Tellurium(0) as a Ligand: Synthesis and Characterization of 2-Pyridyltellurolates of Platinum(II) and Structures of [Pt{2-Te-3-(R)C₅H₃N}₂Te(PR′₃)] (R = H or Me)

Treatment of toluene solutions of the ditellurides [Te₂{C₅H₃N(R)-3}₂] (R = H or Me) with [Pt(PPh₃)₄] yielded two types of complexes, [Pt{2-Te-3-(R)C₅H₃N}₂(PPh₃)₂] (1a−d) as the major products and [Pt{2-Te-3-(R)C₅H₃N}₂Te(PPh₃)] (2a−d) as minor products. The above complexes can also be obtained by the reaction of [PtCl₂(PR′₃)₂] (PR′₃ = PPh₃ or PPh₂(2-C₅H₄N)) with 2 equiv of Na(2-Te-C₅H₃R). The complexes were characterized by elemental analyses and UV−vis, NMR (¹H and ³¹P), and (in part) XPS spectroscopy. The molecular structures of [Pt(2-Te-C₅H₄N)₂Te(PPh₃)] (2a) and [Pt{2-Te-C₅H₃(Me)N}₂Te(PPh₃)] (2b) were established by single crystal X-ray diffraction. Both complexes exhibit a distorted square-planar configuration at the platinum(II) centers. The two mutually trans positioned 2-pyridinetellurolate ligands [2-Te-C₅H₃(R)N] coordinate to the central platinum atom in a monodentate fashion through the tellurium atoms. The tellurium(0) atom adopts a “bent T” configuration as it is bridging the 2-Te- C₅H₃(R)N molecules via N−Te−N bonds (166° angle) and coordinates to Pt^II in the trans position to PPh₃. The novel bis(pyridine)tellurium(0) arrangement resembles the bis(pyridine)iodonium structure. The calculated NICS indices and ELF functions clearly show that the compounds 2a and 2b are aromatic in the region defined by the Te−C−N−Te−Pt five-membered rings.