Reactivities of cyclonickellated complexes with hydroxylamines: formation of κ O -hydroxylamine and κ N -imine adducts and a κ O , κ N -aminoxide derivative.

This report discusses the reactivities of hydroxylamines with a family of nickellacyclic complexes prepared by C-H nickellation of aryl phosphinites. Treating the dimeric complexes κ C ,κ P -{2-OPR 2 ,4-R'-C 6 H 4 } 2 Ni 2 (μ-Br) 2 (R = i-Pr; R' = H, Cl, OMe, NMe 2 ) or their monomeric acetonitrile adducts κ C ,κ P -{2-OPR 2 ,4-R'-C 6 H 4 }Ni(Br)(NCMe) with hydroxylamines showed three types of reactivities depending on the Ni complex, the reaction solvent, and the substrate used: (1) the benzyl-protected substrate PhCH 2 ONH 2 gave simple N-bound adducts with all Ni complexes; (2) the parent Ni dimer (R' = H) reacted with Et 2 NOH and (PhCH 2 ) 2 NOH in CH 2 Cl 2 to give, respectively, the zwitterionic amine oxide κ C ,κ P -{2-OPR 2 -C 6 H 5 }Ni(κ O -ONHEt 2 )Br and the bidentate aminoxide (i-R 2 POPh)Ni{κ O ,κ N -ON(CH 2 Ph) 2 }Br; (3) the analogous reaction of substituted Ni complexes (R' = Cl, OMe, NMe 2 ) with hydroxylamines in acetonitrile gave adducts of imines derived from dehydration of Et 2 NOH and (PhCH 2 ) 2 NOH. The latter reactivity proceeds optimally in acetonitrile, but it also occurs to a lesser extent in C 6 D 6 if the reaction is allowed to go for more than 24 h. Different mechanistic scenarios have been considered to rationalize the observed hydroxylamine → imine transformation.