Cationic indium complexes for the copolymerization of functionalized epoxides with cyclic ethers and lactide

Comparison of Imine- and Phosphinimine-Supported Indium Complexes: Tuning the Reactivity for the Sequential and Simultaneous Copolymerization of Lactide and ε-Caprolactone

Imine- and phosphinimine-supported indium complexes were used as catalysts in the polymerization of racemic lactide and ε-caprolactone as well as their copolymerization by the sequential and simultaneous addition of monomers. Tuning the electronics and sterics of the indium centers by either (i) changing the nature of the nitrogen donors and (ii) coordinating a hemilabile side group had a significant effect on the reactivity of the complexes, their stability, and their control in the synthesis of block copolymers. Specifically, the imine-supported complex (5) showed the highest activity in the homo- and copolymerization of the cyclic esters, in contrast to the phosphinimine-supported complex (7), which was significantly slower and less stable. The presence of morpholine and thiomorpholine hemilabile side groups either reduced the activity or prevented the formation of alkoxide complexes.

Temperature triggered alternating copolymerization of epoxides and lactones via pre-sequenced spiroorthoester intermediates

We report the alternating copolymerization of caprolactone and epoxide through the in situ formation of pre-sequenced spiroorthoester monomer. The reaction is catalyzed by the temperature triggered, bifunctional cationic indium complex (±)-[(NN_iO_tBu)In(CH₂SiMe₃)][B(C₆F₅)₄] (1). 1 can catalyze the coupling of epoxide and lactone to form spiroorthoester at 60 °C and its double ring-opening polymerization at 110 °C to form poly(ether-alt-ester). The post-polymerization modification and degradation of the poly(ether-alt-ester) are further investigated.

We report the alternating copolymerization of caprolactone and epoxide through the in situ formation of pre-sequenced spiroorthoester monomer.

Indium-Catalyzed CO2/Epoxide Copolymerization: Enhancing Reactivity with a Hemilabile Phosphine Donor

Group 13 metal complexes have emerged as powerful catalysts for transforming CO₂ into added-value products. However, direct comparisons of reactivity between Al, Ga, and In catalysts are rare. We report aluminum (1), gallium (2), and indium (3) complexes supported by a half-salen H[PNNO] ligand with a pendent phosphine donor and investigate their activity as catalysts for the copolymerization of CO₂ and cyclohexene oxide. In solution, the P-donor is dissociated for the Al and Ga complexes while for the In complex it exhibits hemilabile behavior. The indium complex shows higher conversion and selectivity than the Al or Ga analogues. The mechanism of the reaction was studied by NMR and FTIR spectroscopy experiments as well as structural characterization of off-cycle catalytic intermediate indium trichloride complex [(PNNO)InCl₃][TBA] (4). This study highlights the impact of a hemilabile phosphine group on group 13 metals and provides a detailed analysis of the initiation step in CO₂/epoxide copolymerization reactions.

Active in Sleep: Iron Guanidine Catalyst Performs ROP on Dormant Side of ATRP

Copolymers are the answer to property limitations of homopolymers. In order to use the full variety of monomers available, catalysts active in more than one polymerization mechanism are currently investigated. Iron guanidine catalysts have shown to be extraordinarily active in ROP of lactide and herein prove their versatility by also promoting ATRP of styrene. The presented iron complex is the first polymerizing lactide and styrene simultaneously to a defined block copolymer in a convenient one-pot synthesis. Both mechanisms work hand in hand with ROP using the dominantly present FeII species on the dormant side of the ATRP equilibrium. This orthogonal copolymerization by a benign iron catalyst opens up new pathways to biocompatible polymerization procedures broadening the scope of ATRP applications.

Strategies for the synthesis of block copolymers with biodegradable polyester segments

Oxygenated block copolymers with biodegradable polyester segments can be prepared in one-pot through sequential or simultaneous addition of monomers. This review highlights the state of the art in this area.

Cationic aluminum, gallium, and indium complexes in catalysis

The introduction of cationic charge allows cationic group 13 complexes to be excellent Lewis acid catalysts. Cationic aluminum, gallium, and indium complexes in catalysis are comprehensively reviewed based on the reaction type.

Synthesis, properties, and catalysis of p-block complexes supported by bis(arylimino)acenaphthene ligands

Bis(arylimino)acenaphthene (Ar-BIAN) ligands have been recognized as robust scaffolds for metal complexes since the 1990 s and most of their coordination chemistry was developed with transition metals. Notably, there have been relatively few reports on complexes comprising main group elements, especially those capitalizing on the redox non-innocence of Ar-BIAN ligands supporting p-block elements. Here we present an overview of synthetic approaches to Ar-BIAN ligands and their p-block complexes using conventional solution-based methodologies and environmentally-benign mechanochemical routes. This is followed by a discussion on their catalytic properties, including comparisons to transition metal counterparts, as well as key structural and electronic properties of p-block Ar-BIAN complexes.

Cationic indium catalysts for ring opening polymerization: tuning reactivity with hemilabile ligands

This is a comprehensive study of the effects of rationally designed hemilabile ligands on the stability, reactivity, and change in catalytic behavior of indium complexes. We report cationic alkyl indium complexes supported by a family of hemi-salen type ligands bearing hemilabile thiophenyl (2a), furfuryl (2b) and pyridyl (2c) pendant donor arms. Shelf-life and stability of these complexes followed the trend 2a < 2b < 2c, showing direct correlation to the affinity of the pendant donor group to the indium center. Reactivity towards polymerization of epichlorohydrin and cyclohexene oxide followed the trend 2a > 2b > 2c with control of polymerization following an inverse relationship to reactivity. Surprisingly, 2c polymerized racemic lactide without an external initiator, likely through an alkyl-initiated coordination-insertion mechanism.

Recent progress in the application of group 1, 2 & 13 metal complexes as catalysts for the ring opening polymerization of cyclic esters

This review focuses on recent developments concerned with the use of well-defined main group complexes as (pre-)catalysts for the ROP of cyclic esters to give aliphatic polyesters; factors influencing catalytic activity, selectivity and polymer properties are all discussed.