Study of the reactivity of palladacycles containing [C(sp2, ferrocene),N,S]− or [C(sp3),N,S]− terdentate ligands with symmetric alkynes

The study of the reactivity of the cyclopalladated complex [Pd{[(η5-C5H3)–CHdouble bond; length as m-dashN–(C6H4–2-SMe)]Fe(η5-C5H5)}Cl] (1c) with the alkynes R1–Ctriple bond; length of mdashC–R1 (with R1 = CO2Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO2C–Ctriple bond; length of mdashC–CO2Me in refluxing CH2Cl2 to give [Pd{[(MeO2C–Cdouble bond; length as m-dashC–CO2Me)(η5-C5H3)–CHdouble bond; length as m-dashN–(C6H4–2-SMe)]Fe(η5-C5H5)}Cl] (2c), which arises from the monoinsertion of the alkyne into the σ[Pd–C(sp2, ferrocene)] bond.However, when the reaction was performed using Ph–Ctriple bond; length of mdashC–Ph or Et–Ctriple bond; length of mdashC–Et no evidence of the insertion of these alkynes into the σ[Pd–C(sp2, ferrocene)] bond was detected.In contrast with these results, when 1c was treated with the Tl[BF4] followed by the removal of the TlCl formed and the subsequent addition of MeO2C–Ctriple bond; length of mdashC–CO2Me the reaction gave 2c and [Pd{[(MeO2C–Cdouble bond; length as m-dashC–CO2Me)2(η5-C5H3)–CHdouble bond; length as m-dashN–(C6H4–2-SMe)]Fe(η5-C5H5)}][BF4] (3c); but when the alkyne was R1–Ctriple bond; length of mdashC–R1 (with R1 = Ph or Et), the ionic palladacycles [Pd{[(R1–Cdouble bond; length as m-dashC–R1)2(η5-C5H3)–CHdouble bond; length as m-dashN–(C6H4–2-SMe)]Fe(η5-C5H5)}][BF4] · CH2Cl2 [with R1 = Ph (5c) or Et (6c)] were isolated. In compounds 3c, 5c and 6c, the mode of binding of the butadienyl unit is η3. The reactions of 2c, 3c, 5c and 6c with PPh3 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{[(MeO2C–Cdouble bond; length as m-dashC–CO2Me)(η5-C5H3)–CHdouble bond; length as m-dashN–(C6H4–2-SMe)]Fe(η5-C5H5)}Cl(PPh3)] (7c), are also described. Compound 7c arises from 2c by cleavage of the Pd–S bond and the incorporation of a PPh3 in the coordination sphere of the palladium. A parallel study focused on the reactions of [Pd{[2-CH2–4,6-Me2–C6H2]–CHdouble bond; length as m-dashN–(C6H4–2-SMe)}Cl] (1d) (with a [Csp3,N,S]− terdentate group) with the three alkynes reveals that the σPd–C(sp2, ferrocene)] bond of 1c is more reactive than the σ[Pd–C(sp3)] bond of 1d.