Carbon-rich Metallacarboranes. 13. Synthesis and Structure of Bis(carboranyl)cobalt Complexes Derived from (C2H5)4C4B8H 8 2-


The reaction of CoCl2 with Et4C4B8H8 2- ion in tetrahydrofuran produced two crystalline dicobalt complexes that were isolated by column and plate chromatography: red (Et4C4B8H8)2Co 2 (1), 35% yield, and red-orange paramagnetic (Et4C4B8H7)2Co 2 (2a), 15%. From two-dimensional (2D) 11B-11B NMR data, 1 is proposed to consist of a pair of 14-vertex closo-Co2C4B8 polyhedra sharing a common Co-Co edge, a previously unknown geometry in metallacarborane chemistry. Electron pairing between the formal Co(II) centers is proposed to account for the observed diamagnetism. The same reaction, when followed by addition of B5H8 - ion, generates several isolable complexes, including 1 (18%) and the minor products 2b (an isomer of 2a), (Et4C4B8H8)-Co(Et4C 4B8H7OC4H8) (3a), (Et4C4B8H7)2CoH (4a), and (Et4C4B4H6)CoH(Et4C 4B8H8) (5). Compound 2b slowly rearranges at room temperature to an isomer, 2c. Treatment of 1 with I2 in acetone at 25°C produces (Et4C4B8H7)2(OCMe 2)2CoH (3c, 22%), isomers of (Et4C4B8H7)2(OH)Co (3d, 8%; 3e, 9%), (Et4C4B8H6OH)2HCo (3f, 11%), and 2b (19%). Products 2a, 2b, 2c, and 4a are proposed to have a direct B-B linkage between their carborane ligands. An X-ray crystallographic study of 3c revealed that the carborane ligands are bridged by an acetone molecule via a B-O-B array in which the direct interligand boron-boron distance is 2.26 Å, considered weakly bonding. The second acetone is coordinated to a single boron atom on one of the cages, and the metal-bonded faces of the carborane ligands are inclined with a dihedral angle of 27.1°. The established and proposed structures are discussed in light of current cluster bonding theory, and implications concerning metal-promoted ligand fusion and coupling processes are considered. Crystal data: [(C2H5)4C4B8H 7]2[OC(CH3)2]2CoH, Mr = 692, space group P21/c, a = 9.897 (7) Å, b = 12.316 (3) Å, c = 33.31 (2) Å, β = 92.35 (3)°, V = 4057 Å3, Z = 4, R = 0.073 for 3054 reflections having Fo 2 > 3σ(Fo 2). © 1985 American Chemical Society.



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© 1985 American Chemical Society (ACS), All rights reserved.