The Nature of Secondary Interactions at Electrophilic Metal Sites of Molecular and Silica-Supported Organolutetium Complexes from Solid-State NMR Spectroscopy

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• 作者：Matthew P. Conley ; Giuseppe Lapadula ; Kevin Sanders ; David Gajan ; Anne Lesage ; Iker del Rosal ; Laurent Maron ; Wayne W. Lukens ; Christophe Copéret ; Richard A. Andersen
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：March 23, 2016
• 年：2016
• 卷：138
• 期：11
• 页码：3831-3843
• 全文大小：602K
• ISSN：1520-5126

文摘

Lu[CH(SiMe₃)₂]₃ reacts with [SiO_2–700] to give [(≡SiO)Lu[CH(SiMe₃)₂]₂] and CH₂(SiMe₃)₂. [(≡SiO)Lu[CH(SiMe₃)₂]₂] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH₃ and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe₃)₂]_3–x[O-2,6-tBu-C₆H₃]_x (x = 0–2) also have secondary Lu···C interactions. The p>1p>H NMR spectrum of Lu[CH(SiMe₃)₂]₃ shows that the −SiMe₃ groups are equivalent to −125 °C and inequivalent below that temperature, ΔGp>⧧p>_{(Tc = 148 K)} = 7.1 kcal molp>–1p>. Both −SiMe₃ groups in Lu[CH(SiMe₃)₂]₃ have p>1p>J_CH = 117 ± 1 Hz at −140 °C. The solid-state p>13p>C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give p>1p>J_CH = 117 ± 2 Hz. The p>29p>Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe₃)₂]_3–x[O-2,6-tBu-C₆H₃]_x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ–Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling’s electroneutrality concept.