A Mixed-Valent Pt(II)–Pt(IV) Complex with 2-(2-Pyridyl)benzimidazole as Bridging Ligand from Concurrent C–H and N–H Bond Activation and Selective Oxidative Addition

High Resolution Image Download MS PowerPoint Slide The dinuclear Pt(II)–Pt(II) complex [Pt 2 (Me) 2 (DMSO) 2 (pbi)] ( 1 ) with Hpbi = 2-(2-pyridyl)benzimidazole was synthesized from [Pt(Me) 2 (DMSO) 2 ] and Hpbi in a 2:1 molar ratio, activating both the C–H and N–H functions of Hpbi. Reaction of 1 with PPh 3 gave [Pt 2 (Me) 2 (PPh 3 ) 2 (pbi)] ( 2) . Reaction of 2 with excess MeI gave the mixed-valent Pt(II)–Pt(IV) complex [Pt 2 (Me) 3 (PPh 3 ) 2 I(pbi)] ( 3 ). Further reaction to the virtual Pt(IV)–Pt(IV) complex [Pt 2 (Me) 4 (PPh 3 ) 2 I 2 (pbi)] ( 4 ) was not observed. An S N 2-like mechanism of the oxidative addition reaction of 2 with MeI was suggested from kinetic measurements using UV–vis absorption spectroscopy and confirmed through mechanistical density functional theory calculations. The major UV–vis absorptions at 300–400 nm were assigned to mixed metal-to-ligand charge transfer (MLCT)/ligand-centered (LC) transitions for the Pt(II) centers of complexes 1, 2, and 3 based on TD-DFT calculations. For the Pt(IV) center of 3, admixtures of ligand-to-metal charge transfer (LMCT) and halide-to-ligand charge transfer (XLCT) were found. At 298 K, in fluid CH 2 Cl 2 solutions 1 to 3 show partially structured emission bands peaking at 523 nm for 1, 524 nm for 2, and at 514 nm for 3 . TD-DFT calculations revealed mixed 3 MLCT/ 3 LC for 1 and 2 and mixed 3 MLCT/ 3 XLCT/ 3 LC character for the excited T 1 state of 3 .