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

Abstract

LiCH3 and LiCH2CH3 react with the complex [Mo2(H)2(μ-AdDipp2)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(AdDipp2)2], 5⋅LiCH3 and 5⋅LiCH2CH3, respectively (AdDipp2=HC(NDipp)2; Dipp=2,6-iPr2C6H3; thf=C4H8O). Due to steric hindrance, only one molecule of LiC6H5 adds to 1⋅thf generating the complex [Mo2(H){μ-HLi(thf)C6H5}(μ-AdDipp2)2], (4⋅LiC6H5). 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 6,7Li,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.