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

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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.

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