Reactions of dithiolenes with diazo compounds: cycloaddition and dissociation of alkylidene groups

Abstract

1,2-Ethylenedithiolatometal complexes CpM(S 2C 2R 1R 2) (Cp  η 5-C 5H 5; M  Co, Rh; R 1, R 2  CO 2Me, Ph, H, CN) ( 1a–h) react with diazo compounds N 2CR 3R 4 (R 3, R 4  H, Ph, CO 2 Et, CO 2 Me) to yield 1 : 1 alkylidene-adducts CpM(S 2C 2R 1R 2(CR 3R 4 ( 2–18) containing a CMS three-membered ring, with the evolution of N 2. Highly regioselective cycloaddition is observed in the reactions of unsymmetrical complexes 1f (M  Co, R 1  H, R 2  CO 2ME) and 1g (M  Rh, R 1  H, R 2  CO 2 Me). The reaction of 1h (M  Co, R 1  H, R 2  Ph) with N 2CH 2 gives two stereoisomers in the ratio of 35:22. The reaction of the alkyne-adduct CpRh{S 2C 2(CO 2Me) 2}{C 2(CO 2Me) 2} with N 2CH 2 gives methylene-adduct 6 (M  Rh, R 1  R 2  CO 2Me, R 3  R 4  H). The crystal and molecular structure of adduct 15 (M  Co, R 1 R 3  H, R 2  CO 2Me, R 4  CO 2 Et) 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(S 2C 6R 5 2R 6 2)(M  Co, Rh; R 5, R 6  H, Cl) ( 1i–l)also react with diazo compounds N 2CR 3R 4 (R 3, R 4  H, CO 2Et, CO 2Me) to yield alkylidene-adducts CpM(S 2C 6R 5 2R 6 2)(CR 3R 4) ( 19–23). Thermal dissociations of adducts 2 (M  Co, R 1  R 2  CO 2Me, R 3  R 4  H) and 3 (M  Co, R 1  R 2  Ph, R 3  R 4  H) in cyclohexene give the corresponding parent complexes ( 1a: M  Co, R 1  R 2  CO 2 Me; and 1b; M Co, R 1  R 2  Ph) and cyclohexene derivatives. Adduct 3 undergoes photodissociation to give the parent complex 1b. A possible reaction mechanism for the cycloaddition is suggested and 1H and 13C NMR data of the alkylidene-adducts are also reported.