Abstract:
In this work are described the reactions of the triply bonded ditungsten
face-sharing bioctahedral (fsbo) halides A(3)[W-2(mu-Cl)(3)Cl-6] (A(+)
= K+ (1), (Bu4N+)-Bu-n (2)) and Na[W-2(mu-Cl)(3)Cl-4(THF)(2)]center
dot(THF)(3) (3), which contain the (W W)(6+) core and have the
a(’2)e(’4) electronic configuration, with a range of 1-alkynes (RC CH,
R = Ph (PA), C7H7 (o-methylphenyl). C7H4F3 (o-trifluoromethylphenyl),
Bu-n, Bu-t, Me3Si, C10H7 (naphthyl)). At ambient temperature complexes 1
and 2 (THF, CH2Cl2) are inactive towards PA, and when activated with
AlCl3 (CH2Cl2) give oligomeric products in low yield, In contrast,
compound 3 acts as a highly efficient uni-component initiator for the
homogeneous or heterogeneous polymerization of the above alkynes
providing polymers with high molecular weight. Small amounts of the
cyclotrimers are also formed. The reaction is very fast in CH2Cl2 or in
bulk and slower in oxygen-coordinating solvents (THF, Et2O). The
conditions dictate the microscopic structure of the polymers formed. The
yield is not significantly affected by the bulk of the alkyl
substituent. The polymerization of PA was studied in more detail. In THF
it is multimodal involving polymerization and equilibration or
degradation steps. Direct evidence in support of the metathetical nature
of the polymerization has been obtained from the in situ examination of
the reaction at Various temperatures ranging from -20 to 20 C by H-1
NMR, and the observation of at least two major active species attributed
to the tungsten-carbene propagating polymerization centers. (C) 2009
Elsevier B.V. All rights reserved.
