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

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

doi:10.1021/om300248r

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

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

Weizmann Institute of Science, Israel

Research output: Contribution to journal › Article

62 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 language	English
Pages (from-to)	4083-4101
Number of pages	19
Journal	Organometallics
Volume	31
Issue number	11
DOIs	https://doi.org/10.1021/om300248r
Publication status	Published - Jun 11 2012

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Organic Chemistry
Inorganic Chemistry

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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

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title = "N-H activation by Rh(I) via metal-ligand cooperation",

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.",

author = "Moran Feller and Yael Diskin-Posner and Shimon, {Linda J.W.} and Eyal Ben-Ari and David Milstein",

year = "2012",

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doi = "10.1021/om300248r",

language = "English",

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T1 - N-H activation by Rh(I) via metal-ligand cooperation

AU - Feller, Moran

AU - Diskin-Posner, Yael

AU - Shimon, Linda J.W.

AU - Ben-Ari, Eyal

AU - Milstein, David

PY - 2012/6/11

Y1 - 2012/6/11

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.

AB - 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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