Supported σ‐Complexes of Li−C Bonds from Coordination of Monomeric Molecules of LiCH₃, LiCH₂CH₃ and LiC₆H₅ to Mo≣Mo Bonds

Abstract

LiCH₃ and LiCH₂ CH₃ react with the complex [Mo₂ (H)₂ (μ-Ad^Dipp2 )₂ (thf)₂ ] (1⋅thf) with coordination of two molecules of LiCH₂ R (R=H, CH₃ ) and formation of complexes [Mo₂ {μ-HLi(thf)CH₂ R}₂ (Ad^Dipp2 )₂ ], 5⋅LiCH₃ and 5⋅LiCH₂ CH₃ , respectively (Ad^Dipp2 =HC(NDipp)₂ ; Dipp=2,6-ⁱ Pr₂ C₆ H₃ ; thf=C₄ H₈ O). Due to steric hindrance, only one molecule of LiC₆ H₅ adds to 1⋅thf generating the complex [Mo₂ (H){μ-HLi(thf)C₆ H₅ }(μ-Ad^Dipp2 )₂ ], (4⋅LiC₆ H₅ ). Computational studies disclose the existence of five-center six-electron bonding within the H-Mo≣Mo-C-Li metallacycles, with a mostly covalent H-Mo≣Mo-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 ^6,7 Li,¹ H and ^6,7 Li,¹³ C NMR coupling constants found for the three-atom H-Li-C chains. By contrast, the phenyl group in 4⋅LiC₆ H₅ coordinates in an η² fashion to the lithium atom through the ipso and one of the ortho carbon atoms.