TITANOCENE COMPLEXES OF RING-OPENED DIBENZOTHIOPHENE AND RELATED DIMERCAPTOBIARYL LIGANDS

This paper describes organotitanium derivatives resulting from the rea ctions of titanocene dichloride with derivatives of dibenzothiophene ( DBT). Lithium cleavage of DBT gives 2,2'-Li(LiS)C12H8 which reacts wit h (C5H5)(2)TiCl2 to give the metallacyclic complex (C5H5)(2)TiSC12H8 ( 1). Two side products were isolated in smaller amounts, the thiolates (C5H5)(2)Ti(SC6H4-2-Ph)(2) (2) and (C5H5)(2)Ti(SC6H4-2-Ph)Cl. DNMR stu dies showed that 1 and its MeC(5)H(4) analog 3 are stereochemically no n-rigid as a result of the folding of the organosulfur chelate. The st ructure of (MeC(5)H(4))(2)TiSC12H8 was verified by single crystal X-ra y diffraction; the complex consists of the expected (MeC(5)H(4))(2)Ti moiety coordinated to the carbon and sulfur of the ring-cleaved DBT. A n attempt to generate 2,2'-Li(LiS)C12H8 via the double metalation of 2 -phenylbenzenethiol with two equivalents of BuLi in the presence of TM EDA, followed by treatment with (C5H5)(2)TiCl2, gave the deep green co mplex (C5H5)(2)TiS2C24H16, (4). Single crystal X-ray diffraction indic ated that 4 is a complex of the 2,2-dimercapto-3,3'-diphenylbiphenyl l igand (2,2'-(LiS)(2)-3,3' Ph(2)C(12)H(6)), resulting from the coupling of two molecules of 1-Ph-2-LiS-3-LiC6H3. DNMR studies showed that thi s 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)(2)TiS2C12H8 (6). Electrochemical studies show that the Ti-IV/III couple is reversible for all new compo unds; the reduction potentials are lower for the chelating dithiolates and highest for the C-S chelate complexes 1 and 3.