Novel types of hydrogen bonds involving transition metal atoms and proton transfer (XH ⋯ M, [MH]+ ⋯ B, [MH]+ ⋯ A−)

Epstein, Lina M.; Крылов, А. Н.; Shubina, Elena S.

doi:10.1016/0022-2860(94)87052-7

Cited by 30 publications

(21 citation statements)

References 15 publications

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“…The lineshape analysis of the 1 H resonance was complicated by the lack of knowledge of J HP data due to broadness in the low-temperature spectra, but a simulation using the rate constant obtained from the 31 P NMR spectrum and a reasonable guess for the J HP values gave a reasonable fit above coalescence, suggesting that the same mechanism is responsible for both H and P exchange processes. A possibility for this mechanism is illustrated in Scheme 3.…”

Section: Resultsmentioning

confidence: 91%

“…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%

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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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Section: Resultsmentioning

confidence: 91%

Section: In Dichloromethanementioning

confidence: 92%

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

et al. 2007

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“…In an MH···HA dihydrogen bond, [7,8] electrons come from a s bonding electron pair of an MÀH bond localized mainly on the hydride ligand. [13] In the same way, hydrogen bonding to metal atoms was found to intermediate metal protonation of transition metal complexes, [14][15][16] and dihydrogen bonding was shown to precede hydride ligand protonation yielding h 2 -H 2 complexes. [1,2,7,[10][11][12] In this case electrons of filled d orbitals of the metal are donated to s Ã AH .…”

Section: Introductionmentioning

confidence: 84%

“…[2] Hydrogen bonds play a key role as initial stage of the proton-transfer reaction to organic bases. [13] In the same way, hydrogen bonding to metal atoms was found to intermediate metal protonation of transition metal complexes, [14][15][16] and dihydrogen bonding was shown to precede hydride ligand protonation yielding h 2 -H 2 complexes. [7,17] Basic knowledge accumulated over the last two decades suggests that a direct proton transfer to a metal lone pair is an unlikely event in the presence of hydride ligands, which are considered to be the kinetic site of proton attack even if classical di(poly)hydride were the thermodynamic protonation product.…”

Section: Introductionmentioning

confidence: 84%

Directionality of Dihydrogen Bonds: The Role of Transition Metal Atoms

Filippov¹,

Belkova²,

Epstein³

et al. 2012

ChemPhysChem

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A theoretical study on two series of electron-rich group 8 hydrides is carried out to evaluate involvement of the transition metal in dihydrogen bonding. To this end, the structural and electronic parameters are computed at the DFT/B3PW91 level for hydrogen-bonded adducts of [(PP(3))MH(2)] and [Cp*MH(dppe)] (M = Fe, Ru, Os; PP(3) = κ(4)-P(CH(2)CH(2)PPh(2))(3), dppe = κ(2)-Ph(2)PCH(2)CH(2)PPh(2)) with CF(3)CH(2)OH (TFE) as proton donor. The results are compared with those of adduct [Cp(2)NbH(3)]⋅TFE featuring a "pure" dihydrogen bond, and classical hydrogen bonds in pyridine⋅TFE and Me(3)N⋅TFE. Deviation of the H⋅⋅⋅H-A fragment from linearity is shown to originate from the metal participation in dihydrogen bonding. The latter is confirmed by the electronic parameters obtained by NBO and AIM analysis. Considered together, orbital interaction energies and hydrogen bond ellipticity are salient indicators of this effect and allow the MH⋅⋅⋅HA interaction to be described as a bifurcate hydrogen bond. The impact of the M⋅⋅⋅HA interaction is shown to increase on descending the group, and this explains the experimental trends in mechanisms of proton-transfer reactions via MH⋅⋅⋅HA intermediates. Strengthening of the M⋅⋅⋅H interaction in the case of electron-rich 5d metal hydrides leads to direct proton transfer to the metal atom.

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“…Additional stabilization originated from the contact between the dihydrogen ligand and the counter-ion. Structural elucidation of quite a few examples of these intermediates allowed for the generalization of the mechanism of the proton transfer processes under consideration [47,48,3]. NMR spectroscopic evidence for the MHÁÁÁHX hydrogen bonding is acquired by upfield shifts of the hydride resonance and a decrease of the relaxation times (T 1min ) [12].…”

Section: Introductionmentioning

confidence: 99%