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)3PNP] are obtained by treatment of [Mo(CO)3(CH3CN)3] with 1 equiv of the
respective PNP ligand. They were found to react with I2 to give novel seven-coordinate pincer complexes
of the types [Mo(PNP)(CO)3I]+ 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)Cl2] 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)X2] (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.

本文报道了一系列基于氮杂环二胺（2,6-二氨基吡啶、N,N'-二-1-十一烯基-2,6-二氨基吡啶、N,N'-二己基-2,6-二氨基吡啶以及2,6-二氨基-4-苯基-1,3,5-三嗪）的新型非手性与手性PNP钳型配体（PNP pincer-type ligands）的钼、铁、钌、镍、钯、铂配合物的合成与表征。通过将相应的氮杂环二胺与2当量的各类非手性及手性R₂PCl化合物在碱存在下反应，可以便捷地以高收率制备得到新型PNP配体。将[Mo(CO)₃(CH₃CN)₃]与1当量的相应PNP配体反应，可得到类型为[Mo(PNP)(CO)₃PNP]的钼PNP配合物。研究发现，这类配合物与碘单质反应后，会生成新型七配位钳型配合物[Mo(PNP)(CO)₃I]⁺和[Mo(PNP)(CO)₂(CH₃CN)I]⁺，具体产物取决于反应溶剂为二氯甲烷（CH₂Cl₂）还是乙腈（CH₃CN）。在乙腈中，将[Fe(H₂O)₆](BF₄)₂与1当量的PNP配体反应，可得到类型为[Fe(PNP)(CH₃CN)₃](BF₄)₂的二阳离子配合物。顺式及反式二氯化物配合物[Ru(PNP)(PPh₃)Cl₂]通过[RuCl₂(PPh₃)₃]与化学计量比的相应PNP配体的配体交换反应制备得到。Ni(II)的阳离子PNP配合物[Ni(PNP)Br]Br通过[NiBr₂(DME)]与1当量PNP配体的反应合成得到。类似地，将[M(COD)X₂]（M=Pd, Pt；X=Cl, Br）与1当量PNP配体反应，可得到阳离子型平面正方形配合物[M(PNP)X]X。若在卤离子清除剂三氟甲磺酸钾（KCF₃SO₃）存在下进行该反应，则可得到类型为[M(PNP)X]CF₃SO₃的配合物，这类配合物在非极性溶剂中的溶解度优于相应的卤化物配合物。已测定了具有代表性的钼、铁、钌、镍及钯PNP配合物的X射线晶体结构。最后，考察了钯配合物作为催化剂，用于部分芳基溴化物与苯硼酸的铃木-宫浦（Suzuki-Miyaura）偶联反应的催化性能。