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.