Polymerization of Lactide with Zinc and Magnesium β-Diiminate Complexes:  Stereocontrol and Mechanism

Chamberlain, Bradley M.; Cheng, Ming; Moore, David R.; Ovitt, Tina M.; Lobkovsky, Emil; Coates, Geoffrey W.

doi:10.1021/ja003851f

Cited by 1,150 publications

(886 citation statements)

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“…For PLA samples, P r (the probability of racemic enchainment) was determined by analysis of the methine region of the homonuclear decoupled 1 H NMR spectra (CDCl 3 ). The equations used to calculate P r were as described by Coates et al [51] The conversions were determined by 1 H NMR integration of the OCHMe resonance relative intensities of the residual rac-lactide and poly(rac-lactide) and integration of the ε-methylene of residual ε-caprolactone and poly(ε-caprolactone).…”

Section: Experimental Section General Considerationsmentioning

confidence: 99%

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

et al. 2011

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A series of zinc complexes was prepared from 4,6‐disubstituted (R,R′) o‐[(4‐methyl‐1‐piperazinyl)methyl]phenols ([ONNR′,R]H) and characterized by elemental analysis, 1H and 13C{1H} NMR spectroscopy, and X‐ray crystallography. Reaction of these products with diethylzinc gave Zn[ONNtBu,tBu]2 (1) as a monometallic complex and {[μ‐ONNR′,R]ZnEt}2 [R′ = Me, R = tBu, (2); R′ = R = tBu (3); R′ = R = tAm (4)] bimetallic species that have distorted tetrahedral environments about the Zn centres. Reaction of 3 and 4 with alcohols gave {[ONNtAm,tAm]Zn(μ‐OR″)}2 [R″ = Bn (5); R″ = Et (6)] bimetallic species in which the Zn centres are bridged by benzyl alkoxide and ethoxide groups, respectively. A morpholinyl derived ligand was also synthesized and characterized (L4H), and its 1:1 stoichiometric reaction with ZnEt2 resulted in complex 7, {[μ‐ONOtBu,tBu]ZnEt}2. The reactivity of complexes 2–7 in the ring‐opening polymerization of rac‐lactide (LA) and ϵ‐caprolactone (ϵ‐CL) was studied. Reactions of carbon dioxide with cyclohexene oxide in the presence of 6 or 7/ROH (R = Bn, Et) afforded cyclohexene carbonate.

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Section: Experimental Section General Considerationsmentioning

confidence: 99%

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

et al. 2011

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“…To date, some of the best catalysts are homogeneous zinc complexes, coordinated by electron‐donating ligands, such as β‐diiminate (BDI),8 bis(amino)phenolates9 or pyrazolyol borates 10. Zinc(II) is an attractive choice of metal ion for such catalysts as it is cheap and combines high activity and selectivity with a lack of color, redox chemistry, and toxicity 11…”

mentioning

confidence: 99%

“…Zinc BDI complexes, originally pioneered by Coates and co‐workers and subsequently investigated by many others,8, 23 are some of the most highly active catalysts (Table 2, A ). In the present case, the ligands combine a “BDI‐like” chelate with an extra imine donor which enhances the electron donation, and which, in turn, results in faster rates.…”

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confidence: 99%

Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity

et al. 2016

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Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di‐ and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly out‐perform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with “folded” ligand conformation shows turnover frequency (TOF) values up to 60 000 h−1 (0.1 mol % loading, 298 K, [LA]=1 m), whilst that with a “planar” conformation is much slower, under similar conditions (TOF=30 h−1). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol % whilst conserving high activity (TOF=12 500 h−1).

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“…It is possible that this difference is a consequence of using a standard that is a different polymer (polystyrene) than the sample being tested. 37,[47][48][49][50] However, the large disparities between the theoretical and experimental molecular weights in the ε-caprolactone and δ-valerolactone polymerizations prompted further examination. Consequently, the polymerizations of ε-caprolactone and δ-valerolactone were carried out at low temperatures.…”

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confidence: 99%

High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

Quan

Diaconescu

2015

Chem. Commun.

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Abstract. An indium complex supported by a ferrocene-derived Schiff base ligand has an unprecedented high activity toward ε-caprolactone, δ-valerolactone, and β-butyrolactone. L-lactide, D,L-lactide, and trimethylene carbonate polymerizations also showed moderate to high activity.Over the past two decades, the ring-opening polymerization of cyclic esters has been increasingly studied because of the promise to produce biodegradable polymers from biomass. In our recent studies, a cerium complex supported by a Schiff base ligand with a ferrocene backbone polymerized L-lactide in a controlled fashion. 24 Phosphinimine analogues with yttrium and indium also demonstrated good activity in lactide and trimethylene carbonate polymerizations. 22 Therefore, we decided to combine indium's activity with the Schiff base, ferrocene-derived ligand in order to study the activity of the resulting complexes toward a broad range of cyclic ester polymerizations. Additional motivation was found from recent studies that point to the biocompatibility, robustness, and high activity of indium catalysts in the ring opening polymerization of cyclic esters. 10,25 Herein, we report a ferrocene-derived Schiff base indium complex that possesses a remarkable range of activity toward cyclic esters and exceptionally fast polymerization rates with lactones. Compound (salfen)In(O t Bu) (salfen = 1,1'-di(2,4-di-tert-butyl-6-iminephenoxy)ferrocene) represents the first indium precatalyst capable of δ-valerolactone polymerization and the most active indium catalyst to date in the polymerization of β-butyrolactone and ε-caprolactone. The polymerization rates of ε-caprolactone are even competitive with those of current industrial catalysts.Compound (salfen)In(O t Bu) was synthesized from the reaction of (salfen)InCl and freshly sublimed KO t Bu. In turn, (salfen)InCl was synthesized by combining InCl3 with K2(salfen), which was generated from H2(salfen) and two equivalents of KH (Eq 1). Needle crystals of (salfen)InCl were isolated from a diethyl ether solution. The solid state molecular structure (Figure 1) shows a distorted octahedral indium center and a THF molecule coordinated trans to the chloride ligand. Similarly to the phosphinimine indium chloride analogue previously reported by us, 22 a long In-Fe distance (3.98 Å) and a staggered configuration of the Cp rings were apparent. Elongation of the In-heteroatom distances compared to other compounds, such as (salen)InCl (salen = N,N ' -bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine (rac-or (R,R)-H2(ONNO))) 9 and (phosfen)In(OPh) (phosfen = 1,1'-di(2-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), 22 by about 0.25 Å possibly compensates for the distortion caused by the staggered Cp rings.

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Polymerization of Lactide with Zinc and Magnesium β-Diiminate Complexes: Stereocontrol and Mechanism

Cited by 1,150 publications

References 40 publications

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity

High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

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