LAUSR

Four different pincer ligands, which prove that the disposition of the donor atoms in pincer ligands allows them to develop a marked ability to form less common coordination polyhedra and to favor unusual metal oxidation states, have been generated starting from OsH6(PiPr3)2 and 2-phenyl-6-(1H-pyrazol-3-yl)pyridine (Hpz-py-Ph) in order to stabilize phosphorescent, pentagonal-bipyramidal osmium(IV) emitters. Complex 1 reacts with the disubstituted heterocycle to give OsH2{κ3-N,N′,C-(pz-py-C6H4)}(PiPr3)2 (2), as a result of the activation of a phenyl o-CH bond and the pyrazolyl NH of the pyridine substituents. The addition of methyl trifluoromethanesulfonate (MeOTf) to 2 produces the methylation of the free N atom of the pz group and the formation of the salt [OsH2{κ3-N,N′,C-(Mepz-py-C6H4)}(PiPr3)2]OTf (3), which undergoes deprotonation of the metal center in the presence of KOtBu. The resulting monohydride OsH{κ3-N,N′,C-(Mepz-py-C6H4)}(PiPr3)2 (4) is unstable and evolves into OsH2{κ3-C,N,C′-(Mepz-py-C6H4)}...