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Issue 40, 2016
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Thermodynamics of N–H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand

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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 (Image ID:c6dt01932c-t1.gif = −1.32 V vs. Fc/Fc+) with the most acidic N–H bond (pKa < 2.6, THF), whereas the ligands CH3CN (Image ID:c6dt01932c-t2.gif = −1.60 V, pKa < 5.5) and I (Image ID:c6dt01932c-t3.gif = −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.

Graphical abstract: Thermodynamics of N–H bond formation in bis(phosphine) molybdenum(ii) diazenides and the influence of the trans ligand

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Publication details

The article was received on 15 May 2016, accepted on 28 Jun 2016 and first published on 29 Jun 2016


Article type: Paper
DOI: 10.1039/C6DT01932C
Citation: Dalton Trans., 2016,45, 15922-15930
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    Thermodynamics of N–H bond formation in bis(phosphine) molybdenum(II) diazenides and the influence of the trans ligand

    M. J. Bezdek and P. J. Chirik, Dalton Trans., 2016, 45, 15922
    DOI: 10.1039/C6DT01932C

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