Asymmetric Hydrogenation

Imamoto, Tsuneo

doi:10.5772/48584

Cited by 9 publications

(10 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Catalytic hydrogenations represent the largest-volume human-made chemical reactions in the world . Many industrially important processes are based on a homogeneous version of this reaction . Single-phase catalysis indeed affords a number of convenient properties such as mild reaction conditions, low cost, operational simplicity, and high activities and selectivities that can be tuned via electronic and steric effects of the ligands, ease of catalyst structure determination, and reaction mechanism analysis that can also be readily probed.…”

Section: Introductionmentioning

confidence: 99%

Why Does Alkylation of the N–H Functionality within M/NH Bifunctional Noyori-Type Catalysts Lead to Turnover?

2017

View full text Add to dashboard Cite

Molecular metal/NH bifunctional Noyori-type catalysts are remarkable in that they are among the most efficient artificial catalysts developed to date for the hydrogenation of carbonyl functionalities (loadings up to ∼10 mol %). In addition, these catalysts typically exhibit high C═O/C═C chemo- and enantioselectivities. This unique set of properties is traditionally associated with the operation of an unconventional mechanism for homogeneous catalysts in which the chelating ligand plays a key role in facilitating the catalytic reaction and enabling the aforementioned selectivities by delivering/accepting a proton (H) via its N-H bond cleavage/formation. A recently revised mechanism of the Noyori hydrogenation reaction (Dub, P. A. et al. J. Am. Chem. Soc. 2014, 136, 3505) suggests that the N-H bond is not cleaved but serves to stabilize the turnover-determining transition states (TDTSs) via strong N-H···O hydrogen-bonding interactions (HBIs). The present paper shows that this is consistent with the largely ignored experimental fact that alkylation of the N-H functionality within M/NH bifunctional Noyori-type catalysts leads to detrimental catalytic activity. The purpose of this work is to demonstrate that decreasing the strength of this HBI, ultimately to the limit of its complete absence, are conditions under which the same alkylation may lead to beneficial catalytic activity.

show abstract

Section: Introductionmentioning

confidence: 99%

Why Does Alkylation of the N–H Functionality within M/NH Bifunctional Noyori-Type Catalysts Lead to Turnover?

2017

View full text Add to dashboard Cite

show abstract

“…Most practical bifunctional catalysts, e.g., (R)-RUCY-XylBINAP 5 or Ru-MACHO 6 developed by Takasago International Corp., are typically composed of oxygensensitive phosphorus (P)-containing ligands, 4c−g usually with C 2 -symmetry. 7 The commercially available PNP ligand family 8 of the general formula R 2 P(CH 2 ) 2 NH(CH 2 ) 2 PR 2 , as shown in Figure 1, in combination with Ru 6,9 and Ir, 9q,10 as well as Cr, 11 Fe, 9i,12 Co, 13 Ni, 14 Mo, 15 W, 15 and Os, 16 have been used as (pre)catalysts in numerous homogeneous hydrogenations of CO 2 , 9a,10j carbonates, 9u esters, 6,9b,d,i,k−n,10a,12a,d,f,g heterocycles, 12c ketones, 10e,13a,d imines, 15 and alkenes, 10e,13a,d,14 transfer hydrogenation of organic formates and cyclic carbonates 9c and ketones, 10d,g,h,13c various acceptorless dehydrogenations, 9e,g,h,p,q,10c,12b,c,e,13b,16,17 catalytic hydrolysis 10f or dehydrogenation 9j,r−t of ammonia or amine boranes, domino-synthesis of indoles, 9f stereospecific polymerization of 1,3-butadiene, 13e,f ethylene tetra-11a and trimerization, 11b and others. 9o,10i,18 The Schneider group reported a variety of PNP-based complexes of Ru, 19 Ir, 20 Pd, 21 Fe, 22 and Rh, 23 some of which are relevant to stoichiometric molecular nitrogen cleavage 19c,23a or C−H 20g bond activation, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…The vast majority of ligands used in homogeneous catalysis are based on P and/or N donor atoms, and an enormous number of such ligands have been designed and synthesized over the past four decades. ,, It is generally accepted that polydentate chelating ligands bearing NH functionalities play a crucial role in so-called bifunctional metal–ligand (M/NH) cooperative molecular catalysis, in which a noninnocent ligand is proposed to directly participate in substrate activation via an N–H group and/or an act of bond cleavage/formation via N–H proton transfer, respectively. Most practical bifunctional catalysts, e.g., ( R )-RUCY-XylBINAP or Ru-MACHO developed by Takasago International Corp., are typically composed of oxygen-sensitive phosphorus (P)-containing ligands, − usually with C 2 -symmetry . The commercially available PNP ligand family of the general formula R 2 P(CH 2 ) 2 NH(CH 2 ) 2 PR 2 , as shown in Figure , in combination with Ru , and Ir, , as well as Cr, Fe, , Co, Ni, Mo, W, and Os, have been used as (pre)catalysts in numerous homogeneous hydrogenations of CO 2 , , carbonates, esters, ,,,,− ,,,,, heterocycles, ketones, ,, imines, and alkenes, ,,, transfer hydrogenation of organic formates and cyclic carbonates and ketones, ,,, various acceptorless dehydrogenations, ,,,,,,,,,,, catalytic hydrolysis…”

Section: Introductionmentioning

confidence: 99%

Air-Stable NNS (ENENES) Ligands and Their Well-Defined Ruthenium and Iridium Complexes for Molecular Catalysis

2015

View full text Add to dashboard Cite

We introduce ENENES, a new family of airstable and low-cost NNS ligands bearing NH functionalities of the general formula E(CH 2 ) m NH(CH 2 ) n SR, where E is selected from −NC 4 H 8 O, −NC 4 H 8 , or −N(CH 3 ) 2 , m and n = 2 and/or 3, and R = Ph, Bn, Me, or SR (part of a thiophenyl fragment). The preparation and characterization of more than 15 examples of well-defined Ru and Ir complexes supported by these ligands that are relevant to bifunctional metal−ligand M/ NH molecular catalysis are reported. Reactions of NNS ligands with suitable Ru or Ir precursors afford rich and diverse solid-state and solution chemistries, producing monometallic molecules as well as bimetallics in which the ligand coordinates to the metal via either bidentate (κ 2 [N,N′] or κ 2 [N′,S]) or tridentate (κ 3 [N,N′,S]) binding modes, depending on the basicity of the sulfur atom, CH 2 chain length (m or n parameter), or identity of the transition metal. In the case of Ir, ligands bearing benzyl substituents lead to unprecedented κ 4 [N,N′,S,C]-tetradentate corestructure complexes of the type [Ir III HCl{κ 4 (N,N′,S,C)−ligand}], resulting from ortho-metalation via C−H oxidative addition. Fourteen of these Ru and Ir complexes have been crystallographically characterized. Air-and moisture-stable complexes of the type trans-[Ru II Cl 2 {κ 3 [N,N′,S]−ligand}(L)] (L = PPh 3 , PCy 3 , DMSO), and others, effect the selective hydrogenation of methyl trifluoroacetate into the important synthon trifluoroacetaldehyde methyl hemiacetal in basic methanol under relatively mild conditions (35−40 °C, 25 bar H 2 ) with reasonable turnover numbers (i.e., > 1000), whereas the air-stable Ir monohydride complexes [Ir III HCl{κ 4 (N,N′,S,C)−ligand}] exhibit excellent catalytic activities and high chemoselectivity for the same reaction, reaching turnover numbers of >10 000.

show abstract

“…Transition-metal-catalyzed asymmetric hydrogenation is one of the most efficient, reliable, and sustainable methods for the synthesis of chiral compounds . Over the past several decades, considerable effort has been devoted to the development of highly enantioselective hydrogenation methods for obtaining optically active chiral products, and some of these methods have been successfully used for the industrial production of chiral pharmaceuticals, fragrances, and agrochemicals .…”

mentioning

confidence: 99%