Synthesis and structural characterisation of primary amine adducts of gallane, RH2N center dot GaH3, and of their decomposition products, [RHNGaH2]n (R = Me, n=3; R = Bu-t, n=2)

Primary amine - gallane adducts, RH2N center dot GaH3 [R = Me ( 1) and tBu ( 2)], have been isolated for the first time from the reaction of [RNH3] Cl with LiGaH4 in Et2O solution at ca. 273 K and characterised by their vibrational and H-1 NMR spectra. The structures of single crystals, grown at low temperatures and determined by X-ray diffraction, reveal pseudo-polymeric arrays of RH2N center dot GaH3 molecules with Ga - N distances of 2.0424( 18) and 2.058( 5) angstrom for 1 and 2, respectively. The adducts decompose at or near ambient temperatures with the elimination of H-2 and formation of the corresponding monoalkylamido derivative [RHNGaH2](n). The crystal structures of these at 150 K consist of either [MeHNGaH2](3) molecules with a 'skew-boat' conformation for the cyclic Ga3N3 skeleton ( 3) or [(BuHNGaH2)-Bu-t](2) molecules with a four-membered Ga2N2 core ( 4), with Ga - N distances averaging 1.986( 8) and 1.991( 3) angstrom for 3 and 4, respectively. The crystalline solids 1, 3 and 4 feature intermolecular N - H center dot center dot center dot H - Ga interactions with H center dot center dot center dot H distances estimated to fall in the range 2.1 - 2.3 angstrom. The significance of these is discussed.