Abstract
The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(η 1-BH 4)] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH 3 scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H) 2(CO)] (4a) and cis-[(iPr-PNP)Fe(H) 2(CO)] (4b). The dihydrido complexes 4a and 4b do not react with acetophenone or benzaldehyde, indicating that these complexes are not intermediates in the catalytic reduction of ketones. NMR studies indicate that the tetrahydridoborate ligand in 1 dissociates prior to ketone reduction. DFT calculations show that the mechanism of the iron-catalyzed hydrogenation of ketones involves alcohol-assisted aromatization of the dearomatized complex [(iPr-PNP*)Fe(H)(CO)] (7) to initially give the Fe 0 complex [(iPr-PNP)Fe(CO)] (21) and subsequently [(iPr-PNP)Fe(CO)(EtOH)] (38). Concerted coordination of acetophenone and dual hydrogen-atom transfer from the PNP arm and the coordinated ethanol to, respectively, the carbonyl carbon and oxygen atoms, leads to the dearomatized complex [(iPr-PNP*)Fe(CO)(EtO)(MeCH(OH) Ph)] (32). The catalyst is regenerated by release of 1-phenylethanol, followed by dihydrogen coordination and proton transfer to the coordinated ethoxide ligand.
| Original language | English |
|---|---|
| Pages (from-to) | 7196-7209 |
| Number of pages | 14 |
| Journal | Chemistry - A European Journal |
| Volume | 18 |
| Issue number | 23 |
| DOIs | |
| Publication status | Published - Jun 4 2012 |
Fingerprint
Keywords
- density functional calculations
- homogeneous catalysis
- hydrogenation
- iron
- pincer ligands
ASJC Scopus subject areas
- Chemistry(all)
Cite this
Iron borohydride pincer complexes for the efficient hydrogenation of ketones under mild, base-free conditions : Synthesis and mechanistic insight. / Langer, Robert; Iron, Mark A.; Konstantinovski, Leonid; Diskin-Posner, Yael; Leitus, Gregory; Ben-David, Yehoshoa; Milstein, David.
In: Chemistry - A European Journal, Vol. 18, No. 23, 04.06.2012, p. 7196-7209.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Iron borohydride pincer complexes for the efficient hydrogenation of ketones under mild, base-free conditions
T2 - Synthesis and mechanistic insight
AU - Langer, Robert
AU - Iron, Mark A.
AU - Konstantinovski, Leonid
AU - Diskin-Posner, Yael
AU - Leitus, Gregory
AU - Ben-David, Yehoshoa
AU - Milstein, David
PY - 2012/6/4
Y1 - 2012/6/4
N2 - The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(η 1-BH 4)] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH 3 scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H) 2(CO)] (4a) and cis-[(iPr-PNP)Fe(H) 2(CO)] (4b). The dihydrido complexes 4a and 4b do not react with acetophenone or benzaldehyde, indicating that these complexes are not intermediates in the catalytic reduction of ketones. NMR studies indicate that the tetrahydridoborate ligand in 1 dissociates prior to ketone reduction. DFT calculations show that the mechanism of the iron-catalyzed hydrogenation of ketones involves alcohol-assisted aromatization of the dearomatized complex [(iPr-PNP*)Fe(H)(CO)] (7) to initially give the Fe 0 complex [(iPr-PNP)Fe(CO)] (21) and subsequently [(iPr-PNP)Fe(CO)(EtOH)] (38). Concerted coordination of acetophenone and dual hydrogen-atom transfer from the PNP arm and the coordinated ethanol to, respectively, the carbonyl carbon and oxygen atoms, leads to the dearomatized complex [(iPr-PNP*)Fe(CO)(EtO)(MeCH(OH) Ph)] (32). The catalyst is regenerated by release of 1-phenylethanol, followed by dihydrogen coordination and proton transfer to the coordinated ethoxide ligand.
AB - The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(η 1-BH 4)] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH 3 scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H) 2(CO)] (4a) and cis-[(iPr-PNP)Fe(H) 2(CO)] (4b). The dihydrido complexes 4a and 4b do not react with acetophenone or benzaldehyde, indicating that these complexes are not intermediates in the catalytic reduction of ketones. NMR studies indicate that the tetrahydridoborate ligand in 1 dissociates prior to ketone reduction. DFT calculations show that the mechanism of the iron-catalyzed hydrogenation of ketones involves alcohol-assisted aromatization of the dearomatized complex [(iPr-PNP*)Fe(H)(CO)] (7) to initially give the Fe 0 complex [(iPr-PNP)Fe(CO)] (21) and subsequently [(iPr-PNP)Fe(CO)(EtOH)] (38). Concerted coordination of acetophenone and dual hydrogen-atom transfer from the PNP arm and the coordinated ethanol to, respectively, the carbonyl carbon and oxygen atoms, leads to the dearomatized complex [(iPr-PNP*)Fe(CO)(EtO)(MeCH(OH) Ph)] (32). The catalyst is regenerated by release of 1-phenylethanol, followed by dihydrogen coordination and proton transfer to the coordinated ethoxide ligand.
KW - density functional calculations
KW - homogeneous catalysis
KW - hydrogenation
KW - iron
KW - pincer ligands
UR - http://www.scopus.com/inward/record.url?scp=84861587160&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84861587160&partnerID=8YFLogxK
U2 - 10.1002/chem.201200159
DO - 10.1002/chem.201200159
M3 - Article
VL - 18
SP - 7196
EP - 7209
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 23
ER -