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

The reactions of CuX ₂ (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX ₂ L ₁ ] ₂ (X = Cl ( 1 ), Br ( 2 ), L ₁ = (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 [(CuX ₂ ) ₂ L ₂ ]n (X = Cl ( 3 ), Br ( 4 ), L ₂ = (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 L ₂ . All complexes contain a binuclear fragment {Cu ₂ (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-N _ax distance is elongated compared to Cu-N _eq . The EPR spectra of compounds 1 - 4 in CH ₃ CN confirm their paramagnetic nature due to the d ⁹ 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 µ _eff ≈ 1.87 and 1.83 µ _B (per each Cu ²⁺ ion), respectively, in the temperature range 50-300 K, which are close to the theoretical spin value (1.73 µ _B ). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu ₂ (μ-X) ₂ X ₂ } (X = Cl, Br) dimers ( J / k _B ≈ 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 µ _eff ≈ 1.72 and 1.70 µ _B 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.