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Sequential reaction intermediates in aliphatic C-H bond functionalization initiated by a bis(μ-oxo)dinickel(III) complex

Inorganic Chemistry, ISSN: 0020-1669, Vol: 45, Issue: 7, Page: 2873-2885
2006
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Article Description

The reaction of [Ni(OH)(Me-tPa)] (1) (Me-tpa = bis(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) with HO causes oxidation of a methylene group on the Me-tpa ligand to give an N-dealkylated ligand and oxidation of a methyl group to afford a ligand-based carboxylate and an alkoxide as the final oxidation products. A series of sequential reaction intermediates produced in the oxidation pathways, a bis(μ-oxo)dinickel(III) ([Ni(O)(Me-tpa)] (2)), a bis(μ-superoxo)dinickel(II) ([Ni(O)(Me-tpa) ] (3)), a (μ-hydroxo)(μ-alkylperoxo)dinickel(II) ([Ni(OH)(Me-tpa)(Me-tpa-CHOO)] (4)), and a bis(μ-alkylperoxo)dinickel(II) ([Ni(Me-tpa-CHOO)] (5)), was isolated and characterized by various physicochemical measurements including X-ray crystallography, and their oxidation pathways were investigated. Reaction of 1 with HO in methanol at -40°C generates 2, which is extremely reactive with HO, producing 3. Complex 2 was isolated only from disproportionation of the superoxo ligands in 3 in the absence of HO at -40°C. Thermal decomposition of 2 under N generated an N-dealkylated ligand Me-dpa ((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) and a ligand-coupling dimer (Me-tpa-CH). The formation of (Me-tpa-CH) suggests that a ligand-based radical Me-tpa-CH is generated as a reaction intermediate, probably produced by H-atom abstraction by the oxo group. An isotope-labeling experiment revealed that intramolecular coupling occurs for the formation of the coupling dimer. The results indicate that the rebound of oxygen to Me-tpa-CH is slower than that observed for various high-valence bis(μ-oxo)dimetal complexes. In contrast, the decomposition of 2 and 3 in the presence of O gave carboxylate and alkoxide ligands, respectively (Me-tpa-COO and Me-tpa-CHO), instead of (Me-tpa-CH), indicating that the reaction of Me-tpa-CH with O is faster than the coupling of Me-tpa-CH to generate ligand-based peroxyl radical Me-tpa-CHOO. Although there is a possibility that the Me-tpa-CHOO species could undergo various reactions, one of the possible reactive intermediates, 4, was isolated from the decomposition of 3 under O at -20°C. The alkylperoxo ligands in 4 and 5 can be converted to a ligand-based aldehyde by either homolysis or heterolysis of the O-O bond, and disproportionation of the aldehyde gives a carboxylate and an alkoxide via the Cannizzaro reaction. © 2006 American Chemical Society.

Bibliographic Details

Cho, Jaeheung; Furutachi, Hideki; Fujinami, Shuhei; Tosha, Takehiko; Ohtsu, Hideki; Ikeda, Osamu; Suzuki, Akane; Nomura, Masaharu; Uruga, Tomoya; Tanida, Hajime; Kawai, Toshihide; Tanaka, Koji; Kitagawa, Teizo; Suzuki, Masatatsu

American Chemical Society (ACS)

Chemistry

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