Influence of alkoxy ligands on the Cp–Al bonding mode in [Cp2Al-μ-OR]2 from X-ray crystallographic and 27Al-NMR spectroscopic solution studies

The dicyclopentadienylaluminium alkoxides of general formula [Cp2Al-μ-OR]2 where R=Me, Et, n-Bu, i-Bu, CH2t-Bu, s-Bu, CH2Ph, C6H4-4-t-Bu (1–8) were prepared by reacting CpNa with ROAlCl2 at the molar ratio 2:1, respectively (2–8) or from the reaction of Cp3Al with alcohol (1). The compounds were characterised by multinuclear NMR (1H, 13C, 27Al) method. The molecular structures of compounds 2, 5 and 6 were determined by X-ray crystallography. The Cp–Al bonding mode in dicyclopentadienylaluminium alkoxides regarding the steric demands of alkoxy groups is discussed based on 27Al-NMR chemical shifts and structural data obtained. The meaningful correlation between Cp ring-slippage and 27Al-NMR chemical shifts was observed.