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

摘要

The mono- and bis-ring substituted zirconocenes with pendant phenyl groups [Zr(#eta#-C_5H_5)(#eta#-C_5H_4CMe_2Ph)Me_2] 2, [Zr(#eta#-C_5H_5)(#eta#-C_5H_4CMe_2C_6H_4Me-p)Me_2] 3, [Zr(#eta#-C_5H_4CMe_2Ph)_2Me_2] 4, and [Zr(#eta#-C_5H_4CMe_2C_6H_4Me-p)_2Me_2] 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(C_6F_5)_3 or [Ph_3C]~+[B(C_6F_5)_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(#eta#-C_5H_5)(#eta#-C_5H_4CMe_2Ph)Me]~+[RB(C_6F_5)_3]~- (R = Me 6a or C_6F_5 6b) and [Zr(#eta#-C_5H_5)(#eta#-C_5H_4CMe_2C_6H_4Me-p)Me]~+[RB(C_6F_5)_3]~- (R = Me 7a or C_6F_5 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#-C_5H_4CMe_2Ph)_2Me]~+[RB(C_6F_5)_3]~- (R = Me 8a or C_6F_5 8b) (derived from 4) and [Zr(#eta#-C_5H_4CMe_2C_6H_4Me-p)_2Me]~+[RB(C_6F_5)_3]~- (R = Me 9a or C_6F_5 9b) (derived from 5), respectively, exhibit more complex behaviour. These observations contrast with those from the previously published benzyl congener [Zr(#eta#-C_5H_4CH_2Ph)_2Me_2] 1 which, with methyl abstracting agent, generates both a solvent separated cation/anion pair and a tight ion pair.