Synthesis of amidogallanes, $(R_2GaNR'_2)_n$ (n = 1-3), has been of considerable current interest due to their potential as single-source precursors for the preparation of gallium nitride (GaN) thin films, employing organometallic chemical vapor deposition (OMCVD). $[Me_2GaNH^tBu]_2$(1), $[Me_2GaNH_2]_3$(2), $[Et_2GaNH^tBu]_2$(3) and $[Et_2GaNH_2]_2$(4) were synthesized. Structures of 1,2,3 and 4 were characterized by NMR, IR and Mass spectroscopy. $^1H$ NMR study shows that the dimeric amido complex undergoes a cis-trans isomerization (1a → 1b) in solution. The equilibrium has been observed to follow reversible first-order kinetics with $ΔH^0$=3.12±0.04 kJ/mol and $ΔS^0$=4.56±0.06 J/K·mol. The activation parameters for the conversion 1a 1b are $ΔH_1$=120.8±7.4 kJ/mol and $ΔS_1$=41.4±2.6 J/K·mol and for the reverse reaction 1b → 1a are $ΔH_{-1}$=117.8±7.9 kJ/mol and $ΔS_{-1}$=37.3±2.5 J/K. mol. The isomerization is markedly accelerated in the presence of pyridine. A crossover experiment indicates that the isomer interconversion is a unimolecular process. On the basis of these data, a possible pathway for the isomerization is proposed. The molecular structure of la has been determined by a single-crystal X-ray diffraction study. The molecular geometry of la consists of a centrosymmeric and dimeric unit with two bridging amido goups and two terminal methyl groups bound to each gallium atom. The two NtBu groups are trans to each other with respect to the $(Ga-N)_2$ ring. The coordination geometry of both the gallium and nitrogen atoms is distorted tetrahedral.
Preparation of GaN thin films has been deposited on the Si(100) single crystal surface for 1 and on the Ni single crystal surface for 4. The optimum temperatures for the formation of GaN thin films were found to be about 550℃ for 1 and about 500℃ for 4. The deposited films were analyzed by using X-ray photoelectron spectroscopy and scanning electron microscopy. The decomposition mechanism of amidogallanes was proposed.
