Half-metallocene 1-aza-1,3-butadiene complexes of tantalum: Auxiliary ligand effects on controlling coordination modes of 1-aza-1,3-butadiene ligand

Article abstract of DOI:10.1246/bcsj.75.1291

We prepared some half-metallocene complexes of tantalum bearing ortho-substituted aryl derivatives of 1-aza-1,3-butadiene ligand. The coordination mode of the 1-aza-1,3-diene (abbr. AD) ligand highly depended on the substituent(s) on the aryl group of the AD ligand and also on the metal center. The number of methyl substituents on the aryl group of the AD ligand differentiated two coordination modes: one methyl substituent, TaCl₂Cp*(η⁴-supine-o-Tol-AD) (1) (Cp* = pentamethylcyclopentadienyl; o-Tol-AD = 1-(2-methylphenyl)-4-phenyl-1-aza-1,3-butadiene), favored an η⁴-supine-coordination mode, while two methyl substituents, TaCl₂Cp*(η²-C,N-Xyl-AD) (5) (Xyl-AD = 2,6-dimethylphenyl-4-phenyl-1-aza-1,3-butadiene), adopted an η²-C,N-imine coordination fashion. Furthermore, the preferential coordination mode of the AD ligand was delicately affected by the substituent(s) on the tantalum center. Dialkylation of 1 led to the formation of TaR₂Cp*(o-Tol-AD) (6: R = Me; 8: R = CH₂Ph) in the dimethyl complex 6. The equilibrium between η⁴-coordination mode and η²-C,N-coordination one was observed and the latter mode was thermally more feasible in solution and as solid state, and the o-Tol-AD ligand predominantly coordinated in an η²-C,N-imine fashin to the tantalum center of 8. In contrast, the monobenzylation of 1 did not change the η⁴-supine coordination mode, giving a monobenzyl complex Cp*TaCl(CH₂Ph)(η⁴-supine-o-Tol-AD) (9). The dibenzyl complex 8 gradually turned to a benzylidene complex Ta(=CHPh)Cp*(η⁴-supine-o-Tol-AD) (10) on heating at 70 °C with the change of the coordination mode from η² to η⁴. Introduction of a 1,3-butadiene ligand to the metal center gave a mixed-ligand complex TaCp*(η²-C,N-o-Tol-AD)(η⁴-s-cis-1, 3-butadiene) (12), in which the metal center adopted an η²-C,N-fashion.

Full text of DOI:10.1246/bcsj.75.1291

Bull. Chem.
Soc. Jpn.
75
6
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 1291–1297 (2002) 1291
The Chemical
Society of Ja-
pan
The Chemical
Society of Ja-
pan
AI
6
15
Half-Metallocene 1-Aza-1,3-butadiene Complexes of Tantalum:
Auxiliary Ligand Effects on Controlling Coordination Modes of
1-Aza-1,3-butadiene Ligand
Half-Metallocene Azabutadiene Complexes of Ta
Y. Matsuo et el.
2002
1291
1297
BCSJA8
0009-2673
01447
12
Yutaka Matsuo, Kazushi Mashima,* and Kazuhide Tani
Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531
(Received December 19, 2001)
19
2001
1
28
2002
We prepared some half-metallocene complexes of tantalum bearing ortho-substituted aryl derivatives of 1-aza-1,3-
butadiene ligand. The coordination mode of the 1-aza-1,3-diene (abbr. AD) ligand highly depended on the substituent(s)
on the aryl group of the AD ligand and also on the metal center. The number of methyl substituents on the aryl group of
the AD ligand differentiated two coordination modes: one methyl substituent, TaCl2Cp*(η4-supine-o-Tol-AD) (1) (Cp*
= pentamethylcyclopentadienyl; o-Tol-AD = 1-(2-methylphenyl)-4-phenyl-1-aza-1,3-butadiene), favored an η4-supine-
coordination mode, while two methyl substituents, TaCl2Cp*(η2-C,N-Xyl-AD) (5) (Xy1-AD = 2,6-dimethylphenyl-4-
phenyl-1-aza-1,3-butadiene), adopted an η2-C,N-imine coordination fashion. Furthermore, the preferential coordination
mode of the AD ligand was delicately affected by the substituent(s) on the tantalum center. Dialkylation of 1 led to the
formation of TaR2Cp*(o-Tol-AD) (6: R = Me; 8: R = CH2Ph) in the dimethyl complex 6. The equilibrium between η4-
coordination mode and η2-C,N-coordination one was observed and the latter mode was thermally more feasible in solu-
tion and as solid state, and the o-Tol-AD ligand predominantly coordinated in an η2-C,N-imine fashin to the tantalum
center of 8. In contrast, the monobenzylation of 1 did not change the η4-supine coordination mode, giving a monobenzyl
complex Cp*TaCl(CH2Ph)(η4-supine-o-Tol-AD) (9). The dibenzyl complex 8 gradually turned to a benzylidene com-
plex Ta(wCHPh)Cp*(η4-supine-o-Tol-AD) (10) on heating at 70 °C with the change of the coordination mode from η2 to
η4. Introduction of a 1,3-butadiene ligand to the metal center gave a mixed-ligand complex TaCp*(η2-C,N-o-Tol-
AD)(η4-s-cis-1,3-butadiene) (12), in which the metal center adopted an η2-C,N-fashion.
2.4.2
Nitrogen substituted 1,3-diene ligands such as 1,4-diaza-
1,3-butadiene (abbr. DAD) and 1-aza-1,3-butadiene (abbr. AD)
have been utilized as unique and versatile supporting ligands
for the late transition metals;1–3 however, these ligands have
only recently been utilized for early transition metals. These
hetero-diene ligands are of perticular interest recently in view
of their versatile, flexible coordination to the metal center as
described in Chart 1, and their ability to stabilize various cata-
lyst precursors for polymerization as well as organic reac-
tions.4 In half-metallocene complexes of group 45–11 and group
5 metals,12–18 the nitrogen substituted diene ligands not only
coordinated in a cis-fashion to the metal center with large con-
tribution of a metallacyclopent-3-ene canonical form, the form
B in Chart 1, but also have two conformations, supine or
prone, relative to the cyclopentadienyl ligand.19 We already re-
ported synthesis and reactions of half-metallocene complexes
bearing 1-phenyl-1-aza-1,3-butadiene (abbr. Ph-AD) and its
para-substituted derivatives.15,20 As an extension of our syn-
theses of these half-metallocene complexes of group 5 metals,
herein we report some tantalum complexes bearing ortho-sub-
stituted aryl AD ligands, whose coordination mode can be con-
trolled depending on substituent(s) on aryl group of the AD
ligand and on the metal center.
Results and Discussion
Synthesis and Characterization of Dichloro Complexes
of Tantalum Having ortho-Substituted Aryl-AD Ligands.
A dichloro complex, TaCl2Cp*(η4-supine-o-Tol-AD) (1) (o-
Tol-AD) = 1-(2-methylphenyl)-4-phenyl-1-aza-1,3-butadiene)
has been prepared by the reduction of TaCl4Cp* (2) (Cp* =
pentamethylcyclopentadienyl) in THF using aluminum activat-
ed by catalytic amounts of HgCl2 in the presence of o-Tol-
AD.20 Alternatively, the reaction of [TaCl2Cp*]2 (3), which
was derived from the amalgam reduction of the complex 2,21,22
with 2 equiv of o-Tol-AD in C6D6 afforded the purple dichloro
complex 1 (Eq. 1). The structure of 1 was already character-
ized by spectroscopic date,20 and was further determined by a
crystallographic study (Fig. 1); the structure is the same as that
of TaCl2Cp*(η4-supine-Ph-AD) (4).15 Selected bond distances
and angles for 1 are listed in Table 1. The AD ligand of 1 coor-
dinates in an η4-fashion to the tantalum atom and the direction
of the AD ligand points toward the Cp* ligand, a supine con-
formation, whose coordination mode and structural features
are essentially the same as those found for the Ph-AD complex
4.15 The methyl substituent of the AD ligand occupied the lo-
cation outside of two ortho-positions of the phenyl group
Chart 1. X = CHR (AD), X = NR (DAD).

1292 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
Half-Metallocene Azabutadiene Complexes of Ta
lum,14 indicating that the interaction of the C(2)–C(3) bond
with the tantalum atom of 1 is much stronger than that of the
DAD complexes. The dissymmetric environment around the
tantalum atom made two Ta–Cl bonds different; the distance
(2.4663(9) Å) of Ta–Cl(1) trans to C(4) is slightly longer than
that (2.4338(9) Å) of Ta–Cl(2) trans to the nitrogen atom. The
narrow angle (78.7(1)°) of N–Ta–C(4) is attributed to the con-
strained geometry of the 5-membered pukered structure of 1.
Fig. 1. Molecular structure of 1 with the labeling scheme.
Hydrogen atoms are omitted for clarity.
Table 1. Selected Bond Distances and Angles for Complex 1
Bond distance (Å)
(1)
Ta–N
1.992(3)
2.372(4)
2.444(3)
2.309(3)
2.4663(9)
2.4338(9)
1.402(5)
1.447(4)
1.379(5)
1.433(5)
1.494(4)
2.112
Ta–C(2)
Ta–C(3)
Ta–C(4)
Ta–Cl(1)
Ta–Cl(2)
N–C(2)
When 2,6-dimethylphenyl-4-phenyl-1-aza-1,3-butadiene
ligand (abbr. Xyl-AD) was used, an η2-C,N-imine complex
TaCl2Cp*(η2-C,N-Xyl-AD) (5) was obtained in 18% yield by
the reduction of 2 by A1/HgCl2 (cat.) in the presence of Xyl-
AD (Eq. 2). The second methyl group at the other ortho-posi-
tion of the aryl group bound to the nitrogen atom prevented the
η4-coordination. The AD ligand of 5 thus coordinated in an
η2-C,N-fashion (Chart 1, C) to the tantalum center as con-
firmed by NMR spectroscopy; the H2 proton appeared at high-
er-field (δ 2.08), while the signals due to the H3 and H4 protons
were observed in olefinic region (δ 6.14 and 5.99, respective-
ly).
N–C(5)
C(2)–C(3)
C(3)–C(4)
C(4)–C(6)
Ta–CCPa)
Bond angles (deg)
N–Ta–C(4)
78.7(1)
Cl(1)–Ta–Cl(2)
N–Ta–Cl(1)
80.63(3)
88.93(8)
82.79(8)
C(4)–Ta–Cl(2)
N–C(2)–C(3)
C(2)–C(3)–C(4)
Ta–N–C(2)
116.4(3)
120.8(3)
86.8(2)
Ta–N–C(5)
147.7(2)
118.0(3)
77.7(2)
134.6(2)
119.9(3)
104.5(3)
C(2)–N–C(5)
Ta–C(4)–C(3)
Ta–C(4)–C(6)
C(3)–C(4)–C(6)
fold angleb)
(2)
a) CCP: Centroid of cyclopentadienyl ring.
b) fold angle: Dihedral angle between the N–Ta–C(4) plane
and N–C(2)–C(3)–C(4) plane.
Dimethylation of Dichloro-AD Complexes of Tantalum.
Treatment of 1 with 1 equiv of MgMe2 in diethyl ether afford-
ed a dimethyl complex, TaMe2Cp*(o-Tol-AD) (6) in 90% yield
bound to the nitrogen atom. The bond distance (1.992(3) Å) of
Ta–N is comparable to that of Ta–N(amido)23–26 and that
(2.010(7) Å) of 4,15 but longer than that of Ta–N(imido).27 The
N–C(2) (1.402(5) Å), C(2)–C(3) (1.379(5) Å), and C(3)–C(4)
(1.433(5) Å) bond lengths are alternated in a long-short-long
sequence as expected for early-transition metal diene complex-
es, to which a contribution of a 1-metallacyclo-3-pentene ca-
nonical structure is dominant. The fold angle (104.5(3)°) be-
tween the best planes defined by atoms Ta, N, C(4) and N,
C(2), C(3), C(4) is narrower than the corresponding fold angle
(120.06–121.35°) found for some DAD complexes of tanta-
1
(Eq. 3). The H NMR spectrum of 6 in benzene-d6 exhibited
two singlet signals due to two magnetically nonequivalent Ta-
CH3 protons at δ −0.82 and 0.07, and additionally displayed a
terminal H4 proton resonance at δ 2.10 and H2 and H3 proton
resonances at the olefinic region (δ 5.66 and 5.96, respective-
ly). These spectral data suggest that the complex 6 adopts the
supine-η4-coordination mode as observed for the complex 1,
being in sharp contrast to the η2-C,N-coordination mode in sol-
id state (vide infra). The equilibrium between η4-coordination
[BULLETIN 2002/06/03 19:24]
01447

Y. Matsuo et el.
Bull. Chem. Soc. Jpn., 75, No. 6 (2002) 1293
Fig. 3. Molecular structure of 7 with the labeling scheme.
Hydrogen atoms are omitted for clarity.
Table 2. Selected Bond Distances and Angles for Dimethyl
Complex 7
Bond distance (Å)
Ta–N
1.91(1)
2.19(1)
2.07(2)
2.03(3)
1.48(2)
1.48(12)
1.33(2)
2.159
Ta–C(2)
Ta–C(6)
Ta–C(7)
N–C(2)
C(2)–C(3)
C(3)–C(4)
Ta–CCPa)
Bond angles (deg)
C(2)–Ta–C(6)
C(2)–Ta–C(7)
N–Ta–C(2)
Ta–N–C(2)
Ta–C(2)–N
111.8(6)
108.7(8)
41.7(4)
79.2(7)
59.1(7)
123.4(10)
122(1)
Ta–C(2)–C(3)
N–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(6)
Ta–N–C(5)
125(1)
126(1)
158.3(10)
122(1)
359.5
C(2)–N–C(5)
Sum of around Nb)
Fig. 2. The variable temperature–NMR spectra of 7 in C6D6.
a) CCP: Centroid of cyclopentadienyl ring.
b) Sun of around N: {Ta–N–C(2)} + {Ta–N–C(5)} +
{C(2)–N–C(5)}.
mode and η2-C,N-coordination one was observed in the H
NMR spectra (10–70 °C) of the complex 6 and its phenyl de-
rivative TaMe2Cp*(Ph-AD) (7)15 (Fig. 2); the signal of H2 of
both complexes was observed in higher field at higher temper-
ature, while the signal of H4 was observed in lower field at
higher temperature. In order to make the structrure of the dim-
ethyl complexes clear by a crystallographic study, we tried to
crystallize 6; however, we were not able to obtain good crys-
tals of 6, but crystals of 7 were found to be suitable for X-ray
analysis. Figure 3 clearly shows that the dimethyl complex 7
has the η2-C,N-coordination mode as expected from the vari-
able temperature NMR spectra. Selected bond distances and
angles are summarized in Table 2. The tantalum center adopts
a three-legged piano stool geometry comprised of a η5-Cp*
1
ligand, two carbon atom of the methyl ligands, and the CwN
moiety of the Ph-AD ligand. The CwN moiety is perpendicu-
lar to the cyclopentadienyl ring. The direction of the nitrogen
atom of CwN moiety points away from the Cp* ligand. This
direction is opposite to the structure of tantalum-imine com-
plex TaMe2Cp*(η2-C,N-2,6-Me2C6H3–NwCMe2) reported by
Royo et al., in which the carbon atom of the imine ligand is
trans to Cp* ligand.28 The bond distance (1.91 Å) of Ta–N is
comparable to those of typical Ta–N(dialkylamido) distances
(ca. 1.93–1.96 Å).25,26 The bond distance (2.19 Å) of Ta–C(2)
is consistent with a single bond, suggesting that the Ta–N–C(2)
moiety forms an azatantalacyclopropane structure.
[BULLETIN 2002/06/03 19:24]
01447

1294 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
Half-Metallocene Azabutadiene Complexes of Ta
(3)
Synthesis and Characterization of Benzyl and Benzyl-
idene Complexes. We already reported the benzylation of
the complex 1, giving a dibenzyl complex, Cp*Ta(CH2Ph)2-
(η2-C,N-o-Tol-AD) (8).20 During the benzylation, the coordi-
nation mode of the AD ligand turned from η4 to η2, as ob-
served in the methylation of 1, and hence this transformation
can be mainly attributed to the steric effect of alkyl groups
bound to the tantalum center. A similar reaction of 5 with
Mg(CH2Ph)2 resulted in a complicated mixture, from which no
products could be isolated. Thus, the stability of dibenzyl
complex sensitively depends on the substituent of the AD
ligand.
Chart 2.
fashion to the η4-supine-one, as confirmed by NMR spectros-
copy. In the H NMR spectrum of 10, a signal due to H4 ap-
1
peared at higher-field (δ 1.62), while the H2 and H3 resonances
were displayed at lower-field (δ 6.03 for H2 and 5.17 for H3).
The selective formation of the benzylidene complex 10 is in
sharp contrast to the formation fo metallacyclic carbene com-
plex 11 (Chart 2) on the thermolysis of a bis(benzyl) complex
bearing a Ph-AD ligand.15
In contrast, a monobenzyl complex Cp*TaCl(CH2Ph)(η4-
supine-o-Tol-AD) (9), which was obtained in 77% yield by the
reaction of 1 with a half equivalent of Mg(CH2Ph)2 in toluene
(Eq. 4), kept the supine-η4-coordination mode of 1. The com-
plex 9 was characterized by NMR spectroscopy as well as
combustion analysis. The chemical shiftvalues of an outer
proton (δ 2.05 for H4) and inner protons (δ 5.39 for H2 and
5.86 For H3) of the o-Tol-AD ligand of 9 are comparable to
those found for 1 and ABq resonances due to TaCH2Ph ap-
peared at δ 1.63 and 2.11 with a coupling constant of 10.5 Hz.
The NOESY experiment indicated that complex 9 has a
supine-η4-o-Tol-AD ligand and that the benzyl group is trans
to the C4 atom.
(5)
Synthesis of AD–Butadinene Complex of Tantalum.
Introduction of a 1,3-butadiene ligand to the metal center led to
a mixed-ligand complex TaCp*(η2-C,N-o-Tol-AD)(η4-s-cis-
1,3-butadiene) (12) (Eq. 6). Treatment of 1 with a slight ex-
cess of the butadiene-megnesium addust [Mg(1,3-butadi-
ene)(thf)2]n in THF gave the mixed-ligand complex 12 as yel-
low microcrystals in 23% yield. This complex was found to be
air- and moisture-sensitive and thermally unstable even in solid
state. The 1H NMR spectrum of 12 exhibited one set of signals
due to both butadiene and AD ligands in an exact 1:1 integral
ratio. The AD ligand was found to coordinate to the metal cen-
ter in an η2-C,N-fashion; the H2 proton of the AD ligand was
observed at a higher field (δ 1.76) than that found for the
dichloro complex having the η4-supine-AD ligand. The H3
and H4 protons were observed in the olefinic region (δ 4.24 and
δ 7.09), the chemical shift values were comparable to those of
the dibenzyl complex 8. The butadiene ligand adopts an η4-
supine-s-cis conformation as judged by NMR spectroscopy;
the signals of six kinds of butadiene protons were observed at
δ −2.13, −1.07, 0.73, 1.89, 4.13, and 5.66. Based on the ob-
served dissymmetric pattern of the butadiene protons, it is like-
ly that an η2-imino moiety coordinated in the plane bisecting
the Cp* and the 1,3-butadiene ligands.
(4)
The dibenzyl complex 8 gradually released toluene via α-
hydrogen abstraction followed by reductive elimination to give
the corresponding benzylidene complex Ta(wCHPh)CP*(η4-
supine-o-Tol-AD) (10) on heating at 70 °C (Eq. 5). This ben-
zylidene complex 10 was not thermally stable and decomposed
during any attempted isolation, and hence 10 was character-
ized in solution by NMR spectroscopy; the 1H NMR spectrum
of 10 exhibited a characteristic α-benzylidene proton signal in
a downfield (δ 8.14), suggesting the presence of a single rota-
1
mer. The 2D H–1H NOESY measurement clearly revealed
that the methyl signal of the Cp* ligand can be correlated to
the α-benzylidene proton, indicating that the phenyl group of
the benzylidene moiety pointed in the direction opposite to the
Cp* ligand, an anti-rotamer. In the 13C NMR spectrum, the
benzylidene carbon atom of 10 appeared at δ 243.4 with a cou-
1
pling constant JC–H = 123 Hz. One notable feature was the
change of the coordination mode of the AD ligand from the η2-
(6)
[BULLETIN 2002/06/03 19:24]
01447

Y. Matsuo et el.
Bull. Chem. Soc. Jpn., 75, No. 6 (2002) 1295
1
MHz, C6D6, 35 °C): δ 11.1 (q, JC–H = 127 Hz, C5Me5), 18.3 (q,
Experimental
1JC–H = 126 Hz, Ar-CH3), 26.6 (q, 1JC–H = 120 Hz, Ta-CH3 trans
to C), 35.3 (q, 1JC–H = 120 Hz, Ta-CH3 trans to N), 69.7 (d, 1JC–H
All maniqulations involving air- and moisture-sensitive organo-
metallic compounds were carried out using the standard Schlenk
techniques under argon. Hexane, THF, and toluene were dried
and deoxygenated by distillation over sodium benzophenone ketyl
under argon. Benzene-d6 and THF-d8 were distilled from Na/K al-
loy and thoroughly degassed by trap-to-trap distillation before use.
Complexes 1,20 2,29 3,21,22 7,15 and 820 were prepared according to
the literature.
= 137 Hz, C4), 107.7 (d, 1JC–H = 181 Hz, C2), 114.4 (d, 1JC–H
=
1
158 Hz, C3), 115.1 (s, C5Me5), 123.1 (d, JC–H = 158 Hz, p-Ph),
1
1
123.5 (d, JC–H = 158 Hz, 6-C6H4), 125.3 (d, JC–H = 160 Hz, 4-
1
1
C6H4), 126.3 (d, JC–H = 160 Hz, 5-C6H4), 126.9 (d, JC–H = 157
1
1
Hz, m-Ph), 127.6 (d, JC–H = 157 Hz, m-Ph), 130.5 (d, JC–H
=
157 Hz, 3-C6H4), 134.9 (s, 2-C6H4), 143.9 (s, ipso-Ph), 150.0 (s, 1-
1
C6H4). The 2D H–1H NOESY spectrum indicates neighboring
protons in the molecule, e. g. (H2 and Ta-CH3 trans to C), (H3 and
Ta-CH3 trans to N), (6-C6H4 and Ta-CH3 trans to C), (o-Ph and
Ta-CH3 trans to N), (C5Me5 and 6-C6H4), (C5Me5 and o-Ph),
(C5Me5 and H4), (o-Ph and H4), (3-C6H4 and Ar-CH3), (H3 and
H4), and so on. IR (KBr): ν(CwC)/cm−1 1605 (s) and ν(CwN)/
cm−1 1510 (s). Anal. Calcd For C28H36CINTa: C, 59.26; H, 6.39;
N, 2.47%. Found: C, 59.00; H, 6.69; N, 2.32%.
The H (500, 400, 300, and 270 MHz), 13C (125, 100, 75, and
1
68 MHz) NMR spectra were measured on a Varian Unity Inova-
500, a JEOL JNM-AL400, a Varian Mercury-300, or a JEOL
GSX-270 spectrometer. When benzene-d6 was used as the sol-
vent, the spectra were referenced to the residual solvent protons at
δ 7.20 in the 1H NMR spectra and to the residual solvent carbons
at δ 128.0 in the 13C NMR spectra. Assignments for H and 13C
1
NMR peaks for some of the complexes were aided by 2D H–1H
1
Preparation of Cp*TaCl(CH2Ph)(o-Tol-AD) (9). To a solu-
tion of 1 (678 mg, 1.11 mmol) in toluene (10 mL) was added a so-
lution of Mg(CH2Ph)2 (0.6 equiv, 113 mg, 0.669 mmol) in toluene
(10 mL). The reaction mixture was allowed to warm to room tem-
perature, and than was stirred at room temperature for 6 h. The re-
sulting solution was cooled at −20 °C for 24 h to give reddish-
purple crystals of 9 (513 mg, 77% yield), mp 150–153 °C (dec).
1H NMR (400 MHz, C6D6, 35 °C): δ 1.63 (d, 2JH–H = 10.5 Hz, 1H,
Ta-CH2Ph), 1.65 (s, 3H, Ar-CH3), 1.76 (s, 15H, C5Me5), 2.05 (d,
COSY, 2D 1H–1H NOESY, and 2D 1H–13C COSY spectra, respec-
tively. Other spectra were recorded by the use of the following in-
struments: IR, JASCO FT/IR-230; UV/vis spectra, JASCO V-570;
elemental analyses, Perkin Elmer 2400. All melting points were
measured in sealed tubes under argon atmosphere and were not
corrected.
η4
Preparation of Cp*TaCl2( -supine-o-Tol-AD) (1). The re-
action of 3 (10 mg, 13 µmol) with two equiv of 1-(2-methylphen-
yl)-4-diphenyl-1-aza-1,3-butadiene (5.7 mg, 26 µmol) in C6D6
quantitatively afforded a purple solution of 1, whose spectral data
(1H and 13C) are superimposed with the reported data for 1.
η2
2
3JH–H = 9.0 Hz, 1H, H4), 2.11 (d, JH–H = 10.5 Hz, 1H, Ta-
3
3
CH2Ph), 5.39 (d, JH–H = 4.9 Hz, 1H, H2), 5.86 (dd, JH–H = 4.9
and 9.0 Hz, 1H, H3), 6.90 (t, 1H, p-Ph of CH2Ph), 6.96 (d, 1H, 3-
C6H4), 7.00 (t, 1H, 4-C6H4), 7.04 (t, 1H, p-Ph of AD), 7.12 (t, 1H,
5-C6H4), 7.24 (t, 2H, m-Ph of CH2Ph), 7.25 (d, 2H, o-Ph of AD),
7.29 (t, 2H, m-Ph of AD), 7.31 (d, 1H, 6-C6H4), 7.55 (d, 2H, o-Ph
Preparation of Cp*TaCl2( -C,N-Xyl-AD) (5).
A mixture
of 2 (752 mg, 1.64 mmol), 1-(2,6-dimethylphenyl)-4-diphenyl-1-
aza-1,3-butadiene (406 mg, 1.72 mmol), aluminum (61 mg, 2.26
mmol), and HgCl2 (5 mg) in THF (40 mL) was stirred at room
temperature for 12 h. After insoluble products were seperated by
centrifugation, all volatiles were removed under reduced pressure.
The resulting solid was extracted with toluene (80 mL, 6 times).
The extract was concentrated under reduced pressure to give 5 as
purple crystalline solids, which were then washed with hexane (10
mL) and dried in vacuo. Purple microcrystals of 5 (112 mg) were
obtained in 18% yield, mp 108–113 °C (dec). 1H NMR (400
MHz, C6D6, 35 °C): δ 1.69 (s, 3H, CH3), 1.85 (s, 15H, C5Me5),
2.08 (br, 1H, H2), 2.57 (s, 3H, CH3), 5.99 (br, H4), 6.14 (br, 1H,
H3), 6.8–7.4 (br m, 8H, aromatic protons). Anal. Calcd For
C27H32Cl2NTa: C, 52.10; H, 5.18; N, 2.25%. Found: C, 52.00; H,
5.23; N, 2.26%.
of CH2Ph). 13C NMR (100 MHz, C6D6, 35 °C): δ 11.7 (q, 1JC–H
=
128 Hz, C5Me5), 18.1 (q, 1JC–H = 128 Hz, Ar-CH3), 55.7 (t, 1JC–H
= 123 Hz, Ta-CH2Ph),75.7 (d, 1JC–H = 133 Hz, C4),114.1 (d, 1JC–H
= 189 Hz, C2), 118.2 (d, JC–H = 162 Hz, C3), 119.2 (s, C5Me5),
1
122.4 (d, 1JC–H = 158 Hz, p-Ph of CH2Ph), 124.7 (d, 1JC–H = 157
Hz, p-Ph of AD), 125.5 (d, 1JC–H = 160 Hz, 6-C6H4), 126.0 (d, 1JC–H
1
=163 Hz, 5-C6H4), 126.5 (d, JC–H = 160 Hz, 4-C6H4), 127.2 (d,
1JC–H = 157 Hz, m-Ph of AD), 127.2 (d, 1JC–H = 157 Hz, m-Ph of
CH2Ph), 128.0 (d, 1JC–H = 157 Hz, o-Ph of CH2Ph), 128.5 (d, 1JC–H
= 157 Hz, o-Ph of AD), 130.9 (d, 1JC–H = 160 Hz, 3-C6H4), 134.9
(s, 2-C6H4), 141.7 (s, ipso-Ph of AD), 147.9 (s, ipso-Ph of CH2Ph),
154.9 (s, 1-C6H4). The 2D H–1H NOESY spectrum indicates
1
neighboring protons in the molecule, e. g. (C5Me5 and o-Ph of
AD), (C5Me5 and 6-C6H4), (H4 and o-Ph of AD), (H2 and o-Ph of
CH2Ph), (H3 and o-Ph of AD), (Me and 3-C6H4), (Ta-CH2Ph and
6-C6H4), and so on. IR (KBr): ν(CwC)/cm−1 1594 (s) and
ν(CwN)/cm−1 1483 (s). Anal. Calcd For C33H37ClNTa: C, 59.69;
H, 5.62; N, 2.11%. Found: C, 59.93; H, 5.72; N, 2.11%.
Preparation of Cp*TaMe2(o-Tol-AD) (6). To a solution of 1
(731 mg, 1.20 mmol) in diethylether (10 mL) at 78 °C was added
a solution of MgMe2 (1.5 equiv, 98 mg, 1.80 mmol) in diethyl
ether (10 mL) via a syringe. The reaction mixture was allowed to
warm to room temperature. After the reaction mixture was stirred
for 2 h at room temperature, all volatiles were removed under re-
duced pressure. The resulting residue was extracted with hexane
(100 mL). The solution was concentrated to precipitate yellow
crystals, which were then washed with hexane to give 6 (610 mg,
90% yield), mp 92–97 °C (dec). 1H NMR (400 MHz, C6D6, 35
°C): δ −0.82 (s, 3H, Ta-CH3 trans to N), 0.07 (s, 3H, Ta-CH3
trans to C), 1.67 (s, 15H, C5Me5), 1.85 (s, 3H, Ar-CH3), 2.10 (d,
Synthesis of Cp*Ta(wCHPh)(o-Tol-AD) (10).
Complex 8
(10 mg, 0.016 mmol) was dissolved in 0.58 mL of C6D6 in a 5-mm
1
NMR tube. The solution was heated to 70 °C for 7 h, and H
NMR was measured. The spectrum showed the formation of 10
along with the signal due to toluene (protons of methyl group: δ
3
2.16). 1H NMR (400 MHz, C6D6, 35 °C): δ 1.62 (d, JH–H = 6.8
Hz, 1H, H4), 1.75 (s, 3H, Me), 1.79 (s, 15H, C5Me5), 5.17 (dd, 3JH–H
= 5.1 and 6.8 Hz, 1H, H3), 6.03 (d, 3JH–H = 5.1 Hz, 1H, H2), 6.8–
7.4 (m, 14H, aromatic protons), 8.14 (s, 1H, TawCHPh). 13C
3
3JH–H = 8.8 Hz, 1H, H4), 5.66 (d, JH–H = 4.9 Hz, 1H, H2), 5.96
(dd, 3JH–H = 4.9 and 8.8 Hz, 1H, H3), 6.96 (d, 1H, 6-C6H4), 7.00 (t,
1H, 4-C6H4), 7.03 (t, 1H, p-Ph), 7.06 (d, 1H, 3-C6H4), 7.08 (d, 2H,
o-Ph), 7.09 (t, 1H, 5-C6H4), 7.31 (t, 2H, m-Ph). 13C NMR (100
1
NMR (100 MHz, C6D6, 35 °C): δ 11.5 (q, JC–H = 127 Hz,
1
1
C5Me5), 18.0 (q, JC–H = 125 Hz, Me), 68.8 (d, JC–H = 138 Hz,
[BULLETIN 2002/06/03 19:24]
01447

1296 Bull. Chem. Soc. Jpn., 75, No. 6 (2002)
Half-Metallocene Azabutadiene Complexes of Ta
Table 3. Crystal Data and Data Collection Perameters of
Table 4. Crystal Data and Data Collection Perameters of
Dichloro Complex 1
Dimethyl Complex 7
Formula
C29H36Cl2NTa
Formula
C27H34NTa
Solvent molecules
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
β/deg
V/Å3
Z
0.5 cyclohexane per 1
650.46
Formula weight
553.52
Crystal system
Space group
a/Å
b/Å
c/Å
triclinic
P1 (No. 2)
10.961(9)
13.701(8)
8.69(1)
94.96(8)
103.62(8)
70.03(5)
1192(1)
2
monoclinic
P21/a (No. 14)
15.3639(8)
9.4285(5)
17.9859(9)
99.781(2)
2567.5(2)
4
α/deg
β/deg
γ/deg
V/Å3
No. of refl. for cell detn. (2θ range) 22672 (5.1–55.0°)
Z
Dcalcd/g cm−3
1.683
1296.00
40.01
R-AXIS-RAPID
213(1)
0.26×0.20×0.12
55
222.0
1.00
5.1, 55.0
24114
5884 (Rint = 0.039)
298
No. of refl. for cell detn. (2θ range) 25 (20–3°)
F(000)
Dcalcd/g cm−3
F(000)
1.542
552.00
46.15
AFC-7R
µ[Mo Kα]/cm−1
Diffractometer
µ[Mo Kα]/cm−1
diffractometer
T/K
T/K
Crystal size/mm
No. of images
296(1)
Crystal size, mm
Scan type
0.24×0.20×0.16
ω–2θ
32
1.84 + 0.30 tanθ
5.0, 55.0
5481 (0.085)
5468
Total oscillation angles/deg
Exposure time/min deg−1
2θmin, 2θmax/deg
No. of refl. measured (Total)
No. of refl. measured (Unique)
No. of variables
R1, wR2 (all data)
R(I > 2.0σ(I))
Scan speed/deg min−1
Scan width/deg
2θmin, 2θmax/deg
Unique data (Rint)
No. of observations
No. of variables
R1, wR2 (all data)
R, Rw
0.042, 0.060
0.027
1.03
262
0.195, 0.149
0.061, 0.062 (I > 3.0σ(I))
2.09
GOF on F2
∆, e/Å−3
1.06, −1.35
GOF on F2
∆, e/Å−3
4.95, −7.21
C4), 105.5 (d, 1JC–H = 181 Hz, C2), 110.0 (d, 1JC–H = 163 Hz, C3),
113.7 (s, C5Me5), 122–131 (m, 1JC–H =155–160 Hz, aromatic car-
bons), 134.2 (s, 2-C6H4), 145.9 (s, ipso-Ph), 149.0 (s, ipso-Ph),
151.7 (s, ipso-Ph), 243.4 (d, 1JC–H = 123 Hz, TawCHPh).
Tables 3 and 4. In the case of AFC-7R four-circle diffractometer,
an empirical absorption correction was applied on the basis of azi-
muthal scans and the data was corrected for Lorentz and polariza-
tion effects. In the case of R-AXIS Rapid imaging plate diffracto-
meter, a symmetry-related absorption correction using the pro-
gram ABSCOR30 was applied. The data was corrected for Lorentz
and polarization effects.
Preparation of Cp*Ta(o-Tol-AD)(1,3-butadiene) (12).
A
solution of [Mg(1,3-butadiene)(thf)2] (1.45 mmlo) in THF (15
mL) was added to a solution of 1 (880 mg, 1.45 mmol) in THF (15
mL) at −78 °C. The reaction mixture was allowed to warm to
room temperature, and than was stirred at room temperature for 12
h. After removal of the solvent the resulting solid was extracted
with hexane (60 mL × 2). The extract was dried in vacuo, and the
residue was washed with hexane (1 mL) to give 12 (198 mg) as
yellow microcrystals in 23% yield. 1H NMR (400 MHz, C6D6, 35
°C; δ −2.13 (t, 1H, CH2w (anti)), −1.07 (t, 1H, CH2w (anti)), 0.73
(t, 1H, CH2w (syn)), 1.74 (s, 3H, Me), 1.76 (d, 1H, H2), 1.89 (t,
1H, CH2w (syn)), 1.91 (s, 15H, C5Me5), 4.13 (m, 1H, wCH–), 4.24
(d, 1H, H3), 5.66 (m, 1H, wCH–), 7.09 (d, 1H, H4), 6.3–7.4 (aro-
matic protons). Elemental analysis did not give any satisfactory
result due to the thermal instability of 12.
Crystallographic Data Collections and Structure Determi-
nation of 1 and 7. The X-ray diffraction studies were carried on
in sealed glass capillaries under an argon atmosphere. A crystal of
complex 7 was mounted on a Rigaku AFC-7R four-circle diffrac-
tometer for data collection using Mo Kα (graphite monochromat-
ed, λ = 0.71069) radiation and a crystal of 1 was mounted on a
Rigaku R-AXIS Rapid imaging plate diffractometer for data col-
lection using Mo Kα (graphite monochromated, λ = 0.71069) ra-
diation. Relevant crystal and data statistics are summarized in
The structure of 7 was solved by a direct method (SHELXS
86)31 and refined by the full-matrix least squares method. The
structure of 1 was solved by heavy-atom Petterson method (PAT-
TY-94)32 and expanded using Fourier techniques (DIRDIF94).32
Measured non-equivalent reflections were used for the structure
determination. In the subsequent refinement, the function Σω
(|Fo| − |Fc|)2 was minimized, where |Fo| and |Fc| are the ob-
served and calculated structure factor amplitudes, respectively.
The agreement indices are defined as R1 = Σ (||Fo| −|Fc||) / Σ|Fo|
2
4
and wR2 = [Σω (Fo − Fc2)2 / Σ (ωFo )]1/2. The positions of all
non-hydrogen stoms for all complexes were found from a differ-
ence Fourier electron density maps and were refined anisotropical-
ly. All hydrogen atoms were placed in calculated positions (C–H
= 0.95 Å) and kept fixed. All calculations were performed using
the teXsan crystallographic software package, and illustrations
were drawn with ORTEP. The CIF date for the two crystals are
deposited as Document No. 75025 at the Office of the Editor of
Bull. Chem. Soc. Jpn. Crystallographic data have been deposited
at the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK and cop-
ies can be obtained on requrest, free of charge, by quoting the pub-
[BULLETIN 2002/06/03 19:24]
01447

Y. Matsuo et el.
Bull. Chem. Soc. Jpn., 75, No. 6 (2002) 1297
lication citation and the deposition nimbners 179143 and 179144.
1471 (1999).
15 K. Mashima, Y. Matsuo, S. Nakahara, and K. Tani, J.
Organomet. Chem., 593/594, 69 (2000).
16 Y. Matsuo, K. Mashima, and K. Tani, Angew. Chem., Int.
Ed., 40, 960 (2001).
17 H. Kawaguchi, Y. Yamamoto, K. Asaoka, and K. Tatsumi,
Organometallics, 17, 4380 (1998).
18 F. Amor, P Gómez-Sal, P. Royo, and J. Okuda, Organome-
tallics, 19, 5168 (2000).
This research was supported by a Grant-in-Aid for Scientific
Research on Priority Areas (A) “Exploitation of Multi-Element
Cyclic Molecules” from the Ministry of Education, Culture,
Sports, Science and Technology, Japan. Y. M. acknowledges
financial supports from the JSPS Research Fellowships for
Young Scientists, 1998-2000.
19 A. Nakamura and K. Mashima, J. Prganomet. Chem., 621,
224 (2001).
References
1
G. van Koten and K. Vrieze, Adv. Organomet. Chem., 21,
20 Y. Matsuo, K. Mashima, and K. Tani, Organometallics, in
press (2001).
151 (1982).
2
H. tom Dieck, L. Stamp, R. Diercks, and C. Müller, Nouv.
21 L. W. Messerle, P. Jennische, R. R. Schrock, and G.
Stucky, J. Am. Chem. Soc., 102, 6744 (1980).
22 L. Messerle, Chem. Rev., 88, 1229 (1988).
23 M. H. Chisholm, J. C. Huffman, and L.-S. Tan, Inorg.
Chem., 20, 1859 (1981).
24 M. H. Chisholm, L.-S. Tan, and J. C. Huffman, J. Am.
Chem. Soc., 104, 4879 (1982).
25 R. D. Profilet, P. E. Fanwick, and I. P. Rothwell, Polyhe-
dron, 12, 1559 (1992).
26 P. N. Riley, J. R. Parker, P. E. Fanwick, and I. P. Rothwell,
Organometallics, 18, 3579 (1999).
27 D. E. Wigley, Prog. Inorg. Chem., 42, 239 (1994).
28 M. V. Galakhov, M. Gómez, G. Jiménez, P. Royo, M. A.
Pellinghelli, and A. Tiripicchio, Organometallics, 14, 1901
(1995).
J. Chim, 9, 289 (1985).
3
4
K. Vrieze, J. Organomet. Chem., 300, 307 (1986).
“Frontiers in Metal-Catalyzed Polymerization,” ed by J. A.
Gladysz, (2000), Vol. 100, pp. 1167.
B. Hessen, J. E. Bol, J. L. de Boer, A. Meetsma, and J. H.
Teuben, J. Chem. Soc., Chem. Commun., 1989, 1276.
J. Scholz, A. Dietrich, H. Schumann, and K.-H. Thiele,
Chem. Ber., 124, 1035 (1991).
J. E. Bol, B. Hessen, J. H. Teuben, W. J. J. Smeets, and A.
L. Spek, Organometallics, 11, 1981 (1992).
G. J. Pindado, M. Thornton-Pett, and M. Bochmann, J.
Chem. Soc., Dalton Trans., 1998, 393.
J. Scholz, S. Kahlert, and H. Görls, Organometallics, 17,
5
6
7
8
9
2876 (1998).
10 S. Kahlert, H. Goerls, and J. Scholz, Angew. Chem., Int.
Ed., 37, 1875 (1998).
29 A. M. Cardoso, R. J. H. Clark, and S. Moorhouse, J. Chem.
Soc., Dalton Trans., 1980, 1156.
11 J. Scholz, G. A. Hadi, K. L. Thiele, H. Goerls, R. Weimann,
H. Schumann, and J. Sieler, J. Organomet. Chem., 626, 243
(2001).
12 L. G. Hubert-Pfalzgraf, A. Zaki, and L. Toupet, Acta Crys-
tallogr., Sect. C, 49, 1609 (1993).
13 K. Mashima, Y. Matsuo, and K. Tani, Chem. Lett., 1997,
767.
14 K. Mashima, Y. Matsuo, and K. Tani, Organometallics, 18,
30 T. Higashi, Rigaku Corporation: Tokyo, Japan (1995).
31 G. M. Sheldrick, “Crystallographic Computing 3,” ed by
G. M. Sheldrick, C. Krüger and R. Goddard, Oxford University
Press (1985).
32 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Boeman,
R. de Gelder, R. Israel, and J. M. M. Smits, “The DIRDIF pro-
gram system, Technical Report of the Crystallography Laborato-
ry,” University of Nijmegen, The Netherland (1994).
[BULLETIN 2002/06/03 19:24]
01447