Comparative study of the reactivity of cyclopalladated compounds containing [C(sp2,ferrocene),N,N′]- terdentate ligands versus symmetric alkynes

Article abstract of DOI:10.1021/om021036y

A comparative study of the reactivity of the cyclopalladated compounds [Pd{[(η⁵-C₅H₃)- CH=N(CH₂)_nNMe₂]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-C₅ H₃)CH=N(CH₂)_nNMe₂]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-C₅H ₃)-CH=N(CH₂)_nNMe₂]Fe (η⁵-C₅H₅)}Cl] (n = 2 (7a), 3 (7b)) and [Pd{[(MeO₂CC=CCO₂Me)₂ (η⁵-C₅H₃)CH=N(CH₂)₃NM e₂]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.