Abstract
The title compound, trimeth-yl(tetra-hydro-furan-κO)aluminium(III), [Al(CH3)3(C4H8O)], is an addition product of tri-methyl-aluminium and tetra-hydro-furan (THF). Instead of a dimeric structure, which is very common for these types of compounds, a monomeric mol-ecular structure is observed. The C-Al-C angles in the mol-ecule are very different from the C-Al-C angles found in dimeric mol-ecular structures, leading to a different symmetry around the AlIII atom. The reasons for these differences are discussed.
Highlights
The title compound, trimethyl(tetrahydrofuran-O)aluminium(III), [Al(CH3)3(C4H8O)], is an addition product of trimethylaluminium and tetrahydrofuran (THF)
The C—Al—C angles in the molecule are very different from the C—Al—C angles found in dimeric molecular structures, leading to a different symmetry around the AlIII atom
The monomer of trimethylaluminium can be observed at high temperatures and low pressure with a trigonal-planar symmetry in the gas phase (Almenningen et al, 1971)
Summary
Trimethylaluminium is present as a dimer at room temperature. Analogously, two monomers are connected by two three-center–two-electron bonds bridging both molecules. The dimeric aluminium structure (AFODUU) observed by Sharma et al (2002) shows very short Al—O bonds for the terminal and bridging isopropoxy groups bound to the tetra-coordinated positions [1.799 (3)–1.685 (3) A ], indicating a strong interaction between aluminium and oxygen in these cases These results support the weak interaction between aluminium and oxygen in the title compound, leading to a slight distortion of the trimethylaluminium and a structure between trigonal– planar and tetrahedral symmetry. In comparison with an ideal tetrahedral coordination sphere, there is a smaller angle for the bridging bonds and a larger angle for the terminal bonds (Stammler et al, 2015) These results are supported by further dimeric molecular structures of trimethylaluminium. For the crystal strucutre of Tm(AlMe4), a large C— Al—C angle for the terminal bonds [118.55 (7) or 119.5 (2)] and two smaller angles [104.84 (7), 108.64 (7) or 105.43 (6), 108.86 (7)] were observed
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