Homogeneous Hydrogenation Catalyzed by Boranes

Ramp, Floyd L.; DeWitt, E. J.; Trapasso, L. E.

doi:10.1021/jo01059a056

Cited by 54 publications

(16 citation statements)

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“…The activation barriers of ∼25.0 kcal/mol indicate that the reactions of 1 or 2 with H 2 are unfavorable in the absence of bases. These results agree well with the experimental findings that H 2 can react with trialkylboranes to produce R 2 BH and RH under forcing conditions 133–136, a process that is generally used for the hydrogenation of organic compounds. The reactions are slightly endothermic but appear to be thermalneutral after the solvent effect is taken into account.…”

Section: Resultssupporting

confidence: 90%

Steric and electronic effects on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃(R = C₆F₅, Ph; R′ = C₆H₂Me₃,tBu, Ph, C₆F₅, Me, H): A computational study

Gao

2010

Int J of Quantum Chemistry

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The steric and electronic effects exerted by the substituents R/R 0 on the heterolytic H 2 -splitting by phosphine-boranes R 3 B/PR 0 3 [R ¼ C 6 F 5 (1), Ph (2); R 0 ¼ C 6 H 2 Me 3 (a), tBu (b), Ph (c), C 6 F 5 (d), Me (e), H (f)] have been studied by performing quantum mechanical density functional theory and RI-MP2 calculations. Energy decomposition analyses based on the block-localized wavefunction method show that the nature of the interaction between R 3 B and PR 0 3 is strongly dependent on the BAP distance. With short BAP distances ($2.1 Å ), the strength of Lewis pairs results from the balance among various energy terms, and both strong and weak dative bonds can be found in this group. However, at long BAP distances (>4.0 Å ), the correlation and dispersion energy (DE corr ) dominates. In other words, the van der Waals (vdW) interaction rules these weakly bound complexes. No ion-pair structures of 1f and 2c-2f can be located as they instantly converge to vdW complexes R 3 BÁÁÁH 2 ÁÁÁPR 0 3 . We thus propose a model, which predicts that when the sum (E hp ) of the hydride affinity (HA) of BR 3 and the proton affinity (PA) of PR 0 3 is higher than 340.0 kcal/mol, the ion-pair [R 3 BH À ][HPR 0þ 3 ] can be observed, whereas with E hp below this value, the ion pair would instantly undergo the combination of proton and hydride with the release of H 2 . The overall reaction energies (1a-1e and 2a-2b) can be best described by a fitting equation with HA(BR 3 ), PA(PR 0 3 ), and the binding energy DE b (BR 3 /PR 0 3 ) as predictor variables:(BR 3 /PR 0 3 ) þ 245.3 kcal/mol. The fitting equation provides quantitative insights into the steric and electronic effects on the thermodynamic aspects of the heterolytic H 2 -splitting reactions. The electronic effects are reflected by HA(BR 3 ) and PA(PR 0 3 ), and DE b can be significantly influenced by the steric overcrowding.a Structural parameters are based on the optimal geometries at the B3LYP/6-31G(d,p) level; the basis sets used for calculations are cc-pVDZ. b Calculated at the RI-MP2/cc-pVDZ level. a 1HHa refers to the ion-pair complex obtained from Lewis pair 1a and so on. b DE zpe;cp b refers to binding energy after ZPE and 50% BSSE corrections.

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Section: Resultssupporting

confidence: 90%

Steric and electronic effects on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃(R = C₆F₅, Ph; R′ = C₆H₂Me₃,tBu, Ph, C₆F₅, Me, H): A computational study

Gao

2010

Int J of Quantum Chemistry

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“…Combining the FLP approach and previous knowledge about borane-catalyzed hydrogenation of alkenes 11,12,13,14 and polyarenes 15,16,17,18 , we propose herein a new general catalytic pathway to the hydrogenation of unsaturated hydrocarbons ( Fig. 1b) and demonstrate its validity by the highly selective hydrogenation of alkynes into cis-alkenes.…”

mentioning

confidence: 85%

A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

et al. 2013

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Recently, a new approach to dihydrogen activation known as frustrated Lewis pairs (FLPs) concept has been introduced 1, 2, 3 . A combination of highly Lewis acidic boranes and sterically hindered bases can split hydrogen heterolytically generating onium (phosphonium, ammonium, etc.) borohydrides. These compounds show reduction activity resembling that of inorganic borohydrides like NaBH 4 , i. e. they are suitable mostly for reduction of polarized multiple bonds. Imines, enamines, silyl ethers 4, 5,6 , α,β-enones 7 , ynones 8 , Nalkylanilines 9 were hydrogenated using stoichiometric or catalytic amounts of FLPs. Due to heterolytic nature of FLP-H 2 adducts, hydrogenation of unactivated multiple C-C bonds using FLPs has some natural limitations, since during the respective step of the catalytic cycle a proton transfer from catalyst to substrate should take place (Fig. 1a). Although Greb et al. have implemented this approach to hydrogenation of alkenes under ambient conditions, this method is predictably restricted to the alkenes with high proton affinity 10 .

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“…While most hydrogenation reactions are catalyzed by transition‐metal complexes, the development of metal‐free hydrogenation catalysts has recently attracted much attention because of their potential benefits of low cost and toxicity 2–4. Early efforts towards the metal‐free catalytic hydrogenation of olefins or polyarenes employed boranes or diboranes, such as i Bu 3 B,2b,c Et 2 BBEt 2 , or Pr 2 BBPr 2 2e,f as catalysts. These reactions require harsh reaction conditions (reaction temperature at 170–225 °C and H 2 pressure at 100 bar), which often led to unwanted pyrolytic chain cleavage.…”

Section: Methodsmentioning

confidence: 99%

Metal‐Free HB(C₆F₅)₂‐Catalyzed Hydrogenation of Unfunctionalized Olefins and Mechanism Study of Borane‐Mediated σ‐Bond Metathesis

Wang

Chen

et al. 2013

Angew Chem Int Ed

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Homogeneous Hydrogenation Catalyzed by Boranes

Cited by 54 publications

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Steric and electronic effects on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃(R = C₆F₅, Ph; R′ = C₆H₂Me₃,tBu, Ph, C₆F₅, Me, H): A computational study

Steric and electronic effects on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃(R = C₆F₅, Ph; R′ = C₆H₂Me₃,tBu, Ph, C₆F₅, Me, H): A computational study

A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

Metal‐Free HB(C₆F₅)₂‐Catalyzed Hydrogenation of Unfunctionalized Olefins and Mechanism Study of Borane‐Mediated σ‐Bond Metathesis

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Homogeneous Hydrogenation Catalyzed by Boranes

Cited by 54 publications

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Steric and electronic effects on the heterolytic H2‐splitting by phosphine‐boranes R3B/PR′3(R = C6F5, Ph; R′ = C6H2Me3,tBu, Ph, C6F5, Me, H): A computational study

Steric and electronic effects on the heterolytic H2‐splitting by phosphine‐boranes R3B/PR′3(R = C6F5, Ph; R′ = C6H2Me3,tBu, Ph, C6F5, Me, H): A computational study

A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

Metal‐Free HB(C6F5)2‐Catalyzed Hydrogenation of Unfunctionalized Olefins and Mechanism Study of Borane‐Mediated σ‐Bond Metathesis

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Steric and electronic effects on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃(R = C₆F₅, Ph; R′ = C₆H₂Me₃,tBu, Ph, C₆F₅, Me, H): A computational study

Steric and electronic effects on the heterolytic H₂‐splitting by phosphine‐boranes R₃B/PR′₃(R = C₆F₅, Ph; R′ = C₆H₂Me₃,tBu, Ph, C₆F₅, Me, H): A computational study

Metal‐Free HB(C₆F₅)₂‐Catalyzed Hydrogenation of Unfunctionalized Olefins and Mechanism Study of Borane‐Mediated σ‐Bond Metathesis