4.3. Reaction Mechanism 2373 4.4. Asymmetric Synthesis 2374 4.5. Outlook 2374 5. Alternating Polymerization of Oxiranes and CO2 2374 5.1. Reaction Outlines 2374 5.2. Catalyst 2376 5.3. Asymmetric Polymerization 2377 5.4. Immobilized Catalysts 2377 6. Synthesis of Urea and Urethane Derivatives 2378 7. Synthesis of Carboxylic Acid 2379 8. Synthesis of Esters and Lactones 2380 9. Synthesis of Isocyanates 2382 10. Hydrogenation and Hydroformylation, and Alcohol Homologation 2382

Transformation of carbon dioxide.

Catalysis for the valorization of exhaust carbon: from CO2 to chemicals, materials, and fuels. technological use of CO2.

23 Stereocontrol of Lactide ROP 6164 231 Isotactic Polylactides 6164 232 Syndiotactic Polylactides 6166 233 Heterotactic Polylactides 6166 3 Anionic Polymerization 6166 4 Nucleophilic Polymerization 6168 41 Mechanistic Considerations 6168 42 Catalysts 6169 421 Enzymes 6169 422 Organocatalysts 6169 43 Stereocontrol of Lactide ROP 6170 44 Depolymerization 6170 5 Cationic Polymerization 6170 6 Conclusion and Perspectives 6171 7 Acknowledgments 6173 8 References and Notes 6173

Controlled ring-opening polymerization of lactide and glycolide.

Biofibres and Biocomposites

The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.

The teraton challenge. A review of fixation and transformation of carbon dioxide

A series of zinc(II) and magnesium(II) alkoxides based upon a β-diiminate ligand framework has been prepared. [(BDI-1)ZnOiPr]2 [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)...

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

Most synthetic polymers are made from petroleum feedstocks. Given the non-renewable nature of these materials, there is increasing interest in developing routes to polymeric materials from renewable resources. In addition, there is a growing demand for biodegradable polymeric materials. Polycarbonates made from CO(2) and epoxides have the potential to meet these goals. Since the discovery of catalysts for the copolymerization of CO(2) and epoxides in the late 1960's by Inoue, a significant amount of research has been directed toward the development of catalysts of improved activity and selectivity. Reviewed here are well-defined catalysts for epoxide-CO(2) copolymerization and related reactions.

Discrete Metal-Based Catalysts for the Copolymerization of CO2 and Epoxides: Discovery, Reactivity, Optimization, and Mechanism

Synthetic routes to zinc β-diiminate complexes are reported. The synthesis of 11 β-diimine [(BDI)-H] ligands, with varying N-aryl substituents and bridging structures, is described. These ligands are converted to (BDI)ZnX complexes (X = OAc, Et, N(SiMe3)2, Br, Cl, OH, OMe, OiPr). X-ray structural data revealed that all zinc complexes examined exist as μ-X-bridged dimers in the solid state, with the exception of the zinc ethyl and amido complexes which were monomeric. Complexes of the form (BDI)ZnOR (R = alkyl, acyl) and (BDI)ZnN(SiMe3)2 are highly active catalysts for the alternating copolymerization of epoxides and CO2. Copolymerizations of cyclohexene oxide (CHO) and CO2 with (BDI-1)ZnX [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene)] and (BDI-2)ZnX [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene)], where X = OAc, Et, N(SiMe3)2, Br, Cl, OH, OMe, OiPr, were attempted at 50 °C and 100 psi CO2. Complexes with X = OAc, N(SiMe3)2, OMe, Oi...

Single-site beta-diiminate zinc catalysts for the alternating copolymerization of CO2 and epoxides: catalyst synthesis and unprecedented polymerization activity.

A series of zinc beta-diiminate (BDI) complexes and their solid-state structures, solution dynamics, and copolymerization behavior with CO(2) and cyclohexene oxide (CHO) are reported. Stoichiometric reactions of the copolymerization initiation steps show that zinc alkoxide and bis(trimethylsilyl)amido complexes insert CO(2), whereas zinc acetates react with CHO. [(BDI-2)ZnOMe](2) [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] and (BDI-1)ZnO(i)Pr [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] react with CO(2) to form [(BDI-2)Zn(mu-OMe)(mu,eta(2)-O(2)COMe)Zn(BDI-2)] and [(BDI-1)Zn(mu,eta(2)-O(2)CO(i)Pr)](2), respectively. (BDI-2)ZnN(SiMe(3))(2) inserts CO(2) and eliminates trimethylsilyl isocyanate to give [(BDI-2)Zn(mu-OSiMe(3))](2). [(BDI-7)Zn(mu-OAc)](2) [(BDI-7) = 3-cyano-2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] reacts with 1.0 equiv of CHO to yield [(BDI-7)Zn(mu,eta(2)-OAc)(mu,eta(1)-OCyOAc)Zn(BDI-7)]. Under typical polymerization conditions, rate studies on the copolymerization exhibit no dependence in [CO(2)], a first-order dependence in [CHO], and orders in [Zn](tot) ranging from 1.0 to 1.8 for [(BDI)ZnOAc] complexes. The copolymerizations of CHO (1.98 M in toluene) and 300 psi CO(2) at 50 degrees C using [(BDI-1)ZnOAc] and [(BDI-2)ZnOAc] show orders in [Zn](tot) of 1.73 +/- 0.06 and 1.02 +/- 0.03, respectively. We propose that two zinc complexes are involved in the transition state of the epoxide ring-opening event.

David Roger Moore

Papers

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

Discrete Metal-Based Catalysts for the Copolymerization of CO2 and Epoxides: Discovery, Reactivity, Optimization, and Mechanism

Single-site beta-diiminate zinc catalysts for the alternating copolymerization of CO2 and epoxides: catalyst synthesis and unprecedented polymerization activity.

Mechanism of the Alternating Copolymerization of Epoxides and CO2 Using β-Diiminate Zinc Catalysts: Evidence for a Bimetallic Epoxide Enchainment

Electronic and Steric Effects on Catalysts for CO2/Epoxide Polymerization: Subtle Modifications Resulting in Superior Activities