d⁰/fⁿ-Mediated Ring-Opening Ziegler Polymerization (ROZP) and Copolymerization with Mono- and Disubstituted Methylenecyclopropanes. Diverse Mechanisms and a New Chain-Capping Termination Process

Abstract

The mono- and disubstituted methylenecyclopropane derivatives 2-phenyl-1-methylenecyclopropane (A) and 7-methylenebicyclo[4.1.0]heptane (B) have been successfully implemented in ring-opening Ziegler polymerization. Homogeneous ethylene + 2-phenyl-1-methylenecyclopropane (A) random copolymerizations are mediated efficiently by the single-site catalysts Cp*2ZrMe+B(C6F5)4 -, [Cp*2LuH]2, [Cp*2SmH]2, and [Cp*2YH]2 (Cp* = C5Me5) to produce a copolymer (C) with A enchained in a ring-opened fashion. Single-site coordinative polymerization of 7-methylenebicyclo[4.1.0]heptane (B) proceeds via either ring-opened or ring-unopened pathways. In the presence of Cp*2ZrMe+ MeB(C6F5)3 - at 0 °C, B undergoes polymerization to afford the insoluble, ring-unopened homopolymer D, which was characterized by CPMAS NMR, DSC, elemental analysis, FTIR, TGA, and XRD. The melting point of polymer D lies above its decomposition temperature (>300 °C). Random copolymerizations of B and ethylene mediated by Cp*2ZrMe+MeB(C6F5)3 - at room temperature result in polymer E, a polyethylene capped by a ring-opened B fragment. The formation of B-capped polymer E is a consequence of a new chain transfer mechanism, as evidenced by a linear relationship between M n and [B]-1. The rate constant for insertion of ethylene is ∼25× greater than the rate constant for insertion of monomer B into the metal−alkyl bond. Random copolymers (F) of ring-opened B and ethylene are produced when the catalysts Me2Si(Me4C5)(tBuN)ZrMe2, Me2Si(Me4C5)(tBuN)TiMe2 (activated by either (C6H5)3C+ B(C6F5)4 - or B(C6F5)3), and [Cp*2LuH]2 are employed.

β-Alkyl Elimination: Fundamental Principles and Some Applications

“…In contrast to the previous examples, metallocene catalysts 25 – 27 and 152 – 159 do not polymerize 2-phenyl-1-methylenecyclopropane (Scheme ). However, catalysts 26 , 155 , 156 , and [Cp* 2 YH] 2 ( 160 ) are capable of copolymerizing 2-phenyl-1-methylenecyclopropane and ethylene . The copolymerization results in two distinct β-elimination sequences, where the C–C­(Ph) bond or the C–C­(H) 2 bond is cleaved.…”

Substituted Ring‐Fused Yttrium Derivatives – X‐ray Crystal Structures of [(L′YCl2·THF)2LiCl·2THF] and [{L′YCl(OH)}6·2THF] (L′ = 2‐Phenyl‐4,5,6,7,8‐hexahydroazulenyl)

“…Treatment of lithium 2-phenyl-1,4,5,6,7,8-hexahydroazulenyl (LЈ, 9) [9b] Crystals suitable for X-ray diffractometry studies were obtained only in the case of complex 11. While attempts to protect the crystals with Fomblin failed, the use of anhy-drous Nujol allowed X-ray data collection at 150 K; this confirmed the analytical and NMR spectroscopic data, which correspond to a complex of formula [(LЈYCl 2 · THF) 2 LiCl·2THF] (LЈ = C7CpPh; Figure 1). Figure 1.…”

“…The lithium salts (C6CpMe)Li (1; HL = 2-methyl-4,5,6,7-tetrahydro-1H-indene), (C7CpMe)Li (2; HL = 2-methyl-1,4,5,6,7,8-hexahydroazulene, and (C8CpMe)Li (3; HL = 2-methyl-4,5,6,7,8,9-hexahydro-1H-cyclopenta [8]annulene, prepared according to the literature procedures, [9a] were treated with YCl 3 in a 2:1 molar ratio to afford the corresponding complexes [L 2 YCl] 2 with L = C6CpMe (4), C7CpMe (5), and C8CpMe (6), and in a 1:1 ratio to give the complexes [(LYCl 2 ·THF) 2 LiCl·2THF] with L = C7CpMe (7) and C8CpMe (8); see Scheme 1. Scheme 1.…”

“…It is known [2] that organolanthanide complexes often do not require a co-catalyst or an activator to show high activity, but they must be previously converted into the corresponding sterically demanding alkyl derivatives [(trimethylsilyl)methyl or bis(trimethylsilyl)-methyl], to prevent β-alkyl elimination, and as intermediates to the more unstable, but much more active, hydrides.…”

“…[1] Besides their activity as catalysts and reagents for a number of reactions, [2] they are also reckoned to be excellent models [3] and very active catalysts for Ziegler-Natta polymerizations of olefins, often without the aid of activators or co-catalysts.…”