Chloride‐Bridged Dinuclear Rhodium(III) Complexes Bearing Chiral Diphosphine Ligands: Catalyst Precursors for Asymmetric Hydrogenation of Simple Olefins

Efficient rhodium(III) catalysts were developed for asymmetric hydrogenation of simple olefins. A new series of chloride‐bridged dinuclear rhodium(III) complexes 1 were synthesized from the rhodium(I) precursor [RhCl(cod)]₂, chiral diphosphine ligands, and hydrochloric acid. Complexes from the series acted as efficient catalysts for asymmetric hydrogenation of (E)‐prop‐1‐ene‐1,2‐diyldibenzene and its derivatives without any directing groups, in sharp contrast to widely used rhodium(I) catalytic systems that require a directing group for high enantioselectivity. The catalytic system was applied to asymmetric hydrogenation of allylic alcohols, alkenylboranes, and unsaturated cyclic sulfones. Control experiments support the superiority of dinuclear rhodium(III) complexes 1 over typical rhodium(I) catalytic systems.     

Asymmetric Hydrogenation of Aryl Perfluoroalkyl Ketones Catalyzed by Rhodium(III) Monohydride Complexes Bearing Josiphos Ligands

The asymmetric hydrogenation of 2,2,2-trifluoroacetophenones and aryl perfluoroalkyl ketones was developed using a unique, well-defined chloride-bridged dinuclear rhodium(III) complex bearing Josiphos-type diphosphine ligands. These complexes were prepared from [RhCl(cod)]₂, Josiphos ligands, and hydrochloric acid. As catalyst precursors, they allow for the efficient and enantioselective synthesis (up to 99 % ee) of chiral secondary alcohols with perfluoroalkyl groups. This system does not require an activating base for the hydrogenation of 2,2,2-trifluoroacetophenones. Additionally, the enantioselective C=O hydrogenations of 2-phenyl-3-(haloacetyl)-indoles, a class of privileged structures in medicinal chemistry, is reported for the first time.     

非螯合型手性双膦铑对脱氢苯丙氨酸的不对称催化加氢反应

报道从Ｄ－甘露醇出发合成手性双膦（２Ｓ，５Ｓ）－３，６－双（二苯膦）－１，４：３，６－双脱水－２，５－双去氧－Ｌ－艾杜醇，原位下ＢＤＰＩ与３种铑配合物作用生成手性非螯合型双膦铑催化剂，常压下对４种脱氢苯丙氨酸衍生物进行不对称催化化反主尖，对反应结果及ｅ．ｅ．值进行了讨论。     

Trinuclear Rhodium Complexes and Their Relevance for Asymmetric Hydrogenation

Various trinuclear rhodium complexes of the type [Rh₃(PP)₃(μ₃‐OH)_x(μ₃‐OMe)_2?x]BF₄ (where PP=Me‐DuPhos, dipamp, dppp, dppe; different ligands and μ‐bridging anions) are presented, which are formed upon addition of bases such as NEt₃ to solvate complexes [Rh(PP)(solvent)₂]BF₄. They were extensively characterized by X‐ray diffraction and NMR spectroscopy (¹⁰³Rh, ³¹P, ¹³C, ¹H). Their in situ formation resulting from basic additives (NEt₃) or basic prochiral olefins (without addition of another base) can cause deactivation of the asymmetric hydrogenation. This effect can be reversed by means of acidic additives.     

BoPhoz类膦-氨基膦配体在Rh-催化β-脱氢氨基酸酯的不对称氢化反应中的应用

将BoPhoz类膦-氨基膦配体应用在Rh-催化β-脱氢氨基酸酯的不对称氢化反应中,考察了配体结构及反应条件对反应结果的影响,并在优化的条件下研究了各种底物的适用范围,产物的对映选择性达81％ee．     

Asymmetric Hydrogenation Using Rhodium Complexes Generated from Mixtures of Monodentate Neutral and Anionic Phosphorus Ligands

A series of monodentate neutral and anionic phosphorus ligands was synthesized and evaluated in the asymmetric rhodium‐catalyzed hydrogenation of functionalized olefins by using either catalysts containing identical ligands or catalysts generated from mixtures of two different ligands. We expected that the combination of an anionic ligand with a neutral ligand would favor the formation of hetero over homo bis‐ligand complexes due to charge repulsion. NMR spectroscopic studies confirmed that charge effects can indeed shift the equilibrium toward the hetero bis‐ligand complexes. In several cases, the combination of a neutral phosphane with an anionic phosphane, one chiral and the other achiral, furnished significantly higher enantioselectivities than analogous mixtures of two neutral ligands. The best results were obtained with a mixture of an anionic phosphoramidite and a neutral phosphoric acid diester. It is supposed that in this case a hydrogen bond between the two ligands additionally stabilizes the hetero ligand combination.     

Enhancing Effects of Salt Formation on Catalytic Activity and Enantioselectivity for Asymmetric Hydrogenation of Isoquinolinium Salts by Dinuclear Halide‐Bridged Iridium Complexes Bearing Chiral Diphosphine Ligands

Asymmetric hydrogenation of 1‐ and 3‐substituted and 1,3‐disubstituted isoquinolinium chlorides using triply halide‐bridged dinuclear iridium complexes [{Ir(H)(diphosphine)}₂(μ‐Cl)₃]Cl has been achieved by the strategy of HCl salt formation of isoquinolines to afford the corresponding chiral 1,2,3,4‐tetrahydroisoquinolines (THIQs) in high yields and with excellent enantioselectivities after simple basic work‐up. The effects of salt formation have been investigated by time‐course experiments, which revealed that the generation of isoquinolinium chlorides clearly prevented formation of the catalytically inactive dinuclear trihydride complex, which was readily generated in the catalytic reduction of salt‐free isoquinoline substrates. Based on mechanistic investigations, including by ¹H and ³¹P{¹H} NMR studies and the isolation and characterization of several intermediates, the function of the chloride anion of the isoquinolinium chlorides has been elucidated, allowing us to propose a new outer‐sphere mechanism involving coordination of the chloride anion of the substrates to an iridium dihydride species along with a hydrogen bond between the chloride ligand and the N‐H proton of the substrate salt.     

手性膦基二茂铁基噁唑啉铱配合物对乙酸肉桂酯衍生物的不对称氢化

以Fc-PHOX, [Ir(cod)Cl]2和NaBArF为原料高产率地合成了一系列手性Ir-Fc-PHOX配合物, 将其应用于乙酸肉桂酯衍生物的不对称氢化反应, 它们被证明是高效的催化剂, 可以得到完全的转化率和优良的对映选择性, 对映体过量高达99.5% ee.     

TiO_2负载的纳米铑簇合物催化丙酮酸乙酯不对称氢化反应的研究

研究了辛可尼定作手性修饰剂修饰的负载型纳米铑簇保物催化剂（0.5% Rh/PVP-TiO_2）催化丙酮酸乙酯不对称氧化反应，在该反应中手性修饰剂辛可尼 定不仅具有对产物生成的手性诱导作用，而且对反应具有明显加速作用；在优化反 应条件后，反应的TOF和对映选择性分别可以达到58.0 min~(-1)和61.9% e.e.。     

苯乙胺衍生的手性膦-亚磷酰胺酯配体在Rh-催化a-烯醇酯膦酸酯的不对称氢化反应中的应用

将苯乙胺衍生的手性膦-亚磷酰胺酯配体应用在Rh-催化α-烯醇酯膦酸酯的不对称氢化反应中,考察了配体结构及反应条件对反应结果的影响,并在优化的条件下研究了各种底物的适用范围,产物的对映选择性最高>99%ee.     

Application of a Supramolecular‐Ligand Library for the Automated Search for Catalysts for the Asymmetric Hydrogenation of Industrially Relevant Substrates

A procedure is described for the automated screening and lead optimization of a supramolecular‐ligand library for the rhodium‐catalyzed asymmetric hydrogenation of five challenging substrates relevant to industry. Each catalyst is (self‐) assembled from two urea‐functionalized ligands and a transition‐metal center through hydrogen‐bonding interactions. The modular ligand structure consists of three distinctive fragments: the urea binding motif, the spacer, and the ligand backbone, which carries the phosphorus donor atom. The building blocks for the ligand synthesis are widely available on a commercial basis, thus enabling access to a large number of ligands of high structural diversity. The simple synthetic steps enabled the scale‐up of the ligand synthesis to multigram quantities. For the catalyst screening, a library of twelve new chiral ligands was prepared that comprised substantial variation in electronic and steric properties. The automated procedures employed ensured the fast catalyst assembly, screening, and direct acquisition of samples for analysis. It appeared that the most selective catalyst was different for every substrate investigated and that small variations in the building blocks had a major impact on the catalyst performance. For two substrates, a catalyst was found that provided the product with outstanding enantioselectivity. The subsequent automated optimization of these two leads showed that an increase of catalyst loading, dihydrogen pressure, and temperature had a positive effect on the catalyst activity without affecting the catalyst selectivity.     

Scorpio-Ligand: Synthesis of Biphenyl-Dihydroazepine Phosphoramidite Ligands for Asymmetric Hydrogenation

A novel dihydroazepine-bridged BIPHEP phosphoramidite ligand with an amino acid moiety in the backbone was synthesized and evaluated in the Rh-catalyzed asymmetric hydrogenation. The scorpion tail-like amino acid backbone is capable of hydrogen bond formation and able to shift the rotamer composition of the biphenyl axis with the two scissor-like arms. Pivaloyl-l -valine was studied as chiral selector unit and compared with pivaloylglycine as the achiral reference substance. The enantiomerization barrier of the pivaloylglycine-modified biphenylamide was determined to be ΔG^≠=110 kJ/mol. In the case of pivaloyl-l -valine, the (S_ax) isomer is thermodynamically favored. Due to the relatively high barrier, the ligand is atropisomeric at room temperature and allows the preparative separation of the stereoisomers. The obtained phosphoramidite ligands were separated by chiral HPLC. For the first eluting rotamer, Rh complex ([Rh(cod)(L)₂]BF₄) was generated in situ and examined in the enantioselective hydrogenation of 2-acetamidoacrylate and methyl 2-acetamido-3-phenylacrylate, achieving enantiomeric excesses of up to 94 %.     

含二茂铁和吡啶单元的手性席夫碱配体在钌催化的不对称氢转移反应中的应用

Chiral Schiff base complexes are very efficient for a wide range of reactions, including expoxidation[1], epoxide ring opening[2], Diels-Alder reaction[3], aldol reaction[4], etc. However, there are only few examples of P-N chelate Schiff bases being used as the chiral ligands in the asymmetric transfer hydrogenation of ketones. Recently, Gao et al[5] reported a series of P,N,N,P Schiff base ligands that have relatively low enantioselectivity in the asymmetric transfer hydrogenation of ketones.