Syntheses and Characterization of Titanium(IV) and Titanium(III) Complexes with (2-Dimethylphosphino)ethane-1-thiolate and (3Dimethylphosphino)propane-1-thiolate as Ligands

Reactions of Cp2TiCl2 (Cp = 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-(kappa_S)2 (1, L = dmpet; 2, L = dmppt) and [Cp2Ti(L(kappa)^2S,P)]BPh4 (3, L = dmpet; 4, L = dmppt). The Ti(III) complexes, Cp2Ti(L-2S,P) (5, L = dmpet; 6, L = dmppt), were prepared by the reaction of Cp2Ti(3-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) (angstrom)) is shorter by 0.14 (angstrom) than Ti(III)-S in 5 (2.4877(7) (angstrom)), while Ti(IV)-P (2.534(1) (angstrom)) was merely 0.05 (angstrom) shorter than Ti(III)-P (2.5844(7) (angstrom)). 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) (angstrom)) was shorter than that in [Cp2Ti(SC2H4PPh2)2Cu]BF4, previously reported by White and Stephan. Structural characterization was also carried out for Cp*Ti(dmpet-S)2(dmpet-2S,P) (8) and CpTiCl2 (dmppt-2S,P) (9), which were obtained by the reactions of Cp*(or Cp)TiCl3 (Cp* = (eta)^5-C5Me5^-) with n equiv (n = 1-3) of L. The mutual site-exchange reaction between phosphorus atoms on a coordinated dmpet in the 2S,P mode and on two other coordinated dmpetʹs in the S mode within complex 8 was analyzed by the variable-temperature 31P{1H} dynamic NMR method. The kinetic parameters for this process, kex^298 = 1.9 × 105 s^-1,(Delta)H^++ = 48 kJ mol^-1, and (delta)S^++ = 17 J mol^-1 K^-1, as well as the rather long Ti(IV)-P distance (2.652(1) (angstrom)), indicate the fluxional nature of the coordination geometry in complex 8.