Syntheses and structures of copper complexes of 3-(6-(1H-pyrazol-1-yl)pyridin-2-yl)pyrazol-1-ide and their excellent performance in the syntheses of nitriles and aldehydes.

Reactions of a pincer ligand 2-(1H-pyrazol-1-yl)-6-(1H-pyrazol-3-yl)pyridine (pzpypzH) with Cu(NO3)2, Cu(ClO4)2, CuSO4, CuCl2 or CuI produced three dinuclear Cu(ii) complexes [{Cu(NO3)}(μ-pzpypz)]2 (1), [{Cu(ClO4)}(μ-pzpypz)]2 (2), [Cu2(μ-SO4)(μ-pzpypz)2]·2MeOH (3·2MeOH), one mononuclear Cu(ii) complex [CuCl2(pzpypzH)] (4) and one trinuclear Cu(i)/Cu(ii) complex [(ICu)(μ-I)2Cu2(μ-pzpypz)2] (5), respectively. Treatment of 4 with two equiv. of AgNO3 in DMF also gave rise to 1. Complexes 1-5 were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Complex 1 or 2 has a dimeric structure in which two {Cu(X)} (X = NO3, ClO4) fragments are interconnected by two μ-pzpypz(-) ligands. 3 also adopts a dimeric structure in which two Cu(ii) centers are interconnected by a pair of μ-pzpypz(-) ligands and one μ-SO4(2-) ion. The Cu(ii) center in 4 is five-coordinated by three N atoms of the pzpypzH ligand and two Cl atoms. In 5, two Cu(ii) centers are bridged by two μ-pzpypz(-) ligands and one CuI3(2-) unit, forming a unique trinuclear structure. Complexes 1-5 displayed high catalytic activity toward the ammoxidation of alcohols to nitriles and the aerobic oxidation of alcohols to aldehydes in H2O. The nitrile or aldehyde products could be readily separated from the catalytic system by extraction and the residual aqueous solution containing 1 retained good activity for several cycles.