Reactions and catalytic applications of a PNCNP pincer palladium hydride complex

Abstract

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.