Lewis base complexes of AlH3: structural determination of monomeric and polymeric adducts by X-ray crystallography and DFT calculations

Abstract

The AlH3 adducts of TMEDA (Me2NCH2CH2NMe2), DIOX (O(CH2CH2)2O), TEA (Et3N), BDMA (PhNMe2), and TMPDA (Me2NCH2CH2CH2NMe2) have each been characterised by single-crystal X-ray diffraction at low temperature, by (1)H, (14)N and (27)Al NMR and FT-Raman and FT-IR spectroscopy, and by DFT calculations and elemental analysis. Hence, AlH3·TMEDA and AlH3·DIOX are both shown to adopt a polymeric structure, with the bidentate ligand bridging two Al centres, each of which adopts a trigonal bipyramidal (TBP) arrangement with equatorial hydride moieties. The 1 : 2 adduct AlH3·2BDMA is monomeric but the geometry at the Al centre resembles closely that of the polymeric TMEDA and DIOX complexes. AlH3·TEA alone adopts a monomeric structure in which the Al centre is tetrahedrally coordinated by three hydride and one amine ligand. The Al-L bond distance of 2.0240(17) Å for AlH3·TEA is the shortest of all the complexes in this study, and AlH3·TEA also possesses the shortest Al-H bonds. AlH3·DIOX has the shortest Al-L bond distance of the polymeric species (2.107(14) Å) on account of the higher electronegativity of the oxygen donor. The structure of AlH3·TMEDA was determined at low temperature (monoclinic space group P2(1)/c), and salient features are compared to the previous room temperature study, for which a highly disordered orthorhombic space group (P2(1)2(1)2(1)) was reported. The polymeric structures appear to be stabilised by a number of intermolecular interactions and unconventional hydrogen bonds; these are most pronounced for AlH3·DIOX, whose chains are connected by highly directional C-H···H-Al bonding with an H···H distance of 2.32(6) Å.

Low-Temperature Deposition of Highly Conductive Aluminum Metal Films on Flexible Substrates Using Liquid Alane MOD Precursors

“…13 C NMR (126 MHz, C 6 D 6 ): δ 48.21 (N- C H 2 ), 9.05 (CH 2 C H 3 ). NMR data are in agreement with the literature …”

Reactivity of NHC Alane Adducts towards N‐Heterocyclic Carbenes and Cyclic (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al−H Bond Activation

“…These adducts are in some cases also accessible through the direct reaction of LiAlH 4 and the ligand (or the ligand salt) with salt elimination. A third important method is the substitution of the trimethylamine ligand of the adduct (NMe 3 ) ⋅ AlH 3 –,–. Depending on the basicity and steric demand of the ligand used, alane adducts stabilized by one or two bases (two‐electron donor ligands) may form .…”

“…A third important method is the substitution of the trimethylamine ligand of the adduct (NMe 3 ) ⋅ AlH 3 –,–. Depending on the basicity and steric demand of the ligand used, alane adducts stabilized by one or two bases (two‐electron donor ligands) may form . Known examples show that NHC‐stabilized alanes have been synthesized so far mainly by salt elimination following the reaction of NHCs with lithium aluminum hydride or by base substitution of (NMe 3 ) ⋅ AlH 3 .…”

Molecular Main Group Metal Hydrides

“…The combination of alcohols (or thiols) with “AlH 3 ” sources or [AlH 4 ] − yields neutral or anionic O-donor substituted aluminum hydrides, respectively. Along these lines, a number of new aluminum hydrides supported by alkoxy, aryloxy, siloxy and thiolate substituents have been reported. − A notable exception exhibiting a unique molecular structure was reported by Roesky in 2004 . Rather than using an organic alcohol, the aluminum hydroxide [( Dipp Nacnac)­Al­(Me)­OH] was combined with two equivalents of Me 3 N·AlH 3 , yielding the molecular aluminoxane [{( Dipp Nacnac)­Al­(Me)­O} 2 (AlH 2 ) 2 ] ( 572 ) (eq 67 ); the corresponding dihydrido-gallium analogue 573 was also prepared. …”