Manganese‐Mediated Synthesis of NHC‐Phosphine Ligand Precursors

Alkylation of N ‐substituted imidazoles ImR’ (R’=2,4,6‐trimethylphenyl, 2,6‐diisopropylphenyl, 1‐adamantyl) with Mn(I) methylenephosphonium complexes [Cp(CO) 2 Mn(η 2 ‐ P,C ‐R 2 P=C(H)Ph)](BF 4 ) (PR 2 =PPh 2 , PCy 2 , trans ‐P C(H)PhCH 2 CH 2 C (H)Ph) followed by photochemical demetallation afforded a series of bidentate NHC‐phosphine ligand precursors [R 2 PC(H)PhImR’](BF 4 ) in moderate to good yield. The same strategy was successfully applied to N ‐functionalized imidazoles ImL (L=2‐pyridyl, CH 2 SMe, CH 2 ImMe) to afford selectively NHC core pincer pre‐ligands featuring phosphine/thioether, phosphine/NHC and phosphine/pyridine side arms. For PCy 2 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.