212064-93-2Relevant academic research and scientific papers
Thermal reactions of titanium thiolates: Terminal titanium sulfides in C-S bond cleavage reactions
Firth, Andrea V.,Witt, Eva,Stephan, Douglas W.
, p. 3716 - 3722 (2008/10/08)
The thermolysis of monocyclopentadienyltitanium thiolate complexes leads to ligand redistributions and C-S bond cleavage reactions. Kinetic study of the C-S bond thermolysis reaction of CpTi(OC6H3-2,6-i-Pr2)(SBn)2 (2) to the sulfide-bridged dimer [CpTi(OC6H3-2,6-i-Pr2)(μ-S)]2 (1) is shown to be first order in 2, consistent with an intramolecular process proceeding via a terminal sulfide intermediate and rapid dimerization (k = 2.8 × 10-6 s-1). The related species CpTi(OC6H3-2,6-i-Pr2)(SBn)Cl (3), CpTi(OC6H3-2,6-i-Pr2)(SMe)2 (4), and CpTi(OC6H3-2,6-i-Pr2)(SPh)2 (5) are thermally stable, although compounds 4 and 5 undergo thermally induced ligand redistribution reactions. These redistribution reactions are thought to occur via a dimeric intermediate in which bridging thiolate ligands are exchanged between two metal centers. A dimeric intermediate is supported by the characterization of the species [CpTi(SR)2(μ-SR)]2 (R = Et (7), Bn (8)) which are dimeric in solution at low temperature and in the solid state. In contrast, Cp*Ti(SBn)3 (9) is monomeric. Efforts to intercept a terminal sulfide intermediate in the formation of 1 were unsuccessful, although reaction of CpTiCl2Me with LiSBn in the presence of PMe3 gives [CpTiCl(μ-S)]2[PMe3Bn] (10) in low yield. The analogue of 2, Cp*Ti(OC6H3-2,6-i-Pr2)(SBn)2, 12, is thermally stable; however, thermolysis of Cp*TiCl(SBn)2 gave [Cp*TiCl(μ-S)]2 (13). Ultimately, the LiCl adduct of a terminal sulfide species Cp*Ti(OC6H3-2,6-i-Pr 2)(μ-S)(μ-Cl)Li(THF)2 (14) was isolated from the reaction of Cp*Ti(OC6H3-2,6-i-Pr2)Cl2 (11) with Li2S. Treatment of (14) with PMe3 generates the monomeric terminal sulfide complex species Cp*Ti(OC6H3-2,6-i-Pr2)(S)(PMe 3) (15), which is unstable, slowly evolving PMe3 affording [Cp*Ti(OC6H3-2,6-i-Pr2)(μ-S)] 2 (16). Compound 16 is also obtained directly by heating solutions of 14. Crystallographic studies of 8,10,12,13,14, and 16 are reported herein. The intermediacy of terminal metal sulfides in C-S processes are discussed.
