Theoretical Investigation and Synthesis Strategy of ‘<i>hypervalent’</i> Carbon

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<i>Hypervalent</i> compounds using main group elements are often used as reagents in the variety of interesting reactions in chemistry, such as in the total synthesis of some important natural products and/or drugs, as molecular switch, as oxidizing agents, in the synthesis of novel polymers, in rearrangement reactions, in oxidative cleavage reactions, in activation of small molecules (such as H₂, O₂, O₃, P₄…) etc. However, although <i>hypervalent</i> compounds of main group elements are well known, there are a few examples in the literature about DFT-calculation and synthesis strategy of <i>hypervalent</i> carbon compounds. Some scientists are still of the opinion that carbon atom does not have the ability to form hypervalent carbon bonds. Therefore, they argue that <i>multiple</i> bonded (more than 4 bond) carbon atoms should be termed "<i>hypercoordinated</i>". The fact is that both “<i>hypervalent</i>” carbon compounds and “<i>hypercoordinated</i>” carbon compounds existed. However, there are certain requirements for a <i>multiple</i> bonded carbon compound to be called "<i>hypervalent</i>". The most important requirements are the bond length, the existence of 3c–4e bonding mode and the bound ligand to carbon. This review discusses the conditions for the <i>hypevalence</i> and summarizes, analyzes the established synthesis strategy and some important DFT-calculation of <i>hypervalent</i> carbon compounds.