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Diverse Reactivity of ECp* (E = Al, Ga) toward Low-Coordinate Transition Metal Amides [TM(N(SiMe3)2)2] (TM = Fe, Co, Zn): Insertion, Cp* Transfer, and Orthometalation

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posted on 03.03.2017, 17:05 by Jana Weßing, Christoph Göbel, Birgit Weber, Christian Gemel, Roland A. Fischer
The reactivity of the carbenoid group 13 metal ligands ECp* (E = Al, Ga) toward low valent transition metal complexes [TM­(btsa)2] (TM = Fe, Co, Zn; btsa = bis­(trimethylsilyl)­amide) was investigated, revealing entirely different reaction patterns for E = Al and Ga. Treatment of [Co­(btsa)2] with AlCp* yields [Cp*Co­(μ-H)­(Al­(κ2-(CH2SiMe2)­NSiMe3)­(btsa))] (1) featuring an unusual heterometallic bicyclic structure that results from the insertion of AlCp* into the TM–N bond with concomitant ligand rearrangement including C−H activation at one amide ligand. For [Fe­(btsa)2], complete ligand exchange gives FeCp*2, irrespective of the employed stoichiometric ratio of the reactants. In contrast, treatment of [TM­(btsa)2] (TM = Fe, Co) with GaCp* forms the 1:1 and 1:2 adducts [(GaCp*)­Co­(btsa)2] (2) and [(GaCp*)2Fe­(btsa)2] (3), respectively. The tendency of AlCp* to undergo Cp* transfer to the TM center appears to be dependent on the nature of the TM center: For [Zn­(btsa)2], no Cp* transfer is observed on reaction with AlCp*; instead, the insertion product [Zn­(Al­(η2-Cp*)­(btsa))2] (4) is formed. In the reaction of [Co­(btsa)2] with the trivalent [Cp*AlH2], transfer of the amide ligands without further ligand rearrangement is observed, leading to [Co­(μ-H)4(Al­(η2-Cp*)­(btsa))2] (5).