Steric C-N bond activation on the dimeric macrocycle [{P(μ-NR)}2(μ-NR)]2.

Dimeric cyclophosphazanes [{P(mu-NR)}(2)(mu-NR)](2) [R = Bu-t (1) and Pr-i (3)] were oxidized with elemental selenium. During these reactions an unexpected C-N bond cleavage and N-H bond formation occurred. Compound 1 produced P-4(mu-(NBu)-Bu-t)(3)(mu-NH)(3)Se-4 (2) where three Bu-t groups were lost in the form of isobutylene. In contrast, during the oxidation of the less sterically hindered 3, the resulting product, P-4(mu-(NPr)-Pr-i)(5)(mu-NH)Se-4 (4), showed only one substituent loss. Theoretical studies confirmed the steric nature of the driving force underlying the different outcomes.