Novel molybdenum-containing organic complexes based on 3,4-dihydroxy-3-cyclobutene-1,2-dione ("squaric acid") and some organic amines 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 with t-butylhydroperoxide (TBHP) and showed high activities and selectivities, comparable to those of the commercially available molydenyl acetylacetonate (MoO2(acac)(2)). (C) 2002 Elsevier Science B.V. All rights reserved.