Coordination of LiH Molecules to Mo≣Mo Bonds: Experimental and Computational Studies on Mo₂LiH₂, Mo₂Li₂H₄, and Mo₆Li₉H₁₈ Clusters

Abstract

The reactions of LiAlH 4 as the source of LiH with complexes that contain (H)Mo≣Mo and (H)Mo≣Mo(H) cores stabilized by the coordination of bulky Ad Dipp2 ligands result in the respective coordination of one and two molecules of (thf)LiH, with the generation of complexes exhibiting one and two HLi(thf)H ligands extending across the Mo≣Mo bond (Ad Dipp2 = HC(NDipp) 2 ; Dipp = 2,6- i Pr 2 C 6 H 3 ; thf = tetrahydrofuran, C 4 H 8 O). A theoretical study reveals the formation of Mo–H–Li three-center–two-electron bonds, supplemented by the coordination of the Mo≣Mo bond to the Li ion. Attempts to construct a [Mo 2 {HLi(thf)H} 3 (Ad Dipp2 )] molecular architecture led to spontaneous trimerization and the formation of a chiral, hydride-rich Mo 6 Li 9 H 18 supramolecular organization that is robust enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by pyridine or 4-dimethylaminopyridine.

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

“…20 Hz. Few one‐bond 7 Li– 1 H couplings can be found in the literature and those reported group in the 6–15 Hz interval [35,43–45] . Accordingly, the ca.…”

“…This work demonstrates that monomeric molecules of LiCH 3 , LiCH 2 CH 3 and LiC 6 H 5 , can coordinate to Mo≣Mo bonds forming stable molecular H−Mo−Mo−C−Li frameworks, in which the high Lewis acidity of the lithium atom is compensated by a strong electronic interaction with an adjacent, polar Mo δ+ −H δ− bond. The bonding within the five‐member H−Mo−Mo−C−Li rings in the LiCH 3 and LiCH 2 CH 3 complexes is best described as a covalently linked H−Mo≣Mo−C group σ‐bonded to the lithium atom through its Mo−H and Mo−C termini, supplemented by direct electron donation from the Mo≣Mo bond to lithium, mostly through its π and σ components, with a smaller contribution of the δ‐bonding electron pair [35,63] . In the lithium aryl complex 4⋅LiC 6 H 5 , the bonding mechanism is neatly different.…”

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

“…[27] The Lewis base role of the LiÀ C bond toward complex In marked contrast with the formation of the above organolithium adducts by the procedure disclosed in Scheme 1, the reaction of dimethyl complex 2•thf with LiAlH 4 as a source of LiH led, as shown in Scheme 3, to a recently characterized hydride-rich Mo 6 Li 9 H 18 cluster. [35] Formation of LiAd Dipp2 , LiAl(CH 3 )H 3 and LiAl(CH 3 ) 2 H 2 [36] byproducts was inferred by 1 H and 7 Li NMR spectroscopy. The latter compounds are possibly Lewis adducts arising from the AlH 3 /LiCH 3 system.…”

“…[34] In agreement with this assumption, the low-temperature (À 20 °C) reaction of 2•thf with 2 equivalents of LiAlH 4 in tetrahydrofuran, gave initially the Mo 2 Li 2 H 4 cluster {Mo 2 [μ-HLi(thf)H] 2 (μ-Ad Dipp2 ) 2 }, which is known to react with extra quantities of LiAlH 4 to ultimately afford the cited Mo 6 Li 9 H 18 cluster. [35] All new complexes in Scheme 1 are very reactive toward traces of H 2 O and O 2 and their manipulation requires use of Schlenk or glove-box techniques. Under an atmosphere of Ar or N 2 , isolated complexes 4 and 5 exhibit fair solution stability at room temperature.…”

“…Contradicting our expectations, instead of forming the anticipated MoÀ CÀ LiÀ HÀ Mo metallacyclic rings, LiH promoted MoÀ CH 3 to MoÀ H bond metathesis [34] and elimination of LiCH 3 , ultimately generating a hydride-rich Mo 6 Li 9 H 18 cluster, recently prepared by our group by a different procedure. [35]…”