| Summary: | 博士 === 國立成功大學 === 化學系碩博士班 === 100 === Through analysis HOMO or LUMO formed by Linear Combination of Bond Orbitals (LCBO), in methylated Ir(ppz)23iq (ppz=1-phenylpyrazole and 3iq=isoquinoline-3-carboxylate), it is seen that both C-H bonding and antibonding (Sigma CH and Sigma*CH) of methyl contribute to HOMO/LUMO. LCBO analysis indicates that, through orbital interaction, Sigma CH destabilizes HOMO (or LUMO) and Sigma*CH stabilizes HOMO (or LUMO). In the cationic Ir(ppy)2HDPA+ complex (ppy=2,2’-phenylpyridine and HDPA=2,2’-dipyridyl amine) the Pi-type orbital interaction between nitrogen’s 2p-orbital, 2p(N), and HOMO/LUMO would push-up HOMO/LUMO (in either free HDPA or coordinated HDPA) even higher. Similar to the amino-nitrogen, fluoro can push up HOMO/LUMO through interaction with HOMO/LUMO as it is introduced to the Ir(ppy)2HDPA+ complex. The extents of destabilizing HOMO (or LUMO) are parallel to the value of %C of the carbon in HOMO (or LUMO) subjected to fluorination. The relative energies of HOMO (or LUMO) among the mono-fluorinated derivatives are governed by the pushing-up effects, which explains the site-dependent characteristics. Fluorination at carbon having larger %C leads to a Pi-destabilization more competitive with the inductive-stabilization. The orbital interaction described above is similar to the orbital interaction employed in the familiar ligand field theory (except that the symmetry-restriction is relaxed): the higher orbital is pushed still higher and the lower orbital is pressed even lower. Combination of the pushing-up effects of fluorination and pressing-down effects of BMe2-substituion on HOMO/LUMO of Ir(ppy)2MDPA+ (MDPA=N-methylated HDPA) gives the interaction diagram describing effects of CF3 on the levels of HOMO/LUMO. The pushing-up effects are exerted by 2p(F), while the pressing-down effects are exerted by Sigma*CF bond orbital. Since the two conflicting Pi-effects are nearly counterbalanced, the net results are well explained by its electron-withdrawing effects.
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