Synthesis and crystal structure of dimeric dialkylaluminium µ-dialkylamido compounds

Abstract

Dialkylaluminium µ-dialkylamido compounds of formula (R¹₂AlNR²₂)₂ (R¹ = Me, Et, Prⁱ, Buⁱ or Bu^t; R² = Me, Et, Prⁱ, Buⁱ or Ph) were synthesized by alkane or arene elimination from the corresponding adduct of formula R¹₃Al·NHR²₂. The crystal structures of the following dimeric compounds were determined: (Me₂AlNEt₂)₂, (Me₂AlNBuⁱ₂)₂, (Et₂AlNPrⁱ₂)₂, (Prⁱ₂AlNMe₂)₂, (Prⁱ₂AlNEt₂)₂, (Buⁱ₂AlNMe₂)₂, (Buⁱ₂AlNEt₂)₂ and also the mononuclear compound Et₂Al(OEt₂)NPh₂. The general trends identified in these structures suggest that the environments around aluminium and nitrogen are affected primarily by their closest alkyl groups, i.e. R¹ and R² respectively, but that loss of a centre of symmetry is dependent only on R². Infrared data can also show the presence of a molecular centre of symmetry. Mass spectroscopic data suggest that dimers are present in the gas phase but they are partially dissociated into monomers which in turn fragment into the more stable species [R¹AlNR²₂]⁺. The NMR data show that aromatic solvents shield the R² protons causing downfield chemical shifts. Low-pressure (10^-2 Torr) thermal decomposition (500–600 °C) to produce films of aluminium nitride was studied.

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