Organolanthanide-catalyzed hydroamination/cyclization reactions of aminoalkynes. Computational investigation of mechanism, lanthanide identity, and substituent effects for a very exothermic C-N bond-forming process

Alessandro Motta, Ignazio L. Fragalà, Tobin J Marks

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Abstract

This contribution focuses on organolanthanide-mediated catalytic hydroamination processes and analyzes the exothermic hydroamination/cyclization of a prototypical aminoalkyne, H 2N(CH 2) 3C≡CR, mediated by Cp 2Sm- complexes, using density functional theory. The reaction is found to proceed in two discrete steps, namely, cyclization with concerted Ln-C and C-N bond formation and subsequent Ln-C protonolysis. Dissociation of the cyclized amine then follows to regenerate the active catalyst. Analysis is carried out for (i) insertion of the triple bond moiety into the Sm-N bond via a four-center transition state, (ii) subsequent Sm-C protonolysis by a second substrate molecule, (iii) the effects of other Ln +3 ions and aminoalkyne R substituents on the reaction energetics, and (iv) comparison to the analogous, essentially thermoneutral process for aminoalkenes. DFT energetic profiles are computed for the turnoverlimiting aminoalkyne C≡C triple bond insertion into the Ln-NH- linkage, and the geometries and stabilities of reactants, intermediates, and products are analyzed. The picture that emerges involves concerted, rate-limiting, exothermic insertion of the alkyne fragment into the Ln-N(amido) bond via a highly organized, seven-membered chairlike cyclic transition state (ΔH calcd= 4.6 kcal/mol, Δ calcd= - 11.9 eu). The resulting cyclized complex then undergoes exergonic protonolysis to yield an amine-amido complex, the likely resting state of the catalyst. Large rate accelerations effected by smaller lanthanide ions and certain alkyne substituents can be understood in terms of approach distances and charge buildup in the cyclization transition state.

Original languageEnglish
Pages (from-to)5533-5539
Number of pages7
JournalOrganometallics
Volume25
Issue number23
DOIs
Publication statusPublished - Nov 6 2006

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Lanthanoid Series Elements
Cyclization
insertion
Alkynes
alkynes
Amines
amines
Ions
catalysts
Catalysts
Discrete Fourier transforms
linkages
Density functional theory
ions
fragments
dissociation
methylidyne
density functional theory
Molecules
Geometry

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

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title = "Organolanthanide-catalyzed hydroamination/cyclization reactions of aminoalkynes. Computational investigation of mechanism, lanthanide identity, and substituent effects for a very exothermic C-N bond-forming process",
abstract = "This contribution focuses on organolanthanide-mediated catalytic hydroamination processes and analyzes the exothermic hydroamination/cyclization of a prototypical aminoalkyne, H 2N(CH 2) 3C≡CR, mediated by Cp 2Sm- complexes, using density functional theory. The reaction is found to proceed in two discrete steps, namely, cyclization with concerted Ln-C and C-N bond formation and subsequent Ln-C protonolysis. Dissociation of the cyclized amine then follows to regenerate the active catalyst. Analysis is carried out for (i) insertion of the triple bond moiety into the Sm-N bond via a four-center transition state, (ii) subsequent Sm-C protonolysis by a second substrate molecule, (iii) the effects of other Ln +3 ions and aminoalkyne R substituents on the reaction energetics, and (iv) comparison to the analogous, essentially thermoneutral process for aminoalkenes. DFT energetic profiles are computed for the turnoverlimiting aminoalkyne C≡C triple bond insertion into the Ln-NH- linkage, and the geometries and stabilities of reactants, intermediates, and products are analyzed. The picture that emerges involves concerted, rate-limiting, exothermic insertion of the alkyne fragment into the Ln-N(amido) bond via a highly organized, seven-membered chairlike cyclic transition state (ΔH calcd= 4.6 kcal/mol, Δ calcd= - 11.9 eu). The resulting cyclized complex then undergoes exergonic protonolysis to yield an amine-amido complex, the likely resting state of the catalyst. Large rate accelerations effected by smaller lanthanide ions and certain alkyne substituents can be understood in terms of approach distances and charge buildup in the cyclization transition state.",
author = "Alessandro Motta and Fragal{\`a}, {Ignazio L.} and Marks, {Tobin J}",
year = "2006",
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T1 - Organolanthanide-catalyzed hydroamination/cyclization reactions of aminoalkynes. Computational investigation of mechanism, lanthanide identity, and substituent effects for a very exothermic C-N bond-forming process

AU - Motta, Alessandro

AU - Fragalà, Ignazio L.

AU - Marks, Tobin J

PY - 2006/11/6

Y1 - 2006/11/6

N2 - This contribution focuses on organolanthanide-mediated catalytic hydroamination processes and analyzes the exothermic hydroamination/cyclization of a prototypical aminoalkyne, H 2N(CH 2) 3C≡CR, mediated by Cp 2Sm- complexes, using density functional theory. The reaction is found to proceed in two discrete steps, namely, cyclization with concerted Ln-C and C-N bond formation and subsequent Ln-C protonolysis. Dissociation of the cyclized amine then follows to regenerate the active catalyst. Analysis is carried out for (i) insertion of the triple bond moiety into the Sm-N bond via a four-center transition state, (ii) subsequent Sm-C protonolysis by a second substrate molecule, (iii) the effects of other Ln +3 ions and aminoalkyne R substituents on the reaction energetics, and (iv) comparison to the analogous, essentially thermoneutral process for aminoalkenes. DFT energetic profiles are computed for the turnoverlimiting aminoalkyne C≡C triple bond insertion into the Ln-NH- linkage, and the geometries and stabilities of reactants, intermediates, and products are analyzed. The picture that emerges involves concerted, rate-limiting, exothermic insertion of the alkyne fragment into the Ln-N(amido) bond via a highly organized, seven-membered chairlike cyclic transition state (ΔH calcd= 4.6 kcal/mol, Δ calcd= - 11.9 eu). The resulting cyclized complex then undergoes exergonic protonolysis to yield an amine-amido complex, the likely resting state of the catalyst. Large rate accelerations effected by smaller lanthanide ions and certain alkyne substituents can be understood in terms of approach distances and charge buildup in the cyclization transition state.

AB - This contribution focuses on organolanthanide-mediated catalytic hydroamination processes and analyzes the exothermic hydroamination/cyclization of a prototypical aminoalkyne, H 2N(CH 2) 3C≡CR, mediated by Cp 2Sm- complexes, using density functional theory. The reaction is found to proceed in two discrete steps, namely, cyclization with concerted Ln-C and C-N bond formation and subsequent Ln-C protonolysis. Dissociation of the cyclized amine then follows to regenerate the active catalyst. Analysis is carried out for (i) insertion of the triple bond moiety into the Sm-N bond via a four-center transition state, (ii) subsequent Sm-C protonolysis by a second substrate molecule, (iii) the effects of other Ln +3 ions and aminoalkyne R substituents on the reaction energetics, and (iv) comparison to the analogous, essentially thermoneutral process for aminoalkenes. DFT energetic profiles are computed for the turnoverlimiting aminoalkyne C≡C triple bond insertion into the Ln-NH- linkage, and the geometries and stabilities of reactants, intermediates, and products are analyzed. The picture that emerges involves concerted, rate-limiting, exothermic insertion of the alkyne fragment into the Ln-N(amido) bond via a highly organized, seven-membered chairlike cyclic transition state (ΔH calcd= 4.6 kcal/mol, Δ calcd= - 11.9 eu). The resulting cyclized complex then undergoes exergonic protonolysis to yield an amine-amido complex, the likely resting state of the catalyst. Large rate accelerations effected by smaller lanthanide ions and certain alkyne substituents can be understood in terms of approach distances and charge buildup in the cyclization transition state.

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