The syntheses and unique chemical properties of metalladithiolene rings (especially in [CpM(S2C2R1R2)]-type complexes) found by our research group are reviewed. The constructions of metalladithiolene rings by one-pot reaction among [CpM(CO)n], alkyne, and elemental sulfur and by the reaction between [CpM(CO)n] and sulfur-containing heterocyclic compounds are described. Several ionic and radical substitution reactions are presented. The substitutions by carbon-centered and sulfur-centered radicals occur in the metalladithiolene rings. Benzoyloxy-substitution by dibenzoyl peroxide (BPO) and succinimido-substitution by N-halosuccinimides (NXS) proceed via ionic mechanisms induced by the heterolysis of BPO and NXS in the interaction with the lone pair electrons at the sulfur atoms. These substitutions are due to the aromatic character of the metalladithiolene rings. The unique addition reactions due to the unsaturated character of the metalladithiolene rings are also described. Diazo compounds and azides react with [CpM(S2C2R1R2)]-type metalladithiolenes to form alkylidene- and imido-bridges between metal and sulfur. Quadricyclane and dimethyl acetylenedicarboxylate add between metal and sulfur. These addition products undergo a variety of types of dissociation: by heating, illumination, or electrochemical redox.

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The reactions of cobaltadithiolene complexes bearing phenyl or ester ligands with tetracyanoethylene oxide (TCNEO) result in the formation of dicyanomethylene-bridged complexes, via dicyanomethylide intermediates. Furthermore, the reaction of cobaltadithiolene complex bearing 4-pyridyl ligands produces pyridinium dicyanomethylide complexes in good yields.

Substitution of the 1-cyano-1-methylethyl group for hydrogen in the nickeladithiolene ring occurs in the reaction of bis(1-phenyl-1,2-ethenedithiolato)nickel(0) with 2,2‘-azobis(isobutyronitrile). A radical mechanism is evidenced by the inhibition of the substitution in the presence of the radical scavenger TEMPO. 2,2‘-Azobis(methyl isobutyrate) and 1,1‘-azobis(1-cyanocyclohexane) undergo similar substitution reactions. The reaction is accompanied by the exchange of dithiolato ligands. Phenylation of the nickeladithiolene ring occurs in the reaction of (phenylazo)triphenylmethane. The cis−trans isomerization and the exchange of dithiolato ligands are discussed in connection with the radical substitution.

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