Complexation of a rigid multi-pyridine ligand bis(2-pyridyl)-1,8-naphthyridine (bpnp) with [Cu(2)(TFA)(4)] (TFA = trifluoroacetate) resulted in the formation of a dinuclear copper(II) complex, namely [Cu(2)(bpnp)(μ-OH)(TFA)(3)] (1). This complex has been characterized by X-ray crystallographic, spectroscopic and elemental analyses. Complex 1 is an efficient catalyst for the oxidative coupling of various 2,6-disubstituted phenols with molecular oxygen. Yields and selectivity depend on the reaction conditions employed, the best results being obtained in isopropanol or dioxane at 90 °C with yields of >99%. Mechanistic pathway of the catalysis is discussed.
Ligands (L(a-c)) based on 2,7-bis(3,5-di-R-pyrazol-1-yl)-1,8-naphthyridine (a, R = H; b, R = CH(3); c, R = Ph) were prepared for the construction of a series of dinickel complexes. Treatment of L(x) with NiCl(2) in an anhydrous methanol/THF solution resulted in the formation of dinuclear complexes [(L(x))(μ-Cl)(2)Ni(2)Cl(2)(CH(3)OH)(2)] (3, x = a; 4, x = b; 5, x = c). These new complexes were characterized by elemental analysis, IR and UV-Vis spectroscopic techniques. The structures of complexes 3 and 4 were further confirmed by X-ray diffraction studies. Interestingly, crystals of 4 were obtained as a co-crystallization of 4 and the methanol substituted species [{(L(b))(μ-Cl)(2)Ni(2)Cl(CH(3)OH)(3)}Cl] (4'). These dinickel complexes have been tested in the catalytic homo-coupling of terminal alkynes with the use O(2) as the oxidant, showing excellent activities. A clear improvement on the catalytic activity of these complexes is observed as compared to the mono-nuclear species.
The direct reaction between 2,7-bis(2-pyridinyl)-1,8-naphthyridine (bpnp) and Pd(CH 3 COO) 2 in CF 3 COOH yields the new dinuclear palladium(II) complex [Pd 2 (bpnp)(μ-OH)(CF 3 CO 2 ) 2 ](CF 3 CO 2 ) (1). Similarly, substitution of Pd(CH 3 CN) 4 (BF 4 ) 2 with bpnp in DMF gives [Pd 2 (bpnp)(μ-OH)(DMF) 2 ](BF 4 ) 3 (2). Treatment of 1 or 2 with Cl − readily provide the chloro-substituted species [Pd(bpnp)(μ-OH)(Cl) 2 ] + . All complexes were characterized by spectroscopic methods, and the structure of 2 was further confirmed by X-ray crystallography. Complex 1 is an efficient catalyst for the reduction of aromatic nitro compounds leading to the corresponding aniline derivatives under atmospheric pressure of hydrogen at 50 °C. The mechanistic pathway of the catalysis is investigated. From the reaction pathway, it is suggested that a facile condensation of nitroso and hydroxylamine intermediates is enabled by the dipalladium system and the desired transformation proceeds smoothly under mild reaction conditions to yield the reduced product.
Diamination of phenylene dihalides with aqueous ammonia to give the corresponding phenylenediamines can be achieved by using a dicopper complex [Cu(2)(bpnp)(OH)(CF(3)COO)(3)] (1) (bpnp = 2,7-bis(pyridine-2-yl)-l,8-naphthyridine) as the catalyst in the presence of Bu(4)NBr and Cs(2)CO(3) in high yields. In addition, 1,3,5-tribromobenzene was converted into benzenetriamine quantitatively under the same conditions. This method offers a new opportunity, particularly simplifying steps and increasing yields, for the preparation of aryl diamines.
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