Chemistry of cobalt bis(1,2-dicarbollide) ion; the synthesis of carbon substituted alkylamino derivatives from hydroxyalkyl derivatives via methylsulfonyl or p-toluenesulfonyl esters

In this paper we report the synthetic procedures providing the C-substitution of the cobalt bis(di-carbollide) sandwich anion [(1,2-C2B9H11)-3,3'-Co](-) with primary, secondary and tertiary alkylamine groups of different length of the aliphatic spacer attached to the carbon C(1) or C(1) and C(1') cage positions. Reaction pathways leading to these compounds proceed via synthesis of mono [(1-X-O-(CH2)(n)-1,2-C2B9H10) (1',2'-C2B9H11)-3,3'-Co]Me4N (where n = 1-3 and X = -SO2CH3 or SO2(-C6H4-4-CH3) esters (2a-f) and diesters [(1,1'-X-O-CH2)(n)-1,2-C2B9H10)(2)-3,3'-Co]Me4N (3a-c) (n = 1 and 2). These compounds are readily accessible in good to excellent yields by reactions of trimethylammonium salts of alkylhydroxy derivatives (1a-e) of the parent ion with methylsulfonyl or p-toluenesulfonyl chloride. The esterifications proceeded with lower conversions only for methylene hydroxy derivatives. The series of primary amines of general formulation [(1-(RRN)-R-1-R-2-(CH2)(n)-1,2-C2B9H10) (1',2'-C2B9H11)-3,3'-Co] (where n = 1-3 and R-1 = R-2 = H) (4a-c), along with the diamine [(1,1'-NH2-C2H5)(2)-1,2-C2B9H10)(2)-3,3'-Co](-) (5), and compounds comprising secondary and tertiary amino functions (R-1 = Bu-n, R-2 = H, R-1 = Bn, R-2 = H and R-1 = R-2 = Et) (6a-h) were prepared in generally good yields by reactions of the esters with ammonia and primary or secondary amines. However, the reactions of the bis(methylene methylsulfonyl) diester resulted in almost quantitative in situ dialkylation of the amine group leading to the formation of a triatomic bridge between two carbon atoms of the cage [(1,1'-mu-(CH2NRCH2-) (1,2-C2B9H10)(2)-3,3'-Co](-) (R = H or Bu) (7a, b). We believe this observation contributes further to rich evidence on the preference of bridge substitutions at the cobalt bis(dicarbollide) cage. (C) 2015 Elsevier B.V. All rights reserved.