Butadiene polymerization with lanthanide catalysts: activity and X-ray diffraction study of neodymium bromide complexes with basic ligands

This paper reports on the study of five neodymium bromide complexes of general formula NdBr3·nL prepared according to the scheme NdBr3·6H2O + 6HC(OCH3)3 → NdBr3·nCH3OH + 6HCO(OCH3) + (12 - n)CH3OH, followed by ligand exchange, leading to neodymium tribromide complexes NdBr3·nL with nL = 4iPrOH (I), 4THF (II), 4Py (III), 2THF (IV) and 2iPrOH (V) where iPr = isopropyl, THF = tetrahydrofuran and Py = pyridine. The catalytic activity of all the above complexes in the polymerization of butadiene is very high and it increases from I to III. The diffraction study of I and II shows that both molecules are monomeric (coordination number 7), indicates that the nature of the NdBr bonds is influenced by ligand substitution, and reveals that the covalent contribution is more important in II than in I. The correlation of these findings with the results obtained from the study on the activity is discussed