P. Kiprof et al. / Journal of Organometallic Chemistry 620 (2001) 113–118
117
tamethylbenzene complex was 0.73 g (0.98 mmol,
43.2%). Anal. Found: C, 20.66; H, 2.96. Calc. for
C13H20Cl12Ti3: C, 20.95; H, 2.70%. The yield of these
complexes can be improved by evaporating CH2Cl2
from the filtrate and by cooling the filtrate as well.
Crystals suitable for X-ray analysis were prepared
from a solution of the titanium(IV) arene complex in
CH2Cl2 that contained an excess of TiCl4. The solution
was kept in a Schlenk tube under argon at room
temperature. A small amount of argon was kept running
into the Schlenk tube through a needle in a rubber
septum for a while to help evaporate some solvent. Then
a rubber cap was used to seal the Schlenk tube. Large
yellow column-shaped single crystals of 2a were formed
over a period of 4 days.
was introduced at a rate such as to produce gentle
reflux. After 2 h stirring at room temperature, 12 ml of
ice cold water were added slowly and then 8 ml of 6 N
sulfuric acid. After separating the organic layer, the
aqueous layer was extracted three times with ether. The
combined ether extracts were dried over anhydrous
Na2CO3, and the ether was removed in vacuo. The yield
was 0.86 g (4.88 mmol; 87.6%). Anal. Found: C, 88.38;
H, 11.32. Calc. for C13H20: C, 88.56; H, 11.44%.
1H-NMR (300 MHz, CDCl3) l: 1.11 (t, J=8 Hz,
CH2CH3); 2.25, 2.23 (s, 15H, ring methyls), 2.72 (q,
J=8 Hz, 2H, CH2). 13C-NMR (75.4 MHz, CDCl3) l:
14.03 (CH2CH3); 16.02, 16.66, 16.71 (ring methyl
groups); 33.48 (CH2), 131.28, 132.20, 132.34, 137.76
(ring carbons); GC/MS: m/z 176 (M+). M.p. 66.0°C.
3.7. Synthesis of (p6-C6Me5Pr)TiCl3]+[Ti2Cl9]− (2b)
3.5. Preparation of pentamethylpropylbenzene
In an analogous procedure, to a Schlenk flask con-
taining a solution of 0.43 g pentamethylpropylbenzene
(2.26 mmol) in 15 ml, 2.5 ml TiCl4 (4.76 g, 24.6 mmol)
were added. The reaction solution turned from colorless
to red–brown upon addition of TiCl4, and a yellow
solid was precipitated out. After filtration, the solid
product was washed with hexane and dried in vacuo at
room temperature. The yield was 0.72 g of the titanium
pentamethylpropylbenzene complex (0.95 mmol,
42.0%).
An 8 ml ethyl ether solution of 0.93 g AlCl3 (6.97
mmol) was added dropwise to a suspension of 0.53 g
LiAlH4 (13.97 mmol) in 14 ml of ether. 5 min later, a
solution containing 1.14 g pentamethylpropionylben-
zene (5.58 mmol) and 0.74 g AlCl3 (5.55 mmol) in 14 ml
ether was introduced at a rate such as to produce gentle
reflux.
After 2 h stirring at room temperature, 12 ml of ice
cold water were added slowly and then 8 ml of 6 N
sulfuric acid. After separating the organic layer, the
aqueous layer was extracted three times with ether. The
combined ether extracts were dried over anhydrous
Na2CO3, and the ether was removed in vacuo to isolate
the product. The yield was 0.91 g (4.78 mmol; 85.6%).
Anal. Found: C, 88.26; H, 11.81. Calc. for C14H22: C,
88.35; H, 11.65%.
3.8. Synthesis of (p6-C6Me5Et)TiCl3]+[AlCl4]−
A suspension of 0.59 g AlCl3 (4.42 mmol) in 15 ml
toluene was treated with 0.84 g TiCl4 (4.43 mmol).
Addition of 0.80 g ethylpentamethylbenzene (4.53
mmol) caused the formation of a bright yellow solid.
After 24 h stirring at room temperature, the suspension
was filtered and the bright yellow solid was washed with
hexane and dried in vacuo affording 1.01 g (2.02 mmol,
45.7% yield) of [(h6-C6Me5Et)TiCl3]+[AlCl4]−. Anal.
Found: C, 30.22; H, 4.30. Calc. for C13H20AlCl7Ti: C,
31.27; H, 4.04%.
1H-NMR (300 MHz, CDCl3) l: 0.96 (t, J=7 Hz, 3H,
CH2CH2CH3); 1.43 (m, 2H CH2CH2CH3); 2.15, 2.17 (s,
15H, ring methyls), 2.56 (m, 2H, CH2CH2CH3). 13C-
NMR (75.4 MHz, CDCl3) l: 14.66 (CH2–CH2CH3);
16.31, 16.74, 16.77 (ring methyl groups); 23.22 (–
CH2CH2CH3); 32.92 (–CH2CH2CH3); 131.56, 132.26,
132.34, 136.55 (ring carbons); 212.61 (CO–CH3). GC/
MS: m/z 190 (M+). M.p. 52.2°C.
4. Conclusion
3.6. Synthesis of (p6-C6Me5Et)TiCl3]+[Ti2Cl9]− (2a)
We have investigated the formation of high-valent d0
titanium arene complexes in order to shed light into the
‘uniqueness’ of the complex [h6-(C6Me6)TiCl3]+
[Ti2Cl9]− (1), which is formed in a reaction of hexam-
ethylbenzene with titanium tetrachloride. Before our
investigations no other arene was observed to form this
type of product. Our investigations show that the
uniqueness of 1 is in part due to the donor abilities of
hexamethylbenzene, and to a large extent due to its low
solubility. By utilizing substituted pentamethylbenzenes
we increased the solubility of the ionic arene complexes
and could show that they form, like hexamethylben-
All operations were carried out in an atomosphere of
argon. The reaction vessels were oven dried before use.
To a Schlenk flask containing a solution of 0.40 g
ethylpentamethylbenzene (2.27 mmol) in 15 ml CH2Cl2,
2.5 ml TiCl4 (4.76 g, 24.6 mmol) were added. The
reaction solution turned from colorless to red–brown
upon addition of TiCl4, and a yellow solid precipitated
out. The reaction mixture was allowed to stir at room
temperature for 1 day. After filtration, the solid product
was washed with hexane and dried in vacuo at room
temperature. The yield for the titanium ethylpen-