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Aggregation patterns in alpha, alpha' stabilized carbocations: Assemley of a sodium cage polymer by slip-stacking of dimers

Henderson, K.W. and Kennedy, A.R. and McDougall, D.J. (2003) Aggregation patterns in alpha, alpha' stabilized carbocations: Assemley of a sodium cage polymer by slip-stacking of dimers. Inorganic Chemistry, 42 (8). pp. 2736-2741. ISSN 0020-1669

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Abstract

The ,'-stabilized carbanion complexes [PhSO2CHCNNa·THF], 3, [t-BuSO2CHCNNa], 4, [PhSO2CHCNK], 5, [t-BuSO2CHCNK], 6, and [MeSO2CHCNLi·TMEDA], 7, have been synthesized via the metalation of the parent (organo)sulfonylacetonitriles by BuLi, BuNa, or BnK in THF solution (or THF/TMEDA in the case of 7). In addition, complexes 3 and 7 have been characterized by single-crystal X-ray analyses and have been found to adopt related structures in the solid state. Complex 7 is a molecular dimer containing a central 12-membered (OSCCNLi)2 ring core, with each metal rendered tetracoordinate by binding to a chelating TMEDA molecule. As found in related complexes, no direct carbanion to lithium contacts are present in the structure of 7. Complex 3 forms a polymeric cage structure composed of associated 'dimeric' (OSCCNNa)2 rings, similar to those found in 7. The larger sodium cations, and the presence of only one THF molecule/metal, allow additional contacts with the anions, leading to hexacoordination at the metal centers. These contacts include long-range transannular Na-N interactions (2.8042(14) î..) across the central dimeric ring and 'interdimer' Na-C connections (2.8718(15) î..). Dissolution of complexes 3-6 and their lithiated derivatives [PhSO2CHCNLi·TMEDA], 1, and [t-BuSO2CHCNLi·THF], 2, in DMSO-d6 results in almost identical chemical shifts for each type of ligand. This suggests that charge-separated complexes of the form [RSO2CHCN]-[M(DMSO-d6)n]+ are formed in highly polar solution