Tri(pyridylmethyl)phosphine: The Elusive Congener of TPA Shows Surprisingly Different Coordination Behavior

Tri­(pyridylmethyl)­phosphine (TPPh), the remarkably elusive congener of tri­(pyridylmethyl)­amine (TPA), has been prepared, as well as the relative tri­(N-methyl-pyridylamino)­phosphine (TPAMP). The coordination properties of these new ligands have been evaluated for chromium­(III), iron­(II), and ruthenium­(II) complexes and compared with the related TPA complexes. In all cases, a different coordination behavior has been observed whereby TPPh and TPAMP always act as tridentate ligands. A chromium­(III) complex [Cr­(TPPh)­Cl3] has been prepared, which has shown low ethylene oligomerization activity. Octahedral low spin iron­(II) complexes [Fe­(TPPh)2]2+ and [Fe­(TPAMP)2]2+ were obtained with two ligands bound to the metal center. Ruthenium­(II) chloro complexes of TPA and TPPh undergo ligand exchange reactions in acetonitrile, and the ruthenium­(II) complex [Ru­(MeCN)2(TPA)]2+ can be oxidized by m-CPBA in acetonitrile to give a transient ruthenium­(IV) oxo complex [Ru­(O)­(MeCN)­(TPA)]2+. Attempts to generate high valent ruthenium­(IV) oxo TPPh or TPAMP complexes could not be achieved, probably due to insufficient stabilization by these strong field ligands.三(吡啶甲基)膦(Tri(pyridylmethyl)phosphine, TPPh)是三(吡啶甲基)胺(Tri(pyridylmethyl)amine, TPA)一类难以获取的同系物，本研究成功实现了其合成，同时还制备了对应的三(N-甲基吡啶氨基)膦(TPAMP)。研究人员对这三种新型配体的配位性能展开了评估，测试体系涵盖铬(III)、铁(II)与钌(II)配合物，并将结果与相关TPA配合物进行了对比。所有测试体系均展现出迥异的配位行为：TPPh与TPAMP始终以三齿配体的形式参与配位。本研究合成了铬(III)配合物[Cr(TPPh)Cl₃]，该配合物表现出较低的乙烯低聚活性。研究人员获得了八面体低自旋铁(II)配合物[Fe(TPPh)₂]²⁺与[Fe(TPAMP)₂]²⁺，其金属中心结合了两个配体分子。TPA与TPPh的钌(II)氯配合物可在乙腈中发生配体交换反应；其中配合物[Ru(MeCN)₂(TPA)]²⁺可在乙腈体系中被间氯过氧苯甲酸(m-CPBA)氧化，得到瞬态钌(IV)氧配合物[Ru(O)(MeCN)(TPA)]²⁺。尝试制备高价钌(IV)氧合TPPh或TPAMP配合物的实验均未成功，这大概率是由于这类强场配体无法为目标配合物提供足够的稳定化作用。