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

The reactivity of Cp*Ga (Cp* = C 5 Me 5 ) towards phosphanylidenephosphoranes of the type Ar TerP(PMe 3 ) ( Ar Ter = Dip Ter 2,6-(2,6-iPr 2 C 6 H 3 ) 2 C 6 H 3 ), Tip Ter 2,6-(2,4,6-iPr 3 C 6 H 2 ) 2 C 6 H 3 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 Dip TerP = GaCp* (1a) and Tip TerP = GaCp* (1b) accompanied by release of PMe 3 . When warming the reaction mixture to ambient temperatures without irradiation, the clean re-formation of Ar TerP(PMe 3 ) and Cp*Ga in a second-order reaction was observed. Upon removal of PMe 3 , 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 Ar TerP along with Cp*Ga. First reactivity studies show that CO 2 and H 2 O cleanly reacted with 1a, affording Dip TerPCO (3) and Dip TerPH 2 (4), respectively.