Terminally Dimetalated Tetramethylethylenediamine (TMEDA) Compounds

Terminally dilithiated tetramethylethylenediamine (TMEDA), LiCH2N(Me)CH2CH2N(Me)CH2Li (1), was prepared by transmetalation from Me3SnCH2N(Me)CH2CH2N(Me)CH2SnMe3 and
n-BuLi. It was isolated as a highly air-sensitive white powder and was characterized by
elemental analysis and by further transmetalation reactions. Compound 1 was used as a
difunctional aminomethylating agent and reacted with R2MCl (R = Me, t-Bu; M = Al, Ga,
In) to give the selective formation of 1,2,2,4,5,5-hexamethyl-1,4-diaza-2,5-dimetallabicyclo[2.2.2]octane (M = Al (2), Ga (3), In (4)) and 2,2,5,5-tetra-tert-butyl-1,4-dimethyl-1,4-diaza-2,5-dimetallabicyclo[2.2.2]octane (M = Al (5), Ga (6)) by simultaneous formation
of two metal−carbon and two dative metal−nitrogen bonds accompanied by two ring closures.
Compounds 2−6 were characterized by elemental analyses, by NMR spectroscopy (1H, 13C,
27Al), and by crystal structure determinations. The 1,4-diazabicyclo[2.2.2]octane-like structure
is favored over potential isomers containing three-membered rings and over polymeric
aggregation. Despite the high steric demand of the tert-butyl groups, this conformation
persists even in the case of 5 and 6.