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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 reversible first-order kinetics with ΔH° = 1.67 ± 0.60 kJ mol-1 and ΔS° = 9.07 ± 2.80 J mol-1 K-1. The activation parameters for the cis → trans conversion are ΔH 1 = 125.8 ± 9.3 kJ mol-1 and ΔS 1 = 89.7 ± 1.2 J mol-1 K-1, and those for the reverse process are ΔH - 1 = 124.2 ± 9.3 kJ mol-1 and ΔS - 1 = 80.7 ± 1.2 J mol-1 K-1. Pyrolysis of 4a,b in the presence of 2 equiv of DMEDA at 190 °C in sealed ampules gives hexameric imidoalanes, (RAlNC2H4NMe2)6 (5a, R = Me; 5b, R = Et), by alkane elimination. Compounds 5a,b can be also prepared by pyrolysis of 2a,b under similar conditions, but in lower yields. The molecular structures of cis-4b and 5b have been determined by single-crystal X-ray diffraction. The molecular geometry of cis-4b involves one four-membered Al2N2 ring and two five-membered AlN2C2 rings of cis conformation, and it has approximate C 2 symmetry with the C 2 axis going through the center of the Al2N2 ring. The hexameric imidoalane 5b consists of a hexagonal prism of the (AlN)6 cage formed by two flat six-membered (AlN)3 rings linked together by six transverse Al−N bonds.

Reactions of Et3SiNH2 with R3Ga in a 1:1 ratio have produced dimeric silylamidogallanes, [R2Ga(μ-NHSiEt3)]2 (1, R = Me, trans:cis = 1.5:1; 2, R = Et, trans:cis = 1.3:1), as a mixture of trans (a) and cis (b) isomers. Purification of 1 by either recrystallization or sublimation gives only trans isomer 1a as colorless crystals. Colorless liquid 2 has been obtained only as a mixture of the two isomers. The trans → cis isomerization of 1 has been studied by 1H NMR spectroscopy. The equilibrium has been observed to follow reversible first-order kinetics with ΔH° = − 0.64 ± 0.03 kJ mol-1 and ΔS° = − 4.4 ± 0.2 J K-1 mol-1. The activation parameters for the trans (1a) → cis (1b) conversion are ΔH 1 ⧧ = 72.4 ± 1.3 kJ mol-1 and ΔS 1 ⧧ = − 38.8 ± 4.5 J K-1 mol-1, and those for the reverse process are ΔH - 1 ⧧ = 73.0 ± 0.4 kJ mol-1 and ΔS - 1 ⧧ = − 34.4 ± 1.7 J K-1 mol-1. The isomerization is markedly accelerated in the presence of Lewis bases. A crossover experiment indicates that the isomer interconversion is a unimolecular process. The thermodynamic and kinetic data have been explained based on the solvent effect and the silyl substituent effect on the nitrogen atom. The molecular structure of 1a has been determined by a single-crystal X-ray diffraction study. The molecular geometry of 1a consists of a centrosymmetric and dimeric unit with two bridging (triethylsilyl)amido groups and two terminal methyl groups bound to each gallium atom. The two silyl groups are trans to each other with respect to the planar (Ga−N)2 ring framework. The coordination geometry of both gallium and nitrogen atoms is distorted tetrahedral.