Complexes of organoaluminium compounds. Part 13. Preparation and nuclear magnetic resonance spectra of the arylamido-compounds AlMe2(NHR′)(R′= Ph, C6H4Me-o, C6H4Me-p, C6H3Me2-2,6) and the imido-compounds AlMe(NR′). Crystal and molecular structures of [{AlMe2(NHC6H4Me-o)}2] and [{AlMe(NPh)}6]

Abstract

The compounds [{AlMe₂(NHR′)}_m](1)[R′= Ph (1a), C₆H₄Me-o(1b), C₆H₄Me-p(1c), C₆H₃Me₂-2,6 (1d)] have been isolated. An X-ray study has shown that compound (1b) crystallises as centrosymmetrical trans dimers with the aromatic rings almost perpendicular to the (AlN)₂ plane. The solid compound (1d) is also obtained as a trans dimer but full structural details have not been determined. In solution, however, all four compounds appear to exist as mixtures of two isomers which are probably trans dimers and trans trimers. On heating the amido-compounds (1) give methane and the imido-compounds [{AlMe(NR′)}_n](2a)–(2d); there is no evidence for formation of mixed amido–imido-compounds. The compound [{AlMe(NPh)}₆](2a) has been shown by an X-ray study to have a cage structure with S₆ symmetry in the solid state, and the hexameric structure in the gas phase is confirmed by mass spectrometry. The o-tolyl derivative (2b) seems to give tetrameric molecules [{AlMe(NC₆H₄Me-2)}₄] and there is evidence that the p-tolyl compound may form a mixture of tetramers and hexamers. The compound [{AlMe₂(NHPrⁿ)}₃] appears from n.m.r. spectra to have the cis configuration in benzene, and [{AlMe₂(NHBu^t)}₂] the trans configuration. There is no evidence for mixtures of isomers. The thermal decomposition of [{AlMe₂(NHPrⁱ)}₂] appears to be catalysed by amines.