TY - JOUR
T1 - Sequential reaction intermediates in aliphatic C-H bond functionalization initiated by a bis(μ-oxo)dinickel(III) complex
AU - Cho, Jaeheung
AU - Furutachi, Hideki
AU - Fujinami, Shuhei
AU - Tosha, Takehiko
AU - Ohtsu, Hideki
AU - Ikeda, Osamu
AU - Suzuki, Akane
AU - Nomura, Masaharu
AU - Uruga, Tomoya
AU - Tanida, Hajime
AU - Kawai, Toshihide
AU - Tanaka, Koji
AU - Kitagawa, Teizo
AU - Suzuki, Masatatsu
PY - 2006/4/3
Y1 - 2006/4/3
N2 - The reaction of [Ni2(OH)2(Me2-tPa)2]2+ (1) (Me2-tpa = bis(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) with H2O2 causes oxidation of a methylene group on the Me2-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) ([Ni2(O)2(Me2-tpa)2]2+ (2)), a bis(μ-superoxo)dinickel(II) ([Ni2(O2)2(Me2-tpa) 2]2+ (3)), a (μ-hydroxo)(μ-alkylperoxo)dinickel(II) ([Ni2(OH)(Me2-tpa)(Me-tpa-CH2OO)]2+ (4)), and a bis(μ-alkylperoxo)dinickel(II) ([Ni2(Me-tpa-CH2OO)2]2+ (5)), was isolated and characterized by various physicochemical measurements including X-ray crystallography, and their oxidation pathways were investigated. Reaction of 1 with H2O2 in methanol at -40°C generates 2, which is extremely reactive with H2O2, producing 3. Complex 2 was isolated only from disproportionation of the superoxo ligands in 3 in the absence of H2O2 at -40°C. Thermal decomposition of 2 under N2 generated an N-dealkylated ligand Me-dpa ((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) and a ligand-coupling dimer (Me-tpa-CH2)2. The formation of (Me-tpa-CH2)2 suggests that a ligand-based radical Me-tpa-CH2• 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-CH2• 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 O2 gave carboxylate and alkoxide ligands, respectively (Me-tpa-COO- and Me-tpa-CH2O-), instead of (Me-tpa-CH2)2, indicating that the reaction of Me-tpa-CH2• with O2 is faster than the coupling of Me-tpa-CH2• to generate ligand-based peroxyl radical Me-tpa-CH2OO•. Although there is a possibility that the Me-tpa-CH2OO• species could undergo various reactions, one of the possible reactive intermediates, 4, was isolated from the decomposition of 3 under O2 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.
AB - The reaction of [Ni2(OH)2(Me2-tPa)2]2+ (1) (Me2-tpa = bis(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) with H2O2 causes oxidation of a methylene group on the Me2-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) ([Ni2(O)2(Me2-tpa)2]2+ (2)), a bis(μ-superoxo)dinickel(II) ([Ni2(O2)2(Me2-tpa) 2]2+ (3)), a (μ-hydroxo)(μ-alkylperoxo)dinickel(II) ([Ni2(OH)(Me2-tpa)(Me-tpa-CH2OO)]2+ (4)), and a bis(μ-alkylperoxo)dinickel(II) ([Ni2(Me-tpa-CH2OO)2]2+ (5)), was isolated and characterized by various physicochemical measurements including X-ray crystallography, and their oxidation pathways were investigated. Reaction of 1 with H2O2 in methanol at -40°C generates 2, which is extremely reactive with H2O2, producing 3. Complex 2 was isolated only from disproportionation of the superoxo ligands in 3 in the absence of H2O2 at -40°C. Thermal decomposition of 2 under N2 generated an N-dealkylated ligand Me-dpa ((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) and a ligand-coupling dimer (Me-tpa-CH2)2. The formation of (Me-tpa-CH2)2 suggests that a ligand-based radical Me-tpa-CH2• 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-CH2• 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 O2 gave carboxylate and alkoxide ligands, respectively (Me-tpa-COO- and Me-tpa-CH2O-), instead of (Me-tpa-CH2)2, indicating that the reaction of Me-tpa-CH2• with O2 is faster than the coupling of Me-tpa-CH2• to generate ligand-based peroxyl radical Me-tpa-CH2OO•. Although there is a possibility that the Me-tpa-CH2OO• species could undergo various reactions, one of the possible reactive intermediates, 4, was isolated from the decomposition of 3 under O2 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.
UR - http://www.scopus.com/inward/record.url?scp=33645911190&partnerID=8YFLogxK
U2 - 10.1021/ic0514243
DO - 10.1021/ic0514243
M3 - 学術論文
C2 - 16562943
AN - SCOPUS:33645911190
SN - 0020-1669
VL - 45
SP - 2873
EP - 2885
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 7
ER -