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1539463 
Journal Article 
N-H Activation by Rh(I) via Metal-Ligand Cooperation 
Feller, M; Diskin-Posner, Y; Shimon, LJW; Ben-Ari, E; Milstein, D 
2012 
1 
Organometallics
ISSN: 0276-7333
EISSN: 1520-6041 
31 
11 
4083-4101 
WOS:000304978700002 
In continuation of our studies on bond activation and
catalysis by pincer complexes, based on metal-ligand cooperation, we present here a rare example
of amine N-H activation by Rh(I) complexes. The novel dearomatized pincer complexes [(PNN*)RhL']
(PNN = 2-(CH2-(PBu2)-Bu-t)-6-(CH2-NEt2)C5H3N, PNN* = deprotonated PNN, L' = N-2 (5), C2H4 (6))
and [((PrPNP)-Pr-i*)Rh'] ((PrPNP)-Pr-i = 2,6-(CH2-(PPr2)-Pr-i)(2)C5H3H, (PrPNP)-Pr-i* =
deprotonated (PrPNP)-Pr-i, L' = C2H4 (7), cyclooctene (9)) were prepared and fully characterized
by NMR and X-ray analysis. Complexes 5-7 and 9 undergo facile N-H activation of anilines
involving aromatization of the pincer ligand without a change in the formal oxidation state of
the metal center to form stable anilide complexes [(PNN)Rh(NHAr)] and [((PrPNP)-Pr-i)Rh(NHAr)]
(Ar = C6H5, o-Br-C6H4, m-Cl-p-Cl-C6H3, p-NO2-C6H4). Anilines possessing electron-withdrawing
groups accelerate the N-H activation and yield more stable anilide complexes. The pincer and the
ancillary ligands also affect the activation rate, which supports an associative mechanism. Spin
saturation transfer experiments show chemical exchange between the pyridylic arm of the pincer
ligand and the NH- protons of anilines prior to and after the N-H activation. The reverse N-H
formation by metal ligand cooperation from the anilide complexes was observed to give free
anilines and dearomatized Rh(I) complexes upon addition of CO or PEt3. Deprotonation of complexes
[(PNL*)Rh(p-NO2-NH2C6H4)] (13, P = L = NEt2; 15, P = L = (PPr2)-Pr-i) yields the dearomatized
anionic complexes [(PNL*)Rh(p-NO2-NH2C6H4)]. An associative mechanism, involving N-H activation
of an apically coordinated aniline in a pentacoordinated Rh(I) complex, is suggested.