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{[(eta(5)-C5H3)-CH=N-(C6H4-2-SMe)]Fe(eta(5)-C5H5)}Cl] (1c) with the alkynes R-1-CdropC-R-1 (with R-1 CO2Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO2C-CdropC- in refluxing CH2Cl2 to give [Pd{[(MeO2C-C=C-CO2Me)(eta(5)-C5H3)-CH=N-(C6H4-2-SMe)]Fe(eta(5)-C5H5)} Cl] (2c), which arises from the monoinsertion of the alkyne into the sigma[Pd-C(Sp(2), ferrocene)] bond. However, when the reaction was performed using 2 Ph-CdropC-Ph or Et-CdropC-Et no evidence of the insertion of these alkynes into the sigma[Pd-C(sp(2), 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-CdropC-CO2Me the reaction gave 2c and [Pd[(MeO2C-C=C-CO2Me)(2)(eta(5)-C5H3)-CH=N-(C6H4-2-SMe)]- Fe(eta(5)-C5H5)}][BF4] (3c); but when the alkyne was R-1-CdropC-R-1 (with R-1 = Ph or Et), the ionic pallaclacycles [Pd{[(R-1-C=C-R-1)(2)(eta(5)-(CH3)-H-5)-CH=N-(C6H4-2-SMe)]Fe(eta(5)-C5H5)}][BF4] . CH2Cl2 [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 eta(3). The reactions of 2c, 3c, 5c and 6c with PPh3 are also reported. The results obtained from these studies reveal that the sigma(Pd-S) bond in 2c is more prone to cleave than in 4c-6c. X-ray crystal structures of 2c, 5c and [Pd [(MeO2C-C=C-CO2Me)(eta(5)-C5H3)-CH=N-(C6H4-2-SMe)]Fe(eta(5)-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-Me-2-C6H2]-CH=N-(C6H4-2-SMe)}Cl] (1d) (with a [Csp(3),N,S](-) terdentate group) with the three alkynes reveals that the sigmaPd-C(sp(2), ferrocene)] bond of Ic is more reactive than the sigma[Pd-C(sp(3))] bond of 1d. (C) 2004 Elsevier B.V. All rights reserved.