期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 18, 期 23, 页码 7196-7209出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201200159
关键词
density functional calculations; homogeneous catalysis; hydrogenation; iron; pincer ligands
资金
- European Research Council (ERC) [246837]
- MINERVA Foundation
- Deutsche Forschungsgemeinschaft (DFG)
The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(?1-BH4)] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1 atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH3 scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H)2(CO)] (4?a) and cis-[(iPr-PNP)Fe(H)2(CO)] (4?b). The dihydrido complexes 4?a and 4?b 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 Fe0 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.
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