Heterobimetallic cerium(iv) oxo clusters supported by a tripodal oxygen ligand

Abstract

Heterometallic Ce^IV/M (M = Mo^VI, Re^VII, V^V) oxo clusters supported by the Kläui tripodal oxygen ligand [(η⁵-C₅H₅)Co{P(O)(OEt)₂}₃]⁻ (L_OEt⁻) have been synthesized and structurally characterized, and the catalytic activity of the Ce^IV/V^V oxo cluster in the oxidation of thioanisoles has been studied. Treatment of [Ce(L_OEt)Cl₃] (1) with [Ag₂MoO₄] afforded the reported Ce^IV/Mo^VI cluster [H₄(CeL_OEt)₆Mo₉O₃₈] (2), whereas that with [AgReO₄] yielded the Ce^IV/Re^VII cluster [{L_OEtCe(ReO₄)₂(H₂O)(μ-ReO₄)}₂] (3) that contains an 8-membered Ce₂Re₂O₄ ring. Treatment of 1 with [Ag₃VO₄] afforded the Ce^IV/V^V cluster [H₂(CeL_OEt)₄(VO)₄(μ₄-O)(μ₃-O)₁₂] (4) containing a {Ce₄V₄O₁₃} oxo-metallic core. The solid-state structure of 4 consists of four {VO₄}³⁻ units bridged by four {L_OEtCe³⁺} moieties and a μ₄-oxo ligand. Each Ce atom in 4 is 9-coordinated, whereas the geometry around each V atom is pseudo square pyramidal with a terminal oxo at the apical position. Cluster 4 is an active catalyst for the oxidation of substituted thioanisoles with tert-butyl hydroperoxide. For example, the oxidation of thioanisole with tert-butyl hydroperoxide in the presence of 0.01 mol% of 4 gave a ca. 30 : 1 mixture of the sulfoxide and sulfone products in 96% yield.