Synthesis and Characterization of the Cycloheptatrienyl Tantalum "Mixed-Sandwich" Compounds (C5R5)Ta(C7H7)

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• 作者：Wontae Noh ; Gregory S. Girolami
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：January 21, 2008
• 年：2008
• 卷：47
• 期：2
• 页码：535 - 542
• 全文大小：175K
• 年卷期：v.47,no.2(January 21, 2008)
• ISSN：1520-510X

文摘

The molecule (cycloheptatrienyl)(cyclopentadienyl)tantalum, (C₅H₅)Ta(C₇H₇) (1), and its methylcyclopentadienyl andpentamethylcyclopentadienyl analogues (C₅H₄Me)Ta(C₇H₇) (2), and (C₅Me₅)Ta(C₇H₇) (3) have been synthesizedby magnesium reduction of the corresponding (C₅R₅)TaCl₄ species in the presence of cycloheptatriene. The crystalstructures of 2 and 3 show that the two rings are planar and essentially parallel to each other. Interestingly, theTa-C distances to the C₇H₇ ring are significantly shorter (by about 0.1 Å) than those to the cyclopentadienyl ring;the difference reflects stronger bonding to the C₇H₇ ring. A comparison with the structures of other (C₅R₅)M(C₇H₇)shows that the M-C distances to the seven-membered ring are especially sensitive to the d-orbital energies of themetal center and its ability to engage in bonding with the ring. For 1-3, the EPR spectra at room temperatureconsist of octets due to the tantalum nuclear spin. Both A_iso and g_iso increase as the number of methyl groups onthe cyclopentadienyl ring increases. EPR spectra of 1-3 as frozen glasses correspond to axial symmetry, and thehyperfine couplings and g factors are deduced from simulations.