Polar‐Group Activated Isospecific Coordination Polymerization of ortho‐Methoxystyrene: Effects of Central Metals and Ligands

Abstract

Stereoselective polymerization of polar vinyl monomers has been a long‐standing challenge because the employed transition‐metal catalysts are easily poisoned by polar groups of monomers. In this contribution, a series of β‐diketiminato rare‐earth metal complexes 1–5 (L1–5Ln(CH2SiMe3)2(THF)n, Ln=Gd–Lu, Y, and Sc) were successfully synthesized. In combination with AliBu3 and [Ph3C][B(C6F5)4], complexes 1 c(Tb)–1 g(Tm) exhibited high activities and excellent isoselectivities for the polymerization of ortho‐methoxystyrene (oMOS), in which, the polar methoxy group of oMOS did not poison but activated the polymerization through σ–π chelation to the active species together with the vinyl group. Moreover, the large Gd‐attached precursor 1 b showed a higher activity, albeit with a slightly decreased isoselectivity. The small Sc‐attached precursor 1 i was completely inert. Meanwhile, the spatial steric arrangement and the coordination mode of the β‐diketiminato ligand could clearly affect and even block oMOS polymerization. This work sheds new light on the coordination polymerization of polar monomers.

Stereoselective Polymerization of an Aromatic Vinyl Monomer to Access Highly Syndiotactic Poly(vinyl alcohol)

“…Recently, rare‐earth metal based catalytic systems have been reported to be extraordinary tolerance toward polar groups, which exhibit high activity and excellent stereo‐selectivity for homo‐ and copolymerizations of polar styrenes. [ 17,18,27–34 ] We report herein the coordination polymerization of BN2VN using a series of half‐sandwich or constrained‐geometry‐configuration (CGC)‐type scandium catalysts ( Figure ) with high activity and distinguished syndioselectivity to give high molecular weight products, which can be transferred to highly syndiotactic poly(vinyl alcohol). The influences of steric hindrance of ligands and polymerization conditions on the catalyst performances as well as structures of the resultant products are investigated.…”

Syndiospecific Polymerization of o-Methoxystyrene and Its Silyloxy or Fluorine-Substituted Derivatives by HNC-Ligated Scandium Catalysts: Synthesis of Ultrahigh-Molecular-Weight Functionalized Polymers

“…62,64 That is to say, the preferential coordination of the Lewis basic heteroatom group of the polar olefin with the Lewis acidic metal center cannot cause the poisoning of rare-earth metal catalysts. Instead, the Lewis basic heteroatom group serves as a neutral donor ligand to reduce both the oxophilicity of the rare-earth metal catalyst and the coordination and activation energies of the double bond with the metal center 48,64 (Scheme 1). However, despite these outstanding developments, all of the known rare-earth metal cation active species [LLnR] + in the coordination polymerization of polar olefins are generated from the half-sandwich or non-metallocene rare-earth metal dialkyl complexes LLnR 2 L' n .…”

“…The coordination (co)­polymerization of polar olefins to prepare high functional polyolefins having superior surface properties, adhesion properties, and compatibility with other types of materials has always been a challenging and high-profile issue in academia and industry. − The most serious difficulty lies in the fact that the high oxyphilic early transition metal catalysts can be easily poisoned by polar olefins because the stronger Lewis basic heteroatom groups of polar olefins have more preferential coordination ability than the weaker Lewis basic double bond to the strong Lewis acidic metal centers. − Subsequently, the low oxyphilic late transition metal catalysts, which are more tolerant of heteroatom functionalities in the monomer and the polymer, have ascended on the history stage and gradually began to open up new areas for the coordination (co)­polymerization of polar olefins such as polar norbornene, acrylates, vinyl ethers, vinyl acetate, vinyl halides, acrylonitrile, CO, etc. − Recently, a significant breakthrough in the coordination (co)­polymerization of polar olefins has been made by the high oxyphilic rare-earth metal catalysts. − Activated by a catalytically equimolar amount of cocatalyst borate and/or an excess of AlR 3 , rare-earth metal alkyl cations [LLnR] + generated from a series of rare-earth metal dialkyl complexes LLnR 2 L' n (Ln is a rare earth metal center, L is a negative monovalent multi-dentate supporting ligand, R is a negative monovalent alkyl ligand, L' n is a neutral ligand like tetrahydrofuran (THF) solvent molecules with a number in the range of 0–2) exhibit high activities and stereoselectivities in the coordination (co)...…”

“…The stereospecific (co)­polymerization mechanisms have been described in detail by Hou, , Cui, − Marks, and Luo , that the presence of redundant empty coordination sites (for the neutral solvent ligand L' n , which are pulled out by AlR 3 ) of high coordination number rare-earth metal cation active species [LLnR] + permits synergic coordination of both a heteroatom group and a double bond of the polar olefin with the metal center or the diminishing oxophilicity of rare earth metal catalysts attributed to the electronic-donating ability of chelating ligands and the preferentially coordinated heteroatom group of the polar olefin make the transition possible from the preferential coordination of the heteroatom group of the polar olefin with the metal center to coordination and insertion of a double bond with the metal center. , That is to say, the preferential coordination of the Lewis basic heteroatom group of the polar olefin with the Lewis acidic metal center cannot cause the poisoning of rare-earth metal catalysts. Instead, the Lewis basic heteroatom group serves as a neutral donor ligand to reduce both the oxophilicity of the rare-earth metal catalyst and the coordination and activation energies of the double bond with the metal center , (Scheme ). However, despite these outstanding developments, all of the known rare-earth metal cation active species [LLnR] + in the coordination polymerization of polar olefins are generated from the half-sandwich or non-metallocene rare-earth metal dialkyl complexes LLnR 2 L' n .…”

β‐Diketiminato Rare‐Earth Metal Complexes: The Influence of Monoatomic Substituents in the N‐aryl Moieties on Structures and Properties

“…Chen's group reported phosphoniomethylidene scandium and lutetium complexes stabilized by β‐diketiminato and their activation toward small molecules , . Cui's group successfully employed β‐diketiminato rare‐earth metal complexes as precursors for cis ‐1,4‐selective polymerization of isoprene and isoselective coordination polymerization of polar heteroatom‐substituted styrene derivatives . Yao and co‐workers exploited a variety of β ‐diketiminate rare‐earth metal complexes .…”