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Full-Text Articles in Physical Sciences and Mathematics
Lactide Cyclopolymerization Kinetics, X-Ray Structure, And Solution Dynamics Of (Tbu-Salamee)Al And A Cautionary Tale Of Polymetalate Formation, Yutan Getzler
Yutan D.Y.L. Getzler
The complex (tBu-SalAmEE)Al (tBu-SalAmEEH3 = N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-2-(2-aminoethoxy)ethanol, 1) catalyzes the ring-expansion polymerization of lactide to form cyclic poly(lactide) (cPLA). The X-ray structure of 1 was determined, its polymerization kinetics were examined and its interactions with Lewis bases were observed. The data from these experiments are consistent with a coordination–insertion mechanism whose rate-determining step is catalyst rearrangement by loss of a hemilabile, datively bound, bridging ligand ether. cPLA was examined by thermogravimetric analysis and found more stable than its linear counterpart. In the course of these studies, we unexpectedly observed the formation of polymetalate (AlMe(tBu-SalAmEE)AlMe2)2 (6), which was characterized (X-ray, EA, and …
Catalytic Carbonylation Of Β-Lactones To Succinic Anhydrides, Yutan Getzler
Catalytic Carbonylation Of Β-Lactones To Succinic Anhydrides, Yutan Getzler
Yutan D.Y.L. Getzler
A well-defined, highly active and selective catalyst for the synthesis of succinic anhydrides from CO and β-lactones is reported. At 200 psi of CO, the catalyst [(N,N‘-bis(3,5-di-tert-butylsalicylidene)phenylenediamino)Al(THF)2][Co(CO)4] carbonylates β-propiolactones to succinic anhydrides in high yield. (R)-β-Butyrolactone is carbonylated to (S)-methylsuccinic anhydride with clean inversion of stereochemistry, while cis-2,3-dimethyl-β-propiolactone yields exclusively trans-2,3-dimethylsuccinic anhydride. These data are consistent with a mechanism involving nucleophilic attack by [Co(CO)4]- on the β carbon of the lactone, followed by CO insertion and anhydride formation.
Lactide Cyclopolymerization By An Alumatrane-Inspired Catalyst, Yutan Getzler
Lactide Cyclopolymerization By An Alumatrane-Inspired Catalyst, Yutan Getzler
Yutan D.Y.L. Getzler
Control of molecular structure is an enduring motivation for chemists. From total synthesis(1) to self-assembly(2) to crystal growth,(3) the pursuit continues unabated. Polymer synthesis, in particular, has seen a revolution in control. It is now possible to precisely predetermine chain length, extent of cross-linking, comonomer incorporation, block length, stereochemistry and topology.(4) There has even been success in sequence control,(5) previously achieved only in biological systems. The difficulties inherent in the synthesis of pure macrocycle(6) have limited their availability, despite their compelling predicted properties. A variety of strategies have been employed but only two avoid …
The Mechanism Of Epoxide Carbonylation By [Lewis Acid]+[Co(Co)4]- Catalysts, Yutan Getzler
The Mechanism Of Epoxide Carbonylation By [Lewis Acid]+[Co(Co)4]- Catalysts, Yutan Getzler
Yutan D.Y.L. Getzler
A detailed mechanistic investigation of epoxide carbonylation by the catalyst [(salph)Al(THF)2]+ [Co(CO)4]- (1, salph = N,N‘-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), THF = tetrahydrofuran) is reported. When the carbonylation of 1,2-epoxybutane (EB) to β-valerolactone is performed in 1,2-dimethoxyethane solution, the reaction rate is independent of the epoxide concentration and the carbon monoxide pressure but first order in 1. The rate of lactone formation varies considerably in different solvents and depends primarily on the coordinating ability of the solvent. In mixtures of THF andcis/trans-2,5-dimethyltetrahydrofuran, the reaction is first order in THF. From spectroscopic and kinetic data, the catalyst resting state was assigned to be the neutral …
Synthesis Of An Epoxide Carbonylation Catalyst: Exploration Of Contemporary Chemistry For Advanced Undergraduates, Yutan Getzler
Synthesis Of An Epoxide Carbonylation Catalyst: Exploration Of Contemporary Chemistry For Advanced Undergraduates, Yutan Getzler
Yutan D.Y.L. Getzler
This lab presents an opportunity for advanced students of organic or inorganic chemistry to prepare a compound that belongs to a recently introduced class of catalyst that are active for the carbonylation of epoxides and related substrates to β-lactones and related products. Epoxides are inexpensive and readily available while β-lactones are not and have broad utility in both small molecule and polymer synthesis. Consequently, these catalysts, and related systems, have been the subject of intense investigation recently. The ability to work with a contemporary system was a major source of excitement and satisfaction to undergraduates at Cornell University who performed …