The redox chemistry of [Ni9C(CO)17]2– and [Ni10(C2)(CO)16]2–: Synthesis, electrochemistry and structure of [Ni12C(CO)18]4– and [Ni22(C2)4(CO)28(Et2S)]2–

This paper reports a detailed study of the oxidation and reduction reactions of simple nickel mono-carbide and mono-acetlyde carbonyl clusters. The reduction of [Ni9C(CO)17]2– with Na/naphtalene affords the new [Ni12C(CO)18]4– mono-carbide cluster. Under the same experimental conditions, [Ni10(C2)(CO)16]2– reacts with Na/naphtalene yielding a mixture of the previously reported [Ni11(C2)(CO)15]4– and [Ni12(C2)(CO)16]4– mono-acetylide tetra-anions. The oxidation reactions of both [Ni9C(CO)17]2– and [Ni10(C2)(CO)16]2–, carried out with miscellaneous reagents, e.g., [C7H7][BF4], [Cp2Fe][PF6], AgNO3, are more complicated and less selective, leading to mixtures of products, among which the previously reported [Ni8C(CO)16]2–, [Ni16(C2)2(CO)23]4–, [Ni38C6(CO)42]6– and [Ni32C6(CO)36]6– species have been identified. Interestingly, oxidation of [Ni10(C2)(CO)16]2– with Pd(Et2S)2Cl2 affords the new tetra-acetylide [Ni22(C2)4(CO)28(Et2S)]2–, even if in low yields. The new species [Ni12C(CO)18]4– and [Ni22(C2)4(CO)28(Et2S)]2– have been structurally characterized by means of single crystal X-ray diffraction. Electrochemical and spectroelectrochemical studies have been performed on [Ni12C(CO)18]4–. This compound can be electrochemically oxidized and reduced reversibly affording [Ni12C(CO)18]3– and [Ni12C(CO)18]5–, respectively. The same species can be obtained by chemical methods but, due to their limited stability during work-up, it has not been possible to isolate them.