Several molybdenum-containing organic complexes based on 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid) have been synthesized and characterized by infrared (IR) spectroscopy, thermogravimetric (TGA) and elemental analyses. The resulting molybdenum complexes were introduced as catalysts in the epoxidation of cyclohexene, 1-octene, 2,4,4-trimethyl-I-pentene, 1,5-cyclooctadiene and 1,5,9-cyclododecatriene with t-butylhydroperoxide (TBHP). The catalytic activities of these complexes for the various alkenes employed as reactants were compared and their versatility as catalysts for the epoxidation reaction was estimated. Thus the most appropriate molybdenum-containing complex was selected, for which the catalytic activity and selectivity were comparable to those of the commercially available molybdenyl acetylacetonate (MoO2(acac)(2)). (c) 2004 Elsevier B.V. All rights reserved.