The rearrangement of diamidosilyl ether ligands to amido-amino-siloxo ligands and their chromium complexes

The synthesis and characterization of three new symmetrical diamidosilyl ether ligands {[RNHSiMe2]2O} (H2[RNON]; R = Propyl, 3,5-Me2Ph, Ferrocenyl) are described. A retro-Brook-type silyl migration from oxygen to nitrogen of the dilithiated ligands {[RNLiSiMe2]2O} (R = Propyl, 3,5-Me2Ph, 2,4,6-Me3Ph, 2,6-iPr2Ph, 3,5-(CF3)2Ph) in THF resulted in new non-symmetrical mixed-donor amido-amino-siloxo ligands of the form {RNLiSiMe2N(R)SiMe2OLi}, termed Li2[RNN’O], in one step and quantitative yield; most were structurally characterized and exhibited a range of aggregate structures including triple-stacked cubes, ladders and rings. Reaction kinetics were determined by VT 1H NMR and show that the rate of rearrangement increases with decreasing steric hindrance, and with increasing electron-donating ability of the R substituents. Several paramagnetic chromium complexes including {Cr[Me3PhNN’O]•THF}2, {Cr[iPr2PhNN’O]}2, {Cr[Me3PhNN’O]2Li2•THF}, {(Cr2[Me3PhNN’O]2)2CrCl2}, and {Cr[PrNON]2} were synthesized. Amido- or siloxo-bridged binding motifs, a very strong ?2-(N,Cipso) arylamido interaction, and a Cr(II) ate complex are featured, along with their magnetic properties and activity towards ethylene polymerization.