Catalysis of Organic..

Zoeller and Barnette 387The first step in achieving the desired increase in turnover number andconcentration was to optimize the catalyst choice. The earlier investigation ofchloroacetone carbonylations was restricted to a description of (Ph 3 P) 2 PdCl 2operating at 110°C and 10 atm (19, 20) under fairly dilute conditions. Based onanalogy to the earlier literature, the only anticipated problem was loss of selectivitydue to reductive dehalogenation of chloropinacolone to pinacolone (PA). A numberof catalysts, including complexes of Ru, Rh, Co, Ir and Pd, were tested for activity inthis study. However, only Pd demonstrated any significant activity. A summary ofthe results with Pd catalysts in the screening process is summarized in Table 1.Table 1. Screening Pd Catalysts for the Carbonylation of α-Chloropinacolone. aSelectivityEntry Catalyst Conversion MPA b PA b TON b1 (Ph 3 P) 2 PdCl 2 59% 84% 8% 4172 (cy-hex 3 P) 2 PdCl 2 82% 95% 2% 6563 (2-pyridyl)PPh 2 :PdCl 2 (2:1) 55% 81% 4% 3784 (o-toluyl) 3 P:PdCl 2 (2:1) 13% 0% 4% 05b(Me 2 Im) 2 PdCl 2 61% 76% 11% 3906b,c(Ms 2 Im) 2 PdCl 2 71% 95% 3% 4437 Ph 2 P(CH 2 ) 2 PPh 2 :PdCl 2 (1:1) 18% 5% 10% 88 Ph 2 P(CH 2 ) 3 PPh 2 :PdCl 2 (1:1) 23% 5% 16% 99 Ph 2 P(CH 2 ) 4 PPh 2 :PdCl 2 (1:1) 28% 8% 17% 1810 Ph 2 P(CH 2 ) 4 PPh 2 :PdCl 2 (2:1) 47% 3% 26% 1011 Ph 2 P(CH 2 ) 4 PPh 2 :PdCl 2 (1:1) 19% 0% 22% 012 (tert-Bu) 3 P:PdCl 2 (4:1) 18% 3% 41% 513 (Ph 3 P):(Ph 3 P) 2 PdCl 2 (2:1) 57% 84% 3% 405(P/Pd= 4)14 (cy-hex 3 P):(cy-hex 3 P) 2 PdCl 2 79% 90% 2% 591(2:1) (P/Pd = 4)15d(Ph 3 P) 2 PdCl 2 49% 88% 7% 43416d(cy-hex 3 P) 2 PdCl 2 72% 91% 2% 65017e(Ph 3 P) 2 PdCl 2 75% 73% 9% 56218e(cy-hex 3 P) 2 PdCl 2 98% 91% 2% 884a Conditions (unless otherwise noted): 11.0 mL (83.8 mmol) chloropinacolone, 30.0mL (0.126 mol) n-Bu 3 N, 110 mL MeOH, 0.1mmol Pd, 5.4 atm CO, 105°C, 3 hb Abbreviations: MPA = methyl pivaloylacetate; PA = Pinacolone; TON = molMPA produced/mol Pd used; Me 2 Im = 1,3-dimethyl imidazoline-2-ylidene (dimethylimidazolium carbene complex); Ms 2 Im = 1,3-di-(2,4,6-trimethylphenyl) imidazoline-2-ylidene (dimesityl imidazolium carbene complex); cy-hex = cyclohexylcUsed 0.127 mmol Pd catalystdConditions: 13.1 mL (0.10 mol) chloropinacolone, 36 mL (0.151 mol) n-Bu 3 N, 110mL MeOH, 0.1mmol Pd, 10.0 atm CO, 105°C, 3 heConditions: 11.0 mL (83.8 mmol) chloropinacolone, 30.0 mL (0.126 mol) n-Bu 3 N(0.151 mol) , 110 mL MeOH, 0.1mmol Pd, 10.0 atm CO, 120°C, 3 h