Synthesis and characterisation of a chiral lanthanoid cluster with an unusually exposed cubane core via concomitant deesterification of ethyl acetate

An unusual chiral lanthanoid cluster has been synthesised and characterised that exhibits a cubane cage motif with a remarkably exposed central core. This discovery stems from the use of a new asymmetric diketone ligand, (Z)-3-hydroxy-3-methyl-1-(1,2:3,4-di-O-isopropylidene-α-d-galactopyranose)prop-2-en-1-one (Hmgp), which incorporates both a methyl terminus and a protected d-galactose moiety to induce chirality. Reaction of this ligand with hydrated holmium chloride results in the formation of a cubane cluster, [Ho4(μ3-OH)4(η2-mgp)6(μ-η2-mgp)(μ-η2-Ac)(H2O)2] (1), which bears seven chiral ligands that form a highly shielded hemisphere and an acetate co-ligand that is postulated to form via deesterification of ethyl acetate.

Herein we report the synthesis of a holmium cubane cluster that exhibits a remarkably exposed central core. The cluster is ligated by seven chiral diketonate ligands that contain a protected carbohydrate group. Concomitant formation of an acetate co-ligand by deesterification of ethyl acetate yields interesting insights into the reactivity of lanthanoid cubane clusters towards simple ester species. The cluster has been characterised by MALDI mass spectrometry, elemental analysis and single crystal X-ray crystallography.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of a new asymmetric sugar-based diketone ligand.
► Characterisation of a chiral lanthanoid cluster.
► Cluster possesses an unusually exposed metal core.
► Cluster de-esterifies ethyl acetate during formation.