Toluene and Ethylbenzene Aliphatic C-H Bond Oxidations Initiated by a Dicopper(II)-μ-1,2-Peroxo Complex

摘要

With an anisole-containing polypyridylamine potential tetradentate ligand ~0L, a μ-1,2-peroxo-dicopper(II) complex [{°LCu~Ⅱ}_2(O_2~(2-))]~(2+) forms from the reaction of the mononuclear compound [Cu~I(~oL)(MeCN)]B(C_6F_5)_4 (~oLCu~I) with O_2 in noncoordinating solvents at -80 ℃. Thermal decay of this peroxo complex in the presence of toluene or ethylbenzene leads to rarely seen C-H activation chemistry; benzaldehyde and acetophenone/1-phenylethanol mixtures, respectively, are formed. Experiments with ~(18)O_2 confirm that the oxygen source in the products is molecular O_2 and deuterium labeling experiments indicate k_H/k_D = 7.5 ± 1 for the toluene oxygenation. The O_2-reaction of [Cu~I(~(Bz)L)(CH_3CN)]~+ (~(Bz)LCu~I) leads to a dicopper(Ⅲ)-bis-μ-oxo species [{~(Bz)LCu~Ⅲ}_2(μ-O~2)_2]~(2+) at -80 ℃, and from such solutions, very similar toluene oxygenation chemistry occurs. Ligand ~(Bz)L is a tridentate chelate, possessing the same moiety found in ~oL, but without the anisole O-atom donor. In these contexts, the nature of the oxidant species in or derived from [{~oLCu~Ⅱ}_2(O_2~(2-))]~(2+) is discussed and likely mechanisms of reaction initiated by toluene H-atom abstraction chemistry are detailed. To confirm the structural formulations of the dioxygen-adducts, UV-vis and resonance Raman spectroscopic studies have been carried out and these results are reported and compared to previously described systems including [{Cu~Ⅱ(~(Py)L)}_2(O_2)]~(2+) (~(Py)L = TMPA = tris(2-methylpy-ridyl)amine). Using (L)Cu~I, CO-binding properties (i.e., v_(C-O) values) along with electrochemical property comparisons, the relative donor abilities of ~OL, ~(Bz)L, and ~(Py)L are assessed.