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Metallohosts Derived from the Assembly of Sugars around Transition Metals:  The Complexation of Alkali Metal Cations

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journal contribution
posted on 17.12.1997, 00:00 by Umberto Piarulli, Andrew J. Rogers, Carlo Floriani, Giuliana Gervasio, Davide Viterbo
The diacetone glucose (DAGH, 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose) monoanion DAG binds as a terminal alkoxo ligand to a variety of transition metals. When it is used in excess, with respect to the oxidation state of the metal, homoleptic anionic complexes [M‘(DAG)6]3- are formed. Such complexes contain oxygen-rich cavities between pairs of DAG ligands appropriate for binding alkali metal cations. The anionic complexes have been obtained by using [Li(DAG)], 1, and [Na(DAG)], 2, whose syntheses and characterization are reported here. The reaction of 1 and 2 with [V(DAG)3] gave [V(DAG)6Li3], 3, and [V(DAG)6Na3], 4, respectively. An alternative synthesis of 3 and 4 involves the metathesis reaction of 1 and 2 with [VCl3(thf)3]. This strategy also led to the synthesis of [Cr(DAG)6Li3], 5, and [Ti(DAG)6Li3], 6. Three pairs of DAG shape a cavity appropriate for three lithium cations in the case of complexes 3, 5, and 6; a cavity is formed for three sodium cations in the case of 4, where the alkali cation is in a tetrahedral O4 environment. In the anionic manganese derivative [Mn(Cl)(DAG)4]3-, the four DAG units arrange in such a way as to bind four Li cations, which form a cationic cage [Mn(Cl)(DAG)4Li4]+, and Cl- is bound inside as [Mn(Cl)(DAG)4Li44-Cl)], 7. Crystallographic details:  4, prism, P21, a = 14.735(10) Å, b = 15.033(9) Å, c = 21.021(10) Å, β = 107.34(2)°, V = 4445(5) Å3, Z = 2, and R = 7.60; 5, prismatic, C2, a = 22.671(9) Å, b = 18.785(5) Å, c = 13.886(4) Å, β = 126.39(2)°, V = 4761(3) Å3, Z = 2, and R = 7.32; 6, prismatic, P21, a = 13.888(5) Å, b = 18.750(5) Å, c = 17.933(5) Å, β = 91.84(2)°, V = 4667(2) Å3, Z = 2, and R = 8.75; 7, prismatic, P21, a = 13.306(7) Å, b = 21.311(11) Å, c = 13.376(6) Å, β = 95.01(2)°, V = 3779(3) Å3, Z = 2, and R = 9.33.

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