Balance of the steric hindrance and solubility of alkoxy ligands for ultrahigh-activity molybdenum-based butadiene coordination polymerization

Abstract

Molybdenum-based (Mo-based) polybutadiene catalysts have stable microstructure orientation and are less affected by common adjustment methods. This property of maintaining itself when external conditions change is called robustness, which is a very valuable feature in industry. However, it is difficult for them to uniformly disperse in organic solvents, which makes Mo-based butadiene catalysts prefer long-chain ligands. In this work, a series of Mo-based catalysts with a low-steric-hindrance alkoxy group as the ligand were synthesized, and the number of ligands was changed to facilitate their solubility. When this type of catalyst was used for coordination polymerization of 1,3-butadiene, the activity significantly improved. Compared with the reported Mo-based catalytic systems using phosphates as ligands, the system we designed ([Cl₂(OCH₃)₂Mo(μ₂-OCH₃)₂Mo(OCH₃)₂Cl₂] as the catalyst precursor) achieved a record high catalytic activity, as high as 6.1 × 10⁵ g mol⁻¹ of Mo, while ensuring that the vinyl content of the product was greater than 80%. The change in the number of alkoxy ligands on the central metal could effectively balance the relationship between the steric hindrance of alkoxy ligands and the solubility of Mo-based catalysts, which was beneficial for improving the catalytic activity in olefin polymerization.