Carbon鈥揌ydrogen Bond Breaking and Making in the Open-Shell Singlet Molecule Cp*2Yb(4,7-Me2phen)

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• 作者：Gr茅gory Nocton ; Corwin H. Booth ; Laurent Maron ; Louis Ricard ; Richard A. Andersen
• 刊名：Organometallics
• 出版年：2014
• 出版时间：December 8, 2014
• 年：2014
• 卷：33
• 期：23
• 页码：6819-6829
• 全文大小：537K
• ISSN：1520-6041

文摘

The adducts formed between the 4,7-Me₂-, 3,4,7,8-Me₄-, and 3,4,5,6,7,8-Me₆-phenanthroline ligands and Cp*₂Yb are shown to have open-shell singlet ground states by magnetic susceptibility and L_III-edge XANES spectroscopy. Variable-temperature XANES data show that two singlet states are occupied in each adduct that are fit to a Boltzmann distribution for which 螖H = 5.75 kJ mol^鈥? for the 4,7-Me₂phen adduct. The results of a CASSCF calculation for the 4,7-Me₂phen adduct indicates that three open-shell singlet states, SS1鈥揝S3, lie 0.44, 0.06. and 0.02 eV, respectively, below the triplet state. These results are in dramatic contrast to those acquired for the phenanthroline and 5,6-Me₂phen adducts, which are ground state triplets ( J. Am. Chem. Soc. 2014, 136, 8626). A model that accounts for these differences is traced to the relative energies of the LUMO and LUMO+1 orbitals that depend on the position the methyl group occupies in the phenanthroline ligand. The model also accounts for the difference in reactivities of Cp*₂Yb(3,8-Me₂phen) and Cp*₂Yb(4,7-Me₂phen); the former forms a 蟽 C鈥揅 bond between C(4)C(4鈥?, and the latter undergoes C鈥揌 bond cleavage at the methyl group on C(4) and leads to two products that cocrystallize: Cp*₂Yb(4-(CH₂),7-Mephen), which has lost a hydrogen atom, and Cp*₂Yb(4,7-Me₂-4H-phen), which has gained a hydrogen atom.