Complexes of organoaluminium compounds. Part 11. Nitric oxide complexes of trimethyl-aluminium and -gallium and the crystal and molecular structure of [Me3Al(ONNMeO)AlMe2]

The compound [Me3Al[graphic omitted]IMe2](1), made from the reaction between trimethylaluminium and nitric oxide, crystallises in the triclinic system, with a= 670.6(1), b= 970.3(2), c= 1 020.9(1) pm, α= 82.37 (1), β= 87.13(1)γ= 72.97 (1)°, space group P, and Z= 2. The structure analysis (diffractometer data, 1 214 reflections, R= 0.092) shows that the ONNMeO ligand forms a five-membered chelate ring and that the trimethylaluminium is co-ordinated to the oxygen atom of the nitroso-group. Principal mean molecular parameters are : AL–C 195.3(11), Al–O 189.5(6), N–O 132.2(8), N–N 125.3(9) pm. The position of maximum basicity in the ring at the nitrosyl oxygen is confirmed by ab initio calculations. N.m.r. studies suggest that, in the presence of bases, the complex (1) rearranges to compounds [AlMe(ONNMeO)2](3) and [Al(ONNMeO)3](4) in which the co-ordination number of aluminium is five or six, respectively. The adduct [GaMe2(ONNMeO)](5) has been obtained from trimethylgallium and nitric oxide.