SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF METALLACARBORANES CONTAINING BRIDGED DICARBOLLIDE LIGANDS

The synthesis and characterization of a family of carbon-bridged metallacarboranes of the type [7,7'-mu-1,n-CnH2n-(7,8-C2B9H10)2M]-(n = 3, M = Co3+ (14); n = 4, M = Co3+ (15), Fe3+ (16), Ni3+ (17a), Cr3+ (18); n = 5, M = Co3+ (19)) and [7,7'-mu-1,5-TosN(CH2CH2-)2-(7,8-C2B9H10)2M]- (M = Co3+ (20), Fe3+ (21)) are described. In each instance, meso and dl isomers were obtained from the reaction of the diastereomeric bridged carborane precursors and metal halide. The tosylated derivatives were separated into meso and dl isomers by HPLC techniques, and all diastereomeric metallacarboranes were spectroscopically characterized. Compounds 14-16 and 17b (Ni4+) have been structurally characterized by single-crystal X-ray diffraction. Compound 14 crystallizes in the triclinic space group P1BAR with a = 10.056 (8) angstrom, b = 11.861 (9) angstrom, c = 17.896 (11) angstrom, alpha = 96.20 (2)-degrees, beta = 96.36 (3)-degrees, gamma = 111.20 (3)-degrees, V = 1952 angstrom3, Z = 2, and R = 0.089. Compound 15 crystallizes in the triclinic space group P1BAR with a = 9.979 (8) angstrom, b = 11.769 (1) angstrom, c = 17.640 (1) angstrom, alpha = 84.46 (2)-degrees, beta = 83.61 (2)-degrees, gamma = 112.79 (2)-degrees, V = 1876 angstrom3, Z = 2, and R = 0.054. Compound 16 crystallizes in the orthorhombic space group B2cb (standing setting Aba2) with a = 9.616 (4) angstrom, b = 10.768 (4) angstrom, c = 18.326 (7) angstrom, V = 1897 angstrom3, Z = 4, and R = 0.027. Compound 17b crystallizes in the monoclinic space group C2/c with a = 21.726 (5) angstrom, b = 9.906 (2) angstrom, c = 35.767 (9) angstrom, beta = 103.04 (9)-degrees, V = 7499 angstrom3, Z = 8, and R = 0.090. The relationship between bridge length and complex formation is examined.