Synthesis, structure and reactivity of PdII complexes with the terdentate imino alcohol ligand C6H3-3,4-(OMe)2–C(H)NCH2CH2OH

Abstract

The reaction of the imino alcohol C₆H₃-3,4-(OMe)₂-C(H)NCH₂CH₂OH, 1, with Pd(OAc)₂ yields the dinuclear orthometallated compound [Pd(μ-OAc){C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ²-C,N}]₂, 2, which, by reaction with excess LiCl in MeOH, can be transformed into the halide-bridged complex [Pd(μ-Cl){C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ²-C,N}]₂, 3. Complex 3 reacts with neutral monodentate ligands L that promote the cleavage of the halide bridging system to give the mononuclear [Pd(Cl){C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ²-C,N}(L)] (L = PPh₃4; py 5) complexes. The OH group does not interact with the Pd atom in complexes 2–5. The reaction of 3 with AgClO₄ in NCMe gives the cationic monosolvate [Pd{C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ³-C,N,O}(NCMe)](ClO₄), 6, in which the orthometallated ligand is now C,N,O-terdentate through coordination of the OH group. The strength of the Pd–O(H) bond has been studied. Complex 6 reacts with an excess of a neutral monodentate ligand L to give [Pd{C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ³-C,N,O}(L)](ClO₄) (L = PPh₃7; py 8), in which the incoming ligand L replaces the NCMe but does not cleave the Pd–O(H) bond. Alternatively, complexes 7 and 8 can be obtained by reaction of 3 with AgClO₄ and L. Complex 6 reacts with bidentate N-donor ligands, yielding [Pd{C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ³-C,N,O}(L–L-κ¹-N)](ClO₄) (L–L = bipy 9; N,N,N′,N′-tmeda 10), in which the bipy or tmeda ligand is coordinated through only one N atom. The rupture of the Pd–O(H) bond can be accomplished by reacting 6 with diphosphine ligands, such as dppe, giving [Pd{C₆H₂-4,5-(OMe)₂-2-C(H)NCH₂CH₂OH-κ²-C,N}(dppe-P,P)](ClO₄), 11. Complexes 4 ·CHCl₃ and 7 have been characterized by X-ray diffraction.