C(sp3)-H Oxidative Addition and Transfer Hydrogenation Chemistry of a Titanium(II) Synthon: Mimicry of Late-Metal Type Reactivity

Two-electron reduction of the Ti-IV compound ((ket)guan)(Im(Dipp)N)Ti(OTf)(2) (3) gives the arene-masked complex ((ket)guan)((6)-Im(Dipp)N)Ti (1) in excellent yield. Upon standing in solution, 1 converts to a Ti-IV metallacycle (4) through dehydrogenation of a pendant isopropyl group. Spectroscopic evidence shows this transformation initially proceeds via the oxidative addition of a C(sp(3))-H bond and can be reversed upon exposure of 4 to H-2. Interestingly, treatment of 1 with cyclohexene gives cyclohexane and 4 via a titanium-mediated transfer hydrogenation reaction, a process that can be extended to catalytically hydrogenate other unsaturated hydrocarbons under mild conditions. These results, rare for the early-metals, suggest 1 possesses chemical characteristics reminiscent of noble, late-metals.