Radical routes to titanium(IV) thiolate complexes: structure and reactivity of (.eta.5-C5H5)TiIII and -TiIV donor and thiolate derivatives

Abstract

Reaction of Cp[sub 2]TiCl[sub 2] with donor ligands such as imidazole or PMe[sub 3] proceeds to a relatively small extent to induce reduction of Ti(IV) yielding the Ti(III) species Cp[sub 2]TiCl(L) with concurrent loss of a chlorine radical. Subsequent reaction of 3 with 1 equiv of 1,3-propanedithiol gives [Cp[sub 2]TiCl][sub 2](SCH[sub 2]CH[sub 2]CH[sub 2]S). In the presence of excess dithiol the known species [Cp[sub 2]Ti(SCH[sub 2]CH[sub 2]CH[sub 2]S)][sub 2] is formed. Related reactions of CpTiCl[sub 3] have been studied. Reaction of CpTiCl[sub 3] with PMe[sub 3] with PMe[sub 3] or PHEt[sub 2] yields the Ti(IV) adducts CpTiCl[sub 3](L) (L = PMe[sub 3], PHEt[sub 2]). Also generated in these reactions are small quantities of the reduced species CpTiCl[sub 2](L)[sub 2] (L = PMe[sub 3], PHEt[sub 2]), which were characterized by EPR spectroscopy. In similar reactions, the reduced species CpTiCl[sub 2](L)[sub 2] (L = imidazole (7c), methylimidazole (7d)) are isolated. Reaction of 7d with 1,3-propanedithiol gives the known species CpTiCl(SCH[sub 2]CH[sub 2]CH[sub 2]S). Reaction of 8 with a donor (imidazole or PMe[sub 3]) and (PhS)[sub 2] gives the product [CpTi(SCH[sub 2]CH[sub 2]S) (SPh)][sub 2]. In a similar reaction, 9 reacts with PMe[sub 3] to generate the Ti(III) species CpTi(SCH[sub 2]-CH[sub 2]CH[sub 2]S)more » (PMe[sub 3])[sub 2], which undergoes subsequent reaction with (PhS)[sub 2] to give the known product CpTi(SCH[sub 2]CH[sub 2]CH[sub 2]S)(SPh). The reactivity, structural, and electrochemical data presented herein suggest that a radical mechanism is operative in the formation of 1, 4, 8-10, and 12. Such a mechanistic proposal does offer an explanation for the previously observed [open quotes]base dependence[close quotes] of thiolate substitution reactions at Ti(IV).« less