This article describes the selective cleavage of coordination bonds by mechanochemical methods and the further application of the thus obtained precursors for a facile preparation of new coordination compounds. In the class of dioxomolybdenum(VI) coordination compounds, [MoO2L(ROH)], where L stands for a tridentate dianionic ONO ligand and ROH represents different alcohol molecules, mechanical treatment induces an exclusive cleavage of the molybdenum–alcohol bond, which can thus be considered as a mechanosensitive bond. Alcohol removal can also be accomplished by heating. Both grinding and heating resulted in highly reactive, coordinatively unsaturated compounds, an orange amorphous pentacoordinated [MoO2L] (I) and the brown polymeric [MoO2L]n ((I)nnn), respectively. Even though both I and (I)nn are stable at room temperature, they can be interconverted using only solvent-free techniques, a conversion followed by a colour change of the sample. The tendency of such unsaturated complexes to complete their coordination spheres was exploited for the efficient solution and solvent-free syntheses of octahedral molybdenum complexes with selected O- and N-donating ligands. Both approaches herein used, solution and solvent-free, have proved to be superior under specific conditions and their respective advantages and weaknesses are discussed.
