Thermochemical Insight into the Reduction of CO to CH3OH with [Re(CO)]+and [Mn(CO)]+Complexes

Wiedner, Eric S.; Appel, Aaron M.

doi:10.1021/ja502316e

Cited by 13 publications

(36 citation statements)

References 58 publications

(116 reference statements)

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“…This finding is consistent with the O atom accepting a proton from the incoming H 2 molecule. Consistent with this finding, the acidity of M(CHOH) + has more of an effect on Δ G ° H2 of the Mn(CO) + and Re(CO) + complexes than does hydricity of M(CHO) …”

Section: Resultscontrasting

confidence: 87%

“…The set of candidate descriptors was composed of the natural charges on the atoms in the M-CO group ( q M , q C , q O ) and the square of the interatomic distances between the same atoms ( r MC 2 , r CO 2 ) in units of Å 2 (to account for electrostatic attraction and repulsion according to Coulomb’s law). To examine the effects of ancillary ligand identity, the computational data set was expanded to include additional [Cp R Mn(L)(NO)(CO)] + and [Cp R Re(L)(NO)(CO)] + complexes (R = H and Me; L = CO and PMe 3 ) that were included in our previous thermodynamic study . Multiple regression analysis of these data points and descriptors was used to identify models that reasonably predicted Δ G ° H2 .…”

Section: Resultssupporting

confidence: 57%

“…The Cr(CHO) complex proved to be too unstable for a reliable measurement of an equilibrium hydride transfer according to eq . As a result, the hydride donor ability of Cr(CHO) was calculated using the same density functional theory (DFT) methodology employed in our previous thermodynamic studies of Re and Mn carbonyl complexes . In analogy to eq , DFT was used to calculate the free energy for hydride transfer from Cr(CHO) to Mo(CO) + , affording Δ G ° H– = 43.1 kcal mol –1 for Cr(CHO) .…”

Section: Resultsmentioning

confidence: 99%

“…To better understand how to reduce CO with molecular catalysts, several groups have measured the thermodynamics for hydride transfer to metal-coordinated CO ligands to afford metal formyl complexes. − However, we have previously shown that it is insufficient to consider only the hydride acceptor ability of the CO ligand since hydrogenation to C1 products involves the net transfer of both a hydride and a proton, affording a hydroxy carbene ligand that can be further reduced. In an experimental study of the well-known complex [CpRe(PPh 3 )(NO)(CO)] + , we demonstrated that hydride transfer to the carbonyl ligand is thermodynamically favorable under basic conditions, while protonation of the resulting formyl ligand is favorable under acidic conditions (Figure A) . This mismatch in the thermodynamics for hydride and proton transfer stems from the large free energy for the net reaction of H 2 addition (Δ G ° H2 = 15.0 kcal/mol) to the carbonyl ligand of [CpRe(PPh 3 )(NO)(CO)] + .…”

Section: Introductionmentioning

confidence: 96%

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Thermodynamic Trends for Reduction of CO by Molecular Complexes

et al. 2021

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Selective reduction of CO 2 into fuels and chemical feedstocks is highly desirable to reduce our dependence on fossil fuels. Most molecular catalysts afford 2e − reduction products, such as CO or HCO 2 − , as opposed to more reduced products. Here we present an analysis of the thermodynamic limitations for reduction of the CO ligand in the form of a series of isostructural group 6 carbonyl complexes, Cp*M(CO) 3 (P(OMe) 3 ) + (M = Cr, Mo, and W). The free energy for stepwise transfer of a hydride (H − ) and a proton (H + ) to the CO ligand, resulting in a hydroxycarbene (CHOH) complex, was measured by equilibration with H − /H + donors and acceptors with known hydricity or acidity. Together, these two reaction steps are equivalent to a net addition of H 2 across the CO ligand. A large and unfavorable free energy for H 2 addition (ΔG°H 2 ) was measured for all three complexes and decreases in the order Cr > Mo > W. The trend for these complexes is opposite to the trend previously reported for group 7 carbonyl complexes, for which ΔG°H 2 decreases moving up the group, Re > Mn. Computational analysis indicates the trends can be described in terms of electrostatic effects, where a low ΔG°H 2 is obtained in complexes that balance the atomic charges of the M−CO fragment of the complex. These findings can be used to design metal carbonyl complexes with a more energetically accessible H 2 addition, which will facilitate the development of molecular catalysts for reduction of CO.

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Section: Resultscontrasting

confidence: 87%

Section: Resultssupporting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

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Thermodynamic Trends for Reduction of CO by Molecular Complexes

et al. 2021

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“…Scheme 47) to hydroxymethyl complexes was investigated as a model for important steps in the reduction of CO to methanol [949]. Although the key studies could not be performed on the metal formyl and M a n u s c r i p t 87 hydroxycarbene complexes in some cases due to stability issues, they could be probed for electronically related acetyl complexes.…”

Section: )mentioning

confidence: 99%