Synthesis and Structure of a Bismuth(III)/Chromium(VI) Oxo Cluster Containing a Bi4Cr4O12 Core

Bismuth(III) compounds containing the Kläui’s oxygen tripodal ligand [CpCo{P(O)(OEt)2}3]− (LOEt–) have been synthesized, and their interactions with dichromate in aqueous media were studied. The treatment of Bi5O(OH)9(NO3)4 with NaLOEt in water afforded [LOEtBi(NO3)2]2 (1), whereas that of BiCl3 with NaLOEt in CH2Cl2 yielded LOEtBiCl2 (2). Chloride abstraction of 2 with AgX afforded [LOEtBiX2]2 [X– = triflate (OTf−) (3), tosylate (OTs−) (4)]. In aqueous solutions at pH > 4, 4 underwent ligand redistribution to give the bis(tripod) complex [(LOEt)2Bi(H2O)][OTs] (5). The treatment of 4 with Na2Cr2O7 in acetone/water afforded the Bi(III)/Cr(VI) oxo cluster [(LOEt)4Bi4(μ3-CrO4)2(μ3-Cr2O7)2] (6) containing a unique Bi4Cr4O12 oxometallic core. Compound 6 oxidized benzyl alcohol to give ca. 6 equiv of benzaldehyde. The reaction between 2 and CrO3 yielded [LOEtBi(OCrO2Cl)]2(μ-Cl)2 (7). The crystal structures of complexes 4–7 have been determined.