Stereocontrolled monoalkylation of mixed-ring complex CpCp′ZrCl2 (Cp′ = 1-neomenthyl-4,5,6,7-tetrahydroindenyl) by lithium, magnesium and aluminum alkyls

The monoalkylation of mixed-ring complex η5-cyclopentadienyl-η5-(1-neomenthyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride (CpCp′ZrCl2) by lithium, magnesium and aluminum alkyls has been studied by the means of NMR spectroscopy. It is shown the reaction of CpCp′ZrCl2 with 1 eq. of RLi (R = Et, nBu) at −78 °C in toluene gives the chiral-at-zirconium complexes CpCp′ZrRCl with epimer ratio 12:1. The use of Grignard reagent (EtMgBr) reduces the epimer ratio to 3:1. The reaction of CpCp′ZrCl2 with AlEt3 in the same conditions yields two diastereomers of complex [CpCp′ZrEt(μ-Cl)·AlEt3] in a ratio 1.6:1, followed by five-membered bimetallic hydride complex [CpCp′Zr(μ-H)(CH2CH2AlEt2] with diastereomeric ratio 10:1. Cyclohexyl isocyanide (CyNC) insertion into the Zr-R bond of CpCp′ZrRCl provides the corresponding η2-iminoacyl complexes CpCp′ZrC(R) = N(Cy)(Cl) (R = Et, nBu), which were characterized by NMR, IR spectroscopy and mass-spectrometry (MALDI/TOF).