Structural and synthetic insights on oxidative homocouplings of alkynes mediated by alkali-metal manganates

Pasquale Mastropierro; Andrew W.J. Platten; Alan R. Kennedy; Eva Hevia; Marina Uzelac

doi:10.1002/chem.202300593

Structural and synthetic insights on oxidative homocouplings of alkynes mediated by alkali-metal manganates

Pasquale Mastropierro, Andrew W.J. Platten, Alan R. Kennedy, Eva Hevia, Marina Uzelac

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Abstract

Exploiting bimetallic cooperation alkali-metal manganate (II) complexes can efficiently promote oxidative homocoupling of terminal alkynes furnishing an array of conjugated 1,3-diynes. The influence of the alkali-metal on these C−C bond forming processes has been studied by preparing and structurally characterizing the alkali-metal tetra(alkyl) manganates [(TMEDA)₂Na₂Mn(CH₂SiMe₃)₄] and [(PMDETA)₂K₂Mn(CH₂SiMe₃)₄]. Reactivity studies using phenylacetylene as a model substrate have revealed that for the homocoupling to take place initial metalation of the alkyne is required. In this regard, the lack of basicity of neutral Mn(CH₂SiMe₃)₂ precludes the formation of the diyne. Contrastingly, the tetra(alkyl) alkali-metal manganates behave as polybasic reagents, being able to easily deprotonate phenylacetylene yielding [{(THF)₄Na₂Mn(C≡CPh)₄}_∞] and [(THF)₄Li₂Mn(C≡CPh)₄]. Controlled exposure of [{(THF)₄Na₂Mn(C≡CPh)₄}_∞] and [(THF)₄Li₂Mn(C≡CPh)₄] to dry air confirmed their intermediary in formation of 1,4-diphenyl-1,3-butadiyne in excellent yields. While the Na/Mn(II) partnership proved to be the most efficient in stoichiometric transformations, under catalytic regimes, the combination of MC≡CAr (M= Li, Na) and MnCl₂ (6 mol %) only works for lithium, most likely due to the degradation of alkynylsodiums under the aerobic reaction conditions.

Original language	English
Article number	e202300593
Number of pages	8
Journal	Chemistry - A European Journal
Volume	29
Issue number	33
Early online date	27 Apr 2023
DOIs	https://doi.org/10.1002/chem.202300593
Publication status	Published - 13 Jun 2023

Data Availability Statement

The data that support the findings of this study are available in the supplementary material of this article.

Funding

We thank the X‐ray crystal structure service unit at the University of Bern for measuring, solving, refining, and summarizing the structure of compounds and . Swiss National Science Foundation (SNF) (projects numbers 206021_177033 and 188573) and Royal Society (University Research Fellowship to M. U.) are acknowledged for the funding of this research. Our thanks are extended to Dr Marco De Tullio (I) for obtaining preliminary data on homocoupling of phenylacetylene with lithium manganate. 5 6

Keywords

1,3-diynes
alkali-metal effect
homocoupling
manganates
metal - metal cooperativity

ASJC Scopus subject areas

Catalysis
Organic Chemistry

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Hevia, Uzelac_ChemEurJAccepted author manuscript, 972 KBLicence: CC BY

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title = "Structural and synthetic insights on oxidative homocouplings of alkynes mediated by alkali-metal manganates",

abstract = "Exploiting bimetallic cooperation alkali-metal manganate (II) complexes can efficiently promote oxidative homocoupling of terminal alkynes furnishing an array of conjugated 1,3-diynes. The influence of the alkali-metal on these C−C bond forming processes has been studied by preparing and structurally characterizing the alkali-metal tetra(alkyl) manganates [(TMEDA)2Na2Mn(CH2SiMe3)4] and [(PMDETA)2K2Mn(CH2SiMe3)4]. Reactivity studies using phenylacetylene as a model substrate have revealed that for the homocoupling to take place initial metalation of the alkyne is required. In this regard, the lack of basicity of neutral Mn(CH2SiMe3)2 precludes the formation of the diyne. Contrastingly, the tetra(alkyl) alkali-metal manganates behave as polybasic reagents, being able to easily deprotonate phenylacetylene yielding [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4]. Controlled exposure of [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4] to dry air confirmed their intermediary in formation of 1,4-diphenyl-1,3-butadiyne in excellent yields. While the Na/Mn(II) partnership proved to be the most efficient in stoichiometric transformations, under catalytic regimes, the combination of MC≡CAr (M= Li, Na) and MnCl2 (6 mol %) only works for lithium, most likely due to the degradation of alkynylsodiums under the aerobic reaction conditions.",

keywords = "1,3-diynes, alkali-metal effect, homocoupling, manganates, metal - metal cooperativity",

author = "Pasquale Mastropierro and Platten, {Andrew W.J.} and Kennedy, {Alan R.} and Eva Hevia and Marina Uzelac",

year = "2023",

month = jun,

day = "13",

doi = "10.1002/chem.202300593",

language = "English",

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T1 - Structural and synthetic insights on oxidative homocouplings of alkynes mediated by alkali-metal manganates

AU - Mastropierro, Pasquale

AU - Platten, Andrew W.J.

AU - Kennedy, Alan R.

AU - Hevia, Eva

AU - Uzelac, Marina

PY - 2023/6/13

Y1 - 2023/6/13

N2 - Exploiting bimetallic cooperation alkali-metal manganate (II) complexes can efficiently promote oxidative homocoupling of terminal alkynes furnishing an array of conjugated 1,3-diynes. The influence of the alkali-metal on these C−C bond forming processes has been studied by preparing and structurally characterizing the alkali-metal tetra(alkyl) manganates [(TMEDA)2Na2Mn(CH2SiMe3)4] and [(PMDETA)2K2Mn(CH2SiMe3)4]. Reactivity studies using phenylacetylene as a model substrate have revealed that for the homocoupling to take place initial metalation of the alkyne is required. In this regard, the lack of basicity of neutral Mn(CH2SiMe3)2 precludes the formation of the diyne. Contrastingly, the tetra(alkyl) alkali-metal manganates behave as polybasic reagents, being able to easily deprotonate phenylacetylene yielding [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4]. Controlled exposure of [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4] to dry air confirmed their intermediary in formation of 1,4-diphenyl-1,3-butadiyne in excellent yields. While the Na/Mn(II) partnership proved to be the most efficient in stoichiometric transformations, under catalytic regimes, the combination of MC≡CAr (M= Li, Na) and MnCl2 (6 mol %) only works for lithium, most likely due to the degradation of alkynylsodiums under the aerobic reaction conditions.

AB - Exploiting bimetallic cooperation alkali-metal manganate (II) complexes can efficiently promote oxidative homocoupling of terminal alkynes furnishing an array of conjugated 1,3-diynes. The influence of the alkali-metal on these C−C bond forming processes has been studied by preparing and structurally characterizing the alkali-metal tetra(alkyl) manganates [(TMEDA)2Na2Mn(CH2SiMe3)4] and [(PMDETA)2K2Mn(CH2SiMe3)4]. Reactivity studies using phenylacetylene as a model substrate have revealed that for the homocoupling to take place initial metalation of the alkyne is required. In this regard, the lack of basicity of neutral Mn(CH2SiMe3)2 precludes the formation of the diyne. Contrastingly, the tetra(alkyl) alkali-metal manganates behave as polybasic reagents, being able to easily deprotonate phenylacetylene yielding [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4]. Controlled exposure of [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4] to dry air confirmed their intermediary in formation of 1,4-diphenyl-1,3-butadiyne in excellent yields. While the Na/Mn(II) partnership proved to be the most efficient in stoichiometric transformations, under catalytic regimes, the combination of MC≡CAr (M= Li, Na) and MnCl2 (6 mol %) only works for lithium, most likely due to the degradation of alkynylsodiums under the aerobic reaction conditions.

KW - 1,3-diynes

KW - alkali-metal effect

KW - homocoupling

KW - manganates

KW - metal - metal cooperativity

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DO - 10.1002/chem.202300593

M3 - Article

AN - SCOPUS:85153761317

SN - 0947-6539

VL - 29

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

IS - 33

M1 - e202300593

ER -

Structural and synthetic insights on oxidative homocouplings of alkynes mediated by alkali-metal manganates

Abstract

Data Availability Statement

Funding

Keywords

ASJC Scopus subject areas

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