- The role of neutral donor ligands in the isoselective ring-opening polymerization of: Rac -β-butyrolactone
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Isoenriched poly-3-hydroxybutyrate (P3HB) is a biodegradable material with properties similar to isotactic polypropylene, yet efficient routes to this material are lacking after 50+ years of extensive efforts in catalyst design. In this contribution, a novel lanthanum aminobisphenolate catalyst (1-La) can access isoenriched P3HB through the stereospecific ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL). Replacing the tethered donor group of a privileged supporting ligand with a non-coordinating benzyl substituent generates a catalyst whose reactivity and selectivity can be tuned with inexpensive achiral neutral donor ligands (e.g. phosphine oxides, OPR3). The 1-La/OPR3 (R = n-octyl, Ph) systems display high activity and are the most isoselective homogeneous catalysts for the ROP of rac-BBL to date (0 °C: Pm = 0.8, TOF ~190 h-1). Combined reactivity and spectroscopic studies provide insight into the active catalyst structure and ROP mechanism. Both 1-La(TPPO)2 and a structurally related catalyst with a tethered donor group (2-Y) operate under chain-end stereocontrol; however, 2-RE favors formation of P3HB with opposite tacticity (syndioenriched) and its ROP activity and selectivity are totally unaffected by added neutral donor ligands. Our studies uncover new roles for neutral donor ligands in stereospecific ROP, including suppression of chain-scission events, and point to new opportunities for catalyst design. This journal is
- Dong, Xiang,Robinson, Jerome R.
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p. 8184 - 8195
(2020/09/07)
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- Rational Synthesis of Metallo-Cations Toward Redox- A nd Alkaline-Stable Metallo-Polyelectrolytes
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Cations are crucial components in emerging functional polyelectrolytes for a myriad of applications. Rapid development in this area necessitates the exploration of new cations with advanced properties. Herein we describe a combination of computational and experimental design of cobaltocene metallo-cations that have distinct electronic and redox properties. One of the direct outcomes on the first synthesis of a complete set of cation derivatives is to discover highly stable cations, which are further integrated to construct metallo-polyelectrolytes as anion-exchange membranes in solid-state alkaline fuel cells. The device performance of these polyelectrolytes under highly basic and oxidative environments is competitive with many organo-polyelectrolytes.
- Zhu, Tianyu,Sha, Ye,Firouzjaie, Horie Adabi,Peng, Xiong,Cha, Yujin,Dissanayake, D. M. M. Mevan,Smith, Mark D.,Vannucci, Aaron K.,Mustain, William E.,Tang, Chuanbing
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supporting information
p. 1083 - 1089
(2020/01/31)
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- ESTERIFICATION AT ROOM TEMPERATURE: A MIXING AFFAIR ONLY
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Carboxylic acids in absolute alcohols, on treatment with thionyl chloride at room temperature give good yields of corresponding esters.
- Kumar, Baldev,Verma, Raman
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p. 1359 - 1364
(2007/10/02)
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- HIGH-TEMPERATURE TRANSFORMATIONS OF ALKYL-SUBSTITUTED ACRYLIC ACIDS IN AQUEOUS SOLUTIONS
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Unlike unsubstituted acrylic acid, β-alkyl-substituted acrylic acids and α-ethyl-acrylic acid undergo hydration to a small degree (up to 4percent) when heated (180 - 230 deg C) with water.The main directions in the transformations are rearrangement through migration of the double bond and decarboxylation.During the rearrangement of α-ethylacrylic acid tiglic acid was obtained with a good yield.
- Salov, V. N.,Zil'berman, E. N.,Usova, N. Yu.
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p. 1778 - 1780
(2007/10/02)
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