ELECTRON-TRANSFER AND ION-PAIR FORMATION .40. SINGLE-CRYSTAL STRUCTURE OF BIS(SODIUM 1,1'-BIPHENYL-2-THIOLATE-DIGLYME) - AN INTERMEDIATE INTHE REDUCTIVE RING-OPENING OF DIBENZOTHIOPHENE

On Na-metal reduction of dibenzothiophene, the five-membered sulfur ri ng opens to form a colorless 1,1'-biphenyl-2-thiolate sodium salt, whi ch, according to its single-crystal structure determination, is a dime r containing a four-membered, twice diglyme-solvated ring (diglyme...N a(+-)SR)(2). Additional measurements provide the following information : cyclic voltammetry in aprotic MeCN solution shows one quasi-reversib le electron transfer at E(1/2)(Red) = -2.58 V. The dibenzothiophene ra dical anion can be generated in aprotic THF solution at a K mirror and characterized by an 81-line ESR spectrum and its simulation. This blu e species is also the first UV/VIS detectable one before the solution changes via green (due to blue + yellow color mixing) to yellow, yield ing across an isosbestic point a second and diamagnetic compound. All of the above results suggest a consecutive two-electron reduction foll owed by an intersystem protonation, M + (e(-)) --> M(.-) (blue) + (e(- )) --> (M(--), yellow?) + (H+) --> MH(-) (colorless), to yield the cry stallized and structurally characterized reaction intermediate. The di glyme-solvated sodium-salt dimer provides a basis for a quantum-chemic al discussion of some facets of the most likely microscopic reduction pathway.