Thermochemical insight into the reduction of CO to CH3OH with [Re(CO)]+ and [Mn(CO)]+ complexes

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Abstract

To gain insight into thermodynamic barriers for reduction of CO into CH3OH, free energies for reduction of [CpRe(PPh3)(NO)(CO)] + into CpRe(PPh3)(NO)(CH2OH) have been determined from experimental measurements. Using model complexes, the free energies for the transfer of H+, H-, and e- have been determined. A pKa of 10.6 was estimated for [CpRe(PPh 3)(NO)(CHOH)]+ by measuring the pKa for the analogous [CpRe(PPh3)(NO)(CMeOH)]+. The hydride donor ability (δG°H -) of CpRe(PPh3)(NO) (CH2OH) was estimated to be 58.0 kcal mol-1, based on calorimetry measurements of the hydride-transfer reaction between CpRe(PPh 3)(NO)(CHO) and [CpRe(PPh3)(NO)(CHOMe)]+ to generate the methylated analogue, CpRe(PPh3)(NO)(CH2OMe). Cyclic voltammograms recorded on CpRe(PPh3)(NO)(CMeO), CpRe(PPh 3)(NO)(CH2OMe), and [CpRe(PPh3)(NO)(CHOMe)] + displayed either a quasireversible oxidation (neutral species) or reduction (cationic species). These potentials were used as estimates for the oxidation of CpRe(PPh3)(NO)(CHO) or CpRe(PPh3)(NO)(CH 2OH) or the reduction of [CpRe(PPh3)(NO)(CHOH)] +. Combination of the thermodynamic data permits construction of three-dimensional free energy landscapes under varying conditions of pH and PH2. The free energy for H2 addition (δG°H 2) to [CpRe(PPh3)(NO)(CO)]+ (+15 kcal mol -1) was identified as the most significant thermodynamic impediment for the reduction of CO. DFT computations on a series of [CpXM(L)(NO) (CO)]+ (M = Re, Mn) complexes indicate that δG°H 2 can be varied by 11 kcal mol-1 through variation of both the ancillary ligands and the metal.

Original languageEnglish
Pages (from-to)8661-8668
Number of pages8
JournalJournal of the American Chemical Society
Volume136
Issue number24
DOIs
Publication statusPublished - Jun 18 2014

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Carbon Monoxide
Free energy
Thermodynamics
Hydrides
Oxidation
Calorimetry
Energy Transfer
Discrete Fourier transforms
Metals
Ligands

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

@article{9792d41a7f1941b0885c7b3091f255b5,
title = "Thermochemical insight into the reduction of CO to CH3OH with [Re(CO)]+ and [Mn(CO)]+ complexes",
abstract = "To gain insight into thermodynamic barriers for reduction of CO into CH3OH, free energies for reduction of [CpRe(PPh3)(NO)(CO)] + into CpRe(PPh3)(NO)(CH2OH) have been determined from experimental measurements. Using model complexes, the free energies for the transfer of H+, H-, and e- have been determined. A pKa of 10.6 was estimated for [CpRe(PPh 3)(NO)(CHOH)]+ by measuring the pKa for the analogous [CpRe(PPh3)(NO)(CMeOH)]+. The hydride donor ability (δG°H -) of CpRe(PPh3)(NO) (CH2OH) was estimated to be 58.0 kcal mol-1, based on calorimetry measurements of the hydride-transfer reaction between CpRe(PPh 3)(NO)(CHO) and [CpRe(PPh3)(NO)(CHOMe)]+ to generate the methylated analogue, CpRe(PPh3)(NO)(CH2OMe). Cyclic voltammograms recorded on CpRe(PPh3)(NO)(CMeO), CpRe(PPh 3)(NO)(CH2OMe), and [CpRe(PPh3)(NO)(CHOMe)] + displayed either a quasireversible oxidation (neutral species) or reduction (cationic species). These potentials were used as estimates for the oxidation of CpRe(PPh3)(NO)(CHO) or CpRe(PPh3)(NO)(CH 2OH) or the reduction of [CpRe(PPh3)(NO)(CHOH)] +. Combination of the thermodynamic data permits construction of three-dimensional free energy landscapes under varying conditions of pH and PH2. The free energy for H2 addition (δG°H 2) to [CpRe(PPh3)(NO)(CO)]+ (+15 kcal mol -1) was identified as the most significant thermodynamic impediment for the reduction of CO. DFT computations on a series of [CpXM(L)(NO) (CO)]+ (M = Re, Mn) complexes indicate that δG°H 2 can be varied by 11 kcal mol-1 through variation of both the ancillary ligands and the metal.",
author = "Eric Wiedner and Aaron Appel",
year = "2014",
month = "6",
day = "18",
doi = "10.1021/ja502316e",
language = "English",
volume = "136",
pages = "8661--8668",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "24",

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TY - JOUR

T1 - Thermochemical insight into the reduction of CO to CH3OH with [Re(CO)]+ and [Mn(CO)]+ complexes

AU - Wiedner, Eric

AU - Appel, Aaron

PY - 2014/6/18

Y1 - 2014/6/18

N2 - To gain insight into thermodynamic barriers for reduction of CO into CH3OH, free energies for reduction of [CpRe(PPh3)(NO)(CO)] + into CpRe(PPh3)(NO)(CH2OH) have been determined from experimental measurements. Using model complexes, the free energies for the transfer of H+, H-, and e- have been determined. A pKa of 10.6 was estimated for [CpRe(PPh 3)(NO)(CHOH)]+ by measuring the pKa for the analogous [CpRe(PPh3)(NO)(CMeOH)]+. The hydride donor ability (δG°H -) of CpRe(PPh3)(NO) (CH2OH) was estimated to be 58.0 kcal mol-1, based on calorimetry measurements of the hydride-transfer reaction between CpRe(PPh 3)(NO)(CHO) and [CpRe(PPh3)(NO)(CHOMe)]+ to generate the methylated analogue, CpRe(PPh3)(NO)(CH2OMe). Cyclic voltammograms recorded on CpRe(PPh3)(NO)(CMeO), CpRe(PPh 3)(NO)(CH2OMe), and [CpRe(PPh3)(NO)(CHOMe)] + displayed either a quasireversible oxidation (neutral species) or reduction (cationic species). These potentials were used as estimates for the oxidation of CpRe(PPh3)(NO)(CHO) or CpRe(PPh3)(NO)(CH 2OH) or the reduction of [CpRe(PPh3)(NO)(CHOH)] +. Combination of the thermodynamic data permits construction of three-dimensional free energy landscapes under varying conditions of pH and PH2. The free energy for H2 addition (δG°H 2) to [CpRe(PPh3)(NO)(CO)]+ (+15 kcal mol -1) was identified as the most significant thermodynamic impediment for the reduction of CO. DFT computations on a series of [CpXM(L)(NO) (CO)]+ (M = Re, Mn) complexes indicate that δG°H 2 can be varied by 11 kcal mol-1 through variation of both the ancillary ligands and the metal.

AB - To gain insight into thermodynamic barriers for reduction of CO into CH3OH, free energies for reduction of [CpRe(PPh3)(NO)(CO)] + into CpRe(PPh3)(NO)(CH2OH) have been determined from experimental measurements. Using model complexes, the free energies for the transfer of H+, H-, and e- have been determined. A pKa of 10.6 was estimated for [CpRe(PPh 3)(NO)(CHOH)]+ by measuring the pKa for the analogous [CpRe(PPh3)(NO)(CMeOH)]+. The hydride donor ability (δG°H -) of CpRe(PPh3)(NO) (CH2OH) was estimated to be 58.0 kcal mol-1, based on calorimetry measurements of the hydride-transfer reaction between CpRe(PPh 3)(NO)(CHO) and [CpRe(PPh3)(NO)(CHOMe)]+ to generate the methylated analogue, CpRe(PPh3)(NO)(CH2OMe). Cyclic voltammograms recorded on CpRe(PPh3)(NO)(CMeO), CpRe(PPh 3)(NO)(CH2OMe), and [CpRe(PPh3)(NO)(CHOMe)] + displayed either a quasireversible oxidation (neutral species) or reduction (cationic species). These potentials were used as estimates for the oxidation of CpRe(PPh3)(NO)(CHO) or CpRe(PPh3)(NO)(CH 2OH) or the reduction of [CpRe(PPh3)(NO)(CHOH)] +. Combination of the thermodynamic data permits construction of three-dimensional free energy landscapes under varying conditions of pH and PH2. The free energy for H2 addition (δG°H 2) to [CpRe(PPh3)(NO)(CO)]+ (+15 kcal mol -1) was identified as the most significant thermodynamic impediment for the reduction of CO. DFT computations on a series of [CpXM(L)(NO) (CO)]+ (M = Re, Mn) complexes indicate that δG°H 2 can be varied by 11 kcal mol-1 through variation of both the ancillary ligands and the metal.

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DO - 10.1021/ja502316e

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