J.D. Soper, W. Kaminsky, J.M. Mayer. Activation of an Anilido Ligand
for Nucleophilic Aromatic Substitution by an Oxidizing Os(IV) Center. J Am.
Chem. Soc. 123 (2001) 5594-5595.
Anearobic treatment of the osmium anilido complex TpOs(NHPh)Cl2 (1) with
piperidine or pyrrolidine in CH3CN gives products with derivatized anilido
ligands, TpOs[NH-p-C6H4-N(c-C5H10)]Cl2 (2) and TpOs[NH-p-C6H4N(c-C4H8)]Cl2
(3) [Tp = hydrotis(1-pyrazolyl)borate]. Compounds 2 and 3 are formed in low
yield (ca. 30%) by nucleophilic substitution reactions in which the oxidizing
Os(IV) center activates the phenyl ring of the amido ligand towards nucleophilic
attack at the para position. The remaining osmium is consumed in oxidizing
the amine-added intermediate, with two equivalents of 1 being converted to
two equivalents of Os(III) aniline complex TpOs(NH2Ph)Cl2 (4). The relative
rates of reaction correlate with the pKa and the sterics of the treating
TpOs(NH-p-C6H4Cl)Cl2 (6) with piperidine to give 2 in quantitative yield.
While anilido (NHAr-) is typically an electron-rich ligand, the anilido ligands
ain1 and 6 are activated towards nucleophilic attack by the oxidizing osmium
(IV) center.