Cyclopentadienyl-based Mg complexes in the intramolecular hydroamination of aminoalkenes: mechanistic evidence for cationic versus neutral magnesium derivatives

Abstract

Neutral and cationic magnesium complexes stabilized by coordination of a cyclopentadienyl ligand with two different neutral hemilabile donor groups [Mg{η⁵-C₅H₃-1,3-(CH₂CH₂NiPr₂)(SiMe₂NPh₂)}X(thf)] (X = Bz (2); N(SiMe₃)₂ (3)) and [Mg{η⁵-C₅H₃-1,3-(CH₂CH₂NiPr₂)(SiMe₂NPh₂)}][BPh₄] (4) have been prepared and characterized. The ¹H-¹³C HMBC and HSQC spectra of compounds 2 and 3 demonstrate the formation of 1,3-substituted cyclopentadienyl compounds and DOSY and ¹H-NMR experiments support the coordination–decoordination in solution of a THF molecule in complex 2. No Schlenk-type ligand redistributions were observed in the chemical behaviour of these magnesium complexes. Compounds 2–4 are active catalysts in the hydroamination of aminoalkenes; stoichiometric reactions and kinetic measurements have been performed to gain an insight into their reaction mechanisms. A key contribution here is the catalytic reactivity of a cationic magnesium compound.