Alkyne-functionalized metallocene complexes: Synthesis, structure, and catalytic ethylene polymerization

Reactions of phenylethynyl lithium with substituted cyclopentenones gave the corresponding pendant phenylethynyl substituted cyclopentadienes. Subsequent deprotonation and transmetallation with TiCl4·2THF, ZrCl4, and Cp∗ZrCl3 yielded the alkyne-functionalized metallocene complexes [C5Me4(CCPh)]2MCl2 [M = Ti (1), Zr (2)], Cp∗[C5Me4(CCPh)]ZrCl2 (3), and Cp∗[C5H2R′2(CCPh)]ZrCl2 [R′ = Me (4), Ph (5)]. These complexes were fully characterized by 1H NMR, 13C NMR, MS spectra, and elemental analysis. The molecular structure of 2 was determined by single crystal X-ray diffraction analysis. Ethylene polymerization was studied with these complexes in the presence of methylaluminoxane (MAO).

Graphical abstractA series of alkyne-functionalized titanocene and zirconocene complexes have been synthesized and used for ethylene polymerization with methylaluminoxane (MAO) as cocatalyst.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Alkyne-functionalized cyclopentadienyl transition-metal complexes have been extensively studied but mainly focused on ferrocene and ruthenocene derivatives, Group 4 metal complexes with an alkyne-functionalized cyclopentadienyl ligand are very limited. In this manuscript, a series of alkyne-functionalized titanocene and zirconocene complexes have been synthesized. ► Single crystal X-ray diffraction analysis showed that in complex [C5Me4(CCPh)]2ZrCl2 (2) the phenylethynyl substituents are almost linear, but the CC triple bond length [1.374(3) Å] is significantly longer than the values of substituted acetylenes. ► When activated with MAO all these complexes are effective catalysts for ethylene polymerization. Among them the asymmetrical phenylethynyl diphenylcyclopentadienyl pentamethylcyclopentadienyl zirconocene shows the highest activity at 40 °C, which is even higher than that of Cp2ZrCl2.