| Summary: | 碩士 === 國立彰化師範大學 === 化學系 === 92 === Abstract
In the last 15 years, the preparation of persistent triplet carbenes and the isolation of singlet carbenes at room temperature represent spectacular achievements. The triplet carbenes have potential use in organic magnets. The stable singlet carbenes, featuring heteroatomic substituent, usually an amino or a phosphino group have been developed for the application of organic synthesis and metal catalysis. In this study, we use density functional theory (DFT) to investigate series of phosphino and amino carbenes, which had been synthesized by Bertrand (Bertrand type carbenes), and N-heterocyclic carbenes (NHCs), which had been synthesized by Arduengo. By studying their structure at singlet state, and activation energy, activation free energy, thermal energy and Gibbs free energy of each reaction which they participate in, we confirm the multiple bonding nature in P-C and N-C bonds, and besides their push-pull nature, bulky steric protection is also needed for Bertrand type carbenes. In addition, when we consider the presence of a solvent in our calculation, we found that it is helpful in increasing the activation energy and lowing the thermal energy of the unfavorable carbenes dimerization in both (phosphino)(silyl)carbenes and amino carbenes. Lastyl, we also study the electronic property of these stable singlet carbenes and the pKa of their protonated forms. The result shows that, in the aqueous solution NHCs are more basic than the push-pull type carbenes which had been synthesized by Bertrand.
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