The role of hydrogen bonds involving the metal atom in protonation of polyhydrides of molybdenum and tungsten of MH4(dppe)2

Shubina, Elena S.; Крылов, А. Н.; Belkova, Natalia V.; Epstein, Lina M.; Borisov, A. P.; Mahaev, V.D.

doi:10.1016/0022-328x(95)05401-a

Cited by 26 publications

(25 citation statements)

References 5 publications

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“…[13] Relative to the complex [Cp*FeH(dppe)] (E j = 1.36 AE 0.02), [25] which prefers to use the hydride site, hydrogen bonding has been shown to occur at the metal site for compounds with both higher basicity factors, for example, [(NP 3 )ReH 3 ] (E j = 1.46 AE 0.01) (NP 3 = N(CH 2 CH 2 PPh 2 ) 3 ) [10] and (PP 3 )RhH (E j = 1.40), [64] and lower ones, for example, [WH 4 (dppe) 2 ] (E j = 1.20). [65] Thus, the reasons for the preference of the metal or hydride site for hydrogen bonding are not clear at the moment. This topic definitely needs further work, both at the experimental and at the theoretical levels, greater understanding and predictive power may be attained.…”

Section: Discussionmentioning

confidence: 99%

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

Belkova

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et al. 2005

Chemistry A European J

133

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The present contribution reports experimental and computational investigations of the interaction between [Cp*Fe(dppe)H] and different proton donors (HA). The focus is on the structure of the proton transfer intermediates and on the potential energy surface of the proton transfer leading to the dihydrogen complex [Cp*Fe(dppe)(H2)]+. With p-nitrophenol (PNP) a UV/Visible study provides evidence of the formation of the ion-pair stabilized by a hydrogen bond between the nonclassical cation [Cp*Fe(dppe)(H2)]+ and the homoconjugated anion ([AHA]-). With trifluoroacetic acid (TFA), the hydrogen-bonded ion pair containing the simple conjugate base (A-) in equilibrium with the free ions is observed by IR spectroscopy when using a deficit of the proton donor. An excess leads to the formation of the homoconjugated anion. The interaction with hexafluoroisopropanol (HFIP) was investigated quantitatively by IR spectroscopy and by 1H and 31P NMR spectroscopy at low temperatures (200-260 K) and by stopped-flow kinetics at about room temperature (288-308 K). The hydrogen bond formation to give [Cp*Fe(dppe)H]HA is characterized by DeltaH degrees =-6.5+/-0.4 kcal mol(-1) and DeltaS degrees = -18.6+/-1.7 cal mol(-1) K(-1). The activation barrier for the proton transfer step, which occurs only upon intervention of a second HFIP molecule, is DeltaH(not equal) = 2.6+/-0.3 kcal mol(-1) and DeltaS(not equal) = -44.5+/-1.1 cal mol(-1) K(-1). The computational investigation (at the DFT/B3 LYP level with inclusion of solvent effects by the polarizable continuum model) reproduces all the qualitative findings, provided the correct number of proton donor molecules are used in the model. The proton transfer process is, however, computed to be less exothermic than observed in the experiment.

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Section: Discussionmentioning

confidence: 99%

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

Belkova

Collange

Dub

et al. 2005

Chemistry A European J

133

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“…A tentative assignment of all observed bands is possible on the basis of previous IR studies into the interaction between CF 3 COOH and various bases, [30][31][32] in combination with the results shown in the previous section. At 200 K the acid self-association equilibrium is shifted to the dimer, exhibiting a strong band at 1780 cm -1 with a shoulder at 1800 cm -1 (Figure 9 the position of the free CF 3 COO -anion [31,32] indicates the formation of either a weakly H-bonded contact ion pair or a solvent-separated ion pair, consistent with the relatively high polarity of CH 2 Cl 2 at low temperatures and the poor proton-donor ability of the [Cp*Mo(dppe)H 4 ] + cation. In reference to Scheme 1, this means that species V is extensively dissociated to VI or that the interaction is loose under these solvent and temperature conditions.…”

Section: In Dichloromethanementioning

confidence: 92%

Solvent Control in the Protonation of [Cp*Mo(dppe)H₃] by CF₃COOH

et al. 2007

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The outcome of the reaction between [Cp*Mo(dppe)H3] [dppe = 1,2‐bis(diphenylphosphanyl)ethane] and trifluoroacetic acid (TFA) is highly dependent on the solvent and the TFA/Mo ratio. The dihydride compound [Cp*Mo(dppe)H2(O2CCF3)] is obtained selectively when the reaction is carried out in aromatic hydrocarbons (benzene, toluene) when using less than one equivalent of TFA. The dihydride is also the end product when THF or MeCN are used as solvent, independent of the TFA/Mo ratio. In benzene/toluene the use of excess acid has a profound effect, resulting in the formation of the tetrahydrido complex [Cp*Mo(dppe)H4]+, which did not further evolve into the dihydrido product. Monitoring of the reaction by NMR and IR spectroscopy under different conditions (solvent, temperature, TFA/Mo ratio) reveals the rapid establishment of an equilibrium between the dihydrogen‐bonded adduct, [Cp*Mo(dppe)H3]···HO2CCF3, the ion‐paired proton‐transfer product, [Cp*Mo(dppe)H4]+···–O2CCF3, and the separated ions, followed by a slower irreversible transformation to the final dihydride product with H2 evolution. The activation parameters of the H2 evolution and M–OR product formation were determined. Excess TFA in low‐polarity solvents stabilizes the separated charged species by forming the homoconjugate anion [CF3COO(CF3COOH)n]–. The effect of the solvent on the course of the reaction can be interpreted in terms of the different polarity, H‐bonding ability, and coordinating power of the various solvent molecules.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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“…[1,2] The kinetic preference for hydride versus metal protonation is now quite firmly established, [3][4][5][6][7][8][9] though exceptions have recently been reported from studies carried out in our laboratories. [10,11] The proton transfer occurs via intermediates, for which characteristic spectroscopic signatures have been established, that contain hydrogen bonds between the proton donor and the proton acceptor (the metal center or a hydride ligand) (see Scheme 1). [12,13] The term "nonclassical hydrogen bonding" has been coined to address these interactions, while H-bonding specifically involving a hydride ligand has also been termed "dihydrogen bonding".…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Bonding and Proton Transfer to the Trihydride Complex [Cp*MoH₃(dppe)]: IR, NMR, and Theoretical Investigations

et al. 2006

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Keywords: Dihydrogen bonding / Hydride ligands / Molybdenum / Proton-transfer mechanism / DFT calculationsThe interaction between [Cp*MoH 3 (dppe)] (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) and a variety of proton donors has been investigated by a combination of experiments and DFT calculations. Weak proton donors [2-monofluoroethanol (MFE) and trifluoroethanol (TFE)] allow the determination of basicity factor (E j = 1.42 ± 0.02) and thermodynamic parameters for the hydrogen bond formation (∆H HB = -4.9 ± 0.2 and -6.1 ± 0.3 kcal mol -1 ; ∆S HB = -15.7 ± 0.7 and -20.4 ± 1 cal mol -1 K -1 for MFE and TFE, respectively). For TFE, a stable low-temperature proton-transfer equilibrium (220-240 K) with the cationic classical tetrahydrido derivative [Cp*MoH 4 (dppe)] + could be investigated independently by UV/Vis (∆H°P T = -2.8 ± 0.4 kcal mol -1 and ∆S°P T = -15 ± 2 cal mol -1 K -1 ) and 1 H NMR (∆H°P T = -2.7 ± 0.5 kcal mol -1 and ∆S°P T = -11 ± 2 cal mol -1 K -1 ) spectroscopy. Upon warming, however, the tetrahydride evolves by dihydrogen loss and formation of a hydride-free diamagnetic product. Stronger proton donors [hexafluoroisopropanol (HFIP), p-nitrophenol (PNP), perfluoro-tert-butyl alcohol (PFTB), and HBF 4 ·OEt 2 ] lead to more extensive proton transfer at lower donor/Mo ratios. A 1:1 proton-transfer stoichiometry is indicated independently by a titration experiment with UV/Vis monitoring for the [Cp*MoH 3 (dppe)]-PNP reaction, and by a stopped-flow kinetics investigation for the

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The role of hydrogen bonds involving the metal atom in protonation of polyhydrides of molybdenum and tungsten of MH4(dppe)2

Cited by 26 publications

References 5 publications

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

Solvent Control in the Protonation of [Cp*Mo(dppe)H₃] by CF₃COOH

Hydrogen Bonding and Proton Transfer to the Trihydride Complex [Cp*MoH₃(dppe)]: IR, NMR, and Theoretical Investigations

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The role of hydrogen bonds involving the metal atom in protonation of polyhydrides of molybdenum and tungsten of MH4(dppe)2

Cited by 26 publications

References 5 publications

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]

Solvent Control in the Protonation of [Cp*Mo(dppe)H3] by CF3COOH

Hydrogen Bonding and Proton Transfer to the Trihydride Complex [Cp*MoH3(dppe)]: IR, NMR, and Theoretical Investigations

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Product

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Solvent Control in the Protonation of [Cp*Mo(dppe)H₃] by CF₃COOH

Hydrogen Bonding and Proton Transfer to the Trihydride Complex [Cp*MoH₃(dppe)]: IR, NMR, and Theoretical Investigations