Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH 3 , LiCH 2 CH 3 and LiC 6 H 5 to Mo≣Mo Bonds.

LiCH 3 and LiCH 2 CH 3 react with the complex [Mo 2 (H) 2 (μ-Ad Dipp2 ) 2 (thf) 2 ] (1⋅thf) with coordination of two molecules of LiCH 2 R (R=H, CH 3 ) and formation of complexes [Mo 2 {μ-HLi(thf)CH 2 R} 2 (Ad Dipp2 ) 2 ], 5⋅LiCH 3 and 5⋅LiCH 2 CH 3 , respectively (Ad Dipp2 =HC(NDipp) 2 ; Dipp=2,6- i Pr 2 C 6 H 3 ; thf=C 4 H 8 O). Due to steric hindrance, only one molecule of LiC 6 H 5 adds to 1⋅thf generating the complex [Mo 2 (H){μ-HLi(thf)C 6 H 5 }(μ-Ad Dipp2 ) 2 ], (4⋅LiC 6 H 5 ). 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⋅LiC 6 H 5 coordinates in an η 2 fashion to the lithium atom through the ipso and one of the ortho carbon atoms.