The synthesis of a series of neodymium complexes supported on modified silica is reported. In an initial step the silanol groups were masked by a Lewis acid (BCl3, AlCl3, TiCl4, ZrCl4, SnCl4, SbCl5, HfCl4), and then a soluble arene complex Nd(eta (6)-C6H5Me)(AlCl4)(3) formed in situ was reacted with the modified silica. The supported complexes are active and highly stereospecific for butadiene polymerization; 1,4-cis insertion is superior by 99%. The catalyst based on a treatment of silica with BCl3 is the most efficient.