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Synthesis, Characterization, and Reactivity of Niobium and Tantalum Complexes Bearing Metal−Nitrogen Bonds. X-ray Molecular Structure of [Nb(C5H4SiMe3){NH(CH2)2-η-NH2}Cl3] and the Novel Tetranuclear Niobium Oxo Derivative [{Nb(C5H4SiMe3)Cl(μ2-O)}4(Cl)23-O)]

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journal contribution
posted on 03.04.2020, 15:14 authored by M. Carmen Maestre, Cristina Paniagua, Eberhardt Herdtweck, Marta E. G. Mosquera, Gerardo Jiménez, Tomás Cuenca
The reaction of the cyclopentadienyl-silyl-amido titanium compound [Ti{η5-C5H4SiMe2-η-N(CH2)2-η-NH2}Cl2] with group 5 metal monocyclopentadienyl complexes [MCpRCl4] (M = Nb, Ta; CpR = C5H4SiMe3 (Cp‘), C5Me5 (Cp*)) afforded the heterobimetallic complexes [TiCl25-C5H4SiMe2-η-N(CH2)2-κ-NH2}MCpRCl4] (M = Nb, CpR = Cp‘, 2a; Cp*, 2b; M = Ta, CpR = Cp‘, 3a; Cp = Cp*, 3b). Compounds 2 evolve at room temperature to give a three-component mixture, the chlorosilyl-substituted cyclopentadienyl titanium compound [Ti(η5-C5H4SiMe2Cl)Cl3], the corresponding mononuclear amido-amino, [NbCpR{NH(CH2)2-η-NH2}Cl3] (CpR = Cp‘, 4a; Cp*, 4b), and the dinuclear imido niobium complexes [{NbCpRCl2}2(μ-N(CH2)2-η-N)] (CpR = Cp‘, 5a; Cp*, 5b). In contrast, the analogue tantalum complexes thermally degraded, when CpR = Cp‘ at normal temperature, whereas when CpR = Cp* at temperatures higher than 50 °C, they gave a unique tantalum complex, the corresponding mononuclear amido-amino derivative [TaCpR{NH(CH2)2-η-NH2}Cl3] (CpR = Cp‘, 6a; Cp*, 6b). Alternatively, these group 5 complexes were prepared by direct reaction of the monocyclopentadienyl derivatives with the corresponding organic diamine, in the appropriate proportion and reaction conditions. Tantalum amino adducts were observed as intermediate species in the course of such reactions, and even the dinuclear derivative [{TaCp*Cl4}2(μ-NH2(CH2)2NH2)] (8) could be isolated. Hydrolysis of the dinuclear imido complex 5a yielded the tricyclic tetranuclear niobium oxo derivative [{NbCp‘Cl(μ2-O)}4(Cl)23-O)] (9), which displays an asymmetrical structure as a consequence of the triply connected oxygen site. These compounds were characterized by elemental analysis and NMR spectroscopy, and the crystal structures of 4a and 9 were determined by X-ray diffraction methods.

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