| Research Abstract |
We investigated here (I) the carbonylation processes of amitnes and alcohols catalyzed by palladium complexes and (2) C-O bond activation by palladium complexes and its application to novel catalytic hydrogenation processes.
Major findings : (a) New direct carbonylation of benzyl alcohol catalyzed by a palladium complex with hydrogen iodide promoter to give phenylacetic acid in excellent yields in aqueous systems was discovered. Application of the carbonylation processes to other arylmethanol analogues provided convenient means to prepare 3-isochromanone, 1, 4-benzeneacetic acid, 2-hydroxybenzeneacetic acid, and 2-naphthaleneacetic acid.
(b)Examination of the reactions of the (phenylacetyl)palladium complexes with secondary amines and alcohols provided supporting evidence for operation of different types of mechanisms for yielding amides and esters. The amide formation is proposed to proceed through coordination of the amine to the palladium center followed by its nucleophilic attack on the acyl group aided by a base. On the other hand, the formation of esters in reaction of acylpalladium with alcohols in the presence of a base is compatible with the reaction mechanism proceeding through an intermediate acyl-alkoxide complex.
(c)Activation of C-O bonds in various oxygen-containing organic compounds such as carboxylic acid anhydrides, carboxylic esters, and diketene by palladium(O) complexes was found to lead to the corresponding products with C-O bond cleavage. Based on these findings, realization of halide-free aldehyde preparation processes by hydrogenation of anhydrides or direct hydrogenation of carboxylic acids in the presence of pivalic anhydride catalyzed by palladium complexes was achieved.
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