Chemistry ofC-Trimethylsilyl-Substituted Heterocarboranes. 24. Synthetic, Spectroscopic, Structural, and Reactivity Studies on Half- and Full-Sandwich Yttracarboranes of 2,3-C₂B₄- and 2,4-C₂B₄-Carborane Ligands

The reaction of YCl 3 with closo - exo -5,6-[(μ-H) 2 Li(THF) 2 ]-1-Li(THF) 2 -2-(SiMe 3 )-3-(R)-2,3-C 2 B 4 H 4 (R = SiMe 3 and Me) or closo - exo -5,6-[(μ-H) 2 Na(THF) 2 ]-1-Na(THF) 2 -2,4-(SiMe 3 ) 2 -2,4-C 2 B 4 H 4 in 1:2 molar ratios in dry benzene produced the yttracarboranes [Li(THF) 4 ]{1-Cl-1-(THF)-2,2‘-(SiMe 3 ) 2 -3,3‘-(R) 2 -4,4‘,5,5‘-Li(THF)[1,1‘- commo -Y(2,3-C 2 B 4 H 4 ) 2 ]} (R = SiMe 3 ( I ), Me ( II )) or {Na(THF) 3 } 2 {[1-(THF)-1-(μ-H) 2 -2,2‘,4,4‘-(SiMe 3 ) 4 -1,1‘- commo -Y(2,4-C 2 B 4 H 4 ) 2 ] 2 } ( III ) in yields of 83%, 80%, and 74%, respectively. Compound I was found to react with excess NaH in dry THF to give a hydridoyttracarborane sandwich 1-H-2,2‘,3,3‘-(SiMe 3 ) 4 -[4,4‘,5-Li(THF)] 2 -[1,1‘- commo -Y(2,3-C 2 B 4 H 4 ) 2 ] ( V ) in 80% yield. Attempts to prepare the half-sandwich yttracarboranes directly from the reaction of YCl 3, Me 3 SiCH 2 MgCl, and 2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 6 proved unsuccessful, instead, the reaction produced the mixed magnesa-/yttracarborane closo- 1-Y-{1,1‘-(μ-Cl) 2 - exo- [5,6-(μ-H) 2 -Mg(THF) 2 ]-1,1‘-(μ-Cl) 2 -[ closo- 1-Mg(THF)-2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 4 ]}-2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 4 (3.5C 6 H 6 ) ( IV ). All compounds were characterized by their IR and 1 H, 11 B, and 13 C NMR spectra; V was also characterized by its 7 Li NMR spectrum. The structures of I, III, and IV were determined by single-crystal X-ray crystallography. Compound I is a bent-sandwich complex in which the Y atom is bonded to two carborane units, a Cl anion, and a THF molecule to give a very distorted tetrahedral arrangement around the metal. The structure of III is a dimer in which each Y atom is bonded to two carboranes and a THF, the fourth coordination site being occupied by a pair of Y−H−B bridges to two adjacent borons in a neighboring carborane.