Reactivity of Ferrocenyl Phosphates Bearing (Hetero-)Aromatics and [3]Ferrocenophanes toward Anionic Phospho-Fries Rearrangements

The temperature-dependent
behavior within anionic phospho-Fries
rearrangements (apFr) of P­(O)­(OFc)n(EAr)3–n (Fc = Fe­(η5-C5H5)­(η5-C5H4); E = O; Ar = phenyl, naphthyls, (R)-BINOL, [3]­ferrocenophanyl;
E = N, 1H-pyrrolyl, 1H-indolyl,
9H-carbazolyl; n = 1–3) is
reported. While Fc undergoes one, the Ph-based apFr depends on temperature.
First, the aryls are lithiated and rearranged, followed by Fc and
N-heterocycles. Addition of Me2SO4 thus gave
methylated Fc, contrary to non-organometallic aromatics giving mixtures
of HO and MeO derivatives. The (R)-BINOL Fc phosphate
gave Fc-rearranged phosphonate in 91% de. Exchanging O- with N-aliphatics
prevented apFr, due to higher electron density at P. Also 1,2-N→C
migrations were observed. X-ray analysis confirms 1D H bridge bonds
for OH and NH derivatives. The differences in reactivity between N-aliphatic
and N-aromatic phosphoramidates were verified by electrochemistry.
The redox potentials revealed lower values for the electron-rich aliphatics,
showing no apFr, preventing a nucleophilic attack at P after lithiation.
Redox separations for multiple Fc molecules are based on electrostatic
interactions.