[en] The Schiff-base condensation of salicylaldehyde and 4-aminobutanehydrazide hydrochloride leads to the hydrazone-based ligand H${}_2$salhyab containing an amino side chain. The reaction of H${}_2$salhyab ⋅ HCl with bis(acetylacetonato)dioxidomolybdenum leads to the formation of [MoO${}_2$(salhycab)(MeOH)] (H${}_2$salhycab=2-((pyrrolidine-2-ylidenehydrazineylidene)methyl)phenol), whereby the amino side chain reacted with the hydrazide carbonyl group to form a cyclic amidine with a pyrrolidine ring leading a new type of tridentate hydrazone ligand with [NNO] donor set. X-ray crystallography revealed the additional coordination of a methanol molecule at the molybdenum(VI) center which leads to the formation of hydrogen-bonded dimers of the neutral complex in the crystal structure. The complex [MoO${}_2$(salhycab)(MeOH)] was found to be an efficient catalyst for the peroxidic oxidation of phenyl methyl sulfide. (© 2021 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH)