Conformationally Flexible Dimeric Salphen Complexes for Bifunctional Catalysis

Appropriate modification of the salphen ligand allows an easy modular design of flexibly linked dimeric salphen species and their complexes, which can act as bifunctional catalysts. A series of chromium salphen systems including monomeric compound and dimers with different spacer lengths were tested for their catalytic performance in β-butyrolactone polymerization and CO2/propylene oxide copolymerization toward biodegradable materials. The results clearly show an enhancement in activity upon dimerization, thus underlining the role of bifunctional catalysis in the studied processes and extending the possible strategies for improvement of catalysts in these reactions

Factors Influencing the Ring-Opening Polymerization of Racemic β-Butyrolactone Using Cr^III(salphen)

The recently discovered ring-opening polymerization (ROP) of β-butyrolactone (β-BL) using CrIII(salphen) as catalyst converts racemic β-BL to isotactic enriched poly(hydroxybutyrate) (PHB). These achiral complexes arrange themselves in a dimeric sandwich-like structure entrapping the growing polymer chain and the monomer. The polymerization mechanism discussed based on previous DFT calculations is supported by kinetic studies in here. Furthermore, the influence of different substitution patterns in salphen complexes on polymerization of β-BL was investigated. In addition, effects of different polymerization starters and additives on the broad molecular weight distribution of PHB have been investigated, which show the limitations of this catalysis

Formation of Methyl Acrylate from CO₂ and Ethylene via Methylation of Nickelalactones

The nickel-induced coupling of ethylene and CO2 represents a promising pathway toward acrylates. To overcome the high bond dissociation energies of the M−O moieties, we worked out an in situ methylation of nickelalactones to realize the β-hydride elimination and the liberation of the acrylate species