Highly Active Yttrium Catalysts for the Ring-Opening Polymerization of ε‑Caprolactone and δ‑Valerolactone

The activity of several yttrium alkoxide and aryloxide complexes supported by a ferrocene-based ligand incorporating two thiol phenolates, thiolfan (1,1′-bis­(2,4-di-<i>tert</i>-butyl-6-thiomethylenephenoxy)­ferrocene), was studied. The <i>tert</i>-butoxide complex could only be isolated in the ate form, while a monophenoxide complex could be obtained for OAr = 2,6-di-<i>tert</i>-butylphenolate. The synthetic utility of these yttrium complexes has been demonstrated by the ring-opening polymerization of cyclic esters, with a high activity toward ε-caprolactone and δ-valerolactone being found for the yttrium phenoxide complex

Highly Active Yttrium Catalysts for the Ring-Opening Polymerization of ε‑Caprolactone and δ‑Valerolactone

The activity of several yttrium alkoxide and aryloxide complexes supported by a ferrocene-based ligand incorporating two thiol phenolates, thiolfan (1,1′-bis­(2,4-di-<i>tert</i>-butyl-6-thiomethylenephenoxy)­ferrocene), was studied. The <i>tert</i>-butoxide complex could only be isolated in the ate form, while a monophenoxide complex could be obtained for OAr = 2,6-di-<i>tert</i>-butylphenolate. The synthetic utility of these yttrium complexes has been demonstrated by the ring-opening polymerization of cyclic esters, with a high activity toward ε-caprolactone and δ-valerolactone being found for the yttrium phenoxide complex

Dinuclear Zinc Salen Catalysts for the Ring Opening Copolymerization of Epoxides and Carbon Dioxide or Anhydrides

A series of four dizinc complexes coordinated by salen or salan ligands, derived from <i>ortho</i>-vanillin and bearing (±)-<i>trans</i>-1,2-diaminocyclohexane (<b>L</b>_<b>1</b>) or 2,2-dimethyl-1,3-propanediamine (<b>L</b>_<b>2</b>) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO₂/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both <b>L</b>_<b>2</b> and imine substituents displays the highest activity. In the ROCOP of CO₂/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h^–1 at a catalyst loading of 0.1 mol %, 30 bar of CO₂, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h^–1 at a catalyst loading of 1 mol % and 100 °C). Poly­(ester-<i>block</i>-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO₂

Dinuclear Zinc Salen Catalysts for the Ring Opening Copolymerization of Epoxides and Carbon Dioxide or Anhydrides

A series of four dizinc complexes coordinated by salen or salan ligands, derived from <i>ortho</i>-vanillin and bearing (±)-<i>trans</i>-1,2-diaminocyclohexane (<b>L</b>_<b>1</b>) or 2,2-dimethyl-1,3-propanediamine (<b>L</b>_<b>2</b>) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO₂/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both <b>L</b>_<b>2</b> and imine substituents displays the highest activity. In the ROCOP of CO₂/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h^–1 at a catalyst loading of 0.1 mol %, 30 bar of CO₂, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h^–1 at a catalyst loading of 1 mol % and 100 °C). Poly­(ester-<i>block</i>-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO₂

Indium Catalysts for Low-Pressure CO₂/Epoxide Ring-Opening Copolymerization: Evidence for a Mononuclear Mechanism?

The alternating copolymerization of CO₂/epoxides is a useful means to incorporate high levels of carbon dioxide into polymers. The reaction is generally proposed to occur by bimetallic or bicomponent pathways. Here, the first indium catalysts are presented, which are proposed to operate by a distinct mononuclear pathway. The most active and selective catalysts are phosphasalen complexes, which feature ligands comprising two iminophosphoranes linked to sterically hindered <i>ortho</i>-phenolates. The catalysts are active at 1 bar pressure of carbon dioxide and are most effective without any cocatalyst. They show low-pressure activity (1 bar pressure) and yield polymer with high carbonate linkage selectivity (>99%) and isoselectivity (<i>P</i>_m > 70%). Using these complexes, it is also possible to isolate and characterize key catalytic intermediates, including the propagating indium alkoxide and carbonate complexes that are rarely studied. The catalysts are mononuclear under polymerization conditions, and the key intermediates show different coordination geometries: the alkoxide complex is pentacoordinate, while the carbonate is hexacoordinate. Kinetic analyses reveal a first-order dependence on catalyst concentration and are zero-order in carbon dioxide pressure; these findings together with in situ spectroscopic studies underpin the mononuclear pathway. More generally, this research highlights the future opportunity for other homogeneous catalysts, featuring larger ionic radius metals and new ligands, to operate by mononuclear mechanisms

Redox Control of Group 4 Metal Ring-Opening Polymerization Activity toward l‑Lactide and ε‑Caprolactone

The activity of several group 4 metal alkoxide complexes supported by ferrocene-based ligands was controlled using redox reagents during the ring-opening polymerization of l-lactide and ε-caprolactone. Switching in situ between the oxidized and reduced forms of a metal complex resulted in a change in the corresponding rate of polymerization. Opposite behavior was observed for each monomer used. One-pot copolymerization of the two monomers to give block copolymers was also achieved