Molybdenum complexes with tridentate NS2 ligands. Synthesis, crystal structures and spectroscopic properties

Abstract

Reaction of the new tridentate NS₂ ligands 2-HSC₆H₄C(Me)NNHC(S)SCH₂Ph (H₂L¹), 2-HSC₆H₄C(Me) NNHC(S)NHCPh₃ (H₂L²), 2-HSC₆H₄CHNNHC(S)NHCPh₃ (H₂L³) and 1-Ph-3-Me-5-HS-C₃N₂-CHNNC(SH)NHCPh₃ (H₂L⁴) with dioxomolybdenum(VI) precursors yielded mononuclear molybdenum(VI) complexes [MoO₂(L¹)(pic)] 1 (pic = 4-methylpyridine), [MoO₂L²(MeOH)]·2.25 MeOH 2 and the dinuclear molybdenum(V) complexes [Mo₂O₃L³₂]·3CH₂Cl₂ 3 and [Mo₂O₃L⁴₂] 4. The molecular structures of 1–3 were determined by single-crystal X-ray analysis. Complexes 1 and 2 each consist of a central cis-MoO₂ unit with a mer co-ordinating tridentate dianionic ligand and one neutral donor molecule completing the octahedral environment of molybdenum(VI). Complex 3 exhibits an anti-Mo₂O₃ group co-ordinated by two mer chelating ligands. The symmetry-related molybdenum(V) centres are in a square pyramidal environment. Infrared, NMR and MS studies evidenced a comparable structure for 4. The reduction of the dioxomolybdenum(VI) compounds 1 and 2, achieved by addition of phosphines like PPh₃, also leads to dinuclear µ-oxo-bridged complexes. The reverse oxidations of the oxomolybdenum(V) complexes are restricted by the nature of the ligand and the oxidizing agents.