Geometry Change in a Series of Zirconium Compounds during Lactide Ring-Opening Polymerization

Dai, Ruxi; Lai, Amy; Alexandrova, Anastassia N.; Diaconescu, Paula L.

doi:10.1021/acs.organomet.8b00620

Cited by 22 publications

(17 citation statements)

References 66 publications

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“…The solid state molecular structure shows a pentacoordinate aluminum center with an eclipsed Cp configuration. The metal‐Fe distance was measured as 3.87 Å, which is shorter than in (thiolfan*)Al(O t Bu) at 4.61 Å, (salfen)In(O t Bu) at 3.98 Å, (salfen)Zr(O i Pr) 2 at 4.05 Å, but comparable to that of (salfen)Co at 3.72 Å . The Al‐heteroatom distances are similar to those in other tetradentate ONNO‐type salen (salen= N,N′ ‐bis(salicylidene)ethylenediamine) supported aluminum complexes…”

Section: Resultsmentioning

confidence: 51%

“…The aluminum analogue, (thiolfan*)Al(O t Bu), was not very selective between the two oxidation states, but could be used to synthesize various AB type diblocks with and without employing redox switching. Related supported ligands could also be used with zirconium as redox switchable catalysts: (salfan)Zr(O t Bu) 2 (salfan=1,1′‐di(2‐ tert ‐butyl‐6‐ N ‐methylmethylenephenoxy)ferrocene, Figure b) had the capability to synthesize an ABC type triblock of PBL‐PCHO‐PLA‐O t Bu, while (salfen)Zr(O i Pr) 2 (salfen=1,1′‐di(2,4‐bis‐ tert ‐butyl‐salicylimino)ferrocene, Figure c) could synthesize an ABA type PLA‐PCHO‐PLA triblock via two redox switches. When the indium analogue, (salfen)In(O t Bu) (Figure d), was examined, a high ring‐opening polymerization activity toward several lactones was observed with the reduced compound, but the catalyst was not redox switchable.…”

Section: Introductionmentioning

confidence: 99%

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Switchable Ring‐Opening Polymerization by a Ferrocene Supported Aluminum Complex

2019

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An aluminum(III) iso‐propoxide complex supported by salfen (1, salfen=1,1′‐di(2,4‐bis‐tert‐butyl‐salicylimino)ferrocene) was synthesized and characterized. Compound 1 can be reversibly oxidized and reduced, and both redox species were surveyed as ring‐opening polymerization catalysts for cyclic esters and cyclohexene oxide. Based on the observed reactivity behavior, 1 could be used as a redox‐switchable catalyst for the formation of AB and ABC type di‐ and triblock copolymers of lactide, cyclohexene oxide, and trimethylene carbonate.

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Section: Resultsmentioning

confidence: 51%

Section: Introductionmentioning

confidence: 99%

Switchable Ring‐Opening Polymerization by a Ferrocene Supported Aluminum Complex

2019

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Section: Historical Design Of Redox-switchable Catalysts Based On Fer...mentioning

confidence: 99%

“…Interestingly, the zirconium analogues, (salfen)Zr(OR) 2 (R = n Pr, i Pr, t Bu), show a somewhat simplified behavior. 40 All three compounds exist as a mixture of cis-β and trans isomers, with the isomer featuring a cis-β geometry found majorly in solution. However, an isomerization between the two was observed at ca.…”

Section: Historical Design Of Redox-switchable Catalysts Based On Fer...mentioning

confidence: 99%

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Redox-Switchable Ring-Opening Polymerization with Ferrocene Derivatives

2019

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CONSPECTUS: Switchable catalysts incorporate stimuli-responsive features and allow synthetic tasks that are difficult or impossible to accomplish in other ways. They mimic biological processes in that they can provide both spatial and temporal control, unlike most reactions promoted by human-made catalysts that usually occur according to carefully optimized conditions. In the area of switchable catalysis, redox-switchable ring-opening polymerization (ROP) has attracted much attention, emerging as a powerful strategy for the development of environmentally friendly biodegradable copolymers, especially those containing blocks with complementary properties. Controlling the sequence and regularity of each copolymeric building block can affect the material properties significantly since they are directly related to the respective microstructures. Such control can be exerted with a well-designed redox-switchable catalyst by timing the oxidation and reduction events. In highly selective systems, one form of the catalyst reacts with a monomer until the redox state of the catalyst is altered, at which point the altered state of the catalyst reacts with another monomer. The reaction time may be varied from one cycle to another to generate various designer multiblock copolymers. The first instance of redox-mediated ROP was described by N. Long and co-workers in 2006. This example, as well as many early reported redox-switchable catalysts, could only achieve an on/off switch of activity toward a single monomer or substrate. However, our efforts brought on a general strategy for designing redox-switchable metal complexes that can catalyze different reactions in two oxidation states. In recent years, our contributions to this research field led to the synthesis of several multiblock copolymers prepared from biorenewable resources. This Account provides an overview of reported redox-switchable polymerization catalysts that allow for complementary reactivity in different oxidation states and highlights the potential of this strategy in preparing biodegradable materials. First, we define the field of redox-switchable catalysis and illustrate the design and significance of our ferrocene-chelating ligands, in which the oxidation state of iron in ferrocene can control the reactivity of the resulting metal complexes remotely. Next, we illustrate recent advances in the synthesis of new biodegradable copolymers including (1) how to tune the activity of the ROP catalysts by exploring various metal centers and ferrocene-based ligand combinations; (2) how to synthesize new multiblock copolymers of cyclic esters, epoxides, and carbonates by redox-switchable ROP; and (3) how to understand the mechanism of these reactions by discussing both experimental and theoretical investigations. By the application and development of redoxswitchable strategies, various novel materials and reactions can be expected in the future.

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Valence‐variable Catalysts for Redox‐controlled Switchable Ring‐opening Polymerization

Pang

et al. 2022

Chemistry An Asian Journal

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As a representative class of sustainable polymer materials, biodegradable polymers have attracted increasing interest in recent years. Despite significant advance of related polymerization techniques, realizing high sequence‐control and easy‐handling in ring‐opening (co)polymerizations still remains a central challenge. To this end, a promising solution is the development of valence‐variable metal‐based catalysts for redox‐induced switchable polymerization of cyclic esters, cyclic ethers, epoxides, and CO2. Through a valence‐determined electron effect, the switch between different catalytically active states as well as dormant state contributes to convenient formation of polymer products with desired microstructures and various practical performances. This redox‐controlled switchable strategy for controlled synthesis of polymers is overviewed in this Review with a focus on potential applications and challenges for further studies.

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Geometry Change in a Series of Zirconium Compounds during Lactide Ring-Opening Polymerization

Cited by 22 publications

References 66 publications

Switchable Ring‐Opening Polymerization by a Ferrocene Supported Aluminum Complex

Switchable Ring‐Opening Polymerization by a Ferrocene Supported Aluminum Complex

Redox-Switchable Ring-Opening Polymerization with Ferrocene Derivatives

Valence‐variable Catalysts for Redox‐controlled Switchable Ring‐opening Polymerization

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