Polynuclear copper(ii) pyrazolate complexes: temperature-dependent protonolysis reactions, crystal structures and high catalytic activity toward the condensation of nitriles with 2-aminoalcohol?

Dalton Transactions Pub Date: 2013-09-10 DOI: 10.1039/C3DT51970H

Abstract

Reaction of Cu(OAc)2·H2O and 1H-pyrazole-3,5-dicarboxylic acid dimethyl ester (Hdcmpz) in MeOH at room temperature afforded one tetranuclear Cu(II)/pyrazolate complex [{Cu2(μ-OAc)2}2(μ-dcmpz)2(μ-OAc)2] (1) in 89% yield. The similar reaction in refluxing MeOH produced a hexanuclear metallamacrocyclic Cu(II)/pyrazolate complex [{Cu(μ-dcmpz)}2(μ-OMe)2]3 (2) in 85% yield. Treatment of the same components under solvothermal conditions resulted in the formation of another tetranuclear Cu(II)/pyrazolate/carboxylate complex [{Cu(MeOH)}4(μ-mcccpz)4] (3, Hmcccpz = 5(3)-(methoxycarbonyl)-1H-pyrazole-3(5)-carboxylic acid) in 30% yield. The mcccpz2? ion in 3 was in situ generated via the hydrolysis of one of two esters on dcmpz ligand. Complexes 1–3 were characterized by elemental analysis, IR and single-crystal X-ray diffraction. An X-ray analysis revealed that 1 contains two {Cu(μ-OAc)}2 fragments that are interconnected by two μ-η2,η2-dcmpz? ligands and two μ-η1,η1-OAc? ions, forming a unique tetrameric structure. Complex 2 is composed of three {Cu(μ-dcmpz)}2 fragments linked by three pairs of μ-OMe? anions, forming a metallamacrocyclic crown structure. 3 consists of four {Cu(MeOH)} fragments linked by two pairs of μ-η1,η2-mcccpz2? ligands, forming a tetrameric [2 × 2] grid-like structure. Complexes 1–3 displayed high catalytic activity toward the condensation of nitriles with 2-aminoalcohol under solvent-free conditions to produce various 2-oxazolines.

Graphical abstract: Polynuclear copper(ii) pyrazolate complexes: temperature-dependent protonolysis reactions, crystal structures and high catalytic activity toward the condensation of nitriles with 2-aminoalcohol
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