Achiral and Chiral Transition Metal Complexes with Modularly Designed Tridentate PNP Pincer-Type Ligands Based on N-Heterocyclic Diamines

摘要

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-diamino-pyridine,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 R_2PCl compounds in the presence of base.Molybdenum PNP complexes of the type [Mo(PNP)(CO)_3PNP] are obtained by treatment of [Mo(CO)_3(CH_3CN)_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)_3I]~+ and [Mo(PNP)(CO)_2(CH_3CN)I]~+ depending of whether the reaction is carried out in CH_2Cl_2 or CH_3CN.With [Fe(H_2O)_6](BF_4)_2 and 1 equiv of PNP ligand in acetonitrile dicationic complexes of the type [Fe(PNP)(CH_3CN)_3](BF_4)_2 are obtained.The cis and trans dichloride complexes [Ru(PNP)(PPh_3)Cl_2] are prepared by a ligand exchange reaction of [RuCl_2(PPh_3)_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 [NiBr_2(DME)] with 1 equiv of PNP ligand.In similar fashion,treatment of [M(COD)X_2](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 KCF_3SO_3,complexes of the type [M(PNP)X]CF_3SO_3 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.