REACTIONS OF DITHIOLENES WITH DIAZO-COMPOUNDS - CYCLOADDITION AND DISSOCIATION OF ALKYLIDENE GROUPS

1,2-Ethylenedithiolatometal complexes CpM(S2C2R1R2) (Cp = eta(5)-C5H5; M = Co, Rh; R1, R2 = CO2Me, Ph, H, CN) (1a-h) react with diazo compounds N2CR3R4 (R3, R4 = H, Ph, CO2Et, CO2Me) to yield 1:1 alkylidene-adducts CpM(S2C2R1R2)(CR3R4) (2-18) containing a C-M-S three-membered ring, with the evolution of N2. Highly regioselective cycloaddition is observed in the reactions of unsymmetrical complexes 1f (M = Co, R1 = H, R2 = CO2Me) and 1g (M = Rh, R1 = H, R2 = CO2Me). The reaction of 1h (M = Co, R1 = H, R2 = Ph) with N2CH2 gives two stereoisomers in the ratio of 35:22. The reaction of the alkyne-adduct CpRh{S2C2(CO2Me)2}{C2(CO2Me)2} with N2CH2 gives methylene-adduct 6 (M = Rh, R1 = R2 = CO2Me, R3 = R4 = H). The crystal and molecular structure of adduct 15 (M = Co, R1 = R3 = H, R2 = CO2Me, R4 = CO2Et) has been determined; the five-membered dithiolene ring is planar, and the plane of the C-Co-S three-membered ring is almost perpendicular to the dithiolene ring. 1,2-Benzenedithiolatometal complexes CpM(S2C6R2(5)R2(6))(M = Co, Rh; R5, R6 = H, Cl) (1i-l) also react with diazo compounds N2CR3R4 (R3, R4 = H, CO2Et, CO2Me) to yield alkylidene-adducts CpM(S2C6R2(5)R2(6))(CR3R4) (19-23). Thermal dissociations of adducts 2 (M = Co, R1 = R2 = CO2Me, R3 = R4 = H) and 3 (M = Co, R1 = R2 = Ph, R3 = R4 = H) in cyclohexene give the corresponding parent complexes (1a: M = Co, R1 = R2 = CO2Me; and 1b; M = Co, R1 = R2 = Ph) and cyclohexene derivatives. Adduct 3 undergoes photodissociation to give the parent complex 1b. A possible reaction mechanism for the cycloaddition is suggested and H-1 and C-13 NMR data of the alkylidene-adducts are also reported.