Orthopalladation of iminophosphoranes: synthesis, structure and study of stability

Abstract

The reaction of Pd(OAc)₂ with polyfunctional iminophosphoranes Ph₃PNCH₂CO₂Me (1a), Ph₃PNCH₂C(O)NMe₂ (1b), Ph₃PNCH₂CH₂SMe (1c) and Ph₃PNCH₂-2-NC₅H₄ (1d), gives the orthopalladated dinuclear complex [Pd(µ-Cl){C₆H₄(PPh₂NCH₂CO₂Me-κ-C,N)-2}]₂ (2a) and the mononuclear derivatives [PdCl{C₆H₄(PPh₂NCH₂CONMe₂-κ-C,N,O)-2}] (2b), [PdCl{C₆H₄(PPh₂NCH₂CH₂SMe-κ-C,N,S)-2}] (2c) and [PdCl{C₆H₄(PPh₂NCH₂-2-NC₅H₄-κ-C,N,N)-2}] (2d). The reaction implies the activation of a C–H bond in a phenyl ring of the phosphonium group, this fact being worthy of note due to the strongly deactivating nature of the phosphonium unit. The palladacycle containing the metallated carbon atom is remarkably stable toward the coordination of incoming ligands, while that formed by the iminic N atom and another heteroatom (O, 2a and 2b; S, 2c; N, 2d) is less stable and the resulting complexes can be considered as hemilabile. The X-ray crystal structures of the cyclopalladated [Pd(µ-Cl){C₆H₄(PPh₂NCH₂CO₂Me-κ-C,N)-2}]₂ (2a), [PdCl{C₆H₄(PPh₂NCH₂–2-NC₅H₄-κ-C,N,N)-2}] (2d), [Pd{C₆H₄(PPh₂NCH₂CONMe₂-κ-C,N,O)-2}(NCMe)](ClO₄) (3b) and [Pd{C₆H₄(PPh₂NCH₂CONMe₂-κ-C,N,O)-2}(py)](ClO₄) (7b), and the coordination compound cis-[Pd(Cl)₂(Ph₃PNCH₂CH₂SMe-κ-N,S)] (8) are also reported.