Synthesis and characterization of aluminum ethyl-(S)-lactate complexes and VT NMR studies of [Bu₂ⁱAl((S)-(-)-μ₂-OC(H)(Me)C(O)OEt))] ₂

The reactions of ethyl-(S)-(-)-lactate with R₃Al in diethyl ether yield the pentacoordinated complexes [R₂Al((S)-(-)-μ₂-OC(H)(Me)C(O)OEt))]₂ (1: R=Me; 2: R=Et; 3: R=Buⁱ). These compounds have been characterized by spectroscopic studies as wells as crystallographic method. These structures show dimeric features containing unusual 5.4.5-fused rings with an Al₂O₂ core and the ester group bonded to Al through the CO. VT NMR studies of compound 3 suggest that the weak (CO)→M dative bond may undergo dissociation in solution, giving rise to the equilibrium with a four-coordinate species among two five-coordinate species at ambient temperature.