Self-assembled tetranuclear molybdenum(vi) complexes with hydrazonato ligands, [MoO2L]4, were tested as (pre)catalysts for cyclooctene and cyclohexene epoxidation without extra organic solvent added. Special attention was addressed to the comparison of oxidizing agents, TBHP in water vs. TBHP in decane. The idea was to test the greenness of the complete process. Density Functional Theory calculations were used to support and explain experimental catalytic result for tetranuclear self-assembled systems.