Synthesis, Characterization, and Reactions of a Half-Metallocene Benzylidene Complex of Tantalum Bearing 2,3-Dimethyl-1,3-butadiene and Pentamethylcyclopentadienyl Ligands

Article abstract of DOI:10.1021/om030313d

A half-metallocene benzylidene complex of tantalum, Ta(CHPh)Cp*(η⁴-supine-2,3-dimethyl-1,3-butadiene) (1), was prepared by treating TaCl₂Cp*(η ⁴-supine-2,3-dimethyl-1,3-butadiene) (2) with Mg(CH ₂Ph)₂ in toluene. The structure of 1 was determined by X-ray analysis, indicating the syn rotamer of the Ta=CHPh moiety; the Ph group points upward toward the Cp* ligand. The coordinatively unsaturated 16-electron complex 1 reacted with some unsaturated organic molecules (ethylene, cyclopentene, and tert-butyl cyanide), an alcohol, and an amine. The cycloaddition of ethylene and cyclopentene gave rise to metallacyclobutanes. The addition of tert-butyl cyanide to 1 afforded an imido tantalum complex, Ta(NC-(^tBu)=CHPh)Cp*(η ⁴-supine-2,3-dimethyl-1,3-butadiene) (6), which was derived from the metathesis reaction of a nascent 2-aza-1-tantalacyclobut-2-ene intermediate. Protonolysis of 1 by addition of methanol and p-methoxyaniline gave a methoxy benzyl complex, Ta(CH₂Ph)(OCH₃)Cp*(η ⁴-supine-2,3-dimethyl-1,3-butadiene) (7), and an amido benzyl complex, Ta(CH₂Ph)(NHC₆H₄OCH ₃)Cp*(η⁴-supine-2,3-dimethyl-1,3-butadiene) (8), respectively. Upon heating at 60 °C, complex 8 was converted to an imido butenyl complex, Ta(CH₂Ph)(NC₆H₄-OCH ₃)(η¹-2,3-dimethyl-2-butene)Cp* (9). Structures of the amido complex 8 and the imido complexes 6 and 9 were determined by X-ray analysis.

Full text of DOI:10.1021/om030313d

3766
Organometallics 2003, 22, 3766-3772
Syn th esis, Ch a r a cter iza tion , a n d Rea ction s of a
Ha lf-Meta llocen e Ben zylid en e Com p lex of Ta n ta lu m
Bea r in g 2,3-Dim eth yl-1,3-bu ta d ien e a n d
P en ta m eth ylcyclop en ta d ien yl Liga n d s
Kazushi Mashima,* Hirotaka Yonekura, Tsuneaki Yamagata, and
Kazuhide Tani
Department of Chemistry, Graduate School of Engineering Science, Osaka University,
Toyonaka, Osaka 560-8531, J apan
Received April 29, 2003
A half-metallocene benzylidene complex of tantalum, Ta(CHPh)Cp*(η4-supine-2,3-dimethyl-
1,3-butadiene) (1), was prepared by treating TaCl2Cp*(η4-supine-2,3-dimethyl-1,3-butadiene)
(2) with Mg(CH2Ph)2 in toluene. The structure of 1 was determined by X-ray analysis,
indicating the syn rotamer of the TadCHPh moiety; the Ph group points upward toward
the Cp* ligand. The coordinatively unsaturated 16-electron complex 1 reacted with some
unsaturated organic molecules (ethylene, cyclopentene, and tert-butyl cyanide), an alcohol,
and an amine. The cycloaddition of ethylene and cyclopentene gave rise to metallacyclobu-
tanes. The addition of tert-butyl cyanide to 1 afforded an imido tantalum complex, Ta(NC-
(tBu)dCHPh)Cp*(η4-supine-2,3-dimethyl-1,3-butadiene) (6), which was derived from the
metathesis reaction of a nascent 2-aza-1-tantalacyclobut-2-ene intermediate. Protonolysis
of 1 by addition of methanol and p-methoxyaniline gave a methoxy benzyl complex, Ta-
(CH2Ph)(OCH3)Cp*(η4-supine-2,3-dimethyl-1,3-butadiene) (7), and an amido benzyl complex,
Ta(CH2Ph)(NHC6H4OCH3)Cp*(η4-supine-2,3-dimethyl-1,3-butadiene) (8), respectively. Upon
heating at 60 °C, complex 8 was converted to an imido butenyl complex, Ta(CH2Ph)(NC6H4-
OCH3)(η1-2,3-dimethyl-2-butene)Cp* (9). Structures of the amido complex 8 and the imido
complexes 6 and 9 were determined by X-ray analysis.
In tr od u ction
including ring-opening metathesis polymerization of
cyclic olefins, and as reagents for alkene formation from
carbonyl compounds.7,8,24,29-31 We have been interested
in the chemistry of half-metallocene-diene complexes
of group 5 metals, in view of their isoelectronic analogy
to that of the metallocene complexes of group 4
metals.32-35 Some alkylidene tantalum metallocene and
Since Schrock initiated study of the chemistry of
alkylidene complexes of niobium and tantalum,1-7 vari-
ous alkylidene complexes of early transition metals have
been prepared using different kinds of supporting
ligands.8-28 Some of these alkylidene complexes have
been applied as catalysts for olefin metathesis reactions,
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Hogerheide, M. P.; Spek, A. L.; van Koten, G. Organometallics 1994,
13, 3259.
* To whom correspondence should be addressed. E-mail: mashima@
chem.es.osaka-u.ac.jp. Fax: 81-6-6850-6296.
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10.1021/om030313d CCC: $25.00 © 2003 American Chemical Society
Publication on Web 08/07/2003

A Half-Metallocene Benzylidene Complex of Ta
Organometallics, Vol. 22, No. 18, 2003 3767
half-metallocene complexes such as Ta(CH2)(CH3)Cp2
(A) and a dibenzyl benzylidene complex (B) have been
F igu r e 1. ORTEP view of 1 showing 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for
clarity.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of 1a
investigated.5,6 We have already reported benzylidene
complexes of tantalum bearing 1,3-butadiene (C) and
o-xylidene (D) ancillary ligands and their catalytic
activity in the stereoselective ring-opening metathesis
polymerization of norbornene.36-38 In the present paper,
we describe the synthesis of a new benzylidene diene
complex of tantalum. The introduction of 2,3-dimethyl-
1,3-butadiene (abbreviated DMBD) to half-metallocene
complexes of tantalum has enabled us to isolate the
phosphine-free benzylidene complex Ta(CHPh)Cp*(η4-
supine-DMBD) (1; Cp* ) pentamethylcyclopentadienyl).
We also report the reactivity of the complex 1 with
various unsaturated organic compounds and protic
substrates.
Ta-C10
Ta-C8
C8-C8*
C10-C11
1.962(4)
2.433(3)
1.395(7)
1.461(5)
Ta-C7
C7-C8
C8-C9
2.198(3)
1.454(5)
1.508(5)
C10-Ta-C7
Ta-C10-C11
114.24(12)
158.1(3)
C7-Ta-C7*
84.12(19)
a
An asterisk indicates that atoms are generated by the sym-
metry transformations x, -y + 1/2, z.
(2,3,3-trimethylallyl)magnesium bromide followed by
the addition of Mg(CH2Ph)2 in THF in the presence of
HMPA afforded the dibenzyl complex Ta(CH2Ph)2Cp-
(η4-supine-DMBD) (3). The observed difference in reac-
tivity might be attributed to the steric congestion
around the metal center and the increased electron-
donor character induced by the methyl groups on the
ligand. The most characteristic feature of 1 is the
stereochemistry of the TadCHPh moiety, which was
found to be a syn rotamer, as evident from NMR
spectroscopy and X-ray analysis: the phenyl group
points upward toward the Cp* ligand. The 1H NMR
spectrum of 1 displayed a singlet resonance at δ 5.88
due to CHPh, and the 13C NMR spectrum showed a
signal at δ 242.8 due to the benzylidene carbon with a
rather small J C-H coupling constant (90 Hz).
Figure 1 shows the discrete structure of 1, and
selected bond distances and angles are listed in Table
1. The DMBD ligand coordinated in an η4-supine fashion
to the tantalum atom. It is noteworthy that the Tad
CHPh moiety in 1 adopts a syn geometry, the same as
that found for B and D. The two methyl groups on the
diene ligand enhance the σ-bond character of the Ta-C
bond, favoring a metallacyclopentene form. The inter-
action between the double bond and vacant d orbital of
the tantalum atom might be weakened, and hence the
R-agostic interaction between CHPh and the same
vacant d-orbital controls the orientation of the Ph group.
The short bond distance (1.962(4) Å) of Ta-C10 and the
large angle (158.1(3)°) of Ta-C10-C11 indicated the
Resu lts a n d Discu ssion
Complex 1 was prepared in 49% yield by the reaction
of TaCl2Cp*(η4-supine-DMBD) (2) with 1 equiv of Mg-
(CH2Ph)2 in toluene. R-Hydrogen abstraction of one of
the two benzyl groups of an intermediate dibenzyl
complex followed by the release of toluene proceeded
spontaneously to give 1. This is in sharp contrast to the
analogous 1,3-butadiene complex TaCl2Cp*(η4-supine-
1,3-butadiene), which reacted with Mg(CH2Ph)2 in
toluene to afford the corresponding dibenzyl complex,
and the coordination of PMe3 was required to stabilize
the corresponding benzylidene complex C upon ther-
molysis.36,38 The reaction of TaCl4Cp with 2 equiv of
(32) Mashima, K.; Fujikawa, S.; Nakamura, A. J . Am. Chem. Soc.
1993, 115, 10990.
(33) Mashima, K.; Fujikawa, S.; Urata, H.; Tanaka, E.; Nakamura,
A. J . Chem. Soc., Chem. Commun. 1994, 1623.
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Tanaka, E.; Nakamura, A. Organometallics 1995, 14, 2633.
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14, 5642.
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metallics 1996, 15, 2431.
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ganometallics 1997, 16, 1345.
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mura, A.; Hamilton, J . G.; Rooney, J . J . Organometallics 1998, 17,
4183.

3768 Organometallics, Vol. 22, No. 18, 2003
Mashima et al.
Sch em e 1
F igu r e 2. ORTEP view of 6 showing 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for
clarity.
presence of an R-agostic interaction between Ta and HR,
as is evident from the small J C-H coupling constant. The
Ta-C10 bond distance is shorter than that (2.044(8) Å)
found for C36 but is longer than those found for D (1.925-
(9) Å)38 and B (1.883(14) Å).6 The long-short-long bond
alternation (C7-C8 ) C7*-C8* ) 1.454(5) Å and C8-
C8* ) 1.395(7) Å) of the diene unit and the obtuse fold
angle (108.2(2)°) between the plane of the diene carbons
and the plane of C7, Ta, and C7* are the consequence
of the large contribution of η2-2σ-metallacyclo-3-pentene,
as found for early-transition-metal-diene complexes;39
thus, the bond distance of Ta-C7 (2.198(3) Å) is longer
than that (2.433(3) Å) of Ta-C8.
Scheme 1 shows some reactions of the 16-electron,
coordinatively unsaturated complex 1. Ethylene and
cyclopentene reacted with 1 to give tantalacyclobutanes
4 and 5, respectively. In the 1H NMR spectra, we
observed dissymmetric signals due to the DMBD ligand.
The resonance due to the â-hydrogen of the metallacy-
clobutanes appeared at rather high field (δ 1.45 for 4
and 0.20 for 5), as typically observed for such four-
membered metallacycles.37,38 These complexes are stable
at room temperature but decompose at elevated tem-
perature (60-80 °C). In the case of norbornene, no
identifiable product was detected due to ROMP of the
monomer, though the activity was very low and only a
trace amount of poly(norbornene) was obtained.36,38
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of 6
Ta-N
1.824(3)
2.205(4)
2.443(4)
1.445(7)
1.514(6)
1.514(6)
1.562(5)
1.473(7)
1.521(6)
Ta-C14
Ta-C12
N-C17
C12-C13
C13-C14
C17-C18
C18-C19
C25-C27
2.192(4)
2.422(4)
1.361(4)
1.390(7)
1.469(6)
1.366(5)
1.454(5)
1.521(7)
Ta-C11
Ta-C13
C11-C12
C12-C15
C13-C16
C17-C25
C25-C28
C25-C26
Ta-N-C17
173.5(2)
74.2(2)
128.0(3)
62.4(2)
Ta-C11-C12
Ta-C12-C11
Ta-C13-C12
Ta-C13-C16
80.2(2)
63.8(2)
72.6(2)
126.9(3)
Ta-C12-C13
Ta-C12-C15
Ta-C13-C14
Ta-C14-C13
N-C17-C18
C11-C12-C13
C13-C12-C15
C12-C13-C16
C18-C17-C25
81.1(2)
125.1(3)
122.8(4)
118.8(5)
121.5(4)
118.0(3)
N-C17-C25
116.9(3)
117.4(5)
121.0(4)
115.7(4)
132.0(3)
C11-C12-C15
C12-C13-C14
C14-C13-C16
C17-C18-C19
complexes such as Ta(NPh)Cl3(thf)(PEt3) (1.765(5) Å),40
[Ta(NC6H4CMe3-2)Cl4(py)]- (1.779(5) Å),41 and Ta-
(NC6H3(iPr)2-2,6)(MeC(2-C5H4N)(CH2NSiMe3)2) (1.808-
(2) Å)42 and some half-metallocene imido complexes
(1.772(5)-1.793(4) Å).28,43-48 This might be attributed
to the interaction of a π-orbital of the nitrogen atom with
a π-orbital of the C17-C18 double bond (1.366(5) Å),
weakening the π-donation from the nitrogen atom to the
metal center.
Treatment of 1 with 1 equiv of tert-butyl cyanide in
toluene resulted in the formation of the imido complex
6, whose formulation and structure were revealed by
spectral data, combustion analysis, and an X-ray study.
An azametallacyclobutene is anticipated as an inter-
mediate, whose metathesis reaction would lead to the
formation of 6. The molecular structure of 6 is shown
in Figure 2, clearly indicating the Z stereochemistry of
the CdC bond. Selected bond distances and angles of 6
are listed in Table 2. The diene unit is normal in its
η4-supine-s-cis coordination to the tantalum atom: the
fold angle between the planes defined by the diene
carbons and C11, Ta, and C14 is 107.5(2)°. The short
Ta-N bond distance (1.824(3) Å) and the large Ta-N-
C17 angle (173.5(2)°) are consistent with a Ta-N imido
fragment. However, the bond distance of Ta-N in 6 is
much longer than those found for some tantalum-imido
Protonolysis of 1 with 1 equiv of methanol in toluene
proceeded readily to give the corresponding benzyl
(40) Rocklage, S. M.; Schrock, R. R. J . Am. Chem. Soc. 1982, 104,
3077.
(41) Nielson, A. J .; Glenny, M. W.; Rickard, C. E. F.; Waters, J . M.
J . Chem. Soc., Dalton Trans. 2000, 4569.
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Mountford, P. Organometallics 2001, 20, 3531.
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Clegg, W.; Hockless, D. C. R.; O’Neil, P. A.; Gibson, V. C. J . Chem.
Soc., Dalton Trans. 1992, 739.
(44) Baldwin, T. C.; Huber, S. R.; Bruck, M. A.; Wigley, D. E. Inorg.
Chem. 1993, 32, 5682.
(45) Galakhov, M. V.; Gome´z, M.; J imenez, G.; Royo, P.; Pellinghelli,
M. A.; Tiripicchio, A. Organometallics 1995, 14, 2843.
(46) Burckhardt, U.; Casty, G. L.; Gavenonis, J .; Tilley, T. D.
Organometallics 2002, 21, 3108.
(47) Sanche´z-Nieves, J .; Royo, P.; Pellinghelli, M. A.; Tiripicchio, A.
Organometallics 2000, 19, 3161.
(39) 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.
(48) Amor, F.; Sanchez-Nieves, J .; Royo, P.; J acobsen, H.; Blacque,
O.; Berke, H.; Lanfranchi, M.; Pellinghelli, M. A.; Tiripicchio, A. Eur.
J . Inorg. Chem. 2002, 2810.

A Half-Metallocene Benzylidene Complex of Ta
Organometallics, Vol. 22, No. 18, 2003 3769
F igu r e 3. ORTEP view of 8 showing 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for
clarity.
F igu r e 4. ORTEP view of 9 showing 50% probability
displacement ellipsoids. Hydrogen atoms are omitted for
clarity.
methoxy complex Ta(OMe)(CH2Ph)Cp*(η4-supine-DMBD)
(7) in quantitative yield. The 1H NMR spectrum of 7
displayed a singlet at δ 3.42 due to methoxy protons
and an AB quartet (δ 1.84 and 2.17 with J ) 12.2 Hz)
due to the benzyl group along with dissymmetric signals
of the DMBD ligand, owing to the coordination of
methoxy and benzyl ligands to the tantalum atom.
Similarly, treatment of 1 with 1 equiv of p-methoxy-
aniline in toluene at -78 °C quantitatively afforded the
amido tantalum complex 8, which can be isolated below
-10 °C. At room temperature 8 gradually turned into
the imido tantalum complex 9, and the conversion was
complete at elevated temperature (eq 1). The proton of
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of 8 a n d 9
8
9
Ta-N
2.016(3)
2.329(5)
2.247(4)
2.517(4)
2.515(4)
2.233(4)
1.415(5)
1.464(6)
1.390(7)
1.452(6)
1.494(7)
1.506(6)
1.499(6)
1.788(3)
2.240(4)
2.187(4)
Ta-C17
Ta-C11
Ta-C12
Ta-C13
Ta-C14
N-C24
1.387(5)
1.522(7)
1.174(9)
1.636(10)
1.657(10)
1.489(7)
1.497(5)
C11-C12
C12-C13
C13-C14
C12-C15
C13-C16
C17-C18
Ta-N-C24
142.5(3)
120.7(3)
82.5(3)
62.3(2)
73.9(3)
133.8(3)
74.0(2)
61.8(2)
136.6(3)
83.2(3)
114.7(4)
123.2(4)
122.1(4)
115.0(4)
124.9(4)
120.0(4)
165.3(3)
122.7(2)
94.2(3)
Ta-C17-C18
Ta-C11-C12
Ta-C12-C11
Ta-C12-C13
Ta-C12-C15
Ta-C13-C12
Ta-C13-C14
Ta-C13-C16
Ta-C14-C13
C11-C12-C13
C13-C12-C15
C11-C12-C15
C12-C13-C14
C12-C13-C16
C14-C13-C16
the nitrogen atom of 8, whose signal in the 1H NMR
spectrum was observed at δ 1.73, migrated to the DMBD
ligand, instead of the benzyl group, and thus 9 has 2,3-
dimethyl-2-butenyl and benzyl ligands. This selective
migration is due to the general tendency that a diene
ligand bound to an early transition metal has a σ-bond-
ing nature and a metallacyclo-3-pentene structure;
hence, the reactivity of the diene moiety is assumed to
likely be higher than that of the benzyl group. Zir-
conocene-imido complexes have been prepared by
reductive elimination of methane from Zr(Me)(NHAr)-
Cp2.49 The complexes 8 and 9 were further characterized
by X-ray analyses.
X-ray structures of 8 and 9 are shown in Figures 3
and 4, respectively, and selected bond distances and
angles are listed in Table 3. Notable structural features
are that the complex 8 has an amido ligand and a
DMBD ligand, while the complex 9 has η1-2,3-dimethyl-
2-butenyl ligand and an imido ligand. The DMBD ligand
132.6(9)
111.5(7)
115.9(6)
112.6(7)
131.6(9)
115.5(6)
of 8 is coordinated in an η4-supine-s-cis fashion to the
tantalum center with a fold angle of 99.5(2)° between
the plane of the diene carbons and the plane of C11,
Ta, and C14. The bond distance (2.016(3) Å) of Ta-N
and the angle (142.5(3)°) of Ta-N-C24 of 8 are normal
for an amido moiety. Complex 9 adopts a three-legged
piano-stool geometry surrounded by two carbon atoms
and one nitrogen atom. The bond distance (1.788(3) Å)
of Ta-N is much shorter than that of the amido complex
8, and the angle (165.3(3)°) of Ta-N-C24 is much
larger than that of 8. The Ta-N bond distance of the
imido complex 9 is longer than that of half-metallocene
imido complexes28,43-48 but is shorter than that of 6.
(49) Walsh, P. J .; Hollander, F. J .; Bergman, R. G. Organometallics
1993, 12, 3705.

3770 Organometallics, Vol. 22, No. 18, 2003
Mashima et al.
hexane (150 mL), and then recrystallization from hexane (2
Con clu sion s
mL) at -20 °C afforded 3 as deep purple crystals in 23% yield,
1
In this contribution, we have described the synthesis
of the stable benzylidene tantalum complex 1, bearing
Cp* and 2,3-dimethyl-1,3-butadiene ligands, as a single
syn rotamer, fully characterized by spectral data and
X-ray analysis. The complex 1 is coordinatively unsat-
urated and reacts with unsaturated organic compounds
and protic compounds. Of particular interest is the
formation of four-membered metallacycles upon reaction
with ethylene and cyclopentene. In the reaction of 1 with
tert-butyl cyanide the selective rupture of the azamet-
allacyclobutene led to the imido complex 6. p-Methoxya-
niline reacted with 1 to afford another imido complex,
9, by stepwise reactions: the first product was the amido
complex 8, which then converted to the amido complex
9 after the proton migration from the nitrogen atom of
the amido group to the diene unit at elevated temper-
ature. The addition of methanol to 1 resulted in the
selective formation of the benzyl methoxy complex 7.
Thus, the phosphine-free benzylidene complex 1 showed
unique reactivity.
mp 85-87 °C dec. H NMR (270 MHz, C6D6, 35 °C): δ -0.41
2
2
(d, J HH ) 5.9 Hz, 2H, H1,4(anti) of DMBD), -0.12 (d, J HH
)
5.8 Hz, 2H, H1,4(syn) of DMBD), 1.14 (d, J HH ) 11.1 Hz, 2H,
2
2
TaCHHPh), 1.76 (d, J HH ) 11.4 Hz, 2H, TaCHHPh), 2.44 (s,
6H, Me of DMBD), 5.61 (s, 5H, C5H5), 6.73 (d, 4H, o-Ph), 6.89
(t, 2H, p-Ph), 7.22 (t, 4H, m-Ph); 13C NMR (75 MHz, C6D6, 10
1
1
°C): δ 20.1 (q, J CH ) 125 Hz, CH3 of DMBD), 60.4 (t, J CH
)
148 Hz, C1,4 of DMBD), 71.3 (t, J CH ) 117 Hz, Ta-CH2Ph),
1
111.6 (d, J CH ) 174 Hz, C5H5), 120.6 (s, C2,3 of DMBD), 122.4
1
(d, 1J CH ) 158 Hz, p-Ph), 126.9 (d, 1J CH ) 153 Hz, o-Ph), 127.9
1
(d, J CH ) 155 Hz, m-Ph), 152.8 (s, ipso-C6H5).
P r ep a r a tion of Ta (CH2CH2CHP h )Cp *(η4-DMBD) (4). In
a solution of 1 (0.26 g, 0.53 mmol) in hexane (15 mL) cooled to
-78 °C, ethylene (atmospheric pressure) was introduced. After
it was stirred for 12 h at 25 °C, the solution gradually turned
red, and then the reaction mixture was evaporated under
reduced pressure to give 4 as microcrystals, which were rinsed
with two portions of hexane: 66% yield, mp 92-96 °C dec. 1H
2
NMR (300 MHz, C6D6, 35 °C): δ -0.54 (d, J HH ) 4.6 Hz, 1H,
2
H1(anti) of DMBD), -0.53 (d, J HH ) 5.6 Hz, 1H, H4(anti) of
DMBD), 0.37 (d, 1H, H1(syn) of DMBD), 0.47 (d, 1H, H4(syn)
of DMBD), 1.24 (s, 3H, Me of DMBD), 1.45 (m, 2H, -CH2-
CHPh, 1,77 (s, 15H, C5Me5), 1.98 (s, 3H, Me of DMBD), 2.18
Exp er im en ta l Section
2
(m, 2H, TaCH2-), 3.07 (t, J HH ) 8.0 Hz, 1H, TaCHPh), 6.83
(d, 2H, o-Ph), 6.91 (t, 2J HH ) 7.4 Hz, 1H, p-Ph), 7.25 (t, 2J HH
)
Gen er a l P r oced u r es. All manipulations involving air- and
moisture-sensitive tantalum complexes were carried out using
the standard Schlenk techniques under argon. Hexane, THF,
toluene, and ether were dried and deoxygenated by distillation
over sodium benzophenone ketyl under argon. Benzene-d6 was
distilled from Na/K alloy and thoroughly degassed by trap-to-
trap distillation before use. The complexes TaCl4Cp and TaCl2-
Cp*(η4-supine-DMBD) (2) were prepared according to the
7.4 Hz, 2H, m-Ph). Anal. Calcd for C25H35Ta: C, 58.14; H, 6.83.
Found: C, 57.81; H, 6.77.
P r ep a r a tion of Ta (CH(C3H6)CHCHP h )Cp *(η4-DMBD)
(5). To a solution of 1 (0.12 g, 0.24 mmol) in toluene (10 mL)
at -78 °C was added cyclopentene (1.0 equiv, 0.24 mmol) via
syringe. The reaction mixture was warmed to room temper-
ature and then stirred for 24 h at room temperature. The
resulting red solution was evaporated to dryness, and then
the product was extracted with hexane (25 mL). Recrystalli-
zation from hexane (0.3 mL) at -20 °C afforded 5 as deep red
crystals in 26% yield, mp 106-108 °C dec. 1H NMR (300 MHz,
C6D6, 10 °C): δ -0.56 (m, 2H, H1,4(anti) of DMBD), 0.20 (m,
1H, CHCHPh), 0.51 (d, 2J HH ) 6.7 Hz, 1H, H1(syn) of DMBD),
literature.39 The H (400, 300, and 270 MHz) and 13C (100 and
1
75 MHz) NMR spectra were measured on a J EOL J NM-AL400,
a Varian UNITY-INOVA-300, or a J EOL GSX-270 spectrom-
eter. All melting points were measured in sealed tubes under
an argon atmosphere and were not corrected.
P r ep a r a tion of Ta (CHP h )Cp *(η4-DMBD) (1). To a solu-
tion of 2 (4.64 g, 9.9 mmol) in toluene (20 mL) cooled to -78
°C was added a suspension of Mg(PhCH2)2 (1.5 equiv, 14.8
mmol) in toluene via syringe, and then the reaction mixture
was stirred for 24 h at 25 °C. The solution turned reddish
brown. All volatiles were removed under reduced pressure to
give a residue, from which the product was extracted with
hexane (400 mL). Recrystallization from a mixture of toluene
(10 mL) and hexane (10 mL) at -20 °C afforded 1 as reddish
brown crystals in 49% yield, mp 116-117 °C dec. 1H NMR (400
2
0.88 (d, J HH ) 5.8 Hz, 1H, H4(syn) of DMBD), 1.57 (s, 15H,
C5Me5), 1.69 (m, 1H, CH2CHHCH2), 2.09 (m, 1H, CH2-
CHHCH2), 2.22 (s, 3H, Me of DMBD), 2.27 (s, 3H, Me of
DMBD), 2.43 (m, 4H, CH2CH2CH2), 3.10 (m, 1H, TaCH-), 3.10
(d, 2J HH ) 9.1 Hz, 1H, TaCHPh-), 6.98-7.30 (m, 5H, Ph). 13
C
NMR (75 MHz, C6D6, 10 °C): δ 11.0 (q, 1J CH ) 127 Hz, C5Me5),
1
1
20.3 (q, J CH ) 126 Hz, Me of DMBD), 22.1 (q, J CH ) 130 Hz,
1
1
Me of DMBD), 32.7 (t, J CH ) 129 Hz, CH2), 33.1 (t, J CH
)
120 Hz, CH2), 36.3 (t, 1J CH ) 131 Hz, CH2), 59.1 (t, 1J CH ) 139
2
MHz, C6D6, 35 °C): δ -0.89 (d, J HH ) 10.3 Hz, 2H, H1,4(anti)
Hz) and 59.9 (t, J CH ) 140 Hz) for C1 and C4 of DMBD, 78.0
1
1
1
of DMBD), 1.92 (s, 15H, C5Me5), 2.60 (s, 6H, CH3 of DMBD),
(d, J CH ) 137 Hz, TaCHPh), 92.7 (d, J CH ) 128 Hz, TaCH),
3.05 (d, J HH ) 10.3 Hz, 2H, H1,4(syn) of DMBD), 5.88 (s, 1H,
2
116.0 (s, C5Me5), 118.5 (s) and 120.9 (s) for C2 and C3 of DMBD,
TadCH), 6.85-7.22 (m, 5H, C6H5). 13C NMR (100 MHz, C6D6,
1
1
122.2 (d, J CH ) 158 Hz, CHCHPh), 126.0 (d, J CH ) 157 Hz,
p-Ph), 127.5 (d, 1J CH ) 154 Hz, o-Ph), 128.3 (d, 1J CH ) 157 Hz,
m-Ph), 150.9 (s, ipso-Ph). Anal. Calcd for C28H39Ta: C, 60.43;
H, 7.06. Found: C, 60.55; H, 6.60.
1
1
35 °C): δ 11.9 (q, J C-H ) 127 Hz, C5Me5), 24.1 (q, J C-H
)
126 Hz, CH3 of DMBD), 59.4 (t, 1J C-H ) 143 Hz, C1,4 of DMBD),
111.5 (s, C5Me5), 121.7 (s, C2,3 of DMBD), 122.6 (d, J C-H
)
1
1
P r ep a r a tion of Ta (NC(tBu )dCHP h )Cp *(η4-DMBD) (6).
To a solution of 1 (0.22 g, 0.44 mmol) in toluene (20 mL) cooled
to -78 °C was added tert-butyl cyanide (1.0 equiv, 0.44 mmol)
via syringe and stirred for 3 h at 25 °C. The solution turned
reddish orange. After all volatiles were removed under reduced
pressure, the product was extracted with hexane (20 mL).
Recrystallization from hexane (0.4 mL) at -20 °C afforded 6
159 Hz, p-C6H5), 126.4 (d, J C-H ) 159 Hz, o-C6H5), 126.6 (d,
1J C-H ) 157 Hz, m-C6H5), 153.5 (s, ipso-C6H5), 242.8 (d, J C-H
) 90 Hz, CHdTa). Anal. Calcd for C23H31Ta: C, 56.56; H, 6.40.
Found: C, 55.98; H, 6.53.
P r ep a r a tion of Ta (CH2P h )2Cp (η4-DMBD) (3). To a solu-
tion of TaCl4Cp (2.14 g, 5.52 mmol) in THF (50 mL) and HMPA
(2 mL) cooled to -78 °C was added a solution of (2,3,3-
trimethylallyl)magnesium bromide (2 equiv, 11.0 mmol). The
reaction mixture was stirred for 24 h at 25 °C and refluxed
for 1 h at 60 °C. To the reaction mixture cooled to -78 °C was
added a suspension of Mg(PhCH2)2 (1.3 equiv, 7.2 mmol) in
ether via syringe, and this mixture was stirred for 2 h at 25
°C. All volatiles were removed under reduced pressure to give
a reddish purple residue. The product was extracted with
1
as red crystals in 48% yield, mp 73-75 °C dec. H NMR (300
2
MHz, C6D6, 35 °C): δ -1.16 (d, J HH ) 10.8 Hz, 1H, H1(anti)
2
of DMBD), -0.75 (d, J HH ) 10.5 Hz, 1H, H1(anti) of DMBD),
1.24 (s, 9H, (CH3)3), 1.87 (s, 15H, C5Me5), 2.18 (s, 3H, Me of
DMBD), 2.35 (s, 3H, Me of DMBD), 3.18 (d, 1H, H1(syn) of
DMBD), 3.24 (d, 1H, H4(syn) of DMBD), 5.44 (s, 1H, dCHPh),
7.10 (t, 1H, p-Ph), 7.27 (t, 2H, m-Ph), 7.75 (d, 2H, o-Ph). 13C

A Half-Metallocene Benzylidene Complex of Ta
Organometallics, Vol. 22, No. 18, 2003 3771
Ta ble 4. Cr ysta l Da ta a n d Da ta Collection P a r a m eter s of 1, 6, 8, a n d 9
complex
1
6
8
9
formula
fw
C
23H31Ta
C28H40NTa
571.56
C30H40NOTa
611.58
C30H40NOTa
611.58
488.42
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
monoclinic
P21/m (No. 11)
8.8250(13)
12.556(2)
8.9251(11)
90.0
93.092(9)
90.0
987.6(3)
2
triclinic
P1h (No. 2)
9.516(4)
9.718(3)
14.636(5)
76.40(3)
79.06(3)
87.99(3)
1291.5(8)
2
triclinic
orthorhombic
Pna21 (No. 33)
18.6968(4)
13.5132(3)
10.4565(2)
90.0
90.0
90.0
2641.90(10)
4
P1h (No. 2)
12.9814(6)
11.5472(5)
10.1734(5)
72.6661(13)
74.8582(13)
66.1851(14)
1314.33(11)
2
Z
no. of rflns for cell determn (θ range, deg)
11 158 (2.84-27.47)
1.643
14 067 (3.05-27.54)
1.470
61 049 (1.74-31.55)
1.545
67 152 (1.86-32.56)
1.538
D
calcd, g cm-3
F(000)
484
5.566
R-AXIS RAPID
213(1)
576
4.269
R-AXIS RAPID
213(1)
616
4.203
R-AXIS RAPID
153(1)
1232
4.182
R-AXIS RAPID
153(1)
µ(Mo KR), mm-1
diffractometer
T, K
cryst size, mm
no. of images
0.36 × 0.32 × 0.08
0.23 × 0.20 × 0.16
0.31 × 0.29 × 0.22
0.35 × 0.34 × 0.27
54
44
180
94
total oscillation angles, deg
exposure time, min deg-1
2θmax, deg
270.0
1.00
55.0
10 706
220.0
1.00
55.0
12 599
540.0
1.00
55.0
25 466
282.0
3.00
55.0
28 460
no. of rflns measd
no. of unique data (Rint
completeness to θ ) 27.50, %
no. of observns
)
2361 (0.0472)
99.6
5897 (0.0255)
99.4
5491
0.2145, 0.5056
311, 0
0.0287, 0.0640
0.0256, 0.0627
6003 (0.0610)
99.6
5898 (0.0297)
99.9
2261
5646
5527
max and min transmissn
no. of variables, restraints
R1, wR2 (all data)
R1, wR2 (I > 2.0σ(I))
Flack param (ø)
0.0950, 0.3246a
180, 0
0.2145, 0.5056b
455, 0
0.0950, 0.3246a
297, 5
0.0209, 0.0543
0.0227, 0.0557
0.0339, 0.0830
0.0315, 0.0816
0.0204, 0.0486
0.0204, 0.0474
0.023(8)
1.023
1.066, -0.698
0.003
GOF on F2
1.050
0.797, -0.929
0.001
1.039
1.152, -1.236
0.002
1.105
2.565, -1.967
0.001
∆F, e Å-3
∆/σ(max)
a
b
Multiscan absorption correction. Numerical absorption correction.
NMR (75 MHz, C6D6, 35 °C): δ 11.3 (q, 1J CH ) 127 Hz, C5Me5),
(10 mL) cooled to -78 °C was added a toluene solution of
p-methoxyaniline (1.1 equiv, 1.37 mmol) via syringe, and then
the solution was stirred, resulting in a red-orange solution.
With the temperature of the solution kept below -10 °C, the
mixture was evaporated to dryness to give 8 as red-orange
microcrystals in 98% yield, mp 104-107 °C dec. 1H NMR (300
1
1
24.2 (q, J CH ) 127 Hz, Me of DMBD), 24.9 (q, J CH ) 128 Hz,
1
Me of DMBD), 31.5 (q, J CH ) 125 Hz, Me3C), 37.1 (s, Me3C),
1
1
59.5 (t, J CH ) 146 Hz) and 60.6 (t, J CH ) 143 Hz) for C1 and
C4 of DMBD, 106.8 (d, J CH ) 149 Hz, dCHPh), 113.1 (s, C5-
1
Me5), 121.6 (s) and 122.2 (s) for C2 and C3 of DMBD, 124.2 (d,
1J CH ) 159 Hz, p-Ph), 127.6 (d, 1J CH ) 156 Hz, o-Ph), 128.3 (d,
1J CH ) 158 Hz, m-Ph), 140.1 (s, ipso-C6H5), 164.6 (s, N-Cd).
Anal. Calcd for C28H40NTa: C, 58.84; H, 7.05; N, 2.45. Found:
C, 58.26; H, 6.90; N, 2.59.
2
MHz, C6D6, 10 °C): δ 0.42 (d, J HH ) 6.0 Hz, 1H, H1(anti) of
DMBD), -0.26 (d, 2J HH ) 4.8 Hz, 1H, H4(anti) of DMBD), 0.29
2
(d, 1H, H4(syn) of DMBD), 0.68 (d, J HH ) 13.2 Hz, 1H,
TaCHH), 0.77 (d, 1H, H1(syn) of DMBD), 1.71 (s, 3H, Me of
DMBD), 1.72 (s, 15H, C5Me5), 1.73 (s, 1H, NH), 2.31 (s, 3H,
Me of DMBD), 3.38 (s, 3H, OMe), 3.51 (d, 1H, TaCHH), 6.76-
7.19 (m, 9H, m-Ph). 13C NMR (75 MHz, C6D6, 10 °C): δ 11.8
P r ep a r a tion of Ta (CH2P h )(OCH3)Cp *(η4-DMBD) (7). To
a solution of 1 (0.53 g, 1.09 mmol) in toluene (10 mL) cooled
to -78 °C was added methanol (1.0 equiv, 1.09 mmol) via
syringe. The reaction mixture was gradually warmed to room
temperature and then stirred for 2 h at 25 °C. The solution
turned red-orange. All volatiles were slowly evaporated to give
complex 7 as deep red microcrystals in 98% yield, mp 113-
117 °C dec. 1H NMR (400 MHz, C6D6, 35 °C): δ -0.36 (d, 2J HH
) 6.8 Hz, 1H, H1(anti) of DMBD), -0.24 (d, 1H, H1(syn) of
1
1
(q, J CH ) 127 Hz, C5Me5), 19.9 (q, J CH ) 126 Hz, Me of
DMBD), 21.5 (q, 1J CH ) 125 Hz, Me of DMBD), 48.8 (t, 1J CH
)
1
1
120 Hz, CH2-Ph), 55.4 (q, J CH ) 143 Hz, OMe), 57.4 (t, J CH
) 143 Hz) and 65.6 (t, 1J CH ) 141 Hz) for C1 and C4 of DMBD,
114.2 (d, 1J CH ) 158 Hz, o-C6H4-OMe), 116.0 (s, C5Me5), 122.6
(d, 1J CH ) 159 Hz, m-C6H4-OMe), 123.1 (s) and 123.5 (s) for C2
2
1
DMBD), 0.27 (d, J HH ) 6.0 Hz, 1H, H4(anti) of DMBD), 0.99
and C3 of DMBD, 123.1 (d, J CH ) 157 Hz, p-Ph), 127.8 (d,
2
1
(d, 1H, H4(syn) of DMBD), 1.83 (s, 15H, C5Me5), 1.84 (d, J HH
1J CH ) 156 Hz, o-Ph), 130.8 (d, J CH ) 154 Hz, m-Ph), 147.3
) 12.2 Hz, 1H, TaCHHPh), 2.10 (s, 3H, Me of DMBD), 2.17
(d, 1H, TaCHHPh), 2.29 (s, 3H, Me of DMBD), 3.42 (s, 3H,
OMe), 6.94 (1H, p-Ph), 7.18 (2H, o-Ph), 7.25 (2H, m-Ph). 13C
NMR (75 MHz, C6D6, 35 °C): δ 11.8 (q, 1J CH ) 127 Hz, C5Me5),
(s, p-C6H4-OMe), 153.2 (s, ipso-C6H4-OMe), 155.8 (s, ipso-Ph).
Anal. Calcd for C30H40NOTa: C, 58.92; H, 6.59; N, 2.29.
Found: C, 58.7; H, 6.46; N, 2.31.
P r ep a r a t ion of Ta (CH 2P h )(NC6H 4OCH 3)Cp *(η1-2,3-
d im eth yl-2-bu ten e) (9). To a solution of 1 (0.40 g, 0.81 mmol)
in toluene (10 mL) cooled to -78 °C was added a toluene
solution of p-methoxyaniline (1.1 equiv, 0.90 mmol) via syringe,
and the mixture was stirred for 2 h at 25 °C and for 12 h at
60 °C, leading to an orange solution, from which 9 was
obtained as orange microcrystals in 94% yield, mp 130-132
1
1
21.1 (q, J CH ) 125 Hz, Me of DMBD), 22.0 (q, J CH ) 122 Hz,
Me of DMBD), 47.8 (t, 1J CH ) 119 Hz, TaCH2Ph), 58.1 (q, 1J CH
1
1
) 141 Hz, OMe), 59.9 (t, J CH ) 145 Hz) and 54.2 (t, J CH
)
142 Hz) for C1 and C4 of DMBD, 118.1 (s, C5Me5), 120.7 (s)
and 130.4 (s) for C2 and C3 of DMBD, 122.2 (d, 1J CH ) 156 Hz,
p-Ph), 127.7 (d, 1J CH ) 155 Hz, o-Ph), 129.1 (d, 1J CH ) 153 Hz,
m-Ph), 154.3 (s, ipso-Ph). Anal. Calcd for C24H35OTa: C, 55.38;
H, 6.78. Found: C, 55.3; H, 6.60.
1
°C dec. H NMR (300 MHz, C6D6, 35 °C): δ 1.52 (s, 3H, Me of
2,3-dimethyl-2-butene), 1.54 (s, 3H, Me of 2,3-dimethyl-2-
2
P r ep a r a tion
DMBD) (8). To a solution of 1 (0.61 g, 1.24 mmol) in toluene
of Ta (CH2P h )(NHC6H4OCH3)Cp *(η4-
butene), 1.78 (d, J HH ) 13 Hz, 1H, TaCHHPh), 1.79 (s, 15H,
C5Me5), 1.91 (d, 1H, TaCHHPh), 2.02 (s, 3H, Me of 2,3-

3772 Organometallics, Vol. 22, No. 18, 2003
Mashima et al.
dimethyl-2-butene), 2.02 (s, 2H, TaCH2), 3.40 (s, 3H, OMe),
6.77-6.83 (m, 4H, C6H4OMe), 6.96 (t, 2J HH ) 7.3 Hz, 1H, p-Ph),
K (8 and 9). Data sets were corrected for Lorentz and
polarization effects. The multiscan absorption correction, using
the program ABSCOR, was applied to the raw data (1, 6, and
8), and the numerical absorption correction using the NUM-
ABS software was applied to the raw data of 9.
2
7.30 (dd, 2H, m-Ph), 7.50 (d, J HH ) 7.3 Hz, 2H, o-Ph). 13C
NMR (75 MHz, C6D6, 35 °C): δ 11.3 (q, 1J CH ) 127 Hz, C5Me5),
1
22.1 (q, J CH ) 125 Hz, Me of 2,3-dimethyl-2-butene), 22.6 (q,
1
1J CH ) 125 Hz, Me of 2,3-dimethyl-2-butene), 23.0 (q, J CH
)
The atomic parameters of most of the atoms for all crystals
were solved by the direct methods of SIR-97.50 The non-
hydrogen atoms were refined anisotropically on F2 by the full-
matrix least-squares method, using SHELXL-97.51 All hydro-
gen atoms of all crystals were located on the difference Fourier
maps. The function minimized was [∑w(Fo2 - Fc2)2] (w ) 1/[σ2-
(Fo2) + (aP)2 + bP]), where P ) (Max(Fo2,0) + 2Fc2)/3 with σ2-
1
126 Hz, Me of 2,3-dimethyl-2-butene), 55.5 (q, J CH ) 143 Hz,
OMe), 66.1 (t, J CH ) 115 Hz, C1 of 2,3-dimethyl-2-butene),
1
68.3 (t, 1J CH ) 131 Hz, CH2-Ph), 114.2 (s) and 115.4 (s) for C2
and C3 of 2,3-dimethyl-2-butene, 123.1 (d, J CH ) 157 Hz,
1
o-C6H4OMe), 125.4 (s, C5Me5), 127.2 (d, 1J CH ) 159 Hz, m-C6H4-
1
1
OMe), 128.1 (d, J CH ) 157 Hz, p-Ph), 129.8 (d, J CH ) 163
Hz, o-Ph), 130.0 (d, J CH ) 153 Hz, m-Ph), 151.3 (s, p-C6H4-
(Fo2) from counting statistics. The functions R1 and wR2 were
1
2
defined as (∑||Fo| - |Fc||)/∑|Fo| and [∑w(Fo - Fc2)2/∑(wFo4)]1/2
,
OMe), 152.3 (s, ipso-C6H4OMe), 156.0 (s, ipso-Ph). Anal. Calcd
for C30H40NOTa: C, 58.92; H, 6.59; N, 2.29. Found: C, 58.4;
H, 6.45; N, 2.50.
respectively. All calculations of least-squares refinements were
performed with SHELXL-97 programs on an Origin 3400
computer of Silicon Graphics Inc. at the Research Center for
Structural Biology Institute for Protein Research, Osaka
University. The geometric parameters and X-ray structure
analysis data for 1, 6, 8, and 9 are summarized in Table 4.
Cr ysta llogr a p h ic Da ta Collection a n d Str u ctu r e De-
ter m in a tion of 1, 6, 8, a n d 9. The crystal evaluation and
data collection were performed on a Rigaku R-AXIS RAPID
diffractometer with Mo KR radiation (λ ) 0.710 69 Å, 50 kV-
40 mA) and a imaging plate detector to crystal distance of 127
mm. The purple crystals of 1 and 6 were coated with silicone
grease and sealed in glass capillaries under an argon atmo-
sphere. The orange crystals of 8 and 9 were fixed on the end
of glass fibers with cyanoacrylate adhesive. All crystals were
placed in a nitrogen stream at 213(1) K (1 and 6) and 153(1)
Ack n ow led gm en t. The present research was sup-
ported in part 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 of J apan.
Su p p or tin g In for m a tion Ava ila ble: Figures giving the
numbering schemes and tables giving crystallographic data
for complexes 1, 6, 8, and 9. This material is available free of
charge via the Internet at http://pubs.acs.org.
(50) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J . Appl. Crystallogr. 1999, 32, 115.
(51) Sheldrick, G. M. Program for the Solution of Crystal Structures;
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
OM030313D