Manganese‐Mediated Synthesis of NHC‐Phosphine Ligand Precursors

Abstract

Alkylation of N‐substituted imidazoles ImR’ (R’ = 2,4,6‐trimethylphenyl, 2,6‐diisopropylphenyl, 1‐adamantyl) with Mn(I) methylenephosphonium complexes [Cp(CO)2Mn(η2‐P,C‐R2P=C(H)Ph)](BF4) (PR2 = PPh2, PCy2, trans‐PC(H)PhCH2CH2C(H)Ph) followed by photochemical demetallation afforded a series of bidentate NHC‐phosphine ligand precursors [R2PC(H)PhImR’](BF4) in moderate to good yield. The same strategy was successfully applied to N‐functionalized imidazoles ImL (L = 2‐pyridyl, CH2SMe, CH2ImMe) to afford selectively NHC core pincer pre‐ligands featuring phosphine/thioether, phosphine/NHC and phosphine/pyridine side arms. For PCy2 derivatives, free NHCs in both bidentate and pincer series generated by deprotonation of the corresponding cationic precursors were shown to be persistent at room temperature.