Comparative study of the reactivity of cyclopalladated compounds containing [C(Sp2,ferrocene),N,N′]-terdentate ligands versus symmetric alkynes

A comparative study of the reactivity of the cyclopalladated compounds [Pd{[(eta(5)-C5H3)-CH=N(CH2)(n)NMe2]Fe(eta(5)-C5H5)}Cl] (n = 2 (2a), 3 (2b)) containing a [C(sp(2), ferrocene),N,N'](-) terdentate group with the symmetric alkynes R(1)CdropCR(1) (with R-1 = Ph, Et, CO2Me) is reported. In the presence of Tl[BF4], these reactions have allowed us to isolate and characterize ionic palladacycles of the general formula [Pd{[((RC)-C-1=CR1)(2)(eta(5)-C5H3)CH=N(CH2)(n)NMe2]Fe(eta(5)-C5H5)}] [BF4] (n = 2, R-1 = Ph (4a), Et (5a), CO2Me (6a); n = 3, R-1 = Ph (4b), Et (5b), CO2Me (6b)) and the neutral derivatives [Pd{[(MeO2CC=CCO2Me)(eta(5)-C5H3)-CH=N(CH2)(n)NMe2]Fe(eta(5)-C5H5)}Cl] (n = 2 (7a), 3 (7b)) and [Pd{[(MeO2CC=CCO2Me)(2)(eta(5)-C5H3)CH=N(CH2)(3)NMe2]Fe(eta(5)-C5H5)}Cl] (8b). Compounds 4-6 and 8b arise from the bis insertion of the corresponding alkynes into the sigma[Pd-C(sp(2), ferrocene)] bond of 2, while the formation of 7 involved the insertion of only one molecule of MeO(2)CCdropCCO(2)Me. The mode of binding of the butadienyl unit is eta(3) in 4-6 and eta(1) in 8b. Compounds 7 could also be isolated in a higher yield from the reaction of equimolar amounts of MeO(2)CCdropCCO(2)Me and the corresponding compound 2 in refluxing CH2Cl2. The X-ray crystal structures of 4a,b, 5b, and 8b are also reported and confirm the mode of binding of the ferrocenyl ligand to the palladium in these compounds.