Living Metathesis Polymerization of Several Substituted Acetylenes by MoOCl4–Et3Al–EtOH

Abstract

ABSTRACT:Living polymerization of several substituted acetylenes such as [o-(trimethylsilyl)phenyl]acetylene (o-Me3Si-phenylacetylene), 1-chloro-1-octyne, (o-methylphenyl)acetylene (o-Me-phenylacetylene) was investigated by using a MoOC14-based catalyst, MoOCI 4 -Et 3 Al-EtOH (I: I: 3--4). It was proved that o-Me3Si-phenylacetylene polymerizes in a living fashion with the MoOClcEt 3 Al-EtOH catalyst in the temperature range 0--30oC. The MwiM. was as small as 1.05. The absolute M. values of poly(o-Me 3 Si-phenylacetylene) were determined by vapor pressure osmometry (VPO), and the following relationship was obtained; M. (VPO)= 1.28 x M. (GPC; polystyrene calibration). The activation parameters for the polymerization of o-Me 3 Si-phenylacetylene were determined as 11H* = 73 kJ mol-1 and 11S* = -13 J mol-1 K _,_ MoOClcEt3Al-EtOH induced the living polymerization of l-chloro-1-octyne as well to give a polymer with small polydispersity. Polymerization of o-Mephenylacetylene formed a stereoregular living polymer having an MwiM. of 1.2 and 90% cis structure. Polymerizations of a few other phenylacetylenes having bulky ortho substituents also yielded living polymers, which is a tendency similar to those with previous Mo0Cl4 -based catalysts.KEY WORDS Living Metathesis Polymerization I Molybdenum Catalyst I Substituted Acetylene I Ternary Catalyst I Stereoregularity I Use of transition metal catalysts enables the synthesis of polymers from various monomers such as rx-olefins, cycloolefins and acetylenes, which hardly polymerize in other polymerization processes. 1 In recent years, a variety of living polymerizations have been achieved by using transition-metal catalysts, typical examples of which are living polymerization of rx-olefins 2 -5 and living ringopening metathesis polymerization (ROMP) of cycloolefins. 6 -8 Living polymerization of substituted acetylenes has also been accomplished by use of several transition-metal catalysts including Schrock carbenes, 9 -13 Mo0Cl 4 -based catalysts, 14 -16 and rhodium complexes.17·18 Schrock carbenes induce the living polymerization of rx,w-diynes, 9 · 10 ethynylferrocene, 11 and orthosubstituted phenylacetylenes. 12 · 13 Certain rhodium-based catalysts polymerize phenylacetylene in a living manner to give a stereoregular living polymer. 17 · 18Previously, we found that the Mo0Cl 4 -n-Bu 4 SnEt0Hjtoluene (catalyst/solvent) system effects the living polymerization of various substituted acetylenes such as ortho-substituted phenylacetylenes, 1-chloro-1-alkynes and t-butylacetylene. 14 · 15 Our recent studies on the Mo0Cl4-based catalysts have focused on the availability of cocatalysts. 19 -22 It was consequently found that Et2Zn 19 and n-BuLi 20 work as effective cocatalysts in the MoOCl4-cocatalyst-EtOH system to achieve excellent living polymerization of [o-(trifluoromethyl)phenyl]-acetylene (o-CF 3 -phenylacetylene). In both cases, poly-( o-CF 3 -phenylacetylene) with quite narrow molecular weight distribution (MWD) (M wf Mn < 1.03) is attainable in quantitative yield. Interes...

Compelling mechanistic data and identification of the active species in tungsten-catalyzed alkyne polymerizations: conversion of a trianionic pincer into a new tetraanionic pincer-type ligand

“…Various transition metal-based catalysts capable of substituted acetylene polymerization exist and two types of mechanisms for chain growth have been identied: metathesis and insertion. 24 In the metathesis mechanism, the active species are metal-alkylidenes [25][26][27][28][29][30][31][32][33][34] or -alkylidynes, [35][36][37] in which an alkyne [2 + 2] cycloaddition provides metallacyclobutenes or metallacyclobutadienes, respectively. Retrocycloaddition, followed by additional alkyne monomer units, promotes chain growth.…”