SYSTEMATIC BUILDUP OF HIGH-NUCLEARITY OSMIUM MERCURY CLUSTERS

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 = Cl2a, Br2b or 12c) 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.