Photochemical formation and reversible base-induced cleavage of a phosphagallene

Abstract

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.