Three pyrazole-3-carboxylic acid complexes as efficient solvent-free heterogeneous catalysts for CC bond formation

Three new pyrazole-3-carboxylic acid complexes, Cr(Hpca)3·2H2O (1), Ni2(pca)2(H2O)6·2H2O (2) and [Pb2(Hpca)4]n (3), have been synthesized and fully characterized. Notably, these novel complexes show efficient catalytic activities for Knoevenagel condensation (yield up to 97%) and the catalyst can be recycled without losing activity.170