Synthesis of N-Methyl-o-phenylenediamine-Bridged Bis(phenolato) Lanthanide Alkoxides and Their Catalytic Performance for the (Co)Polymerization of rac-Butyrolactone and l-Lactide

Hydroborative Depolymerization of Polyesters and Polycarbonates to Diols Catalyzed by Heterogeneous Lanthanum Materials La(CH2C6H4NMe2-o)3@SBA-15

Chemical recycling is a promising strategy to establish a circular plastic economy, and it is still in an early stage of development. In this work, the reductive depolymerization of polyesters and polycarbonates into their corresponding borylated alcohols promoted by heterogeneous lanthanum materials was described. Grafting the easily accessible lanthanum tris(aminobenzyl) complex La(CH2C6H4NMe2-o)3 (1) onto the partially dehydroxylated silica support SBA-15 (SBA-15500 or SBA-15700) gave the inorganic-organic hybrid materials 1@SBA-15500 and 1@SBA-15700. These hybrid lanthanum materials, in combination with pinacolborane (HBpin), could serve as highly active heterogeneous catalysts for the selective depolymerization of aliphatic and aromatic polyesters, as well as polycarbonates into their corresponding borylated diols through a hydroboration reaction under mild conditions. The lanthanum materials exhibited a practical application in plastic waste recycling for their easy preparation, high catalytic efficiency, and recyclable property.

Synthesis of Rare Earth Metal Complexes Stabilized by Amine Bridged Bis(phenolato) Ligands and Their Performance in the Polymerization of rac-β-Butyrolactone

A series of rare earth alkoxides bearing amine-bridged bis(phenolato) ligands were synthesized through sequential reactions of RE(C5H5)3(THF) (RE = Y, Lu) or Nd[N(SiMe3)2]3 with bis(phenols) LH2 and CF3CH2OH. Complexes REL(OCH2CF3)(THF)n (1-6) bearing different aryl-substituents were obtained in good yields of 59-70 %. They were applied in the ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL), which showed good activity (TOF up to 27,300 h-1), resulting in syndiotactically enriched poly(3-hydroxybutyrate) (PHB) (Pr up to 0.86) with narrow polydispersities (PDI ≤ 1.27). The yttrium complex 3 bearing bulky o-1,1-diphenylethyl substituents outperformed other complexes, suggesting that the smaller ionic radii of metal centers and bulky ortho substituents of ancillary ligands play crucial roles in controlling the activity and stereoselectivity in ROP of rac-BBL. Kinetics of the polymerization of rac-BBL initiated by complex 3 was investigated, which revealed first order dependences on the monomer and initiator concentrations, respectively.

Synthesis of Mono- and Dinuclear Aluminum Complexes Bearing Aromatic Amino-Phenolato Ligands: A Comparative Study in the Ring-Opening Polymerization of Cyclohexene Oxide

Dinuclear aluminum methyl complexes bearing aromatic diamine-bridged tetra(phenolato) ligands and the mononuclear aluminum methyl complex with the phenylamine-bridged bis(phenolato) ligand have been synthesized and characterized. Structure determination revealed that the Al-Al distances in these dinuclear aluminum complexes are tunable by the choice of the suitable aromatic backbone of the diamine-bridged tetra(phenolato) ligands. The catalytic behaviors of these mono- and dinuclear aluminum complexes for cyclohexene oxide (CHO) polymerization were investigated. The activities of these dinuclear Al complexes were observed to increase with the decrease of Al-Al distances, and the dinuclear Al complexes appeared to have better catalytic activity than the mononuclear Al complex, even if the Al-Al distance is as long as 9.401 Å. Dinuclear aluminum complex 2, with the shortest Al-Al distance (7.236 Å), showed the highest activity toward CHO polymerization with TOFs up to 6460 h-1 in neat CHO at 30 °C. Furthermore, comparative kinetic studies revealed that the polymerization is first-order for CHO concentration, and the reaction orders for initiator concentration are different for the mono- and dinuclear Al complexes. The polymerization mechanism study revealed that both the methyl and phenolate groups were involved in the initiation process.