Synthesis and Structural Characterization of closo- and exo-nido-Lanthanacarboranes

Treatment of anhydrous LaCl 3 with 1 equiv of Na 2 [7,8-R 2 - nido -7,8-R 2 C 2 B 9 H 9 ] in THF afforded sandwich complexes closo- {(THF) 2 Na}{(R 2 C 2 B 9 H 9 ) 2 La(THF) 2 } (R = H ( 1 ), R = C 6 H 5 CH 2 ( 2 )) in good yield. Reaction of SmI 2 with an equimolar amount of Na 2 [7,8- nido- 7,8-(C 6 H 5 CH 2 ) 2 C 2 B 9 H 9 ] in THF, followed by the addition of 1,2-dimethoxyethane (DME), generated the dimeric exo-nido- [((C 6 H 5 CH 2 ) 2 C 2 B 9 H 9 )Sm(DME) 2 ] 2 ·DME ( 3 ) in 70% yield. All complexes were characterized by 1 H, 13 C, and 11 B NMR and IR spectroscopy as well as complexometric metal analyses. The molecular structures of complexes 1 and 3 were further confirmed by X-ray analyses. The coordination geometry of complex 1 is best described as distorted tetrahedral with two η 5 -bonded C 2 B 9 H 11 ligands and two coordinated THF molecules. In the centrosymmetric dimer 3, each of the two dibenzyldicarbollide ligands serves as a bridging ligand for two Sm atoms while bonding to one via upper belt B−H bonds (containing two carbon atoms) and the other through lower belt B−H bonds.