Catalytic polymerization of alkynes with the quadruply bonded octachloroditungsten anion

In this work are described the reactions of the quadruply bonded ditungsten complexes Na4[W2Cl8(THF)x] (1) and [W2Cl4(PMe3)4] (2), which contain the W24+ core and have the σ2π4δ2 electronic configuration, as well as of the mononuclear [WCl4(THF)2] (3) with alkynes R1CCH, R2CCR3 (R1 = Ph (4), nBu, tBu, Me3Si, C10H7 (naphthyl), C12H9 (biphenyl); R2R3Me, R2Me, R3nPr; R2R3Et; R2Ph, R3Me; R2Ph, R3Et; R2R3Ph; R2R3AcO). 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 THF. 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 (Mn < 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 1H 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.

The quadruply bonded halide Na4[W2Cl8(THF)x] (W24+, σ2π4δ2) is an efficient single-component initiator for the high-yield homogeneous or heterogeneous polymerization of monosubstituted alkynes. Internal alkynes are polymerized less effectively with the yield decreasing by increasing the steric requirements of the substrate. The polymerization of phenylacetylene in THF proceeds in a multistage manner. Direct evidence for the metathetical nature of this reaction is also presented.Figure optionsDownload as PowerPoint slide