2
30
F. Montilla et al. / Journal of Organometallic Chemistry 626 (2001) 227–232
2.5. Reactions carried out in neat arylisocyanates
2.6. Reactions carried out in toluene: preparation of
H R N C O (R=CH C H ) (4)
2
3
3
2
2
3
6
4
2
.5.1. Cyclotrimerisation of arylisocyanates using
p-CH C H NCO (1.89 g, 14.2 mmol) was added to a
3
6
4
CpCo(CO) as catalyst
2
toluene (15 ml) solution of CpCo(CO) (0.10 g, 0.55
2
A mixture of CpCo(CO) (0.10 g, 0.55 mmol) and
2
mmol). The resulting red solution was stirred at 50°C
for 24 h and the toluene was then removed under
vacuum. The red oil was washed with n-pentane and
the resulting solid was extracted with diethyl ether.
Cooling the solution at −20°C afforded the compound
as a white crystalline solid. Yield: 0.12 g (7%). No
presence of the trimer was observed.
When the reaction was repeated at the same condi-
tions, but heated at 85°C for 24 h, 0.17 g of 4 was
p-CH C H NCO (1.89 g, 14.2 mmol) was heated at
3
6
4
5
2
0°C. A solid precipitated out of the red solution. After
4 h, 20 ml of n-pentane was added to remove the
unreacted isocyanate. The white solid was washed with
0 ml of n-pentane for two repetitions and dried under
1
4
reduced pressure to give 0.87 g (41% yield) of (p-
CH C H NCO) .
3
6
4
3
The reaction was repeated using visible light (200 W).
Yield: 1.12 g (53%).
obtained (yield: 10%).
1
H-NMR (CHCl -d, l ppm): 7.30–7.26 (m, 12, CH,
1
3
H-NMR (CHCl -d, l ppm): 8.92 (sa, 2, NH), 7.39–
3
13
1
Ph), 2.40 (s, 9, CH3). C{ H}-NMR (100 MHz,
CHCl -d, l ppm): 149.0 (s, CO), 139.4, 131.2, 130.1,
1
m/z: 400. Anal. Found: C, 72.19; H, 5.22 N, 10.68.
Calc. for C H N O : C, 72.18; H, 5.26; N, 10.50%.
The cyclotrimerisation of PhNCO using the same
procedure described above gave the corresponding
trimer (PhNCO) (yield: 21%). Spectroscopic data are
7
.11 (m, 12, CH, Ph), 2.46 (s, 3, CH ), 2.32 (s, 6,
3
13
1
3
CH ). C{ H}-NMR (100 MHz, CHCl -d, l ppm):
3
3
28.2 (s, CH), 21.1 (s, CH ). Mass spectrum (EI+)
3
1
1
53.8 (s, CO), 140.0, 134.8, 134.1, 134.0, 131.2, 129.6,
20.8 (s, CH), 21.1 (s, CH ), 20.6 (s, CH ). Mass
3
3
2
4
21
3
3
spectrum (EI+) m/z: 374. Anal. Found: C, 73.92; H,
6
.26; N, 11.05. Calc. for C H N O : C, 73.93; H, 6.17;
23 23 3 2
N, 11.26%.
3
in agreement with those reported in the literature [11].
3
. Results and discussion
The solubility test of the catalyst consists in the
2.5.2. Cyclotrimerisation of arylisocyanates using
Ni(cod) as catalyst
2
visual inspection through the sapphire windows of the
high-pressure cell. A known amount of catalyst was
placed inside the cell under inert conditions, then it was
A mixture of Ni(cod)2 (0.06 g, 0.22 mmol) and
PhNCO (1.1 g, 9.2 mmol) was stirred at 60°C for 24 h.
Using the same procedure described above, a solid was
obtained corresponding to (PhNCO)3 (yield: 0.14 g,
connected to a high-pressure line and CO was trans-
2
ferred into the cell using a pneumatic pump. The tem-
perature of the cell was kept constant at 40°C. When a
single phase (total disappearance of the solid) was
observed inside the cell, a measure of the pressure was
taken, and the solubility calculated in mole per kilo-
13%).
Reaction of Ni(cod) (0.025 g, 0.09 mmol) and p-
2
CH OC H NCO (0.58 g, 3.9 mmol) afforded the corre-
3
6
4
sponding trimer as a white solid. Mass spectrum (EI+)
m/z: 448. Yield: 0.32 g (56%). Spectroscopic data are in
agreement with those reported in the literature [11].
When the cyclotrimerisation reaction of PhNCO with
gram. The complex CpCo(CO) is very soluble, giving a
2
beautiful red colour, CpCoPPh Me is moderately solu-
3
2
ble, whereas the complex Ni(cod) , as it was previously
2
Ni(cod) as catalyst was repeated adding four equiva-
2
reported by Kreher et al. [5a], is practically insoluble.
lents of PPh , after 24 h at room temperature (r.t.), a
3
However, when Ni(cod) is mixed with an excess of
2
total conversion to the trimer was observed. If toluene
is used as solvent, after 24 h at 40°C only a 17% yield
of trimer was formed.
arylisocyanate in scCO , a light yellow mixture is
2
formed, showing that the arylisocyanate acts as a co-
solvent giving rise to a small solubility of the complex.
After these measurements, the starting compounds were
No formation of trimer was achieved when a solution
of PPh (0.23 g, 0.88 mmol) and PhNCO (1.1 g, 9.2
3
recovered in all cases, no reaction with CO was ob-
2
mmol) was stirred at r.t. for 24 h.
served for any of the compounds.
In order to compare the results obtained using scCO2
as reaction medium, the reactions of the arylisocyanates
ArNCO (Ar=Ph, p-CH C H , p-CH OC H ) and the
2
.5.3. Cyclotrimerisation of arylisocyanates using
CpCo(CH ) (PPh ) as catalyst
3
2
3
3
6
4
3
6
4
CpCo(CH ) (PPh ) (0.017 g, 0.04 mmol) and PhNCO
catalysts (CpCo(CO) , CpCoPPh Me or Ni(cod)2)
3
2
3
2 3 2
(
2
(
0.31 g, 2.52 mmol) were mixed and stirred at r.t. After
4 h, all the initial PhNCO had trimerised to give
PhNCO) . The reaction was worked out using the
were performed, in the first place, simply by direct
mixture of the catalyst with the neat liquid aryliso-
cyanate, without the use of a solvent (these results are
presented in Table 2). Trimers of the corresponding
3
same procedure described in Section 2.4.1.