Metal-to-Ligand Alkylation on Organolanthanide Complexes Stabilized by Thiazole Containing Amidopyridinate Ligands: Synthesis, Characterization and Catalytic activity in the Isoprene polymerization

Neutral LnIII-dialkyl (YIII, LuIII, ErIII, YbIII) complexes supported by tridentate N-,N,N monoanionic methylthiazole- or benzothiazole-amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed a progressive rearrangement of the coordination sphere in the benzothiazole-containing systems through an unprecedented metal-to-ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric YIII species stabilized by a trianionic N-,N,N-,S- ligand as the result of metal-to-ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y-H group to the imino fragment of a second equivalent of the ring-opened intermediate. DFT calculations are used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, selected organolanthanides from this series, especially in their cationic form, are good candidates for the effective and selective isoprene (IP) polymerization. The catalytic performance of differently activated organolanthanides in the IP polymerization will be discussed.