Reactions of AlR3 (R = Me, Et) with H2NCH2CH2NMe2: Synthesis and Characterization of Amido- and Imidoalanes

The reactions of R3Al (R = Me, Et) with N,N-dimethylethylenediamine (DMEDA) in a 1:1 molar ratio produce adducts, R3Al·NH2C2H4NMe2 (1a, R = Me; 1b, R = Et), which upon heating in refluxing toluene result in alkane elimination to afford the chelated monomers (2a, R = Me; 2b, R = Et), respectively. Compounds 2a,b form adducts with 1 equiv of R3Al through the 3-coordinate nitrogen atom to produce (3a, R = Me; 3b, R = Et), which can be alternatively prepared by the reaction of R3Al with DMEDA in a 2:1 molar ratio by alkane elimination at room temperature. Thermolysis of 3a,b at 140 °C in sealed ampules produces a mixture of cis and trans isomers of tetrametallic imidoalanes, (4a, R = Me; 4b, R = Et). Slow recrystallization of the isomeric mixture affords crystals of only the cis isomer for both 4a and 4b, but in solution cis-4a and cis-4b equilibrate with the respective trans isomers. The cis → trans isomerization of 4a has been studied by 1H NMR spectroscopy. The equilibrium has been observed to follow rever...