Readily available Ti-based in situ catalytic system for oxo/imido heterometathesis

Abstract

We investigate Ti(NEt₂)₄ supported on silica dehydroxylated at 700 °C as an easily accessible pre-catalyst for oxo/imido heterometathesis reactions. Being activated with TolNH₂, the supported Ti amide (SiO)Ti(NEt₂)₃ (1) demonstrates catalytic activity in the imidation of ketones with N-sulfinylamines comparable with the most active previously described well-defined imido catalyst (SiO)Ti(NtBu)(Me₂Pyr)(py)₂ (2) (Me₂Pyr = 2,5-dimethylpyrrolyl), which implies the in situ formation of surface imido species in this system. The materials obtained via treatment of 1 with anilines (TolNH₂ (1a) and p-MeOC₆H₄¹⁵NH₂ (1b)) were studied with IR, EA and ¹H, ¹³C, ¹⁵N and 2D solid-state NMR, although the proposed imido intermediate has not been detected, pointing towards tris-amides (SiO)Ti(NHC₆H₄X)₃ (X = Me, OMe) being the major surface species in the isolated materials 1a and 1b. The system 1/TolNH₂ was tested in a range of imidation reactions and demonstrated excellent performance for express high-yielding preparation of ketimines, formamidines, lactone imidates and sulfurdiimines, making it a convenient alternative to the well-defined supported Ti imido catalysts.