The Nature of the Dimethyl-aluminum (-gallium and -indium) Methylphenylamide Dimers in Solution and the Molecular Structure of (CH3)2 InN (CH3)- (C6H5)2

摘要

The solution properties of ((CH3)2MN(CH3)(C6H5))2 (M=Al,Ga,In) and the crystalline state of the indium derivative were investigated. All compounds exist in solution as mixtures of cis and trans geometrical isomers. The cis isomer is the predominant species for the aluminum and gallium compounds, whereas the trans isomer is more abundant in the case of indium. An X-ray structural study of the indium derivative identified the trans isomer in the solid state. The complex ((CH3)2InN(CH3)(C6H5))2 crystallizes in a centrosymmetric triclinic space group. The In-N (bridging) distances are In-N(1)= 2.280(2)A and In-N(1') = 2.284(2)A, the In...In' distance is 3.363A, and the indium-methyl bond lengths are defined by In-C(1) = 2.156(4)A and In-C(2) = 2.149(4)A. The dimerization and/or isomerization reactions in solution were investigated by H1 NMR spectroscopy by evaluating the effects of solvent and temperature on the cis/trans isomer ratios. All data are consistent with the hypotheses that the aluminum-nitrogen dimer is formed by a concerted pi-cycloaddition reaction but the gallium and indium dimers are formed by a series of metal-nitrogen bond forming reactions. The influence of these proposed dimerization reactions on the potential for polymer formation are discussed.