Titanocene complexes of ring-opened dibenzothiophene and related dimercaptobiaryl ligands

This paper describes organotitanium derivatives resulting from the reactions of titanocene dichloride with derivatives of dibenzothiophene (DBT). Lithium cleavage of DBT gives 2,2′-Li(LiS)C₁₂H₈ which reacts with (C₅H₅)₂TiCl₂ to give the metallacyclic complex (C₅H₅)₂TiSC₁₂H₈ (1). Two side products were isolated in smaller amounts, the thiolates (C₅H₅)₂Ti(SC₆H₄-2-Ph)₂ (2) and (C₅H₅)2Ti(SC₆H₄-2-Ph)Cl. DNMR studies showed that 1 and its MeC₅H₄ analog 3 are stereochemically non-rigid as a result of the folding of the organosulfur chelate. The structure of (MeC₅H₄)₂TiSC₁₂H₈ was verified by single crystal X-ray diffraction; the complex consists of the expected (MeC₅H₄)₂Ti moiety coordinated to the carbon and sulfur of the ring-cleaved DBT. An attempt to generate 2,2′-Li(LiS)C₁₂H₈ via the double metalation of 2-phenylbenzenethiol with two equivalents of BuLi in the presence of TMEDA, followed by treatment with (C₅H₅)₂TiCl₂, gave the deep green complex (C₅H₅)₂TiS₂C₂₄H₁₆ (4), Single crystal X-ray diffraction indicated that 4 is a complex of the 2,2-dimercapto-3,3′-diphenylbiphenyl ligand (2,2′-(LiS)₂-3,3′-Ph₂C₁₂H₆), resulting from the coupling of two molecules of 1-Ph-2-LiS-3-LiC₆H₃. DNMR studies showed that this complex is stereochemically rigid. The free dithiol was liberated by treatment of 4 with anhydrous HCl. The complex of the unsubstituted 2,2′-dimercaptobiphenyl was prepared by treatment of 2,2′-Li(LiS)C₁₂H₈ with one equivalent of sulfur followed by quenching the reaction with titanocene dichloride to give (C₅H₅)₂TiS₂C₁₂H₈ (6). Electrochemical studies show that the Ti^IV/III couple is reversible for all new compounds; the reduction potentials are lower for the chelating dithiolates and highest for the C-S chelate complexes 1 and 3.