The co-ordination of small molecules by manganese(II) phosphine complexes. Part 3. The dependence on the nature of the halogen in [MnX2(PR3)](X = Cl, Br, or I; R3= PhMe2, PhEt2, PhPrn 2, PhBun 2, PhBui 3, Prn 3, Bun 3, or Ph3) on adduct formation with sulphur dioxide in the solid state and in tetrahydrofuran solution

The reaction of the complexes [MnX2(PR3)](X = Cl, Br, or I; R3= PhMe2, PhEt2, PhPrn2, PhBun2, PhBui2, Prn3, Bun3, or Ph3) with sulphur dioxide in the solid state, in toluene slurries and in tetrahydrofuran (thf) has been studied. In all three systems a strong dependence on the nature of the halide is observed. For X = Cl, no reaction takes place; for X = I, all complexes irreversibly absorb SO2; for X = Br a borderline exists and the nature of the phosphine is important, viz. trialkylphosphines promote SO2 binding, whereas complexes containing phenyl-substituted phosphines (except PPhMe2) are inactive towards SO2. The reaction stoicheiometry is unusual, [MnX2(PR3)(SO2)x](for measurements in the solid state x= 0.66, for thf solution x= 0.65–0.76). Although [MnI2(PPh3)] does not bind dioxygen it forms an adduct with sulphur dioxide in the solid state and in thf.