Mononuclear and polynuclear molybdenum(vi) complexes with the interchangeable coordination site

Mononuclear and polynuclear dioxomolybdenum(vi) complexes with the tridentate Schiff base ligand have been prepared by the reaction of [MoO2(acac)2] with N-4-methoxysalicylidene-2-amino-3-hydroxypyridine (H2L, 1) in methanol, ethanol or acetonitrile. All the prepared complexes of the general formulae [MoO2L(ROH)], [MoO2LD], {[MoO2L]2D′}·D′ and [MoO2L]n consist of the cis-MoO22+ core coordinated by dianionic form of the Schiff-base ligand, L2−, in the tridentate manner through two deprotonated hydroxyl groups and one imino nitrogen atom. The octahedral coordination around the molybdenum atom is completed by neutral monodentate O- or N-donor ligands (ROH: R = CH3 or C2H5; D: py = pyridine; γ-pic = γ-picoline; imid = imidazole; bipy = 4,4′-bipyridine). The combination of molybdenum coordination preferences and the ligand donor capabilities have led to the complexes with the labile sixth coordination site, which could be readily exchanged with the competitive ligand by tuning reaction conditions (solvent, atmosphere). All the complexes have been studied by means of elemental analysis, IR spectroscopy and thermogravimetric analysis. The crystal structures of ligand 1, four mononuclear [MoO2LD] or [MoO2L(ROH)] and one dinuclear {[MoO2L]2D′}·D′ complex [ROH = methanol (2), D = pyridine (5), γ-picoline (6), imidazole (7), D′ = 4, 4-bipyridine (8)] have been determined by the single crystal X-ray structure analysis.

The mononuclear and polynuclear dioxomolybdenum(vi) complexes of the general formula [MoO2LROH], [MoO2LD], {[MoO2L]2D′}·D′ and [MoO2L]n with N-4-methoxysalicylidene-2-amino-3-hydroxypyridine as the tridentate ligand are described. The octahedral coordination around molybdenum atom is completed by the weekly bonded monodentate O- or N-donor molecules. The molybdenum(vi) cation showed selectivity for one type of neutral ligands, favoring coordination of all N-donor over O-donor ligand. The studied molybdenum(vi) complexes with CH3OH and C2H5OH as O-donors could be convenient for application in the catalysis.Figure optionsDownload as PowerPoint slide