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A Systematic Study of Structure and E−H Bond Activation Chemistry by Sterically Encumbered Germylene Complexes
, Usher Matthew, V. Protchenko Andrey, Campos Jesús, L. Kolychev Eugene, Tirfoin Rémi, Aldridge Simon
Published in Wiley
Volume: 22
Issue: 33
Pages: 11685 - 11698

A series of new germylene compounds has been synthesized offering systematic variation in the σ- and π-capabilities of the α-substituent and differing levels of reactivity towards E−H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn)] (16: ERn=NHDipp, CH(SiMe3)2, P(SiMe3)2, Si(SiMe3)3 or B(NDippCH)2; terphenyl=C6H3Mes2-2,6=ArMes or C6H3Dipp2-2,6=ArDipp; Dipp=C6H3iPr2-2,6, Mes=C6H2Me3-2,4,6), while the related complex [{(Me3Si)2N}Ge{B(NDippCH)2}] (8) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X-ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ-donating boryl or silyl ancillary donors. HOMO–LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)-germylene system [ArMesGe{B(NDippCH)2}] (6-Mes), which features a wide C-Ge-B angle (110.4(1)°) and (albeit relatively weak) ancillary π-acceptor capabilities, has the smallest HOMO–LUMO gap (119 kJ mol−1). These features result in 6-Mes being remarkably reactive, undergoing facile intramolecular C−H activation involving one of the mesityl ortho-methyl groups. The related aryl(silyl)-germylene system, [ArMesGe{Si(SiMe3)3}] (5-Mes) has a marginally wider HOMO–LUMO gap (134 kJ mol−1), rendering it less labile towards decomposition, yet reactive enough to oxidatively cleave H2 and NH3 to give the corresponding dihydride and (amido)hydride. Mixed aryl/alkyl, aryl/amido and aryl/phosphido complexes are unreactive, but amido/boryl complex 8 is competent for the activation of E−H bonds (E=H, B, Si) to give hydrido, boryl and silyl products. The results of these reactivity studies imply that the use of the very strongly σ-donating boryl or silyl substituents is an effective strategy for rendering metallylene complexes competent for E−H bond activation.

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JournalData powered by TypesetEuropean Journal
PublisherData powered by TypesetWiley
Open AccessNo