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

摘要

The existence of a CH-#pi# 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 AD spectroscopies, and X-ray diffraction method. The crystal structure of [{Cu(p-mPhe)(phen)}_2 {Cu(phen)_2}(#mu#_3-CO_3)](ClO_4)_2 has revealed a marked structural feature suggesting CH-#pi# and/or #pi#-#pi# interactions, although [Cu(L-o-mPhe)(phen)(H_2O)]ClO_4 does not show any interaction. AD spectra in the d-d region for [Cu(L-o-mPhe)(phen)]ClO_4, [Cu(L-m-mPhe)(phen)]ClO_4, and [Cu(L-p-mPhe)(phen)]ClO_4 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)]ClO_4 <= [Cu(L-m-mPhe)(phen)]ClO_4 < [Cu(L-o-mPhe)(phen)]ClO_4. ~1H NMR spectra of [Pd(L-o-mPhe)(phen)]ClO_4, [Pd(L-m-mPhe)(phen)]ClO_4, and [Pd(L-p-mPhe)(phen)]ClO_4 have exhibited larger ring current shifts for m-and p-CH_3 protons of the latter twocomplexes both in D_2O and in DMSO-d_6, whereas o-CH_3 protons for the former complex do not. The magnitudes have greatly been reduced in this order: [Pd(L-p-mPhe)(phen)]ClO_4<=[Pd-(L-m-mPhe)(phen)]ClO_4 in D_2O-dioxane-d_8, but not for [Pd(L-o-mPhe)(phen)]ClO_4.