Direct and facile synthesis of carbon substituted alkylhydroxy derivatives of cobalt bis(1,2-dicarbollide), versatile building blocks for synthetic purposes

Abstract

Reactions of lithiated cobalt bis(1,2-dicarbollide)(1⁻) anion (1⁻) in presence of paraformaldehyde, ethylene oxide or trimethylene oxide led to the substitution of 1⁻ at the C-atoms resulting in the high yield formation of monosubstituted alkylhydroxy derivatives [(1-HO(CH₂)_n-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁻ (n = 1–3) isolated as caesium salts (Cs2, Cs3, Cs4) along with disubstituted products of general formulation [(HO(CH₂)_n-1,2-C₂B₉H₁₀)₂-3,3′-Co(III)]⁻ (n = 1–3) (Cs5, Cs6 and Cs7). Disubstituted compounds are in fact a mixture of diastereoisomers denoted as 1,1′-anti(rac-), 1,2′-syn- and in case of Cs6 and Cs7 also 1,2-vicinal-isomer, from which only the anti-isomer could be isolated in pure form in case of shorter chain compounds Cs5 and Cs6. All these alkylhydroxy derivatives can serve as versatile precursors for the generation of a variety of functional molecules. Thus, reaction of Me₃NH4 with NaH and one equivalent of POCl₃ provided after hydrolysis the phosphorylated [(1-(HO)₂P(O)OC₃H₆-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁻ derivative, isolated in the form of trimethylammonium salt, Me₃NH8 as the main product whereas reaction with half of the equivalent produces a high yield of phosphoric acid diester (Me₃NH)₂9 comprising in its structure two cages connected via propyl spacers to the central part. The calcium salt Ca(10)₂ of bridged ion [μ-(HOP(O)(OC₃H₆)₂)-(1,2-C₂B₉H₁₀)₂-3,3′-Co(III)]⁻ resulted from reaction of Me₃NH7 with NaH and one equivalent of POCl₃ followed by hydrolysis and addition of CaCl₂. All new compounds were characterized by multinuclear NMR spectroscopy and mass spectrometry and the structure of Me₃NH3 and that of the respective salts of the pure anti-stereoisomer of dialkylhydroxy derivatives Cs5 and Me₃NH6 were established by X-ray crystallography.