A plethora of methods have been developed over the years so that carbon dioxide can be used as a reactant in organic synthesis. Given the abundance of this compound, its utilization in synthetic chemistry, particularly on an industrial scale, is still at a rather low level. In the last 35 years, considerable research has been performed to find catalytic routes to transform CO(2) into carboxylic acids, esters, lactones, and polymers in an economic way. This Review presents an overview of the available homogeneous catalytic routes that use carbon dioxide as a C(1) carbon source for the synthesis of industrial products as well as fine chemicals.

ContentsI. Introduction 3197 II. LReO 3 Compounds and Derivatives 3199 A. Inorganic XReO 3 Compounds and Derivatives 3199 1. Dirhenium Heptaoxide, Re 2 O 7 , and Derivatives 3199 2. Halides and Pseudohalides of Type XReO 3 and Their Adducts 3200 3. R 3 EOReO 3 Compounds and Their Adducts (E ) C, Si, Sn, Ge, Sn, Pb) 3202 4. The Amido R 2 NReO 3 , the Phosphiniminato Complexes, and Their Adducts 3204 5. The Carboxylato Complexes (RCOO)-ReO 3 and Their Adducts 3204 6. The [L 3 ReO 3 ] + and [L 3 ReO 3 ] Complexes 3205 7. Miscellaneous Inorganic LReO 3 Derivatives 3206 8. Structural and Spectroscopic Characterization 3206 9. Reactions of Re 2 O 7 and XReO 3 Compounds 3208 B. Organic RReO 3 Compounds and Derivatives 3209 1. The Alkyl RReO 3 Derivatives 3209 2. The Methyl(vinyl)ReO 3 Complex 3212 3. Allyl, Benzyl, and Pseudoallylic Compounds 3212 4. The Alkinyl RReO 3 Derivatives 3212 5. The Aryl Derivatives 3213 6. The Cyclopentadienyl Derivatives 3213 7. The Indenyl Derivative 3214 8. Structural and Spectroscopic Characterization 3215 9. Reactions of Organic RReO 3 Compounds 3220 10. Applications 3223 III. The L 3 ReO 2 Compounds and Derivatives 3230 A. Inorganic X 3 ReO 2 Derivatives 3230 B. Organic and Mixed Derivatives 3231 IV. The L 4 Re 2 O 5 Compounds and Derivatives 3234 V. The L 5 ReO Compounds and Derivatives 3234 VI. The Re(VII) Imido Compounds and Derivatives 3234 A. The Inorganic XRe(NR) 3 Derivatives 3235 B. The Organic RRe(NR) 3 Derivatives 3236 C. The Inorganic X 3 Re(NR) 2 Derivatives 3236 D. The Organic R 3 Re(NR) 2 Derivatives 3237 E. Miscellaneous Polynuclear and Mixed Imido and Oxo−Imido Derivatives 3238 F. The X 5 Re(NR) Derivatives 3238 G. Reactions of XRe(NR) 3 Complexes 3238 H. Reactions of X 3 Re(NR) 2 and Derivatives 3239 1. The Imido−Alkyne XR(NAr) x (η 2 -C 2 R 2 ) 3-x Complexes 3239 2. The Imido−Alkylidene and Imido−Alkylidyne Complexes 3240 I. Structural Studies 3241 VII. Conclusions 3243 VIII. Abbreviations 3243 IX. Acknowledgments 3243 X. References 3243 3197

The synthesis of cyclic carbonates through coupling of carbon dioxide with epoxides is 100 % atom economical and is already performed on an industrial scale. Its impact regarding the use of carbon dioxide as a renewable carbon source is expected to grow significantly in the near future, so that the development of efficient catalysts is of high interest in academia and industry. To improve the carbon footprint and sustainability of the cycloaddition reaction, the use of organocatalytic methods is a promising approach. Herein, available metal-free catalysts for the preparation of cyclic carbonates are described and elaborated concerning the overall sustainability of the process. Therefore, the required reaction conditions, as well as the activity of the catalysts and their reusability, are compared and evaluated. In addition to ammonium-, phosphonium-, or imidazolium-based single-component catalysts and their supported analogues, the growing field of research concerning dual catalysts are also discussed in detail.

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