Oxo-transfer catalysis from t-BuOOH with C-H bond insertion using tridentate Schiff-base-chelate complexes of ruthenium(III)

摘要

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived by condensation of aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) with 2-aminobenzoic acid, and bidentate ligands (2,2'-bipyridine or picolinic acid). [Ru-111(cpsd)(bipy)(H2O)](+) (1), [Ru-111(cpsd)(pic)(H2O)] (2), [Ru-111(cppc)(bipy)(H2O)](2+) (3) and [Ru-111(cppc)(pic)(H2O)](+) (4) complexes (where, cpsd(2-) = (N-(2-carboxyphenyl)salicylaldiminato); cppc(-) = N-2-carboxyphenylpyridine-2-carboxaldiminato; bipy = 2,2'-bipyridine and pic(-) = picolinate) were characterized by analytical, spectral (IR and UV-Vis), conductance, magnetic moment and electrochemical studies. Catalysis of hydrocarbon oxidations for cyclohexene, cyclohexane, cyclohexanol, toluene, benzyl alcohol, and tetrahydrofuran have been studied using various O-atom transfer agents (t-BuOOH, H2O2, NaOCl, KHSO5 and pyridinium-N-oxide). The influence of product yield as a function of solvent was evaluated for CH2Cl2, CH3CN, and 1,4-dioxane. Coordinating solvents suppress the reactivity by inhibiting coordination of t-BuOOH, and compete for the Ru-V=O group through their own intrinsic C-H reactivity. The main pathway transfers the oxo group from the [RuO(TDL)(XY)] intermediate, TDL = cpsd(2-) and cppc(2-); XY = bipy or pic(-), with insertion of the oxo group into a C-H bond of all substrates tested (rather than olefin epoxidation for cyclohexene). A mechanism involving intermediacy of a high valent Ru(V)-oxo species is proposed for the catalytic oxidation processes. (C) 2003 Published by Elsevier B.V. [References: 64]