Photochemical formation and reversible base-induced cleavage of a phosphagallene.

The reactivity of CpGa (Cp = CMe) towards phosphanylidenephosphoranes of the type TerP(PMe) (Ter = Ter 2,6-(2,6-iPrCH)CH), Ter 2,6-(2,4,6-iPrCH)CH 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 TerP = GaCp* (1a) and TerP = GaCp* (1b) accompanied by release of PMe. When warming the reaction mixture to ambient temperatures without irradiation, the clean re-formation of TerP(PMe) and CpGa in a second-order reaction was observed. Upon removal of PMe, 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 TerP along with CpGa. First reactivity studies show that CO and HO cleanly reacted with 1a, affording TerPCO (3) and TerPH (4), respectively.