Photochemical formation and reversible base-induced cleavage of a phosphagallene

The reactivity of Cp*Ga (Cp* = C₅Me₅) towards phosphanylidenephosphoranes of the type ^ArTerP(PMe₃) (^ArTer = ^DipTer 2,6-(2,6-iPr₂C₆H₃)₂C₆H₃), ^TipTer 2,6-(2,4,6-iPr₃C₆H₂)₂C₆H₃ was investigated. While no thermal reaction was observed (in line with DFT results), irradiation at 405 nm at low temperatures resulted in the formation of phosphagallenes ^DipTerP = GaCp* (1a) and ^TipTerP = GaCp* (1b) accompanied by release of PMe₃. When warming the reaction mixture to ambient temperatures without irradiation, the clean re-formation of ^ArTerP(PMe₃) and Cp*Ga in a second-order reaction was observed. Upon removal of PMe₃, 1a and 1b were isolated and fully characterized. Both derivatives were found to be labile and decomposed to the phosphafluorenes 2a and 2b, indicating generation of the transient phosphinidene ^ArTerP along with Cp*Ga. First reactivity studies show that CO₂ and H₂O cleanly reacted with 1a, affording ^DipTerPCO (3) and ^DipTerPH₂ (4), respectively.