Reactivities of cyclonickellated complexes with hydroxylamines: formation of κO-hydroxylamine and κN-imine adducts and a κO, κN-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 κC,κP-{2-OPR2,4-R′-C6H4}2Ni2(μ-Br)2 (R = i-Pr; R′ = H, Cl, OMe, NMe2) or their monomeric acetonitrile adducts κC,κP-{2-OPR2,4-R′-C6H4}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 PhCH2ONH2 gave simple N-bound adducts with all Ni complexes; (2) the parent Ni dimer (R′ = H) reacted with Et2NOH and (PhCH2)2NOH in CH2Cl2 to give, respectively, the zwitterionic amine oxide κC,κP-{2-OPR2-C6H5}Ni(κO-ONHEt2)Br and the bidentate aminoxide (i-R2POPh)Ni{κO,κN-ON(CH2Ph)2}Br; (3) the analogous reaction of substituted Ni complexes (R′ = Cl, OMe, NMe2) with hydroxylamines in acetonitrile gave adducts of imines derived from dehydration of Et2NOH and (PhCH2)2NOH. The latter reactivity proceeds optimally in acetonitrile, but it also occurs to a lesser extent in C6D6 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. [ABSTRACT FROM AUTHOR]