Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine: Formation of Complexes with Bound Amines

Shaoguang Zhang, R Morris Bullock

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature 1H and 31P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis- and trans-isomers. The structures of both cis-CpMo(CO)(PEtNMePEt)H and trans-CpMo(CO)(PPhNMePPh)H were determined by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(PEtNMePEt)H and CpMo(CO)(PPhNMePPh)H in CH3CN are both irreversible at slow scan rates and quasireversible at higher scan rates, with E1/2 = -0.36 V (vs Cp2Fe+/0) for CpMo(CO)(PEtNMePEt)H and E1/2 = -0.18 V for CpMo(CO)(PPhNMePPh)H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C]+[A]- (A = B(C6F5)4 or BArF4; [ArF = 3,5-bis(trifluoromethyl)phenyl]) afforded "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes that feature the amine bound to the metal. Displacement of the κ3 Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)]+. The kinetics of this reaction were studied by 31P{1H} NMR spectroscopy for [CpMo(CO)(κ3-PEtNMePEt)]+, providing the activation parameters ΔH = 21.6 ± 2.8 kcal/mol, ΔS = -0.3 ± 9.8 cal/(mol K), Ea = 22.1 ± 2.8 kcal/mol. Protonation of CpMo(CO)(PEtNMePEt)H affords the Mo dihydride complex [CpMo(CO)(κ2-PEtNMePEt)(H)2]+, which loses H2 to generate [CpMo(CO)(κ3-PEtNMePEt)]+ at room temperature. Our results show that the pendant amine has a strong driving force to form stable "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2]+ complexes by formation of a Mo-N dative bond. CpMo(CO)(dppp)H (dppp = 1,3-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2]+. (Chemical Equation Presented).

Original languageEnglish
Pages (from-to)6397-6409
Number of pages13
JournalInorganic Chemistry
Volume54
Issue number13
DOIs
Publication statusPublished - Jul 6 2015

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Bearings (structural)
dihydrides
Molybdenum
Hydrides
hydrides
molybdenum
Amines
amines
Protonation
Ligands
ligands
Nuclear magnetic resonance spectroscopy
Hydrogen
nuclear magnetic resonance
electrochemical oxidation
Electrochemical oxidation
propane
Isomers
spectroscopy
elimination

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine : Formation of Complexes with Bound Amines. / Zhang, Shaoguang; Bullock, R Morris.

In: Inorganic Chemistry, Vol. 54, No. 13, 06.07.2015, p. 6397-6409.

Research output: Contribution to journalArticle

@article{67a13d2a813e41b1a35042892a5755c3,
title = "Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine: Formation of Complexes with Bound Amines",
abstract = "CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature 1H and 31P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis- and trans-isomers. The structures of both cis-CpMo(CO)(PEtNMePEt)H and trans-CpMo(CO)(PPhNMePPh)H were determined by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(PEtNMePEt)H and CpMo(CO)(PPhNMePPh)H in CH3CN are both irreversible at slow scan rates and quasireversible at higher scan rates, with E1/2 = -0.36 V (vs Cp2Fe+/0) for CpMo(CO)(PEtNMePEt)H and E1/2 = -0.18 V for CpMo(CO)(PPhNMePPh)H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C]+[A]- (A = B(C6F5)4 or BArF4; [ArF = 3,5-bis(trifluoromethyl)phenyl]) afforded {"}tuck-in{"} [CpMo(CO)(κ3-PNP)]+ complexes that feature the amine bound to the metal. Displacement of the κ3 Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)]+. The kinetics of this reaction were studied by 31P{1H} NMR spectroscopy for [CpMo(CO)(κ3-PEtNMePEt)]+, providing the activation parameters ΔH‡ = 21.6 ± 2.8 kcal/mol, ΔS‡ = -0.3 ± 9.8 cal/(mol K), Ea = 22.1 ± 2.8 kcal/mol. Protonation of CpMo(CO)(PEtNMePEt)H affords the Mo dihydride complex [CpMo(CO)(κ2-PEtNMePEt)(H)2]+, which loses H2 to generate [CpMo(CO)(κ3-PEtNMePEt)]+ at room temperature. Our results show that the pendant amine has a strong driving force to form stable {"}tuck-in{"} [CpMo(CO)(κ3-PNP)]+ complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2]+ complexes by formation of a Mo-N dative bond. CpMo(CO)(dppp)H (dppp = 1,3-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2]+. (Chemical Equation Presented).",
author = "Shaoguang Zhang and Bullock, {R Morris}",
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T1 - Molybdenum Hydride and Dihydride Complexes Bearing Diphosphine Ligands with a Pendant Amine

T2 - Formation of Complexes with Bound Amines

AU - Zhang, Shaoguang

AU - Bullock, R Morris

PY - 2015/7/6

Y1 - 2015/7/6

N2 - CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature 1H and 31P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis- and trans-isomers. The structures of both cis-CpMo(CO)(PEtNMePEt)H and trans-CpMo(CO)(PPhNMePPh)H were determined by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(PEtNMePEt)H and CpMo(CO)(PPhNMePPh)H in CH3CN are both irreversible at slow scan rates and quasireversible at higher scan rates, with E1/2 = -0.36 V (vs Cp2Fe+/0) for CpMo(CO)(PEtNMePEt)H and E1/2 = -0.18 V for CpMo(CO)(PPhNMePPh)H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C]+[A]- (A = B(C6F5)4 or BArF4; [ArF = 3,5-bis(trifluoromethyl)phenyl]) afforded "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes that feature the amine bound to the metal. Displacement of the κ3 Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)]+. The kinetics of this reaction were studied by 31P{1H} NMR spectroscopy for [CpMo(CO)(κ3-PEtNMePEt)]+, providing the activation parameters ΔH‡ = 21.6 ± 2.8 kcal/mol, ΔS‡ = -0.3 ± 9.8 cal/(mol K), Ea = 22.1 ± 2.8 kcal/mol. Protonation of CpMo(CO)(PEtNMePEt)H affords the Mo dihydride complex [CpMo(CO)(κ2-PEtNMePEt)(H)2]+, which loses H2 to generate [CpMo(CO)(κ3-PEtNMePEt)]+ at room temperature. Our results show that the pendant amine has a strong driving force to form stable "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2]+ complexes by formation of a Mo-N dative bond. CpMo(CO)(dppp)H (dppp = 1,3-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2]+. (Chemical Equation Presented).

AB - CpMo(CO)(PNP)H complexes (PNP = (R2PCH2)2NMe, R = Et or Ph) were synthesized by displacement of two CO ligands of CpMo(CO)3H by the PNP ligand; these complexes were characterized by IR and variable temperature 1H and 31P NMR spectroscopy. CpMo(CO)(PNP)H complexes are formed as mixture of cis- and trans-isomers. The structures of both cis-CpMo(CO)(PEtNMePEt)H and trans-CpMo(CO)(PPhNMePPh)H were determined by single crystal X-ray diffraction. Electrochemical oxidation of CpMo(CO)(PEtNMePEt)H and CpMo(CO)(PPhNMePPh)H in CH3CN are both irreversible at slow scan rates and quasireversible at higher scan rates, with E1/2 = -0.36 V (vs Cp2Fe+/0) for CpMo(CO)(PEtNMePEt)H and E1/2 = -0.18 V for CpMo(CO)(PPhNMePPh)H. Hydride abstraction from CpMo(CO)(PNP)H with [Ph3C]+[A]- (A = B(C6F5)4 or BArF4; [ArF = 3,5-bis(trifluoromethyl)phenyl]) afforded "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes that feature the amine bound to the metal. Displacement of the κ3 Mo-N bond by CD3CN gives [CpMo(CO)(PNP)(CD3CN)]+. The kinetics of this reaction were studied by 31P{1H} NMR spectroscopy for [CpMo(CO)(κ3-PEtNMePEt)]+, providing the activation parameters ΔH‡ = 21.6 ± 2.8 kcal/mol, ΔS‡ = -0.3 ± 9.8 cal/(mol K), Ea = 22.1 ± 2.8 kcal/mol. Protonation of CpMo(CO)(PEtNMePEt)H affords the Mo dihydride complex [CpMo(CO)(κ2-PEtNMePEt)(H)2]+, which loses H2 to generate [CpMo(CO)(κ3-PEtNMePEt)]+ at room temperature. Our results show that the pendant amine has a strong driving force to form stable "tuck-in" [CpMo(CO)(κ3-PNP)]+ complexes, and also promotes hydrogen elimination from [CpMo(CO)(PNP)(H)2]+ complexes by formation of a Mo-N dative bond. CpMo(CO)(dppp)H (dppp = 1,3-bis(diphenylphosphino)propane) was studied as a Mo diphosphine analogue without a pendant amine, and the product of protonation of this complex gives [CpMo(CO)(dppp)(H)2]+. (Chemical Equation Presented).

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