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.