Quantitative Evaluation of d-π Interaction in Copper(I) Complexes and Control of Copper(I)-Dioxygen Reactivity

Takao Osako, Yoshimitsu Tachi, Matsumi Doe, Motoo Shiro, Kei Ohkubo, Shunichi Fukuzumi, Shinobu Itoh

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Crystal structures of the copper(I) complexes 1x, 2, and 3 of a series of tridentate ligands L1x, L2, and L3, respectively (L1 x: p-substituted derivatives of N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine; X = H, Me, OMe, Cl, NO 2; L2: N,N-bis[2-(2-pyridyl)ethyl]-2-methyl-2-phenylethylamine; L3: N,N-bis[2-(2-pyridyl)ethyl]-2,2-diphenylethylamine) were solved to demonstrate that all the copper(I) complexes involve an η2 copper-arene interaction with the phenyl ring of the ligand sidearm. The Cu1 ion in each complex has a distorted tetrahedral geometry consisting of the three nitrogen atoms (one tertiary amine nitrogen atom and two pyridine nitrogen atoms) and C1-C2 of the phenyl ring of ligand sidearm, whereby the Cu-C distances of the copper-arene interaction significantly depend on the para substituents. The existence of the copper-arene interaction in a nonpolar organic solvent (CH2Cl2) was demonstrated by the observation of an intense MLCT band around 290 nm, and the magnitude of the interaction was evaluated by detailed analysis of the 1H and 13C NMR spectra and the redox potentials E1/2 of the copper ion, as well as by means of the ligand-exchange reaction between the phenyl ring and CH3CN as an external ligand. The thermodynamic parameters ΔH° and ΔS° for the ligand-exchange reaction with CH3CN afforded a quantitative measure for the energy difference of the copper-arene interaction in the series of copper(I) complexes. Density functional studies indicated that the copper(I)-arene interaction mainly consists of the interaction between the dz2 orbital of Cu 1 and a π orbital of the phenyl ring. The copper(I) complexes 1x reacted with O2 at -80°C in CH2Cl 2 to give the corresponding (μ-η22-peroxo)dicopper(II) complexes 4, the formation rates k obs of which were significantly retarded by stronger d-π interaction, while complexes 2 and 3, which exhibit the strongest d-π interaction showed significantly lower reactivity toward O2 under the same experimental conditions. Thus, the d-π interaction has been demonstrated for the first time to affect the copper(I)-dioxygen reactivity, and represents a new aspect of ligand effects in copper(I)-dioxygen chemistry.

Original languageEnglish
Pages (from-to)237-246
Number of pages10
JournalChemistry - A European Journal
Issue number1
StatePublished - 5 Jan 2004


  • Copper
  • N ligands
  • O-O activation
  • Pi interactions
  • Substituent effects


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