We report the preparation, structural characterization, and detailed lactide polymerization behavior of a new Zn(II) alkoxide complex, (L(1)ZnOEt)(2) (L(1) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state, nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L(1)ZnOEt predominates in solution. The polymerization of lactide using this complex proceeded with good molecular weight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadings of <0.1% that yielded M(n) as high as 130 kg mol(-)(1). The effect of impurities on the molecular weight of the product polymers was accounted for using a simple model. Detailed kinetic studies of the polymerization reaction enabled integral and nonintegral orders in L(1)ZnOEt to be distinguished and the empirical rate law to be elucidated, -d[LA]/dt = k(p)[L(1)ZnOEt][LA]. These studies also showed that L(1)ZnOEt polymerizes lactide at a rate faster than any other Zn-containing system reported previously. This work provides important mechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metal alkoxide complexes.

Highly active zinc catalyst for the controlled polymerization of lactide.

This Perspective article summarizes efforts paid in our group to develop efficient metal-based catalysts for the immortal ring-opening polymerization (iROP) of cyclic esters in the presence of large amounts of alcohols (ROH) as chain transfer agents. The catalyst systems reviewed include discrete organometallic complexes based on rare earths, magnesium, calcium and more specifically zinc, as well as simple systems employing metal triflate salts, notably Al(OTf)3, for the (stereo)controlled iROP of lactide (LA), β-butyrolactone (BBL) and trimethylenecarbonate (TMC). Special emphasis is given to systems that allow the use of minute amounts of metal catalysts and large loadings of both monomer and alcohol for the rapid and productive formation of functional polyesters (H–Pol–OR) with controlled molecular features.

Metal-catalyzed immortal ring-opening polymerization of lactones, lactides and cyclic carbonates.

Interest in the utility of polylactide as a commodity polymer has increased significantly in recent years due to numerous environmental advantages over conventional petrochemically derived plastics. As such, the development of novel catalyst systems for the ring opening polymerization of lactide has seen tremendous progress in the past decade. In particular, divalent metals (i.e.Mg, Ca and Zn) supported by monoanionic ancillary scaffolds are appealing because of their low toxicity and cost. A much less common approach involves the use of neutral ligands in combination with the aforementioned divalent metal centres. The additional valence thus renders it possible, upon reaction with traditional Lewis or Bronsted acid activators, to generate sterically and electronically unsaturated species, akin to the most widely employed olefin polymerization catalysts. This Perspective is not intended as a comprehensive review, but rather a systematic highlight of key contributions, which have served to extend the forefront of this exciting field.

Complexes of Mg, Ca and Zn as homogeneous catalysts for lactide polymerization.

A review. Many discrete cationic complexes have been designed and exhibited increasingly impressive catalytic performances for the ROP of epoxides and cyclic esters. The current state-of-the-art suggests that major breakthroughs cannot be foreseen in the homopolymn. of epoxides, due to the nature of the assocd. mechanisms, and as a consequence, interest in the use of metal cations to polymerize epoxides has dwindled. It seems to the authors that in view of the activated monomer mechanism that is often assocd. with discrete metal cations, this is clearly an area where the use of rationally devised cationic complexes could bring original breakthroughs.

Discrete Cationic Complexes for Ring-Opening Polymerization Catalysis of Cyclic Esters and Epoxides

Hydrogen-bonding organocatalysts for ring-opening polymerization

Activated Zinc Complexes Supported by a Neutral, Phosphinimine-Containing Ligand: Synthesis and Efficacy for the Polymerization of Lactide

Cationic Organomagnesium Complexes as Highly Active Initiators for the Ring-Opening Polymerization of ε-Caprolactone

Zinc complexes of the potentially bidentate neutral mono- phosphinimine ligand 4-(ArN=PPh2)dibenzofuran were prepared. Two derivatives of this framework were studied, which differ in the steric demand of the N-aryl group (Ar = Dipp, Mes). The ligand interacts with diethylzinc in solution but does not form a tightly bound complex, whereby the degree of association is found to be dependent on tem- perature. However, isolable complexes are formed upon reaction with the more Lewis acidic precursors ZnCl2 and Zn(C6F5)2. In this way, the ZnCl2 complexes 1 and 2 and Zn(C6F5)2 complexes 3 and 4 were

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Synthesis and Structural Diversity of ZnCl2 and Zn(C6F5)2 Complexes of a Phosphinimine Ligand

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Benjamin J. Ireland

Papers

Complexes of Mg, Ca and Zn as homogeneous catalysts for lactide polymerization.

Activated Zinc Complexes Supported by a Neutral, Phosphinimine-Containing Ligand: Synthesis and Efficacy for the Polymerization of Lactide

Cationic Organomagnesium Complexes as Highly Active Initiators for the Ring-Opening Polymerization of ε-Caprolactone

Synthesis and Structural Diversity of ZnCl2 and Zn(C6F5)2 Complexes of a Phosphinimine Ligand

CationicOrganomagnesiumComplexesasHighlyActiveInitiatorsforthe Ring-Opening Polymerization of ε-Caprolactone