Synthesis and crystal structure of dimeric dialkylaluminiumµ-dialkylamido compounds

Dialkylaluminium µ-dialkylamido compounds of formula (R 1 2 AlNR 2 2 ) 2 (R 1 = Me, Et, Pr i , Bu i or Bu t ; R 2 = Me, Et, Pr i , Bu i or Ph) were synthesized by alkane or arene elimination from the corresponding adduct of formula R 1 3 Al·NHR 2 2 . The crystal structures of the following dimeric compounds were determined: (Me 2 AlNEt 2 ) 2 , (Me 2 AlNBu i 2 ) 2 , (Et 2 AlNPr i 2 ) 2 , (Pr i 2 AlNMe 2 ) 2 , (Pr i 2 AlNEt 2 ) 2 , (Bu i 2 AlNMe 2 ) 2 , (Bu i 2 AlNEt 2 ) 2 and also the mononuclear compound Et 2 Al(OEt 2 )NPh 2 . 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. R 1 and R 2 respectively, but that loss of a centre of symmetry is dependent only on R 2 . 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 [R 1 AlNR 2 2 ] + . The NMR data show that aromatic solvents shield the R 2 protons causing downfield chemical shifts. Low-pressure (10 -2 Torr) thermal decomposition (500–600 °C) to produce films of aluminium nitride was studied.