Reversible oxidative-addition and reductive-elimination of thiophene from a titanium complex and its thermally-induced hydrodesulphurization chemistry

The masked Ti(ii) synthon ((Ket)guan)(eta(6)-Im(Dipp)N)Ti (1) oxidatively adds across thiophene to give ring-opened ((Ket)guan)(Im(Dipp)N)Ti[kappa(2)-S(CH)(3)CH] (2). Complex 2 is photosensitive, and upon exposure to light, reductively eliminates thiophene to regenerate 1 - a rare example of early-metal mediated oxidative-addition/reductive-elimination chemistry. DFT calculations indicate strong titanium pi-backdonation to the thiophene pi*-orbitals leads to the observed thiophene ring opening across titanium, while a proposed photoinduced LMCT promotes the reverse thiophene elimination from 2. Finally, pressurizing solutions of 2 with H-2 (150 psi) at 80 degrees C leads to the hydrodesulphurization of thiophene to give the Ti(iv) sulphide ((Ket)guan)(Im(Dipp)N)Ti(S) (3) and butane.