Study of the reactivity of palladacycles containing [C(sp 2, ferrocene),N,S] − or [C(sp 3),N,S] − terdentate ligands with symmetric alkynes

Abstract

The study of the reactivity of the cyclopalladated complex [Pd{[(η 5-C 5H 3)–CH N–(C 6H 4–2-SMe)]Fe(η 5-C 5H 5)}Cl] ( 1c) with the alkynes R 1–C C–R 1 (with R 1 = CO 2Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO 2C–C C–CO 2Me in refluxing CH 2Cl 2 to give [Pd{[(MeO 2C–C C–CO 2Me)(η 5-C 5H 3)–CH N–(C 6H 4–2-SMe)]Fe(η 5-C 5H 5)}Cl] ( 2c), which arises from the monoinsertion of the alkyne into the σ[Pd–C(sp 2, ferrocene)] bond.However, when the reaction was performed using Ph–C C–Ph or Et–C C–Et no evidence of the insertion of these alkynes into the σ[Pd–C(sp 2, ferrocene)] bond was detected.In contrast with these results, when 1c was treated with the Tl[BF 4] followed by the removal of the TlCl formed and the subsequent addition of MeO 2C–C C–CO 2Me the reaction gave 2c and [Pd{[(MeO 2C–C C–CO 2Me) 2(η 5-C 5H 3)–CH N–(C 6H 4–2-SMe)]Fe(η 5-C 5H 5)}][BF 4] ( 3c); but when the alkyne was R 1–C C–R 1 (with R 1 = Ph or Et), the ionic palladacycles [Pd{[(R 1–C C–R 1) 2(η 5-C 5H 3)–CH N–(C 6H 4–2-SMe)]Fe(η 5-C 5H 5)}][BF 4] · CH 2Cl 2 [with R 1 = Ph ( 5c) or Et ( 6c)] were isolated. In compounds 3c, 5c and 6c, the mode of binding of the butadienyl unit is η 3. The reactions of 2c, 3c, 5c and 6c with PPh 3 are also reported. The results obtained from these studies reveal that the σ(Pd–S) bond in 2c is more prone to cleave than in 4c– 6c. X-ray crystal structures of 2c, 5c and [Pd{[(MeO 2C–C C–CO 2Me)(η 5-C 5H 3)–CH N–(C 6H 4–2-SMe)]Fe(η 5-C 5H 5)}Cl(PPh 3)] ( 7c), are also described. Compound 7c arises from 2c by cleavage of the Pd–S bond and the incorporation of a PPh 3 in the coordination sphere of the palladium. A parallel study focused on the reactions of [Pd{[2-CH 2–4,6-Me 2–C 6H 2]–CH N–(C 6H 4–2-SMe)}Cl] ( 1d) (with a [Csp 3,N,S] − terdentate group) with the three alkynes reveals that the σPd–C(sp 2, ferrocene)] bond of 1c is more reactive than the σ[Pd–C(sp 3)] bond of 1d.