Systematic build-up of high-nuclearity osmium–mercury clusters

Abstract

The cluster dianion [Os₁₀C(CO)₂₄]^2–1 has been studied as a substrate for redox condensations with mercury(II) electrophiles. Its reaction with HgX₂(X = Cl, Br or I) initially generates the halogenomercury-capped clusters [Os₁₀C(CO)₂₄(HgX)]^–(X = Cl 2a, Br 2b or I 2c) which undergo redistribution reactions in solution. This can be prevented by blocking one co-ordination site of the Hg atom with a CF₃ group, thus producing the stable monoanion [Os₁₀C(CO)₂₄(HgCF₃)]^–2d. The structures of the [N(PPh₃)₂]⁺ salt of 2b and the [PPh₄]⁺ salt of 2d were established by single-crystal X-ray structure analysis. The reaction of 1 with 0.5–0.7 equivalent of Hg(O₃SCF₃)₂ leads to selective formation of the Hg-linked cluster dianion [{Os₁₀C(CO)₂₄}₂Hg]^2– the structure of which was determined by X-ray crystallography as its [N(PPh₃)₂]⁺ salt. The limits of this synthetic concept are set by the redox behaviour of the cluster. The cluster build-up achieved with 1 does not take place with its tetrahydrido analogue [Os₁₀H₄(CO)₂₄]^2–, which is instead oxidised by mercury salts to yield the radical monoanion.