Bonding Energies and Structural Study of Alkylaluminium

Neutral aluminium alkyls are well known to act as ethylene oligomerization and polymerization catalysts and cocatalysts. On the basis of the full optimization of alkylaluminium compounds with Ganssian 98 program package at the B3LYP/6-31G** level,the selected structures and bonding energies were investigated extensively. The geometries and bonding energies of AlR3 (R=H,CH3,C2H5,C3H7,C4H9)and Al(C2H5)2R'(R'=C2H5,C3H7,C4H9,C5H11,C6H13)were investigated extensively,and we found that,along with the prolongation of carbon chains the terminal C-C bond is shortened gradually until to a constant value of about 0.1532 nm in C4H9; and the bonding energy almost remains constant. The dative bonding of C2H4 to Al(C2H5) 3,whose bonding energy is only 15.30 kJ/mol,is very weak.