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Quantitative Evaluation of d–π Interaction in Copper( i) Complexes and Control of Copper( i) –Dioxygen Reactivity
Author(s) -
Osako Takao,
Tachi Yoshimitsu,
Doe Matsumi,
Shiro Motoo,
Ohkubo Kei,
Fukuzumi Shunichi,
Itoh Shinobu
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305263
Subject(s) - copper , reactivity (psychology) , control (management) , chemistry , computer science , organic chemistry , medicine , alternative medicine , pathology , artificial intelligence
Crystal structures of the copper( i) complexes 1 X , 2 , and 3 of a series of tridentate ligands L1 X , 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 η 2 copper–arene interaction with the phenyl ring of the ligand sidearm. The Cu I 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 C 1 C 2 of the phenyl ring of ligand sidearm, whereby the CuC distances of the copper–arene interaction significantly depend on the para substituents. The existence of the copper–arene interaction in a nonpolar organic solvent (CH 2 Cl 2 ) 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 1 H and 13 C NMR spectra and the redox potentials E 1/2 of the copper ion, as well as by means of the ligand‐exchange reaction between the phenyl ring and CH 3 CN as an external ligand. The thermodynamic parameters Δ H o and Δ S o for the ligand‐exchange reaction with CH 3 CN 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 d z 2orbital of Cu I and a π orbital of the phenyl ring. The copper( i) complexes 1 X reacted with O 2 at −80 °C in CH 2 Cl 2 to give the corresponding (μ‐η 2 :η 2 ‐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 O 2 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.