Dinuclear group 4 alkoxides: Excellent initiators for ring-opening polymerization of cyclic esters

Benzimidazolin-2-iminato Hafnium Complexes: Synthesis, Characterization, and Catalytic Addition of Alcohols to Carbodiimides

“…Hafnium complexes have mainly been used for the catalytic homo- and copolymerization of α-olefins − and as Lewis acid catalysts in various organic transformations including the polymerization of cyclic esters. − More recently, Hf–MOF complexes have been utilized in the catalytic activation of small molecules. − Among the group-IV metals, hafnium is considered to be the most oxophilic metal when compared with zirconium and titanium, as illustrated by their corresponding metal–oxygen bond dissociation energies (Ti–O = 666 kJ/mol, Zr–O = 766 kJ/mol, and Hf–O = 801 kJ/mol) . Hence, the strong metal–oxygen bond and the high electrophilicity of the metal have precluded the use of organometallic complexes of hafnium in processes involving oxygen-containing moieties with acidic protons. − We have postulated that if, during a stoichiometric or a catalytic process, we start with a metal–oxygen bond and after the transformation we end up with a different metal–oxygen bond, then, theoretically, we are not paying thermodynamically for the M–O bond; however, we need to have the energy of activation to be able to execute the process. − …”

“…moieties to carbodiimides have received substantial interest in recent years, and various types of catalysts have been used such as main-group metal centers, copper, lanthanides, actinides, ,,,, and titanium . Inspired by the observation that hafnium–oxygen moieties can be an active motif in catalytic processes, ,,− ,,− ,,,− we started to design our ligands toward the synthesis of hafnium complexes. On the one hand, we need a ligand that is highly nucleophilic to allow the stabilization of the metal complex and to ensure that the ligand will remain attached to the metal after the catalytic process.…”

Synthesis and characterization of Ti-/Zr-diphenylpropanedione complexes and their application in the ring opening polymerization of Ɛ-caprolactone

“…There are many examples of the use of metal-alkoxides based catalytic systems in polymerization reactions for manufacturing polymeric substances such as polyether, polylactone, and poly-lactides (11)(12)(13)(14). Due to their biocompatibility and biodegradability, these polymers have a lot of potential usage in medical, agricultural, and packaging areas (12)(13)(14)(15).…”

“…Catalysts including single-site or reduced number of alkoxide groups stabilized with βdiketone have had a breakthrough impact in polymer synthesis. With the aim of these catalysts' molecular weights, molecular weight distributions and stereochemistry of polymers and copolymers can be controlled (15). The general formula of these catalysts are LnMOR or LnM(OR)2 (M:Metal, Ln: β-diketone) where the OR is an alkoxy group that initiates the polymerization (16,17).…”