Copolymerization of Phthalic Anhydride with Epoxides Catalyzed by Amine-Bis(Phenolate) Chromium(III) Complexes

The effect of ligand structure on the catalytic activity of amine-bis(phenolate) chromium(III) complexes in the ring-opening copolymerization of phthalic anhydride and a series epoxides was studied. Eight complexes differing in the donor-pendant group (R₁) and substituents (R₂) in phenolate units were examined as catalysts of the model reaction between phthalic anhydride and cyclohexane oxide in toluene. They were used individually or as a part of the binary catalytic systems with nucleophilic co-catalysts. The co-catalyst was selected from the following organic bases: PPh₃, DMAP, 1-butylimidazole, or DBU. The binary catalytic systems turned out to be more active than the complexes used individually, and DMAP proved to be the best choice as a co-catalyst. When the molar ratio of [PA]:[epoxide]:[Cr]:[DMAP] = 250:250:1:1 was applied, the most active complex (R₁-X = CH₂NMe₂, R₂ = F) allowed to copolymerize phthalic anhydride with differently substituted epoxides (cyclohexene oxide, 4-vinylcyclohexene oxide, styrene oxide, phenyl glycidyl ether, propylene oxide, butylene oxide, and epichlorohydrin) within 240 min at 110 °C. The resulting polyesters were characterized by M_n up to 20.6 kg mol^-1 and narrow dispersity, and they did not contain polyether units.

Synthesis of amino-phenolate manganese complexes and their catalytic activity in carbon dioxide activation and oxidation reactions

Two manganese(III) compounds were studied as catalysts for the reaction of carbon dioxide with propylene oxide, styrene oxide, and cyclohexene oxide, and formed cyclic carbonate products selectively under solvent free conditions in the presence of an ionic co-catalyst such as TBAB or PPNCl. Variable temperature kinetic studies allowed the activation energy for propylene carbonate formation to be determined (64 kJ mol−1). The catalysts showed good stability in these reactions and overall turnover numbers (TON) of up to 6000 were observed. The complexes showed low activity for the aerobic oxidation of 4-methyoxybenzylalcohol to the corresponding aldehyde, achieving up to 40% conversion in 72 h. However, near quantitative conversion of 1,2-diphenyl-2-methoxyethanol to provide up to 90% yield of benzaldehyde could be achieved over the course of 5 days. Both complexes showed similar reactivity in the two catalytic processes, and this is likely due to the weakly coordinating nature of the pendant donor within the tetradentate ligand.

Chromium Diamino-bis(phenolate) Complexes as Catalysts for the Ring-Opening Copolymerization of Cyclohexene Oxide and Carbon Dioxide

Chromium diamino-bis(phenolate) complexes, CrXL [where L = 6,6'-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2,4-dimethylphenolato) and X = Cl^- (1), OH^- (2), and N₃^- (3)], were prepared and characterized by MALDI-TOF MS and single-crystal X-ray diffraction. Complex 1 crystallized as two linkage isomers, specifically a green chloride-bridged dimer (1) and a pink asymmetrically bridged isomer exhibiting one chloride bridging atom and one bridging phenolate oxygen (1'). Adventitious moisture during sample handling causes the formation of hydroxide-containing complex 2. The reaction of 1 with PPNN₃ (where PPN = bis(triphenylphosphine)iminium) permits the isolation of a crystalline chromium azide complex, 3, which was structurally authenticated. Complex 1 showed good activity toward the ring-opening copolymerization of cyclohexene oxide and carbon dioxide with an added chloride, azide, or 4-(dimethylamino)pyridine (DMAP) cocatalyst to give a completely alternating polycarbonate with a narrow molecular weight dispersity.

Cobalt amino-bis(phenolate) complexes for coupling and copolymerization of epoxides with carbon dioxide

Electron-withdrawing groups on phenolate donors enhance polycarbonate production from CO₂ and cyclohexene oxide by Co(ii) amino-bis(phenolate) complexes.

Synthesis and characterization of trimetallic cobalt, zinc and nickel complexes containing amine-bis(benzotriazole phenolate) ligands: efficient catalysts for coupling of carbon dioxide with epoxides

New trimetallic cobalt, nickel and zinc complexes 1-3 coordinated by amine-bis(benzotriazole phenolate) ligands and ancillary acetate groups have been developed for the use of CO₂/epoxide coupling. All complexes were structurally characterized by single crystal X-ray crystallography; tri-Co complex 1 is the first solid-state example in which three different geometrical configurations exist in the same benzotriazole phenoxide metal complex. Tri-nuclear complexes 1 and 2 with cobalt and zinc metal centers were demonstrated to be very active catalysts for cycloaddition of cyclohexene oxide with CO₂ in the presence of ammonium salt co-catalysts to give cis-cyclohexene carbonate under the conditions of 80 °C and 300 psi initial CO₂ pressure. Particularly, tri-cobalt complex 1 was found to efficiently couple CO₂ with epoxides showing broad substrate scope, producing the corresponding cyclic organic carbonates with good activities and high selectivities. This is a successful example of catalysis for cyclic carbonate synthesis using one cobalt(ii) complex as a homogeneous catalyst.

Mechanistic Studies of Cyclohexene Oxide/CO2 Copolymerization by a Chromium(III) Pyridylamine-Bis(Phenolate) Complex

Chromium(III) chlorido amine-bis(phenolate) complexes paired with nucleophilic co-catalysts are a promising family of catalysts for the copolymerization of CO₂ and epoxides to selectively produce polycarbonates with a very high degree of carbonate linkages. Single-component catalyst systems can be prepared, where the neutral nucleophile, 4-dimethylaminopyridine (DMAP), is coordinated to the metal site to provide a stable octahedral Cr^III complex. These complexes possess the potential for both anionic (from the chlorido ligand) or neutral (DMAP) nucleophilic epoxide ring-opening during the proposed rate-determining initiation step. Concentration effect studies support a first-order dependence of the polymerization rate on the concentration of single-component catalyst. End-group analysis of polycarbonates by MALDI-TOF MS indicate the presence of predominantly DMAP-initiated chains as well as the occurrence of chain-transfer events resulting in ether linkages, likely from the presence of cyclohexene diol formed by the reaction of cyclohexene oxide and adventitious water.

Coupling Reactions of Carbon Dioxide with Epoxides Catalyzed by Vanadium Aminophenolate Complexes

A series of vanadium compounds supported by tetradentate aminobis(phenolate) ligands were screened for catalytic reactivity in the reaction of propylene oxide (PO) with CO₂ : [VO(OMe)(O₂ NO^BuMeMeth )], [VO(OMe)(ON₂ O^BuMe )], [VO(OMe)(O₂ NN^BuBuPy )], and [VO(OMe)(O₂ NO^BuBuFurf )]. They showed similar reactivities, but reaction rates were higher for [VO(OMe)(ON₂ O^BuMe )], which was studied in more detail. Turnover frequencies for conversion of PO over 500 h^-1 were observed. Activation energies were determined experimentally through in situ IR spectroscopy for propylene carbonate (48.2 kJ mol^-1 ), styrene carbonate (45.6 kJ mol^-1 ), and cyclohexene carbonate (54.7 kJ mol^-1 ) formation.

Ring-opening copolymerisation of cyclohexene oxide and carbon dioxide catalysed by scorpionate zinc complexes

New bimetallic heteroscorpionate zinc complexes have been developed and used as efficient catalysts for the synthesis of poly(cyclohexene carbonate).