Evidence for cationic Group 4 zirconocene complexes with intramolecular phenyl co-ordination

Abstract

The mono- and bis-ring substituted zirconocenes with pendant phenyl groups [Zr(η-C5H5)(η-C5H4CMe2Ph)Me2] 2, [Zr(η-C5H5)(η-C5H4CMe2C6H4Me-p)Me2] 3, [Zr(η-C5H4CMe2Ph)2Me2] 4, and [Zr(η-C5H4CMe2C6H4Me-p)2Me2] 5 have been prepared. The crystal structures of 3 and 4 have been determined. Compounds 2–5 react with methyl abstracting reagents such as B(C6F5)3 or [Ph3C]+[B(C6F5)4]– to form cationic zirconocene complexes 6–9 as solvent separated ion pairs as shown by low temperature NMR spectroscopy. For the cationic complexes [Zr(η-C5H5)(η-C5H4CMe2Ph)Me]+[RB(C6F5)3]– (R = Me 6a or C6F56b) and [Zr(η-C5H5)(η-C5H4CMe2C6H4Me-p)Me]+[RB(C6F5)3]– (R = Me 7a or C6F57b) evidence for the co-ordination of a phenyl group to the zirconium centre via agostic C–H–M interaction was obtained by NMR spectroscopy. These cationic complexes can be considered as models for solvent adducts in Kaminsky catalysts. The cationic complexes [Zr(η-C5H4CMe2Ph)2Me]+[RB(C6F5)3]– (R = Me 8a or C6F58b) (derived from 4) and [Zr(η-C5H4CMe2C6H4Me-p)2Me]+[RB(C6F5)3]– (R = Me 9a or C6F59b) (derived from 5), respectively, exhibit more complex behaviour. These observations contrast with those from the previously published benzyl congener [Zr(η-C5H4CH2Ph)2Me2] 1 which, with methyl abstracting agent, generates both a solvent separated cation/anion pair and a tight ion pair.