Département de chimie moléculaire

The sterically hindered salen ligands featuring biphenyl and tetramethyl putrescine linkers were synthesized and chelated to copper. The resulting complexes CuLbp{,}tBu{,} CuLbp{,}OMe{,} CuLpu{,}tBu and CuLpu{,}OMe were structurally characterized{,} showing a significanty tetrahedrally distorted metal center. The complexes show two reversible oxidation waves in the range 0.2 to 0.8 V vs. Fc+/Fc. A further reduction wave is detected in the range −1.4 to −1.7 V vs. Fc+/Fc. It is reversible for CuLbp{,}tBu and CuLbp{,}OMe and assigned to the CuII/CuI redox couple. One-electron oxidation of CuLbp{,}OMe{,} CuLpu{,}tBu and CuLpu{,}OMe was performed chemically and electrochemically. It is accompanied by a quenching of the EPR resonances. Phenoxyl radical formation was established by X-Ray diffraction on the cations [CuLbp{,}OMe]+ and [CuLpu{,}OMe]+{,} whereby the coordination sphere is elongated upon oxidation with quinoidal distributions of bond distances. The cations exhibit a NIR band of moderate intensity in their optical spectrum{,} supporting their classification as class II mixed-valent radical species according to the Robin Day classification. The proposed electronic structures are supported by DFT calculations. The cations [CuLbp{,}OMe]+{,} [CuLpu{,}tBu]+ and [CuLpu{,}OMe]+ were active towards aerobic oxidation of the unactivated alcohol 2-phenylethanol{,} with TON numbers up to 58 within 3 h.