Pyridine-amido aluminum catalyst precursors for 1,3-butadiene transition-metal-free stereospecific polymerization

Abstract

Aluminum-based transition-metal-free catalysts for α-olefin polymerization have garnered extensive research interest from academia and industries over the past two decades. However, it has been a long-standing challenge to achieve the polymerization of conjugated dienes by such aluminum-based catalysts. In this work, we developed a series of aluminum-based catalyst precursors for the transition-metal-free polymerization of 1,3-butadiene (Bd), which have the formula [pyridine-2-CMe₂N(Ar)-κ²N,N′]AlMe₂. X-ray diffraction analysis demonstrated the monomeric nature of these aluminum complexes and the bidentate coordination of the ligands. Upon activation of methylaluminoxane (MAO), all the above complexes could initiate the polymerization of 1,3-butadiene at room temperature. By adjusting the ligands, the microstructures of the resultant polymers could be effectively regulated, yielding cis-1,4-polybutadiene or vinyl polybutadiene. Under the optimized polymerization conditions, a catalytic activity approaching 528 g of polymer/[(mol of Al)·h] and a high cis-1,4-selectivity of up to 90.8% were realized.