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The Synthesis and Reactivity of Group 4 Zwitterionic Complexes of the Type M t + CH 2 AlCl 3 − : One‐Component Stereoselective Polymerization and Oligomerization Catalysts for Olefins and Acetylenes
Author(s) -
Eisch John J.,
Otieno Peter O.
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400190
Subject(s) - chemistry , zwitterion , polymerization , phenylacetylene , polymer chemistry , benzophenone , reactivity (psychology) , medicinal chemistry , catalysis , photochemistry , organic chemistry , polymer , medicine , alternative medicine , pathology , molecule
A reinvestigation of the interaction of TiCl 4 with 2 equiv. of Me 3 Al in toluene between −78 °C and 25 °C over 24 h has now established that the ultimate black product obtained is an associated zwitterion of the type [Ti + −CH 2 −AlCl 3 − ] n , supported by multinuclear NMR spectroscopy and mass spectrometric and gasometric analyses of the gases evolved (CH 4 , H 2 ) upon its protolysis. Chemical reactions of the zwitterion have corroborated specific aspects of its proposed structure: 1) its methylene character, by its transformation of benzophenone into 1,1‐diphenylethylene; 2) its divalent titanium content, by the substantial reductive dimerization of benzophenone to tetraphenylethylene, and 3) its Lewis acidic Ti center, by its catalytic isomerization of trans ‐stilbene oxide to 1,1‐diphenylacetaldehyde. Similar individual reactions of ZrCl 4 or HfCl 4 with Me 3 Al have led to the analogous zwitterions [Zr + −CH 2 −AlCl 3 − ] n and [Hf + −CH 2 −AlCl 3 − ] n , respectively. These zwitterions of Ti, Zr and Hf have been proven to be capable of the cyclotrimerization and/or polymerization of acetylenes with varying facility, as evidenced by their catalytic action on 1‐hexyne, phenylacetylene, di‐ n ‐butylacetylene, and diphenylacetylene. Furthermore, all three zwitterions were able to polymerize ethylene, without any added cocatalyst, with an activity following the order Zr > Ti > Hf. The Ti and Zr zwitterions effected the stereoselective polymerization of propylene to yield 50% of isotactic polymer, and all three catalysts induced the polymerization of 1‐hexene to yield 85% (Zr, Hf) or 100% (Ti) of isotactic polymer. These oligomerizations and stereoselective polymerizations of acetylenes and olefins can be rationalized through a model for the active site resembling a three‐membered metallacyclopropa(e)nium ion intermediate formed from the attack of the Group 4 metal zwitterion on the unsaturated hydrocarbon. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)