Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 27. Synthetic, Spectroscopic, Structural, and Reactivity Studies on d0 Hafnacarboranes of 2,3-C2B4-Carborane Ligands

The sodium/lithium compounds closo-exo-Li(THF)-1-Na(THF)-2-(SiMe3)-3-(R)-2,3-C2B4H4 (R = SiMe3, Me, H), were found to react with several different hafnium reagents to produce half- and full-sandwich and mixed-ligand chlorohafnacarboranes in good yields. The reaction of the sodium/lithium compounds with HfCl4 in 2:1 molar ratios produced the full-sandwich complexes 1-Cl-1-(THF)-2,2‘-(SiMe3)2-3,3‘-(R)2-4‘,5,5‘,6-Li(THF)n-[1,1‘-commo-Hf(2,3-C2B4H4)2] (R = SiMe3, n = 2 (I); R = Me, n = 1 (II); R = H, n = 1 (III)) in yields of 77%, 65%, and 71%, respectively. When R = SiMe3, a 1:1 molar ratio of carborane to HfCl4 gave the half-sandwich species [Li(THF)2][1,1,1-(Cl)3-closo-1-Hf-2,3-(SiMe3)2-2,3-C2B4H4] (V) in 77% yield. On the other hand, both 2:1 and 1:1 reaction ratios of carborane (R = Me) to Cp*HfCl3 gave only the mixed-ligand sandwich compound 1,1‘-(Cl)2-2-(SiMe3)-3-(Me)-4,5-Li(THF)-1,1‘-commo-Hf[(η5-C5Me5)(η5-2,3-C2B4H4)] (IV) in 82% yield. All compounds were characterized by infrared spectroscopy, 1H, 1...