Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η5-C5Me4H) 2Zr]2(μ2,η2, η2-N2): Observation of side-on and end-on diazenido complexes in the reduction of N2 to hydrazine

Wesley H. Bernskoetter; Jaime A. Pool; Emil Lobkovsky; Paul J. Chirik

doi:10.1021/ja050387b

Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η⁵-C₅Me₄H) ₂Zr]₂(μ₂,η², η²-N₂): Observation of side-on and end-on diazenido complexes in the reduction of N₂ to hydrazine

Wesley H. Bernskoetter
, Jaime A. Pool
, Emil Lobkovsky
, Paul J. Chirik

Research output: Contribution to journal › Article › peer-review

59 Scopus citations

Abstract

Functionalization of the N₂ ligand in the side-on bound dinitrogen complex, [(η⁵-C₅Me₄H) ₂Zr]₂-(μ₂,η², η²-N₂), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocene diazenido complexes, [(η⁵-C₅Me₄H)₂Zr(C≡CR)] ₂(μ₂,η²,η²-N ₂H₂) (R = ⁿBu, ^tBu, Ph). Characterization of [(η⁵- C₅Me₄H) ₂Zr(C≡CCMe₃)]₂(μ₂, η²,η²-N₂H₂) by X-ray diffraction revealed a side-on bound diazenido ligand in the solid state, while variable-temperature ¹H and ¹⁵N NMR studies established rapid interconversion between η¹,η¹ and η²,η² hapticity of the [N₂H ₂]^2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(η⁵-C ₅Me₄H)₂ZrX]₂(μ₂, η¹,η¹-N₂H₂) (X = Cl, I, OTf, CH₂Ph, CH₂SiMe₃), afforded η¹,η¹ coordination of the [N₂H ₂]^2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases π-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(η⁵-C₅Me₄H)₂ZrH] ₂(μ₂,η²,η²-N ₂H₂), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting α-migration and N₂ cleavage up to temperatures of 115 °C. Dinitrogen functionalization with [(η⁵-C₅Me₄H)₂Zr] ₂(μ₂,η²,η²-N ₂) was also accomplished by addition of proton donors. Weak Bronsted acids such as water and ethanol yield hydrazine and (η⁵-C ₅Me₄H)₂Zr(OH)₂ and (η⁵-C₅Me₄H)₂-Zr(OEt) ₂, respectively. Treatment of [(η⁵-C ₅Me₄H)₂Zr]₂(μ₂, η²,η²-N₂) with HNMe₂ or H₂NNMe₂ furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(η⁵-C ₅Me₅)₂Zr(η¹-N₂)] ₂(μ₂,η¹,η¹-N ₂) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.

Original language	English (US)
Pages (from-to)	7901-7911
Number of pages	11
Journal	Journal of the American Chemical Society
Volume	127
Issue number	21
DOIs	https://doi.org/10.1021/ja050387b
State	Published - Jun 1 2005
Externally published	Yes

All Science Journal Classification (ASJC) codes

Catalysis
General Chemistry
Biochemistry
Colloid and Surface Chemistry

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Bernskoetter, W. H., Pool, J. A., Lobkovsky, E., & Chirik, P. J. (2005). Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η⁵-C₅Me₄H) ₂Zr]₂(μ₂,η², η²-N₂): Observation of side-on and end-on diazenido complexes in the reduction of N₂ to hydrazine. Journal of the American Chemical Society, 127(21), 7901-7911. https://doi.org/10.1021/ja050387b

Bernskoetter, Wesley H. ; Pool, Jaime A. ; Lobkovsky, Emil et al. / Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η⁵-C₅Me₄H) ₂Zr]₂(μ₂,η², η²-N₂) : Observation of side-on and end-on diazenido complexes in the reduction of N₂ to hydrazine. In: Journal of the American Chemical Society. 2005 ; Vol. 127, No. 21. pp. 7901-7911.

@article{f737008617e14074827d194637883b8a,

title = "Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η5-C5Me4H) 2Zr]2(μ2,η2, η2-N2): Observation of side-on and end-on diazenido complexes in the reduction of N2 to hydrazine",

abstract = "Functionalization of the N2 ligand in the side-on bound dinitrogen complex, [(η5-C5Me4H) 2Zr]2-(μ2,η2, η2-N2), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocene diazenido complexes, [(η5-C5Me4H)2Zr(C≡CR)] 2(μ2,η2,η2-N 2H2) (R = nBu, tBu, Ph). Characterization of [(η5- C5Me4H) 2Zr(C≡CCMe3)]2(μ2, η2,η2-N2H2) by X-ray diffraction revealed a side-on bound diazenido ligand in the solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion between η1,η1 and η2,η2 hapticity of the [N2H 2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(η5-C 5Me4H)2ZrX]2(μ2, η1,η1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded η1,η1 coordination of the [N2H 2]2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases π-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(η5-C5Me4H)2ZrH] 2(μ2,η2,η2-N 2H2), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting α-migration and N2 cleavage up to temperatures of 115 °C. Dinitrogen functionalization with [(η5-C5Me4H)2Zr] 2(μ2,η2,η2-N 2) was also accomplished by addition of proton donors. Weak Bronsted acids such as water and ethanol yield hydrazine and (η5-C 5Me4H)2Zr(OH)2 and (η5-C5Me4H)2-Zr(OEt) 2, respectively. Treatment of [(η5-C 5Me4H)2Zr]2(μ2, η2,η2-N2) with HNMe2 or H2NNMe2 furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(η5-C 5Me5)2Zr(η1-N2)] 2(μ2,η1,η1-N 2) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.",

author = "Bernskoetter, \{Wesley H.\} and Pool, \{Jaime A.\} and Emil Lobkovsky and Chirik, \{Paul J.\}",

year = "2005",

month = jun,

day = "1",

doi = "10.1021/ja050387b",

language = "English (US)",

volume = "127",

pages = "7901--7911",

journal = "Journal of the American Chemical Society",

issn = "0002-7863",

publisher = "American Chemical Society",

number = "21",

}

Bernskoetter, WH, Pool, JA, Lobkovsky, E & Chirik, PJ 2005, 'Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η⁵-C₅Me₄H) ₂Zr]₂(μ₂,η², η²-N₂): Observation of side-on and end-on diazenido complexes in the reduction of N₂ to hydrazine', Journal of the American Chemical Society, vol. 127, no. 21, pp. 7901-7911. https://doi.org/10.1021/ja050387b

Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η⁵-C₅Me₄H) ₂Zr]₂(μ₂,η², η²-N₂): Observation of side-on and end-on diazenido complexes in the reduction of N₂ to hydrazine. / Bernskoetter, Wesley H.; Pool, Jaime A.; Lobkovsky, Emil et al.
In: Journal of the American Chemical Society, Vol. 127, No. 21, 01.06.2005, p. 7901-7911.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(η5-C5Me4H) 2Zr]2(μ2,η2, η2-N2)

T2 - Observation of side-on and end-on diazenido complexes in the reduction of N2 to hydrazine

AU - Bernskoetter, Wesley H.

AU - Pool, Jaime A.

AU - Lobkovsky, Emil

AU - Chirik, Paul J.

PY - 2005/6/1

Y1 - 2005/6/1

N2 - Functionalization of the N2 ligand in the side-on bound dinitrogen complex, [(η5-C5Me4H) 2Zr]2-(μ2,η2, η2-N2), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocene diazenido complexes, [(η5-C5Me4H)2Zr(C≡CR)] 2(μ2,η2,η2-N 2H2) (R = nBu, tBu, Ph). Characterization of [(η5- C5Me4H) 2Zr(C≡CCMe3)]2(μ2, η2,η2-N2H2) by X-ray diffraction revealed a side-on bound diazenido ligand in the solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion between η1,η1 and η2,η2 hapticity of the [N2H 2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(η5-C 5Me4H)2ZrX]2(μ2, η1,η1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded η1,η1 coordination of the [N2H 2]2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases π-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(η5-C5Me4H)2ZrH] 2(μ2,η2,η2-N 2H2), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting α-migration and N2 cleavage up to temperatures of 115 °C. Dinitrogen functionalization with [(η5-C5Me4H)2Zr] 2(μ2,η2,η2-N 2) was also accomplished by addition of proton donors. Weak Bronsted acids such as water and ethanol yield hydrazine and (η5-C 5Me4H)2Zr(OH)2 and (η5-C5Me4H)2-Zr(OEt) 2, respectively. Treatment of [(η5-C 5Me4H)2Zr]2(μ2, η2,η2-N2) with HNMe2 or H2NNMe2 furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(η5-C 5Me5)2Zr(η1-N2)] 2(μ2,η1,η1-N 2) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.

AB - Functionalization of the N2 ligand in the side-on bound dinitrogen complex, [(η5-C5Me4H) 2Zr]2-(μ2,η2, η2-N2), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocene diazenido complexes, [(η5-C5Me4H)2Zr(C≡CR)] 2(μ2,η2,η2-N 2H2) (R = nBu, tBu, Ph). Characterization of [(η5- C5Me4H) 2Zr(C≡CCMe3)]2(μ2, η2,η2-N2H2) by X-ray diffraction revealed a side-on bound diazenido ligand in the solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion between η1,η1 and η2,η2 hapticity of the [N2H 2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(η5-C 5Me4H)2ZrX]2(μ2, η1,η1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded η1,η1 coordination of the [N2H 2]2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases π-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(η5-C5Me4H)2ZrH] 2(μ2,η2,η2-N 2H2), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting α-migration and N2 cleavage up to temperatures of 115 °C. Dinitrogen functionalization with [(η5-C5Me4H)2Zr] 2(μ2,η2,η2-N 2) was also accomplished by addition of proton donors. Weak Bronsted acids such as water and ethanol yield hydrazine and (η5-C 5Me4H)2Zr(OH)2 and (η5-C5Me4H)2-Zr(OEt) 2, respectively. Treatment of [(η5-C 5Me4H)2Zr]2(μ2, η2,η2-N2) with HNMe2 or H2NNMe2 furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(η5-C 5Me5)2Zr(η1-N2)] 2(μ2,η1,η1-N 2) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.

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