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

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 mcccpz(2-) 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-η(2),η(2)-dcmpz(-) ligands and two μ-η(1),η(1)-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-η(1),η(2)-mcccpz(2-) 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.