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

Abstract

The masked Ti(II) synthon (^Ketguan)(η⁶-Im^DippN)Ti (1) oxidatively adds across thiophene to give ring-opened (^Ketguan)(Im^DippN)Ti[κ²-S(CH)₃CH] (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 π-backdonation to the thiophene π*-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 H₂ (150 psi) at 80 °C leads to the hydrodesulphurization of thiophene to give the Ti(IV) sulphide (^Ketguan)(Im^DippN)Ti(S) (3) and butane.