Study of the Reaction Products of TaCl 5 with Acetylene in Benzene–a Catalyst for Alkyne Cyclotrimerization

— Products of reaction between TaCl 5 and C 2 H 2 in benzene, with the composition TaCl 3.7 C 15 H 22 —heterogeneous catalysts for cyclotrimerization of alkynes—have been studied using scanning electron microscopy, IR spectroscopy, and X-ray photoelectron spectroscopy (XPS). The catalysts consist of spherical particles with an average diameter of 70 nm. According to the XPS results, the elemental composition of their surface is TaCl 1.80 C 28 O 3 . The tantalum 4 f 7/2 and 5 p 3/2 binding energies ( E b ) obtained, 26.3 and 37.2 eV, indicate that the oxidation state of tantalum on the surface of the material is 5+. After Ar + ion etching, we observe, in addition to Ta 5+ , 4 f 7/2 and 5 p 3/2 lines at E b = 23.8 and 34.6 eV, respectively, which demonstrates that the oxidation state of tantalum in the active catalyst is 3+. The Cl 2 p line has the form of two overlapping doublets with binding energies of 198.7 and 200.1 eV, due to the presence of bridging and terminal chlorine atoms in the catalytically active complex. The binding energy E b (C 1 s ) = 284.2 eV corresponds to cyclic unsaturated hydrocarbons with conjugated bonds of the hydrocarbon matrix. The catalyst is stable in high vacuum and undergoes no charging when exposed to an X-ray beam, which suggests that it has weak dielectric properties.