Reaction of Al(tBu)3 with [R2Al{µ-O(CH2)nNMe2}]2: dependence on the extent of intra-molecular Al· · ·N coordination

Abstract

Reaction of Al(^tBu)₃ with (^tBu)₃Al[O(H)CH₂CH₂CH₂NMe₂] yielded the Lewis acid–base complex [(^tBu)₂Al{µ-OCH₂CH₂CH₂N(Me)₂Al(^tBu)₃}]₂ 1. Compound 1 is also formed directly when 2 equivalents of Al(^tBu)₃ reacts with 1 equivalent of [(^tBu)₂Al(µ-OCH₂CH₂CH₂NMe₂)]₂. In contrast, the reaction of 2 equivalents of Al(^tBu)₃ with 1 equivalent of [Me₂Al(µ-OCH₂CH₂NMe₂)]₂ yielded Me₂Al(µ-OCH₂CH₂NMe₂)Al(^tBu)₃ 2. The molecular structure of compound 2 shows the AlMe₂ moiety chelate bound to the anionic bidentate ligand, while the Al(^tBu)₃ unit is bonded to the anionic terminus of the ligand. The formation of compound 1 is proposed to occur via the tert-butyl analog of compound 2, i.e., (^tBu)₂Al(µ-OCH₂CH₂CH₂NMe₂)Al(^tBu)₃, which is unstable due to significant ^tBu· · ·^tBu inter-ligand interactions. The implications of the differences in products is discussed with respect to the extent of intra-molecular Al· · ·N coordination in compounds of the general formula [R₂Al{µ-O(CH₂)_nNMe₂}]₂.