Syntheses and reactivities of azido coordinated CpCo(dithiolene) complexes

Azido coordinated dithiolene complexes [CpCo(N3){S2C2(CO2Me)2}(S-CHR1R2)], where R1, R2=H (4a); R1=H, R2=SiMe3 (4b); R1=H, R2=CO2Et (4c), were synthesized by the reactions of the corresponding Cl− coordinated precursors [CpCo(Cl){S2C2(CO2Me)2}(S-CHR1R2)] (3a–3c) with sodium azide. The Cl− coordinated complex 3d (R1, R2=CO2Me) did not produce any N3− coordinated complexes but formed the CR1R2-bridged alkylidene adduct [CpCo{S2C2(CO2Me)2}(CR1R2)] (2d; R1, R2=CO2Me). The structure of 4a was determined by X-ray diffraction study. In the molecular structure of 4a, the coordinated N3− ligand and CHR1R2 group were located at the same side with respect to the dithiolene ring (syn form), although the corresponding Cl− precursor (3a; R1, R2=H) was anti form. A structural conversion of syn/anti was conceivable during the Cl−/N3− ligand exchange. Thermal (80°C) and photochemical reactions (Hg lamp) of 4a–4c were performed. Among them, 4c was relatively well reacted compared with the others to form the CR1R2-bridged alkylidene adduct (2c; R1=H, R2=CO2Et), followed by a formal HN3 elimination, and the reaction also produced non-adduct of the cobalt dithiolene complex [CpCo{S2C2(CO2Me)2}] (1). The electrochemical 1e− reduction of 4c underwent a formal N3− ligand elimination, and successive second reduction caused the CHR1R2 group elimination or reformed the CR1R2-bridged alkylidene adduct 2c.