Thermodynamics of N-H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand

Máté J. Bezdek; Paul J. Chirik

doi:10.1039/c6dt01932c

Thermodynamics of N-H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand

Máté J. Bezdek, Paul J. Chirik

Chemistry

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Abstract

A series of bis(phosphine) molybdenum(ii) diazenides [(dppe)₂Mo(NNCy)(I)], [(dppe)₂(CH₃CN)Mo(NNCy)][BArF₂₄] and [(dppe)₂)(3,5-(CF₃)₂C₆H₃CN)Mo(NNCy)][BArF₂₄] (dppe = 1,2-bis(diphenylphosphino)ethane; Cy = cyclohexyl; ArF₂₄ = (3,5-(CF₃)₂C₆H₃)₄) were synthesized and structurally characterized. Treatment of the diazenido complexes with a stoichiometric amount of [H(OEt₂)₂][BArF₂₄] afforded the corresponding molybdenum(iv) hydrazido species [(dppe)₂Mo(NNHCy)(I)][BArF₂₄], [(dppe)₂(CH₃CN)Mo(NNHCy)][BArF₂₄]₂ and [(dppe)₂(3,5-(CF₃)₂C₆H₃CN)Mo(NNHCy)][BArF₂₄]₂, enabling the study of N-H bond dissociation free energies (BDFEs) in the classical Chatt-type bis(phosphine) diazenide platform as a function of ligand (L) trans to the nitrogenous fragment. Deprotonation and electrochemical experiments established that the trans nitrile 3,5-(CF₃)₂C₆H₃CN afforded the least reducing molybdenum(iv) hydrazido complex in the series (E°_red = -1.32 V vs. Fc/Fc⁺) with the most acidic N-H bond (pK_a < 2.6, THF), whereas the ligands CH₃CN (E°_red = -1.60 V, pK_a < 5.5) and I^- (E°_red = -2.03 V, pK_a = 9.3) gave more reducing complexes with less acidic N-H bonds. Computational (DFT) studies confirm weak N-H bond strengths of 32.8 (L = I^-), 35.4 (L = CH₃CN) and 36.2 kcal mol^-1 (L = 3,5-(CF₃)₂C₆H₃CN) in the hydrazido series.

Original language	English (US)
Pages (from-to)	15922-15930
Number of pages	9
Journal	Dalton Transactions
Volume	45
Issue number	40
DOIs	https://doi.org/10.1039/c6dt01932c
State	Published - 2016

All Science Journal Classification (ASJC) codes

Inorganic Chemistry

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10.1039/c6dt01932c

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@article{4d573a039344487a9f519835703b94f2,

title = "Thermodynamics of N-H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand",

abstract = "A series of bis(phosphine) molybdenum(ii) diazenides [(dppe)2Mo(NNCy)(I)], [(dppe)2(CH3CN)Mo(NNCy)][BArF24] and [(dppe)2)(3,5-(CF3)2C6H3CN)Mo(NNCy)][BArF24] (dppe = 1,2-bis(diphenylphosphino)ethane; Cy = cyclohexyl; ArF24 = (3,5-(CF3)2C6H3)4) were synthesized and structurally characterized. Treatment of the diazenido complexes with a stoichiometric amount of [H(OEt2)2][BArF24] afforded the corresponding molybdenum(iv) hydrazido species [(dppe)2Mo(NNHCy)(I)][BArF24], [(dppe)2(CH3CN)Mo(NNHCy)][BArF24]2 and [(dppe)2(3,5-(CF3)2C6H3CN)Mo(NNHCy)][BArF24]2, enabling the study of N-H bond dissociation free energies (BDFEs) in the classical Chatt-type bis(phosphine) diazenide platform as a function of ligand (L) trans to the nitrogenous fragment. Deprotonation and electrochemical experiments established that the trans nitrile 3,5-(CF3)2C6H3CN afforded the least reducing molybdenum(iv) hydrazido complex in the series (E°red = -1.32 V vs. Fc/Fc+) with the most acidic N-H bond (pKa < 2.6, THF), whereas the ligands CH3CN (E°red = -1.60 V, pKa < 5.5) and I- (E°red = -2.03 V, pKa = 9.3) gave more reducing complexes with less acidic N-H bonds. Computational (DFT) studies confirm weak N-H bond strengths of 32.8 (L = I-), 35.4 (L = CH3CN) and 36.2 kcal mol-1 (L = 3,5-(CF3)2C6H3CN) in the hydrazido series.",

author = "Bezdek, {M{\'a}t{\'e} J.} and Chirik, {Paul J.}",

note = "Publisher Copyright: {\textcopyright} 2016 The Royal Society of Chemistry.",

year = "2016",

doi = "10.1039/c6dt01932c",

language = "English (US)",

volume = "45",

pages = "15922--15930",

journal = "Dalton Transactions",

issn = "1477-9226",

publisher = "Royal Society of Chemistry",

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TY - JOUR

T1 - Thermodynamics of N-H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand

AU - Bezdek, Máté J.

AU - Chirik, Paul J.

PY - 2016

Y1 - 2016

N2 - A series of bis(phosphine) molybdenum(ii) diazenides [(dppe)2Mo(NNCy)(I)], [(dppe)2(CH3CN)Mo(NNCy)][BArF24] and [(dppe)2)(3,5-(CF3)2C6H3CN)Mo(NNCy)][BArF24] (dppe = 1,2-bis(diphenylphosphino)ethane; Cy = cyclohexyl; ArF24 = (3,5-(CF3)2C6H3)4) were synthesized and structurally characterized. Treatment of the diazenido complexes with a stoichiometric amount of [H(OEt2)2][BArF24] afforded the corresponding molybdenum(iv) hydrazido species [(dppe)2Mo(NNHCy)(I)][BArF24], [(dppe)2(CH3CN)Mo(NNHCy)][BArF24]2 and [(dppe)2(3,5-(CF3)2C6H3CN)Mo(NNHCy)][BArF24]2, enabling the study of N-H bond dissociation free energies (BDFEs) in the classical Chatt-type bis(phosphine) diazenide platform as a function of ligand (L) trans to the nitrogenous fragment. Deprotonation and electrochemical experiments established that the trans nitrile 3,5-(CF3)2C6H3CN afforded the least reducing molybdenum(iv) hydrazido complex in the series (E°red = -1.32 V vs. Fc/Fc+) with the most acidic N-H bond (pKa < 2.6, THF), whereas the ligands CH3CN (E°red = -1.60 V, pKa < 5.5) and I- (E°red = -2.03 V, pKa = 9.3) gave more reducing complexes with less acidic N-H bonds. Computational (DFT) studies confirm weak N-H bond strengths of 32.8 (L = I-), 35.4 (L = CH3CN) and 36.2 kcal mol-1 (L = 3,5-(CF3)2C6H3CN) in the hydrazido series.

AB - A series of bis(phosphine) molybdenum(ii) diazenides [(dppe)2Mo(NNCy)(I)], [(dppe)2(CH3CN)Mo(NNCy)][BArF24] and [(dppe)2)(3,5-(CF3)2C6H3CN)Mo(NNCy)][BArF24] (dppe = 1,2-bis(diphenylphosphino)ethane; Cy = cyclohexyl; ArF24 = (3,5-(CF3)2C6H3)4) were synthesized and structurally characterized. Treatment of the diazenido complexes with a stoichiometric amount of [H(OEt2)2][BArF24] afforded the corresponding molybdenum(iv) hydrazido species [(dppe)2Mo(NNHCy)(I)][BArF24], [(dppe)2(CH3CN)Mo(NNHCy)][BArF24]2 and [(dppe)2(3,5-(CF3)2C6H3CN)Mo(NNHCy)][BArF24]2, enabling the study of N-H bond dissociation free energies (BDFEs) in the classical Chatt-type bis(phosphine) diazenide platform as a function of ligand (L) trans to the nitrogenous fragment. Deprotonation and electrochemical experiments established that the trans nitrile 3,5-(CF3)2C6H3CN afforded the least reducing molybdenum(iv) hydrazido complex in the series (E°red = -1.32 V vs. Fc/Fc+) with the most acidic N-H bond (pKa < 2.6, THF), whereas the ligands CH3CN (E°red = -1.60 V, pKa < 5.5) and I- (E°red = -2.03 V, pKa = 9.3) gave more reducing complexes with less acidic N-H bonds. Computational (DFT) studies confirm weak N-H bond strengths of 32.8 (L = I-), 35.4 (L = CH3CN) and 36.2 kcal mol-1 (L = 3,5-(CF3)2C6H3CN) in the hydrazido series.

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U2 - 10.1039/c6dt01932c

DO - 10.1039/c6dt01932c

M3 - Article

C2 - 27378665

AN - SCOPUS:84991387283

SN - 1477-9226

VL - 45

SP - 15922

EP - 15930

JO - Dalton Transactions

JF - Dalton Transactions

IS - 40

ER -

Thermodynamics of N-H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand

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