Carbon monoxide reaction towards nickel(II) tetracoordinated phosphine complexes in aqueous-alcoholic solution

Tetracoordinated NiL2X2 (X = Cl, Br; L = PEt3, PEt2Ph, PEtPh2) react with CO in aq.-alc. soln., to give Ni(0) carbonyls, via reductive carbonylation. The redn. was not obsd. for L = PPh3. NiX2(diphos) {X = Cl, Br; diphos = PPh2(CH2)nPPh2 (n = 2,3)} give redn. only in basic medium with partial oxidn. of the ligand. A possible mechanism for the reductive carbonylation is discussed