Reversible Sigma C鈥揅 Bond Formation Between Phenanthroline Ligands Activated by (C5Me5)2Yb

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• 作者：Gr茅gory Nocton ; Wayne W. Lukens ; Corwin H. Booth ; Sergio S. Rozenel ; Scott A. Medling ; Laurent Maron ; Richard A. Andersen
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：June 18, 2014
• 年：2014
• 卷：136
• 期：24
• 页码：8626-8641
• 全文大小：698K
• 年卷期：v.136,no.24(June 18, 2014)
• ISSN：1520-5126

文摘

The electronic structure and associated magnetic properties of the 1,10-phenanthroline adducts of Cp*₂Yb are dramatically different from those of the 2,2鈥?bipyridine adducts. The monomeric phenanthroline adducts are ground state triplets that are based upon trivalent Yb(III), f¹³, and (phen^{鈥⑩€?/sup> ) that are only weakly exchange coupled, which is in contrast to the bipyridine adducts whose ground states are multiconfigurational, open-shell singlets in which ytterbium is intermediate valent ( J. Am. Chem. Soc 2009, 131, 6480; J. Am. Chem. Soc 2010, 132, 17537). The origin of these different physical properties is traced to the number and symmetry of the LUMO and LUMO+1 of the heterocyclic diimine ligands. The bipy鈥⑩€?/sup> has only one 蟺*₁ orbital of b₁ symmetry of accessible energy, but phen鈥⑩€?/sup> has two 蟺* orbitals of b₁ and a₂ symmetry that are energetically accessible. The carbon p_蟺-orbitals have different nodal properties and coefficients and their energies, and therefore their populations change depending on the position and number of methyl substitutions on the ring. A chemical ramification of the change in electronic structure is that Cp*₂Yb(phen) is a dimer when crystallized from toluene solution, but a monomer when sublimed at 180鈥?90 掳C. When 3,8-Me₂phenanthroline is used, the adduct Cp*₂Yb(3,8-Me₂phen) exists in the solution in a dimer鈥搈onomer equilibrium in which 螖G is near zero. The adducts with 3-Me, 4-Me, 5-Me, 3,8-Me₂, and 5,6-Me₂-phenanthroline are isolated and characterized by solid state X-ray crystallography, magnetic susceptibility and L_III-edge XANES spectroscopy as a function of temperature and variable-temperature 1H NMR spectroscopy.}