Towards the synthesis of high boron content polyanionic multicluster macromolecules

Abstract

Reported are further consequences of the dioxane ring-opening in [3,3’-Co(8-(CH2CH2O)2-1,2-C2B9H10)(1’,2’-C2B9H11)] [1] with twelve-vertex carborane mono- and dianions. The removal of one BH vertex from the 1,2-carborane part of the double-cluster monoanions of type [1’’-X-2’’-R-closo-1’’,2’’-C2B10H11]- [2]- (where X = [3,3’-Co(8-(CH2CH2O)2-1,2-C2B9H10)(1’,2’-C2B9H11)]- and R = H [2]-, CH3 [8]- and C6H5 [9]-) via heating with ethanolic KOH or CsF led to the isolation of a series of orange dianions having as general formula [7’’-X-8’’-R-7’’,8’’-nido -C2B9H11]2- (R = H, [11]2-; CH3, [12]2- and C6H5, [13]2-). The same procedure applied to the dianionic triple-cluster compound [1’’,2’’-X2-1’’,2’’-closo-C2B10H10]2- [5]2- yielded the trianionic species [7’’,8’’-X2-7’’,8’’-nido -C2B9H10]3- [14]3-. Boron degradation of the related 1,7-carborane anion [1’’-X-1’’,7’’-closo-C2B10H11]- [3]- was achieved upon heating with CsF in ethylene glycol to generate the [7’’-X-7’’,9’’-nido-C2B9H11]2- [15]2- dianion. However, the degradation of the corresponding [1’’,7’’-X2-1’’,7’’-closo-C2B10H10]2- [6]2- dianion under the same conditions led only to the cleavage of the ether chain with no possible isolation the expected [7’’,9’’-X2-7’’,9’’-nido-C2B9H10]3- trianion. The study has been complemented by experimental procedures leading to the still not fully reported starting monoanionic compounds [2]-, [8]-, [9]- and [3]- and to the starting dianions [5]2- and [6]2-. The anions containing the eleven-vertex moiety can be isolated as either Cs+ or [N(CH3)4]+ salts and can be converted into other salts via metathesis with suitable counter-cations. The structure of all compounds isolated in this study has been suggested on the basis of NMR and MS methods. The disarticulation of complex 11B NMR spectra has been successfully achieved in this work and has been proven to be a powerful tool for the characterization of multicluster boron containing molecules.