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{[(η5-C5H3)CHN(CH2) n NMe2]Fe(η5-C5H5)}Cl] (n = 2 (2a), 3 (2b)) containing a [C(sp2,ferrocene),N,N‘]- terdentate group with the symmetric alkynes R1C⋮CR1 (with R1 = 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{[(R1CCR1)2(η5-C5H3)CHN(CH2) n NMe2]Fe(η5-C5H5)}][BF4] (n = 2, R1 = Ph (4a), Et (5a), CO2Me (6a); n = 3, R1 = Ph (4b), Et (5b), CO2Me (6b)) and the neutral derivatives [Pd{[(MeO2CCCCO2Me)(η5-C5H3)CHN(CH2) n NMe2]Fe(η5-C5H5)}Cl] (n = 2 (7a), 3 (7b)) and [Pd{[(MeO2CCCCO2Me)2(η5-C5H3)CHN(CH2)3NMe2]Fe(η5-C5H5)}Cl] (8b). Compounds 4−6 and 8b arise from the bis insertion of the corresponding alkynes into the σ[Pd−C(sp2,ferrocene)] bond of 2, while the formation of 7 involved the insertion of only one molecule of MeO2CC⋮CCO2Me. The mode of binding of the butadienyl unit is η3 in 4−6 and η1 in 8b. Compounds 7 could also be isolated in a higher yield from the reaction of equimolar amounts of MeO2CC⋮CCO2Me 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.