A Bis(μ-oxo)dicopper(III) Complex with Aromatic Nitrogen Donors:  Structural Characterization and Reversible Conversion between Copper(I) and Bis(μ-oxo)dicopper(III) Species

Abstract

Transformation of (µ-η 2 :η 2 -peroxo)dicopper(II) complexes bearing sterically bulky tridentate N,N′,N′′-trisubstituted tacn 2 to square pyramidal bis(µ-oxo)dicopper(III) complexes has been reported by Tolman et al. 3 In certain instances, they have observed a monooxygenase activity of the bis(µ-oxo)dicopper(III) complexes for the coordinated ligand as substrate. A different type of square planar bis(µ-oxo)dicopper(III) complexes having peralkylated-1,2-cyclohexanediamine ligands have been also prepared by Stack et al. 4 Very recently, partial formation of a bis(µ-oxo)dicopper(III) complex with a tridentate ligand containing two pyridyl sidearms 5 and a bis(µ-oxo)dicopper(III) complex with a bidentate ligand containing a pyridyl group have been reported. 6 However, there is no crystallographically characterized bis(µ-oxo)dicopper(III) complex having aromatic nitrogen donors. Thus, it is important to explore how the nature of the donor atoms and the stereochemistry of supporting ligands influence the formation, structure, and reactivity of bis(µ-oxo)dicopper(III) complexes.Karlin et al. have demonstrated that a copper(I) complex having a tetradentate tripodal tpa ligand, [Cu(tpa)(NCCH 3 )] + , reacts with O 2 to form a trans-(µ-1,2-peroxo)dicopper(II) complex ([Cu 2 (O 2 )-(tpa) 2 ] 2+ ) in a trigonal bipyramidal structure (λ max ( , M -1 cm -1 ) ) ∼440 nm (4000), 525 nm (11500), and ∼590 nm (7600)). 7 Previously we found that [Cu(Me-tpa)] + in acetone at -70 °C generates a trans-(µ-1,2-peroxo)dicopper(II) species, whereas the reaction of [Cu(Me 2 -tpa)] + (1a) with O 2 (Cu:O 2 ) 2:1) in acetone at -70 °C does not form a trans-(µ-1,2-peroxo)dicopper(II) species, but produces a brown species (1b, λ max ( , M -1 cm -1 ) ) 378 nm ( ∼22 000, 0.1 mM), 494 nm (330, 10 mM)). 8 Thus,

A Mononuclear Alkylperoxocopper(II) Complex as a Reaction Intermediate in the Oxidation of the Methyl Group of the Supporting Ligand

“…+ (1), [2] as confirmed by the ESI-TOF mass spectrum. Compound 1 then reacts with further H 2 O 2 to give the selective formation of 4 (Supporting Information).…”

“…[2] We also found that reaction of the bis(mhydroxo)dinickel(II) complex [Ni 2 (Me 2 -tpa) 2 (5) together with N-dealkylation of the Me 2 -tpa ligand. [3,4] A similar bis(m-alkylperoxo)dicopper(II) complex (6) has been reported by Tolman and co-workers in the reaction of the (m-h 2 :…”

“…[5] Herein we report the formation of the novel mononuclear alkylperoxocopper(II) complex [Cu(Me-tpa-CH 2 [2,6] at À40 8C resulted in a rapid color change from pale blue to green. The ESI-TOF mass spectrum of the green solution shows a prominent signal at m/z 412.1, which can be assigned to the mononuclear complex 4 (see Supporting Information).…”

“…[1] Previously, we have found that the reaction of a copper(I) complex bearing the tetradentate tripodal ligand Me 2 -tpa (bis(6-methyl-2-pyridylmethyl) (2-pyridylmethyl) (2), which undergoes regioselective N-dealkylation of the Me 2 -tpa ligand by H-atom abstraction from a methylene group upon decomposition (Scheme 1). [2] We also found that reaction of the bis(mhydroxo)dinickel(II) complex [Ni 2 (Me 2 -tpa) 2 (5) together with N-dealkylation of the Me 2 -tpa ligand.…”

A Mononuclear Alkylperoxocopper(II) Complex as a Reaction Intermediate in the Oxidation of the Methyl Group of the Supporting Ligand

“…[9] As mentioned already, the selective oxidation of the methyl group of Me 2 -tpa starts with the reaction of 1 with H 2 O 2 . To clarify the formation pathway of 4, we investigated the source of the oxygen in Me-tpa-CH 2 situation is in marked contrast to the formation of 5 and 6, where exogenous O 2 is the sole oxygen source. [3][4][5] A possible reactive species derived from the Me 2 -tpa ligand and some modified species derived from H 2 O 2 and O 2 is the ligand radical Me-tpa-CH 2 C, which has also been proposed for the formation of 5 and 6.…”