ORGANOTRANSITION-METAL METALLACARBORANES .31. METALLACARBORANE STAIRCASE OLIGOMERS - STEPWISE ASSEMBLY VIA TETRADECKER STACKING REACTIONS

Bis(cobaltacarborane) complexes bridged by fulvalene or 1,4-bis(tetramethylcyclopentadienyl)benzene ligands, and containing reactive carborane C2B3 end rings, are effective synthons for the stepwise construction of air-stable multisandwich oligomers and polymers that are soluble in organic solvents. Bridge deprotonation of the end rings followed by coordination of two such units to a central transition metal (Ni(IV), Co(IV), Co(III)H) formed multilevel species having a central tetradecker sandwich linked to double-decker end units. The latter groups have exposed C2B3 rings on which the same reaction sequence can be repeated to generate progressively larger oligomers. Products having 5-17 metal atoms have been isolated via chromatography on silica and representative complexes characterized via H-1 and B-11 NMR, UV-visible, and FAB mass spectra. X-ray diffraction studies established the structures of a 5-cobalt complex, [(Et2C2B3H5)Co(C5Me4)C6H4(C5Me4)Co(Et2C2B3H-4,5-Cl2)]2Co (4b), containing a central Co-Co-Co tetradecker sandwich, and a fulvalene-bridged dimer, [(Et2C2B3H2-4,6-Br2-5-Me)Co(C5H4)]2 (2c). Crystal data for 4b: M = 1632.0; monoclinic, space group C2/c; Z = 4; a = 33.57(1) angstrom, b = 8.720(3) angstrom, c = 29.412(5) angstrom; beta = 109.95(2)degrees; V = 8093(4) angstrom3; R = 0.083 for 3250 reflections having I > 3.5sigma(I). Crystal data for 2c: M = 828.9; monoclinic, space group P2(1)/n; Z = 2; a = 9.956(4) angstrom, b = 13.439(5) angstrom, c = 11.327(4) angstrom; beta = 103.87(2)degrees; V = 1471(2) angstrom3; R = 0.038 for 1477 reflections having I > 2sigma(I).