Opening the black box of mixed-metal TMP metallating reagents: direct cadmation or lithium-cadmium transmetallation?

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Abstract

Designed to remove some of the mystery surrounding mixed-metal TMP (2,2,6,6-tetramethylpiperidide) metallating reagents, this study examines in detail "LiCd(TMP)(3)'' in its own right. Previously established as an excellent "cadmating'' (Cd-H exchange) reagent towards a wide variety of aromatic substrates, "LiCd(TMP)(3)'' has been investigated by H-1, C-13 and Cd-113 NMR studies as well as by DOSY NMR spectroscopy. This evidence puts a question mark against its ate formulation implying it exists in THF solution as two independent homometallic amides. Exploring the reactivity of "LiCd(TMP)(3)'' with anisole as a test substrate, both experimentally by NMR studies and theoretically by DFT studies suggests a two-step lithiation/transmetallation process in which the initially formed ortho-lithiated species undergoes a reaction with Cd(TMP)(2) to form new Cd-C and Li-N bonds. For completeness, the homometallic cadmium component Cd(TMP)(2) has been comprehensively characterised for the first time including a crystal structure determination revealing a near-linear N-Cd-N arrangement.

LanguageEnglish
Pages2700-2707
Number of pages8
JournalChemical Science
Volume3
Issue number9
Early online date5 Jul 2012
DOIs
Publication statusPublished - 2012

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Cadmium
Lithium
Metals
Nuclear magnetic resonance
Substrates
Discrete Fourier transforms
Amides
Nuclear magnetic resonance spectroscopy
2,2,6,6-tetramethylpiperidide
Crystal structure

Keywords

  • mixed-metal TMP
  • metallating reagents
  • homometallic amides
  • homometallic cadmium

Cite this

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title = "Opening the black box of mixed-metal TMP metallating reagents: direct cadmation or lithium-cadmium transmetallation?",
abstract = "Designed to remove some of the mystery surrounding mixed-metal TMP (2,2,6,6-tetramethylpiperidide) metallating reagents, this study examines in detail {"}LiCd(TMP)(3)'' in its own right. Previously established as an excellent {"}cadmating'' (Cd-H exchange) reagent towards a wide variety of aromatic substrates, {"}LiCd(TMP)(3)'' has been investigated by H-1, C-13 and Cd-113 NMR studies as well as by DOSY NMR spectroscopy. This evidence puts a question mark against its ate formulation implying it exists in THF solution as two independent homometallic amides. Exploring the reactivity of {"}LiCd(TMP)(3)'' with anisole as a test substrate, both experimentally by NMR studies and theoretically by DFT studies suggests a two-step lithiation/transmetallation process in which the initially formed ortho-lithiated species undergoes a reaction with Cd(TMP)(2) to form new Cd-C and Li-N bonds. For completeness, the homometallic cadmium component Cd(TMP)(2) has been comprehensively characterised for the first time including a crystal structure determination revealing a near-linear N-Cd-N arrangement.",
keywords = "mixed-metal TMP, metallating reagents, homometallic amides, homometallic cadmium",
author = "Armstrong, {David R.} and Alan Kennedy and Mulvey, {Robert E.} and Parkinson, {John A.} and Robertson, {Stuart D.}",
year = "2012",
doi = "10.1039/c2sc20392h",
language = "English",
volume = "3",
pages = "2700--2707",
journal = "Chemical Science",
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T1 - Opening the black box of mixed-metal TMP metallating reagents

T2 - Chemical Science

AU - Armstrong, David R.

AU - Kennedy, Alan

AU - Mulvey, Robert E.

AU - Parkinson, John A.

AU - Robertson, Stuart D.

PY - 2012

Y1 - 2012

N2 - Designed to remove some of the mystery surrounding mixed-metal TMP (2,2,6,6-tetramethylpiperidide) metallating reagents, this study examines in detail "LiCd(TMP)(3)'' in its own right. Previously established as an excellent "cadmating'' (Cd-H exchange) reagent towards a wide variety of aromatic substrates, "LiCd(TMP)(3)'' has been investigated by H-1, C-13 and Cd-113 NMR studies as well as by DOSY NMR spectroscopy. This evidence puts a question mark against its ate formulation implying it exists in THF solution as two independent homometallic amides. Exploring the reactivity of "LiCd(TMP)(3)'' with anisole as a test substrate, both experimentally by NMR studies and theoretically by DFT studies suggests a two-step lithiation/transmetallation process in which the initially formed ortho-lithiated species undergoes a reaction with Cd(TMP)(2) to form new Cd-C and Li-N bonds. For completeness, the homometallic cadmium component Cd(TMP)(2) has been comprehensively characterised for the first time including a crystal structure determination revealing a near-linear N-Cd-N arrangement.

AB - Designed to remove some of the mystery surrounding mixed-metal TMP (2,2,6,6-tetramethylpiperidide) metallating reagents, this study examines in detail "LiCd(TMP)(3)'' in its own right. Previously established as an excellent "cadmating'' (Cd-H exchange) reagent towards a wide variety of aromatic substrates, "LiCd(TMP)(3)'' has been investigated by H-1, C-13 and Cd-113 NMR studies as well as by DOSY NMR spectroscopy. This evidence puts a question mark against its ate formulation implying it exists in THF solution as two independent homometallic amides. Exploring the reactivity of "LiCd(TMP)(3)'' with anisole as a test substrate, both experimentally by NMR studies and theoretically by DFT studies suggests a two-step lithiation/transmetallation process in which the initially formed ortho-lithiated species undergoes a reaction with Cd(TMP)(2) to form new Cd-C and Li-N bonds. For completeness, the homometallic cadmium component Cd(TMP)(2) has been comprehensively characterised for the first time including a crystal structure determination revealing a near-linear N-Cd-N arrangement.

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KW - homometallic amides

KW - homometallic cadmium

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