Synthesis and reactivity of novel niobocene complexes containing allyl or 1-azaallyl ligands. X-ray crystal structure of [Li{η3-N(SiMe 3)C(tBu)CH2}]3

Article abstract of DOI:10.1021/om980716r

The lithium 1-azaallyl complex [Li{η³-N(SiMe ₃)C(^tBu)CH₂}]₃ (1), has been prepared, and its X-ray crystal structure was determined. The niobocene(III) allyl and 1-azaallyl complexes Cp′₂Nb[

Full text of DOI:10.1021/om980716r

5874
Organometallics 1998, 17, 5874-5879
Syn th esis a n d Rea ctivity of Novel Niobocen e Com p lexes
Con ta in in g Allyl or 1-Aza a llyl Liga n d s. X-r a y Cr ysta l
Str u ctu r e of [Li{η3-N(SiMe3)C(tBu )CH2}]3
Antonio Antin˜olo,† Carmen Huertas,† Isabel del Hierro,† Michael F. Lappert,‡
Antonio Otero,*,† Sanjiv Prashar,† Ana M. Rodriguez,† and Elena Villasen˜or†,‡
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Facultad de Quı´micas,
Campus Universitario, Universidad de CastillasLa Mancha, 13071-Ciudad Real, Spain, and
The Chemistry Laboratory, University of Sussex, Brighton BN1 9QJ , U.K.
Received August 20, 1998
The lithium 1-azaallyl complex [Li{η3-N(SiMe3)C(tBu)CH2}]3 (1), has been prepared, and
its X-ray crystal structure was determined. The niobocene(III) allyl and 1-azaallyl complexes
Cp′2Nb[η3-CH2C(R)CH2] (Cp′ ) η5-C5H4SiMe3; R ) H (2), Me (3)) and Cp′2Nb[N(SiMe3)C(tBu)-
CH2] (4) have been synthesized. Oxidation of 2 and 3 by O2 yields Cp′2Nb[η1-CH2C(R)CH2]-
(O) (R ) H (5), Me (6)). The complexes CpNb(dNtBu)[η1-CH2C(R)CH2]Cl (Cp ) η5-C5H5; R
) H (7), Me (8)) have also been prepared. Oxidation of 2-4 by PbCl2 gave Cp′2Nb[η1-CH2C-
(R)CH2]Cl (R ) H (9), Me (10)) and Cp′2Nb[N(SiMe3)C(tBu)CH2]Cl (11). Cp′2Nb[η1-CH2C-
(R)CH2](L) (L ) CO (12), CN(2,6-Me2-C6H3) (13)) were prepared by the reaction of
Cp′2NbCl(L) with ClMg(CH2CHCH2).
The use of 1-azaallyl ligands in the preparation of
niobocene complexes,13 and more recently the tantalum
allyl complexes (η5-C5Me5)Ta(dNR)[η1-CH2CHCH2][η3-
CH2CHCH2] (R ) SitBu3, 2,6-iPr-C6H3) have also been
prepared.14 In addition, the synthesis of amidinate
complexes of niobium15 and tantalum16 have been
published and in these complexes the amidinate acts
as a chelating rather than η3 ligand. In connection with
our studies on the use of unsaturated molecules in the
synthesis of new families of niobium organometallics,
we report here our results on the reactivity of [Cp′2-
NbCl]2, Cp′ ) η5-C5H4SiMe3, with lithium 1-azaallyl and
allyl reagents to give new niobocene complexes, namely
Cp′2Nb[N(SiMe3)C(tBu)CH2] and Cp′2Nb[η3-CH2C(R)-
CH2], and some of their transformations, particularly
to oxo- and chloroniobium species. The reactivity of
CpNb(dNtBu)Cl2, Cp ) η5-C5H5, and Cp′2NbCl(L) to-
ward allyl reagents was also considered.
novel metal complexes has recently received attention.1
Complexes have been prepared with various metals
from differing groups in the periodic table (Li,2 K,2 V,3
Cu,1b Zr,2,4 Mo,5 Ru,6 Sn,1b,7 Ce,8 Nd,8 Sm,8 Yb,8,9 W,5
Pb,7 Th10) but there are no examples of Nb complexes.
Furthermore, there are only a relatively small number
of η3-allyl complexes of niobium and tantalum despite
the synthesis of Cp2Nb(η3-C3H5) being first reported in
1970.11 This was followed by the preparation of Cp2M-
(R) (M ) Nb, Ta; R ) 1-methylallyl, 2-methylallyl).12
Nakamura et al have also synthesized a family of allyl
* Corresponding author. E-mail: aotero@qino-cr.uclm.es.
† Universidad de Castilla-La Mancha.
‡ University of Sussex.
(1) (a) Lappert, M. F.; Liu, D.-S. J . Organomet. Chem. 1995, 500,
203. (b) Hitchcock, P. B.; Hu, J .; Lappert, M. F.; Layh, M.; Liu, D.-S.;
Severn, J . R.; Shun, T. Anales de Qu´ımica, Int. Ed. 1996, 92, 186.
(2) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J . Chem. Soc., Chem.
Commun. 1994, 2637.
(3) de With, J .; Horton, A. D.; Orpen, A. G. Organometallics 1993,
12, 1493.
(4) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S.; Ryan, E. J .
Polyhedron 1995, 14, 2745.
(5) (a) Daff, P. J .; Kaltsoyannis, N. J . Chem. Soc., Dalton Trans.
1995, 1925. (b) Daff, P. J .; Monge, A.; Palma, P.; Poveda, M. L.; Ruiz,
C.; Valerga, P.; Carmona, E. Organometallics 1997, 16, 2263. (c)
Amador, U.; Daff, P. J .; Poveda, M. L.; Ruiz, C.; Carmona, E. J . Chem.
Soc., Dalton Trans. 1997, 3145.
The lithium 1-azaallyl complex, [Li{η3-N(SiMe3)C(tBu)-
CH2}]3 (1), was prepared by the reaction of tBuCN and
LiCH2SiMe3.17 The proposed reaction pathway involves
initial formation of Li[NdC(CH2SiMe3)tBu] followed by
a 1,3-silicotropic rearrangement to yield the isolated
isomer 1 (see Scheme 1). This method is similar to that
utilized in the synthesis of the dimeric lithium 1-azaallyl
complex [Li{η3-N(SiMe3)C(tBu)CHSiMe3}]2.2
1 was initially characterized by NMR spectroscopy.
(6) Kuhlman, R.; Folting, K.; Caulton, K. G. Organometallics 1995,
14, 3188.
1
Its H NMR spectra showed the expected signals for the
tert-butyl and trimethylsilyl protons (see Experimental
Section). In addition, two broad signals, at 3.79 and 4.44
ppm, were observed and assigned to the CH2 protons of
(7) Hitchcock, P. B.; Lappert, M. F.; Layh, M. Inorg. Chim. Acta
1998, 268, 181.
(8) Hitchcock, P. B.; Lappert, M. F.; Shun, T. J . Organomet. Chem.
1997, 549, 1.
(9) Hitchcock, P. B.; Holmes, S. A.; Lappert, M. F.; Shun, T. J . Chem.
Soc., Chem. Commun. 1994, 2691.
(10) Hitchcock, P. B.; Hu, J .; Lappert, M. F.; Shun, T. J . Organomet.
Chem. 1997, 536-537, 473.
(11) Sietger, F. W.; Liefde Meijer, H. J . J . Organomet. Chem. 1970,
23, 177.
(12) (a) Van Baalen, A.; Groenenboom, C. J .; Liefde Meijer, H. J . J .
Organomet. Chem. 1974, 74, 240. (b) Tebbe, F. N.; Parshall, G. W. J .
Am. Chem. Soc. 1971, 93, 3793.
(13) Yasuda, H.; Arai, T.; Okamoto, T.; Nakamura, A. J . Organomet.
Chem. 1989, 361, 161.
(14) Antonelli, D. M.; Leins, A.; Stryker, J . M. Organometallics 1997,
16, 2500.
(15) Stewart, P. J .; Blake, A. J .; Mountford, P. Inorg. Chem. 1997,
36, 1982.
(16) Dawson, D. Y.; Arnold, J . Organometallics 1997, 16, 1111.
(17) Lappert, M. F.; Liu, D.-S. Unpublished work.
10.1021/om980716r CCC: $15.00 © 1998 American Chemical Society
Publication on Web 12/03/1998

Novel Niobocene Complexes
Organometallics, Vol. 17, No. 26, 1998 5875
Sch em e 1. P r op osed Mech a n ism in th e Syn th esis
of [Li{η3-N(SiMe3)C(tBu )CH2}]3 (1)
the azaallyl ligand with the broadening of these signals
being due to the close proximity of lithium. However,
7
in the Li and 13C NMR spectra of 1 Li-C coupling was
not observed.
The molecular structure of 1 was established by X-ray
crystal studies. The molecular structure and atomic
numbering scheme are shown in Figure 1. A summary
of X-ray and refinement data can be found in Table 1.
The structure reveals a trimer made up of three
mutually bonded Li atoms, with each being linked to
an azaallyl ligand. The nitrogen atom of this ligand
bridges two Li atoms of the central core with essentially
the same bond distances (1.99(1)-2.092(9) Å). The
azaallyl ligand is bonded to the Li atom in form η3 with
average bond distances of Li-N 2.010 (10) Å, Li-Ccentral
2.296 (11) Å, and Li-Cterminal 2.361(11) Å. The C-N and
C-C bond distances for the three azaallyl ligands are
normal for this type of ligand and comparable with other
related compounds.2 The Li3N3 trimeric unit consists of
alternate Li and N atoms forming an approximately
planar six-membered ring. Li(1) and Li(2) are situated
furthest from the average plane at distances of -0.13-
(1) and 0.17(1) Å, respectively. The average Li-Li
distance is 2.970(12) Å, and the average N-Li-N and
Li-N-Li angles are 143.9(9) and 95.2(4)°, respectively.
The bonding mode in 1 clearly indicates η3 character
nevertheless the compound can also be regarded as a
lithium amide with additional Li-C contacts.18 It should
be noted that the crystal data collected is poor and is
due to the low intensity of diffraction of the crystal and
F igu r e 1. Molecular structure and atom-labeling scheme
for [Li{η3-N(SiMe3)C(tBu)CH2}]3 (1). Selected average dis-
tances (Å): Li-Li, 2.970(12); Li-Na, 2.002(9); Li-Nd, 2.018-
(10); Li-Cc, 2.296(11); Li-Ct, 2.361(11); Cc-Na, 1.411(8);
Cc-Ct, 1.350(8). Selected average angles (deg): Li-Li-Li,
60.0(3); N-Li-N, 143.9(5); Li-N-Li, 95.2(4); Li-Na-Cc,
81.4(4); Li-Ct-Cc, 70.5(4); Li-Cc-Ct, 75.8(4); Li-Cc-Na,
61.3(3); Na-Cc-Ct, 121.2(5); Cc-Nd-Li, 123.3(4) (Cc and
Ct are the central and terminal carbon atoms, respectively,
of the azaallyl ligand; Na is the nitrogen atom pertaining
to the same azaallyl ligand and Nd to that of a neighboring
ligand). The tBu and SiMe3 groups show rotational disorder
and have been refined isotropically.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for [Li{η3-N(SiMe3)C(tBu )CH2}]3 (1)
empirical formula
fw
C27H60Li3N3Si3
531.87
wavelength (Å)
0.71070
cryst syst
triclinic
space group
a (Å)
P1h
9.530(10)
12.346(6)
16.90(2)
79.11(7)
80.70(10)
67.89(6)
1800(3)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
t
the disorder of Bu and SiMe3 groups.
volume (Å3)
Z
2
1 is one of the very few examples of a Li3 cluster. Only
three other compounds of this type have previously been
reported, [LiN(SiMe3)2]3,19 trimeric [R-(1,13,3-tetra-
methyl-2-indanyline)benzyl]lithium20 and a trimeric bis-
(trimethylsilyl)phenylamidinato cyanobenzene lithium
compound.21
The rarity of allyl complexes of the heavy group 5
elements has led us to prepare allyl complexes of
niobium and to study their reactivity. The eighteen
electron allyl complexes Cp′2Nb[η3-CH2C(R)CH2] (Cp′ )
η5-C5H4SiMe3) (R ) H (2), Me (3)) were prepared by the
density (calculated) (g/cm3)
absorption coefficient (cm-1
F(000)
0.981
1.49
588
)
cryst size (mm)
θ range for data collection (deg)
index ranges
0.20 × 0.17 × 0.13
2.03 to 28.00
0 e h e 12, -14 e k e 16,
-21 e l e 22
8684
3213
0.916
0.0919
0.2442
no. of indep reflcns
no. of obsd reflcns [I > 2σI]
GOF
R1 [I > 2σI]
wR2 [I > 2σI]
largest diff. Peak and hole (e/Å3)
0.355 and -0.374
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]0.5
.
a
(18) See, for example: (a) Setzer, W. N.; Schleyer, P. v. R.; Adv.
Organomet. Chem. 1985, 24, 353. (b) Weiss, E. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1501. (c) Lithium Chemistry; Sapse, A.-M., Schleyer,
P. v. R., Eds.; Wiley-Interscience Publications: New York, 1995. (d)
Mulvey, R. E.; Chem. Soc. Rev. 1991, 20, 167.
(19) Rogers, R. D.; Atwood J . L.; Gruening, R. J . Organomet. Chem.
1978, 157, 229.
(20) Knorr, R.; Hoang, T. P.; No¨th, H.; Linti, G. Organometallics
1992, 11, 2669.
(21) Gabauer, T.; Deknicke, K.; Goesmann, H.; Feuske, D. Z.
Naturforsch., Teil B 1994, 49, 1444.
reaction of [Cp′2NbCl]2 and the corresponding Grignard
reagent (eq 1; see Chart 1).
2 and 3 were characterized spectroscopically, and
1
their H NMR spectra showed a system corresponding
to that associated with metal complexes with η3 coor-
dination of the allyl ligand, namely the presence of syn

5876 Organometallics, Vol. 17, No. 26, 1998
Antin˜olo et al.
Ch a r t 1
F igu r e 2. Proposed structure for Cp′2Nb[η3-CH2C(R)CH2]
(R ) H (2), Me (3)).
F igu r e 3. Proposed structure for Cp′2Nb[N(SiMe3)C(tBu)-
CH2] (4).
The compounds were characterized by IR and NMR
spectroscopy. The 1H NMR spectra of 5 and 6 reveal
the two cyclopentadienyl rings to be equivalent indicat-
ing a change in the plane of symmetry from σv to σh.
The disappearance of the anti and syn proton signals
is also observed. The signals associated with the allyl
ligand are typical to those normally seen for η1-allyl
systems (e.g. [Me2Si(η5-C5H4)2]Nb(dNtBu)[η1-CH2CH-
CH2]22), namely, three signals corresponding to the CH2
bonded to the metal center, the central group C(R) and
the olefinic protons for the terminal CH2. The various
coupling constants are given in Table 2.
and anti protons. In addition this type of coordination
of the allyl ligand results in the inequivalency of the
two cyclopentadienyl rings and thus two signals are
1
observed in H NMR spectra for the SiMe3 substituents
To prepare allyl complexes of niobium(V) imides the
sixteen electron half-sandwich complexes, CpNb(dNtBu)-
[η1-CH2C(R)CH2]Cl (R ) H (7), Me (8)), were prepared
(see Experimental Section). Four signal are observed in
1H NMR spectra for the protons of the cyclopentadienyl
ring. This is due to a plane of symmetry (σv) which
makes the protons H2 and H5 and H3 and H4 in each
ring equivalent (see Figure 2).
To explore the differences between allyl and azaallyl
compounds of niobium the preparation of the niobocene-
(III) 1-azaallyl complex, Cp′2Nb[N(SiMe3)C(tBu)CH2] (4),
was carried out. Complex 4 offers the first example of a
1-azaallyl complex of niobium and was synthesized by
the reaction of [Cp′2NbCl]2 and [Li{η3-N(SiMe3)C(tBu)-
CH2}]3 (1) in THF (eq 2).
23
(eq 4) by the action of CpNb(dNtBu)Cl2 with the
corresponding allylmagnesium chloride.
The expected eighteen electron species CpNb(dNtBu)-
[η3-CH2C(R)CH2]Cl were not observed. 1H NMR spectra
of 7 and 8 are very similar to those recorded for 5 and
6 indicating that the allyl ligand is η1 coordinated to
the metal center (see Experimental Section). The vari-
ous coupling constants are given in Table 2. It should
be noted that 7 and 8 possess chirality about the
niobium atom.
A green oil was obtained which was shown to be
chemically pure by NMR spectroscopy. The 1H NMR
spectrum of 4 reveals that the cyclopentadienyl ligands
are equivalent due to a σh plane of symmetry and thus
rules out the possible η3 coordination of the 1-azaallyl
ligand that was observed in the allyl complexes 2 and
3. The proposed structure of 4 (see Figure 3), with the
1-azaallyl ligand adopting a chelating mode of coordina-
tion to the metal center is in complete agreement with
the spectroscopic data.
The oxidation of 2 and 3 by O2 (eq 3) yielded the
eighteen electron complexes Cp′2Nb[η1-CH2C(R)CH2](O)
(R ) H (5), Me (6)) which result in a change of bonding
mode of the allyl ligand from η3 to η1.
The one-electron oxidation of 2-4 by PbCl2 has also
been carried out and led to the formation of the niobium-
(IV) complexes Cp′2Nb[η1-CH2C(R)CH2]Cl (R ) H (9),
Me (10)) (eq 5) and Cp′2Nb[N(SiMe3)C(tBu)CH2]Cl (11)
(eq 6).
In addition to IR spectroscopy and microananalysis,
9-11 were characterized by ESR spectroscopy. The ESR
spectra for the paramagnetic niobium(IV) complex 9
gave a value of giso ) 1.9913 with a hyperfine splitting
93Nb
a
of 99.7 G, analogous to other niobocene(IV)
complexes, with the unpaired electron mainly located
(22) Antin˜olo, A.; Otero, A.; Prashar, S.; Rodriguez, A. M. Organo-
metallics in press (MS#OM980561N).

Novel Niobocene Complexes
Organometallics, Vol. 17, No. 26, 1998 5877
Ta ble 2. Cou p lin g Con sta n ts for th e η1- a n d η3-Allyl Com p lexes 2, 3, 5-8, 12, a n d 13
2J anti-syn
3J anti-H
3J syn-H
Cp′2Nb[η3-CH2CHCH2] (2)
6.1 Hz
4.8 Hz
15.1 Hz
9.8 Hz
Cp′2Nb[η3-CH2C(Me)CH2] (3)
3J (1H-1H)
2J gem(1H-1H)
3J cis(1H-1H)
3J trans(1H-1H)
Cp′2Nb[η3-CH2CHCH2](O) (5)
8.3 Hz
3.5 Hz
3.0 Hz
2.6 Hz
3.0 Hz
2.5 Hz
2.8 Hz
8.4 Hz
16.8 Hz
Cp′2Nb[η3-CH2C(Me)CH2](O) (6)
CpNb(dNtBu)[η1-CH2CHCH2]Cl (7)
CpNb(dNtBu)[η1-CH2C(Me)CH2]Cl (8)
Cp′2Nb[η1-CH2CHCH2](CO) (12)
Cp′2Nb[η1-CH2CHCH2](CNAr) (13)
8.1 Hz
9.9 Hz
16.8 Hz
8.5 Hz
8.4 Hz
10.3 Hz
9.8 Hz
16.7 Hz
16.6 Hz
at the metal center.24 Similar results were obtained for
10 and 11. Reduction of 9-11 by Na/Hg recuperated
the starting products 2-4. In the case of 11 it was not
possible to determine if the η1-azaallyl ligand was
bonded to the metal center by the nitrogen or carbon
atom of said ligand.
mmol) in Et2O (100 mL) at 0 °C. The resulting green solution
was allowed to warm to room temperature and stirred for 12
h. Solvent was removed in vacuo, and the residue was heated
(40 °C) for 1 h. The solid was extracted into hexane (100 mL).
The solution was concentrated (20 mL) and cooled (-30 °C) to
give white crystals of the title compound (3.85 g, 81%). 1H
NMR (200 MHz, C6D6): δ 0.23 (9H, s, SiMe3), 1.13 (9H, s,
CMe3), 3.79 (1H), 4.44 (1H) (m, CH2). 7Li{1H} NMR (300 MHz,
C6D6): 0.54. 13C{1H} NMR (300 MHz, C6D6): 4.49 (SiMe3),
31.20 (CMe3), 38.90 (CMe3), 92.00 (CH2), 175.70 (CN). Anal.
Calcd for C27H60Li3N3Si3: C, 62.97; H, 11.37; N, 7.90. Found
C, 62.86; H, 11.16; N, 7.91.
Finally, the η1-allyl eighteen-electron niobocene(III)
complexes Cp′2Nb[η1-CH2CHCH2](L) (L ) CO (12), CN-
(2,6-Me2-C6H3) (13)) were prepared by the reaction of
Cp′2NbCl(L)25 and ClMg(CH2CHCH2) (eq 7).
12 and 13 were characterized spectroscopically. In the
1H NMR spectra of 12 and 13, similar to those observed
for 5 and 6, the expected signals for the η1-allyl ligand
and the equivalency of the cyclopentadienyl rings can
clearly be seen. The various coupling constants are given
in Table 2.
In conclusion, we have prepared novel allyl and
1-azaallyl complexes of niobium in various oxidation
states and by NMR spectroscopy we have been able to
determine the coordination mode (η3, η1, or chelating)
of the allyl or azaallyl ligand. In addition, the molecular
structure of the lithium 1-azaallyl complex, [Li{η3-
N(SiMe3)C(tBu)CH2}]3 (1), offers one the very few Li3-
cluster compounds reported to date.
Cp ′2Nb[η3-CH2CHCH2] (2). A 2 M solution of ClMgCH2-
CHCH2 in THF (0.87 mL, 1.74 mmol) was added to a stirring
solution of [Cp′2NbCl]2 (0.70 g, 0.87 mmol) in THF (50 mL) at
-30 °C. The green solution was allowed to warm to room
temperature and stirred for 6 h. Solvent was removed in vacuo
and the remaining green oil extracted in hexane. A green
crystalline solid was obtained by concentrating (5 mL) and
cooling (-30 °C) the solution (0.59 g, 83%). 1H NMR (200 MHz,
C6D6): δ 0.16 (9H), 0.22 (9H) (s, SiMe3), 0.70 (dd, 2H, CH2anti),
3
2.75 (dd, 2H, 2H, CH2syn) (2J anti-syn ) 6.1 Hz, J anti-H ) 15.1
3
Hz, J syn-H ) 9.8 Hz), 2.40 (m, 1H, CH2CHCH2), 3.21 (2H),
3.29 (2H), 4.36 (2H), 5.17 (2H) (m, C5H4). 13C{1H} NMR (300
MHz, C6D6): δ 1.19, 1.33 (SiMe3), 38.93 (CH2), 82.69 (CH2CH-
CH2), 77.34 (C1), 86.49 (C1), 92.67, 92.92, 95.78, 97.68 (C5H4).
Anal. Calcd for C19H31NbSi2: C, 55.86; H, 7.65. Found C, 55.64;
H, 7.49.
Exp er im en ta l Section
Cp ′2Nb[η3-CH2C(Me)CH2] (3). The preparation of 3 was
1
carried out in an identical manner to 2 (yield 89%). H NMR
Gen er a l P r oced u r es. All reactions were preformed using
standard Schlenk-tube techniques in an atmosphere of dry
nitrogen. Solvents were distilled from appropriate drying
agents and degassed before use.
(200 MHz, C6D6): δ 0.24 (9H), 0.28 (9H) (s, SiMe3), 0.86 (d,
2H, CH2anti), 2.73 (dd, 2H, 2H, CH2syn) (2J anti-syn ) 4.8 Hz), 1.53
(s, 3H, CH2C(Me)CH2), 3.20 (2H), 3.38 (2H), 4.47 (2H), 5.17
(2H) (m, C5H4). 13C{1H} NMR (300 MHz, C6D6): δ 1.35, 1.42
(SiMe3), 40.89 (CH2), 30.55 (CH2C(Me)CH2), 82.79 (CH2C(Me)-
CH2), 77.95 (C1), 85.26 (C1), 92.86, 94.63, 95.86, 97.04 (C5H4).
Anal. Calcd for C20H33NbSi2: C, 56.85; H, 7.87. Found C, 56.99;
H, 8.00.
Cp ′2Nb[N(SiMe3)C(tBu )CH 2] (4). THF (100 mL) was
added to a solid mixture of [Cp′2NbCl]2 (0.96 g, 1.19 mmol)
and 1 (0.42 g, 0.79 mmol) and the resulting green solution was
allowed to stir at room temperature for 12 h. Solvent was
removed in vacuo and the green residue extracted into hexane
(75 mL). Hexane was removed under reduced pressure to yield
a green oil of the title complex (1.15 g, 90%). 1H NMR (200
MHz, C6D6): δ 0.19 (s, 18H, C5H4SiMe3), 0.26 (s, 9H, NSiMe3),
1.05 (9H, s, CMe3), 1.75 (s, 2H, CH2),), 4.05 (2H), 4.10 (2H),
4.85 (2H), 5.08 (2H) (m, C5H4). 13C{1H} NMR (300 MHz,
C6D6): δ 1.82 (C5H4SiMe3), 6.44 (NSiMe3), 26.32 (CH2), 30.82
(CMe3), 38.59 (CMe3), 89.65 (C1), 92.72, 97.69, 97.96, 102.28
(C5H4), 147.96 (CN).
The complexes (η5-C5H5)Nb(dNtBu)Cl,23 Cp′2NbCl(L) (L )
CO, CN(2,6-Me2C6H3)),25 [NbCp′2Cl]2,26 and Li(CH2SiMe3)27
were prepared as described earlier. The THF solution of ClMg-
t
(CH2CHCH2) and BuCN were purchased from Aldrich and
used directly. The Et2O solution of ClMg(CH2C(Me)CH2) was
prepared by normal methods. ESR spectra were taken at the
X-band with a Bruker ESP 300 spectrometer. IR spectra were
recorded on a Perkin-Elmer PE 883 IR spectrophotometer. 1H
and 13C spectra were recorded on Varian FT-300 and Varian
Gemini FT-200 spectrometers and referenced to the residual
deuterated solvent. Microanalyses were carried out with a
Perkin-Elmer 2400 microanalyzer.
[Li{η3-N(SiMe3)C(tBu )CH2}]3 (1). tBuCN (2.96, mL, 26.79
mmol) was added to a solution of Li(CH2SiMe3) (2.52 g, 26.79
(23) 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.
(24) Antin˜olo, A.; Fajardo, M.; de J esu´s, E.; Mugnier, Y.; Otero, A.
J . Organomet. Chem. 1994, 470, 127.
(25) Antin˜olo, A.; de Ilarduya, J . M.; Otero, A.; Royo, P.; Lanfredi,
A. M. M.; Tiripicchio, A. J . Chem. Soc., Dalton Trans. 1988, 2685.
(26) Antin˜olo, A.; Espinosa, P.; Fajardo, M.; Go´mez-Sal, P.; Lo´pez-
Mardomingo, C.; Martin-Alonso, A.; Otero, A. J . Chem. Soc., Dalton
Trans. 1995, 1007.
(27) Tecle, B.; Rahman, A. F. M. M.; Oliver, J . P. J . Organomet.
Chem. 1986, 317, 267.
Cp ′2Nb[η1-CH2CHCH2](O) (5). A solution of 2 (0.28 g, 0.68
mmol) in hexane was stirred for 30 min, at room temperature,
under one atmosphere of O2. A color change was observed from
green to yellow. Hexane was removed in vacuo to yield the
title complex as a yellow solid (0.29 g, 100%). IR (Nujol) ν-
1
(NbdO) 906 cm-1. H NMR (200 MHz, C6D6): δ 0.25 (s, 18H,
SiMe3), 2.85 (d, 2H, CH2-CHdCH2) 3J (1H-1H) ) 8.3 Hz, 4.80

5878 Organometallics, Vol. 17, No. 26, 1998
Antin˜olo et al.
(cis), 4.95 (trans) (dd, 2H, CH2-CHdCH2) 2J gem(1H-1H) ) 3.5
Hz, 3J cis(1H-1H) ) 8.4 Hz, 3J trans(1H-1H) ) 16.8 Hz, 5.00 (2H),
5.38 (2H), 5.98 (2H), 6.00 (2H) (m, C5H4), 6.40 (m, 1H, CH2-
CHdCH2). 13C{1H} NMR (300 MHz, C6D6): δ 0.63 (SiMe3),
37.00 (CH2-CHdCH2), 108.42, 113.16, 115.69, 121.23, 123.17
(C1) (C5H4), 106.27 (CH2-CHdCH2), 145.66 (CH2-CHdCH2).
Anal. Calcd for C19H31NbOSi2: C, 53.76; H, 7.36. Found C,
53.49; H, 7.29.
a stirring solution Cp′2NbCl(CO) (0.50 g, 1.16 mmol) in THF
(25 mL) at -30 °C and allowed to stir for 3 h at this
temperature. Solvent was removed in vacuo and the remaining
brown oil extracted in hexane (50 mL). A reddish brown
crystalline solid was obtained by concentrating (15 mL) and
cooling (-30 °C) the solution (0.27 g, 53%). IR (Nujol) ν(CO)
1
1930 cm-1. H NMR (200 MHz, C6D6): δ 0.05 (s, 18H, SiMe3),
1.21 (d, 2H, CH2-CHdCH2) 3J (1H-1H) ) 8.5 Hz, 4.43 (cis),
Cp ′2Nb[η1-CH2C(Me)CH2](O) (6). The preparation of 6
was carried out in an identical manner to 5 (yield 100%). IR
(Nujol) ν(NbdO) 905 cm-1. 1H NMR (200 MHz, CDCl3): δ 0.26
(s, 18H, SiMe3), 1.76 (s, 3H, CH2C(Me)dCH2), 4.53 (s, 2H,
CH2C(Me)dCH2), 4.85 (cis), 4.98 (trans) (m, 2H, CH2C(Me)d
4.51 (trans) (dd, 2H, CH2-CHdCH2) J gem(1H-1H) ) 2.5 Hz,
2
3
3J cis(1H-1H) ) 10.3 Hz, J trans(1H-1H) ) 16.7 Hz, 4.35 (2H),
4.41 (2H), 4.68 (2H), 4.87 (2H) (m, C5H4), 6.14 (m, 1H, CH2-
CH)CH2). 13C{1H} NMR (300 MHz, C6D6): δ 0.13 (SiMe3),
38.95 (CH2-CHdCH2), 91.22, 95.79 (C1), 97.14, 99.66, 100.81
(C5H4), 102.87 (CH2-CHdCH2), 152.93 (CH2-CHdCH2), 265.43
(CO). Anal. Calcd for C20H3NbOSi2: C, 55.03; H, 7.16. Found
C, 54.72; H, 7.05.
2
CH2) J gem(1H-1H) ) 3.0 Hz, 6.32 (4H), 6.45 (2H), 6.61 (2H),
(m, C5H4). 13C{1H} NMR (300 MHz, CDCl3): δ 1.30 (SiMe3),
29.01 (CH2C(Me)dCH2), 36.68 (CH2C(Me)dCH2), 108.15 (CH2C-
(Me)dCH2), 145.66 (CH2C(Me)dCH2), 114.48, 114.66, 116.65,
121.69, 124.45 (C1) (C5H4). Anal. Calcd for C209H33NbOSi2: C,
54.77; H, 7.58. Found C, 54.51; H, 7.43.
Cp ′2Nb[η1-CH2CHCH2]{CN(2,6-Me2-C6H3)} (13). A 2 M
solution of ClMgCH2CHCH2 in THF (0.62 mL, 1.24 mmol) was
added to a stirring Cp′2NbCl{CN(2,6-Me2C6H3)} (0.55 g, 1.03
mmol) in THF (25 mL) at -30 °C and allowed to stir for 3 h at
this temperature. Solvent was removed in vacuo and the
remaining brown oil extracted in hexane (50 mL). A reddish
brown crystalline solid was obtained by concentrating (15 mL)
and cooling (-30 °C) the solution (0.32 g, 57%). IR (Nujol) ν-
Cp Nb(dNtBu )[η1-CH2CHCH2]Cl (7). A 2M solution of
ClMgCH2CHCH2 in THF (0.56 mL, 1.12 mmol) was added to
a stirring solution of CpNb(dNtBu)Cl2 (0.36 g, 0.93 mmol) in
THF (25 mL) at -30 °C and allowed to stir for 3 h at room
temperature. Solvent was removed in vacuo and the remaining
yellow oil extracted in hexane. Solvent was removed in vacuo
and the remaining yellow oil extracted in hexane (50 mL). A
yellow crystalline solid was obtained by concentrating (15 mL)
and cooling (-30 °C) the solution (0.16 g, 43%). IR (Nujol) ν-
(CN) 2095 cm-1 1H NMR (200 MHz, C6D6): δ 0.11 (s, 18H,
.
SiMe3), 1.39 (d, 2H, CH2-CHdCH2), 3J (1H-1H) ) 8.4 Hz, 2.22
(s, 6H, Me), 4.49 (cis), 4.58 (trans) (dd, 2H, CH2-CHdCH2)
3
3
2J gem(1H-1H) ) 2.8 Hz, J cis(1H-1H) ) 9.8 Hz, J trans(1H-1H)
) 16.6 Hz, 4.61 (4H), 4.94 (2H), 5.16 (2H) (m, C5H4), 6.25 (m,
1H, CH2-CHdCH2), 6.68-6.80 (m, 3H, Ph). 13C{1H} NMR
(300 MHz, C6D6): δ 0.47 (SiMe3), 19.24 (Me), 39.05 (CH2-CHd
CH2), 92.27, 96.43, 98.81 (C1), 103.28, 104.56 (C5H4), 103.85
(CH2-CHdCH2), 153.78 (CH2-CHdCH2), 124.10, 125.05,
126.93, 130.38, 131.45, 132.16 (Ph) 232.09 (CN). Anal. Calcd
for C28H40NNbSi2: C, 62.31; H, 7.47; N, 2.60. Found C, 62.52;
H, 7.55; N, 2.68.
1
(NbdN) 1240 cm-1. H NMR (200 MHz, C6D6): δ 0.90 (s, 9H,
CMe3), 2.65 (d, 2H, CH2-CHdCH2) 3J (1H-1H) 8.1 Hz, 4.80 (cis),
2
4.95 (trans) (dd, 2H, CH2-CHdCH2) J gem(1H-1H) ) 2.6 Hz,
3
3J cis(1H-1H) ) 9.9 Hz, J trans(1H-1H) ) 16.8 Hz, 5.45 (s, 5H,
C5H5), 6.45 (m, 1H, CH2-CHdCH2). 13C{1H} NMR (300 MHz,
C6D6): δ 31.00 (CMe3), 36.53 (CH2-CHdCH2), 70.05 (CMe3),
108.61 (C5H5)2, 103.72 (CH2-CHdCH2), 150.67 (CH2-CHd
CH2). Anal. Calcd for C12H19ClNNb: C, 47.16; H, 6.27; N, 4.58.
Found C, 46.92; H, 6.22; N, 4.49.
X-r a y Str u ctu r e Deter m in a tion for [Li{η3-N(SiMe3)C-
(tBu )CH2}]3 (1). Crystals of 1 were grown by cooling (-30 °C)
a hexane solution. A crystal of 1 was sealed in Lindemann
capillary under dry nitrogen and used for data collection.
Intensity data were collected on a NONIUS-MACH3 diffrac-
tometer equipped with a graphite monochromator MoKR
radiation (λ ) 0.7107 Å). 8684 collected reflections (2 e θ e
28), with 3213 observed reflections for I > 2σ(I). No absorption
correction was applied (µ ) 1.49 cm-1). The structure was
solved by a combination of direct methods28 and Fourier
Cp Nb(dNtBu )[η1-CH2C(Me)CH2]Cl (8). The preparation
of 8 was carried out in an identical manner to 7 (yield 58%).
1
IR (Nujol) ν(NbdN) 1255 cm-1. H NMR (200 MHz, C6D6): δ
0.92 (s, 9H, CMe3), 1.92 (s, 3H, CH2C(Me)dCH2), 2.65 (s, 2H,
CH2C(Me)dCH2), 4.76 (cis), 4.82 (trans) (m, 2H, CH2C(Me)d
CH2) 2J gem(1H-1H) ) 3.0 Hz, 5.46 (s, 5H, C5H5). 13C{1H} NMR
(300 MHz, CDCl3): δ 31.27 (CMe3), 25.29 (CH2C(Me)dCH2),
35.71 (CH2C(Me)dCH2), 68.70 (CMe3), 103.71 (CH2C(Me)d
CH2), 156.89 (CH2C(Me)dCH2), 109.00 (C5H5). Anal. Calcd for
C
12H19ClNNb: C, 47.84; H, 6.62; N, 4.38. Found C, 47.52; H,
2 29
synthesis and then refined by full-matrix least-squares on F .
6.49; N, 4.40.
The tBu and SiMe3 groups showed rotational disorder and were
refined isotropically with different occupancies. The rest of
non-hydrogen atoms were anisotropic, and hydrogen atoms
were included in their calculated positions as fixed isotropic
contributors. Crystallographic data are given in Table 1. Other
detailed data are supplied in the Supporting Information.
Cp ′2Nb[η1-CH2CHCH2]Cl (9). PbCl2 (0.12 g, 0.44 mmol)
was added to a yellow solution of 2 (0.36 g, 0.88 mmol) in THF
(50 mL) and left in an ultrasonic bath for 1 h. The mixture
was filtered to remove the lead metal. Solvent was removed,
from the red filtrate, in vacuo to yield a brown solid of the
93
title complex 9 (0.39 g, 100%). ESR giso ) 1.9913, a
99.7
Nb
G. IR (Nujol) ν(SiMe3) 1246 cm-1, ν(C5H4) 834 cm-1, ν(Nb-Cl)
278 cm-1. Anal. Calcd for C19H31ClNbSi2: C, 51.40; H, 7.04.
Found C, 51.02; H, 6.91.
Cp ′2Nb[η1-CH2C(Me)CH2]Cl (10). The preparation of 10
Ack n ow led gm en t. The authors gratefully acknowl-
edge financial support from the Direccio´n General de
Ensen˜anza Superior e Investigacio´n, Spain (Grant. No.
PB 95-0023-C02-01), Unio´n Fenosa and the European
Unio´n for a postdoctoral grant to S.P. under the Human
Capital and Mobility Program (Contract No. ERB-
CHRXCT930281). We would also like to thank Prof.
Mugnier from the University of Dijon (France), for
providing ESR data and Dr. J in Hu (University of
Sussex, U.K.) for helpful advice.
was carried out in an identical manner to 9 (yield 100%). (0.56
93
g, 100%). %). ESR giso ) 1.9983, a
99.9 G. IR (Nujol) ν-
Nb
(SiMe3) 1246 cm-1, ν(C5H4) 834 cm-1, ν(Nb-Cl) 279 cm-1. Anal.
Calcd for C20H33ClNbSi2: C, 52.45; H, 7.26. Found C, 52.13;
H, 7.10.
Cp ′2Nb[N(SiMe3)C(tBu )CH2]Cl (11). The preparation of
11 was carried out in an identical manner to 9 (yield 100%).
ESR giso ) 1.977, a
110.0 G. IR (Nujol) ν(SiMe3) 1245 cm-1
,
93
Nb
ν(C5H4) 820 cm-1, ν(Nb-Cl) 256 cm-1. Anal. Calcd for C25H46
-
(28) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 435.
(29) Sheldrick, G. M. SHELXL-97: Program for the Refinement of
Crystal Structures from Diffraction Data; University of Go¨ttingen:
Go¨ttingen, Germany, 1997.
ClNNbSi3: C, 52.38; H, 8.09; N, 2.44. Found C, 52.52; H, 7.95;
N, 2.30.
Cp ′2Nb [η1-CH 2CH CH 2](CO) (12). A 2 M solution of
ClMgCH2CHCH2 in THF (0.70 mL, 1.40 mmol) was added to

Novel Niobocene Complexes
Organometallics, Vol. 17, No. 26, 1998 5879
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
crystal data (Table SI), non-hydrogen atom coordinates (Table
SII), complete bond distances and angles (Table SIII), aniso-
tropic displacement parameters (Table SIV), hydrogen atom
coordinates (Table SV), and ORTEP and crystal packing
drawings (16 pages). Ordering information is given on any
current masthead page. A list of structure factors is available
on request from the authors.
OM980716R