Polymerization of terminal alkynes with a triply bonded ditungsten halo-complex

In this work are described the reactions of the triply bonded ditungsten face-sharing bioctahedral (fsbo) halides A3[W2(μ-Cl)3Cl6] (A+ = K+ (1), nBu4N+ (2)) and Na[W2(μ-Cl)3Cl4(THF)2]·(THF)3 (3), which contain the (WW)6+ core and have the a′2e′4 electronic configuration, with a range of 1-alkynes (RCCH, R = Ph (PA), C7H7 (o-methylphenyl), C7H4F3 (o-trifluoromethylphenyl), nBu, tBu, 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 1H NMR, and the observation of at least two major active species attributed to the tungsten-carbene propagating polymerization centers.

The triply bonded, triply halo-bridged complex Na[W2(μ-Cl)3Cl4(THF)2]·(THF)3 (W26+, a′2e′4) is an efficient single-component initiator for the high-yield homogeneous or heterogeneous polymerization of monosubstituted alkynes. The bulk of the alkyl substituents does not significantly affect the yield of the reaction. The conditions dictate the microscopic structure of the polymers formed. The polymerization of phenylacetylene (PA) in THF is multimodal involving both polymerization and equilibration/depolymerization steps. Directly obtained evidence by 1H NMR indicate the metathetical nature of the polymerization.Figure optionsDownload as PowerPoint slide