Group 13 Lewis acids have long played a leading role as catalysts in organic synthesis, extending from the discovery of AlCl₃-catalysis by Friedel and Crafts in 1877 through the Aufbau-synthesis of unsolvated aluminum alkyls from ethylene by Ziegler in 1952 and culminating in the discovery of poly(methylaluminoxane) (MAO) cocatalysis of olefin polymerization by Sinn and Kaminsky in 1976. In our current work we present how electronic and steric contributions of the ligands attached to the particular Group 13 metal can modulate the resultant Lewis acidity. The inherent Lewis acidity of the Group 13 metal center itself is further dependent upon the extent that its available np_z-orbital might interact with adjacent unshared or pi-electrons of the ligand system. In order to evaluate the effect of such electronic factors on their Lewis acidity, both a series of vicinal or ortho-arylene bidentate Group 13 organoboron and organoaluminum candidate acids, as well as their antiaromatic metallole analogs, have been synthesized by exchange reactions between the corresponding organotin compound and the appropriate metal halide. Their Lewis acidity has been evaluated based upon their efficacy as a cocatalyst with titanocene(IV) methyl chloride or titanocene(IV) dichloride in effecting the polymerization of ethylene. A further comparative study of the cocatalytic activity of methylaluminum dichloride versus the polymeric mixture, poly(methylaluminoxane), with either Cp₂TiE₂ or Cp₂ZrE₂ (E = Cl or Me) has clearly shown that factors other than simple Lewis acidity are operative in the catalytic action of MAO.