Monoanionic salicylaldimine ligands with (thio)phosphoryl pendant arms: Synthesis and complexing features

Schiff base condensation of o-(thio)phosphorylated anilines with salicylaldehyde affords novel salicylaldimine ligands 1a,b with (thio)phosphoryl pendant arms. Under base-induced deprotonation, 1a,b readily form complexes with Re(I) (2a,b), Pd(II) (3a,b), and Ni(II) (4) ions, featuring κ2-N,O (3a) or κ3-X,N,O (X = O, S) (in the other cases) coordination mode depending on the nature of the substituent X in the P = X moiety. In the absence of a base, the interaction of 1b with (PhCN)2PdCl2 yields molecular complex 5 which can be readily transformed into 3b under action of triethylamine. Moreover, complex 3b with the deprotonated form of the ligand can be also readily synthesized by the template assembling of the corresponding aniline and salicylaldehyde on the Pd(II) ion in the presence of Et3N. All the complexes are characterized by spectroscopic techniques (NMR, IR, and Raman) and in some cases by X-ray diffraction analysis. Palladium complex 3b was found to be active (pre)catalyst for the Suzuki cross-coupling of aryl bromides with phenylboronic acid.