N-H activation by Rh(I) via metal-ligand cooperation

Moran Feller, Yael Diskin-Posner, Linda J W Shimon, Eyal Ben-Ari, David Milstein

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

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-(CH 2-P tBu 2)-6-(CH 2-NEt 2)C 5H 3N, PNN* = deprotonated PNN, L′ = N 2 (5), C 2H 4 (6)) and [( iPrPNP)RhL′] ( iPrPNP = 2,6-(CH 2-P iPr 2) 2C 5H 3N, iPrPNP* = deprotonated iPrPNP, L′ = C 2H 4 (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 [( iPrPNP)Rh(NHAr)] (Ar = C 6H 5, o-Br-C 6H 4, m-Cl-p-Cl-C 6H 3, p-NO 2-C 6H 4). 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 PEt 3. Deprotonation of complexes [(PNL)Rh(p-NO 2-NH 2C 6H 4)] (13, P = P tBu 2, L = NEt 2; 15, P = L = P iPr 2) yields the dearomatized anionic complexes [(PNL)Rh(p-NO 2-NH 2C 6H 4)]. An associative mechanism, involving N-H activation of an apically coordinated aniline in a pentacoordinated Rh(I) complex, is suggested.

Original languageEnglish
Pages (from-to)4083-4101
Number of pages19
JournalOrganometallics
Volume31
Issue number11
DOIs
Publication statusPublished - Jun 11 2012

Fingerprint

Aniline Compounds
Metals
Chemical activation
aniline
activation
Ligands
Anilides
ligands
metals
methylidyne
Aromatization
Deprotonation
X ray analysis
Carbon Monoxide
Catalysis
catalysis
Amines
Protons
amines
Nuclear magnetic resonance

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Feller, M., Diskin-Posner, Y., Shimon, L. J. W., Ben-Ari, E., & Milstein, D. (2012). N-H activation by Rh(I) via metal-ligand cooperation. Organometallics, 31(11), 4083-4101. https://doi.org/10.1021/om300248r

N-H activation by Rh(I) via metal-ligand cooperation. / Feller, Moran; Diskin-Posner, Yael; Shimon, Linda J W; Ben-Ari, Eyal; Milstein, David.

In: Organometallics, Vol. 31, No. 11, 11.06.2012, p. 4083-4101.

Research output: Contribution to journalArticle

Feller, M, Diskin-Posner, Y, Shimon, LJW, Ben-Ari, E & Milstein, D 2012, 'N-H activation by Rh(I) via metal-ligand cooperation', Organometallics, vol. 31, no. 11, pp. 4083-4101. https://doi.org/10.1021/om300248r
Feller M, Diskin-Posner Y, Shimon LJW, Ben-Ari E, Milstein D. N-H activation by Rh(I) via metal-ligand cooperation. Organometallics. 2012 Jun 11;31(11):4083-4101. https://doi.org/10.1021/om300248r
Feller, Moran ; Diskin-Posner, Yael ; Shimon, Linda J W ; Ben-Ari, Eyal ; Milstein, David. / N-H activation by Rh(I) via metal-ligand cooperation. In: Organometallics. 2012 ; Vol. 31, No. 11. pp. 4083-4101.
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N2 - 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-(CH 2-P tBu 2)-6-(CH 2-NEt 2)C 5H 3N, PNN* = deprotonated PNN, L′ = N 2 (5), C 2H 4 (6)) and [( iPrPNP)RhL′] ( iPrPNP = 2,6-(CH 2-P iPr 2) 2C 5H 3N, iPrPNP* = deprotonated iPrPNP, L′ = C 2H 4 (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 [( iPrPNP)Rh(NHAr)] (Ar = C 6H 5, o-Br-C 6H 4, m-Cl-p-Cl-C 6H 3, p-NO 2-C 6H 4). 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 PEt 3. Deprotonation of complexes [(PNL)Rh(p-NO 2-NH 2C 6H 4)] (13, P = P tBu 2, L = NEt 2; 15, P = L = P iPr 2) yields the dearomatized anionic complexes [(PNL)Rh(p-NO 2-NH 2C 6H 4)]. An associative mechanism, involving N-H activation of an apically coordinated aniline in a pentacoordinated Rh(I) complex, is suggested.

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