Controlled Synthesis of Novel Aryloxide Polynuclear Aluminum Species. Study of Their Catalytic Properties in Polymerization Processes

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.

σ-Hole triel bonds in aluminium derivatives

This communication reports the synthesis and X-ray characterization of a new mononuclear aluminium compound exhibiting an intramolecular σ-hole triel bonding interaction. It is compared with a dinuclear aluminium compound, previously reported by us, where the aluminium atoms participate in two concurrent σ-hole triel bonding interactions. To our knowledge, such behaviour has not been previously described in the literature.

Heterobimetallic aluminate derivatives with bulky phenoxide ligands: a catalyst for selective vinyl polymerization

New aluminates as active catalysts for vinyl polymerization are described, as well as a strategy to crosslinked polymers from GMA in a controlled fashion.

Salen complexes of zirconium and hafnium: synthesis, structural characterization and polymerization studies

Salen complexes of zirconium and hafnium were synthesized and used as effective catalysts for the polymerization of lactide and ε-CL and homopolymerization, copolymerization and coupling of epoxides with CO₂.

Phenoxide and alkoxide complexes of Mg, Al and Zn, and their use for the ring-opening polymerization of ℇ-caprolactone with initiators of different natures

A new packing polymorph of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(tetrahydrofuran-κO)magnesium, [Mg(C₁₅H₂₃O)₂(C₄H₈O)₂] or Mg(BHT)₂(THF)₂, (BHT is the 2,6-di-tert-butyl-4-methylphenoxide anion and THF is tetrahydrofuran), (1), has the same space group (P2₁) as the previously reported modification [Nifant'ev et al. (2017d). Dalton Trans. 46, 12132-12146], but contains three crystallographically independent molecules instead of one. The structure of (1) exhibits rotational disorder of the tert-butyl groups and positional disorder of a THF ligand. The complex of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(μ₂-ethyl glycolato-κ²O,O':κO)dimethyldialuminium, [Al₂(CH₃)₂(C₄H₇O₃)₂(C₁₅H₂₃O)₂] or [(BHT)AlMe(OCH₂COOEt)]₂, (2), is a dimer located on an inversion centre and has an Al₂O₂ rhomboid core. The 2-ethoxy-2-oxoethanolate ligand (OCH₂COOEt) displays a μ₂-κ²O,O':κO semi-bridging coordination mode, forming a five-membered heteronuclear Al-O-C-C-O ring. The same ligand exhibits positional disorder of the terminal methyl group. The redetermined structure of the heptanuclear complex octakis(μ₃-benzyloxo-κO:κO:κO)hexaethylheptazinc, [Zn₇(C₂H₅)₆(C₇H₇O)₈] or [Zn₇(OCH₂Ph)₈Et₆], (3), possesses a bicubic Zn₇O₈ core located at an inversion centre and demonstrates positional disorder of one crystallographically independent phenyl group. Cambridge Structural Database surveys are given for complexes structurally analogous to (2) and (3). Complexes (2) and (3), as well as derivatives of (1), are of interest as catalysts for the ring-opening polymerization of ℇ-caprolactone, and polymerization results are reported.

Bimetallic salen aluminum complexes: cooperation between reactive centers in the ring-opening polymerization of lactides and epoxides

In dinuclear aluminum complexes, opportunely designed to have proximal coordinative pockets, the communication between the two reactive centers allows enhanced catalytic performances.

Synthesis and structural characterization of titanium and zirconium complexes containing half-salen ligands as catalysts for polymerization reactions

Ti(iv) and Zr(iv) complexes of tridentate half-salen ligands were synthesized for the polymerization of lactide and ε-CL, homopolymerization, copolymerization and coupling of epoxides with CO₂. All the complexes were found to be effective catalysts for different polymerization reactions.

Heterometallic aluminates: alkali metals trapped by an aluminium aryloxide claw

A series of heterometallic aluminium-alkali metal species [AlMMe2{2,6-(MeO)2C6H3O}2]n have been isolated for lithium, sodium and potassium. These compounds can be generated by the reaction of [AlMe2{2,6-(MeO)2C6H3O}]2 with the metallated phenol [M{2,6-(MeO)2C6H3O}]n or through the reaction of the mixture of AlMe3 and the appropriate alkali metal alkyl base with two equivalents of 2,6-dimethoxyphenol. In the heterometallic species obtained, the {AlMe2{2,6-(MeO)2C6H3O}2}(-) moiety is observed and could be described as a claw which fixes the alkali ion by the phenoxide oxygen atoms while the methoxy groups help to stabilize their coordination sphere. All compounds have been characterized by NMR spectroscopy and X-ray diffraction methods. Catalytic studies reveal that these compounds are active in ring-opening polymerization of L-lactide.

Ring-opening polymerization of cyclohexene oxide using aluminum amine–phenolate complexes

Al(iii) catalysts at concentrations as low as 0.001% ring-open cyclohexene oxide to yield high molecular weight polyether with narrow dispersity.

Alternative aluminum-based cocatalysts for the iron-catalyzed oligomerization of ethylene

Multinuclear aluminum cocatalysts have been obtained by the reaction of various phenols, alcohols or diols with trimethylaluminum and were used in situ or as isolated, well-defined species, for the activation of an iron(ii) or an iron(iii) pre-catalyst for the oligomerization of ethylene.