A mixt. of Pd(OAc)2 and TBA4[ﾎｳ-SiW10O34(H2O)2] (TBA-SiW10, TBA = [(n-C4H9)4N]+) showed high catalytic activities for hydration of various kinds of structurally diverse nitriles including arom., aliph., heteroarom., and double bond-contg. ones. For hydration of 3-cyanopyridine, the turnover frequency was 860 h-1, and the turnover no. reached up to 670. A dipalladium-substituted ﾎｳ-Keggin silicodecatungstate, [ﾎｳ-H2SiW10O36Pd2(OAc)2]4- (I), was successfully synthesized by the reaction of [ﾎｳ-SiW10O34(H2O)2]4- with Pd(OAc)2 in a mixed solvent of acetone and water. The crystal structure of I was a monomeric, dipalladium-substituted, ﾎｳ-Keggin silicodecatungstate with bidentate acetate ligands. Compd. I showed similar activities and selectivities to those of a simple mixt. of Pd(OAc)2 and TBA-SiW10. The kinetic, mechanistic, and d. functional theory calcn. studies show that the dipalladium site plays an important role in the present hydration, and the nucleophilic attack of a hydroxide or water to the nitrile carbon atom is included in the rate-detg. step. [on SciFinder(R)]
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