Reactions of $MMe_3$ (M = Al, Ga) with N,N-dimethylethylenediamine (DMEDA, $NH_2C_2H_4NMe_2$) as a bidentate nitrogen donor ligand have been investigated to prepare single-source precursors for AlN and GaN thin films. Combination of $AlMe_3$ and DMEDA in a 1 : 1 ratio at room temperature affords a five-coordinated adduct, $Me_3Al:NH_2C_2H_4NMe_2$ (1). Thermolysis of 1 in refluxing toluene results in a monomeric amidoallane $Me_2AlNHC_2H_4NMe_2$ (2) as colorless liquid. Pyrolysis of 2 at 190℃ in a sealed ampoule yields a tetrameric cubane-type imidoallane $(MeAlNC_2H_4NMe_2)_4$ (3), which is the first example of an internal base stabilized imidoallane. Reactions of $MMe_3$ (M = Al, Ga) with DMEDA in a 2 : 1 ratio produce $(Me_3Al)(Me_2Al)NHC_2H_4NMe_2$ (4) and $Me_3Ga:NH_2C_2H_4NMe_2:GaMe_3$ (6), respectively. Thermolysis of 4 at 140℃ and 6 at 210℃ in sealed ampoules give respective tetrametallic ring compound, $[Me_2M(\mu-NCH_2CH_2N(Me)_2M(Me)_2)]_2$ (M = Al (5), Ga (7)). Compounds 1~7 have been characterized by Mass and NMR spectroscopy.
$^1H$ NMR studies of the dimeric imido complexes 5 and 7 reveal that both compounds undergo a cis - trans isomerization in solution. The equilibrium has been observed to follow reversible first - order kinetics with $\DeltaH^{\circ}= 1.67\pm06kJ/mol$ and $\DeltaS^{\circ}=9.07\pm0.28J/mol \codt K$ for 5, and $\DeltaH^{\circ}=-3.35\pm0.17kJ/mol$ and $\DeltaS^{\circ}=-10.38\pm0.17J/mol \codt K$ for 7. The activation parameters for the conversion of cis-isomer (5a) to trans-isomer (5b) are $\DeltaH_1^{\ddagger}= 125.8\pm9.3kJ/mol$ and $\DeltaS^{\ddagger}_1=89.7\pm1.2J/mol \cod tK$ and for that of 5b to 5a, $\DeltaH_{-1}^{\ddagger}=124.2\pm9.3kJ/mol$ and $\DeltaS_{-1}^{\ddagger}=80.7\pm1.2J/mol\ codt K$. For the conversion of cis-isomer (7a) to trans-isomer (7b) are $\DeltaH_1^{\ddagger}=144.6\pm6.2kJ/mol$ and $\DeltaS_1^{\ddagger}=105.8\pm1.5J/mol\codtK$ and for that of 7b to 7a, $\DeltaH_{-1}^{\ddagger}=147.6\pm6.4kJ/mol$ and $\DeltaS_{-1}^{\ddagger}= 115.4\pm1.5J/mol \codt K$.
Preparation of AlN thin films on the Si(111) single crystal surfaces has been examined with liquid single-precursor 2 using OMCVD method at temperatures between 500℃ and 900℃ and at pressures below $10^{-5}$ Torr. The deposited thin films have been analyzed by X-ray photoelectron spectroscopy and scanning electron microscope.
