Field Desorption Mass Spectrometric Analysis of Ethylene Polymerization Initiated by the Anthracenide Yttrium Complex, (C5H5)Y(C14H10)(THF)2.

Yttrium anthracenide complex CpY(C14H10)(THF)2 (1) catalyzes ethylene polymerization under mild conditions. The initiation polymerization step has been modeled by a reaction of 1 and of its Lu analog (3) with t-BuCN, resulting in the formation of mono-insertion products CpLn(-C14H10-(t-Bu)C=N-)(THF)2 (Ln= Y(5), Lu (6)). Crystal structures of 1, CpY(C14H10)(1,4-dioxane)2 (2) and 6 have been determined by the X-ray diffraction analysis. Field desorption mass spectrometry (FD MS) has been used to analyze polymerization products (oligoethylene and its copolymer with pent-1-ene) formed on 1 under various conditions. The thorough analysis of FD MS data enabled us to detect end groups and to suggest a plausible mechanism for ethylene polymerization. The proposed mechanism explains formation of all detected polymer species.