Novel Copper(II) Complexes with Dipinodiazafluorene Ligands: Synthesis, Structure, Magnetic and Catalytic Properties

Abstract

The reactions of CuX2 (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX2L1]2 (X = Cl (1), Br (2), L1 = (1R,3R,8R,10R)-2,2,9,9-Tetramethyl-3,4,7,8,9,10-hexahydro-1H-1,3:8,10-dimethanocyclopenta [1,2-b:5,4-b’]diquinolin-12(2H)-one) and [(CuX2)2L2]n (X = Cl (3), Br (4), L2 = (1R,3R,8R,10R,1’R,3’R,8’R,10’R)-2,2,2’,2’,9,9,9’,9’-Octamethyl-1,1’,2,2’,3,3’,4,4’,7,7’,8,8’,9,9’,10,10’-hexadecahydro-1,3:1’,3’:8,10:8’,10’-tetramethano-12,12’-bi(cyclopenta [1,2-b:5,4-b’]diquinolinylidene). The complexes were characterized by IR and EPR spectroscopy, HR-ESI-MS and elemental analysis. The crystal structures of compounds 1, 2 and 4 were determined by X-ray diffraction (XRD) analysis. Complexes 1–2 have a monomeric structure, while complex 4 has a polymeric structure due to additional coordinating N,N sites in L2. All complexes contain a binuclear fragment {Cu2(μ-X)2×2} (X = Cl, Br) in their structures. Each copper atom has a distorted square-pyramidal coordination environment formed by two nitrogen atoms and three halogen atoms. The Cu-Nax distance is elongated compared to Cu-Neq. The EPR spectra of compounds 1–4 in CH3CN confirm their paramagnetic nature due to the d9 electronic configuration of the copper(II) ion. The magnetic properties of all compounds were studied by the method of static magnetic susceptibility. For complexes 1 and 2, the effective magnetic moments are µeff ≈ 1.87 and 1.83 µB (per each Cu2+ ion), respectively, in the temperature range 50–300 K, which are close to the theoretical spin value (1.73 µB). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu2(μ-X)2X2} (X = Cl, Br) dimers (J/kB ≈ 25 and 31 K for 1 and 2, respectively) or between dimers (θ′ ≈ 0.30 and 0.47 K for 1 and 2, respectively) were found at low temperatures. For compounds 3 and 4, the magnetic susceptibility is well described by the Curie–Weiss law in the temperature range 1.77–300 K with µeff ≈ 1.72 and 1.70 µB for 3 and 4, respectively, and weak antiferromagnetic interactions (θ ≈ −0.4 K for 3 and −0.65 K for 4). Complexes 1–4 exhibit high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The maximum yield of cyclohexane oxidation products reached 50% (complex 3). Based on the data on the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play a decisive role in the oxidation reaction. The initial products in reactions with alkanes are alkyl hydroperoxides.

Novel Copper(II) Complexes with BIAN Ligands: Synthesis, Structure and Catalytic Properties of the Oxidation of Isopropylbenzene

“…The Cu-Br bond lengths in 2 are slightly different (2.3517(6) and 2.3385(6)Å). Cu-Br distances are in the range of 2.354-2.391 Å in Cu(II) complexes with dipinodiazafluorenes [68].…”

“…Indeed, copper(II) complexes with various nitrogen-donor ligands are effective catalysts in the processes of activation (oxygenation) of C-H bonds in saturated hydrocarbons and other organic compounds [61][62][63][64][65][66][67]. For example, one of the latest works reported on the high catalytic activity of Cu(II) complexes with N-donor dipinodiazafluorenes in the oxidation of alkanes and alcohols by peroxides [68]. At the same time, there are no data in the literature on the reactivity of copper(II) complexes with BIAN-type ligands in radical chain oxidations.…”

Hybrid Silsesquioxane/Benzoate Cu7-Complexes: Synthesis, Unique Cage Structure, and Catalytic Activity

“…Copper complexes have systematically demonstrated high activity in these oxidation processes [ 80 , 81 , 82 , 83 , 84 , 85 ]. Recently, we also have found several copper complexes exhibited high efficiency in the oxidation of organic compounds with peroxides [ 86 , 87 , 88 , 89 , 90 , 91 , 92 ].…”

Magnetic, Optical, and Thermic Properties of SrLnCuSe3 (Ln = Dy, Ho, Er, Tm) Compounds

“…Magnetization measurements were performed using a Quantum Design MPMS-XL SQUID magnetometer in the temperature range 1.77-300 K at magnetic fields up to 10 kOe [27,28]. In order to determine the paramagnetic component of the molar magnetic susceptibility, χ p (T), the temperature-independent diamagnetic contribution, χ d , and a possible magnetization of ferromagnetic micro-impurities, χ FM (T), were evaluated and subtracted from the measured values of the total molar susceptibility χ = M/H.…”