New sterically encumbered arylimido hexamolybdates for organic oxidation reactions

Abstract

Facile synthesis of mono- and di-functionalised arylimido hexamolybdates, (ⁿBu₄N)₂[Mo₆O₁₈(L1)] (1), (ⁿBu₄N)₂[Mo₆O₁₇(L1)₂] (2) and (ⁿBu₄N)₂[Mo₆O₁₈(L2)] (3) (L1 = 4-bromo-2,6-diisopropylaniline, L2 = 2,2′,6,6′-tetraisopropylbenzidine), has been achieved through the reaction of parent (ⁿBu₄N)₂[Mo₆O₁₉] (4) with a series of aniline derivatives. The arylimido derivatives 1–3 have been characterised by both analytical and spectroscopic studies (¹H NMR, IR, UV-Vis and mass spectral studies), apart from structural elucidation of all the three compounds by single crystal X-ray diffraction studies. Steric hindrance at the ortho-positions of the arylamine seems to strengthen and effectively protect the newly formed MoN bonds. The surface modification of the hexamolybdate by aryl amines results in the transformation of otherwise inactive parent compound 4 into useful catalysts 1–3, which effectively catalyse the oxidation of cyclohexene to cyclohexene epoxide and benzyl alcohol to benzaldehyde and benzoic acid.