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?

Chemical Science Pub Date: 2012-12-03 DOI: 10.1039/C2SC21750C

Abstract

Complex [tBuOCO]W[triple bond, length as m-dash]C(tBu)(THF)2 (1) {where tBuOCO = [2,6-(tBuC6H3O)2C6H3]3?, THF = tetrahydrofuran} polymerizes acetylenes (R-phenylacetylene (R = H, p-OMe, p-F, 3,5-diCF3), 1-decyne, 3,3-dimethyl-1-butyne, and trimethylsilylacetylene) to form π-conjugating polymers. Upon treating 1 with 2 equiv. of phenylacetylene in toluene-d8 at ?35 °C, two isolable products form. These two products are [O2C(tBuC[double bond, length as m-dash])W(η2-HC[triple bond, length as m-dash]CPh)] (2-tttBu) and [O2C(PhC[double bond, length as m-dash])W(η2-HC[triple bond, length as m-dash]CtBu)] (2-Ph) {where OC(tBuC[double bond, length as m-dash])O = [2,6-(tBuC6H3O)2C6H3(tBuC[double bond, length as m-dash])]4?, OC(PhC[double bond, length as m-dash])O = [2,6-(tBuC6H3O)2C6H3(PhC[double bond, length as m-dash])]4?} and derived from an apparent reductive alkylidyne migratory insertion into a metal–arene bond. Complexes 2-tttBu and 2-Ph polymerize acetylene and a wide variety of monosubstituted acetylenes including phenylacetylene derivatives, 1-decyne, 3,3-dimethyl-1-butyne and trimethylsilylacetylene. With a substrate to catalyst loading ratio of 25?000?:?1, complex 2-tttBu polymerizes phenylacetylene with a turnover number (TON) of 17?233. Additionally, 2-tttBu polymerizes phenylacetylene and 1-decyne with catalytic activities up to 5.64 × 106 gPPA mol?1 h?1 and 7.98 × 106 gPA mol?1 h?1, respectively. 2-tttBu also polymerizes the disubstituted acetylene, 1-phenyl-1-propyne. NMR spectroscopic and single crystal X-ray structural studies provide compelling evidence for polymer chain growth via an insertion ring-expansion mechanism.

Graphical abstract: 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
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