Palladacycles Based on 8‑Aminoquinoline Carboxamides of Cobalt and Iron Sandwich Compounds and a New Method to α‑Alkylate Cp Rings of Metal Sandwich Carboxamides

Reactions
of {η5-C5H4[C­(O)­Cl]}­Co­(η4-C4Ph4) and {η5-C5H4[C­(O)­Cl]}­Fe­(η5-Cp) with
8-aminoquinoline resulted in cobalt and iron sandwich derived carboxamides.
The reaction of these carboxamides with Pd­(OAc)2 in acetonitrile
resulted in α­C–H activation of the Cp rings of
the sandwich compounds and formation of novel palladacycles 3 and 4, having both N–H and one α-C–H
hydrogen atom of the Cp ring displaced and palladium forming a square
planar complex with acetonitrile as the fourth ligand. These air-stable
palladacycles reacted with MeI and EtI in acetic acid, resulting in
mono- and 2,5-di-α-alkylated sandwich carboxamides,
thereby providing a new method to realize Cp-multisubstituted sandwich
compounds. Selectivity in α-substitution was observed in the
presence of NaHCO3. The cobalt sandwich carboxamide 1, the new palladacycles 3 and 4, and the 2,5-dimethylated cobalt sandwich carboxamide 5 have also been structurally characterized using single-crystal X-ray
structural studies.