The Zwitterion (8,8 '-mu-CH2O(CH3)-(1,2-C2B9H10)2-3,3 '-Co](0) as a Versatile Building Block To Introduce Cobalt Bis(Dicarbollide) Ion into Organic Molecules
Plesek, J; Gruener, B; Sicha, V; Bohmer, V; Cisarova, I
The synthesis of a new bridged [8,8'-mu-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'-mu-(CH3O)-(1,2-C2B9H10)2-3,3'-Co](0) derivative (3), the new zwitterion [(8-(CH3)(2)O-1,2-C2B9H10)-(1',2'-C2B9H11)-3,3'-Co](0) (4), and two anionic compounds-the known [(8,8'-Cl-2-1,2-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)(3)P (6d)) adjacent to the cluster via a methylene spacer. The reactions with alcoholates or phenolates, demonstrated by the isolation of a derivative with X = 1-0(4-t-Bu-C6H4) (T) 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'-mu-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 (H-1, C-13, and B-11) and mass spectrometry.