TY - JOUR
TI - Catalytic polymerization of alkynes with the quadruply bonded octachloroditungsten anion
AU - Georgios Floros
AU - Nikolaos Saragas
AU - Patrina Paraskevopoulou
AU - Ioannis Choinopoulos
AU - Spyros Koinis
AU - Nikolaos Psaroudakis
AU - Marinos Pitsikalis
AU - Konstantinos Mertis
JO - Journal of Molecular Catalysis A: Chemical
PY - 2008
VL - 289
TODO - 1-2
SP - 76--81
PB - ELSEVIER BV
SN - 1381-1169
TODO - 10.1016/j.molcata.2008.04.012
TODO - polymerization; metathesis; alkynes; ditungsten; quadruple bond
TODO - In this work are described the reactions of the quadruply bonded
ditungsten complexes Na-4[W2Cl8(THF)(x)] (1) and [W2Cl4(PMe3)(4)]
(2), which contain the W(2)4(+) core and have the sigma(2)pi(4)delta(2)
electronic configuration, as well as of the mononuclear [WCl4(THF)(2)]
(3) with alkynes (RC)-C-1  CH, (RC)-C-2  CR3 (R-1 =Ph (4), Bu-n, Bu-t,
Me3Si, (CH7)-H-10 (naphthyl), C12H9 (biphenyl); R-2=R-3=Me, R-2=Me,
R-3=Pr-n; R-2=R-3=Et; R-2=Ph, R-3=Me; R-2=Ph, R-3=Et; R-2=R-3=Ph;
R-2=R-3=ACO). Complex 1 acts as an efficient single-component initiator
for the homogeneous or heterogeneous high-yield polymerization of
monosubstituted alkynes. The reaction is very fast in CH2Cl2 or
heterogeneously and slow in THE The yield is not significantly affected
by the bulk of the alkyl substituents. The reaction is not so efficient
with internal alkynes, and is limited to those bearing the less
sterically demanding substituents. Polymerization of 4 in THF shows that
the reaction comprises three distinct steps. The first is very fast (t=
3 min), with consumption of nearly half of 4 (ca. 42%), producing
Poly(4). The polymer formed is degraded equally fast regenerating 4 (ca.
23%) and oligomeric species (M-n < 1000). Subsequent polymerization is
slower and complete within 8 h. Direct evidence for the metathetical
mechanism of the polymerization was obtained by the in situ examination
of the above reaction by H-1 NMR at various temperatures. In contrast,
complex 2 alone or activated with EtAlCl2 is unreactive towards 4,
whereas 3 produces Poly(4) in small yield (20%) and very broad
polydispersity. (C) 2008 Elsevier B.V. All rights reserved.
ER -