Synthesis and characterization of binuclear [ONXO]-type amine-bis(phenolate) copper(II) complexes

Magnetostructural Properties of Some Doubly-Bridged Phenoxido Copper(II) Complexes

Three new tripod tetradentate phenolate-amines (H2L1, H2L4 and H2L9), together with seven more already related published ligands, were synthesized, and characterized. With these ligands, two new dinuclear doubly-bridged-phenoxido copper(II) complexes (3, 4), and six more complexes (1, 2, 5–8), a new trinuclear complex (9) with an alternative doubly-bridged-phenoxido and –methoxido, as well as the 1D polymer (10) were synthesized, and their molecular structures were characterized by spectroscopic methods and X-ray single crystal crystallography. The Cu(II) centers in these complexes exhibit distorted square-pyramidal arrangement in 1–4, mixed square pyramidal and square planar in 5, 6, and 9, and distorted octahedral (5+1) arrangements in 7 and 8. The temperature dependence magnetic susceptibility study over the temperature range 2–300 K revealed moderate–relatively strong antiferromagnetic coupling (AF) (|J| = 289–145 cm−1) in complexes 1–6, weak-moderate AF (|J| = 59 cm−1) in the trinuclear complex 9, but weak AF interactions (|J| = 3.6 & 4.6 cm−1) were obtained in 7 and 8. No correlation was found between the exchange coupling J and the geometrical structural parameters of the four-membered Cu2O2 rings.

Gallium (III) Complexes Based on Aminobisphenolate Ligands: Extremely High Active ROP-Initiators from Well-Known and Easily Accessible Compounds

We report herein the synthesis and full characterizations of the first examples of gallium complexes based on "privileged" aminobisphenolate ligands which are easily available. These complexes turned out to be extremely active in the ring-opening polymerization of ε-caprolactone even at room temperature and highly active in the ROP of L-lactide. The combination of factors such as the easy availability of these compounds and the supposedly low toxicity, together with the extremely high activity in ROP, allows us to consider these compounds as suitable for use on an industrial scale for the synthesis of biodegradable polymers for biomedical applications.

Crossover from Antiferromagnetic to Ferromagnetic Exchange Coupling in a New Family of Bis-(μ-phenoxido)dicopper(II) Complexes: A Comprehensive Magneto-Structural Correlation by Experimental and Theoretical Study

Five neutral bis(μ-phenoxido)dicopper(II) complexes, [Cu₂(L^Me,Me,Me)₂] (1), [Cu₂(L^Me,Me,Et)₂]·CH₂Cl₂ (2), [Cu₂(L ^{i-Pr,i-Pr,i-Pr})₂]·2H₂O (3), [Cu₂(L ^t-Bu,Me,i-Pr)₂] (4), and [Cu₂(L ^{t-Bu,t-Bu,i-Pr})₂]·H₂O (5) have been synthesized and characterized by single-crystal X-ray diffraction analyses, magnetic studies, and density functional theory (DFT) calculations, in which the ligands [H₂L^Me,Me,Me = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N',N'-dimethylethylene-1,2-diamine, H₂L^Me,Me,Et = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N',N'-dimethylethylene-1,2-diamine, H₂L ^{i-Pr,i-Pr,i-Pr} = N,N-bis(2-hydroxy-3,5-diisopropylbenzyl)-N',N'-diisopropylethylene-1,2-diamine, H₂L ^t-Bu,Me,i-Pr = N,N-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-N',N'-diisopropylethylene-1,2-diamine, and H₂L ^{t-Bu,t-Bu,i-Pr} = N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N',N'-diisopropylethylene-1,2-diamine] contain the same [O,N,N,O]-donor atoms combination but differ in substituents at phenol rings and at an amino nitrogen atom. The effect of these remote substituents on the nature of exchange coupling interactions (ferromagnetic vs antiferromagnetic) between the copper(II) ions has been investigated. The average Cu-O-Cu angle, Cu-O-Cu-O torsion angle, and Cu···Cu separation in 1-5 are varied systematically by these remote ligand substituents in the range 98.6-83.3°, 26.0-46.5°, and 2.982-2.633 Å, respectively. As a result, the intramolecular spin-spin coupling in these complexes are changing gradually from a strong antiferromagnetic (J = -395 cm^-1, where Ĥ = -JŜ ₁ Ŝ ₂) to a moderate ferromagnetic (J = +53.2 cm^-1) regime. The crossover angle at which the magnetic interaction changes from antiferromagnetic to ferromagnetic (J = 0) is determined to be ca. 87° for this series of dicopper(II) complexes. DFT calculations support the experimentally determined crossover angle and disclose various magneto-structural correlations in the series 1-5.

A Binuclear Copper(II) Complex with Diphenoxido-bridges: Synthesis, Characterisation, Crystal Structure and Predicting the Magnetic Coupling Constant

Reaction of copper(II) acetate with 1,1′-[(2,2-dimethylpropane-1,3-diyl)bis(nitrilomethylidyne)]-di-2-naphthol (H2L) gave the diphenoxido-bridged binuclear copper(II) complex [Cu2L2]. Its crystal structure shows a slightly distorted square pyramidal geometry around both of the copper(II) ions. In the symmetric Cu2O2 core, each of the phenoxido bridges occupies an equatorial position around one of the copper(II) centres. A broken symmetry (BS) computation based on density functional theory (DFT) evaluated the magnetic interaction in the complex using the (U)B3LYP level of theory in association with the basis sets LANL2DZ for the copper atoms and 6-31G** for the other atoms. The calculations showed ferromagnetic interaction between the two magnetic copper(II) centres with a magnetic coupling constant (J) of 1.16 cm−1.

Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity

A diphenoxido-bridged dinuclear copper(II) complex, [Cu(2)L(2)(ClO(4))(2)] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu(2)L(2)(OH)]ClO(4) (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu···Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k(cat) = 233.4 h(-1)) than compound 1 (k(cat) = 93.6 h(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.