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Supported σ-Complexes of Li‒C Bonds from Coordination of Monomeric Molecules of LiCH3, LiCH2CH3 and LiC6H5 to MoMo Bonds

IIQ

Marina Pérez Jiménez, Jesús Campos, Jesús Jover, Santiago Álvarez, Ernesto Carmona Angew. Chem. Int. Ed. 2021, Vol. 61, e2021 16009

LiCH₃ and LiCH₂CH₃ react with complex [Mo₂(H)2(μ-Ad^Dipp2)₂(thf)₂] (1 thf) with coordination of two molecules of LiCH₂R (R=H,CH₃) and formation of complexes [Mo₂{μ-HLi(thf)CH₂R}₂(Ad^Dipp2)₂], 5 LiCH₃ and 5 LiCH₂CH₃ , respectively (Ad^Dipp2=HC(NDipp)₂; Dipp=2,6-iPr₂C₆H₃ ; thf=C₄H₈O). Due to steric hindrance, only one molecule of LiC₆H₅ adds to 1 thf generating complex [Mo₂(H){μ-HLi(thf)C₆H₅}(μ-Ad^Dipp2)₂], (4 LiC₆H₅). Computational studies disclose the existence of five-center six-electron bonding within the H‒MoMo‒C‒Li metallacycles, with a mostly covalent H‒MoMo‒C group and predominantly ionic Li‒C and Li‒H interactions. However, the latter bonds exhibit non-negligible covalency, as indicated by X-ray, computational data and the large one-bond 6,7Li, 1H and 6,7Li, 13C NMR coupling constants found for the three-atom H‒Li‒C chains. By contrast, the phenyl group in 4 LiC₆H₅ coordinates in an η² fashion to the lithium atom through the ipso and one of the ortho carbon atoms.

https://doi.org/10.1002/anie.202116009

 

Marina Pérez