Nickel phosphinite pincer complexes as catalysts for deoxygenative hydroboration of amides to amines

Azamat Yessengazin; Aziza Adilkhanova; Valeriya Frolova; Andrey Y. Khalimon

Abstract

Deoxygenative reduction of readily available carboxamides is considered as an attractive approach for preparation of a variety of primary, secondary and tertiary amines.[1,2] However, significantly reduced electrophilic character of amides, compared to other carbonyl compounds, makes their reduction a challenging task.[3] Herein we report preparation of a series of iminophosphinite POCNR, aminophosphinite POCNR2 and bis(phosphinite) POCOP pincer complexes of Ni(II) and evaluation of their catalytic activity in deoxygenative hydroboration of amides with HBPin to give the corresponding amines. Among all primary, secondary and tertiary amides, superior reactivity in hydroboration reactions was demonstrated for secondary substrates. Bis(phosphinite) hydride complex (POCOP)NiH proved the most active in reduction of secondary amides, tolerating internal alkene, ester, nitrile, heteroaromatic and tertiary amide functionalities. Preferable hydroboration of secondary amides was also demonstrated in the presence of primary amide groups. The reactions were conducted at 40-80 °C, representing a rare example of a base-metal catalytic system for selective deoxygenation of secondary amides to the corresponding amines under mild conditions. Whereas (POCOP)NiH catalyzed selective deoxygenation of secondary amides, primary amide substrates were hydroborated to the corresponding N,N-diborylamines using an iminophosphinite derivative (POCNDmp)Ni(CH2SiMe3) (Dmp = 2,6-dimethylphenyl) as a catalyst. Our mechanistic and kinetic studies suggested that deoxygenative hydroboration reactions proceed via a direct C-O bond cleavage route, which is triggered by dehydrogenative N-borylation to access more electrophilic N-borylamides amenable to addition of HBPin to the carbonyl group.

[1] Khalimon, A. Y.; Gudun, K. A.; Hayrapetyan, D. Catalysts 2019, 9, 490.
[2] Khalimon A. Y. Dalton. Trans. 2021, 50, 17455-17466.
[3] Werkmeister, S.; Junge, K.; Beller, M. Org. Process Res. Dev. 2014, 18, 289–302.

Original language	English
Publication status	Published - Mar 2023
Event	American Chemical Society Meeting Spring 2023: Crossroads of Chemistry - Indianapolis, IN, United States Duration: Mar 26 2023 → Mar 30 2023 https://www.acs.org/meetings/acs-meetings/spring-2023.html

Conference

Conference	American Chemical Society Meeting Spring 2023
Abbreviated title	ACS Meeting Spring 2023
Country/Territory	United States
City	Indianapolis, IN
Period	3/26/23 → 3/30/23
Internet address	https://www.acs.org/meetings/acs-meetings/spring-2023.html

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ACS Spring 2023 abstractFinal published version, 474 KBLicence: CC BY-NC

Cite this

@conference{235f13fc3b324969a9eab2d6d2b2c7a6,

title = "Nickel phosphinite pincer complexes as catalysts for deoxygenative hydroboration of amides to amines",

abstract = "Deoxygenative reduction of readily available carboxamides is considered as an attractive approach for preparation of a variety of primary, secondary and tertiary amines.[1,2] However, significantly reduced electrophilic character of amides, compared to other carbonyl compounds, makes their reduction a challenging task.[3] Herein we report preparation of a series of iminophosphinite POCNR, aminophosphinite POCNR2 and bis(phosphinite) POCOP pincer complexes of Ni(II) and evaluation of their catalytic activity in deoxygenative hydroboration of amides with HBPin to give the corresponding amines. Among all primary, secondary and tertiary amides, superior reactivity in hydroboration reactions was demonstrated for secondary substrates. Bis(phosphinite) hydride complex (POCOP)NiH proved the most active in reduction of secondary amides, tolerating internal alkene, ester, nitrile, heteroaromatic and tertiary amide functionalities. Preferable hydroboration of secondary amides was also demonstrated in the presence of primary amide groups. The reactions were conducted at 40-80 °C, representing a rare example of a base-metal catalytic system for selective deoxygenation of secondary amides to the corresponding amines under mild conditions. Whereas (POCOP)NiH catalyzed selective deoxygenation of secondary amides, primary amide substrates were hydroborated to the corresponding N,N-diborylamines using an iminophosphinite derivative (POCNDmp)Ni(CH2SiMe3) (Dmp = 2,6-dimethylphenyl) as a catalyst. Our mechanistic and kinetic studies suggested that deoxygenative hydroboration reactions proceed via a direct C-O bond cleavage route, which is triggered by dehydrogenative N-borylation to access more electrophilic N-borylamides amenable to addition of HBPin to the carbonyl group.[1] Khalimon, A. Y.; Gudun, K. A.; Hayrapetyan, D. Catalysts 2019, 9, 490.[2] Khalimon A. Y. Dalton. Trans. 2021, 50, 17455-17466.[3] Werkmeister, S.; Junge, K.; Beller, M. Org. Process Res. Dev. 2014, 18, 289–302.",

author = "Azamat Yessengazin and Aziza Adilkhanova and Valeriya Frolova and Khalimon, {Andrey Y.}",

year = "2023",

month = mar,

language = "English",

note = "American Chemical Society Meeting Spring 2023 : Crossroads of Chemistry, ACS Meeting Spring 2023 ; Conference date: 26-03-2023 Through 30-03-2023",

url = "https://www.acs.org/meetings/acs-meetings/spring-2023.html",

}

TY - CONF

T1 - Nickel phosphinite pincer complexes as catalysts for deoxygenative hydroboration of amides to amines

AU - Yessengazin, Azamat

AU - Adilkhanova, Aziza

AU - Frolova, Valeriya

AU - Khalimon, Andrey Y.

PY - 2023/3

Y1 - 2023/3

N2 - Deoxygenative reduction of readily available carboxamides is considered as an attractive approach for preparation of a variety of primary, secondary and tertiary amines.[1,2] However, significantly reduced electrophilic character of amides, compared to other carbonyl compounds, makes their reduction a challenging task.[3] Herein we report preparation of a series of iminophosphinite POCNR, aminophosphinite POCNR2 and bis(phosphinite) POCOP pincer complexes of Ni(II) and evaluation of their catalytic activity in deoxygenative hydroboration of amides with HBPin to give the corresponding amines. Among all primary, secondary and tertiary amides, superior reactivity in hydroboration reactions was demonstrated for secondary substrates. Bis(phosphinite) hydride complex (POCOP)NiH proved the most active in reduction of secondary amides, tolerating internal alkene, ester, nitrile, heteroaromatic and tertiary amide functionalities. Preferable hydroboration of secondary amides was also demonstrated in the presence of primary amide groups. The reactions were conducted at 40-80 °C, representing a rare example of a base-metal catalytic system for selective deoxygenation of secondary amides to the corresponding amines under mild conditions. Whereas (POCOP)NiH catalyzed selective deoxygenation of secondary amides, primary amide substrates were hydroborated to the corresponding N,N-diborylamines using an iminophosphinite derivative (POCNDmp)Ni(CH2SiMe3) (Dmp = 2,6-dimethylphenyl) as a catalyst. Our mechanistic and kinetic studies suggested that deoxygenative hydroboration reactions proceed via a direct C-O bond cleavage route, which is triggered by dehydrogenative N-borylation to access more electrophilic N-borylamides amenable to addition of HBPin to the carbonyl group.[1] Khalimon, A. Y.; Gudun, K. A.; Hayrapetyan, D. Catalysts 2019, 9, 490.[2] Khalimon A. Y. Dalton. Trans. 2021, 50, 17455-17466.[3] Werkmeister, S.; Junge, K.; Beller, M. Org. Process Res. Dev. 2014, 18, 289–302.

AB - Deoxygenative reduction of readily available carboxamides is considered as an attractive approach for preparation of a variety of primary, secondary and tertiary amines.[1,2] However, significantly reduced electrophilic character of amides, compared to other carbonyl compounds, makes their reduction a challenging task.[3] Herein we report preparation of a series of iminophosphinite POCNR, aminophosphinite POCNR2 and bis(phosphinite) POCOP pincer complexes of Ni(II) and evaluation of their catalytic activity in deoxygenative hydroboration of amides with HBPin to give the corresponding amines. Among all primary, secondary and tertiary amides, superior reactivity in hydroboration reactions was demonstrated for secondary substrates. Bis(phosphinite) hydride complex (POCOP)NiH proved the most active in reduction of secondary amides, tolerating internal alkene, ester, nitrile, heteroaromatic and tertiary amide functionalities. Preferable hydroboration of secondary amides was also demonstrated in the presence of primary amide groups. The reactions were conducted at 40-80 °C, representing a rare example of a base-metal catalytic system for selective deoxygenation of secondary amides to the corresponding amines under mild conditions. Whereas (POCOP)NiH catalyzed selective deoxygenation of secondary amides, primary amide substrates were hydroborated to the corresponding N,N-diborylamines using an iminophosphinite derivative (POCNDmp)Ni(CH2SiMe3) (Dmp = 2,6-dimethylphenyl) as a catalyst. Our mechanistic and kinetic studies suggested that deoxygenative hydroboration reactions proceed via a direct C-O bond cleavage route, which is triggered by dehydrogenative N-borylation to access more electrophilic N-borylamides amenable to addition of HBPin to the carbonyl group.[1] Khalimon, A. Y.; Gudun, K. A.; Hayrapetyan, D. Catalysts 2019, 9, 490.[2] Khalimon A. Y. Dalton. Trans. 2021, 50, 17455-17466.[3] Werkmeister, S.; Junge, K.; Beller, M. Org. Process Res. Dev. 2014, 18, 289–302.

M3 - Abstract

T2 - American Chemical Society Meeting Spring 2023

Y2 - 26 March 2023 through 30 March 2023

ER -