2013 – Present

(54) Catal. Sci. Technol. 2020 DOI: 10.1039/d0cy01741h

“Cationic Aluminum, Gallium, and Indium Complexes in Catalysis”

Neutral heavier group 13 metals aluminum, gallium, and indium have been utilized as Lewis acid catalysts in various organic transformations ranging from classical organic reactions to polymerization reactions. The introduction of cationic charge can enhance the Lewis acidity of metal centers and allow cationic group 13 complexes to be excellent catalysts in Lewis acid catalysis, ….
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(53) Macromolecules 2020, 53(20), 8819-8828

“One-pot Synthesis of Oxygenated Block Copolymers by Polymerization of Epoxides and Lactide Using Cationic Indium Complexes”

Cationic indium complexes were used as catalysts for the copolymerization of epoxides and racemic lactide (rac-LA) via sequential addition to form high molecular weight block copolymers. Mechanistic studies and control experiments indicate that the epoxide is polymerized by a cationic mechanism to yield a neutral alkoxide indium species that subsequently polymerizes the lactide ….
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(52) ACS Catal. 2020, 10, 6488−6496

“Indium-catalyzed block copolymerization of lactide and methyl methacrylate by sequential addition”

We report a metal-mediated sequential addition synthetic route for copolymerization of lactide (or e-caprolactone) and methyl methacrylate. We synthesized a series of neutral and cationic indium complexes supported by tridentate Schiff base ligands and investigated their reactivities for the homo- and copolymerization of lactide or e-caprolactone and methyl methacrylate. ….
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(51) Chem. Sci. 2020, 11, 6485−6491

“Cationic indium catalysts for ring opening polymerization: Tuning reactivity with hemilabile ligands”

This is a comprehensive study of the effects of rationally designed hemilabile ligands on the stability, reactivity, and change in catalytic behavior of indium complexes.  We report cationic alkyl indium complexes supported by a family of hemi-salen type ligands bearing hemilabile thiophenyl (2a), furfuryl (2b) and pyridyl (2c) pendant donor arms. Shelf-life and stability of these complexes ….
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(50) Inorg. Chem. 2020, 59, 5546−5557

“Dinucleating Amino-Phenolate Platform for Zinc Catalysts: Impact on Lactide Polymerization”

We report imine and amine-based dinucleating ligands bearing a bisphenol backbone and explore their coordination chemistry with zinc complexes to form zinc alkyl, alkoxide, acetate, and amide complexes.  Full characterization of the complexes shows that this ligand framework can support dinuclear and trinuclear complexes. We explore the reactivity of the zinc alkyl and alkoxide  ….
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(49) Chem. Commun. 2019, 55, 3347-3350

“Cationic indium complexes for the copolymerization of functionalized epoxides with cyclic ethers and lactide”

We report the first example of discrete cationic indium complexes for the copolymerization of epoxides, cyclic ethers, and lactide. [SalenIn][SbF6] in particular proved to be a highly active catalyst for the homo-polymerization of functionalized epoxides and their copolymerization with other cyclic ethers THF, oxetane and oxepane. ….
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(48) Coord. Chem. Rev. 2019 380, 35–57

“Dinuclear catalysts for the ring opening polymerization of lactide”

Discrete metal initiators are comprised of an electropositive metal center, an ancillary ligand, and an initiating group such as an amide or an alkoxide. This difference in polarity between the electrophilic metal centers and the nucleophlic initiators often leads to catalyst aggregation. Partially due to this phenomenon, bimetallic catalysts, either dimeric, tethered, or dinucleating, are gaining attention as catalysts ….
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(47) ChemCatChem 2018, 10, 3219 – 3222

“Coupling of Epoxides and Lactones by Cationic Indium Catalysts To Form Functionalized Spiro-Orthoesters”

We prepared a cationic indium catalyst for the conversion of epoxides and lactones into spiro-orthoesters (SOEs), a family of expanding monomers. The cationic indium alkyl complexes were synthesized and fully characterized. The reaction of e-caprolactone with 1,2-epoxy-7-octene resulted in the formation of 2-(hex-5-en-1-yl)-1,4,6-trioxaspiro[4.6]undecane (SOE1) with full conversion of both components ….
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(46) ACS Sustainable Chem. Eng., 2018, 6, 1650–1661

“Synthesis and thermorheological analysis of biobased lignin-graft-poly(lactide) copolymers and their blends”

Despite numerous accounts of biobased composite materials through blending and copolymerization of lignin and other polymers, there are no systematic studies connecting the synthetic methodology, molecular structure, and polymer topology with ….
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(45) Acc. Chem. Res. 2017, 50, 2861−2869
“Indium catalysts for ring opening polymerization: Exploring the importance of catalyst aggregation”

Inexorably, the environmental persistence and damage caused by polyolefins have become major drawbacks to their continued long-term use. Global shifts in thinking from fossil-fuel to renewable biobased resources have urged researchers to focus their attention  ….
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(44) J. Rheol. 2017, 61(6), 1137-1148
“Aromatic interactions in aryl-capped polylactides: A thermorheological investigation”

A series of aryl-capped poly(lactide)s (PLAs) were synthesized by living ring-opening polymerization with a chain transfer agent (also referred to as immortal polymerization, iROP) using a previously reported dinuclear indium catalyst, [(NNO)InCl]2(μ-Cl)(μ-OEt) (A) ….
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(43) ACS Catal. 2017 7, 6413–6418
“Air- and Moisture Stable Indium Salan Catalysts for Living Multiblock PLA Formation in Air”

We introduce an air- and moisture-stable hydroxy-bridged indium salan complex as a highly active and controlled catalyst for the ring- opening polymerization of cyclic esters in air. The reversible activation of this complex with linear and branched alcohols ….
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(42) Dalton Trans. 2017 46, 6723–6733
“Impact of Aryloxy Initiators on the Living and Immortal Polymerization of lactide”

This report describes two different methodologies for the synthesis of aryl end-functionalized poly (lactide)s (PLAs) catalyzed by indium complexes. In the first method, a series of para-functionalized phenoxy-bridged dinuclear indium complexes …
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(41) Macromolecules 2017 50 (6), 2535–2546
“Binary Blends of Entangled Star and Linear poly(hydroxybutyrate): Effect of Constraint Release and Dynamic Tube Dilation”

In order to further understand the relaxation behavior of binary blends of star and linear chains, new polymer blends consisting of linear poly(hydroxybutyrate) (PHB) matrix and PHB star molecules are designed, and their dynamics is investigated by varying the star concentrations  …
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(40) Inorg. Chem. 2017 56 (3), 1375–1385
“A Comparison of Gallium and Indium Alkoxide Complexes as Catalysts for Ring-Opening Polymerization of Lactide”

The impact of the metal size and Lewis acidity on the polymerization activity of group 13 metal complexes was studied, and it was shown that, within the same ligand family, indium complexes are far more reactive and selective than their gallium analogues. To this end …
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(39) Macromolecules 2016 49 (23), 8812–8824
“Highly Active Chiral Zinc Catalysts for Immortal Polymerization of β‐Butyrolactone Form Melt Processable Syndio-Rich Poly(hydroxybutyrate)”

Highly crystalline poly(hydroxybutyrate) suffers from high melting point and entanglement molecular weight. This leads to low melt strength, limits processing through regular techniques, and precludes many applications. In this work we report a series of racemic …
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(38) Inorg. Chem. 2016, 55(18), 9445–9453
“The role of nitrogen donors in zinc catalysts for lactide ring opening polymerization”

The electronic effects of nitrogen donors in zinc catalysts for ring opening polymerization of cyclic esters were investigated. Alkyl and benzyloxy zinc complexes supported by tridentate diamino- and aminoimino phenolate ligands were synthesized and their …
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(37) Inorg. Chem. 2016, 55(11), 5365–5374
“Dinucleating ligand platforms supporting indium and zinc catalysts for cyclic ester polymerization”

The synthesis of the first alkoxide-bridged indium complex supported by a chiral dinucleating ligand platform (1), along with its zinc analogue (2), is reported. Both complexes are synthesized in a one-pot reaction starting from a chiral dinucleating …
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(36) Macromolecules 2016, 49(3), 909–919
“A comparison of the rheological and mechanical properties of isotactic, syndiotactic, and heterotactic PLA”

A series of poly(lactide) (PLA) samples, exhibiting various levels of syndiotactic enrichment, were formed via the ring-opening polymerization of meso-lactide using two families of novel dinuclear indium catalysts…
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(35) Macromolecules 2015, 48 (18), 6672–6681
“Synthesis and Rheological Characterization of Star-Shaped and Linear Poly(hydroxybutyrate)”

Indium and zinc complexes, [(NNOtBu)InCl]2(μ-Cl)(μ-OTHMB) (2) and (NNiOtBu)Zn(CH2CH3) (3), were used to produce monodispersed three- and six-armed star-shaped PHBs using tris(hydroxymethyl)benzene (THMB) and…
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(34) Chem. Sci., 2015, 6, 5284–5292
“Overcoming aggregation in indium salen catalysts for isoselective lactide polymerization.”

A methodology for controlling aggregation in highly active and isoselective indium catalysts for the ring opening polymerization of racemic lactide is reported. A series of racemic and enantiopure dinuclear…
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(33) Dalton Trans. 2015, 44, 14248 – 14254
“Star-shaped PHB-PLA block copolymers: Immortal polymerization with dinuclear indium catalysts”

The first example of a one-component precursor to star-shaped polyesters, and its utilization in the syn- thesis of previously unknown star-shaped poly(hydroxybutyrate)–poly(lactic acid) block copolymers,…
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(32) Dalton Trans. 2015, 44, 6126 – 6139
“Effect of steric changes on the isoselectivity of dinuclear indium catalysts for lactide polymerization”

Functionalized diaminophenolates as ligands for dinuclear indium catalysts were investigated in the ring-opening polymerization of lactide. An increase in the steric bulk of the ligand…
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(31) Inorg. Chem. 2014, 53(18), 9897−9906
“Probing the role of secondary vs. tertiary amine donor ligands for indium catalysts in lactide polymerization”

The role of the central amine donor in a previously reported dinuclear indium catalyst, [NMe2NHO)InCl]2(m-Cl)(m-OEt) (1), for the polymerization of lactide was investigated through…
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(30) J. Am. Chem. Soc. 2014, 136(32), 11264–11267
“Redox Control of Group 4 Metal Ring-Opening Polymerization Activity toward l-Lactide and ε-Caprolactone”

The activity of several group 4 metal alkoxide complexes supported by ferrocene-based ligands was controlled using redox reagents during the ring-opening polymerization of l-lactide and…
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(29) Inorg. Chem. 2014, 53(13), 6828–6836
“The role of aggregation in the synthesis and polymerization activity of SalBinap indium alkoxide complexes”

The reaction of racemic SalBinap ligand, (±)-H2(ONN*OMe) with InCl3 and excess NaOEt generated a mixture of two dinuclear compounds [(µ-κ2-ONN*OMe)In(µ-OEt)]2 (1a) and [κ4-ONN*OMe)In(µ-OEt)]2…
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(28) Organometallics 2013, 32(23), 6950–6956
“Theoretical Investigation of Lactide Ring-Opening Polymerization Induced by a Dinuclear Indium Catalyst”

A DFT study of the ring-opening polymerization of lactide (LA) induced by a dinuclear indium catalyst supported by a chiral diamino phenoxy ligand, [(NNHO)InCl]2(μ-Cl)(μ-OEt) (1), is reported….
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(27) Macromolecules 2013, 46, 3965−3974
“PLA-PHB-PLA triblock copolymers: Synthesis by sequential addition and investigation of mechanical and rheological properties”

The dinuclear indium catalyst [(NNO)InCl]2(μ-OEt)(μ-Cl), previously reported to be highly active for the living ring-opening polymerization of cyclic esters lactide (LA) and…
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(26) Chem. Commun. 2013, 49, 4295-4297
“A highly active and site selective indium catalyst for lactide polymerization”
Invited article in the “Emerging Investigators” issue.

Chiral indium salen complexes are highly active, isoselective catalysts for the ring opening polymerization of racemic lactide. The polymerizations are well controlled…
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