Controlled Polymerization of ϵ‐Caprolactone using Aluminum and Zinc Complexes with Iminophosphorane Ligands

Abstract

Several novel aluminum complexes [Al(R1)2{o‐O C(R)=C(H)P(Ph2)=N)C6H4(3,5‐Me2 ‐pyrazolyl)} (R=Ph, R1=Me, 3; R=Ph, R1=Et, 4; R=tBu, R1=Me, 5) had been prepared. These aluminum complexes were structurally characterized by nuclear magnetic resonance spectroscopy (1H, 13C and 31P) and elemental analyses. The aluminum complex 3 was determined by X‐ray diffraction. The catalytic activities of the aluminum complexes towards the ring‐opening polymerization (ROP) of ϵ‐caprolactone (ϵ‐CL) were investigated. Catalysis of two known zinc complexes with the same ligands, [Zn(Et) {o‐(OC(R)=C(H)P(Ph2)=N)C6H4(3,5‐Me2‐pyrazolyl)}] (R=Ph, 6; R=tBu, 7), in the ROP of ϵ‐CL was also determined. The catalytic results show that these complexes are effective catalysts in the ROP of ϵ‐CL. Kinetics of the polymerization was studied. These polymerizations reaction are consistent with the first‐order kinetic equation. The molecular weight of the polycaprolactone (PCL) is linear with the monomer conversion, and the molecular weight distribution is narrow. These kinetic studies confirm that the catalytic process is controllable.

Halogenated β‐diketiminato magnesium complexes: Preparation, characterization, and catalysis for ring‐opening polymerization of aliphatic lactones

“…[1][2][3][4] As a powerful strategy for the preparation of polyester, the organometallicspromoted ring-opening polymerization (ROP) of aliphatic lactones has attracted great attentions. [5][6][7][8] To date, plenty of organometallics have been demonstrated as efficient catalysts for the ROP of lactones, such as alkali metals (Li, 9 K [10][11] ), alkaline-earth metals (Mg, [12][13][14][15][16][17][18] Ca, 19 Ba 20 ), aluminum, [21][22][23][24][25] tin, 26 rare-earth metals [27][28][29][30][31][32][33][34] and some transition metals (Ti, 35 Zr, 36 V, 37 Fe, [38][39] Zn [40][41][42][43] ). Among them, the magnesium-based complex has attracted special attention due to its high activity and low toxicity.…”

Ring-Opening Polymerization of ε-Caprolactone Utilizing Aluminum Alkyl Complexes Bearing Dianionic Scorpionate Ligands

“…Metal-mediated processes have been a specific area of interest for the ROP of cyclic esters as well-defined biodegradable polymers with controlled chain lengths are produced. , Aluminum-based systems are especially attractive due to the large abundance of the metal, its low cost, and its high Lewis acidity. ,− When developing catalytic systems, though, the ancillary ligands surrounding the aluminum center play a key role in determining the reactivity and selectivity of the catalyst. Over the past several decades, aluminum complexes bearing bidentate, − tridentate, − and tetradentate ,, ligands have been explored in the literature, a selection of which are shown in Figure . ,− Notably, aluminum alkyl complexes supported by salen − or salan − ligands have seen particular success in this field. These species form five-coordinate pre-catalysts that can polymerize cyclic esters with narrow PDIs after being activated with benzyl alcohol.…”