Serendipitous synthesis of [η 5-1,2,4,5,6-pentakis(trimethylsilyl)cyclohexadienyl]-(η 5-cyclopentadienyl)titanium(II) and its 4-alkyl derivatives

Article abstract of DOI:10.1021/om950760w

The titanium-magnesium complex [(η⁵-C₅H₅)Ti][μ-η ²:η²-C₂(SiMe₃)₂] ₂[η⁵-C₅H₅Mg] (1) containing perpendicularly bridging bis(

Full text of DOI:10.1021/om950760w

1268
Organometallics 1996, 15, 1268-1274
Ser en d ip itou s Syn th esis of
[η5-1,2,4,5,6-P en ta k is(tr im eth ylsilyl)cycloh exa d ien yl]-
(η5-cyclop en ta d ien yl)tita n iu m (II) a n d Its 4-Alk yl
Der iva tives
Vojtech Varga,† Miroslav Pola´sˇek,† J o¨rg Hiller,‡ Ulf Thewalt,‡
Petr Sedmera,§ and Karel Mach*,†
J . Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejsˇkova 3, 182 23 Prague 8, Czech Republic, Universita¨t Ulm, Sektion fu¨r Ro¨ntgen- und
Elektronenbeugung, D-89069 Ulm, Germany, and Institute of Microbiology, Academy of
Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic
Received September 25, 1995X
The titanium-magnesium complex [(η5-C5H5)Ti][µ-η2:η2-C2(SiMe3)2]2[(η5-C5H5)Mg] (1)
containing perpendicularly bridging bis(trimethylsilyl)acetylene ligands reacts with excess
(trimethylsilyl)ethyne to give mainly (η5-1,2,4,5,6-pentakis(trimethylsilyl)cyclohexadienyl)-
(η5-cyclopentadienyl)titanium(II) (2). The X-ray crystal structure of 2 showed that the SiMe3
group at C(6) is in an exo-position and that the planes of the Cp ring and of the dienyl part
of the Chx ring are nearly parallel. The dihedral angle 4.9° between these planes is mainly
due to tilting of the cyclohexadienyl ring by the C(1) and C(5) side toward the titanium
atom. Analogous reactions of 1 with tert-butylethyne, cyclohexylethyne, 1-hexyne, and
phenylethyne afforded (η5-1,2,5,6-tetrakis(trimethylsilyl)cyclohexadienyl)(η5-cyclopenta-
dienyl)titanium(II) derivatives 3-6 containing the 1-alkyne substituent at C(4).
In tr od u ction
cyclohexadienyl anion (Dmchx).6 In this way, bis(η5-
6,6′-dimethylcyclohexadienyl)metal (Dmchx)2M) com-
plexes were obtained for Ti, V, Cr, Fe,7a and Mo.7b Of
the titanium complexes, so far only (Dmchx)2Ti,
(Dmchx)2Ti(PF3), and (Dmchx)2Ti(CO) have been de-
scribed and the X-ray crystal structure of the carbonyl
complex has been determined.7a The η5-cyclohexadienyl
complexes are closely related to both the η5-cyclo-
pentadienyl (Cp) and open U-shaped η5-pentadienyl
complexes by structural features, and their chemical
properties classify them as intermediate compounds
between both types of metallocenes. Therefore, they
were included in a comprehensive review on transition-
metal η5-pentadienyl complexes emphasizing the com-
parison of open metallocenes and metallocenes.8 It is
of interest that contrary to all other transition metal
elements 14-electron titanocene and zirconocene com-
pounds have only recently been characterized as open
1,5-bis(trimethylsilyl)pentadienyl derivatives.9
η5-Cyclohexadienyl complexes are widely accessible
by nucleophilic addition of H- or R- to [(arene)M(L)]+
complexes, e.g., for L ) arene and M ) Mn, Fe, Re, Ru,1a
Rh, Ir, Ru,1b and Fe,1c for L ) cyclopentadienyl and M
) Fe, Co, Rh2a and Ru,2b for L ) (CO)4 and M ) V,3a
and for L ) (CO)3 and M ) Mn,3b Rh,3c and Re.3d An
alternative access is based on the hydrogen abstraction
from η4-cyclohexadiene e.g., in the carbonyl complexes
of Fe4ab and Mn.4c
The mechanisms of the formation of metal η5-cyclo-
hexadienyl complexes were thoroughly reviewed.5
Direct metathetical synthesis from transition-metal
halides and main group metal cyclohexadienide salts
is generally applicable using the stable 6,6′-dimethyl-
* To whom correspondence should be addressed.
† J . Heyrovsky´ Institute.
Here we report an unusual synthesis of half-open 14-
electron (η5-1,2,4,5,6-pentasubstituted cyclohexadienyl)-
(η5-cyclopentadienyl)titanium(II) compounds, whose cy-
clohexadienyl ligands are generated from acetylenic
precursors at the (η5-cyclopentadienyl)titanium(II) moi-
ety. These transient species arise from the Ti-Mg
complex containing two perpendicularly bridging bis-
(trimethylsilyl)acetylene ligands, [(η5-C5H5)Ti][µ-η2:η2-
C2(SiMe3)2]2[(η5-C5H5)Mg]10 (1), upon interaction with
1-alkynes.
‡ Universita¨t Ulm.
§ Institute of Microbiology.
X Abstract published in Advance ACS Abstracts, J anuary 15, 1996.
(1) (a) J ones, D.; Pratt, L.; Wilkinson, G. J . Chem. Soc. 1962, 4458-
4463. (b) Grundy, S. L.; Smith, A. J .; Adams, H.; Maitlis, P. M. J . Chem.
Soc., Dalton Trans. 1984, 1747-1754. (c) Helling, J . F.; Braitsch, D.
M. J . Am. Chem. Soc. 1970, 92, 7207-7208.
(2) (a) Khand, I. U.; Pauson, P. L.; Watts, W. E. J . Chem. Soc. C
1969, 2024-2030 and references therein. (b) Crocker, M.; Froom, S.
F. T.; Green, M.; Nagle, K. R.; Orpen, A. G.; Thomas, D. M. J . Chem.
Soc., Dalton Trans. 1987, 2803-2814.
(3) (a) Calderazzo, F. Inorg. Chem. 1966, 5, 429-434. (b) Winkhaus,
G.; Pratt, L.; Wilkinson, G. J . Chem. Soc. 1961, 3807-3813. (c)
Cetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Torroni, S.; Atwood,
J . L.; Hunter, W. E.; Zaworotko, M. J . J . Organomet. Chem. 1980, 188,
C31-C35. (d) Bird, P. H.; Churchill, M. R. J . Chem. Soc., Chem.
Commun. 1967, 777-778.
(4) (a) Fischer, E. O.; Fischer, R. D. Angew. Chem. 1960, 72, 919.
(b) Paquette, L. A.; Daniels, R. G.; Gleiter, R. Organometallics 1984,
3, 560-567. (c) Winkhaus, G.; Wilkinson, G. Proc. Chem. Soc. 1960,
311-312.
(5) Kane-Maguire, L. A. P.; Honig, E. D.; Swigart, D. A. Chem. Rev.
1984, 84, 525-543.
(6) Bates, R. B.; Gosselink, D. W.; Kaczynski, J . A. Tetrahedron Lett.
1967, 199-204.
(7) (a) DiMauro, P. T.; Wolczanski, P. T. Organometallics 1987, 6,
1947-1954. (b) DiMauro, P. T.; Wolczanski, P. T.; Pa´rka´nyi, L.; Petach,
H. H. Organometallics 1990, 9, 1097-1106.
(8) Ernst, R. D. Chem. Rev. 1988, 88, 1255-1291.
(9) Gedridge, R. W.; Arif, A. M.; Ernst, R. D. J . Organomet. Chem.
1995, 501, 95-100.
0276-7333/96/2315-1268$12.00/0 © 1996 American Chemical Society

(η5-Cyclopentadienyl)titanium(II) Complexes
Organometallics, Vol. 15, No. 4, 1996 1269
Ta ble 1. 1H NMR Da ta (δ) for Com p ou n d s 2-6a
Exp er im en ta l Section
group multiplicity
2
3b
4b
5b
6b
Gen er a l Da ta . Manipulation with all air-sensitive re-
agents, synthesis, isolation, and spectroscopic measurements
were carried out under vacuum using all-sealed glass devices
equipped with breakable seals. The solvents THF, hexane,
toluene, and benzene-d6 (95.5% atom % D) (all Aldrich) were
dried by refluxing over LiAlH4 and stored as solutions of
dimeric titanocene,11 (C10H8)[(C5H5)TiH]2, under metal valves
on a high-vacuum line. Terminal acetylenes (trimethylsilyl)-
ethyne, tert-butylethyne, 1-hexyne, cyclohexylethyne, and
phenylethyne (Aldrich) were purified by vacuum distillation
and by storing for several hours as solutions of the dimeric
titanocene. Then they were distilled into storage ampules on
a vacuum line. The compound [(η5-C5H5)Ti][µ-η2:η2-C2(SiMe3)2]2-
[(η5-C5H5)Mg] (1) was obtained from the reduction of (C5H5)2-
TiCl2 by excess magnesium in the presence of at least 2 equiv
of bis(trimethylsilyl)acetylene.10 1H and 13C NMR spectra were
measured on a Varian VXR-400 spectrometer (400 and 100
MHz, respectively) in C6D6 at 25 °C. Samples were referenced
to the solvent signal (δH 7.15, δC 128.00 ppm). The assignment
of spectra is based on results of APT, COSY, delay-COSY,
HOM2DJ , and HETCOR experiments. ESR spectra were
recorded on an ERS-220 spectrometer (German Academy of
Sciences, Berlin) in the X-band at room temperature. Infrared
spectra of hexane solutions were registered on a UR-75
instrument (Zeiss, J ena, Germany) using KBr cuvettes filled
under argon. KBr pellets of crystalline 2 were prepared under
purified nitrogen in a glovebox (Braun) and were measured
in an air-protecting cuvette on a Mattson Galaxy 2020 IR
spectrometer. UV-vis spectra were recorded on a Varian Cary
17D spectrometer in the range 270-2000 nm using all-sealed
quartz cells (Hellma). Elemental analyses were carried out
only for crystalline products of high purity.
Cp
s
s
s
s
s
s
s
6.217c 6.237c 6.173c 6.110c
0.135 -0.044 -0.298
6.100c
0.411
5.640
sp3-CH
sp2-CH
0.194
5.099
5.673
5.713
5.381
SiMe3
0.020e 0.013
0.030 -0.024 -0.125
d
0.224e 0.031
0.055
0.243
0.272
0.044
0.242
0.306
0.028
0.213
0.336
0.250
0.216
0.279
a
b
400 MHz, 25 °C, C6D6. Additional signals of substituents
from the terminal acetylene are as follows. 3: 1.148 (s, 9H, t-Bu).
4: 0.484 (dm, J ) 12.4 Hz, Hâ-eq), 0.692 (ddd, J ) 12.6, 12.4, 12.0,
3.4 Hz, Hâ-ax), 1.046 (m, Hδ-ax), 1.072 (m, Hγ-ax), 1.313 (m, Hγ-
ax), 1.545 (m, Hγ-eq), 1.583 (m, Hδ-eq), 1.704 (dddd, J ) 13.0, 13.0,
12.8, 3.6, Hâ-ax), 1.811 (m, Hγ-eq), 2.247 (dddd, J ) 12.0, 11.6,
3.2, 3.2 Hz, HR), 2.562 (dm, J ) 13.0 Hz, Hâ-eq). Long-range
coupling between the proton at 5.381 ppm and protons at 2.247
ppm (HR) and 0.692 ppm (Hâ-ax) was detected by delay-COSY. 5:
0.901 (t, 3 H, J ) 7.0 Hz, Me), 1.315 (m, 2 H-γ), 1.361 (m, H-â),
1.584 (m, H-â′), 1.834 (ddd, J ) 14.2, 11.2, 5.2 Hz, H-R), 2.660
(ddd, J ) 14.2, 10.9, 4.8 Hz, H-R′). Long-range coupling between
the proton at 5.099 ppm and R-protons of the side chain (2.660
and 1.834 ppm) was detected by delay-COSY. 6: 6.906 (2H, m,
Ph-ortho), 6.944 (1 H, m, Ph-para), 7.073 (2 H, m, Ph-meta). c 5
d
H. 9 H if not otherwise stated. e 18 H.
Ta ble 2. 13C NMR Da ta (δ) for Com p ou n d s 2-6a
group multiplicity
2
3b
109.80c 110.26c 109.89c 109.76c 110.83c
26.08 25.07 23.01 25.66 25.78
4b
5b
6b
Cp
d
d
d
s
sp3-CH
sp2-CH
sp2-C
121.39 114.00 109.57 110.92 114.80
118.27d 106.29 111.57 112.78 111.63
132.48d 112.90 119.47 120.41 115.06
121.91 123.36 123.27 120.65
s
s
s
132.76 128.97 128.51 121.69
2.34e
2.87f
3.20f
2.49e
3.14e
3.34e
5.17e
2.65e
3.15e
3.30e
3.63e
2.47e
2.91e
2.97e
3.48e
2.41e
2.65e
2.87e
3.53e
P r ep a r a tion of [η5-C6H2(SiMe3)5](η5-C5H5)TiII (2). (Tri-
methylsilyl)acetylene (1.5 mL, 10 mmol) was added to a
solution of [(C5H5)Ti][µ:η2:η2-C2(SiMe3)2]2[Mg(C5H5)] (1) (1.5
mmol) in toluene (15 mL). The red color of the solution
changed immediately to brown-green. After 2 h of stirring at
room temperature, all volatiles were evaporated at a maximum
60 °C under vacuum into a trap cooled by liquid nitrogen. The
residue was extracted with 20 mL of hexane. The solution
was separated, and its volume was reduced to 5 mL. The clear
solution was transfered to a multiarm crystallization vessel.
Slow crystallization of 2 was induced by slight cooling of the
arm used for condensing solvent. The resulting polycrystalline
solid was washed by condensing hexane vapors until washings
were bright green. The remainder was dissolved in hexane,
and the procedure was repeated. The bright green crystals
were dried in vacuum and collected. The yield of crystalline
2 was 0.41 g (50%). The mother liquor contained another
portion of 2 (ca. 20-30% of the overall titanium content), but
its isolation was not effective. 2: EI-MS (direct inlet, 80-130
°C, m/z (%)) 552 (M+•, 3.5), 479 (100), 407 (3), 327 (12), 311
(19), 113 (21), 73 (59); analysis, 552.2357, error +3.7 × 10-3
for C26H52Si5Ti, 479.1905, error +1.7 × 10-3 for C23H43Si4Ti,
327.0876, error +2.4 × 10-3 for C14H27Si3Ti, 311.0564, error
+2.3 × 10-3 for C13H23Si3Ti, 279.1396, error +2.5 × 10-3 for
SiMe3
q
q
q
q
a
b
100 MHz, 25 °C, C6D6. Additional signals of substituents
from the terminal acetylene are as follows. 3: 34.53 (q, 3C, Me),
38.35 (s). 4: 26.42 (t, C-δ), 27.70 (t, C-γ′), 27.83 (t, C-γ), 34.54 (t,
C-â′), 39.15 (t, C-â), 46.47 (d, C-R). 5: 14.18 (q, C-δ), 23.35 (t,
C-γ), 34.65 (t, C-â), 38.43 (t, C-R). 6: 126.09 (d, Ph-para), 127.83
(d, 2 C, Ph-meta), 129.36 (d, 2 C, Ph-ortho), 146.48 (s, Ph-ipso).c 5
d
C. 2 C. e 3 C. f 6 C.
P r ep a r a tion of [η5-C6H2(ter t-C4H9)(SiMe3)4](η5-C5H5)Ti
(3). The same procedure as for 2 afforded 0.18 g (22%) of green
crystalline solid. The overall production of 3 was estimated
to be more than 60%, but its purification by crystallization
was extremely difficult due to high solubility in hexane of 3
and byproducts. 3: EI-MS (direct inlet, 80-130 °C, m/z (%))
536 (M+•, 4), 479 (2), 463 (100), 311 (13), 295 (7), 279 (15), 113
(24), 73 (70); analysis, 536.2618, error +0.7 × 10-3 for C27H52
-
Si4Ti, 463.2148, error +0.4 × 10-3 for C24H43Si3Ti, 311.1125,
error +0.5 × 10-3 for C15H27Si2Ti; 1H NMR and 13C NMR
spectra are given in Tables 1 and 2, respectively; IR (hexane)
1246 (vs), 1200 (m), 1150 (w), 1106 (m), 1058 (w), 1013 (s),
942 (s), 888 (m,sh), 836 (vs), 790 (s), 772 (s), 750 (s), 684 (m),
642 (m), 584 (w), 574 (w), 515 (w), 436 (w); UV-vis (hexane,
C
14H27Si3; 1H NMR and 13C NMR spectra are listed in Tables
1 and 2, respectively; IR (KBr) 2951 (s), 2899 (s), 1447 (m),
1402 (s), 1246 (vs), 1150 (m), 1107 (s), 1055 (m), 1013 (m), 949
(m), 837 (vs), 785 (s), 748 (s), 681 (s), 635(s), 588 (w), 580 (w),
511 (m), 500 (m), 478 (m), 442 (w), 419 (m) cm-1; IR (hexane)
1262 (sh) in addition to the bands found in KBr (within (3
cm-1); UV-vis (hexane, 23 °C) 318, 350 sh, 412, 565, 813 nm;
EDAX (KR) Ti:Si ratio 1:4-6. Anal. Calcd for C26H52Si5Ti:
C, 56.5; H, 9.5. Found: C, 56.8; H, 9.6.
23 °C) 315 sh, 415 sh, 580, 840 sh, nm. Anal. Calcd for C27H52
Si4Ti: C, 60.4; H, 9.5. Found: C, 60.8; H, 9.7.
-
P r ep a r a tion of [η5-C6H2(C6H11)(SiMe3)4](η5-C5H5)Ti (4).
The same procedure as for 2 afforded a green waxy solid which
crystallized on cooling to -18 °C. The yield of the green waxy
solid was ca. 0.4 g (50%). The portion of 4 remaining in the
mother liquor was estimated to be another 10-20%. 4: EI-
MS (direct inlet, 80-130 °C, m/z (%)) 562 (M+•, 4), 479 (2),
463 (100), 311 (13), 295 (7), 279 (15), 113 (24), 73 (70); 1H NMR
and 13C NMR spectra are collected in Tables 1 and 2,
respectively; IR (hexane) 1262 (m, sh), 1248 (s), 1150 (w), 1106
(s), 1058 (w), 1013 (s), 961 (m), 889 (m, sh), 870 (s, sh), 838
(vs), 787 (s), 777 (s), 750 (s), 682 (m), 637 (m), 583 (w), 510
(10) Varga, V.; Mach, K.; Schmid, G.; Thewalt, U. J . Organomet.
Chem. 1993, 454, C1-C4. (b) Varga, V.; Mach, K.; Schmid, G.; Thewalt,
U. J . Organomet. Chem. 1994, 475, 127-137.
(11) Antropiusova´, H.; Dosedlova´, A.; Hanusˇ, V.; Mach, K. Transition
Met. Chem. 1981, 6, 90-93.

1270 Organometallics, Vol. 15, No. 4, 1996
Varga et al.
Ta ble 4. Cr ysta llogr a p h ic Da ta for 2
Ta ble 3. EP R P a r a m eter s of P r esu m ed Ti(III)-Mg
Tw eezer Com p lexes
formula
fw
C26H52Si5Ti
553.00
[Cp 2Ti(η1-CtCR)2]-[Mg(CtCR]+ a
cryst color, habit
cryst dimens (mm)
cryst system
space group
a (Å)
green, irregular
0.3 × 0.4 × 0.6
monoclinic
P21/c, No. 14
10.400(9)
32.693(22)
10.415(10)
110.80(5)
4
3311(7)
1.11
4.06
48
4521
4036
3014
292
0.053, 0.057
-0.25 to +0.31
compd
R
g
aH (G)
aTi (G)
2a
SiMe3
SiMe3
t-C4H9
c-C6H11
n-C4H9
phenyl
1.9920
1.9935
1.9907
1.9912
1.9912
1.9916
0
0
0
8.6
7.3
9.3
9.2
9.0
8.8
b
3a
4a
5a
6a
2.7 (triplet)
2.3 (quintuplet)
0
b (Å)
c (Å)
â (deg)
a
b
Solutions in hexane, 23 °C. Parameters for [(C5HMe4)2Ti(η1-
CtCSiMe3)2]-[Mg(THF)Cl]+ (toluene, 20 °C).12
Z
V (Å3)
D
calc (g‚cm-3
)
µ(Mo KR), (cm-1
2θmax (deg)
)
(m), 478 (w), 458 (w), 438 (w); UV-vis (hexane, 23oC) 350 sh,
410, 575, 865 nm.
tot. no. of reflcns
P r ep a r a t ion of [η5-C6H 2(n -C4H 9)(SiMe3)4](η5-C5H 5)Ti
(5). The same procedure as for 2 afforded a dirty green waxy
solid. Yield: 0.16 g (20%). 5: EI-MS (direct inlet, 80-100oC,
m/z (%)) 536 (M+•, 2.5), 463 (100), 461 (30), 309 (11); IR
(hexane) 1260 (s, sh), 1246 (vs), 1150 (w), 1116 (s), 1050 (w),
1011 (s), 962 (s), 840 (vs), 787 (s), 778 (s, sh), 750 (s), 683 (s),
636 (s), 510 (m); 1H NMR and 13C NMR spectra are described
in Tables 1 and 2, respectively. The presence of impurities
was discernible from both the NMR spectra and UV-vis
spectra. The latter showed the absorption bands of 5 at 570
and 860 nm as shoulders on the background increasing in
intensity to shorter wavelengths.
no. of unique reflcns
reflcns with Fo g 2σ(Fo)
no. of params refined
a
residuals: R; Rw
resid density (e/Å3)
a
For the 3014 reflections with Fo g 2σ(Fo); 2θ e 48°.
(trimethylsilyl)benzene, apparently 1,2,4- and 1,3,5-isomers.
By analogy with the titanium-catalyzed cyclotrimerization of
1-alkynes14 the unsymmetrical isomer should be prevailing.
In addition, tetrakis(trimethylsilyl)benzene was also detected
in a comparable quantity. This was isolated by liquid column
chromatography as a crystalline solid and identified to be the
1,2,4,5-isomer by comparing its EI-MS and 1H and 13C NMR
spectra with the authentic compound.15 Volatiles from the
reaction mixture for obtaining 4 were distilled off under
vacuum at room temperature, the residue was dissolved in a
minimum amount of hexane, and 4 was crystallized out. The
main portion of the mother liquor was quenched by water, the
organic products were extracted by hexane and the solvent
was evaporated. The resulting white solid was analyzed by
MS from direct inlet. The main product was tris(tri-
methylsilyl)cyclohexylbenzene: EI-MS (direct inlet, 130-150
°C, m/z (%)) 376 (M+•), 361, 345, 289, 279, and 273. Peaks
attributable to tris(cyclohexyl)benzene were also registered
(m/z 324 M+• and fragment ions). Both types of organic
byproducts were detected as impurities in the mass spectrum
of 6 (see above).
X-r a y Sin gle-Cr ysta l An a lysis of 2. A crystal fragment
was mounted into a Lindemann glass capillary under purified
nitrogen in a glovebox (Braun) and was sealed by wax. The
X-ray measurements were carried out on a Phillips PW 1100
four-circle diffractometer. Intensity data were collected by the
θ/2θ method using graphite-monochromated Mo KR radiation
(λ ) 0.710 69 Å) at room temperature. The positions of the Ti
and Si atoms were determined by the Patterson method.
Atomic coordinates and anisotropic thermal parameters of all
non-hydrogen atoms were refined by the least-squares method.
Hydrogen atoms were constrained to idealized geometries with
a C-H distance of 1.08 Å. The PC ULM package16 was used
for all calculations. Crystallographic data for 2 are listed in
Table 4. Atomic coordinates of non-hydrogen atoms are given
in Table 5.
P r ep a r a tion of [η5-C6H2(C6H5)(SiMe3)4](η5-C5H5)Ti (6).
The same procedure as for 2 gave a green waxy solid. Yield:
0.14 g (16%). 6: EI-MS (direct inlet, 130-140 °C, m/z (%)) 556
(M+•; 3), 483 (100), 411 (4), 331 (9), 315 (18), 113 (18), 73 (the
sample contained triphenylbenzene (m/z 306, M+•) and mainly
tris(trimethylsilyl)phenylbenzene (m/z 370, M+• not observed,
355, 339, 283, 267) which contributed to the intensity of m/z
73 in the spectrum of 6); H NMR and 13C NMR spectra are
1
reported in Tables 1 and 2, respectively; IR (hexane) 1597 (m),
1265 (m, sh), 1250 (s), 1148 (w), 1108 (s), 1060 (w), 1013 (w),
960 (m), 896 (m, sh), 843 (vs), 792 (s), 784 (s), 755 (s), 703 (s),
676 (m), 640 (w), 584 (w), 450 (w), 417 (w); UV-vis (hexane,
23oC) 315, 360 sh, 420, 580, 860 nm.
P a r a m a gn etic Byp r od u cts. Mother liquors from crystal-
lization of 2-6 were diluted by hexane, and their EPR spectra
were measured at room temperature. The spectra revealed
the presence of one major type of paramagnetic products which
were denoted 2a -6a . Their EPR parameters are collected in
Table 3. High g-values 1.9907-1.9920, narrow line widths
∆Hpp ) 1.5-3.0 G, and aTi ) 8.6-9.3 G are close to the
parameters found for the TiIII-Mg tweezer complex [(η5-
C5HMe4)2Ti(η1-CtCSiMe3)2]-[Mg(THF)Cl]+ (toluene, 22 °C: g
) 1.9935, ∆Hpp ) 2.0 G, aTi ) 7.3 G).12 Therefore the
byproducts are proposed to be the [(η5-C5H5)2Ti(η1-CtCR)2]-[Mg-
(CtCR]+ complexes with acetylide groups derived from the
corresponding 1-alkynes. The hyperfine splittings observed
in the spectra of 4a (triplet) and 5a (quintuplet) (Table 3) are
consistent with the coupling to 2 and 4 equivalent protons on
the R-carbon atoms of the substituents at two equivalent
acetylide tweezer arms. This coupling has been recently
observed in the [(η5-C5Me5)2Ti(η1-CtCR)2]-[Mg(CtCR]+ com-
plexes generated in the (η5-C5Me5)2TiCl2/i-PrMgCl/THF/1-
alkyne catalytic systems for linear head-to-tail dimerization
of 1-alkynes or by the interaction of [(C5Me5)2Ti(η1-CtCSiMe3)2]--
[Mg(THF)Cl]+ with the above mentioned 1-alkynes.13
Resu lts a n d Discu ssion
Addition of a 7-fold excess of 1-alkynes to [(η5-C5H5)-
Ti][µ-η2:η2-C2(SiMe3)2]2[(η5-C5H5)Mg] (1) in toluene re-
Or ga n ic Byp r od u cts. Volatiles from the reaction mixture
for obtaining 2 were distilled in vacuum at a maximum
temperature 60 °C overnight into a trap cooled by liquid
nitrogen. Then, most of hexane was pumped off. GC MS of
the distillate revealed a mixture of two isomers of tris-
(14) Calderazzo, F.; Marchetti, F.; Pampaloni, G.; Hiller, W.;
Antropiusova´, H.; Mach, K. Chem. Ber. 1989, 122, 2229-2238.
(15) Mach, K.; Turecˇek, F.; Antropiusova´, H.; Hanusˇ, V. Organo-
metallics 1986, 5, 1215-1219.
(16) Bru¨ggemann, R.; Debaerdemaeker, T.; Mu¨ller, B.; Schmid, G.;
Thewalt, U. ULM-Programmsystem (1. J ahrestagung der Deutschen
Gesellschaft fu¨r Kristallografie, Mainz, J une 9-12, 1992; Abstracts,
p 33). This includes the SHELX-76 Program for Crystal Structure
Determination (Sheldrick, G. M. University of Cambridge, Cambridge,
England, 1976).
(12) Troyanov, S. I.; Varga, V.; Mach, K. Organometallics 1993, 12,
2820-2824.
(13) Mach, K.; Varga, V.; Gyepes, R. XVIth International Conference
on Organometallic Chemistry, Brighton, England, J uly 1994; Book of
Abstracts, OB 17.

(η5-Cyclopentadienyl)titanium(II) Complexes
Organometallics, Vol. 15, No. 4, 1996 1271
Ta ble 5. Atom ic Coor d in a tes a n d Equ iva len t
Isotr op ic Tem p er a tu r e F a ctor s (Å2) for Com p lex 2
atom
x
y
z
Ueq
Ti(1)
C(1)
0.1203(1)
0.1776(4)
0.3178(1)
0.2782(6)
0.3366(6)
0.4909(5)
0.1750(4)
0.3089(1)
0.4144(6)
0.4269(7)
0.2217(7)
0.0515(4)
-0.0666(4)
-0.1993(1)
-0.1833(7)
-0.1788(7)
-0.3790(5)
-0.0692(4)
-0.1889(1)
-0.2449(7)
-0.3490(5)
-0.0993(6)
0.0264(4)
-0.0578(1)
-0.2195(5)
-0.0994(6)
0.0547(6)
0.3125(7)
0.2083(9)
0.1075(8)
0.1487(9)
0.2793(9)
0.1144(1)
0.1173(1)
0.0853(1)
0.0300(2)
0.0888(2)
0.0956(2)
0.1595(1)
0.2010(1)
0.1952(2)
0.2046(2)
0.2517(2)
0.1735(2)
0.1497(2)
0.1787(1)
0.2339(2)
0.1742(3)
0.1641(2)
0.1063(1)
0.0637(1)
0.0621(2)
0.0610(2)
0.0146(2)
0.1002(1)
0.1247(1)
0.1532(2)
0.0803(2)
0.1617(2)
0.1113(3)
0.1275(3)
0.0982(3)
0.0635(3)
0.0722(3)
0.2086(1)
0.4181(4)
0.5402(1)
0.4958(6)
0.7270(5)
0.5282(6)
0.3744(4)
0.4411(1)
0.6288(5)
0.3429(7)
0.4229(7)
0.2672(4)
0.1863(4)
0.0455(1)
0.0909(8)
-0.1240(5)
0.0243(6)
0.2289(4)
0.1481(1)
-0.0452(5)
0.1927(6)
0.2153(5)
0.3830(4)
0.5033(1)
0.4141(5)
0.5970(5)
0.6307(5)
0.1379(7)
0.0312(8)
-0.0160(6)
0.0627(9)
0.1593(7)
0.033(1)
0.033(1)
0.040(1)
0.062(1)
0.062(1)
0.059(1)
0.032(1)
0.051(1)
0.086(1)
0.081(1)
0.084(1)
0.032(1)
0.033(1)
0.044(1)
0.097(1)
0.067(1)
0.066(1)
0.030(1)
0.047(1)
0.079(1)
0.073(1)
0.062(1)
0.029(1)
0.035(1)
0.044(1)
0.050(1)
0.063(1)
0.086(1)
0.063(1)
0.081(1)
0.090(1)
0.048(1)
Si(1)
C(11)
C(12)
C(13)
C(2)
Si(2)
C(21)
C(22)
C(23)
C(3)
C(4)
Si(4)
C(41)
C(42)
C(43)
C(5)
Si(5)
C(51)
C(52)
C(53)
C(6)
Si(6)
C(61)
C(62)
C(63)
C(70)
C(80)
C(90)
C(100)
C(110)
F igu r e 1. View of the PLUTO plot of 2 with methyl groups
omitted for clarity.
thermally robust and can be sublimed in high vacuum
without decomposition. They appeared to be unreactive
toward all the above 1-alkynes, BTMSA, THF, 2,2′-
bipyridyl, ethylene, and carbon monoxide under ambient
pressure and temperature. The compounds are very
highly soluble in hexane, and their purification by
fractional crystallization from organic and organo-
metallic byproducts is extremely difficult. Well-resolved
NMR spectra obtained at ambient temperature prove
the diamagnetism of the compounds.
The 1H and 13C NMR spectra of 2-6 showed the
presence of one cyclopentadienyl (Cp) ligand and one
pentasubstituted cyclohexadienyl (Chx) ligand, the lat-
ter arising from the cross-cycloaddition of two molecules
of bis(trimethylsilyl)acetylene (BTMSA) and one mol-
ecule of 1-alkyne. The spectra of the Chx ligands
showed the presence of one SiMe3 group and one proton
on the sp3 carbon atom C(6), three other SiMe3 groups,
one substituent identical with that contained in 1-alkyne,
one proton on an sp2 carbon atom, and four quaternary
sp2 carbon atoms. In 2, the pairs of quaternary sp2
carbon atoms C(1) and C(5) and C(2) and C(4) were
equivalent whereas in 3-6 all the carbon atoms were
different. The spatial proximity of the substituent R
and the sp2 C-H proton was inferred from the ap-
propriate delay-COSY cross peaks for 4 and 5 (see
footnote to Table 1). However, no such proof could be
obtained for 3 and 6 because of the absence of protons
at the CR atoms of substituents. It is interesting to note
that all protons and carbons of cyclohexyl substituent
in 4 were magnetically nonequivalent; this phenomenon
was also observed for the two R-protons in 5 but was
entirely absent for the phenyl protons in 6.
sulted in a rapid reaction yielding 4-alkyl derivatives
of [η5-1,2,5,6-tetrakis(trimethylsilyl)cyclohexadienyl](η5-
cyclopentadienyl)titanium(II) (2-6) as the main prod-
ucts (eq 1). The common structure of products 2-6
(1)
The analogous structure of 2 and 3-6 is further
supported by the common features of their EI-MS
fragmentation patterns. The molecular ions most easily
loose one SiMe3 radical (m/z 73) (probably from the C(6)
atom), and the formed ions release either silaisobutylene
(m/z 72) (minor pathway) or the fragment m/z 152,
C9H16Si (major pathway). The latter pathway involves
a transfer of the CH2SiMe3 group from the six-mem-
bered ring to the C5H5 ring, and the adduct C9H16Si,
probably (trimethylsilyl)cyclohexadiene, is eliminated
from the titanium-containing ion. The remaining ion
in this fragmentation pathway is apparently [C5H2-
(SiMe3)2R]Ti+, where R is the substituent from the
corresponding 1-alkyne. The transfer of a larger ring
obtained from the reaction of 1 with (trimethylsilyl)-
ethyne, tert-butylethyne, cyclohexylethyne, 1-hexyne,
and phenylethyne, respectively, follows from the X-ray
crystal structure of 2 (Figure 1), the consistent assign-
ment of 1H (Table 1) and 13C NMR spectra (Table 2) of
all the compounds, and common features in their MS,
IR, and UV-vis spectra. The crystal structure deter-
mination of 2 revealed that it is (η5-1,2,4,5,6-pentakis-
(trimethylsilyl)cyclohexadienyl)(η5-cyclopentadienyl)-
titanium(II), the first structurally characterized 14-
electron half-open titanocene. Compounds 2-6 are

1272 Organometallics, Vol. 15, No. 4, 1996
Varga et al.
Ta ble 6. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for [η5-C6H2(SiMe3)5](η5-C5H5)TiII (2)
(a) Bond Distances (Å)
Ti(1)-C(1)
2.050(4)
2.186(4)
2.218(5)
2.200(4)
2.073(4)
1.582(4)
2.355(12)
1.875(9)
1.872(4)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(1)-C(6)
Ti(1)-CE(2)
C(6)-Si(6)
1.451(6)
1.443(6)
1.445(6)
1.490(6)
1.572(6)
1.585(6)
2.047(9)
1.937(4)
Ti(1)-C(2)
Ti(1)-C(3)
Ti(1)-C(4)
Ti(1)-C(5)
Ti(1)-CE(1)
Ti(1)-C(Cp)av
C(1-5)-Si(1-5)av
Si(1-6)-C(Me)av
(b) Bond Angles (deg)
CE(1)-Ti(1)-CE(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(2)-C(1)-C(6)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(1)-C(6)-C(5)
C(1)-C(6)-Si(6)
C(5)-C(6)-Si(6)
164.7(1)
117.1(4)
128.3(4)
110.9(3)
116.1(4)
110.7(3)
114.0(3)
110.2(3)
109.9(3)
Si(1)-C(1)-C(2)
131.8(3)
115.4(3)
129.7(3)
113.2(3)
115.0(3)
128.9(3)
131.2(3)
116.5(3)
Si(1)-C(1)-C(6)
C(1)-C(2)-Si(2)
Si(2)-C(2)-C(3)
C(3)-C(4)-Si(4)
Si(4)-C(4)-C(5)
C(4)-C(5)-Si(5)
Si(5)-C(5)-C(6)
F igu r e 2. ORTEP drawing of 2, with ellipsoids drawn at
the 50% probability level.
carbon atom to a smaller ring is well-known for, e.g.,
(η7-cycloheptatrienyl)(η5-cyclopentadienyl)titanium.17
The infrared spectra of 2-6 are dominated by strong
absorption bands of trimethylsilyl groups and afford no
much information. It is worthwhile to mention strong
bands at 1011-1013 cm-1 and at 1105-1116 cm-1
occurring in the spectra of all the compounds. The
former can be assigned to the Cp ligand, and the latter
to the Chx ligands.18 The absence of an absorption band
at 2800 cm-1 confirms the absence of the C-H bond in
the exo-position at the carbon atom C(6).3d The elec-
tronic absorption spectra show the presence of two
intense absorption bands in regions 565-580 nm and
813-870 nm which should belong to metal-to-ligand CT
transitions. Their molar extinction coefficients are
estimated to be higher than 102 L‚cm‚mol-1. This is
consistent with a strong metal-ligand orbital mixing
which is facilitated by a small separation between the
HOMO and LUMO orbitals in the Chx ligand.8 The
absorption bands of the longest wavelength (813-860
nm) reached the extreme of 813 nm for 2 (electron-
withdrawing SiMe3 group), but the differences between
the alkyl derivatives 3-6 were low (840-860 nm). The
intense bands at shorter wavelengths were discernible
in high-purity compounds 2, 3, and 6; in other cases they
were partly or completely overshadowed by an intense
absorption of a brown impurity.
Cr ysta l Str u ctu r e of [η5-C6H2(SiMe3)5](η5-C5H5)-
TiII (2). The ORTEP drawing of 2 with the atom-
numbering scheme is shown in Figure 2. Selected bond
lengths and bond angles are listed in Table 6. The
molecule has no symmetry element due to the distortion
of the Chx ligand and a partly staggered conformation
of the Chx and Cp ligands. Five sp2 carbon atoms of
the Chx ring form a least-squares plane with a maxi-
mum atom deviation of 0.035 Å. The sp3 carbon atom
C(6) is 0.653 Å above this plane and the attached
trimethylsilyl group is oriented in the exo-position. The
dihedral angle between the ring plane and the plane
F igu r e 3. Schematic representation of angles around the
Ti atom in 2 (dotted lines, normals to least-squares planes
of Chx and Cp ligands).
through the C(1), C(6), and C(5) atoms is 48.6o. The
silicon atoms Si(1)-Si(5) lie significantly out of the ring
plane, and these atoms are directed toward the Ti atom.
The largest declination from the plane was found for
Si(1) and Si(5) (ca. 0.2 Å). The Chx ligand is tilted
toward the titanium atom by the side bearing the sp3
carbon atom C(6) (vide infra). The cyclopentadienyl (Cp)
ring defines the least-squares plane with maximum
carbon atom deviation from the plane of only 0.004 Å.
The Ti-C(100) bond is the shortest one (2.343(9) Å), and
this corresponds to the tilt of the ring plane to the
titanium atom by 1.2°. The planes of the Chx and Cp
rings are thus inclined to each other, and the dihedral
angle between them is 4.9°. Since the center CE(1) of
the atoms of the dienyl fragment of the Chx ligand
(C(1)-C(5)) is located close to C(3), the angle between
the Ti-CE(1) connection and the normal to the Chx
plane is as large as 19.1°. It accounts for the discrep-
ancy between the values of the CE(1)-Ti-CE(2) angle
(164.7°) and the angle of normal vectors to both the
planes (175.1°) (Figure 3).
The average values of important bond lengths in 2
are compared with the values for (Dmchx)2Ti(CO)7a (7)
and similar compounds (Cp)Ti(Dmp)(PEt3) (Dmp ) η5-
2,4-dimethylpentadienyl),20 (Cp)Ti(Cht) (Cht ) η7-cy-
cloheptatrienyl),21 and (Cp)Ti(Cot) (Cot ) η8-cyclo-
octatetraene dianion)22 in Table 7. It shows that the
Ti-Cn distance to a larger ring or Dmp is generally
(17) (a) Verkouw, H. T.; van Owen, H. O. J . Organomet. Chem. 1973,
59, 259-266. (b) Verkouw, H. T.; Veldman, M. E. E.; Groenenboom,
C. J .; van Oven, H. O.; de Liefde Meijer, H. J . J . Organomet. Chem.
1975, 102, 49-56.
(18) A strong band at 1012-1015 cm-1 has been assigned to δ or
γ(C-H) vibrations of the Cp ligand in titanocene dihalides;19 however,
we have observed a strong absorption band at 1020 cm-1 for (C5Me5)2-
TiCl2 and this has to be assigned to a ring vibration. In 2-6 both the
assignments are possible for absorption bands of pentasubstituted
(20) Mele´ndez, E.; Arif, A. M.; Ziegler, M. L.; Ernst, R. D. Angew.
Chem., Int. Ed. Engl. 1988, 27, 1099-1101.
(21) Zeinstra, J . D.; De Boer, J . L. J . Organomet. Chem. 1973, 54,
207-211.
cyclohexadienyl ligand at 1106-1116 cm-1
.
(19) Druce, P. M.; Kingston, B. M.; Lappert, M. F.; Spalding, T. R.;
Srivastava, R. C. J . Chem. Soc. A 1969, 2106-2110.

(η5-Cyclopentadienyl)titanium(II) Complexes
Organometallics, Vol. 15, No. 4, 1996 1273
(η5-C6H7)Co[P(C6H11)2CH2]2.25 This direction of ring tilt
is also common in partly methyl-substituted Cp rings
where the unsubstituted part of the ring is at closer
distance to the metal than the substituted one.26 In the
titanium complexes, this was recently observed for (η5-
C5HMe4)2TiIII and -TiIV halides27 and the isodicyclo-
pentadienyl complex (η5-C10H11)Ti[(µ-Cl)2AlCl2]2.28 The
opposite ring tilt in 2 cannot be attributed to a bonding
interaction between the Ti atom and the Si(1) and Si(5)
atoms, remarkably declined from the Chx ring plane
toward the Ti atom, because their distance from the
titanium atom is as large as 3.466 and 3.471 Å,
respectively. More likely, the direction of the C-Si
bonds is induced by the orbital hybridization at C(1) and
C(5) resulting from an envelope folding of the Chx
ligand.
A low dihedral angle between the Chx and Cp ring
planes (φ 4.9°) classifies 2 to be a pseudometallocene
with parallel ligand planes. The angle φ was found to
deviate only slightly from zero in crystal structures of
titanocene-like compounds (Cp)Ti(Cht),21 (Cp)Ti(Cot),22
(Cp*)Ti(Cht) (Cp* ) η5-C5Me5), and (Cp*)Ti(Cot),29
where the parallel orientation of rings is stabilized by
the presence of one larger ring. The values of φ were
2.1, 1.9, 3.9, and 1.6°, respectively. The large value of
φ in (Cp*)Ti(Cht) indicates that a steric congestion due
to the methyl substituents in Cp* ring has no influence
on the parallel orientation of the rings. Thus, crystal
packing effects are probably responsible for the observed
deviations from parallel structures in the above ex-
amples as well as in 2.
Rea ction s betw een 1 a n d 1-Alk yn es. Compound
1 was found to be stable toward the internal acetylenes
although it induced their slow cyclotrimerization.10b In
contrast, it rapidly reacted with 1-alkynes yielding a
mixture of products. Compounds 2-6 were always the
main products whose yields were estimated to be
between 60-80% although the isolated yields were, due
to difficult purification, much lower. The other identi-
fied products were tris(trimethylsilyl)alkylbenzenes and
the cyclotrimers of 1-alkynes. Minor amounts of
1-alkynes remained unreacted. EPR evidence was
obtained (see Table 3) for the presence of paramagnetic
TiIII byproducts, presumably Ti-Mg tweezer complexes
of the type [(Cp)2Ti(η1-CtCR)2]-[Mg(CtCR)]+.
A possible reaction pathway leading to 2-6 is pro-
posed in Scheme 1. It involves the cleavage of 1 by
1-alkyne yielding (Cp)MgCtCR and a transient bis[η2-
C2(SiMe3)2](cyclopentadienyl)titanium(II) hydride com-
plex which rearranges with intramolecular hydrogen
transfer to give a titanacyclopentadiene skeleton.30 As
follows from the structure of 2, the insertion of 1-alkyne
into the Ti-C bond is controlled by a greater steric
congestion at the SiMe3 group compared to the (Cp)Ti
moiety. The titanacycloheptatriene ring contraction
accompanied by the change of σ- to π-bonding mode of
Ti(II) to the cyclohexadienyl ligand accomplishes the
Ta ble 7. Aver a ge Va lu es of Ti-C a n d C-C Bon d
Len gth s a n d Ti-Rin g Dista n ces (Ti-R) in 2 a n d
Rela ted Com p ou n d s (Å)a
Ti-CCp Ti-Cn C-CCp C-Cn Ti-RCp Ti-Rn ref
2
7
2.355 2.145 1.374 1.457 2.046 1.495
2.331
1.392
1.911 7a
20
(Cp)Ti(Dmp) 2.346 2.240
(Cp)Ti(Cht)
(Cp)Ti(Cot)
2.321 2.194 1.396 1.397 1.994 1.490 21
2.353 2.323 1.396 1.395 2.030 1.439 22
a
The distances pertinent to the Cp ligand are denoted “Cp”;
those to the other ligand “n”; Ti-R is the normal distance from
the least-squares plane of the ring to the Ti atom.
shorter than Ti-CCp and that except for (Cp)Ti(Cot) the
Ti-C bonds shorten as the C-C bonds lengthen in the
pertinent ligand and vice versa. These effects are most
prominent in 2, where, however, the data for the Cp ring
distances exert large anisotropic thermal parameters.
This is probably due to the ring libration around the
axis perpendicular to the ring plane. A similar effect
was observed for both rings in (Cp)Ti(Cht)21 and in (Cp)-
Ti(Cot),22 where the libration shortening of the Ti-C
and C-C bonds was estimated to be in the range of 0.01
Å. The C-CCp and Ti-CCp bond lengths in 2 were not
corrected for this effect; however, it should not differ
much from the above figure. The anisotropic thermal
parameters for the carbon atoms of Chx ring are ca. 3×
smaller and do not show a remarkable directional
dependence. The Ti-Cn bonds in 2 are thus reliably
shorter by about 0.2 Å than the Ti-CCp bonds, which is
the largest difference among the compounds listed in
Table 7. In contrast, the average π-bond length in the
Chx ring C(1)-C(5) [(C-C)av 1.457(6) Å] is by far the
longest. The average length for the outer bonds C(1)-
C(2) and C(4)-C(5) (1.470 Å) is longer than the average
of the corresponding inner bonds (1.444 Å), which is at
variance to the situation in 7,7a [(Dmchx)Mo(CO)2]2,7b
and in most metal-pentadienyl compounds.8 This can
be due to an electron-releasing effect of the SiMe3 groups
at the C(1) and C(5) atoms, inducing a partial trianionic
form of the dienyl ligand.23 The inner angle C(2)-C(3)-
C(4) (128.3°) of the Chx ligand is much larger than the
angles C(1)-C(2)-C(3) (117.1°) and C(3)-C(4)-C(5)
(116.1°), and this is again the opposite situation to that
in 7 and in other above mentioned compounds.8 The
C-Si bond lengths from the ring carbon atoms C(1),
C(2), and C(5) as well as all the Si-C bonds to Me
groups fall into the range 1.857-1.891 Å. The average
values with errors typical of the particular bond type
are given in Table 6. The C(6)-Si(6) bond is remarkably
longer than others, and hence its value of 1.937(4) Å
was not included into the set of averaged bond lengths.
The structure of 2 differs from that of 7 also by the
direction of the ring tilt with respect to the titanium
atom. In contrast to 2, the Dmchx ring side bearing
the sp3 carbon atom is tilted farther away from the
titanium atom.7a The analogous tilting was also found,
e.g., in the crystal structure of η5-cyclohexadienyl
complexes [(η5-C5Me5)Ir(η5-C6H6CH2NO2)][BF4],1b (η5-
C6H2(Me)(CMe3)2O)Rh(PPh3)2,3c (η5-C6H7)Mn(CO)3,24 and
(25) J onas, K. Angew. Chem., Int. Ed. Engl. 1985, 24, 295-311.
(26) Howie, R. A.; McQuillan, G. P.; Thompson, D. W.; Lock, G. A.
J . Organomet. Chem. 1986, 303, 213-220.
(27) Troyanov, S. I.; Rybakov, V. B.; Thewalt, U.; Varga, V.; Mach,
K. J . Organomet. Chem. 1993, 447, 221-225.
(22) Kroon, P. A.; Helmholdt, R. B. J . Organomet. Chem. 1970, 25,
451-454.
(23) Kralik, M. S.; Stahl, L.; Arif, A. M.; Strouse, C. E.; Ernst, R. D.
Organometallics 1992, 11, 3617-3621.
(24) Churchill, M. R.; Scholer, F. R. Inorg. Chem. 1969, 8, 1950-
1955.
(28) Mach, K.; Hiller, J .; Thewalt, U.; Sivik, M. R.; Bzowej, E. I.;
Paquette, L. A.; Zaegel, F.; Meunier, P.; Gautheron, B. Organometallics
1995, 14, 2609-2612.
(29) Kool, L. B.; Rausch, M. D.; Rogers, R. D. J . Organomet. Chem.
1985, 297, 289-299.

1274 Organometallics, Vol. 15, No. 4, 1996
Varga et al.
Sch em e 1
2] cyclotrimerization (for reviews see ref 34a,b) of 2
molecules of Me3SiCtCSiMe3 with HCtCSiMe3 is
improbable to proceed without participation of a Ti-H
moiety. Furthermore, the subsequent hydride addition
to thus formed pentakis(trimethylsilyl)benzene would
not account for the formation of only one isomer of the
cyclohexadienyl ligand.
Tris(trimethylsilyl)alkylbenzenes formed as main
byproducts probably originate in a side reaction of the
intermediate titanacycloheptatriene (Scheme 1). It can
be visualized as a transfer of one SiMe3 group to
titanium which leads to a rapid elimination of C6H2R-
(SiMe3)3 and the formation of a highly reactive (Cp)Ti-
(SiMe3) species. The combination of the latter with a
released (Cp)MgCtCR in the presence of 1-alkyne may
lead to the Ti(III) paramagnetic byproducts of the above
suggested tweezer nature. Very low amounts of tri-
alkylbenzenes were probably obtained by the catalytic
cyclotrimerization of 1-alkynes catalyzed by 1 before it
decomposed to give 2.
formation of 2-6. It is noteworthy that the proposed
mechanism involves the oxidative addition followed by
reductive elimination steps between TiII and TiIV as it
is generally accepted for the cyclotrimerizations of
acetylenes14 and butadiene.33 An alternative [2 + 2 +
Ack n ow led gm en t. This work was supported by the
Grant Agency of the Academy of Sciences of the Czech
Republic (Grant No. 440403), by the Grant Agency of
the Czech Republic (Grant No. 203/93/0143), and by the
Fonds der Chemischen Industrie.
(30) Bis(trimethylsilyl)acetylene (BTMSA) is reluctant to cyclotri-
merize because of steric crowding in the products; however, the
titanium-catalyzed cross-additions to conjugated double-bond systems
are known.31 The (Cp)2Ti(η2-BTMSA) complex does not react with
excess BTMSA to give
a
titanacyclopentadiene derivative.32 The
formation of the titanacyclopentadiene skeleton in the present case is
enabled by the hydrogen transfer forming thus an sp3 carbon atom in
the carbon chain and by the absence of steric hindrance at the (Cp)Ti
moiety.
(31) (a) Mach, K.; Antropiusova´, H.; Petrusova´, L.; Hanus, V.;
Turecˇek, F.; Sedmera, P. Tetrahedron 1984, 40, 3295-3302. (b) Mach,
K.; Antropiusova´, H.; Petrusova´, L.; Turecˇek, F.; Hanus, V.; Sedmera,
P.; Schraml, J . J . Organomet. Chem. 1985, 289, 331-339. (c) Mach,
K.; Antropiusova´, H.; Hanusˇ, V.; Sedmera, P. Coll. Czech. Chem.
Commun. 1989, 54, 3088-3091.
(32) Burlakov, V. V.; Polyakov, A. V.; Yanovsky, A. I.; Struchkov,
Yu. T.; Shur, V. B.; Vol’pin, M. E.; Rosenthal, U.; Go¨rls, H. J .
Organomet. Chem. 1994, 476, 197-206.
(33) Pola´cˇek, J .; Antropiusova´, H.; Petrusova´, L.; Mach, K. J . Mol.
Catal. 1990, 58, 53-73.
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
atomic positional and thermal parameters, anisotropic thermal
parameters, bond distances, valence angles, least-squares
planes and atomic deviations therefrom, and important inter-
molecular contacts and figures showing views of the unit cell
(13 pages). Ordering information is given on any current
masthead page.
OM950760W
(34) (a) Vollhardt, K. P. C. Acc. Chem. Res. 1977, 10, 1-8. (b) Schore,
N. E. Chem. Rev. 1988, 88, 1081-1119.