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

The study of the reactivity of the cyclopalladated complex Pd{(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (1c) with the alkynes R¹-CC-R¹ (with R¹ = CO₂Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO₂C-CC-CO₂Me in refluxing CH₂Cl₂ to give Pd{(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (2c), which arises from the monoinsertion of the alkyne into the σPd-C(sp², ferrocene)] bond.However, when the reaction was performed using Ph-CC-Ph or Et-CC-Et no evidence of the insertion of these alkynes into the σPd-C(sp², ferrocene)] bond was detected.In contrast with these results, when 1c was treated with the TlBF₄] followed by the removal of the TlCl formed and the subsequent addition of MeO₂C-CC-CO₂Me the reaction gave 2c and Pd{(MeO₂C-CC-CO₂Me)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}]BF₄] (3c); but when the alkyne was R¹-CC-R¹ (with R¹ = Ph or Et), the ionic palladacycles Pd{(R¹-CC-R¹)₂(η⁵-C₅H₃)-CHN-(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-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(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]-CHN-(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 σPd-C(sp³)] bond of 1d.