Well-Defined Iron Catalysts for the Acceptorless Reversible Dehydrogenation-Hydrogenation of Alcohols and Ketones (original) (raw)
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Journal of the American Chemical Society, 2009
Cyclopentadienone iron alcohol complexes generated from the reactions of [2,5-(SiMe 3 ) 2 -3,4-(CH 2 ) 4 (η 5 -C 4 COH)]Fe(CO) 2 H (3) and aldehydes were characterized by 1 H NMR, 13 C NMR, and IR spectroscopy. The benzyl alcohol complex [2,5-(SiMe 3 ) 2 -3,4-(CH 2 ) 4 (η 5 -C 4 C=O)]Fe (CO) 2 (HOCH 2 C 6 H 5 ) (6-H) was also characterized by X-ray crystallography. These alcohol complexes are thermally unstable and prone to dissociate the coordinated alcohols. The alcohol ligand is easily replaced by other ligands such as PhCN, pyridine, and PPh 3 . Dissociation of the alcohol ligand in the presence of H 2 leads to the formation of iron hydride 3. The reduction of aldehydes by 3 was carried out in the presence of both potential intermolecular and intramolecular traps. The reaction of 3 with PhCHO in the presence of 4-methylbenzyl alcohol as a potential intermolecular trapping agent initially produced only iron complex 6-H of the newly formed benzyl alcohol. However, the reaction of 3 with 4-(HOCD 2 )C 6 H 4 CHO (11-d 2 ), which possesses a potential intramolecular alcohol trapping agent, afforded two alcohol complexes, one with the newly formed alcohol coordinated to iron and the other with the trapping alcohol coordinated. The intramolecular trapping experiments support a mechanism involving concerted transfer of a proton from OH and hydride from Fe of 3 to aldehydes. The kinetics and mechanism of the hydrogenation of benzaldehyde catalyzed by 3 are presented.
Iron-based nanocatalyst for the acceptorless dehydrogenation reactions
Nature Communications, 2017
Development of sustainable catalytic systems for fundamentally important synthetic transformations and energy storage applications is an intellectually stimulating challenge. Catalytic dehydrogenation of feedstock chemicals, such as alcohols and amines to value-added products with the concomitant generation of dihydrogen is of much interest in the context of hydrogen economy and is an effective alternative to the classical oxidation reactions. Despite a number of homogeneous catalysts being identified for the acceptorless dehydrogenation, the use of high price and limited availability of precious metals and poor recovery of the catalyst have spurred interest in catalysis with more earth-abundant alternatives, especially iron. However, no report has described a reusable iron-based heterogeneous catalyst for oxidant-free and acceptorless dehydrogenation reactions. Here we replace expensive noble metal catalysts with an inexpensive, benign, and sustainable nanoscale iron catalyst for t...
Low-Valent Iron(I) Amido Olefin Complexes as Promotors for Dehydrogenation Reactions
Angewandte Chemie (International ed. in English), 2015
Fe(I) compounds including hydrogenases show remarkable properties and reactivities. Several iron(I) complexes have been established in stoichiometric reactions as model compounds for N2 or CO2 activation. The development of well-defined iron(I) complexes for catalytic transformations remains a challenge. The few examples include cross-coupling reactions, hydrogenations of terminal olefins, and azide functionalizations. Here the syntheses and properties of bimetallic complexes [MFe(I) (trop2 dae)(solv)] (M=Na, solv=3 thf; M=Li, solv=2 Et2 O; trop=5H-dibenzo[a,d]cyclo-hepten-5-yl, dae=(N-CH2 -CH2 -N) with a d(7) Fe low-spin valence-electron configuration are reported. Both compounds promote the dehydrogenation of N,N-dimethylaminoborane, and the former is a precatalyst for the dehydrogenative alcoholysis of silanes. No indications for heterogeneous catalyses were found. High activities and complete conversions were observed particularly with [NaFe(I) (trop2 dae)(thf)3 ].