Ligand oxidation in N4 tetradentate Schiff base complexes catalyzed by copper(II) hexafluoroacetylacetonate dihydrate: reaction details and structures

Abstract

dibenzo[e,n][1,4,8,12]tetraazacyclopentaadecine [H 2 (3,2 mac)], i.e. M(2,2 mac) and M(3,2 mac), are oxidized in chloroform at room temperature under atmospheric conditions in the presence of Cu(hfa) 2 ؒ(H 2 O) 2 to the oxamide (N-CH 2 -CH 2 -N-to N-CO-CO-N-). If Cu(hfa) 2 ؒ(H 2 O) 2 is present in stoichiometric amounts the isolated product of the reaction is the dinuclear complex, M(3,2 oxomac)Cu(hfa) 2 . The dinuclear complex can also be prepared by direct reaction of M(3,2 oxomac) (prepared by another method) with Cu(hfa) 2 ؒ(H 2 O) 2 . The dinucleation reaction of M(3,2 oxomac) with M(hfa) 2 is quite general but the ligand oxidation of M(3,2 mac) is specific for Cu(hfa) 2 ؒ(H 2 O) 2 . Reaction of Cu(3,2 mac) with Hhfa or H 2 (3,2 mac) with Cu(hfa) 2 ؒ(H 2 O) 2 results not in oxidation of the macrocycle but in protonation to give Cu{H 2 (3,2 mac)}(hfa) 2 . The oxidation of Cu(3,2 mac) in an 18 O 2 atmosphere does not result in a significant incorporation of 18 O. However, nearly quantitative incorporation of 18 O is achieved when the reaction is carried out under air in the presence of H 2 18 O. The structures of Cu(3,2 mac), Cu(3,2 oxomac), Cu(3,2 oxomac) Cu(hfa) 2 and Cu{H 2 (3,2 mac)}(hfa) 2 are reported.

Revisiting the Synthesis and Nucleophilic Reactivity of an Anionic Copper Superoxide Complex

“…The complex is a rare example of a stable, structurally characterized copper­(II) enolate. Long postulated as key intermediates in aldol and related reactions, − copper enolates typically contain copper­(I) and relatively few have been isolated, most likely because of their high reactivity. − Also relevant to this work are the coupling of acetaldehyde by an (NHC)­copper­(I) hydroxide complex, and the recently reported catalytic aldol coupling of benzaldehydes and acetone by a neutral copper­(II) superoxide complex . Exposure of [NBu 4 ]­[LCu­(OCC­(Me)­Ph)] to benzaldehyde or propionaldehyde did not yield C–C-coupled products [gas chromatography (GC)/mass spectrometry (MS)], a result that we presume derives from the steric hindrance of its supporting ligand.…”

Synthesis and characterization of a novel Gd(III)–Cu(II) dinuclear adduct

“…[4] The reactions described in this work are part of an effort to expand the type of bridging ligand used to link Gd(III) and Cu (II). In previous work we demonstrated the effectiveness of Cu(2,2-oxomac) [5] and Cu(3,2-oxomac) [6] (see figure 1) as dinucleating ligands by the preparation of adducts between these complexes and M(hfa) 2 (M = Cu or Ni) in which two oxamide oxygen atoms on adjacent carbon atoms of the macrocycles serve as linkages between Cu(II) and M (II). The affinity of gadolinium for oxygen donors suggested the reaction of Gd(hfa) 3 with the copper macrocycles to yield similar dinuclear adducts with the desired Gd(III)-Cu(II) linkage.…”

“…The same effect is observed for the dinuclear complex formed by the reaction of Cu(3,2-oxomac) with Cu(hfa) 2 . [6] For Cu(2,2-oxomac)Gd(hfa) 3 , however, a gross distortion is observed. The angle between the N 4 and the "oxamide" planes is increased to 13.4°, effectively "bending" the oxamide bridge out of the N 4 plane.…”

Oxidative dehydrogenation of a new tetra-amine N4-donor macrocycle tunes the nickel(ii) spin state from high spin to low spin

“…The mechanism of such oxidative dehydrogenation is not fully understood; however when it occurs in the presence of a metal ion the higher oxidation states of the metal ion may be involved. 9 Sodium borohydride reduction of HL Et gave the amine macrocycle HL aa as an off-white solid in 93% yield (Scheme 1). Complexation of HL aa with Ni(BF 4 ) 2 •6H 2 O and one equivalent of base (Et 3 N) in air, in a 1 : 2 mixture of dichloromethane and methanol, followed by diethyl ether vapour diffusion into the dark green solution, gave the nickel(II) complex of the deprotonated singly oxidatively dehydrogenated macrocycle, 1), as a dark red-black solid in 75% yield.…”