Achiral and chiral transition metal complexes with modularly designed tridentate PNP pincer-type ligands based on N-heterocyclic diamines

The synthesis and characterization of a series of molybdenum, iron, ruthenium, nickel, palladium, and platinum complexes containing new achiral and chiral PNP pincer-type ligands based on the N-heterocyclic diamines 2,6-diaminopyridine, N,N'-di-10-undecenyl-2,6-diaminopyridine, N,N'-dihexyl-2,6-diaminopyridine, and 2,6-diamino-4-phenyl-1,3,5-triazine are reported. The new PNP ligands are prepared conveniently in high yield by treatment of the respective N-heterocyclic diamines with 2 equiv of a variety of achiral and chiral R2PCl compounds in the presence of base. Molybdenum PNP complexes of the type [Mo(PNP)(CO)(3)PNP] are obtained by treatment of [Mo(CO)(3)(CH3CN)(3)] with 1 equiv of the respective PNP ligand. They were found to react with I-2 to give novel seven-coordinate pincer complexes of the types [Mo(PNP)(CO)(3)I](+) and [Mo(PNP)(CO)(2)(CH3CN)I](+) depending of whether the reaction is carried out in CH2Cl2 or CH3CN. With [Fe(H2O)(6)](BF4)(2) and 1 equiv of PNP ligand in acetonitrile dicationic complexes of the type [Fe(PNP)(CH3CN)(3)](BF4)(2) are obtained. The cis and trans dichloride complexes [Ru(PNP)(PPh3)Cl-2] are prepared by a ligand exchange reaction of [RuCl2(PPh3)(3)] with a stoichiometric amount of the respective PNP ligand. Cationic PNP complexes of Ni(II), [Ni(PNP)Br]Br, were synthesized by the reaction of [NiBr2(DME)] with 1 equiv of PNP ligand. In similar fashion, treatment of [M(COD)X,] (M = Pd, Pt; X = Cl, Br) with 1 equiv of PNP ligand yields the cationic square-planar complexes [M(PNP)X]X. If the reaction is carried out in the presence of the halide scavenger KCF3SO3 , complexes of the type [M(PNP)X]CF3SO3 are obtained, which are better soluble in nonpolar solvents than the analogous halide compounds. X-ray structures of representative Mo, Fe, Ru, Ni, and Pd PNP complexes have been determined. Finally, the use of the palladium complexes as catalysts for the Suzuki-Miyaura coupling of some aryl bromides and phenyl boronic acid has been examined.