Syntheses and characterization of titanium(IV) and titanium(III) complexes with (2-dimethylphosphino)ethane-1-thiolate and (3-dimethylphosphino)propane-1-thiolate as ligands

Article abstract of DOI:10.1021/ic034353l

Reactions of Cp₂TiCl₂ (Cp = η ⁵-cyclopentadienide) with 2 or 1 equiv of hybrid P-S ligands (L), (CH₃)₂P(CH₂)_nS^- n = 2, dmpet; n = 3, dmppt), produced new dicyclopentadienyltitanium(IV) complexes with L, Cp₂Ti(L-κS)₂ (1, L = dmpet; 2, L = dmppt) and [Cp₂Ti(L-κ²S,P)]BPh₄ (3, L = dmpet; 4, L = dmppt). The Ti(III) complexes, Cp₂Ti(L-κ²S,P) (5, L = dmpet; 6, L = dmppt), were prepared by the reaction of Cp ₂Ti(η³-C₃H₅) with 1 equiv of L. The structures of complexes 1-6 were confirmed by X-ray diffraction analyses. It was found that complexes 3 and 5 were isostructural around Ti(IV) and Ti(III) centers: the Ti(IV)-S bond length in 3 (2.3498(9) A) is shorter by 0.14 A than Ti(III)-S in 5 (2.4877(7) A), while Ti(IV)-P (2.534(1) A) was merely 0.05 A shorter than Ti(III)-P (2.5844(7) A). The redox potential between 3 and 5 in acetonitrile was -1.14 V vs the ferricinium/ferrocene couple. A heterobimetallic complex that has the frame of complex 1, [Cp₂Ti(dmpet)₂Cu]PF₆ (7), was also isolated and structurally characterized: the Ti-Cu distance (2.95(1) A) was shorter than that in [Cp₂Ti(SC₂H₄PPh ₂)₂Cu]BF₄, previously reported by White and Stephan. Structural characterization was also carried out for Cp*Ti(dmpet-κS)₂(dmpet-κ²S,P) (8) and CpTiCl₂(dmppt-κ²S,P) (9), which were obtained by the reactions of Cp*(or Cp)TiCl₃ (Cp* = η ⁵-C₅Me₅^-) with n equiv (n = 1-3) of L. The mutual site-exchange reaction between phosphorus atoms on a coordinated dmpet in the κ²S,P mode and on two other coordinated dmpet's in the κS mode within complex 8 was analyzed by the variable-temperature ³¹P{¹H} dynamic NMR method. The kinetic parameters for this process, k_ex²⁹⁸ = 1.9 × 10⁵ s ^-1, ΔH? = 48 kJ mol^-1, and ΔS? = 17 J mol^-1 K^-1, as well as the rather long Ti(IV)-P distance (2.652(1) A), indicate the fluxional nature of the coordination geometry in complex 8.