Complexes of heteroscorpionate trispyrazolylborate ligands. Part XIII: Molybdenum complexes of hydrobis(5-methyl-3-phenylpyrazolyl)(3-methyl-5-phenylpyrazolyl)borate, hydrotris(3-(2-thienyl)-5-methylpyrazolyl)borate and tetranuclear molybdenum(V) complex

The molybdenum complexes of hydrotrispyrazolylborate ligands were studied. Hydrotris(5-methyl-3-(2-thienyl)pyrazol-1-yl)borate (TpTh,Me) was coordinated in η3 mode to molybdenum in [Et4N][TpTh,MeMo(CO)3] and TpTh,MeMo(CO)3(η3-allyl) complexes in solid state as was determined crystallographically. The heteroscorpionate hydrobis(5-methyl-3-phenylpyrazol-1-yl)(3-methyl-5-phenylpyrazol-1-yl)borate (Tp″) complexes: [Et4N][Tp″Mo(CO)3] and Tp″Mo(CO)3(η3-allyl) were synthesized and their dynamic behavior and reactivity was studied and compared with standard [Et4N][T∗Mo(CO)3] and Tp∗Mo(CO)3(η3-allyl) pair. All studied tricarbonyl complexes are reversibly oxidized at very low potentials, whereas the allyl compounds require much higher potentials for a generally irreversible oxidation to proceed. The oxidation products of Mo(0) and Mo(II) complexes with iodine and/or TBHP were characterized spectroscopically. The product of oxidation of Tp∗Mo(CO)3I with oxygen was tetranuclear linear molybdenum(V) complex with terminal metal ions coordinated to Tp∗ ligands and inner molybdenum(V) ions surrounded exclusively by oxygen donors.

The hydrotris(3-(2-thienyl)-5-methylpyrazolyl)borate (Tp′) coordinates to molybdenum in κ3 fashion in [Et4N] [Tp′Mo(CO)3] and Tp′Mo(CO)3(allyl) complexes. The aerial oxidation of Tp∗Mo(CO)2(I) led to the unique tetranuclear linear complex of molybdenum(V) with two Tp∗ terminal ligands and terminal oxo as well as bridging oxo donors. The molybdenum(0) and (II) complexes were also synthesized and studied by the 1H NMR spectroscopy and electrochemical measurements.Figure optionsDownload as PowerPoint slide