Organometallics
Article
mother liquor. These crystals were collected, washed with cold diethyl
ether, and briefly dried in vacuo. Yield: 0.76 g (67% with respect to
starting 6-thf-OEt ) of turquoise crystals of 5-thf-OEt . Elemental
and stirred at 0 °C. Then 2.7 mL (1.51 mmol) of a halide-free
phenyllithium solution (0.56 M) in diethyl ether was added dropwise
with a syringe. The color of the red solution immediately turned
green, and within 5 min the red deposit dissolved completely. The
dark green reaction solution is stable for several months at −40 °C. In
order to crystallize 4-thf, a part of this solution was transferred into a
glass flask which was cooled with liquid nitrogen to −50 °C. During
this treatment the green solution turned red and purple crystals
precipitated. The crystals were completely covered with oil and
mounted on a loop for X-ray diffraction experiments. Attention!If the
temperature of the crystals increases above −50 °C, the crystals melt and
freeze again giving a purple glassy solid. During drying of crystalline 4-
thf on a Schlenk frit at −70 °C, the substance converted to a green
oily mass. Therefore, the performance of a reliable elemental analysis
was impossible.
2
2
analysis (C H CrLi O , M: 669.7): calcd: Cr 7.76. Found: Cr 7.80.
4
2
51
2
3
1
Improved Synthesis of [{(thf) Li} CrPh ] (5-thf) according to
2
2
5
26
Heyn. A solution of 0.67 g (1.00 mmol) of turquoise 5-thf-OEt in
2
5
mL of THF was refluxed for a few minutes. Then the warm flask was
cooled immediately down in an ethanol−dry-ice bath to −78 °C. The
cold solution was layered with 3 mL of n-pentane and stored
overnight at −40 °C. Big green crystals of 5-thf grew at the glass wall.
In one batch, some yellow crystals of [(thf) Li] [{(thf)Li} CrPh ] (6-
4
2
6
thf) were formed on the bottom of the flask. The green product was
collected on a Schlenk frit, washed with n-pentane, and dried for a
short time in vacuo. Yield: 0.42 g (57% with respect to starting 5-thf-
OEt ) of 5-thf as green crystals. Elemental analysis (C H CrLi O ,
Acidolysis of [{(Et
O)Li} CrPh
3
] with 2 equiv of HCl−Et
O. A
2
6
2
suspension of 0.758 g (1.0 mmol) of Li
CrPh ·3 Et O in 10 mL of
2
46 57
2
4
3
6
2
M:739.8): calcd: Cr 7.03. Found: Cr 7.14. The compound was
diethyl ether and 69 μL (0.5 mmol) of mesitylene as internal standard
were cooled and stirred in Schlenk flask covered with a septum. Next,
identical with Heyn’s Li CrPh ·3.5THF.
2
5
Synthetic Alternatives for [(12-crown-4)Li(thf)] [CrPh ] (5-
1.18 mL (2.0 mmol) of HCl−OEt solution (1.7 M) were added with
2
2
5
thf-12C4). Synthesis Variant 1. Compound 5-thf-OEt (0.47 g, 0.70
a syringe. During this handling the yellow substrate dissolved and
intermediately a sparingly soluble purple solid precipitated which
immediately dissolved at −40 °C yielding a dark brown solution
which was warmed to room temperature. Diluted sulfuric acid was
added. The organic layer was decanted and dried with anhydrous
2
mmol) was dissolved in 10 mL of diethyl ether and at 0 °C, 0.26 g
(
1.48 mmol) of 12-crown-4 were added with a syringe. During this
procedure, a microcrystalline solid precipitated from the green
solution which was collected on a Schlenk frit (G4), washed with
diethyl ether and dried in vacuo in the dark. Yield: 0.62 g (93% with
sodium sulfate. Then, 0.2 mL of [D ]benzene were added to 0.5 mL
6
1
respect to starting 5-thf-OEt ) of 5-thf-12C4 as small light green
of this solution and studied by H NMR spectroscopy. In the
2
6
crystals.
spectrum the resonances of the (η -arene)chromium complexes (2-π,
Synthesis Variant 2. Compound 6-thf-OEt (0.85 g, 1.13 mmol)
was suspended at 0 °C in 20 mL of THF and stirred. Then 0.62 g
3.52 mmol) of 12-crown-4 was added with a syringe. During this
handling, the yellow substrate dissolves yielding a green solution.
Soon thereafter, a green solid precipitated which was collected on a
Schlenk frit, washed with THF, and dried in vacuo in the dark. Yield:
3-π (major product), and 4-π) as well as benzene and biphenyl
2
(major product) were observed besides small signals of impurities.
1
6
65
(
H NMR (400.1 MHz, in C
6
D
6
): 2-π: δ 4.08 (12H, s, η -C
6
H
6
).
6
6
3-π: δ 4.18 (1H, t, p-CH, η -Ph), 4.25 (2H, t, m-CH, η -Ph), 4.73
6
(2H, d, J = 5.2 Hz, o-CH, η -Ph). The signals of the noncoordinated
phenyl group are covered by the signals of biphenyl. The signals of the
6
6
1
5
5
.05 g (98% with respect to starting 6-thf-OEt ) of green platelets of
η -C H ligand are very broad at 297 K. 4-π: δ 4.26 (p-CH, η -Ph),
6 6
2
6
6
-thf-12C4. Elemental analysis (C H CrLi O , M: 948.0): calcd Cr
4.35 (4H, t, m-CH, η -Ph), 4.85 (4H, d, J = 5.2 Hz, o-CH, η -Ph).
5
4
73
2
10
.48. Found: Cr 5.54. The crystals were very sensitive toward light
The signals of the noncoordinated phenyl groups are covered by the
66
and heat. In contact with [D ]THF the compound already degraded
signals of biphenyl.
Synthesis of [{(thf)Li}CrPh
(4.58 mmol) of 5-thf-OEt in 50 mL of diethyl ether was suspended
at −40 °C and stirred. Then, 2.72 mL (4.62 mmol) of a HCl−OEt
8
II
above 40 °C.
] (3-Cr -thf). A suspension of 3.07 g
3 2
Synthesis of [{(Et O)Li} OCrPh ] (3-Li O) (by Degradation
2
2
2
3 2
2
of 5-thf-OEt in Boiling Diethyl Ether). A solution of 0.75 g (1.12
2
2
mmol) of 5-thf-OEt in 10 mL of diethyl ether was refluxed for 5 h.
solution (1.7 M) were added. During this treatment a microcrystalline
purple substance precipitated. Warming to −20 °C led to a complete
conversion to a brown solution with a white precipitate. The solids
were removed at −20 °C by filtration with a frit covered with
diatomaceous earth and stored at −40 °C. At this temperature, a dark
red-brown substance crystallized and was collected on a Schlenk frit,
washed with very cold diethyl ether, and briefly dried in vacuo. Yield:
2
This treatment led to formation of a microcrystalline precipitate in the
green solution. Then the reaction solution was stored overnight at
20 °C. The precipitate was collected on a Schlenk frit, washed with
−
cold diethyl ether, and briefly dried in vacuo. Yield: 0.30 g (58% with
respect to starting 5-thf-OEt ) of 3-Li O as emerald green crystals.
2
2
Elemental analysis (C H Cr Li O , M: 922.8): calcd: Cr 11.27.
5
2
70
2
4
6
Found: Cr 11.46.
0.91 g (55% with respect to starting 5-thf-OEt
2
) of dark red-brown
Li , M: 724.7):
II
Alternative Single-Crystal Preparation of 3-Li O (by
crystals of 3-Cr -thf. Elemental analysis (C44
H
46Cr
2
O
2 2
2
Degradation of 6-thf-OEt in Diethyl Ether at Room Temper-
calcd: Cr 14.35. Found: Cr 14.15. In solution, this compound already
degraded above −15 °C. Stirring at room temperature in diethyl ether
yielded a black precipitate (π-3, π-2, and π-4), benzene, and biphenyl,
besides small amounts of unknown compounds.
2
ature). A suspension of 0.76 g (1.0 mmol) of 6-thf-OEt in 20 mL of
2
diethyl ether was kept at room temperature for 3 days. During this
time, the majority of the yellow crystals dissolved forming a green
II
solution, and large emerald green crystals of 3-Li O grew at the wall
Preparation of [(thf) Li] [Cr Ph ] (3-Cr -thf ). Compound 3-
2
4
2
2
6
4
II
of the Schlenk flask, suitable for X-ray crystal structure determination.
Cr -thf (1.22 g, 1.68 mmol) was dissolved at room temperature in 50
mL of THF. The dark red solution was filtered and then stored at −20
°C. Red crystals precipitated and were collected on a Schlenk frit,
washed with cold THF, and briefly dried in vacuo. Yield: 1.56 g (80%
Improved Protocol for the Preparation of Salt-Free Phenyl
6
4
Lithium Solution in Diethyl Ether According to Wittig.
Diphenyl mercury (3.0 g, 10.6 mmol) was slowly added into a stirred
slurry of 0.90 g (130 mmol) of lithium sand (⌀ ≈ 50 μm) in 20 mL of
diethyl ether. The solid diphenyl mercury was added in a manner that
the reaction mixture kept warm. After the exothermic reaction was
finished, the Schlenk tube was put for 5 min in an ultrasound cleaning
bath. Then the reaction mixture was filtered by a Schlenk frit. The
concentration of phenyl lithium was determined from an acidimetric
titration of an aliquot of the filtrate. Yield: 74% (calcd with respect to
starting diphenyl mercury).
II
II
with respect to starting 3-Cr -thf) of 3-Cr -thf as red crystals.
4
Elemental analysis (C H Cr Li O , M: 1157.3): calcd: Cr 8.99.
6
8
94
2
2
8
II
Found: Cr 9.13. After stirring of a solution of 3-Cr -thf in [D ]THF
4
8
for 1 h at 40 °C, the solution was cooled to −40 °C. Finally only red
crystals of the substrate were obtained.
II
Reaction of [(thf) Li] [Cr Ph ] (3-Cr -thf ) with Lithiumphen-
4
2
2
6
4
II
yl. Compound 3-Cr -thf (2.26 g, 1.95 mmol) was suspended in 50
4
mL of THF at −40 °C and stirred. Then 6.5 mL of halide-free
phenyllithium (3.90 mmol) in diethyl ether (0.6 M) was added
dropwise. During this handling, the deposit dissolved leading to a red
solution. The volume of this solution was reduced to half of the
Crystal Preparation of [Li(thf) ] [cis-(thf) Ph Cr]·2THF (4-thf)
4
2
4
3
4
(
(
Modified Protocol According to Schmiedeknecht). Ph Cr-
3
thf) ·0.25dx (3, 0.78 g, 1.50 mmol) was suspended in 6 mL of THF
3
J
Organometallics XXXX, XXX, XXX−XXX
Fischer, Reinald
