Abstract
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 MgBr2 in a 1:1 molar ratio produced closo-1-Mg(TMEDA)-2,4-(SiMe3)2-2,4-C2B4H4 (III), while a 2:1 molar ratio gave [Li(TMEDA)2]2[commo-1,1‘-Mg{2,4-(SiMe3)2-2,4-C2B4H4}2] (VI). The yields ranged from 73% for III to 94% for II. On the other hand, the 1:1 molar ratio reaction of the THF-solvated 2,4-C2B4 disodium compound with MeMgBr, followed by the addition of 1 equiv of the THF-solvated monosodium compound of the 2,3-C2B4 carborane did not give the expected mixed-ligand complex but produced a 50:50 mixture of IV and [Li(THF)2]2[commo-1,1‘-Mg{2,4-(SiMe3)2-2,4-C2B4H4}2] (VII) in nearly quantitative yields. The magnesacarboranes were characterized by their infrared spectra, chemical analysis, H1, 11B, and 13C NMR spectra, and, in the case of VII, by its 7Li NMR spectrum. Compounds I, II, and IV were further characterized by single-crystal X-ray analysis. Compound I crystallizes as a dimer in which a Mg occupies the apical position above the pentagonal face of one carborane and is bonded to the unique boron of the other carborane in the dimer through a Mg−H−B bridge. The structure of II is one in which a TMEDA-solvated Mg is exo-polyhedrally bonded to two 2,3-C2B4 monoanionic ligands through a pair of Mg−H−B bridges, while in IV, the two carborane dianions are η5-bonded to a Mg in a more conventional endo-sandwich complex. The reactions with MeMgBr are thought to proceed through the formation of a methylmagnesacarborane intermediate which undergoes further reaction to give the final products. The 11B NMR spectra of I−VII were analyzed with the aid of ab initio GIAO molecular orbital calculations.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call