Reactions and catalytic applications of a PNCNP pincer palladium hydride complex.

A palladium(II) hydride complex supported by a benzene-based PNCNP pincer ligand, [2,6-(tBu2PNH)2C6H3]PdH (1), has been synthesized via two different routes: the reaction of the corresponding chloride complex with LiAlH4 and the reaction of the corresponding nitrate complex with KOCH3. Complex 1 exhibits strong deprotonating ability and versatile catalytic activity. Acetamide can be readily deprotonated by complex 1 to form the corresponding acetamido complex, [2,6-(tBu2PNH)2C6H3]PdNHC(O)CH3, in high yield. Complex 1 is an active catalyst for both the dehydrogenation of methanol to formaldehyde under mild conditions and direct hydration of nitriles to primary amides. Particularly, the direct hydration of nitriles to primary amides catalysed by complex 1 represents the most efficient palladium catalytic system for this type of reaction. A wide range of nitriles have been successfully hydrated to primary amides with 100% selectivity and good to excellent isolated yields. The possible reaction mechanisms are discussed.