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The activation of carbon dioxide by transition metal complexes has been extensively studied. both experimentally and theoretically. 1 Central reactions in this chemistry are the insertion of C02 into M-X bonds. where X = H. C. 0. and N. (eq. 1-4). We are presently investigating the mechanistic aspects of these reaction processes and will herein deSCribe our current level of understanding. Comparisons of the pathway of the carbon-carbon bond fonning process in transition metal chemistry with the well known analogous chemistry involving organolithium reagents will be presented. Furthermore. the role of these reaction types in both homogeneous and heterogenous catalytic processes leading to useful chemicals will be elaborated. _OM (1) lMt-H + ~ lMlopi _OM (2) [Mt-R + C0. 2 [M]0. 2CR _OM (3) [Mt-OR+ ~ [M]0. 2COR _OM (4) [Mt-NR2 + C0. 2 [M]~CNR2 Insertion of C02 into the Metal-Hydride Bond. The reaction of anionic group 6 (Cr. Mo. W) transition metal hydrides with carbon dioxide to afford metalloformates occurs readlly at ambient temperature and 2 reduced pressures of carbon dioxide. This insertion process is referred to the normal pathway (Scheme 1). There are no documented cases of C02 insertion into the metal hydride bond to provide the alternative. metallocarboxylic acid. isomer (referred in Scheme 1 as abnormal). 3 Recent theoretical studies ascribe this preference to an unfavorable electrostatic interaction and poorer orbital overlap in the latter pro 4 cess. Nevertheless.
Table des matières
Utilization of Carbon Dioxide as a Source of Carbon : a Challenge of Great Intellectual Significance for Scientists.- Market and Application of Merchant CO2.- Theoretical Studies of Carbon Dioxide Organometallic Reactivity.- The Organometallic Chemistry of Carbon Dioxide Pertinent to Catalysis.- Catalytic Incorporation of CO2 for the Synthesis of Organic Compounds.- Photoreduction of Carbon Dioxide to Formate and Photo-oxidation of Carbon Monoxide to Carbon Dioxide by the Use of Transition Metal Complexes and Visible Light.- Electrochemical Syntheses Involving Carbon Dioxide.- Mammalian and Plant Carbonic Anhydrases: Structure, Function, Mechanism and Control.- Carbonic Anhydrases : the Mechanistic, Spectroscopic and Model Studies.- The Mechanism of Action of Carbonic Anhydrase.- Computer Simulation of Zinc-Containing Enzymes.- Mechanism of Carboxylation by Biotin Enzymes.- Carbamate Synthases and Kinases.- Carboxyphosphate: Predicted Chemical Properties, Synthesis and Role as an Intermediate in Enzymic Reactions.- Biological Utilization of Carbon Dioxide. Enzymic Catalysis Patterns Involving Biotin, ATP, and Bicarbonate.- Chemical Roles of B12-Derivatives in the Bacterial C1-Metabolism.- One-Carbon Metabolism of Anaerobic Bacteria : Challenge for Chemistry.- Increasing Photosynthesis by Genetic Manipulation: Difficulties and Prospects.- The Kinetic Properties of Ribulosebisphosphate Carboxylase.- Rubisco : Active-Site Characterization and Mechanistic Implications.- Structural and Functional Aspects of the Photosynthetic Fixation of Carbon Dioxide.- Coupling between the Light and Dark Reactions of Oxygen Evolution and CO2 Fixation in Photosynthesis: Early Experiments in Photosynthesis Revisited.- Conclusions.- List of Short Communications.- List of Participants.- Analytical index.- Appendix A Abstracts of lectures not available as full papers.- Appendix B Abstracts of short communications.
