Experimental and Computational Studies on Quadruply Bonded Dimolybdenum Complexes with Terminal and Bridging Hydride Ligands

Abstract

This contribution focuses on complex [Mo2(H)2(μ‐AdDipp2)2] (1) and tetrahydrofuran and pyridine adducts [Mo2(H)2(μ‐AdDipp2)2(L)2] (1⋅thf and 1⋅py), which contain a trans‐(H)Mo≣Mo(H) core (AdDipp2=HC(NDipp2)2; Dipp=2,6‐iPr2C6H3). Computational studies provide insights into the coordination and electronic characteristics of the central trans‐Mo2H2 unit of 1, with four‐coordinate, fourteen‐electron Mo atoms and ϵ‐agostic interactions with Dipp methyl groups. Small size C‐ and N‐donors give rise to related complexes 1⋅L but only one molecule of P‐donors, for example, PMe3, can bind to 1, causing one of the hydrides to form a three‐centered, two‐electron (3c‐2e) Mo‐H→Mo bond (2⋅PMe3). A DFT analysis of the terminal and bridging hydride coordination to the Mo≣Mo bond is also reported, along with reactivity studies of the Mo−H bonds of these complexes. Reactions investigated include oxidation of 1⋅thf by silver triflimidate, AgNTf2, to afford a monohydride [Mo2(μ‐H)(μ‐NTf2)(μ‐AdDipp2)2] (4), with an O,O’‐bridging triflimidate ligand.

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

“…In this context, we envisioned that quadruply bonded hydride central units [Mo 2 (H) n ] ( n = 1, 2) could be utilized to build the target molecular architectures. As represented in structure A of Figure 1 , such dimolybdenum dihydride units possess strong hydride character 45 and feature Mo–Mo separations of close to 2.10 Å, with Mo–H vectors nearly perpendicular to the Mo–Mo bond. 45 Here, we discuss the synthesis and structure of complexes 3·thf and 4·thf ( Figure 1 ) that contain one and two formally monoanionic, bridging H–Li(thf)–H ligands, respectively, spanning the Mo≣Mo bond.…”

“…As represented in structure A of Figure 1 , such dimolybdenum dihydride units possess strong hydride character 45 and feature Mo–Mo separations of close to 2.10 Å, with Mo–H vectors nearly perpendicular to the Mo–Mo bond. 45 Here, we discuss the synthesis and structure of complexes 3·thf and 4·thf ( Figure 1 ) that contain one and two formally monoanionic, bridging H–Li(thf)–H ligands, respectively, spanning the Mo≣Mo bond. We also study the unexpected formation of a unique, hydrocarbon-soluble, hydride-rich Mo 6 Li 9 H 18 cluster, 5·thf , formally resulting from the trimerization of unobserved monomer [Mo 2 {μ-HLi(thf)H} 3 (μ-Ad Dipp2 )], with the loss of a molecule of tetrahydrofuran.…”

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

“…In all likelihood this is due to steric hindrance, as demostrated recently during studies of the reactivity of complex 1•thf toward classical donor ligands such as pyridines and tertiary phosphines. [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.…”

“…[24] Moreover, the coordination and electronic unsaturation of the electrophilic coordinated E atom will probably make mandatory that robust EÀ X bond coordination of simple hydrides, [25] or alkyls like LiCH 3 , Mg(CH 3 ) 2 or Al(CH 3 ) 3 , be supported by intramolecular electronic interactions with close donor atoms. [6,21] On these grounds, we envisaged that the trans-(X)Mo� � Mo(X) cores of the [Mo 2 (X) 2 (μ-Ad Dipp2 ) 2 ] complexes shown in Figure 1 (X=H, 1; CH 3 , 2; Ad Dipp2 = HC(NDipp) 2 ; Dipp = 2,6-i Pr 2 C 6 H 3 ), [26,27] could act as templates for stabilization of σ-EÀ C and σ-EÀ H interactions. Besides warranting mutual cooperative effects, the Mo(X) moieties of 1 and 2, at a short separation of ca.…”

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

“…Coordination of a second molecule of LiC 6 H 5 did not prove feasible. In all likelihood this is due to steric hindrance, as demostrated recently during studies of the reactivity of complex 1⋅thf toward classical donor ligands such as pyridines and tertiary phosphines [27] …”