4430 Organometallics, Vol. 24, No. 18, 2005
Belli Dell’Amico et al.
All reactions and manipulations were carried out under a
was filtered, and the solid was washed with heptane (3 × 5
controlled (dinitrogen, or carbon monoxide, as specified)
atmosphere. The gas-volumetric measurements were carried
out according to the method described by Calderazzo and
mL). The solid was dried in vacuo (101 mg) and identified as
2
PtCl (COD) by comparison with an authentic sample (IR in
1
195
Nujol, H NMR, and Pt NMR [peak at -3329 ppm] in 1,2-
dichloroethane). An analogous experiment was carried out in
1,2-dichloroethane, where the product is soluble, with similar
1
9a
Cotton.
The compounds cis-Pt(CO)
2
3
-1
2
Cl
2
(λmax 255, ꢀmax 4831 M
2
cm- ), PtCl
1
(COD),
19
and cis-[PtCl
(CO)(1-cyclohexene)]
9a
results. No carbonylation of PtCl
20 °C in toluene at atmospheric pressure.
Synthesis of PtCl (NBD) from cis-PtCl
2
2
(COD) was observed at
-
1
-1
(
1a, λmax 261 nm, ꢀmax 4839 M cm ) were prepared according
to the literature. PtCl (NBD) was prepared either according
to the literature or by an original method described below.
Synthesis of PtCl (NBD). An aqueous solution of K [PtCl
6.0 mmol) was introduced in a 250 mL flask. NBD (3.2 mL,
0 mmol) in 1,2-dichloroethane and a catalytic amount of
NBu ]Cl (1.0 mmol) were added. The biphasic reaction
2
2
2
(CO)
20 mL of 1,2-dichloroethane was
saturated at room temperature with CO, and NBD (0.074 mL,
0.69 mmol) and a fragile glass ampule containing cis-PtCl
(CO) (147 mg, 0.46 mmol) were then introduced. At 21.7 °C
2
. In a gas-
1
9c
19a
volumetric apparatus,
2
2
4
]
(
3
[
2
-
2
4
(total pressure 772 Torr), the ampule was broken and the
evolved gas was measured. At the end of the reaction (about
1 h) a volume of CO corresponding to a CO/Pt molar ratio of
1.94 was measured. No carbonyl bands (IR) were observed in
mixture was refluxed for 5 h. The substantially colorless
aqueous layer was separated at room temperature and dis-
carded. Heptane (25 mL) was added to the organic colorless
layer, and the resulting suspension was filtered. The solid
product was washed with heptane (3 × 10 mL) and dried in
1
95
the supernatant solution. In the Pt NMR spectrum of the
solution (with some C added), only one signal at -3117 ppm
2
due to PtCl (NBD) was present. The carbonylation of PtCl -
6 6
D
vacuo (1.34 g, 62.3% yield). Anal. Calcd for C
7 8 2
H Cl Pt: C, 23.5;
2
H, 2.3. Found: C, 23.3; H, 2.2. IR (Nujol, KBr windows):
440w, 1310s, 1254w, 1242w, 1226m, 1180m, 1115w, 1030w,
(NBD), monitored gas-volumetrically, did not proceed at
22 °C in 1,2-dichloroethane, at atmospheric pressure of CO.
Equilibrium Constants and Thermodynamic Param-
eters Determination. IR Measurements. The CO/olefin
substitutions on cis-PtCl (CO) were studied by IR spectros-
1
9
6
92w, 980m, 951m, 936w, 906w, 882w, 848m, 832w, 774m,
78w and 612 cm-1. 1H NMR (C
D
Cl
): 5.3 (m, 4 H, JPt-H 68
2
2
2
4
1
95
Hz); 4.3 (m, 2 H); 1.6 (s, 2 H) ppm.
CD Cl ): -3117 ppm.
Synthesis of cis-[PtCl
monoxide, to a solution of cis-PtCl
2 2
Pt NMR (CH Cl +
2
2
-
1
2
2
copy in the CO stretching region (2200-2000 cm ) at atmo-
spheric pressure. After addition of the olefin under CO, the
reaction mixture was monitored by IR until equilibrium was
CO
2
(CO)(1-octene)], 1b. Under carbon
(CO) (502 mg, 1.56 mmol)
2
2
in 1,2-dichloroethane (200 mL) was added dropwise 1-octene
up to an olefin/Pt molar ratio of 60. The reaction was IR
reached. The final and initial absorbance of the ν band of
-1
cis-Pt(CO) Cl at 2178 cm was used for the evaluation of the
2
2
-
1
monitored through the bands at 2178 and 2136 cm due to
equilibrium constants according to eq 5. In each spectrum the
solvent contribution was subtracted, the olefin and CO con-
tribution being negligible. The measurements were performed
at PTOT ) 1 atm and T ) 21 °C by using a Specac P/N 21000
variable-temperature cell, consisting of a 0.1 mm cell equipped
-
1
2 2
cis-PtCl (CO) and at 2124 cm , due to the substitution
product. After consumption of the starting platinum complex,
the solution was evaporated to dryness and the solid residue
was treated with heptane (25 mL). The suspension was
filtered, and the colorless product was dried in vacuo and
with CaF windows inserted in a container supplied with KBr
2
sealed in vials under N
2
(360 mg, 57% yield). Due to its air
windows. In all cases the equilibrium constants were ap-
proximated to the concentration ratio according to eq 5. The
olefin was always used in large excess, and its equilibrium
concentration was considered to coincide with the initial one.
The CO concentration in saturated 1,2-dichloroethane at 1 atm
sensitivity, reliable elemental analyses could not be obtained.
However, the substance is spectroscopically pure. IR, Nujol,
-
1
KBr windows: νCO 2121 cm ; 1,2-dichloroethane, CaF
2
win-
-
1
dows:
cells): λmax 261 nm (ꢀ ) 4225 M cm ). H NMR (C
νCO 2124 cm . UV-vis (1,2-dichloroethane, quartz
-
1
-1
1
-3
24a
6
D
6
) (see
(5.5 × 10 M) was calculated after taking into account the
b
3
2
24b
structure below): 3.75 (d, H , 1 H, JH-H 14.6 Hz, JPt-H 53.5
solvent vapor pressure.
a
3
2
c
-2
Hz); 4.35 (d, H , 1 H, JH-H 7.3 Hz, JPt-H 68.9 Hz); 5.35 (m,H ,
In a typical experiment, a solution of cis-PtCl (CO) (∼10
2
2
1
1
1
3
H); 1.61 (m, 2 H) ppm and a group of multiplets at about
M) was prepared in a Schlenk tube under CO. Olefin solutions
of known concentration were stored under CO. A 1.0 mL
sample of the platinum-containing solution was added to 1.0
mL of the olefin solution, and the mixture was stirred (3 h)
under CO and then used to fill the IR cell, which was kept at
the same temperature as the reaction mixture.
1
3
1
ppm (m, 11 H). C NMR (C
6
D
6
): 152.1 (CO, JPt-C 1635 Hz);
1
1
12.5 (CH
2
dCH, JPt-C 104 Hz); 76.9 (CH
2
dCH, JPt-C 123 Hz);
7.8; 31.6; 29.7; 28.8; 22.8; 14.3 ppm. 1 Pt NMR (C
95
D
):
6
6
-
3708 ppm.
Equilibrium constants for reactions 3 and 4 at 21 °C have
been obtained as the averaged values of five independent
experiments carried out by using alkene concentrations in the
-
1
range 0.9-2.4 M (cyclohexene) and (0.8-1.3) × 10
1-octene).
UV Measurements. For equilibria 3 and 4, a series of
M
(
2 2 2
Synthesis of PtCl (COD) from cis-PtCl (CO) . By oper-
ating in a gas-volumetric apparatus, 20 mL of toluene was
saturated at room temperature with CO, and COD (0.203 mL,
1
9a
experiments at different temperatures were carried out and
studied by UV spectroscopy in the range 400-200 nm. In each
spectrum the solvent and olefin contribution was subtracted.
Corrections for the variation of solvent density with temper-
ature were not applied. The CO concentration was calculated
1
.65 mmol) and a fragile flame-sealed glass ampule containing
cis-PtCl (CO) (267 mg, 0.83 mmol) were then introduced. At
1.2 °C (total pressure 752 Torr), the fragile ampule was
2
2
2
mechanically broken and the evolved gas was measured. At
the end of the reaction (about 1 h) a volume of CO correspond-
ing to a CO/Pt molar ratio of 1.94 had been evolved. The
content of the reactor was evaporated to dryness, and the
residue was added of 1,2-dichloroethane (40 mL). The suspen-
sion was filtered, the filtrate was evaporated to dryness, and
heptane (10 mL) was added to the residue. The suspension
24
as in the case of the IR experiments, and its value (5.5 ×
-3
10
M) was assumed to be constant in the experimental
temperature range. This approximation is justified by the low
-1
4
value of the solution enthalpy of CO (0.79 kJ mol in CCl in
25
the range 283-318 K ) and by the fact that the partial
(
24) (a) L u¨ hring, P.; Schumpe, A. J. Chem.-Eng. Data 1989, 34, 250.
(
b) Handbook of Chemistry and Physics, 82nd ed.; Lide, D. R., Ed.;
(
23) Bagnoli, F.; Belli Dell’Amico, D.; Calderazzo, F.; Englert, U.;
CRC Press: Boca Raton, 2001-2002; pp 6-72.
(25) Tominaga, T.; Battino, R.; Gorowara, H. K.; Dixon, R. D. J.
Chem.-Eng. Data 1986, 31, 175.
Marchetti, F.; Herberich, G. E.; Pasqualetti, N.; Ramello, S. J. Chem.
Soc., Dalton Trans. 1996, 4317.