Catalysis of Organic..

Zoeller and Barnette 391above 120°C. A closer look at the impact of temperature on selectivity is shown inTable 5 where the response to temperature was examined at (i) constant partialpressure of CO and (ii) at constant total pressure. Selectivity losses becameincreasingly severe with higher temperature and optimal performance was achievedat about 120-130°C. This loss of selectivity is similar to the decrease observed withincreasing temperatures in the earlier screening runs using (Ph 3 P) 2 PdCl 2 as a catalyst.Fortunately, in the case of (cy-hex 3 P) 2 PdCl 2 catalysts this phenomenon is notobserved until higher temperatures are attained. Access to higher temperatureregimes allows (cy-hex 3 P) 2 PdCl 2 catalysts to be operated at substantially higherreaction rates without the significant selectivity losses observed when using theearlier (Ph 3 P) 2 PdCl 2 catalyst at higher temperatures.Table 4. Effect of Pressure on Conversion and Selectivity aGaugeSelectivityEntryT(°C)Pressure(atm)bP co(atm) Conversion MPA PA TON1 120 5.4 1.4 78% 91% 3.2% 94502 120 8.5 4.4 89% 88% 3.7% 102803 120 17.0 12.9 68% 88% 2.6% 79604 120 34.0 29.9 57% 60% 2.1% 45705 130 8.5 2.7 92% 78% 3.3% 94706 130 17.0 11.2 78% 82% 3.3% 84207 130 34.0 28.2 84% 69% 2.4% 7600aConditions: 33.0 mL chloropinacolone, 90 mL Bu 3 N, 31.0 mL MeOH; catalyst:14.0 mg (0.019 mmol) (cy-hex 3 P) 2 PdCl 2 + 28.0 mg. (0.1 mmol) of cy-hex 3 P, 3 h, COpressure, and temperature as indicated.bP co (partial CO pressure) calculated by subtracting the partial pressure of MeOHand Bu 3 N from the total pressure.Table 5. Effect of Temperature at Constant Partial Pressure CO and Constant GaugePressureGaugeSelectivityEntryT(°C)Pressure(atm)bP co(atm) Conversion MPA PA TON1 110 7.1 4.4 38% 40% 2% 20002 120 8.5 4.4 89% 88% 4% 102803 130 10.2 4.4 89% 82% 3% 97404 140 12.2 4.4 97% 80% 6% 102205 150 13.6 4.4 97% 69% 11% 88706 120 17.0 12.9 68% 88% 3% 79607 130 17.0 11.2 78% 82% 3% 84208 140 17.0 9.2 97% 80% 9% 103409 150 17.0 6.7 99% 59% 24% 7690