Cyclopentadienylaluminum donor–acceptor complexes – Molecular and supramolecular structure

Abstract

Lewis acid–base complexes of cyclopentadienylaluminum derivatives Me x Cp 3− x Al ( x = 0–2) and trimethylaluminum with selected aromatic amines (L): dmap = 4-dimethylaminopyridine, py–Me = 4-methylpyridyne, were synthesized and characterized by 1H, 13C, 27Al NMR: Cp 3Al · dmap ( 1), Cp 3Al · py–Me ( 2), MeCp 2Al · dmap ( 3), MeCp 2Al · py–Me ( 4), Me 2CpAl · dmap ( 5), Me 2CpAl · py–Me ( 6), Me 3Al · py–Me ( 7). 1H NMR studies of 3– 6 revealed small amounts of the ligand redistribution products. The crystal structures of 1, 2 and 3 were determined by single X-ray diffraction studies. The compounds 1, 2 and 3 are monomeric with Cp ligands bonded to the aluminum center in η 1(σ), η 1(π) manner. The change of Cp–Al bond character from η 1(π) to η 1(σ) was found to reasonable correlate with the aromaticity of Cp − ligand described by HOMA index. Analysis of close intra- and intermolecular contacts showed presence of CH⋯π interactions leading to the formation of 2-D supramolecular networks. It was found that these interactions impact on the coordination sphere of aluminum and the conformation of Cp ring.