Borabenzene derivatives.: 29.: Synthesis and structural diversity of bis(boratabenzene)scandium complexes.: Structures of [ScCl(C5H5BMe)2]2, [ScCl(3,5-Me2C5H3BNMe2)2]2, and ScCl[3,5-Me2 C5H3BN(SiMe3)2]2

The bis(boratabenzene)scandium complexes 3-5 are synthesized from solvent-free lithium boratabenzenes and ScCl3 in toluene (110 degrees C, 3 days). Complex [ScCl(C5H5BMe)(2)](2) (3) possesses a doubly chloro-bridged dinuclear structure with four facially coordinated boratabenzene ligands. Compound [ScCl(3,5-Me2C5H3BNMe2)(2)](2) (4) differs from 3 in that each scandium atom binds to one boratabenzene in an unprecedented N-B-C-2 coordination mode and facially to the second boratabenzene ligand; in solution 4 is fluxional, displaying only one type of boratabenzene ligand with effective lateral symmetry. Complex ScCl[3,5-Me2C5H3BN(SiMe3)(2)](2) (5) is mononuclear because of the bulkiness of its boratabenzene. Metalation of the 1,2,3,6-tetrahydroborinine 3-CH2-5-MeC5H5BNMe2 (9) affords the solvent-free boratabenzene Li(3,5-Me2C5H3BNMe2) (7). The mixture of 1,2- and 1,4-dihydroborines 3,5-Me2C5H4BNMe2 (10a,b) (accessible from 9 by isomerization) can be transformed into the solvent-free boratabenzene Li[3,5-Me2C5H3BN(SiMe3)(2)] (8) by (i) treatment with BCl3 to give the chloro derivatives 11a,b, (ii) subsequent amination with NH(SiMe3)(2)/NEt3, and (iii) metalation with LiN(SiMe3)(2).