Intercalation of the oxo-transfer molybdenum(VI) complex [MoO2{O2CC(S) Ph2}2]2– into a zinc(II)–aluminium(III) layered double hydroxide host. Catalysis of the air oxidalton of thiols

Abstract

The intercalation of bis(2.2-diphenyl-2-sulfidoacetato)dioxomolybdate(VI)[MoO₂{O₂CC(S)Ph₂}₂]^2–1 into an hydrotalcite-like zinc(II)-aluminium(III) layered double hydroxide by anion exchange yielded [Zn_3–xAl_x(OH)₆]^x+[{MoO₂[O₂CC(S)Ph₂]₂}y//₂(NO₃)_x–y]^x–·H₂O (x= 0.75). Data from powder X-ray diffraction, IR and diffuse reflectance spectroscopy and thermogravimetnc analysis confirmed intercalation within a 13 Å-height gallery, indicating that the molybdenum anion probably lies with its cis-dioxomolybdenum(VI) plane parallel to the hydroxide layers. Complex 1, immobilized in the layered double hydroxide, operates as an effective heterogeneous catalyst for the oxiDalton of thiols (PhSH) by either dioxygen or air as evaluated by gas chromatography. The active oxidant is [MoO₂{O₂CC(S)Ph₂}₂]^2–, while a molybdenum(VI) species acts as the reductant by interaction with dioxygen to regenerate the molybdenum(VI) oxidant This constitutes the first reported heterogeneous catalyst containing an oxo-transfer Mo^VIO₂complex capable of activating dioxygen. Oxidalion proceeds in ethanolic solutions without deactivation by water or excess thiol even at relatively high temperatures (up to 80°C). It is, therefore, concluded that intercalation of [MoO₂{O₂CC(S)Ph₂}₂]^2– into the layered double hydroxide host inhibits the formation of a catalytically inactive molybdenum(V) species which was previously observed under homogeneous conditions.