Cyclopentadienyl-Silyl-Amido versus Imido Niobium Complexes. The Role of Additional Amine Functionalities: A Combined Experimental and Theoretical Study

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• 作者：M. Carmen Maestre ; Marta E. G. Mosquera ; Heiko Jacobsen ; Gerardo Jimé ; nez ; Tomá ; s Cuenca
• 刊名：Organometallics
• 出版年：2008
• 出版时间：March 10, 2008
• 年：2008
• 卷：27
• 期：5
• 页码：839 - 849
• 全文大小：421K
• 年卷期：v.27,no.5(March 10, 2008)
• ISSN：1520-6041

文摘

The reaction of the chlorosilyl-substituted cyclopentadienyl niobium compound [Nb(η⁵-C₅H₄SiMe₂Cl)Cl₄] (1) with 1 equiv of propylenediamine or N-methylpropylenediamine in toluene in the presence of 2 equiv of NEt₃ affords the cyclopentadienyl-silyl-amido-amine derivatives [Nb{η⁵-C₅H₄SiMe₂-η-N(CH₂)₃-η-NHR}Cl₃] (R = H, 3a; Me, 3b). In contrast, a similar reaction using the N,N-dimethylpropylene diamine regiospecifically yields the imido compound [Nb(η⁵-C₅H₄SiMe₂Cl){N(CH₂)₃NMe₂}Cl₂] (4a). However, treatment of 1 with 3 equiv of N-methylpropylene diamine in the absence of NEt₃ gives the imido complex [Nb(η⁵-C₅H₄SiMe₂Cl){N(CH₂)₃NHMe}Cl₂] (4b). The reaction of 1 with 0.5 equiv of NH₂(CH₂)₃NH₂ in the presence of 2 equiv of NEt₃ proceeds with the formation of the tethered dinuclear diimido compound [{Nb(η⁵-C₅H₄SiMe₂Cl)Cl₂}₂{μ-N(CH₂)₃-η-N}] (5a). Analogous dinuclear diimido compounds [{Nb(η⁵-C₅H₄SiMe₂Cl)Cl₂}₂{μ-N(CH₂)_n-η-N}] (n = 4, 5b; 5, 5c) are obtained when 1 reacts with longer unsubstituted diamines NH₂(CH₂)_nNH₂ (n = 4 and 5), regardless of the reaction proportions. The transient dinuclear diamine adducts of such a process, [{Nb(η⁵-C₅H₄SiMe₂Cl)Cl₄}₂{μ-NH₂(CH₂)_n-η-NH₂}] (n = 3, 6a; 4, 6b; 5, 6c), have been prepared and isolated when these reactions were performed in the absence of a base. All compounds have been characterized by elemental analysis and NMR spectroscopy, and the crystal structures of the complexes [Nb{η⁵-C₅H₄SiMe₂-η-N(CH₂)₂NMe₂}Cl₃] (2c) and [{Nb(η⁵-C₅H₄SiMe₂Cl)Cl₄}(μ-NH₂(CH₂)₄NH₂)] (6b) have been determined by X-ray diffraction methods. The experimental work has been assisted by DFT calculations to determine the role played by the pendant amine group in this kind of process and the cause for the highfield shifted resonances for the cyclopentadienyl ipso-carbon in constrained-geometry complexes.