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

The mono- and bis-ring substituted zirconocenes with pendant phenyl groups [Zr(eta-C5H5)(eta-C5H4CMe2Ph)Me-2] 2, [Zr(eta-C5H5)(eta-C5H4CMe2C6H4Me-p)Me -2] 3, [Zr(eta-C5H4CMe2Ph)(2)Me-2] 4, and [Zr(eta-C5H4CMe2C6H4Me-p)(2)Me-2] 5 have been prepared. The crystal structures of 3 and 4 have been determin ed. 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. F or the cationic complexes [Zr(eta-C5H5)(eta-C5H4CMe2Ph)Me](+)[RB(C6F5)(3)]( -) (R=Me 6a or C6F5 6b) and [Zr(eta-C5H5)(eta-C5H4CMe2C6H4Me-p)Me](+)[RB(C6 F5)(3)](-) (R=Me 7a or C6F5 7b) 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(eta-C5H4 CMe2Ph)(2)Me](+)[RB(C6F5)(3)](-) (R=Me 8a or C6F5 8b) (derived from 4) and [Zr(eta-C5H4CMe2C6H4Me-p)(2)Me](+)[RB(C6F5)(3)](-) (R=Me 9a or C6F5 9b) (de rived from 5), respectively, exhibit more complex behaviour. These observat ions contrast with those from the previously published benzyl congener [Zr( eta-C5H4CH2Ph)(2)Me-2] 1 which, with methyl abstracting agent, generates bo th a solvent separated cation/anion pair and a tight ion pair.