Article
Organometallics, Vol. 28, No. 24, 2009 6999
Scheme 3. Decarbonylation of a Copolymer Chaina
a If a six-membered chelate is formed between the metal center and the growing polymer chain, it acts as a trapping ligand and must be disrupted
before decarbonylation can proceed. R represents the growing polymer chain, and L∩L represents a bidentate ligand.
Scheme 4. Possible Mechanism for the Isomerization of the Catalytic Species from the Complex with the Pd-C Bond cis to the Phosphine
to the Complex with the Pd-C Bond trans to the Phosphine That Begins with a Pseudorotation of the Phosphine-Sulfonate Liganda
a R represents the growing polymer chain, and L represents a coordinated monomer.
Conclusions
121.49 MHz for 31P, or 75.4 MHz for 13C NMR spectra. 31P and
13C spectra were obtained with proton decoupling. Quantitative
13C experiments were performed using a zgig pulse sequence and
a delay of 120 s before each scan. High-pressure NMR tubes
were obtained from Wilmad with a Quick Pressure Valve, 5 mm
diameter, 0.77 mm wall thickness, and an 8 in. length.
We have demonstrated the synthesis of a series of non-
alternating copolymers of ethene with carbon monoxide
using a neutral palladium catalyst bearing a phosphine-
sulfonate ligand. It is possible to control the degree of carbon
monoxide incorporation from 0-50 mol % by varying the
monomer feed ratio and reaction temperature.
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NMR data for 1: HNMR (CD2Cl2): δ (ppm) 0.22 (d, 3H,
PdCH3); 3.68 (s, 6H, OCH3); 6.99 (dd, 2H, Ar); 7.06 (b, 2H, Ar);
7.36 (m, 2H, Ar); 7.50 (m, 3H, Ar); 7.58 (t, 2H, Ar); 7.92 (t, 1H,
Ar); 8.06 (dd, 1H, Ar); 8.75 (dd, 2H, Py). 31P NMR (CD2Cl2): δ
By examining the kinetic and thermodynamic parameters,
we found that the catalyst displays an unusually small differ-
ence in its binding affinities for ethene and carbon monoxide.
However, the difference in monomer binding affinity alone is
not sufficient to explain the degree of nonalternation actually
observed in this system. It appears that decarbonylation also
plays a significant role in the nonalternation. Unlike the
traditional cationic palladium complexes that catalyze the
alternating copolymerization, the neutral complex formed
from the anionic ligand disfavors the formation of Pd-O
chelates by coordination of the carbonyl group on the growing
polymer chain. This, in turn, facilitates ethene coordination to
the metal and subsequent insertion. We also found that the rate
of decarbonylation in the traditional cationic diphosphine
system is higher than in the neutral phosphine-sulfonate system
when chelation is absent.
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23.4 ppm. 2: H NMR (CD2Cl2): δ (ppm) 1.84 (s, 3H, PdC-
(O)CH3); 3.78 (s, 6H, OCH3); 7.03 (dd, 2H, Ar); 7.10 (m, 2H,
Ar); 7.34 (m, 2H, Ar); 7.53 (m, 3H, Ar); 7.60 (m, 2H, Ar); 7.77
(m, 2H, Ar); 7.95 (t, 1H, Ar); 8.09 (dd, 1H, Ar); 8.81 (d, 2H, Py);
31P NMR (CD2Cl2): δ 11.0 ppm. 13C NMR (CD2Cl2): δ 227
ppm (PdC(O)CH3). 3: 1H NMR (CD2Cl2): δ (ppm) 1.30 (m, 2H,
PdCH2CH2C(O)CH3); 1.89 (s, 3H, PdCH2CH2C(O)CH3); 2.11
(b, 2H, PdCH2CH2C(O)CH3); 3.70 (s, 6H, OCH3); 7.02 (dd, 2H,
Ar); 7.09 (dd, 2H, Ar); 7.34 (m, 2H, Ar); 7.50 (dd, 3H, Ar); 7.59
(t, 2H, Ar); 7.67 (b, 2H, Ar); 7.90 (t, 1H, Ar); 8.09 (m, 1H, Ar);
8.79 (d, 2H, Py). 31P NMR (CD2Cl2): δ 23.6 ppm. 13C NMR
(CD2Cl2): δ 216 ppm (PdCH2CH2C(O)CH3). 4: 1H NMR
(CD2Cl2, -70 °C): δ (ppm) 0.8-1.1 (b, 2H, (PdCH2CH2-
C(O)CH3); 1.4 (s, 3H, PdCH2CH2C(O)CH3); 1.5-1.7 (b, 2H,
PdCH2CH2C(O)CH3); 3.6 (b, 3H, OCH3); 3.8 (b, 3H, OCH3);
5.4 (s, free ethene); 6.7-8.0 (17H, Ar); 8.7 (b, 1H, Py); 8.8 (b,
1H, Py). 31P NMR (CD2Cl2, -70 °C): δ 27.0 ppm. 13C NMR
(CD2Cl2, -70 °C): δ 201 ppm (PdCH2CH2C(O)CH3). 5:
1H NMR (CD2Cl2, -70 °C): δ (ppm) 0.8-1.1 (b, 2H, (PdCH2-
CH2C(O)CH3); 1.4 (s, 3H, PdCH2CH2C(O)CH3); 1.5-1.7 (b,
2H, PdCH2CH2C(O)CH3); 3.6 (b, 3H, OCH3); 3.8 (b, 3H,
OCH3); 6.7-8.0 (17H, Ar); 8.7, 8.8 (b, 2H, Py). 31P NMR
(CD2Cl2, -70 °C): δ 26.6 ppm. 13C NMR (CD2Cl2, -70): δ
201 (PdCH2CH2C(O)CH3). 6: 1H NMR (CD2Cl2): δ (ppm)
0.8 (b, 2H, PdCH2CH2CH3) 1.0 (b, 3H, PdCH2CH2CH3) 1.3
(b, 2H, PdCH2CH2CH3) 3.7 (s, 6H, OCH3); 5.5 (s, free ethene);
6.9-8.2 (17H, Ar); 8.8, 8.9 (b, 2H, Py). 31P NMR (CD2Cl2):
δ 27.1 ppm. 7: 1H NMR (CD2Cl2): δ (ppm) 1.76 (s, 3H,
PdC(O)CH3); 3.73 (s, 6H, OCH3); 7.00 (dd, 2H, Ar); 7.09 (b,
2H, Ar); 7.34 (dd, 2H, Ar); 7.50 (m, 3H, Ar); 7.60 (t, 2H, Ar);
7.93 (t, 1H, Ar); 8.03 (dd, 1H, Ar); 8.73 (d, 2H, Py). 31P NMR
(CD2Cl2): δ 11.4 ppm. 13C NMR (CD2Cl2): δ 227 ppm
(PdC(O)CH3).
Experimental Procedures
Chemical manipulations, with the exception of polymer
workup and analysis, were performed under a dry nitrogen
atmosphere using a glovebox or Schlenk techniques. All sol-
vents, with the exception of NMR solvents, were distilled over
CaH2 and degassed using the freeze-pump-thaw technique.
Ultra-high-purity ethene and ultra-high-purity carbon monox-
ide were obtained from MG Industries and used without further
purification. Deuterated NMR solvents and 13CO were ob-
tained from Cambridge Isotope Laboratories and used without
further purification. Palladium acetate (99%) was purchased
from Johnson Matthey and used as received. The phosphine-
sulfonate ligand was synthesized by following the literature
procedure.15 Palladium-methyl complex 1 was synthesized by
following the literature procedure.8
Nuclear magnetic resonance spectroscopy was performed
using a Bruker DPX-300 spectrometer equipped with a vari-
able-temperature, multinuclear probe at 300.13 MHz for H,
Differential scanning calorimetry was performed by heating
3 mg of copolymer samples at a rate of 20 °C min-1 from 40 to
300 °C using a TA Instruments model DSC Q100.
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