Reactions of the titanaallene intermediate [Cp*2Ti=C=CH2] with isonitriles: An approach to the chemistry of radialene type molecules

Article abstract of DOI:10.1021/om000929s

The titanaallene intermediate [Cp*₂Ti=C=CH₂] (2), obtained via methane elimination from Cp*₂Ti(CH=CH₂)Me (1), reacts with an excess of cyclohexylisonitrile (CyNC), to give the five-membered metallacycle Cp*₂TiC(=NCy)C(=NCy)C(=CH₂)C=NCy (4), which exhibits a radialene substructure. This reaction occurs by a [2+1] addition followed by subsequent insertion of two molecules of isonitrile. A [2+1] addition product is isolated from the reaction of 1 with 2,6-dimethylphenylisonitrile (ArNC) in 1:2 ratio in the form of the azabutatriene complex [Cp*₂Ti(CNAr)(η²-H₂CC=C=NAr) (5). The X-ray structure analysis of 5 reveals a pentacoordinated geometry consisting of a η²-C,C-azabutatriene moiety stabilized by a further ArNC ligand. Whereas 5 is stable in the solid state (dec 102-105°C), in solution (20°C) one molecule of isonitrile is released. Subsequent intramolecular C-H bond activation and C-C bond formation afford product 7. The latter can be directly isolated from reaction of 2 with 1 equiv of ArNC. The treatment of the titanaallene species 2 with 3 equiv of ArNC leads, through the insertion of two isonitrile molecules into the Ti-CH₂ bond in complex 5, to the five-membered ring complex 8, Cp*₂TiC(=NAr)C(=NAr)CH₂C=C=NAr. The molecular structure of 8 shows a planar titanacyclopentane. Density functional theory calculations confirm the terminal C,C-coordination mode as found in 5 as the preferred arrangement against the C,N- or internal, C,C-coordination modes.

Full text of DOI:10.1021/om000929s

1354
Organometallics 2001, 20, 1354-1359
Rea ction s of th e Tita n a a llen e In ter m ed ia te
[Cp *2TidCdCH2] w ith Ison itr iles: An Ap p r oa ch to th e
Ch em istr y of Ra d ia len e Typ e Molecu les†
Cristina Santamar´ıa, Ru¨diger Beckhaus,* Detlev Haase, Rainer Koch,
Wolfgang Saak, and Isabelle Strauss
Inorganic Chemistry Department, Carl von Ossietzky Universita¨t Oldenburg,
26111 Oldenburg, Germany
Received October 31, 2000
The titanaallene intermediate [Cp*2TidCdCH2] (2), obtained via methane elimination
from Cp*2Ti(CHdCH2)Me (1), reacts with an excess of cyclohexylisonitrile (CyNC), to give
the five-membered metallacycle Cp*2TiC(dNCy)C(dNCy)C(dCH2)CdNCy (4), which exhibits
a radialene substructure. This reaction occurs by a [2+1] addition followed by subsequent
insertion of two molecules of isonitrile. A [2+1] addition product is isolated from the reaction
of 1 with 2,6-dimethylphenylisonitrile (ArNC) in 1:2 ratio in the form of the azabutatriene
complex [Cp*2Ti(CNAr)(η2-H2CCdCdNAr) (5). The X-ray structure analysis of 5 reveals a
pentacoordinated geometry consisting of a η2-C,C-azabutatriene moiety stabilized by a further
ArNC ligand. Whereas 5 is stable in the solid state (dec 102-105 °C), in solution (20 °C)
one molecule of isonitrile is released. Subsequent intramolecular C-H bond activation and
C-C bond formation afford product 7. The latter can be directly isolated from reaction of 2
with 1 equiv of ArNC. The treatment of the titanaallene species 2 with 3 equiv of ArNC
leads, through the insertion of two isonitrile molecules into the Ti-CH2 bond in complex 5,
to the five-membered ring complex 8, Cp*2TiC(dNAr)C(dNAr)CH2CdCdNAr. The molecular
structure of 8 shows a planar titanacyclopentane. Density functional theory calculations
confirm the terminal C,C-coordination mode as found in 5 as the preferred arrangement
against the C,N- or internal C,C-coordination modes.
In tr od u ction
Free radialenes (polymethylenecycloalkanes (Scheme
2))7 have received considerable attention by both theo-
retical and experimental chemists because of their
π-electronic arrangement and in order to understand
their potential as electron donors and acceptors.7 Due
to the generally high reactivity exhibited by these
species, the syntheses are limited to a few selected
examples, often highly substituted.9 Heteroradialenes
of type II, prepared from 3,4-dilithiohexadienes10 or
Cumulated bond systems, particularly butatrienes
and derivatives thereof, in the coordination sphere of
transition metals1,2 are of fascinating interest due to the
variety of possible coordination modes, dynamic behav-
ior, and synthetic applications (Scheme 1).3 Particularly,
migration processes of metal centers along hydrocarbon
backbones are of current interest in organometallic
chemistry.4-6 On the other hand, cumulene complexes
can also serve as an alternative sources of radialenes.7,8
(4) For an example of dynamic properties: sliding processes of
Cp*2M (Ti, Zr),4a Cp2V4b fragments along a polyyne chain; for CpCo,5
chain-walking in polymerization reactions.6 (a) Pellny, P.-M.; Burlakov,
V. V.; Arndt, P.; Baumann, W.; Spannenberg, A.; Rosenthal, U. J . Am.
Chem. Soc. 2000, 122, 6317-6318. (b) Choukroun, R.; Donnadieu, B.;
Lorber, C.; Pellny, P.-M.; Baumann, W.; Rosenthal, U. Chem. Eur. J .
2000, 6, 4505-4509.
† Dedicated to Professor Dr. Peter Ko¨ll on the occasion of his 60th
birthday.
* Corresponding author. Tel: +49 441 798 3656. Fax: +49 441 798
3581. E-mail: ruediger.beckhaus@uni-oldenburg.de.
(1) For selected butatriene complexes see M ) Ir,1a M ) Rh,1b,c,d
M
) Pt,1e M ) Cr,1f and M ) Ti.2 (a) Ohmura, T.; Yorozuya, S.-I.;
Yamamoto, Y.; Miyaura, N. Organometallics 2000, 19, 365-367. (b)
Werner, H.; Laubender, M.; Wiedemann, R.; Windmu¨ller, B. Angew.
Chem. 1996, 108, 1330-1332; Angew. Chem., Int. Ed. Engl. 1996, 35,
1237-1239. (c) Song, L.; Arif, A. M.; Stang, P. J . J . Organomet. Chem.
1990, 395, 219-226. (d) Stang, P. J .; White, M. R.; Maas, G. Organo-
metallics 1983, 2, 720-725. (e) White, M. R.; Stang, P. J . Organome-
tallics 1983, 2, 1654-1658. (f) Schubert, U.; Gro¨nen, J . Chem. Ber.
1989, 122, 1237-1245.
(5) Fritch, J . R.; Vollhardt, K. P. C. J . Am. Chem. Soc. 1978, 100,
3643-3644.
(6) Mo¨hring, V. M.; Fink, G. Angew. Chem. 1985, 97, 982-984;
Angew. Chem., Int. Ed. Engl. 1985, 24, 1001-1003.
(7) Hopf, H.; Maas, G. Angew. Chem. 1992, 104, 953-977; Angew.
Chem., Int. Ed. Engl. 1992, 31, 931-955.
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111, 3761-3762. (b) Iyoda, M.; Tanaka, S.; Otani, H.; Nose, M.; Oda,
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Angew. Chem., Int. Ed. Engl. 1995, 35, 210-212.
(9) [5]-Radialenes as substructures are found in bowl-shaped
corannulenes;9a,b dynamic Li complexes of [4]-radialenes.9c (a) Sastry,
G. N.; Rao, H. S. P.; Bednarek, P.; Priyakumar, U. D. Chem. Commun.
2000, 843-844. (b) Mehta, G.; Sarma, P. V. V. S. Chem. Commun.
2000, 19-20. (c) Sekiguchi, A.; Matsuo, T.; Sakurai, H. Angew. Chem.
1998, 110, 1751-1754; Angew. Chem., Int. Ed. 1998, 37, 1661-1664.
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Angew. Chem., Int. Ed. Engl. 1985, 24, 571-572.
(3) (a) Wentrup, C.; Flammang, R. J . Phys. Org. Chem. 1998, 11,
350-355. (b) Bunz, U. H. F. Angew. Chem. 1994, 106, 1127-1131;
Angew. Chem., Int. Ed. Engl. 1994, 33, 1073-1076. (c) Lange, T.;
Gramlich, V.; Amrein, W.; Diederich, F.; Gross, M.; Boudon, C.;
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Int. Ed. Engl. 1995, 34, 805-809.
10.1021/om000929s CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/01/2001

Chemistry of Radialene Type Molecules
Organometallics, Vol. 20, No. 7, 2001 1355
Sch em e 1
Sch em e 3
temperature, the five-membered metallacycle 4 is iso-
lated in the form of black crystals (Scheme 3). Alterna-
tive insertion reactions of the isonitrile into the Ti-C
σ-bond of 1, as a general way to iminoacyl complexes,16,17
are not observed.
1
The H NMR spectrum of 4 shows as a remarkable
feature the chemical shifts of the exo-methylene protons
at δ 4.80 and 4.54 ppm. The 13C NMR spectrum reveals
resonances at δ 228.0 and 226.1 ppm, corresponding to
the σ-Ti-iminoacyl carbons, and the absorptions at δ
166.5 ppm (CdN) and 149.0 ppm (CdC) are assigned
to the ring carbon atoms in â-position. The mass
spectrum shows the expected molecular peak (m/z 671)
and the consecutive losses of three isonitrile molecules.
In the IR spectrum appear four bands at ν 1630 (m),
1596 (m), 1583 (m), and 1543 (s) cm-1, corresponding
to the CdN and CdC stretching vibration. An exact
assignment to clarify not only the CdX (X ) N, C)
vibrations but also the hapticity (η1 or η2) of the
iminoacyl groups16 is not possible due to the wide
interval found for conjugated systems with double
carbon-nitrogen (1660-1480 cm-1) and carbon-carbon
bonds (ν e 1620 cm-1).18 All these data are in agreement
with the proposed heteroradialene structure of 4 shown
in Scheme 3. The primary [2+1] cycloaddition product
3 was not detectable, even if understoichiometric amounts
of isonitrile are used. However, the formation of 3 is in
accordance with the known reactivity of isonitriles with
transition metal carbene complexes.19 Formation of 4
can be explained in terms of symmetric or asymmetric
insertion in 3 of two further isontrile molecules.
Sch em e 2
directly from butatrienes, are known.11 The strained
structure of type II molecules leads often to rearrange-
ments.2,11c For five-membered titanacyclocumulenes a
dimerization to [4]-radialenes complexes has been ex-
tensively investigated.12 In continuation of our investi-
gations on the highly reactive titanaallene intermediate
[Cp*2TidCdCH2] (2),13,14 preferentially generated by
methane elimination from [Cp*2Ti(CHdCH2)CH3] (1),
we report several trapping experiments of 2 with
isonitriles to give heteroradialene type molecules.
Resu lts a n d Discu ssion
A more detailed insight into these processes becomes
available by using 2,6-dimethylphenylisonitrile (ArNC,
Ar ) 2,6-Me2C6H3). Treatment of 1 with ArNC in 1:2
molar ratio in n-hexane, within the temperature range
0-20 °C to eliminate methane, gives a dark orange
solutions from which the complex 5 was isolated in 65%
yield as orange crystals (see Scheme 4) suitable for an
X-ray diffraction analysis.
Molecu la r Str u ctu r e of Com p lex 5. Dark orange
crystals of 5 were obtained from a diluted hexane
solution at 5 °C. The molecular structure is shown in
Figure 1, and the relevant geometrical parameters are
summarized in Table 1. The complex 5 possesses a
pentacoordinated geometry consisting of an isonitrile
The CR-nucleophilic titanallene species [Cp*2TidCd
CH2] (2)15 undergoes facile reactions with isonitriles. If
diethyl ether solutions of 1 are added to an excess of
cyclohexylisonitrile, CyNC (Cy ) C6H11) at -40 °C, and
the solution is then allowed to slowly warm to room
(11) Derivatives of B,11a Si,11b,c and Sn.11d (a) Maercker, A.; Brieden,
W.; Schmidt, T.; Lutz, H. D. Angew. Chem. 1989, 101, 477-479; Angew.
Chem., Int. Ed. Engl. 1989, 28, 477-479. (b) Maercker, A.; Brieden,
W.; Kastner, F. and Mannschreck, A. Chem. Ber. 1991, 124, 2033-
2036. (c) Yamamoto, T.; Kabe, Y.; Ando, W. Organometallics 1993, 12,
1996-1997. (d) Maercker, A.; Bauers, F.; Brieden, W.; J ung, M.; Lutz,
H. D. Angew. Chem. 1988, 100, 413-414; Angew. Chem., Int. Ed. Engl.
1988, 27, 404-405.
(12) Pellny, P.-M.; Burlakov, V. V.; Peulecke, N.; Baumann, W.;
Spannenberg, A.; Kempe, R.; Francke, V.; Rosenthal, U. J . Organomet.
Chem. 1999, 578, 125-132.
(13) Beckhaus, R.; Santamaria, C. J . Organomet. Chem. 2000, in
press.
(14) (a) Beckhaus, R. Angew. Chem. 1997, 109, 694-722; Angew.
Chem., Int. Ed. Engl. 1997, 36, 686-713. (b) Beckhaus, R.; Oster, J .;
Sang, J .; Strauss, I.; Wagner, M. Synlett 1997, 241-249. (c) Beckhaus,
R. J . Chem. Soc., Dalton Trans. 1997, 1991-2001.
(15) (a) Beckhaus, R.; Flatau, S.; Troyanov, S. I.; Hofmann, P. Chem.
Ber. 1992, 125, 291-299. (b) Beckhaus, R.; Thiele, K.-H.; Stro¨hl, D. J .
Organomet. Chem. 1989, 369, 43-54.
(16) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059-1079.
(17) Starting from methylenetitanacyclobutanes insertion reactions
in the Ti-Csp3 become dominant over the addition to 2. Beckhaus,
R.; Zimmermann, C.; Wagner, T.; Herdtweck, E. J . Organomet. Chem.
1993, 460, 181-189.
(18) Socrates, G. Infrared Characteristic Group Frequences; J . Wiley
& Sons Ltd.: Chichester, 1980.
(19) Aumann, R. Angew. Chem. 1988, 100, 1512-1524; Angew.
Chem., Int. Ed. Engl. 1988, 27, 1456-1467.

1356 Organometallics, Vol. 20, No. 7, 2001
Santamar´ıa et al.
Sch em e 4
F igu r e 1. ORTEP plot of 5 at 50% probability ellipsoids.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
Ti-C(1)
2.249(2)
2.200(2)
2.098(2)
1.424(3)
2.149
C(2)-C(3)
N(1)-C(3)
N(2)-C(12)
N(1)-C(4)
N(2)-C(13)
1.264(3)
1.262(3)
1.167(3)
1.418(3)
1.405(3)
Ti-C(2)
Ti-C(12)
C(1)-C(2)
Ti-Cp*(3)(Cen)
Ti-Cp*(2)(Cen)
2.135
C(12)-Ti-C(2)
C(12)-Ti-C(1)
C(2)-Ti-C(1)
N(2)-C(12)-Ti
C(1)-C(2)-Ti
108.66(8)
71.37(8)
37.31(8)
C(3)-C(2)-Ti
C(3)-C(2)-C(1)
C(2)-C(1)-Ti
138.23(19)
148.1(2)
69.46(12)
178.24(18) C(12)-N(2)-C(13) 173.7(2)
73.24(12) C(3)-N(1)-C(4) 123.5(2)
Cp*(3)-Ti-Cp*(2) 140.2
N(1)-C(3)-C(2) 170.7(3)
R ) o-Me3SiOPh 2200 cm-1 25b
2110 cm-1 (KBr)26). In the π-acceptor derivatives
(Cp2Ti(CNAr)2 2038, 1937 cm-1 26
low values are also
found.
;
free isontriles ArNC
)
On the basis of the structural data, the C-C coordi-
nation in 5 could be best described as a titanacyclopro-
pane with a higher π-content in the C-C bond, consis-
tent with a lower back-donation from titanium to the
olefinic unit.
molecule and a η2-azabutatriene moiety in the equato-
rial plane of a Cp*2 fragment.
The coordination of the azabutatriene ligand to the
decamethyltitanocene fragment leads to an increase in
the C(1)-C(2) bond length, from 1.337(2) Å for free
ethylene20 to 1.424(3) Å. This feature compares to those
The NMR spectrum of 5 shows a signal for the Cp*
ligands, in accordance with C2v symmetry in solution,
and the characteristic signals for azabutatriene and
isonitrile ligands. The 13C NMR spectrum reveals the
resonances of the heterocumulene (Ar-NdCRdCâd
CγH2) which exhibit absorptions at δ 231.4 ppm for the
R-carbon, while the â-carbon appears at δ 66.9 ppm.
These values are more or less in agreement with those
found for free ketenimines (RNdCRdCâR2, CR: δ 187-
195 ppm, Câ: δ 37-78 ppm).27 The γ-carbon of the
heterocumulene shows a resonance at δ 43.5 ppm (1J CH
) 128.5 Hz), following the tendency before. It is also
remarkable that in the 13C NMR spectrum the singlet
at δ 173.6 ppm assigned to the coordinated isonitrile
lies in the same region as the free ligand (2,6-Me2C6H3-
NC, δ 170.4 ppm).26 Additionally, in the IR spectrum a
band at 2000 cm-1 corresponding to the stretching
>CdCdN is observed and compares well to that found
for organic keteneimines.19,27
found for (C5Me4R)2Ti(η-C2H4) (R ) Me, 1.438(5) Å,21
R
) SiMe3, 1.442(9) Å22) and other ethylene complexes.23
As a consequence of the isonitrile coordination as
additional π-acceptor ligand, the Ti(3)-C(1) and Ti(3)-
C(2) bond lengths of 2.249(2) and 2.200(2) Å, respec-
tively, are significantly longer than those in (η-C5Me4R)2-
Ti(η-C2H4) (R ) Me, 2.160(4) Å,21 R ) SiMe3, 2.167(4)
Å22). Moreover, it is found that the Ti-Cp*(centroid)
distances of 2.149 and 2.135 Å are also longer than the
corresponding bond lengths in the titanium-ethylene
complexes (R ) Me, 2.092(4) Å,21 R ) SiMe3, 2.129 Å22),
reflecting the previous fact. The N(1)-C(3) distance in
the azabutatriene fragment is close to that reported for
a carbon-nitrogen double bond (1.28 Å).16,24 The N(2)-
C(12) bond length of 1.167(3) Å in the coordinated
isonitrile is elongated compared with C-N distances in
pure σ-donor complexes (TiCl4‚2RNC,
R )
tBu
1.145(10), 1.137(10) Å;25a R ) o-Me3SiOPh 1.142(5) Å25b).
This fact is also reflected in the low ν CtN absorption
Whereas the complex 5 is thermally stable up to 102
°C in the solid state, in solution the dissociation of the
coordinated isontrile is observed (t1/2 ) 12 h, 20 °C). An
analogous situation was reported by Rausch et al. for
at 2066 cm-1 (TiCl4‚2RNC, R ) tBu 2210, 2226 cm-1 25a
;
(20) Bartell, L. S.; Roth, E. A.; Hollowell, C. D.; Kuchitsu, K.; Young,
J . E. J . J . Chem. Phys. 1965, 42, 2683-2686.
(21) Cohen, S. A.; Auburn, P. R.; Bercaw, J . E. J . Am. Chem. Soc.
1983, 105, 1136-1143.
(22) Horacek, M.; Kupfer, V.; Thewalt, U.; Stepnicka, P.; Polasek,
M.; Mach, K. Organometallics 1999, 18, 3572-3578.
(23) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1-S83.
(24) March, J . Advanced Organic Chemistry, 4th ed.; J ohn Wiley &
Sons: New York, 1992; pp 1-1495.
(25) (a) Carofiglio, T.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
Inorg. Chem. 1989, 28, 4417-4419. (b) Hahn, F. E.; Lu¨gger, T. J .
Organomet. Chem. 1995, 501, 341-346.
(26) Kool, L. B.; Rausch, M. D.; Alt, H. G.; Engelhardt, H. E.;
Herberhold, M. J . Organomet. Chem. 1986, 317, C38-C40.
(27) Barker, M. W.; McHenry, W. E. Ketene Imines. In The
Chemistry of Ketenes, Allenes, and Related Compounds; Patai, S., Ed.;
J ohn Wiley and Sons: Chichester, 1980; pp 701-720.

Chemistry of Radialene Type Molecules
Organometallics, Vol. 20, No. 7, 2001 1357
the Cp2M(CNR)2 (M ) Ti, Zr; R ) 2,6-Me2-dimethyl-
phenyl).26 The decomposition process of a benzene-d6
solution of 5, followed by 1H NMR spectroscopy in a
sealed tube, leads to free isonitrile and a mixture of
products from which compound 7 could be identified.
The latter could also be isolated as a green micro-
crystalline solid as the unique product of the reaction
of the titanocenevinylidene intermediate [Cp*2TidCd
CH2] (2) with (2,6-Me2C6H3)NC in 1:1 ratio. Apparently,
the [Cp*2Ti(H2CdCdCdNAr)] (6) intermediate under-
goes an intramolecular rearrangement under C-H bond
activation and C-C coupling to give 7 (see Scheme 4).
Similar processes of C-C bond formation between Cp*
and π-ligands have been studied in titanacumulene and
acetylene complexes.28 The decomposition of 5 via
intermediate 6 to yield 7 corresponds effectively to a
“sliding” of the titanium center along the azabutatriene
chain.
This behavior induced us to carry out DFT calcula-
tions on the model system Cp2Ti‚‚‚H2CdCdCdNH in
order to evaluate the stabilities of the three cycloaddi-
tion products shown in Scheme 1 (X ) NH). The
symmetric structure II (or 6 in Scheme 4) is the least
favorable product. The titanaazacyclopropane corre-
sponding to I is about 25 kJ /mol more stable than II.
The most stable product compared to type II is the one
of type III (corresponding to 5), being 30 kJ /mol lower
in energy. These findings support the experimental
observations of a nonisolable intermediate 6, which
rearranges to either 5 or 7 under the appropriate
conditions.
F igu r e 2. ORTEP plot of 8 at 50% probability ellipsoids.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 8
Ti(1)-C(1)
2.176(2)
2.275(2)
1.520(3)
1.289(4)
2.114
N(1)-C(5)
N(1)-C(6)
C(2)-C(3)
N(2)-C(3)
N(3)-C(4)
1.241(3)
1.420(4)
1.500(4)
1.258(3)
1.278(3)
Ti(1)-C(4)
C(1)-C(2)
C(1)-C(5)
Ti(1)-Cp*(3)(Cen)
Ti(1)-Cp*(4)(Cen)
2.106
C(1)-Ti(1)-C(4)
79.39(9) C(2)-C(1)-Ti(1)
114.15(18)
114.9(2)
122.1(2)
121.2(2)
116.4(2)
121.5(2)
111.20(15)
C(5)-N(1)-C(6) 125.3(3)
C(3)-N(2)-C(14) 122.5(2)
C(4)-N(3)-C(22) 129.0(2)
C(5)-C(1)-C(2) 117.6(2)
C(3)-C(2)-C(1)
N(2)-C(3)-C(2)
N(2)-C(3)-C(4)
C(2)-C(3)-C(4)
An indicative feature of the proposed structure for 7
is the characteristic “tucked in”29 splitting pattern in
1
the H NMR spectrum, consisting of one Cp* signal (δ
C(5)-C(1)-Ti(1) 127.00(18) N(3)-C(4)-C(3)
N(3)-C(4)-Ti(1) 127.17(18) C(3)-C(4)-Ti(1)
N(1)-C(5)-C(1) 170.1(3)
1.62 ppm, 15H), four nonequivalent methyl groups (δ
1.07, 1.47, 1.70, 2.34 ppm, each 3H), and a diastereotopic
methylene group of the fulvene moiety (1H NMR δ 3.29,
3.92 ppm, 2J HH ) 14 Hz; 13C NMR δ 31.2 ppm, J ) 124.8
Hz). The low-field shift of the fulvene methylene group
indicates a nonmetal-coordinated fulvene ligand. Fur-
ther signals at δ 4.04 ppm (J HH ) 1.5 Hz), 4.26 ppm
(J HH ) 1.8 Hz), and δ 4.34 ppm are attributed to
methylene (>CdCH2) and methyne (-CHdNAr) pro-
tons, respectively. To determine the correlation between
the proton and the carbon resonances of the methylene
Cp*(3)-Ti(1)-Cp*(4) 137.3
at 353 K, but no coalescence of both methyl groups was
observed. The resonance of the iminoacyl carbon is
observed at 160.8 ppm, and the IR spectrum shows an
absorption band at ν 1586 cm-1 attributable to the
CdN stretching. The molecular ion (m/z 475, 100%) and
the fragment [(M+ - C5Me5), 63%] were observed in the
mass spectrum (EI). The spectroscopic and analytical
data for complex 7 lead us to the formulation given in
the Scheme 4. Unfortunately, all attempts to obtain
crystals suitable for X-ray diffraction studies have been
unsuccessful.
1
and methyne groups, a two-dimensional H-13C NMR
spectrum was acquired. An interesting feature in the
1H NMR spectrum of 7 is the two broad singlets at
-0.52 and 2.50 ppm assigned to the methyl substituents
of the aromatic ring, indicating a very low rotation of
the bulky Ar groups around the Cipso-NAr bond.30 This
situation is also observed for the protons in meta-
position of the aryl group. When heating a d8-toluene
solution of 7, coalescence of the aromatic protons occurs
The vinylmethyl derivative 1 reacts also with (2,6-
Me2C6H3)NC in a 1:3 ratio in diethyl ether as solvent
to afford a dark orange solution, from which the five-
membered metallacycle 8 is obtained as black crystals
(see Scheme 3). The solid compound is stable under
nitrogen atmosphere at room temperature but decom-
poses slowly (days) in benzene-d6 solution with forma-
(28) (a) Rosenthal, U.; Pellny, P.-M.; Kirchbauer, F. G.; Burlakov,
V. V. Acc. Chem. Res. 2000, 119-129. (b) Pellny, P.-M.; Kirchbauer,
F. G.; Burlakov, V. V.; Baumann, W.; Spannenberg, A.; Rosenthal, U.
Chem. Eur. J . 2000, 6, 81-90. (c) Horacek, M.; Stepnicka, P.; Gyepes,
R.; Cisarova, I.; Polasek, M.; Mach, K.; Pellny, P.-M.; Burlakov, V. V.;
Spannenberg, A.; Rosenthal, U. J . Am. Chem. Soc. 1999, 121, 10638-
10639. (d) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann,
W.; Spannenberg, A.; Rosenthal, U. J . Am. Chem. Soc. 1999, 121,
8313-8323.
(29) McDade, C.; Green, J . C.; Bercaw, J . E. Organometallics 1982,
1, 1629-1634.
(30) Fandos, R.; Meetsma, A.; Teuben, J . H. Organometallics 1991,
10, 2665-2671.
1
tion of 5 and free isonitrile. H and 13C NMR spectra
are in full accordance with the proposed structure and
also compatible with the solid-state structure deter-
mined by single-crystal X-ray diffraction.
Molecu la r Str u ctu r e of Com p lex 8. The molecular
structure in the solid state of compound 8 is shown in
Figure 2. Crystallographic parameters and selected
geometrical details are listed in Table 2 and Table 3,
respectively.

1358 Organometallics, Vol. 20, No. 7, 2001
Santamar´ıa et al.
Ta ble 3. Exp er im en ta l Cr ysta llogr a p h ic Da ta for 5
a n d 8
symmetric azabutriene complexes 3 and 6 can be
proposed as intermediates. In such a way, subsequent
reactions of 3 with further C6H11NC leads to 4, whereas
7 is formed spontaneously by intramolecular rearrange-
ment of 6. On the other hand, the formation of the
metallacycle 8 is understandable by isontrile insertion
in the Ti-CH2 bond of the asymmetric coordinated
complex 5. Formally, in the formation of 4 and 8 from
1, three molecules of isonitrile are consumed. Double-
insertion products derived from 1 are not observed.
Additionally, C,N-coordination modes, as expected for
early transition metals (type I),31 were not found. In
summary, these reactions demonstrate the great ver-
satility of 2 as building block in reactions with unsatur-
ated substrates. Particularly, the dynamic behavior of
cumulated bond systems in the coordination sphere of
transition metals is illustrated.
5
8
empirical formula C40H50N2Ti
C49H59N3Ti
fw
606.72
737.89
cryst size (mm)
cryst syst.
space group
a (Å)
0.70 × 0.4 × 0.45
monoclinic
P21/n
0.95 × 0.54 × 0.17
monoclinic
C2/c
9.3420(3)
23.1750(16)
b (Å); â (deg)
27.0745(13); 92.576(4) 8.9653(4); 91.069(8)
c (Å)
13.2827(5)
3356.2(2)
4
39.855(3)
8279.4(9)
8
cell vol V (Å3)
Z
F calcd (g cm-3
)
1.201
1.184
µ (mm-1
θrange (deg)
)
0.285
0.243
2.65-25.96
2.02-26.06
no. of indep reflns 6139 [R(int) ) 0.0347] 7476 [R(int) ) 0.0824]
no. of obsd reflns 5035
5700
[I>2σ(I)]
R(F) (%)
Rw(F) (%)
GOF
4.72
5.76
1.045
6.16
8.06
1.055
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations of the de-
scribed compounds were carried out under exclusion of air and
moisture using Schlenk line or glovebox techniques. Solvents
were distilled prior to use. (2,6-Me2C6H3)NC and cyclohexyl-
isonitrile were purchased from Aldrich and used without
further purification. Cp*2Ti(CHdCH2)Me (1) was synthesized
according to the published procedure.32a,b C, H, and N analyses
were performed at the Analytischen Laboratorien in Lindlar
(Germany); the C, H, and N analysis of 4 was made in the
Institut fu¨r Anorganische Chemie der RWTW Aachen. 1H
NMR and 13C NMR spectra were recorded on a Bruker AM
300 or Bruker 500 AVANCE spectrometer, and chemical shifts
are referenced to residual protons or carbons of the solvent or
to TMS. In the case of the complex 4 a Varian VXR-300
spectrometer was used. Electron impact (IE) mass spectra were
recorded on a Finnigan MAT 212 or on a Finnigan MAT CH
5-DF spectrometer for 4. IR spectra were taken with a BIO-
RAD FTS-7 spectrophotometer or, as in the case of the complex
4, with a Perkin-Elmer 1720X spectrophotometer, using KBr
pellets.
The X-ray diffraction analysis of 8 shows a planar
metallacyclopentane in which the titanium can be
considered as pseudotetrahedric with Ti-Cp* distances
of 2.106 and 2.114 Å and a Cp*-Ti-Cp* angle of 137.3°.
The Ti(1)-C(1) and Ti(1)-C(4) bond distances of 2.176
(2) and 2.275(2) Å, respectively, correspond to a single
Ti-Csp2 bond and compare well with other five-
membered ring compounds.17 The exocyclic double-bond
lengths N(1)-C(5) (1.241(3) Å), N(2)-C(3) (1.258(3) Å),
N(3)-C(4) (1.278(3) Å), and C(1)-C(5) (1.289(4) Å) are
in the expected range.24
The molecular ion (m/z 737) was observed in the
EIMS spectrum. The 1H NMR spectrum reveals a signal
for the Cp*-methyl protons indicating the planarity of
the titanacyclopentane ring. Instead of the character-
istic signals of the exo-methylene group found in 4, the
1H and 13C NMR spectra of 8 show a metallacycle
1
methylene group (1H, δ 3.41 (s); 13C, δ 42.4 ppm, J CH
) 128.4 Hz). The 13C NMR spectrum shows a signal at
233.0 ppm consistent with a σ-Ti-iminoacyl carbon. The
resonances of the R-carbon atom in the ketenimine
fragment and the iminoacyl carbon â to the titanium
center have similar chemical shifts (δ 169.2 and 169.5
ppm), and we have not attempted to assign them. The
IR spectrum shows absorptions at ν 1591 cm-1, assigned
to the CdN stretching, and ν 1955 cm-1 due to the >Cd
CdN stretching in the heterocumulene fragment. In
accord with the spectroscopic and structural data the
formation mechanism of 8 can be explained by the
insertion of two molecules of isonitrile into the Ti-CH2
bond of the η2-C,C-azabutatriene moiety in complex 5.
P r ep a r a tion of 4. To a -10 °C cooled solution of cyclo-
hexylisonitrile (0.59 mL, 4.83 mmol) in 30 mL of ether was
added a -40 °C cooled solution of Cp*2Ti(CHdCH2)Me (1) (0.58
g, 1.61 mmol) in 30 mL of diethyl ether. After 1 h at room
temperature, the dark brown solution was concentrated to
about 20 mL and cooled to 5 °C for 1 day to afford small black
crystals of 4 (0.36 g, 33%). Spectral and analytical data for 4:
mp 127-130 °C (dec); IR (KBr, cm-1) (CdX; X ) C, N) ν 1630
(m), 1596 (m), 1583 (m), 1543 (s); MS (EI, m/z, rel int) 671
([M+], 1%), 562 ([M+ - CNCy], 3%), 453 ([M+ - 2CNCy], 56%),
344 ([M+ - 3CNCy], 23%), 317 ([M+ - CNCy - C2H3], 100%);
1H NMR (300 MHz, C6D6, 27 °C) δ 1.83 (s, 30H, C5(CH3)5),
3
2.30-1.20 (m, 30H, HCy), 4.23, 3.59, 3.52 (tt, J HH ) 4 Hz, 10
2
Hz, 1H, >N-CH), 4.80, 4.54 (d, J HH ) 2 Hz, 1H, dCH2); 13C-
{1H} NMR (75 MHz, C6D6, 27 °C) δ 12.2 (C5(CH3)5), 25.9, 25.4,
24.3 (3-CCy), 26.7, 26.5, 26.4 (4-CCy), 35.7 (2-CCy), 64.5, 63.7,
59.5 (1-CCy), 107.4 (>CdCH2), 123.0 (C5(CH3)5), 149.0 (>Cd
CH2), 166.5 (>CdN), 228.0, 226.1 (Ti-C). Anal. Calcd for
Con clu sion s
Starting from the titanaallene intermediate [Cp*Tid
CdCH2] (2) and isonitriles RNC (R ) C6H11, 2,6-
Me2C6H3), the formation of metallacyclic systems with
radialene substructures is shown. An azabutatriene
complex, formed by [2+1] addition, could be isolated in
the form of the isonitrile adduct 5, which is character-
ized by a terminal η2-C-C bond coordination mode. This
fact is in accordance with the general behavior of type
III molecules, which are found to be thermodynamically
more stable than the symmetric coordinated butatriene
derivatives (type II).1b However, the formation of the
C
43H65N3Ti (Mτ ) 671.89): C, 76.87; H, 9.75; N, 6.25. Found:
C, 77.11; H, 10.11; N, 6.14.
P r ep a r a tion of 5. (2,6-Me2C6H3)NC (0.31 g, 2.39 mmol)
solved in 40 mL of precooled hexane was added to a solution
of 1 (0.43 g, 1.19 mmol) in hexane (30 mL) at -78 °C. The
reaction mixture was stirred and warmed to room tempera-
(31) Venne-Dunker, S.; Ahlers, W.; Erker, G.; Fro¨hlich, R. Eur. J .
Inorg. Chem. 2000, 1671-1678.
(32) (a) Beckhaus, R.; Oster, J .; Wagner, T. Chem. Ber. 1994, 127,
1003-1013. (b) Luinstra, G. A.; Teuben, J . H. Organometallics 1992,
11 (1), 1793-1801.

Chemistry of Radialene Type Molecules
Organometallics, Vol. 20, No. 7, 2001 1359
3
ture. After that, the solution was cooled to 5 °C for one night
to afford dark orange crystals suitable for X-ray diffraction
analysis (470 mg, 65%). Spectral and analytical data for 5: mp
102-105 °C (dec); IR (KBr, cm-1) ν 2066 s (CtNR), 2000 s
(RNdCdC), 1589 s (CdNR); MS (EI, m/z, rel int) 606 [(M+),
91%], 486 [(M+ - NR), 44%], 475 [(M+ - CNR), 33%], 340 [(M+
- CNR - C5Me5), 37%], 318 [(M+ - CNR-RNCdCdCH2),
10%], 303 [(M+ - CNR-RNCdCdCH2-Me), 100%]; 1H NMR
(500 MHz, C6D6, 27 °C) δ 1.49 (s, 2H, dC-CH2), 1.67 (s, 30H,
7.4 Hz, 1H, p-Harom.), 6.90, 6.95, 6.96 (d, J HH ) 7.4 Hz, 2H,
m-Harom.); 13C NMR (125 MHz, C6D6, 27 °C) δ 13.0 (q, J ) 126.1
Hz, C5(CH3)5), 19.59, 19.6, 22.5 (qd, J ) 125.3 Hz, 2,6-
Me2C6H3), 42.4 (t, J ) 128.4 Hz, >CH2), 86.0 (t, J ) 7.2 Hz,
2
>CdCdNR), 125.7 (m, C5(CH3)5), 121.3, 123.2, 123.5, 123.8,
126.1, 127.9, 128.3, 128.4, 128.6, 128.7, 130.3 (m, Carom.), 144.4,
147.6, 156.0 (m, Cipso), 169.2, 169.5 (s, >CâdNR, dCdC-NR),
233.0 (s, Ti-CR). Anal. Calcd for C49H59N3Ti (Mτ ) 737.89):
C, 79.76; H, 8.06; N, 5.69. Found: C, 79.67, H, 8.04; N, 5.64.
Cr ysta l Str u ctu r e Deter m in a tion s. Data for the struc-
tures 5 and 8 were collected on a STOE-IPDS diffractometer
with graphite-monochromated Mo KR radiation (λ ) 0.71073).
A summary of crystals data and intensity collection and
refinement parameters is reported in Table 3.
Intensity measurements were performed at 193(2) K in
sealed glass capillaries. The structure of all complexes was
solved by direct phase determination (SHELXL 97)33 and
refined on F2 (SHELXL 97)33 with anisotropic thermal param-
eters for all non-hydrogen atoms.
3
C5(CH3)5), 2.29, 2.71 (s, 6H, 2,6-Me2C6H3), 6.74, 7.15 (d, J HH
3
) 7.6 Hz, 2H, m-Harom.) 6.81, 6.95 (t, J HH ) 7.5 Hz, 1H,
p-Harom.); 13C NMR (125 MHz, C6D6, 27 °C) δ 11.7 (q, J ) 125.2
Hz, C5(CH3)5), 19.7 (q, J ) 122.7 Hz, 2,6-Me2C6H3), 43.5 (t, J
≈ 152 Hz, dC-CH2), 66.9 (s, dC-CH2), 110.5 (m, C5(CH3)5),
122.1 (d, m-Carom.), 128.3 (d, p-Carom.), 128.4 (d, p-Carom.), 128.7
(d, m-Carom.), 130.0 (m, o-Carom.), 134.6 (m, o-Carom.), 148.7 (s,
C
ipso), 173.6 (s, CtNR), 231.4 (s, RNdCdC-CH2). Anal. Calcd
for C40H50N2Ti (Mτ ) 606.68): C, 79.18; H, 8.31; N, 4.61.
Found: C, 79.02, H, 8.49; N, 4.50.
P r ep a r a tion of 7. Preparation is similar to that of 5 from
0.42 g (1.16 mmol) of Cp*2Ti(CHdCH2)Me and (2,6-Me2C6H3)-
NC (0.15 g, 1.16 mmol) in hexane (60 mL). A green crystalline
solid of 7 was obtained with a 78% yield. Spectral and
analytical data for 7: mp 95-100 °C (dec); IR (KBr, cm-1) ν
1672, 1634 (w, CdC), 1586 (s, CdN); MS (EI, m/z, rel int) 475
[(M+), 100%], 340 [(M+ - C5Me5), 63%], 303 [(M+ - C12H14N),
11%], 181 [(M+ - C12H14N-C5Me5), 15%]; 1H NMR (500 MHz,
C6D6, 27 °C) δ -0.51 (ws, 3H, 2,6-Me2C6H3), 1.07, 1.47, 1.70,
2.34 (s, 3H, C5(CH3)5CH2), 1.62 (s, 15H, C5(CH3)5), 2.50 (ws,
Com p u ta tion a l Deta ils. The DFT calculations have been
carried out using the hybrid functional Becke3LYP,34 employ-
ing the program package Gaussian 98.35 All structures were
optimized and verified as local minima at the B3LYP/6-31G-
(d) level of theory.
Ack n ow led gm en t. This work was supported by the
Deutsche Forschungsgemeinschaft, the Karl-Ziegler
Stiftung der GDCH, and the Fonds der Chemischen
Industrie. C.S. thanks the Ministerio de Educacio´n y
Cultura and the Alexander von-Humboldt-Stiftung for
a postdoctoral fellowship.
2
3H, 2,6-Me2C6H3), 3.29, 3.92 (dd, J HH ) 14 Hz, 1H, C5-
(CH3)5CH2), 4.04 (m, 1H, J HH ) 1.5 Hz, -CdCH2), 4.26 (m,
1H, J HH ) 1.8 Hz, -CdCH2), 4.34 (s, 1H, -CHdNAr), 6.41,
(t, 1H, p-Harom.), 6.68, 6.84 (ws, 1H, m-Harom.); 13C NMR (125
MHz, C6D6, 27 °C) δ 9.9, 10.5, 12.3, 14.8 (q, J ) 125.6 Hz,
C5(CH3)4CH2), 11.8 (q, J ) 125.5 Hz, C5(CH3)5), 23.1 (qd, J )
124.4 Hz, 2,6-Me2C6H3), 31.2 (t, J ) 124.8 Hz, C5(CH3)4CH2),
98.5 (t, J ) 155.8 Hz, -CdCH2), 116.7 (d, J ) 157.4 Hz, -CHd
NAr), 114.5, 124.1, 128.3, 156.8 (m, J ) 157.1 Hz, 2,6-
Me2C6H3), 114.7, 116.7, 121.6, 129.7, 131.8 (m, C5(CH3)4CH2),
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystal structure details for 5 and 8 are available free of charge
via the Internet at http://pubs.acs.org. Additionally crystal-
lographic data (excluding structure factors) for the structures
5 and 8 have been deposited with the Cambridge Data Centre
as supplementary publications nos. CCDC 151666 (5) and
151665 (8). Copies of the data can be obtained free of charges
on application to CCDC, 12 Union Road, Cambridge CB21EZ,
U.K. (fax (+44) 1223-336-033; e-mail deposit@aadc.cam.ac.uk).
120.9 (m, C5(CH3)5), 160.8 (s, -CdCH2). Anal. Calcd for C31H41
-
NTi (Mτ ) 475.52): C, 78.29; H, 8.69; N, 2.94. Found: C, 78.10,
H, 8.88; N, 2.80.
OM000929S
P r ep a r a tion of 8. A 150 mL Schlenk flask was charged
with Cp*2Ti(CHdCH2)Me (1) (1.00 g, 2.77 mmol) in diethyl
ether (50 mL) and cooled at -78 °C. A precooled solution of
(2,6-Me2C6H3)NC (1.10 g, 2.77 mmol) in 40 mL diethyl ether
was added, and the reaction mixture was allowed to warm to
room temperature. The solution was filtered and concentrated
under reduced pressure. After one night at room temperature,
black crystals of 8 (1.79 g, 87%) were isolated. Spectral and
analytical data for 8: mp 137-140 °C (dec); IR (KBr, cm-1) ν
1955 (s, CdCdN), 1591 (m, CdN); MS (EI, m/z, rel int) 737
[(M+), 16%], 607 [(M+ - CNR), 41%], 602 [(M+ - C5Me5),
100%], 475 [(M+ - 2CNR), 19%], 471 [(M+ - C5Me5 - CNR),
19%], 340 [(M+ - C5Me5 - 2CNR), 31%]; 1H NMR (500 MHz,
(33) Sheldrick, G. M. SHELXS97, Programm for Structure Solutions;
University of Go¨ttingen, 1997.
(34) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785-
789. (b) Becke, A. D. J . Chem. Phys. 1993, 98, 5648-5652.
(35) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.;
Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .; Barone, V.;
Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford,
S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma,
K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J . B.;
Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.;
Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen, W.; Wong, M.
W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.; Pople, J . A.
Gaussian 98, Revision A.7; Gaussian, Inc.: Pittsburgh, PA, 1998.
C6D6, 27 °C) δ 1.84 (s, 30H, C5(CH3)5), 2.10, 2.23, 2.44 (s, 6H,
3
2,6-Me2C6H3), 3.41 (s, 2H, >CH2), 6.74, 6.81, 6.85 (t, J H,H
)