212064-92-1Relevant academic research and scientific papers
Monocyclopentadienyl-Titanium Aryloxide Sulfide Complexes
Firth, Andrea V.,Stephan, Douglas W.
, p. 4726 - 4731 (2008/10/08)
In this report we extend titanium-sulfide chemistry, describing the syntheses, structures, and chemistry of monocyclopentadienyl-titanium aryloxide sulfide complexes. Reduction of Cp'Ti(OC6H3-2,6-i-Pr2)Cl2 (Cp' = Cp (1), Cp(*) (3)) with n-BuLi affords the Ti(III) compounds [CpTi(OC6H3-2,6-i-Pr2)(μ-Cl)]2 (2) and [Cp(*)Ti(OC6H3-2,6-i-Pr2)(μ-Cl)]2 (4). Compound 2 is oxidized by moisture, giving [CpTi(OC6H3-2,6-i-Pr2)Cl]2(μ-O) (5). Oxidation of 4 by sulfur led to a mixture of uncharacterized products: however, reaction of 3 with 2 equiv of n-BuLi followed by subsequent addition of sulfur afforded a new diamagnetic species, Cp(*)Ti(OC6H3-2,6-i-Pr2)S5 (6). Oxidation of 2 by S8 yields [CpTi(OC6H3-2,6-i-Pr2)]2(μ-S)(μ-S2) (7). Reaction of the known sulfide-bridged dimer [CpTi(OC6H3-2,6-i-Pr2)(μ-S)]2 (8) with sulfur provides an alternative route to 7. The conversion of 7 to 8 is reversible as reaction of 7 with PPh3 yields SPPh3 and 8 quantitatively. Reaction of 1 with Li2S proceeds cleanly to give 8. Reduction of CpTi(OC6H3-2,6-i-Pr2)(SPh)Cl (9) with n-BuLi affords the diamagnetic product [CpTi(OC6H3-2,6-i-Pr2)(μ-SPh)]2 (10), which reacts with phenylpyridine to generate the paramagnetic species CpTi(OC6H3-2,6-i-Pr2)(SPh)(NC5H4Ph) (11). Attempts to isolate a monosulfide-bridged complex are described. Isolation of a monosulfide-bridged species, [CpTi(OC6H3-2,6-i-Pr2)2]2(μ-S) (14), is achieved via reaction of [CpTi(OC6H3-2,6-i-Pr2)2Cl (13) with Li2S. Structural data for 2,4-7, 10, and 14 are reported. Comparisons are made with the related titanocene-sulfide systems, and the implications are considered.
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.
