Homoleptic Divalent Dialkyl Lanthanide-Catalyzed Cross-Dehydrocoupling of Silanes and Amines

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• 作者：Aradhana Pindwal ; Arkady Ellern ; Aaron D. Sadow
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 13, 2016
• 年：2016
• 卷：35
• 期：11
• 页码：1674-1683
• 全文大小：602K
• 年卷期：0
• ISSN：1520-6041

文摘

The rare-earth bis(alkyl) compound Sm{C(SiHMe₂)₃}₂THF₂ (1b) is prepared by the reaction of samarium(II) iodide and 2 equiv of KC(SiHMe₂)₃. This synthesis is similar to that of previously reported Yb{C(SiHMe₂)₃}₂THF₂ (1a), and compounds 1a,b are isostructural. Reactions of 1b and 1 or 2 equiv of B(C₆F₅)₃ afford SmC(SiHMe₂)₃HB(C₆F₅)₃THF₂ (2b) or Sm{HB(C₆F₅)₃}₂THF₂ (3b), respectively, and 1,3-disilacyclobutane {Me₂Si-C(SiHMe₂)₂}₂ as a byproduct. Bands from 2300 to 2400 cm^–1 assigned to ν_BH in the IR spectra and highly paramagnetically shifted signals in the ¹¹B NMR spectra of 2b and 3b provided evidence for Sm-coordinated HB(C₆F₅)₃. Compounds 1a,b react with the bulky N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazol-2-ylidene (ImtBu) to displace both THF ligands and give three-coordinate monoadducts Ln{C(SiHMe₂)₃}₂ImtBu (Ln = Yb (4a), Sm (4b)). Complexes 4a,b catalyze cross-dehydrocoupling of organosilanes with primary and secondary amines at room temperature to give silazanes and H₂, whereas 1a,b are not effective catalysts under these conditions. Second-order plots of ln{[Et₂NH]/[Ph₂SiH₂]} vs time for 4a-catalyzed dehydrocoupling are linear and indicate first-order dependences on silane and amine concentrations. However, changes in the experimental rate law with increased silane concentration or decreased amine concentration reveal inhibition by silane. In addition, excess ImtBu or THF inhibit the reaction rate. These data, along with the structures of 4a,b, suggest that the bulky carbene favors low coordination numbers, which is important for accessing the catalytically active species.