(R = n-Pr)

[100031-33-2]  · C20H24CoN2O2  · Bis(N-propylsalicylideneaminato)cobalt(II)  · (MW 383.35) (R = i-Pr)


(catalyst for the conversion of arylglyoxals to a-aryl-a-hydroxyacetic esters1)

Physical Data: mp 226-234 °C (R = i-Pr).2

Solubility: sol CHCl3, benzene, and dioxane; slightly sol ethanol and cyclohexane; insol petroleum ether.

Form Supplied in: red crystals.

Preparative Methods: a solution of bis(salicylaldehyde)cobalt(II) dihydrate and a slight excess of propylamine in methanol is heated at reflux in the presence of a trace amount of formaldehyde for 10 to 40 min.3 As the mixture is cooled, red crystals separate out. The crystals are filtered quickly and dried in vacuo.

Purification: recrystallization from i-PrOH/CHCl3 (i-Pr).4

Handling, Storage, and Precautions: unlike the N-i-propylsalicylidene CoII complex, the N-n-propylsalicylidene CoII complex is readily oxidized by oxygen in the atmosphere.3 It is thus necessary to carry out the above procedure in an oxygen-free atmosphere.

a-Phenyl-a-hydroxyacetic Ester.

Bis(N-n-propylsalicylideneaminato)cobalt(II) catalyzes the highly selective transformation of phenylglyoxal to a-phenyl-a-hydroxyacetic ester (eq 1).1 After a solution of phenylglyoxal (1) (1.0 mmol) and N-n-propylsalicylidene CoII complex (2a) (0.2 mmol) in a mixture of i-PrOH (40 mL) and 1,2-dichloroethane (20 mL) was heated at 60 °C for 8 h under oxygen atmosphere, the metal complex was separated, and the solvent was evaporated to afford a 97:3 mixture of i-propyl mandelate (3) and i-propylphenyl glyoxylate (4) in 93% yield. N-i-Propylsalicylidene CoII complex (2b) also catalyzes this transformation; however, a lower yield (31%) of i-propyl mandelate (3) was obtained. The hydroxocobalt(III) complex, CoIII(OH),5 which is generated from irreversible oxidation of the CoII complex in alcoholic solvents, is believed to be the reactive catalytic species.

1. Maruyama, K.; Murakami, Y.; Yoda, K.; Mashino, T.; Nishinaga, A. CC 1992, 1617.
2. Sacconi, L.; Paoletti, P.; Ciampolini, M. JACS 1963, 85, 411.
3. (a) Nishikawa, H.; Yamada, S. BCJ 1964, 37, 1154. (b) Sacconi, L.; Ciampolini, M.; Maggio, F.; Cavasino, F. P. JACS 1962, 84, 3246.
4. Horrocks, W. D. Jr.; Burlone, D. A. ICA 1979, 35, 165.
5. Nishinaga, A.; Kondo, T.; Matsuura, T. CL 1985, 905.

Sangho Koo

Myong Ji University, Kyung Ki Do, Korea

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