Structural Evidence for an Intramolecular CH–π Interaction in Ternary Metal (Cu(II), Pd(II)) Complexes Involving o-/m-/p-Methyl Substituted Phenylalanine and 1,10-Phenanthroline

Mamoru Mizutani, Shinya Tomosue, Hitoshi Kinoshita, Koichiro Jitsukawa, Hideki Masuda, Hisahiko Einaga

doi:10.1246/bcsj.72.981

<jats:title>Abstract</jats:title> <jats:p>The existence of a CH-π interaction has clearly been demonstrated by use of the ternary metal (Cu(II), Pd(II)) complexes involving o-/m-/p-methyl substituted l-phenylalanine (l-o-mPhe, l-m-mPhe, l-p-mPhe) and 1,10-phenanthroline (phen) on the basis of 1H NMR, electronic absorption, and CD spectroscopies, and X-ray diffraction method. The crystal structure of [{Cu(p-mPhe)(phen)}2{Cu(phen)2}(μ3-CO3)](ClO4)2 has revealed a marked structural feature suggesting CH-π and/or π–π interactions, although [Cu(l-o-mPhe)(phen)(H2O)]ClO4 does not show any interaction. CD spectra in the d–d region for [Cu(l-o-mPhe)(phen)]ClO4, [Cu(l-m-mPhe)(phen)]ClO4, and [Cu(l-p-mPhe)(phen)]ClO4 in aqueous solution have exhibited an obvious negative Cotton effect, and the magnitudes have significantly been reduced in dioxane/water in the order: [Cu(l-p-mPhe)(phen)]ClO4 ≤ [Cu(l-m-mPhe)(phen)]ClO4 < [Cu(l-o-mPhe)(phen)]ClO4. 1H NMR spectra of [Pd(l-o-mPhe)(phen)]ClO4, [Pd(l-m-mPhe)(phen)]ClO4, and [Pd(l-p-mPhe)(phen)]ClO4 have exhibited larger ring current shifts for m- and p-CH3 protons of the latter two complexes both in D2O and in DMSO-d6, whereas o-CH3 protons for the former complex do not. The magnitudes have greatly been reduced in this order: [Pd(l-p-mPhe)(phen)]ClO4 ≤ [Pd(l-m-mPhe)(phen)]ClO4 in D2O–dioxane-d8, but not for [Pd(l-o-mPhe)(phen)]ClO4.</jats:p>

Structural Evidence for an Intramolecular CH–π Interaction in Ternary Metal (Cu(II), Pd(II)) Complexes Involving <i>o</i>-/<i>m</i>-/<i>p</i>-Methyl Substituted Phenylalanine and 1,10-Phenanthroline

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