Butyllithium Deprotonation vs Alkali Metal Reduction of Cobalt Dicarbollide: A New Synthetic Route to C-Substituted Derivatives

Reduction of Cs[Co(1,2-C 2 B 9 H 11 ) 2 ] (Cs[ I ]) with 1 equiv of Na(Hg) amalgam or Cs metal forms the cobalt(II) dianion, [Co(1,2-C 2 B 9 H 11 ) 2 ] 2 - ( II ), which reverts to I upon exposure to 0.5 equiv of I 2 . The molecular structure of [Cs 2 (DME) 4 ][Co(1,2-C 2 B 9 H 11 ) 2 ] shows the carbon atoms of dianion II occupy transoid rotational geometry about the cobalt center, consistent with isoelectronic nickel(III) bis(dicarbollide). Reaction of THF solutions of I with 1.0 and 2.0 equiv of n -butyllithium forms purple Cs[Co(LiC 2 B 9 H 10 )(C 2 B 9 H 11 )] (Cs[ I -Li]) and blue Cs[Co(LiC 2 B 9 H 10 ) 2 ] (Cs[ I -Li 2 ]), respectively. Treating I -Li and I -Li 2 with water causes reversion to I; reaction with D 2 O forms a dicarbollide C−D bond (IR: ν(CD/CH) = 2275/3040 cm - 1 ). Mono- and dilithio(cobalt dicarbollide) react with alkyl halides (R−X) to form the corresponding alkyl(cobalt dicarbollide) complexes, [Co(RC 2 B 9 H 10 )(C 2 B 9 H 11 )] - and [Co(RC 2 B 9 H 10 ) 2 ] - ( I -R and I -R 2; R = CH 3, C 6 H 13 ). Alkylation of I -Li 2 using methyl iodide gives a mixture of meso and rac isomers of [Co(1-Me-1,2-C 2 B 9 H 10 ) 2 ] - ( I -1,1‘-Me 2 ). In contrast, treating I -Li,Me (generated via deprotonation of I -Me) with methyl iodide forms [Co(1,2-Me 2 -1,2-C 2 B 9 H 9 )(C 2 B 9 H 11 )] - ( I -1,2-Me 2; 30%), plus meso- and rac - I -1,1‘-Me 2 (70% total). The stereochemistry of alkylation is kinetically determined by the sites of deprotonation. Reaction of I -Li 2 with 2 equiv of CH 3 OCH 2 CH 2 OCH 2 Cl (MEM-Cl) produces only the structurally characterized rac isomer of Cs[ I -1,1‘-MEM 2 ]. Crystal data for [Cs 2 (DME) 4 ][Co(C 2 B 9 H 11 ) 2 ]: triclinic P 1̄, a = 9.7930(10) Å, b = 10.1300(10) Å, c = 12.1010(10) Å, α = 101.13°, β = 98.16°, γ = 114.09°, V = 1042.1(2) Å 3, Z = 1. Crystal data for Cs[Co(1-MEM-1,2-C 2 B 9 H 10 ) 2 ]: monoclinic P 2 1 / c, a = 11.5780(10) Å, b = 14.0880(10) Å, c = 16.998(2) Å, β = 96.21°, V = 2756.3(4) Å 3, Z = 4.