
both are 86.8(2) and 86.1(2)°, respectively. Furthermore,
the Si2 and Si3 atoms of the (trimethylsilyl)methyl
groups are close to equidistant to the silicon atoms of
the trimethylsilyl substituents of the Cp′ ring and the
alkyne ligand, Si1, Si4, and Si5. The average of the
distances Nb-C(alkyne) is 2.090 (6) Å, and the C41-
C51 distance is 1.323(7) Å; both values are just inside
the range expected for a four-electron-donor alkyne
ligand7f,12b,16,22,23 in which the C-C bond order is less
1
alkyne ligand.22 The H NMR spectra of complexes 1-5
show an AA′BB′ spin system for the proton atoms of
(16) Smith, G.; Schrock, R. R.; Churchill, M. R.; Youngs, W. J . Inorg.
Chem. 1981, 20, 387.
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P. J . Organomet. Chem. 1996, 518, 37. (b) Castro, A.; Galakhov, M.
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DNMR Spectroscopy; Academic Press: New York, 1975. (c) de Castro,
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Organomet. Chem. 1996, 514, 51. (d) Carrington, A.; McLachlan, A.
D. Introduction to Magnetic Resonance; Wiley: New York, 1979; p 210.
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S. Organometallics 1991, 10, 143.

296 Organometallics, Vol. 21, No. 2, 2002
Galindo et al.
Ta ble 3. Ca lcu la ted Bon d Dista n ces (Å) a n d
An gles (d eg) for NbCp Me2(HCCH) Mod el Com p lex
a n d , for Com p a r ison , Selected Exp er im en ta l Da ta
for 3
Ta ble 2. Ca lcu la ted Bon d Dista n ces (Å) a n d
An gles (d eg) for NbCp Cl2(HCCH) Mod el Com p lex
a n d , for Com p a r ison , Selected Exp er im en ta l Da ta
for Nb(η5-C5H4Me)Cl2(4-Me-C6H4CCC6H4-4-Me)
NbCpCl2(HCCH)
NbCpMe2(HCCH)
parallel
conformn
perpendicular
conformn
parallel
conformn
perpendicular
conformn
structural
data
structural
data
BP86 B3LYP BP86 B3LYP
exptl
BP86 B3LYP BP86 B3LYP
exptl
Nb-C(1)
2.497
2.474
2.441
2.439
2.472
2.099
2.099
2.383
2.382
1.328
2.511
2.485
2.443
2.442
2.485
2.092
2.092
2.390
2.390
1.314
2.581
2.457
2.421
2.458
2.581
2.077
2.086
2.385
2.385
1.334
2.584
2.462
2.430
2.462
2.584
2.069
2.081
2.392
2.392
1.321
2.447
2.417
2.380
2.377
Nb-C(1)
2.574
2.534
2.462
2.461
2.532
2.092
2.092
2.198
2.198
1.342
2.597
2.554
2.474
2.474
2.553
2.084
2.084
2.201
2.201
1.331
2.573
2.526
2.446
2.446
2.526
2.074
2.103
2.208
2.208
1.341
2.582
2.539
2.462
2.462
2.539
2.068
2.098
2.209
2.209
1.329
2.544(6)
2.490(7)
2.403(8)
2.400(6)
2.461(6)
2.092(5)
2.087(6)
2.193(6)
2.198(5)
1.323(7)
Nb-C(2)
Nb-C(3)
Nb-C(4)
Nb-C(5)
Nb-C(6)
Nb-C(7)
Nb-Cl(1)
Nb-Cl(2)
C(6)-C(7)
Nb-C(2)
Nb-C(3)
Nb-C(4)
Nb-C(5)
Nb-C(6)
Nb-C(7)
Nb-C(8)
Nb-C(9)
C(6)-C(7)
2.428
2.063(5)
2.079(5)
2.353(2)
2.365(2)
1.307(7)
Cl(1)-Nb-Cl(2) 102.0
101.7
89.3
118.4
118.4
89.3
36.6
141.4
141.4
112.0
109.5
89.6
109.5
89.6
37.4
139.4
138.5
112.2
109.5
89.8
109.5
89.8
37.1
140.2
139.5
99.4(1)
88.6(1)
119.3(2)
119.3(2)
92.5(2)
36.8(2)
142.3a
C(8)-Nb-C(9) 101.0
C(8)-Nb-C(6) 87.2
C(8)-Nb-C(7) 116.5
C(9)-Nb-C(6) 116.7
C(9)-Nb-C(7) 87.4
C(6)-Nb-C(7) 37.4
97.8
87.9
116.4
116.4
87.9
37.3
136.6
136.6
111.2
109.3
89.1
109.3
89.1
37.5
137.7
134.3
110.7
109.3
89.1
109.3
89.1
37.2
138.0
135.1
106.6(2)
111.2(2)
90.5(2)
110.7(2)
89.2(2)
Cl(1)-Nb-C(6)
Cl(1)-Nb-C(7)
Cl(2)-Nb-C(6)
Cl(2)-Nb-C(7)
C(6)-Nb-C(7)
H-C(6)-C(7)
H-C(7)-C(6)
89.1
118.4
118.3
89.1
36.9
140.5
140.5
36.9(2)
H-C(6)-C(7)
H-C(7)-C(6)
136.3
136.4
140.7(5)a
139.7(5)a
144.4a
a
a
C-C-C bond angle.
Si-C-C bond angle.
compounds [NbCp′Cl2(ArCCAr)] (Cp′ ) η5-C5H4Me;
Ar ) 4-MeC6H4)12b and 3, respectively. Bond distances
concerning the niobium-cyclopentadienyl moiety are
slightly overestimated (maximum deviation 0.07 Å),
probably due to the consideration of the Cp model
instead of the actual cyclopentadienyl groups. A similar
overestimation of the Nb-Cp bond distances has been
recently observed.25 The other bond distances agree
within ca. 0.03 Å. On the other hand, there is good
agreement found with respect to the bond angles. The
largest deviation appears to be about 5°. The calculated
Cl-Nb-Cl and Me-Nb-Me bond angles change sub-
stantially with the orientation of the alkyne ligand.
Thus, for example, in the chloro complex the Cl-Nb-
Cl angle goes from ca. 102° (parallel; experimental data
99.4(1)°) to ca. 112° (perpendicular), while for the methyl
derivative the corresponding Me-Nb-Me bond angle
changes from ca. 99° (parallel) to ca. 111° (perpendicu-
lar; experimental data 106.6(2)°). A second comparison
can be made with a Ta complex,26 [TaCp*Me2(η2-C6H4)],
which possesses a benzyne perpendicular to the Cp
plane. The bond distances around the Ta center, the
C-C alkyne length (1.364(5) Å), and the main angles
(for example, Me-Ta-Me at 107.7(3)°) compares well,
despite the different metal, with the computed analo-
gous values for the perpendicular conformation in the
[NbCpMe2(HCCH)] model.
than 3. Furthermore, the C51-C41-Si4 (139.7(5)°) and
C41-C51-Si5 (140.7(5)°) bond angles show a consider-
able distortion from those of the free ligand, as has been
reported for similar tantalum derivatives.12b,16 In accord
with such distortion, the metal-alkyne moiety may be
viewed as a metallacyclopropene with the niobium atom
in a formal +5 oxidation state.24 The C21-Nb-C31
(106.6(2)°) bond angle is larger than the Cl1-Nb-Cl2
(99.4°) bond angle found in the dichloride complex [Nb-
(η5-C5H4Me)Cl2(ArCCAr)] (Ar ) 4-MeC6H4),12b in which
the alkyne ligand adopts a parallel disposition to the
η5-C5H4Me ring.
DF T Ca lcu la t ion s on [Nb (η5-C5H 5)R 2(H CCH )]
(R ) Cl, Me) Mod el Com p lexes. A theoretical analysis
was carried out within the density functional theory
(DFT) on [Nb(η5-C5H5)R2(HCCH)] (R ) Cl, Me) model
complexes. Our aim was the study of the preferential
disposition of the alkyne ligand in these type of com-
plexes, and we have considered the parallel and the
perpendicular conformations (always with respect to the
Cp plane) of the HCCH ligand in these two models.
Selected calculated parameters and, for comparison,
experimental data from X-ray crystallography have been
collected in Tables 2 and 3. The use of BP86 or B3LYP
functionals does not produce significant changes in the
structural parameters or in the energetics of the system.
The final optimized geometries are shown in Figures 2
and 3, and their coordinates are collected as Supporting
Information (Tables S6-S17).
With regard to the energetics of the system (see Table
4), the perpendicular conformation is always found to
be more stable than the parallel one. The energy
difference between the two conformations is computed
to be around 1.5 kcal mol-1 when chlorides are the
coligands, while for the methyl derivative the stabiliza-
tion of the perpendicular isomers increases up to ca. 7.5
kcal mol-1. We located the transition state connecting
In general, we can observe a quite satisfactory agree-
ment between the calculated and experimental values
of geometrical parameters. The former corresponds to
the parallel conformation in [NbCpCl2(HCCH)] and the
perpendicular disposition in [NbCpMe2(HCCH)] model
complexes, while for the latter we have selected the
(25) Kolehmainen, E.; Laithia, K.; Nissinen, M.; Linnanto, J .;
Perje´ssy, A.; Gautheron, B.; Broussier, R. J . Organomet. Chem. 2000,
613, 7.
(24) (a) Tatsumi, K.; Hoffmann, R.; Templeton, J . L. Inorg. Chem.
1982, 21, 466. (b) Steigerwald, M. L.; Goddard, W. A. J . Am. Chem.
Soc. 1985, 107, 5027.
(26) Churchill, M. R.; Youngs, W. J . Inorg. Chem. 1979, 18, 1697.

Alkyl Alkyne Cyclopentadienyl Niobium Complexes
Organometallics, Vol. 21, No. 2, 2002 297
F igu r e 2. Optimized structures of the [NbCpCl2(HCCH)] model complex (parallel and perpendicular conformations).
F igu r e 3. Optimized structures of the [NbCpMe2(HCCH)] model complex (parallel and perpendicular conformations).
Ta ble 4. Rela tive En er gies (k ca l/m ol) of
[Nb(η5-C5H5)R2(HCCH)] (R ) Cl, Me) Mod el
Com p lexes
On the other hand, the theoretical data for dialkyl
compounds of model formulation [NbCpR2(HCCH)] are
in agreement with a preferential disposition of the
alkyne ligand lying perpendicular to the Cp plane, such
as that observed in the structure of 3. This conformation
is characterized by a R-Nb-R angle higher than that
observed for the parallel conformation, to maximize the
parallel
conformn
perpendicular
conformn
barrier of
rotation
model complex BP86 B3LYP BP86 B3LYP BP86 B3LYP
NbCpCl2(HCCH)
NbCpMe2(HCCH) 8.1
1.1
1.4
7.5
0
0
0
0
3.5
8.3
3.5
7.9
overlap with the π (b1) and π * (b2) MO orbitals of the
||
alkyne ligand.24a The rather low computed barrier of
rotation (8 kcal mol-1) compares well with the data
obtained by DNMR spectroscopy for 3 (with bulkier
substituents).
the parallel and perpendicular conformations of the
alkyne ligand for the two models. The computed values
for the barrier of rotation (Table 4) are around 3.5 kcal
mol-1 when chlorines are the coligands and around 8
kcal mol-1 for the methyl derivative.
Rea ction s w ith 2,6-Me2C6H3NC. When 1 equiv of
the isocyanide 2,6-Me2C6H3NC was added to benzene-
d6 solutions of the dialkyl alkyne complexes 2-4 under
a rigorously dry inert gas in a sealed NMR tube, reddish
solutions corresponding to alkyl alkyne η2-iminoacyl
[NbCp′R{η2-C(R)dNAr}(Me3SiCCSiMe3)] (Cp′ ) η5-
C5H4SiMe3; Ar ) 2,6-Me2C6H3; R ) Me (6), CH2SiMe3
(7), CH2CMe3 (8)) complexes as the unique reaction
products were obtained (see Scheme 2). Complexes 6-8
were characterized by NMR spectroscopy. The insertion
process is instantaneous. After the coordination of the
isocyanide, the migration of one alkyl group to the
electrophilic isocyanide carbon atom takes place, giving
an η2-iminoacyl complex.
Previous EHMO calculations have been reported for
the [NbCpCl2(HCCH)] model12b and also for the [Nb-
TpCl2(HCCH)] model.13e The barrier to rotation of the
alkyne ligand was calculated to be ca. 6 kcal mol-1 when
the Cp is present, the parallel conformation being the
most stable. In contrast, for the Tp model, although the
alkyne lies in the molecular plane which bisects the
N-Nb-N angle (“perpendicular conformation”), there
is only a small energy difference between the two
possible orientations for the ligand. Our data (computed
barrier of 3.5 kcal mol-1) agrees with such analyses, and
it seems that for dichloride compounds of model formu-
lation [NbCpCl2(HCCH)] the importance of the elec-
tronic and steric properties of the substituents in the
actual alkyne can govern the preferential adoption of
one conformation.
When the same reactions were carried out in a
Schlenk tube using hexane as solvent, only the complex
7 could be isolated as a crystalline red solid. The

298 Organometallics, Vol. 21, No. 2, 2002
Galindo et al.
Sch em e 2a
a
Reagents and conditions: (i) 1 equiv of ArNC, NMR tube, benzene-d6, room temperature; (ii) 1 equiv of ArNC, Schlenk tube,
hexane, room temperature.
complexes 6 and 8 are unstable at room temperature,
and while 6 is partially transformed into the imido
niobacyclopent-3-ene complex 9, the η2-iminoacyl de-
rivative 8 decomposes to an unidentified products
mixture.
mation can be rationalized in terms of migration of the
second metal-bonded methyl group to the iminoacyl
carbon center to give the intermediate 9i (see Scheme
4). Similar azametallacyclopropane species have been
proposed and isolated in the reactions of dichloro
dimethyl pentamethylcyclopentadienyl niobium28 and
tantalum29 complexes with isocyanides and their struc-
tures confirmed by X-ray diffraction methods. Rear-
rangement of the intermediate 9i leads probably to an
imido niobacyclobutene species, and then the migration
of a hydrogen atom takes place and a last rearrange-
ment gives the imido niobacyclopent-3-ene complex 9.
The formation of complexes 10 and 11 can be ex-
plained via imido niobacyclobutene intermediates, and
when R′′ ) SiMe3, the migration of the hydrogen atom
and subsequent rearrangement leads to 10, which is a
niobacyclopropane complex with a vinyl substituent η2-
coordinated to the metal center. However, a different
pathway may be proposed by formation of an azanio-
bacyclopentatriene species12i,30 as a result of the in-
tramolecular coupling between both alkyne and imino-
acyl ligands. When R′′ ) CMe3, the C-H activation of
a methyl group of the tert-butyl fragment and a last
rearrangement leads to the imido niobacyclohept-2-ene
complex 11. This behavior is probably due to the steric
The imido niobacyclopent-3-ene complex [NbCp′(NAr)-
{η4-CH(SiMe3)C(SiMe3)dC(Me)CH2}] (Cp′ ) η5-C5H4-
SiMe3; Ar ) 2,6-Me2C6H3; 9) can be prepared by
treatment of the alkyne dimethyl derivative 2 with 1
equiv of isocyanide in hexane at 40-50 °C over 12 h.
On the other hand, if the alkyne (trimethylsilyl)methyl
η2-iminoacyl complex 7 is heated to 80 °C in hexane over
12 h, the imido niobacyclopropane(vinyl) derivative
[NbCp′(NAr){η4-CH(SiMe3)C(SiMe3)C(CH2SiMe3)dCH-
(SiMe3)}] (Cp′ ) η5-C5H4SiMe3; Ar ) 2,6-Me2C6H3; 10)
can be isolated as a crystalline red solid, whose struc-
ture was determined by X-ray diffraction methods (see
Scheme 3). Identical results can be obtained by thermal
treatment of the 1:1 mixture of 3 and 2,6-Me2C6H3NC.
In contrast to this behavior, the reaction between the
alkyne bis(neopentyl) complex 4 and isocyanide leads,
in the first step, to an alkyne neopentyl η2-iminoacyl
complex but this species is gradually transformed into
the imido niobacyclohept-2-ene complex [NbCp′(NAr)-
{η2-CH2CMe2CH2CH(CH2CMe3)C(SiMe3)dC(SiMe3)}]
(Cp′ ) η5-C5H4SiMe3; Ar ) 2,6-Me2C6H3; 11), whose
structure may be proposed on the basis of the NMR
spectroscopic data.
(27) 9i: 1H NMR (δ, ppm; in benzene-d6) 6.40 (m, 1H), 6.12 (m, 1H),
5.79 (m, 1H), 5.35 (m, 1H, H4C5SiMe3), 2.36 (s, 6H, Nb-CMe2-N(2,6-
Me2C6H3)), 2.32 (s, 3H), 1.81 (s, 3H, Nb-CMe2N(2,6-Me2C6H3)), 0.46
(s, 9H), 0.30 (s, 9H, Me3SiCCSiMe3), 0.25 (s, 9H, Me3SiC5H4).
(28) Castro, A.; Galakhov, M. V.; Go´mez, M.; Go´mez-Sal, P.; Mart´ın,
A.; Sa´nchez, F.; Velasco, P. Eur. J . Inorg. Chem. 2000, 2047.
(29) Galakhov, M. V.; Go´mez, M.; J imenez, G.; Royo, P.; Pellinghelli,
M. A.; Tiripicchio, A. Organometallics 1995, 14, 1901.
When the formation processes of the complexes 9-11
1
are followed by H NMR spectroscopy, only in the case
of complex 9 can the intermediate alkyne azanioba-
cyclopropane derivative 9i27 be detected. This transfor-

Alkyl Alkyne Cyclopentadienyl Niobium Complexes
Organometallics, Vol. 21, No. 2, 2002 299
Sch em e 3a
a
Reagents and conditions: (i) 1 equiv of ArNC, hexane, 12 h, 40-50 °C; (ii) 1 equiv of ArNC, hexane, 12 h, 80 °C; (iii) 1 equiv
of ArNC, benzene-d6, 6 days, room temperature; (iv) hexane, 12 h, 80 °C.
and electronic differences between -SiMe3 and -CMe3
groups. Therefore, the decreased steric hindrance of the
tert-butyl group permits a closer approach to the metal
and the activation of a C-H bond gives the complex 11.
All of the complexes 6-11 were found to be soluble
in most organic solvents, including alkanes. They are
extremely air- and moisture-sensitive, and rigorously
dried solvents and handling under dry inert gases were
found to be imperative for sucessful preparations.
The alkyl alkyne η2-iminoacyl complex 7 shows the
νj(CdC)16,19 and νj(CdN)28,31,32 IR absorptions at 1573
and 1585 cm-1, while the presence of the imido ligand
in the complexes 9 and 10 is confirmed by the absorption
bands located at 1297 and 1286 cm-1, respectively,
corresponding to the νj(NbdN)17,32 stretching vibration.
The 1H and 13C{1H} NMR data (see the Experimental
Section) of the complexes 6-11 are in agreement with
the proposed structures for the alkyl alkyne η2-iminoacyl
(6-8), imido niobacyclopent-3-ene (9), imido niobacy-
clopropane(vinyl) (10), and imido niobacyclohept-2-ene
(11) complexes. The pseudooctahedral complexes 6-8
1
show in their H NMR spectra two inequivalent methyl
groups for the 2,6-Me2C6H3 moiety, which is consistent
with the slow rotation of the aryl group around the
N-Ci(aryl) bond. Furthermore, the 1H and 13C{1H}
NMR spectra of such complexes show an ABCD spin
system and five carbon resonances, respectively, for the
(trimethylsilyl)cyclopentadienyl ring due to the chiral
character of the metal center.
The complex 9 exhibits a NMR behavior which is
consistent with a diene ligand in an s-cis conformation
similar to that observed in other group 5 metal-diene
derivatives.33 The three resonances assigned to the
proton and carbon atoms of the three trimethylsilyl
groups show that these groups are bonded to three
different carbon atoms. The proton and carbon atoms
of the cyclopentadienyl ring are inequivalent, but while
in its 13C{1H} NMR spectrum there are five carbon
(30) (a) Curtis, M. D.; Real, J . J . Am. Chem. Soc. 1986, 108, 4688.
(b) Hirpo, W.; Curtis, M. D. J . Am. Chem. Soc. 1988, 110, 5218. (c)
Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc.
1988, 110, 8235. (d) Hessen, B.; Teuben, J . H. J . Organomet. Chem.
1989, 367, C18. (e) Curtis, M. D.; Real, J .: Hirpo, W.; Butler, W. M.
Organometallics 1990, 9, 66. (f) Hessen, B.; Meetsma, A.; Bolhuis, F.
V.; Teuben, J . H. Organometallics 1990, 9, 1925. (g) Kriley, C. E.;
Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1993,
12, 2051.
(31) (a) Chisholm, M. H.; Hammond, C. E.; Ho, D.; Huffman, J . C.
J . Am. Chem. Soc. 1986, 108, 7860. (b) Durfee, L. D.; Rothwell, I. P.
Chem. Rev. 1988, 88, 1059. (c) Lubber, T. V.; Plo¨ssl, K.; Norton, J . R.;
Miller, M. H.; Anderson, O. P. Organometallics 1992, 11, 122.
(32) (a) Nugent, W. A.; Haymore, B. L. Coord. Chem. Rev. 1980, 31,
123. (b) Rocklage, S. M.; Schrock, R. R. J . Am. Chem. Soc. 1982, 104,
3077. (c) Nugent, W. A.; Mayer, J . M., Metal-Ligand Multiple Bonds;
Wiley: New York, 1988. (d) Bradley, D. C.; Hursthouse, M. B.; Howes,
A. J .; de M. J elfs, A. N.; Runnacles, J . D.; Thornton-Pett, M. J . Chem.
Soc., Dalton Trans. 1991, 841. (e) Williams, D. N.; Mitchell, J . P.; Poole,
A. D.; Siemeling, U.; Clegg, W.; Hockless, D. C. R.; O’Neil, P. A.; Gibson,
V. C. J . Chem. Soc., Dalton Trans. 1992, 739. (f) Wigley, D. E. Prog.
Inorg. Chem. 1994, 42, 239. (g) Castro, A.; Galakhov, M. V.; Go´mez,
M.; Go´mez-Sal, P.; Mart´ın, A.; Sa´nchez, F. J . Organomet. Chem. 2000,
595, 36.
1
resonances, in the H NMR spectrum we only detected
three signals in a 1:2:1 relation, due probably to the
overlapping between the resonances of the proton atoms
located in the 3- and 4-positions of the ring, whose
carbon atoms resonate at very close chemical shifts (δ).
The inequivalent o-methyl (phenyl) groups of the imido
moiety show two signals in the characteristic region for
(33) (a) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee,
K.; Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. Soc.
1985, 107, 2410. (b) Okamoto, T.; Yasuda, H.; Nakamura, A.; Kai, Y.;
Kanehisa, N.; Kasai, N. J . Am. Chem. Soc. 1988, 110, 5008. (c)
Mashima, K.; Kaidzu, M.; Nakayama, Y.; Nakamura, A. Organome-
tallics 1997, 16, 1345. (d) Mashima, K.; Kaidzu, M.; Tanaka, Y.;
Nakayama, Y.; Nakamura, A.; Hamilton, J . G.; Rooney, J . J . Organo-
metallics 1998, 17, 4183. (e) Strauch, H. C.; Wibbeling, B.; Fro¨hlich,
R.; Erker, G.; J acobsen, H.; Berke, H. Organometallics 1999, 18, 3802.

300 Organometallics, Vol. 21, No. 2, 2002
Galindo et al.
Sch em e 4
such ligands.17,32g Although the assignment of the
resonances at δ 2.33 (Me) and δ 0.20 (SiMe3) to the
substituents of the central carbon atoms -C(Me)d
C(SiMe3)- in the niobacyclopent-3-ene fragment is
unequivocal, in the 13C{1H} NMR spectrum the carbon
atoms C3 and C4 present very close chemical shifts and
therefore we have tentatively assigned to such carbon
atoms the signals at δ 123.5 and 122.05, respectively.
The relative shielding of these olefinic carbons (they
usually appear at δ >130) can be ascribed to the
π-electronic density transfer to an electronically defi-
cient niobium(V) center. The proton resonance located
at δ 3.40 corresponds to the Nb-CH(SiMe3) fragment,
while the diasterotopic methylene protons of the Nb-
CH2C(Me)d moiety appear as an AB system. In the 13C-
{1H} NMR spectra broad resonances are observed for
both carbon atoms, as is usual for sp3 carbon atoms
directly bonded to the niobium. In accord with these
data, we propose an s-cis conformation for the diene
ligand in a η4-niobacyclopent-3-ene bond system.
The unusual conformation of the diene ligand in the
complex 10 was deduced after a detailed and combined
analysis of the NMR spectroscopic and X-ray diffraction
data, which strongly suggests that the diene ligand is
bonded in a η2-niobacyclopropane fashion with a vinyl
substituent η2-coordinated to the metal center. The
complex 10 exhibits the 1H NMR signals of two different
CH(SiMe3) groups (δ 3.10, 1.80), the resonance located
at low field being assigned to the group bonded to the
vinyl fragment. The relative shielding of this proton can
be rationalized by the coordination of the carbon atom
to the metal center. In the 13C{1H} NMR spectrum the
signal at δ 88.4 (1J C-H ) 118.8 Hz) is assigned to the
vinylic carbon C4, while the resonance at δ 76 (1J C-H
)
114.9 Hz) corresponds to C1 of the niobacyclopropane
moiety. The signal located at δ 121.1 can be assigned
to the C3 atom of the vinyl fragment, but that corre-
sponding to the C2 atom of the niobacyclopropane
system cannot be observed, probably because of its low
intensity and broad signal. The rest of the resonances
for the five SiMe3 substituents and for the C5H4SiMe3
ring are as expected for the proposed structure.
The molecular structure and atom-labeling scheme of
10 are shown in Figure 4, while relevant geometrical
parameters are summarized in Table 5. Compound 10
can be described as a 18e monomer species with a
niobium atom coordinated to a (trimethylsilyl)cyclopen-
tadienyl ligand and to an imido group and forms a
niobacyclopropane system with a η2-vinyl susbstituent.
In relation to the imido disposition, the Nb1-N1 bond
distance (1.806(3) Å) and the Nb1-N1-C21 angle
(166.1(3)°) are similar to those found in other imido
niobium and tantalum derivatives.34 However, the 2,6-
Me2C6H3 moiety is slightly folded toward the Cp′ ring.
Frequently, in the diene mono(cyclopentadienyl) nio-
bium and tantalum compounds,33a,d,35 the diene ligand
(34) (a) Herrmann, W. A.; Weichselbaumer, G.; Paciello, R. A.;
Fischer, R. A.; Herdtweck, E.; Okuda, J .; Marz, D. N. Organometallics
1990, 9, 489. (b) Antonelli, D. M.; Schaefer, W. P.; Parkin, G.; Bercaw,
J . E. J . Organomet. Chem. 1993, 462, 213. (c) Galakhov, M. V.; Go´mez,
M.; J imenez, G.; Pellinghelli, M. A.; Royo, P.; Tiripicchio, A. Organo-
metallics 1994, 13, 1564; 1995, 14, 2843. (d) Castro, A.; Galakhov, M.
V.; Go´mez, M.; Go´mez-Sal, P.; Martin, A.; Royo, P. J . Organomet.
Chem. 1998, 554, 185.

Alkyl Alkyne Cyclopentadienyl Niobium Complexes
Organometallics, Vol. 21, No. 2, 2002 301
bonding system between the niobium center and such
ligands (see Figure 4). Thus, C31-C32, C32-C33, and
C33-C34 bond distances of 1.406(6), 1.456(5), and
1.460(6) Å, respectively, show that the first corresponds
to the vinyl group and is shorter than the other two.
The Nb-C33 (2.267(4) Å) and Nb-C34 (2.329(4) Å) bond
distances correspond to the carbon atoms of the nioba-
cylopropane fragment and are shorter than the Nb-
C31 (2.426(4) Å) and Nb-C32 (2.379(4) Å) bond dis-
tances. The torsion angle formed by the carbon atoms
of the ligand C31-C32-C33-C34 is 120.62(1)°, while
in the case of a normal diene ligand this angle would
be 0°. Moreover, the carbon atom C31 is located 1.07 Å
away from the plane formed by C32, C33, and C34. In
summary, we propose this bonding system to be con-
stituted of a “diene” C31-C32-C33-C34 fragment
linked to the metal through the C33-C34 atoms,
forming a niobacyclopropane ring and the donor vinyl
substituent C31dC32.
1
The complex 11 shows in its H NMR spectrum the
expected four signals for the methyl protons of the
trimethylsilyl and tert-butyl fragments and simulta-
neously presents inequivalency for the proton atoms of
the C5H4SiMe3 ring and the methyl groups of the 2,6-
Me2C6H3 moiety in the imido ligand. The proton atoms
of the methylene group directly bonded to niobium show
an AB spin system, while the corresponding -CH2-
CHCH2- fragment exhibits an ABCDE spin system,
which permits us to make the assignment. In the 13C-
{1H} NMR spectrum all expected resonances are present,
in agreement with the proposed structure.
F igu r e 4. ORTEP drawing of compound 10. Thermal
ellipsoids are shown at the 50% level.
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 10
Nb(1)-N(1)
Nb(1)-C(34)
Nb(1)-C(31)
Si(3)-C(38)
Si(5)-C(34)
C(31)-C(32)
C(32)-C(38)
1.806(3)
2.329(4)
2.426(4)
1.897(4)
1.866(4)
1.406(6)
1.528(5)
Nb(1)-C(33)
Nb(1)-C(32)
Si(2)-C(31)
Si(4)-C(33)
N(1)-C(21)
C(32)-C(33)
C(33)-C(34)
2.267(4)
2.379(4)
1.876(4)
1.905(4)
1.385(5)
1.456(5)
1.460(6)
Con clu sion s
N(1)-Nb(1)-C(33)
C(33)-Nb(1)-C(34)
C(33)-Nb(1)-C(32)
N(1)-Nb(1)-C(31)
C(34)-Nb(1)-C(31)
C(21)-N(1)-Nb(1)
N(1)-C(21)-C(22)
C(32)-C(31)-Si(2)
Si(2)-C(31)-Nb(1)
99.1(1) N(1)-Nb(1)-C(34)
37.0(1) N(1)-Nb(1)-C(32)
36.4(1) C(34)-Nb(1)-C(32)
102.2(1) C(33)-Nb(1)-C(31)
96.6(1) C(32)-Nb(1)-C(31)
166.1(3) N(1)-C(21)-C(26)
120.8(4) C(26)-C(21)-C(22) 120.4(4)
131.3(3) C(32)-C(31)-Nb(1) 71.2(2)
135.1(2) C(31)-C(32)-C(33) 117.8(3)
107.7(1)
119.3(1)
63.9(1)
62.8(1)
34.0(1)
118.9(4)
The direct alkylation of [NbCp′Cl2(Me3SiCCSiMe3)]
(Cp′ ) η5-C5H4SiMe3; 1) with the appropriate amount
of alkylating reagent leads to the formation of the
dialkyl alkyne complexes [NbCp′R2(Me3SiCCSiMe3)]
(Cp′ ) η5-C5H4SiMe3; R ) Me (2), CH2SiMe3 (3), CH2-
CMe3 (4), CH2C6H5 (5)), whose structural studies reveal
consistency with the expected three-legged piano-stool
environment. Theoretical studies on the [Nb(η5-C5H5)-
R2(HCCH)] (R ) Cl, Me) model complexes rationalize
the disposition of the alkyne ligand in these complexes.
Reaction of dialkyl alkyne derivatives 2-4 with 1 equiv
of 2,6-Me2C6H3NC occurs through the initial formation
of the alkyl alkyne η2-iminoacyl compounds [NbCp′R-
{η2-C(R)dNAr}(Me3SiCCSiMe3)] (Cp′ ) η5-C5H4SiMe3;
Ar ) 2,6-Me2C6H3; R ) Me (6), CH2SiMe3 (7), CH2CMe3
(8)) but leads to different coupling products, depending
on R. When hexane solutions of 2 and 3 were treated
with 1 equiv of isocyanide at 40-50 °C (2) and 80 °C
(3), respectively, the imido niobacyclopent-3-ene [NbCp′-
(NAr){η4-CH(SiMe3)C(SiMe3)dC(Me)CH2}] (Cp′ ) η5-
C5H4SiMe3; Ar ) 2,6-Me2C6H3; 9) and imido niobacyclo-
propane(vinyl) [NbCp′(NAr){η4-CH(SiMe3)C(SiMe3)C-
(CH2SiMe3)dCH(SiMe3)}] (Cp′ ) η5-C5H4SiMe3; Ar )
2,6-Me2C6H3; 10) complexes are obtained, probably via
azaniobacyclopropane intermediates. If R ) CH2CMe3,
after the initial formation of the non-stable η2-iminoacyl
complex 8, its spontaneous conversion takes place to
give the imido niobacylohept-2-ene [NbCp′(NAr){η2-CH2-
CMe2CH2CH(CH2CMe3)C(SiMe3)dC(SiMe3)}] (Cp′ ) η5-
C5H4SiMe3; Ar ) 2,6-Me2C6H3; 11) complex, but the
intermediate species could not be observed when the
C(31)-C(32)-C(38) 120.7(3) C(33)-C(32)-C(38) 120.7(3)
C(31)-C(32)-Nb(1) 74.8(2) C(33)-C(32)-Nb(1) 67.6(2)
C(38)-C(32)-Nb(1) 119.5(3) C(34)-C(33)-C(32) 117.3(3)
C(34)-C(33)-Si(4)
C(34)-C(33)-Nb(1)
Si(4)-C(33)-Nb(1)
C(33)-C(34)-Nb(1)
C(32)-C(38)-Si(3)
124.1(3) C(32)-C(33)-Si(4)
73.8(2) C(32)-C(33)-Nb(1)
121.8(2) C(33)-C(34)-Si(5)
69.2(2) Si(5)-C(34)-Nb(1)
117.0(3)
118.6(3)
76.0(2)
135.9(3)
134.2(2)
forms a metallacyclopent-3-ene system with a preferred
supino conformation, although there are examples with
a prono conformation. Furthermore, the diene ligand
can adopt an s-trans conformation, as has been observed
in bis(cyclopentadienyl) zirconium,36 mono(cyclopenta-
dienyl) molybdenum,37 and cationic bis(cyclopentadi-
enyl) tantalum38 complexes. In our case, the crystallo-
graphic data determined for the C-C ligand and Nb-
C(ligand) distances do not permit us to propose the same
(35) Mashima, K.; Fujikawa, S.; Tanaka, Y.; Urata, Y.; Oshiki, T.;
Tanaka, E.; Nakamura, A. Organometallics 1995, 14, 2633.
(36) Kai, Y.; Kanehisa, N.; Miki, K.; Kasai, N.; Mashima, K.;
Nagasuna, K.; Yasuda, H.; Nakamura, A. J . Chem. Soc., Chem.
Commun. 1982, 191.
(37) Hunter, A. D.; Legzdins, P.; Nurse, C. R.; Einstein, F. W. B.;
Willis, A. C. J . Am. Chem. Soc. 1985, 107, 1791.
(38) Strauch, H. C.; Erker, G.; Fro¨hlich, R. Organometallics 1998,
17, 5746.

302 Organometallics, Vol. 21, No. 2, 2002
Galindo et al.
(w), 835 (vs), 692 (w), 632 (w), 480 (w). 1H NMR (δ, ppm; in
benzene-d6): 6.17 (m, 2H), 5.74 (m, 2H, H4C5SiMe3), 0.55 (s,
6H, Nb-Me2), 0.36 (s, 18H, Me3SiCCSiMe3), 0.21 (s, 9H, Me3-
SiC5H4). 13C{1H} NMR (δ, ppm; in benzene-d6): 249.49 (Me3-
SiCCSiMe3), 116.6 (C2,5), 114.6 (Ci), 103.02 (C3,4, C5H4SiMe3),
40.4 (br, Nb-Me2), 0.94 (Me3SiCCSiMe3), 0.36 (Me3SiC5H4).
Anal. Calcd for C18H37Si3Nb: C, 50.20; H, 8.66. Found: C,
50.26; H, 8.54.
reaction was followed by 1H NMR spectroscopy. The
NMR spectroscopic data of the coupling products con-
firmed for the diene ligand an s-cis conformation in the
complex 9, while in the complex 10 such a ligand
presents an unusual coordination mode and forms with
the metal center a niobacyclopropane system with an
η2-vinyl substituent.
The data for 3 are as follows. Yield: 0.85 g (70%). IR (Nujol
Exp er im en ta l Section
mull; νj, cm-1): 1570 (s), 1244 (vs), 1177 (m), 1046 (m), 908
1
(m), 839 (vs), 682 (w), 626 (w). H NMR (δ, ppm; in benzene-
All operations were carried out under a dry argon atmo-
sphere using standard Schlenk-tube and cannula techniques
or in a conventional argon-filled glovebox. Solvents were
refluxed over an appropriate drying agent and distilled and
degassed prior to use: benzene-d6 and hexane (Na/K alloy) and
d6): 6.65 (m, 2H), 5.74 (m, 2H, H4C5SiMe3), 1.61, 1.13 (AB,
4H, J H-H ) 9 Hz, Nb-(CH2SiMe3)2), 0.39 (br, 18H, Me3-
2
SiCCSiMe3), 0.34 (s, 9H, Me3SiC5H4), -0.08 (s, 18H, Nb-(CH2-
SiMe3)2). 13C{1H} NMR (δ, ppm; in benzene-d6): 250 (Me3-
SiCCSiMe3), 118.92 (C2,5), 117.08 (Ci), 100.11 (C3,4, C5H4SiMe3),
56.28 (br, Nb-(CH2SiMe3)2), 3.42 (Nb-(CH2SiMe3)2), 1.45 (Me3-
SiCCSiMe3), 0.57 (Me3SiC5H4). Anal. Calcd for C24H53Si5Nb:
C, 50.13; H, 9.29. Found: C, 49.96; H, 9.37.
39
tetrahydrofuran (sodium-benzophenone). NbCp′Cl4 and
LiCH2CMe340 were prepared as described previously. Reagent
grade Me3SiCtCSiMe3 (Aldrich), MgClR (R ) Me, 3 M in OEt2;
R ) CH2SiMe3, 1 M in OEt2; R ) CH2C6H5, 2 M in THF;
Aldrich), 2,6-Me2C6H3NC (Fluka), and Al and HgCl2 (Panreac)
were purchased from commercial sources and were used
without further purification.
The data for 4 are as follows. Yield: 0.63 g (55%). IR (Nujol
mull; νj, cm-1): 1566 (m), 1246 (vs), 1176 (m), 1044 (m), 909
1
(m), 834 (vs), 676 (w), 630 (w), 485 (m). H NMR (δ, ppm; in
benzene-d6): 6.85 (m, 2H), 5.68 (m, 2H, H4C5SiMe3), 2.58, 0.92
Infrared spectra were recorded on Perkin-Elmer 883 and
Spectrum 2000 spectrophotometers (4000-200 cm-1) with
samples as Nujol mulls between CsI plates or in polyethylene
pellets. 1H and 13C{1H} NMR spectra were recorded on Varian
Unity 300 and Varian Unity 500 Plus spectrometers; chemical
shifts were referenced to the 13C (δ 128) and residual 1H (δ
7.15) resonances of the benzene-d6 solvent. C, H, and N
analyses were carried out with a Perkin-Elmer 2400 micro-
analyzer.
2
(AB, 4H, J H-H ) 9 Hz, Nb-(CH2CMe3)2), 0.87 (s, 18H, Nb-
(CH2CMe3)2), 0.41 (br, 18H, Me3SiCCSiMe3), 0.36 (s, 9H, Me3-
SiC5H4). 13C{1H} NMR (δ, ppm; in benzene-d6): 249.8 (Me3-
SiCCSiMe3), 119.55 (C2,5), 116.11 (Ci), 98.6 (C3,4, C5H4SiMe3),
82.40 (br, Nb-(CH2CMe3)2), 36.07 (Nb-(CH2CMe3)2), 35.7 (br,
Nb-(CH2CMe3)2), 1.91 (br, Me3SiCCSiMe3), 0.66 (Me3SiC5H4).
Anal. Calcd for C26H53Si3Nb: C, 57.53; H, 9.84. Found: C,
57.24; H, 9.77.
The data for 5 are as follows. Yield: 0.49 g (40%). IR (Nujol
Syn th esis of [Nb(η5-C5H4SiMe3)Cl2(Me3SiCCSiMe3)] (1).
Tetrahydrofuran (100 mL) was added to a weighed mixture
of [Nb(η5-C5H4SiMe3)Cl4] (2.00 g, 5.38 mmol), aluminum
powder (0.50 g, 18.52 mmol), and mercury(II) chloride (0.10
g, 0.37 mmol) at room temperature. The mixture was stirred
and Me3SiCtCSiMe3 (1.22 mL, 5.38 mmol) added under
rigorously anhydrous conditions. After 12 h, the resulting
suspension was decanted and filtered and the solvent was
removed under reduced pressure. The residue was extracted
with hexane (2 × 25 mL), and after filtration, the purple
solution was concentrated to 15 mL and cooled to -40 °C to
afford 1 as purple crystals. Yield: 1.95 g (77%). IR (Nujol mull;
νj, cm-1): 1638 (m), 1249 (vs), 1168 (m), 1040 (w), 888 (m), 839
mull; νj, cm-1): 1556 (m), 1246 (vs), 1177 (m), 1096 (w), 1042
1
(m), 903 (s), 834 (vs), 689 (m), 624 (w), 479 (w). H NMR (δ,
ppm; in benzene-d6): 7.03 (t, 4H), 6.90 (m, 6H, Nb-(CH2C6H5)2),
5.66 (m, 2H), 5.17 (m, 2H, H4C5SiMe3), 2.40, 2.14 (AB, 4H,
2J H-H ) 9 Hz, Nb-(CH2C6H5)2), 0.38 (br, 18H, Me3SiCCSiMe3),
0.004 (s, 9H, Me3SiC5H4). 13C{1H} NMR (δ, ppm; in benzene-
d6): 240.43 (Me3SiCCSiMe3), 143.56, 130.29, 124.38 (Co, Cp,
Cm, Nb-(CH2C6H5)2), 114.09 (C2,5), 113.03 (Ci), 109.7 (C3,4
,
C5H4SiMe3), 58.41 (br, Nb-(CH2C6H5)2), 1.94 (Me3SiCCSiMe3),
0.77 (Me3SiC5H4). Anal. Calcd for C30H45Si3Nb: C, 61.82; H,
7.78. Found: C, 61.61; H, 7.66.
Syn th esis of [NbCp ′R{η2-C(R)dNAr }(R′CCR′)] (Cp ′ )
η5-C5H4SiMe3; R′ ) SiMe3; Ar ) 2,6-Me2C6H3; R ) Me (6),
CH2SiMe3 (7), CH2CMe3 (8)). Com p ou n d s 6 a n d 8. To a
solution of 2 or 4 (0.15 g; R ) Me, 0.35 mmol; R ) CH2CMe3,
0.26 mmol) in benzene-d6 (0.7 mL) was added 2,6-Me2C6H3-
NC (R ) Me, 0.046 g, 0.35 mmol; R ) CH2CMe3, 0.034 g, 0.26
mmol) in a valved NMR tube under rigorously anhydrous
1
(vs), 630 (w), 341 (m). H NMR (δ, ppm; in benzene-d6): 6.03
(m, 2H), 5.71 (m, 2H, H4C5SiMe3), 0.28 (s, 9H, Me3SiC5H4),
0.23 (s, 18H, Me3SiCCSiMe3). 13C{1H} NMR (δ, ppm; in
benzene-d6): 231.72 (Me3SiCCSiMe3), 122.11 (Ci, C5H4SiMe3),
121.91 (C2,5), 111.91 (C3,4, C5H4SiMe3), 0.35 (Me3SiCCSiMe3),
-0.52 (Me3SiC5H4). Anal. Calcd for C16H31Cl2Si3Nb: C, 40.76;
H, 6.63. Found: C, 40.80; H, 6.49.
Syn th esis of [NbCp ′R2(R′CCR′)] (Cp ′ ) η5-C5H4SiMe3;
R′ ) SiMe3; R ) Me (2), CH2SiMe3 (3), CH2CMe3 (4),
CH2C6H5 (5)). A solution of 1 (1.00 g, 2.12 mmol) in hexane
(30 mL) was treated with MgClR (4.24 mmol; R ) Me, 1.42
mL of a 3 M solution in diethyl ether; R ) CH2SiMe3, 4.20 mL
of a 1 M solution in diethyl ether; R ) CH2C6H5, 2.12 mL of a
2 M solution in tetrahydrofuran) or LiCH2CMe3 (0.33 g, 4.24
mmol) at -78 °C, and the mixture was warmed slowly to room
temperature and then stirred for a further 12 h. The resulting
suspension was decanted and filtered and the filtrate concen-
trated to 10 mL; when the temperature was lowered overnight
to -40 °C, 2-5 were deposited as brown-orange microcrystal-
line solids.
1
conditions. The reaction was monitored by H NMR spectros-
copy until no further changes were observed. The final
spectrum was indicative of complete transformation of the
starting material and confirmed the formation of 6 and 8 in
quantitative yield.
The data for 6 are as follows. 1H NMR (δ, ppm; in benzene-
d6): 6.86 (m, 2H), 6.72 (m, 1H, Nb-C(Me)dN(2,6-Me2C6H3)),
5.66 (m, 1H), 5.62 (m, 1H), 5.52 (m, 1H), 5.38 (m, 1H, C5H4-
SiMe3), 2.37 (s, 3H, Nb-C(Me)dNAr), 1.70 (s, 3H), 1.14 (s, 3H,
Nb-C(Me)dN(2,6-Me2C6H3)), 0.84 (s, 3H, Nb-Me), 0.40 (s,
18H, Me3SiCCSiMe3), 0.13 (s, 9H, C5H4SiMe3).
The data for 8 are as follows. 1H NMR (δ, ppm; in benzene-
d6): 6.87 (m, 2H), 6.77 (m, 1H, Nb-C(CH2CMe3)dN(2,6-
Me2C6H3)), 6.57 (m, 1H), 6.15 (m, 1H), 5.99 (m, 2H, C5H4-
SiMe3), 2.79, 2.70 (AB, 2H, 2J H-H ) 14.4 Hz, Nb-C(CH2CMe3)d
The data for 2 are as follows. Yield: 0.55 g (60%). IR (Nujol
2
NAr), 2.44, 2.10 (AB, 2H, J H-H ) 13.2 Hz, Nb-CH2CMe3),
mull; νj, cm-1): 1581 (m), 1247 (vs), 1177 (m), 1046 (m), 919
1.85 (s, 3H), 1.45 (s, 3H, Nb-C(CH2CMe3)dN(2,6-Me2C6H3)),
1.06 (s, 9H, Nb-C(CH2CMe3)dNAr), 0.99 (s, 9H, Nb-CH2CMe3),
0.49 (s, 18H, Me3SiCCSiMe3), 0.07 (s, 9H, C5H4SiMe3).
Com p ou n d 7. Under rigorously anhydrous conditions,
hexane (30 mL) was added to a mixture of the complex 3 (0.70
(39) Andreu, A. M.; J alo´n, F. A.; Otero, A.; Royo, P. J . Chem. Soc.,
Dalton Trans. 1987, 953.
(40) Tessier-Youngs, C.; Beachley, O. T., J r. Inorg. Synth. 1986, 24,
95.

Alkyl Alkyne Cyclopentadienyl Niobium Complexes
Organometallics, Vol. 21, No. 2, 2002 303
Ta ble 6. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
Deta ils for 3 a n d 10
g, 1.22 mmol) and 2,6-Me2C6H3NC (0.16 g, 1.22 mmol). After
this mixture was stirred for 3 h at room temperature, the
resulting solution was filtered and the filtrate was concen-
trated to a volume of ca. 10 mL. Cooling at -40 °C overnight
led to the deposition of a red microcrystalline solid identified
as 7.
3
10
chem formula
fw
C
24H53NbSi5
C33H62NNbSi5
706.20
575.02
T (K)
293(2)
293(2)
The data for 7 are as follows. IR (Nujol mull; νj, cm-1): 1585
(w), 1561 (m), 1244 (s), 1178 (m), 1095 (w), 1041 (m), 904 (m),
837 (vs), 666 (w), 625 (w), 478 (w). 1H NMR (δ, ppm; in
benzene-d6): 6.84 (m, 2H), 6.74 (m, 1H, Nb-C(CH2SiMe3)d
N(2,6-Me2C6H3)), 6.17 (m, 1H), 5.84 (m, 1H), 5.79 (m, 2H, C5H4-
λ (Mo KR), Å
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
0.71073
P21/c
9.785(3)
18.734(4)
19.007(6)
0.71073
P1h
10.243(5)
10.381(4)
20.174(8)
89.38(2)
89.48(2)
70.63(2)
2023.6(15)
2
1.159
2
SiMe3), 3.06, 2.90 (AB, 2H, J H-H ) 11.5 Hz, Nb-C(CH2-
93.94(2)
SiMe3)dNAr), 1.90 (s, 3H), 1.54 (s, 3H, Nb- C(CH2SiMe3)d
2
N(2,6-Me2C6H3)), 1.04, 0.88 (AB, 2H, J H-H ) 12.5 Hz, Nb-
3476.0(17)
4
1.099
CH2SiMe3), 0.49 (s, 18H, Me3SiCCSiMe3), 0.13 (s, 9H, C5H4-
SiMe3), 0.04 (s, 9H, Nb-C(CH2SiMe3)dNAr), -0.20 (s, 9H,
Nb-CH2SiMe3). 13C{1H} NMR (δ, ppm; in benzene-d6): 247.32
(Me3SiCCSiMe3), 220.53 (Nb-C(CH2SiMe3)dNAr), 144.84 (Ci,
Nb-C(CH2SiMe3)dN(2,6-Me2C6H3)), 131.2, 130, 126.2 (Co, Cp,
Cm, Nb-C(CH2SiMe3)dN(2,6-Me2C6H3)), 109.58 (Ci, C5H4-
SiMe3), 112.11, 106.34, 105.35, 104.97 (C5H4SiMe3), not ob-
served (Nb-CH2SiMe3), 33.74 (Nb-C(CH2SiMe3)dNAr), 19.37,
19.16 (Nb-C(CH2SiMe3)dN(2,6-Me2C6H3)), 4.16 (Me3SiCCSi-
Me3), 2.67 (C5H4SiMe3), 0.54 (Nb-C(CH2SiMe3)dNAr), 0.46
(Nb-CH2SiMe3). Anal. Calcd for C33H62NSi5Nb: C, 56.13; H,
8.85; N, 1.98. Found: C, 56.07; H, 9.08; N, 1.84.
Z
F
calcd, g cm-3
µ, mm-1
0.528
0.466
θ range, deg
index ranges
3.01-25.09
0 e h e 11,
0 e k e 22,
-22 e l e 22
6500
3.03-24.98
0 e h e 12,
-11 e k e 12,
-23 e l e 23
7502
no. of data collected
no. of unique data
6119 (R(int) )
0.0390)
7070 (R(int) )
0.0194)
no. of params refined
goodness of fit on F2
final R indices
298
0.979
361
0.878
R1 ) 0.0550,
wR2 ) 0.1295
R1 ) 0.1460,
wR2 ) 0.1641
0.491 and -0.464
R1 ) 0.0536,
wR2 ) 0.1508
R1 ) 0.0639,
wR2 ) 0.1701
1.390 and -1.214
(I > 2σ(I))a
Syn th esis of [NbCp ′(NAr ){η4-CH2C(Me)dC(SiMe3)CH-
(SiMe3)}] (Cp ′ ) η5-C5H4SiMe3; Ar ) 2,6-Me2C6H3; 9). 2,6-
Me2C6H3NC (0.21 g, 1.63 mmol) was added to a solution of 2
(0.70 g, 1.63 mmol) in hexane (30 mL) and the reaction mixture
heated for 12 h at 40-50 °C. The brown solution was filtered,
concentrated to ca. 10 mL, and cooled to -40 °C to give 9 as
brown crystals. Yield: 0.64 g (70%). IR (Nujol mull; νj, cm-1):
1586 (m), 1297 (m), 1245 (vs), 1178 (s), 1093(s), 1045 (s), 903
R indices (all data)
largest diff peak
and hole, e Å-3
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) {[∑w(Fo2 - Fc2)2]/[∑w(Fo2)2]}1/2
.
a
(-C(CH2SiMe3)dCH(SiMe3)), 117 (Ci, C5H4SiMe3), 110.88,
107.44, 107.25, 104.70 (C5H4SiMe3), not observed (Nb-CH-
(SiMe3)C(SiMe3)-), 88.4 (1J C-H ) 118.8 Hz, CH(SiMe3)dC(CH2-
SiMe3)-), 76 (1J C-H ) 114.9 Hz, Nb-CH(SiMe3)C(SiMe3)-),
30.8 (-C(CH2SiMe3)dCH(SiMe3)), 21.03, 20.14 (NbdN(2,6-
Me2C6H3)), 4.83, 3.83, 2.57, 0.09, 0.00 (Nb-CH(SiMe3)C-
(SiMe3)-, -C(CH2SiMe3)dCH(SiMe3), C5H4SiMe3). Anal. Calcd
for C33H62NSi5Nb: C, 56.13; H, 8.85; N, 1.98. Found: C, 56.18;
H, 8.89; N, 1.79.
1
(s), 833 (vs), 629 (w), 483 (w). H NMR (δ, ppm; in benzene-
d6): 6.93 (m, 2H), 6.67 (m, 1H, NbdN(2,6-Me2C6H3)), 6.19 (m,
1H), 6.06 (m, 2H), 5.14 (m, 1H, C5H4SiMe3), 3.70, -0.33 (AB,
2H, 2J H-H ) 8 Hz, Nb-CH2-), 3.40 (s, 1H, Nb-CH(SiMe3)-),
2.33 (s, 3H, Nb-CH2C(Me)dC(SiMe3)-), 2.13 (s, 3H), 2.06 (s,
3H, NbdN(2,6-Me2C6H3)), 0.21 (s, 9H), 0.20 (s, 9H), 0.01 (s,
9H, Nb-CH(SiMe3)-, Nb-CH(SiMe3)C(SiMe3)dC(Me)-, C5H4-
SiMe3). 13C{1H} NMR (δ, ppm; in benzene-d6): 139.10 (Ci, Nbd
N(2,6-Me2C6H3)), 127.98, 127.38, 126.90 (Co, Cp, Cm, NbdN(2,6-
Me2C6H3)), 123.5 (Nb- CH2C(Me)dC(SiMe3)-), 122.05 (Nb-
CH2C(Me)dC(SiMe3)-), 111 (Ci, C5H4SiMe3), 112.45, 110.72,
106.3, 106.06 (C5H4SiMe3), 64.5 (br, Nb-CH2C(Me)dC(SiMe3)-
), 63.75 (br, Nb-CH(SiMe3)C(SiMe3)d), 28.15 (Nb-CH2C(Me)d
C(SiMe3)-), 19.93, 18.95 (NbdN(2,6-Me2C6H3)), 3.28, 2.03, 0.62
(Nb-CH(SiMe3)-, Nb-CH(SiMe3)C(SiMe3)dC(Me)-, C5H4-
SiMe3). Anal. Calcd for C27H46NSi3Nb: C, 57.72; H, 8.25; N,
2.49. Found: C, 57.80; H, 8.20; N, 2.20.
Syn th esis of [NbCp ′(NAr ){η2-C(SiMe3)dC(SiMe3)CH-
(CH2CMe3)CH2CMe2CH2}] (Cp ′ ) η5-C5H4SiMe3; Ar ) 2,6-
Me2C6H3; 11). A benzene-d6 (0.7 mL) solution of the complex
8 was prepared as we have described above and heated at room
temperature for several days in a sealed NMR tube. The
transformation was monitored by NMR spectroscopy until no
further change was observed. After 6 days, the formation of
1
11 was confirmed by its H and 13C{1H} NMR spectra and the
data are as follows. 1H NMR (δ, ppm; in benzene-d6): 6.93 (m,
2H), 6.84 (m, 1H, NbdN(2,6-Me2C6H3)), 6.00 (m, 1H), 5.73 (m,
1H), 5.31 (m, 1H), 5.21 (m, 1H, C5H4SiMe3), 3.46 (m, He), 2.77,
Syn t h esis of [Nb Cp ′(NAr ){η4-CH (SiMe3)C(SiMe3)C-
(CH2SiMe3)dCH(SiMe3)}] (Cp ′ ) η5-C5H4SiMe3; Ar ) 2,6-
Me2C6H3; 10). A hexane (30 mL) solution of 7 (0.70 g, 0.99
mmol) was heated at 80 °C for 12 h in a sealed tube. After the
tube was opened, the solution was filtered, concentrated to ca.
10 mL, and cooled to -40 °C to give 10 as red crystals, which
were filtered out and dried under vacuum. Yield: 0.56 g (80%).
IR (Nujol mull; νj, cm-1): 1586 (w), 1286 (m), 1245 (vs), 1169
2
2.38 (AB, 2H, J H-H ) 13 Hz, Nb-CH2-), 2.36 (s, 6H, Nbd
2
N(2,6-Me2C6H3)), 1.95 (dd, Hd, J c-d ) 14.6 Hz), 1.65 (dd, Hc,
3J c-e ) 1.6 Hz), 1.40 (s, 3H), 0.96 (s, 3H, -CH2CMe2CH2-),
1.16 (dd, Hb), 0.95 (dd, Ha), 0.69 (s, 9H, -C(SiMe3)CH-
(CH2CMe3)CH2-), 0.43 (s, 9H), 0.24 (s, 9H), 0.13 (s, 9H, Nb-
C(SiMe3)-, -C(SiMe3)dC(SiMe3), C5H4SiMe3). 13C{1H} NMR
(δ, ppm; in benzene-d6): 215.3 (Nb-(Me3Si)CdC(SiMe3)-),
149.70 (Nb-(Me3Si)CdC(SiMe3)-), 135.96 (Ci, NbdN(2,6-
Me2C6H3)), 135.54, 128.73, 125.05 (Co, Cp, Cm, NbdN(2,6-
Me2C6H3)), 119.54 (Ci, C5H4SiMe3), 113.94, 113.45, 111.39,
109.66 (C5H4SiMe3), 61.03 (-CHe(CH2CMe3)), 53.57 (Nb-
CH2-), 52.74 (-CH(CHa,bCMe3)), 47.01 (-CHc,d-), 36.66, 33.64
(Nb-CH2CMe2CH2-), 30.43 (-C(SiMe3)CH(CH2CMe3)CH2-),
23.44, 22.9 (NbdN(2,6-Me2C6H3)), 2.79, 1.88, 0.47 (Nb-
C(SiMe3)-, -C(SiMe3)dC(SiMe3), C5H4SiMe3). After recrys-
tallization in hexane the complex 11 was always isolated as
an impure microcrystalline reddish solid; therefore, satisfac-
tory elemental analyses could not be obtained.
1
(w), 1093 (w), 1047 (w), 906 (m), 832 (vs), 694 (w), 636 (w). H
NMR (δ, ppm; in benzene-d6): 6.92 (m, 1H), 6.82 (m, 1H), 6.68
(m, 1H, NbdN(2,6-Me2C6H3)), 6.70 (m, 1H), 6.06 (m, 1H), 5.85
(m, 1H), 4.55 (m, 1H, C5H4SiMe3), 3.10 (s, 1H, H(SiMe3)Cd
C(CH2SiMe3)-), 2.52 (s, 3H), 2.25 (s, 3H, NbdN(2,6-Me2C6H3)),
1.8 (s, 1H, Nb-CH(SiMe3)C(SiMe3)-), 1.55, 0.95 (AB, 2H,
2J H-H ) 13 Hz, -C(CH2SiMe3)dCH(SiMe3)), 0.54 (s, 9H), 0.43
(s, 9H), 0.18 (s, 9H), 0.15 (s, 9H), 0.08 (s, 9H, Nb-CH(SiMe3)C-
(SiMe3)-, -C(CH2SiMe3)dCH(SiMe3), C5H4SiMe3). 13C{1H}
NMR (δ, ppm; in benzene-d6): 147.82 (Ci, NbdN(2,6-Me2C6H3)),
131.6, 127.7, 122.23 (Co, Cp, Cm, NbdN(2,6-Me2C6H3)), 121.11

304 Organometallics, Vol. 21, No. 2, 2002
Galindo et al.
Cr ysta l Str u ctu r e Deter m in a tion of Com p ou n d s 3 a n d
10. Crystallographic and experimental details of the crystal
structure determinations are given in Table 6. Suitable
crystals of complexes 3 and 10 were mounted on an Enraf-
Nonius Cad 4 automatic four-circle diffractometer with bisect-
ing geometry, equipped with a graphite-oriented monochro-
mator and Mo KR radiation (λ ) 0.710 73 Å). Data were
collected at room temperature. Intensities were corrected for
Lorentz and polarization effects in the usual manner. No
absorption or extinction corrections were made.
nalization of the analytically computed Hessian (vibrational
frequency calculations). The calculations were performed using
the Gaussian-98 package.46
Ack n ow led gm en t. We thank the DGICYT (Projects
PB97-0761 and PB97-0740) for financial support.
Note Ad d ed in P r oof. Due to the consideration of d
polarization functions (C and Cl atoms) in the calcula-
tions at the B3LYP level in our work, there are small
differences in the structural parameters and energies
with respect to those reported by E. Le Grognec, R. Poli,
P. Richard in J . Chem. Soc., Dalton Trans. 2000, 1499
for the model complex NbCpCl2(HCCH).
The structures were solved, using the WINGX package,41
by direct methods (SHELXS-97) and refined by least squares
against F2 (SHELXL-97).42 In 3, disorder appeared for the
carbon atoms of the methyl groups linked to Si2 and were
refined in two positions with 50% of occupancy. All non-
hydrogen atoms were anisotropically refined. The deepest hole,
-0.46, is located 1.06 Å from Nb1 and the highest peak, 0.49,
at 1.07 Å from C12. The hydrogen atoms were positioned
geometrically and refined by using a riding model, except those
of the disordered methyl groups. In 10, all non-hydrogen atoms
were anisotropically refined. The deepest holee, -1.21, is
located 0.95 Å from Nb1 and the highest peak, 1.39, at 1.02 Å
from Nb1. The hydrogen atoms were positioned geometrically
and refined by using a riding model.
Com p u ta tion a l Deta ils. The electronic structure and
geometries of the [Nb(η5-C5H5)R2(HCCH)] (R ) Cl, Me) model
complexes were computed within the density functional theory
at the BP8643 and B3LYP44 level using the LANL2DZ45 basis
set. A set of d polarization functions was added on C and Cl
atoms. Geometries were optimized under no symmetry con-
straint. Parallel and perpendicular conformations of the alkyne
ligand, with respect to the Cp group, were considered. The
optimized geometries were characterized as energy minima
or first-order saddle points (transition structures) by diago-
Su p p or tin g In for m a tion Ava ila ble: Tables of experi-
mental details of the X-ray studies, atomic coordinates and
equivalent isotropic thermal parameters, bond distances and
angles, anisotropic displacement parameters, and hydrogen
atom coordinates for 3 and 10 (Tables S1-S5 for 3 and S18-
S22 for 10) and tables of atomic coordinates for optimized
structures of [NbCpCl2(HCCH)] and [NbCp(Me)2(HCCH)] model
complexes (Tables S6-S17). This material is available free of
charge via the Internet at http://pubs.acs.org.
OM010521A
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