Six-Vertex Hydrogen-Rich Cp2M2B4H8 Dimetallaboranes of the Second- and Third-Row Transition Metals: Effects of Skeletal Electron Count on Preferred Polyhedr

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• 作者：Adrian M. V. Br芒nzanic ; Alexandru Lupan ; R. Bruce King
• 刊名：Organometallics
• 出版年：2014
• 出版时间：November 24, 2014
• 年：2014
• 卷：33
• 期：22
• 页码：6443-6451
• 全文大小：472K
• ISSN：1520-6041

文摘

The complete series of hydrogen-rich six-vertex cyclopentadienyl dimetallaboranes Cp₂M₂B₄H₈ (Cp = 畏⁵-C₅H₅; M = Ir, Ru/Os, Re, Mo/W, and Ta), including the experimentally known Ir, Ru, and Re derivatives synthesized by Fehlner and co-workers, have now been examined by density functional theory. The nature of the central M₂B₄ polyhedra in the lowest energy Cp₂M₂B₄H₈ structures relates to the skeletal electron count as determined by the Wade鈥揗ingos rules. Thus, the lowest energy Cp₂Ir₂B₄H₈ structures with 16 Wadean skeletal electrons have central pentagonal-pyramidal Ir₂B₄ units similar to that of the known pentagonal-pyramidal B₆H₁₀. The lowest energy Cp₂M₂B₄H₈ (M = Ru, Os) structures with 14 Wadean skeletal electrons have central capped-tetragonal-pyramidal rather than octahedral M₂B₄ units. However, isomeric Cp₂M₂B₄H₈ (M = Ru, Os) structures with central M₂B₄ octahedra are found at energies starting at 鈭?5 kcal/mol (M = Ru) and 鈭?0 kcal/mol (M = Os) above the capped-tetragonal-pyramidal global minima. The lowest energy electron poorer Cp₂M₂B₄H₈ structures (M = Re, Mo, W, Ta) have central M₂B₄ bicapped tetrahedra with the metal atoms at the degree 5 vertices. Higher energy Cp₂Re₂B₄H₈ structures include capped-tetragonal-pyramidal structures with surface Re鈺怰e double bonds and a pentagonal-pyramidal structure with a surface Re鈮e triple bond. The lowest energy Cp₂M₂B₄H₈ (M = Mo, W) structures appear to have surface M鈺怣 double bonds and thus also the 12 skeletal electrons for their bicapped-tetrahedral structures. However, the lowest energy likewise bicapped-tetrahedral Cp₂Ta₂B₄H₈ structure is best interpreted in having CpTa units with 16-electron rather than 18-electron tantalum configurations and a surface Ta鈥揟a single bond.