Reversible and Irreversible [2+2] Cycloaddition Reactions of Heteroallenes to a Gallaphosphene.

[2+2] Cycloaddition reactions of gallaphosphene L(Cl)GaPGaL 1 (L = HC[C(Me)N(2,6- i- Pr 2 C 6 H 3 )] 2 ), with carbodiimides [C(NR) 2 ; R = i -Pr, Cy] and isocyanates [RNCO; R = Et, i -Pr, Cy] yielded four-membered metallaheterocycles LGa(Cl)P[ μ -C(X)NR]GaL (X = NR, R = i -Pr 2 , Cy 3 ; X = O, R = Et 4 , i -Pr 5 , Cy 6 ). Compounds 4 - 6 reversibly react with CO 2 via [2+2] cycloaddition at ambient temperature to the six-membered metallaheterocycles LGa(Cl)P[ μ -C(O)O]- μ -C(O)N(R)GaL (R = Et 7 , i -Pr 8 , Cy 9 ). Compounds 2 - 9 were characterized by IR and heteronuclear ( 1 H, 13 C{ 1 H}, 31 P{ 1 H}) NMR spectroscopy and elemental analysis, while quantum chemical calculations provided a deeper understanding on the energetics of the reactions.