Biometal Derivatives as Catalysts for the Ring-Opening Polymerization of Trimethylene Carbonate. Optimization of the Ca(II) Salen Catalyst System

Abstract

Schiff base derivatives of the biometals (Zn, Mg, Ca) in the presence of anion initiators have been shown to be very effective catalysts for the ring-opening polymerization of trimethylene carbonate (TMC or 1,3-dioxan-2-one) to poly(TMC) devoid of oxetane linkages. The order of catalytic activity as a function of metal was found to be Ca(II) . Mg(II) > Zn(II). Optimization of the calcium system was achieved utilizing a salen ligand with tert-butyl substituents in the 3,5-positions of the phenolate rings and an ethylene backbone for the diimine along with an azide ion initiator. These conditions led to a TOF of 1286 h -1 for a melt polymerization carried out at 86 °C. Solution studies in tetrachloroethane demonstrated the polymerization reaction to proceed via a mechanism first order in [monomer], [(salen)Ca], and [anion initiator] and to involve TMC ring-opening by way of acyl-oxygen bond cleavage. The activation parameters were determined to be ∆H q ) 20.1 kJ/mol and ∆S q ) -128 J/(mol K).

Alkaline-Earth Metal Complexes in Homogeneous Polymerization Catalysis

“…The related Ca homoleptic complex {ON} 2 Ca(THF) 2 (74) containing two imino-phenolate ligands {NO} À was inactive towards CL under the same conditions. At the same time, Darensbourg and coworkers reported several {ONNO}Ca complexes supported by a variety of Schiff base derivatives (75)(76)(77), where the nature of the bridge and electronic and steric properties were tuned (Scheme 10) [96]. In combination with one equiv of additional anionic initiator (X -¼ Cl Alkaline-Earth Metal Complexes in Homogeneous Polymerization Catalysis{Ca(OMe) 2 } n , in combination with 2 equiv of BnOH for the ROP of L-LA (Fig.…”

Heteroleptic Tin(II) Initiators for the Ring‐Opening (Co)Polymerization of Lactide and Trimethylene Carbonate: Mechanistic Insights from Experiments and Computations

“…[d] Determined following end‐group analysis by 1 H NMR spectroscopy. [e] Determined by size exclusion chromatography versus polystyrene standards and corrected by factors of 0.5836 for L ‐LA and 0.7323a for TMC. [f] Taken from reference 7g.…”

Ring‐opening polymerization of cyclic esters by pincer complexes derived from alkaline earth metals

“…The first were developed by Chisholm et al ., which described calcium complexes supported by sterically encumbered tris(pyrazolyl)borates . However, ancillary ligands able to stabilize heteroleptic species are still very limited, and the most popular examples are essentially restricted to aminotrop(on)iminates, β‐diketiminates or Schiff‐base ligands . In the last few years, some examples of stable cationic calcium complexes have been reported by Carpentier et al …”