The Zwitterion [8,8-μ-CH2O(CH3)-(1,2-C2B9H10)2-3,3-Co]0 as a Versatile Building Block To Introduce Cobalt Bis(Dicarbollide) Ion into Organic Molecules
Abstrakt
The synthesis of a new bridged [8,8-μ-CH2O(CH3)-(1,2-C2B9H10)2-3,3-Co]0 derivative (2), arising from the acid-catalyzed reaction of cobalt bis(1,2-dicarbollide)(1) ion with formaldehyde, is reported. The proposed reaction path is supported by the isolation of side products including two zwitterionic compounds, the known bridged [8,8-μ-(CH3O)-(1,2-C2B9H10)2-3,3-Co]0 derivative (3), the new zwitterion [(8-(CH3)2O-1,2-C2B9H10)-(1,2-C2B9H11)-3,3-Co]0 (4), and two anionic compounds-the known [(8,8-Cl2-1,2-C2B9H10)2-3,3-Co] and the newly characterized dimethoxy derivative [(8,8-(CH3O)2-1,2-C2B9H10)2-3,3-Co] of the cobalt bis(dicarbollide) ion.
Compound 2 serves as a versatile building block for the construction of zwitterionic derivatives, as exemplified by the synthesis of a series of compounds of general formulation [(8-X-CH2-1,2-C2B9H10)(8-CH3O-1,2-C2B9H10)-3,3-Co]0 (6). Compounds of type 6 bear organic end groups (X = NC5H5 (6a), C6H13NH2 (6b), 2-HOC2H4NH2 (6c), (C6H5)3P (6d)) adjacent to the cluster via a methylene spacer.
The reactions with alcoholates or phenolates, demonstrated by the isolation of a derivative with X = 1-O(4-t-Bu-C6H4) (7-) in low yield, seem less advantageous due to the competing demethylation of the oxonium bridge in 2, which results in the preferential formation of the anion [8,8-μ-CH3O-(1,2-C2B9H10)2-3,3-Co] (8-). A similar side reaction was found to occur in the synthesis of a tetrasubstituted tert-butyl-calix[4]arene (9-), where one calixarene OH site was methylated producing the metallacarborane ion 8- instead of the bridge opening.
The molecular structures of 6a,c-e, 8-, and 9- were determined by single-crystal X-ray diffraction analyses, and all compounds were characterized by high-resolution NMR (1H, 13C, and 11B) and mass spectrometry.