Rare-earth metal bis(silylamide) complexes supported by ferrocene-substituted amidinate and their performance in cis -1,4 selective polymerization of isoprene

DFT and ONIOM Simulation of 1,3-Butadiene Polymerization Catalyzed by Neodymium-Based Ziegler-Natta System

Using modern methods of quantum chemistry, a theoretical substantiation of the high cis-stereospecificity of 1,3-butadiene polymerization catalyzed by the neodymium-based Ziegler-Natta system was carried out. For DFT and ONIOM simulation, the most cis-stereospecific active site of the catalytic system was used. By analyzing the total energy, as well as the enthalpy and Gibbs free energy of the simulated catalytically active centers, it was found that the coordination of 1,3-butadiene in the trans-form was more favorable than in the cis-form by 11 kJ/mol. However, as a result of π-allylic insertion mechanism modeling, it was found that the activation energy of cis-1,3-butadiene insertion into the π-allylic neodymium-carbon bond of the terminal group on the reactive growing chain was 10-15 kJ/mol lower than the activation energy of trans-1,3-butadiene insertion. The activation energies did not change when both trans-1,4-butadiene and cis-1,4-butadiene were used for modeling. That is, 1,4-cis-regulation was due not to the primary coordination of 1,3-butadiene in its cis-configuration, but to its lower energy of attachment to the active site. The obtained results allowed us to clarify the mechanism of the high cis-stereospecificity of 1,3-butadiene polymerization by the neodymium-based Ziegler-Natta system.

Investigation of the Coordination Chemistry of a Bisamidinate Ferrocene Ligand with Cu, Ag, and Au

The coordination chemistry of a ferrocene ligand with one bulky amidinate function attached to each ring toward two different coinage metal precursors was investigated. In dependence of the metal and the co-ligands, "ansa" type structures and non-bridged structures were obtained. Six different compounds are reported. In the "ansa" type structures, short Fe-M (M = Cu, Ag) distances were observed in the molecular structures in the solid state. However, theoretical calculations (DFT) did not reveal a stabilizing metal-metal interaction. Instead, dispersion interactions within the ligand and between the ligand and metal seem to represent the main stabilization forces.

Redox-controlled syndio-specific polymerization of styrene catalyzed by ferrocenyl functionalized half-sandwich scandium complexes

Redox-controlled polymerization is one of the new and efficient strategies to precisely construct the microstructures of polymeric materials, and thus has received increasing attention in the chemical community. Salt metathesis of ScCl₃ with 1 equiv. of Fc(1-C₉H₆)Li (where Fc = ferrocenyl group), followed by the addition of 2 equiv. of LiCH₂C₆H₄NMe₂-o in THF at room temperature gave the ferrocenyl functionalized half-sandwich scandium bis(o-dimethylaminobenzyl) complex [Fc(1-C₉H₆)]Sc(CH₂C₆H₄NMe₂-o)₂ (1) in 89% isolated yield. This complex was characterized by elemental analysis, FT-IR spectroscopy, NMR spectroscopy and single-crystal X-ray diffraction. Treatment of 1 with 1 equiv. of [Ph₃C][B(C₆F₅)₄] in THF generated the THF-coordinated cationic half-sandwich scandium mono(o-dimethylaminobenzyl) complex {[Fc(1-C₉H₆)]Sc(CH₂C₆H₄NMe₂-o)}{[B(C₆F₅)₄]} (2-THF₂). Switching in situ between the oxidized and reduced forms of active THF-free species (originally generated from 1/[Ph₃C][B(C₆F₅)₄] in situ) resulted in the redox-controlled syndio-specific polymerization of styrene.

Aluminum complexes with new non-symmetric ferrocenyl amidine ligands and their application in CO2 transformation into cyclic carbonates

A set of alkyl aluminum complexes supported by non-symmetric ferrocenyl amidine ligands were used as catalysts for the preparation of cyclic carbonates from epoxides and carbon dioxide using Bu₄NI as a co-catalyst.