CHEMISTRY OF C-TRIMETHYLSILYL-SUBSTITUTED HETEROCARBORANES. 23. SYNTHETIC,SPECTROSCOPIC, AND STRUCTURAL INVESTIGATION ON HALF- AND FULL-SANDWICH MAGN ESACARBORANES OF 2,3- AND 2,4-C2B4 CARBORANE LIGANDS

The reaction of nido-1-Na(L)n-2-(SiMe3)-3-(R)-2,3-C2B4H5 (n = 2, L = THF, R = SiMe3; n = 1, L = TMEDA, R = SiMe3 or Me) or closo-exo-5,6-[(μ-H)2Li(L)n]-1-Li(L)n-2,4-(SiMe3)2-2,4-C2B4H4 (n = 2, L = THF; n = 1, L = TMEDA) with various magnesium reagents produced a number of different magnesacarboranes. The product of a 1:1 molar ratio reaction of the 2,3-C2B4 monosodium compound (R = SiMe3 and L = TMEDA) with MeMgBr was the half-sandwich magnesacarborane closo-1-Mg(TMEDA)-2,3-(SiMe3)2-2,3-C2B4H4 (I), while when R = Me, the same reaction conditions gave the novel full-exo-sandwich complex commo-exo-4,4‘,5,5‘-Mg(TMEDA)[2-(SiMe3)-3-(Me)-2,3-C2B4H5]2 (II). The full-endo-sandwich magnesacarboranes [Na(THF)2]2[commo-1,1‘-Mg{2,3-(SiMe3)2-2,3-C2B4H4}2] (IV) and [Na(TMEDA)]2[commo-1,1‘-Mg{2,3-(SiMe3)2-2,3-C2B4H4}2] (V) were the exclusive products when the appropriate monosodium compound reacted with Mg(Bu)2 in 2:1 molar ratios. Reaction of closo-exo-5,6-[(μ-H)2Li(TMEDA)]-1-Li(TMEDA)-2,4-(SiMe3)2-2,4-C2B4H4 with MgBr...