新型手性稀土配合物的合成、表征及其在不对称催化反应中的应用

作为符合绿色化学标准的稀土三氟甲磺酸盐Ln(OTf)3化合物打破了传统路易斯酸催化的模式，以其在水中稳定、催化用量少(一般少于10 mol％)和可回收再用的独特性质而受到广泛关注。Ln(OTf)3化合物可以催化许多有机合成反应，得到多种多样重要的合成中间体。但是，到目前为止，手性     

Chiral iridium(I) bis(NHC) complexes as catalysts for asymmetric transfer hydrogenation

The common use of NHC complexes in transition‐metal mediated C–C coupling and metathesis reactions in recent decades has established N‐heterocyclic carbenes as a new class of ligand for catalysis. The field of asymmetric catalysis with complexes bearing NHC‐containing chiral ligands is dominated by mixed carbene/oxazoline or carbene/phosphane chelating ligands. In contrast, applications of complexes with chiral, chelating bis(NHC) ligands are rare. In the present work new chiral iridium(I) bis(NHC) complexes and their application in the asymmetric transfer hydrogenation of ketones are described. A series of chiral bis(azolium) salts have been prepared following a synthetic pathway, starting from L ‐valinol and the modular buildup allows the structural variation of the ligand precursors. The iridium complexes were formed via a one‐pot transmetallation procedure. The prepared complexes were applied as catalysts in the asymmetric transfer hydrogenation of various prochiral ketones, affording the corresponding chiral alcohols in high yields and moderate to good enantioselectivities of up to 68%. The enantioselectivities of the catalysts were strongly affected by the various, terminal N‐substituents of the chelating bis(NHC) ligands. The results presented in this work indicate the potential of bis‐carbenes as stereodirecting ligands for asymmetric catalysis and are offering a base for further developments. Copyright © 2010 John Wiley & Sons, Ltd.     

Self-supported chiral catalysts for heterogeneous enantioselective reactions

The development of heterogeneous chiral catalysts for enantioselective reactions is highly desirable in order to overcome some drawbacks of homogeneous catalysts. Different from the conventional approaches by using various types of supports or biphasic systems for the recovery and reuse of homogeneous catalysts, a conceptually new strategy for heterogenization of homogeneous chiral catalysts, that is, a "self-supporting" approach, has been developed to use homochiral metal-organic coordination polymers generated by the self-assembly of chiral multitopic ligands with metal ions, and thus obviates the use of any support. In this concept article, the success of this "self-supporting" strategy will be exemplified in heterogeneous catalysis of asymmetric carbonyl-ene, sulfoxidation, epoxidation, and asymmetric hydrogenation reactions.     

Synergistic effect of binary component ligands in chiral catalyst library engineering for enantioselective reactions

This article highlights our recent efforts in the development of highly efficient and cost-effective chiral catalysts for asymmetric reactions through a combinatorial approach by assembling the component ligands (at least one of which is in non-racemic form, while the other might be optically pure, racemic or achiral) with metal ions to generate modular chiral catalyst libraries. The synergistic effect of the binary ligands in terms of both enantioselectivity and activity of the catalysis has been observed in a variety of catalyst systems, including catalysts containing Ti(IV), Zn(II), Rh(I) or Ru(II) ions, for asymmetric hetero-Diels-Alder, carbonyl-ene, alkylation, and hydrogenation reactions, respectively.     

Asymmetric Borohydride Reduction of Acetophenone Catalyzed by Chiral Salen-Co(Ⅱ) Complex Using Sodium Borohydride

Development of efficient catalytic asymmetric reactions is the most challenging task in current synthetic chemistry; much effort has been devoted to create the chiral metal complexes of asymmetric catalysis. In the last two decades' many brand-new ligands had been synthesized and their combination with various metal ions has been applied in asymmetric catalysis. However, most ligands have only narrow applications and their use is limited to some reactions. Exceptionally, a few ligands and their metal complexes such as binaphthol, semicollin,and binap show wide applicability. Chiral salen ligand is one of such ligands and their metal complexes are now used as the catalysts for a variety of asymmetric reactions such as epoxidation^[1], aziridination^[2], cyclopropanation^[3], Diels-Alder reaction^[4], asymmetric transfer hydrogenation of aromatic ketones^[5] and kinetic resolution of racemic epoxides^[6] and so on.     

Symmetrical and unsymmetrical pincer complexes with group 10 metals: synthesis via aryl C-H activation and some catalytic applications

Aryl-based pincer metal complexes with anionic terdentate ligands have been widely applied in organic synthesis, organometallic catalysis and other related areas. Synthetically, the most simple and convenient method for the construction of these complexes is the direct metal-induced C(aryl)-H bond activation, which can be fulfilled by choosing the appropriate functional donor groups in the two side arms of the aryl-based pincer preligands. In this perspective, we wish to summarize some results achieved by our group in this context. Successful examples include symmetrical chiral bis(imidazoline) NCN pincer complexes with Ni(II), Pd(II) and Pt(II), bis(phosphinite) and bis(phosphoramidite) PCP pincer Pd(II) complexes, unsymmetrical (pyrazolyl)phosphinite, (amino)phosphinite and (imino)phosphinite PCN pincer Pd(II) complexes, chiral (imidazolinyl)phosphinite and (imidazolinyl)phosphoramidite PCN pincer complexes with Ni(II) and Pd(II) as well as unsymmetrical (oxazolinyl)amine and (oxazolinyl)pyrazole NCN' pincer Pd(II) complexes. Among them, the P-donor containing complexes are efficiently synthesized by the "one-pot phosphorylation/metalation" method. The obtained symmetrical and unsymmetrical pincer complexes have been used as catalysts in Suzuki-Miyaura reaction (Pd), asymmetric Friedel-Crafts alkylation of indole with trans-β-nitrostyrene (Pt) as well as in asymmetric allylation of aldehyde and sulfonimine (Pd). In the Suzuki couplings conducted at 40-50 °C, some unsymmetrical Pd complexes exhibit much higher activity than the related symmetrical ones which can be attributed to their faster release of active Pd(0) species resulting from the hemilabile coordination of the ligands. Literature results on the synthesis of some related pincer complexes as well as their activities in the above catalytic reactions are also presented.     

手性pybox-金属络合物及其在不对称催化反应中的应用

具有C2对称性的双噁唑啉型吡啶(pybox)是一类有效的手性配体,能与许多金属离子配位,其手性催化性能已得到越来越多的关注。本文综述了手性配体pybox和pybox-金属络合物的合成方法,特别是近年来pybox-金属络合物在不对称催化反应如不对称环丙烷化反应、不对称Diels-Alder反应、1,3-偶极环加成反应、不对称aldol反应等中应用的最新进展。     

Enantiomeric self-recognition in homo- and heterodinuclear macrocyclic lanthanide(III) complexes

The controlled formation of lanthanide(III) dinuclear μ-hydroxo-bridged [Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes (where X = H(2)O, NO(3)(-), or Cl(-)) of the enantiopure chiral macrocycle L is reported. The (1)H and (13)C NMR resonances of these complexes have been assigned on the basis of COSY, NOESY, TOCSY, and HMQC spectra. The observed NOE connectivities confirm that the dimeric solid-state structure is retained in solution. The enantiomeric nature of the obtained chiral complexes and binding of hydroxide anions are reflected in their CD spectra. The formation of the dimeric complexes is accompanied by a complete enantiomeric self-recognition of the chiral macrocyclic units. The reaction of NaOH with a mixture of two different mononuclear lanthanide(III) complexes, [Ln(1)L](3+) and [Ln(2)L](3+), results in formation of the heterodinuclear [Ln(1)Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes as well as the corresponding homodinuclear complexes. The formation of the heterodinuclear complex is directly confirmed by the NOESY spectra of [EuLuL(2)(μ-OH)(2)(H(2)O)(2)](4+), which reveal close contacts between the macrocyclic unit containing the Eu(III) ion and the macrocyclic unit containing the Lu(III) ion. While the relative amounts of homo- and heterodinuclear complexes are statistical for the two lanthanide(III) ions of similar radii, a clear preference for the formation of heterodinuclear species is observed when the two mononuclear complexes contain lanthanide(III) ions of markedly different sizes, e.g., La(III) and Yb(III). The formation of heterodinuclear complexes is accompanied by the self-sorting of the chiral macrocyclic units based on their chirality. The reactions of NaOH with a pair of homochiral or racemic mononuclear complexes, [Ln(1)L(RRRR)](3+)/[Ln(2)L(RRRR)](3+), [Ln(1)L(SSSS)](3+)/[Ln(2)L(SSSS)](3+), or [Ln(1)L(rac)](3+)/[Ln(2)L(rac)](3+), results in mixtures of homochiral, homodinuclear and homochiral, heterodinuclear complexes. On the contrary, no heterochiral, heterodinuclear complexes [Ln(1)L(RRRR)Ln(2)L(SSSS)(μ-OH)(2)X(2)](n+) are formed in the reactions of two different mononuclear complexes of opposite chirality.     

The combinatorial approach to asymmetric hydrogenation: phosphoramidite libraries, ruthenacycles, and artificial enzymes

For a more general implementation of asymmetric catalysis in the production of fine chemicals, the screening for new catalysts and ligands must be dramatically accelerated. This is possible with a high-throughput experimentation (HTE) approach. However, implementation of this technology requires the rapid preparation of libraries of ligands/catalysts and consequently dictates the use of simple ligands that can be readily synthesised in a robot. In this concept article, we describe how the development of new ligands based on monodentate phosphoramidites enabled the development of an integral HTE protocol for asymmetric hydrogenation. This "instant ligand library" protocol makes it possible to synthesise 96 ligands in one day and screen them the next day. Further diversity is possible by using mixtures of monodentate ligands. This concept has already led to an industrial application. Other concepts, still under development, are based on chiral ruthenacycles as new transfer hydrogenation catalysts and the use of enzymes as ligands for transition-metal complexes.     

金属催化的不对称氢化反应研究进展与展望

手性过渡金属络合物催化的不对称氢化反应是合成光学活性化合物的重要方法. 本文从手性配体及手性催化剂、不对称催化新反应、新方法和新策略三个方面简要评述新世纪以来过渡金属催化的不对称氢化反应研究领域的新进展. 从新世纪初至今, 手性单磷配体得到了复兴, 出现了如MonoPhos、SiPhos、DpenPhos等高效单齿亚磷酰胺酯配体; 磷原子手性(P-手性)配体也得到了快速发展, 如BenzP*、ZhanPhos、TriFer等已成为新的高效手性双膦配体; 螺环骨架手性配体成为新世纪手性配体设计合成的亮点, 除了SiPhos、SIPHOX、SpinPHOX等高效手性螺环配体外, 手性螺环吡啶胺基磷配体SpiroPAP的铱催化剂成为目前最高效的分子催化剂. 不对称催化氢化新反应研究也取得了突破, 如非保护烯胺、杂芳环化合物及N-H亚胺的氢化等反应都实现了高对映选择性. 自组装手性催化剂、树枝状手性催化剂、铁磁性纳米负载的可回收手性催化剂, 以及“混合”配体手性催化剂等新方法和新策略也在不对称催化氢化反应中得到了应用. 然而, 手性过渡金属络合物催化的不对称氢化研究仍然充满挑战, 也期待新的突破.     

Stereogenic‐Only‐at‐Metal Asymmetric Catalysts

Chirality is an essential feature of asymmetric catalysts. This review summarizes asymmetric catalysts that derive their chirality exclusively from stereogenic metal centers. Reported chiral‐at‐metal catalysts can be divided into two classes, namely, inert metal complexes, in which the metal fulfills a purely structural role, so catalysis is mediated entirely through the ligand sphere, and reactive metal complexes. The latter are particularly appealing because structural simplicity (only achiral ligands) is combined with the prospect of particularly effective asymmetric induction (direct contact of the substrate with the chiral metal center). Challenges and solutions for the design of such reactive stereogenic‐only‐at‐metal asymmetric catalysts are discussed.     

Copper(II)‐Catalyzed Nitroaldol (Henry) Reactions: Recent Developments

Self‐assembled copper(II) complexes are described as effective catalysts for nitroaldol (Henry) reactions on water. The protocol involves a heterogeneous process and the catalysts can be recovered and recycled without loss of activity. Further, C2‐symmetric N,N′‐substituted chiral copper(II) salan complexes are found to be more effective catalysts than chiral copper(II) salen complexes for reactions in homogeneous catalysis, with high enantioselectivities. The reactions involve bifunctional catalysis, bearing the properties of a Brønsted base, as well as a Lewis acid, to effect the reaction in the absence of external additives.     

Long-lived near-infrared luminescent lanthanide complexes of imidodiphosphinate "shell" ligands

Near-infrared emitting complexes of Nd(III), Er(III), and Yb(III) based on hexacoordinate lanthanide ions with an aryl functionalized imidodiphosphinate ligand, tpip, have been synthesized and fully characterized. Three tpip ligands form a shell around the lanthanide with the ligand coordinating via the two oxygens leading to neutral complexes, Ln(tpip)3. In the X-ray crystal structures of Er(III) and Nd(III) complexes there is evidence of CH-pi interactions between the phenyl groups. Photophysical investigations of solution samples of the complexes demonstrate that all complexes exhibit relatively long luminescence lifetimes in nondeuteurated solvents. Luminescence studies of powder samples have also been recorded for examination of the properties of NIR complexes in the solid state for potential material applications. The results underline the effective shielding of the lanthanide by the twelve phenyl groups of the tpip ligands and the reduction of high-energy vibrations in close proximity to the lanthanide, both features important in the design of NIR emitting lanthanide complexes.     

Chiral monophosphines as ligands for asymmetric organometallic catalysis

Chelating chiral diphosphines are often used as ligands of organometallic complexes. However monophosphines, or more generally ligands with one phosphorus linked to one or several heteroatom, may also be useful. This review gives the main results obtained in that area, by considering the classes of monodentate chiral ligands bearing one P(III) atom and involved in asymmetric catalysis with organometallic complexes.     

Impact of Na- and K-C pi-interactions on the structure and binding of M3(sol)n(BINOLate)3Ln catalysts

Shibasaki's heterobimetallic complexes M3(THF)n(BINOLate)3Ln [M = Li, Na, K; Ln = lanthanide(III)] are among the most successful asymmetric Lewis acid catalysts. Why does M3(THF)n(BINOLate)3Ln readily bind substrates when M = Li but not when M = Na or K? Structural studies herein indicate Na- and K-C cation-pi interactions and alkali metal radius may be more important than even lanthanide radius. Also reported is a novel polymeric [K3(THF)2(BINOLate)3Yb]n structure that provides the first evidence of interactions between M3(THF)n(BINOLate)3Ln complexes.     

The preparation and utility of bis(sulfinyl)imidoamidine ligands for the copper-catalyzed Diels-Alder reaction

The design and preparation of a novel class of ligands based on the sulfinyl imine functionality is described. In particular, an efficient and modular synthesis of bis(sulfinyl)imidoamidine (siam) ligands is reported. The versatility of the synthetic sequence is demonstrated by the preparation of various analogues to explore the effect of substitution about the ligand framework on catalytic activity. The utility of the siam ligands in asymmetric catalysis is demonstrated in the Cu(II)-catalyzed Diels-Alder reaction where highly enantio- and diastereoselective reactions are reported for a range of N-acyloxazolidinone dienophile and diene substrate combinations. Of particular note is the efficiency of these asymmetric catalysts for reactions involving challenging and relatively unreactive acyclic diene substrates. Finally, structural data are provided for several ligands as well as metal-ligand complexes.     

The asymmetric power of chiral ligands determined by competitive asymmetric autocatalysis

Asymmetric autocatalytic reactions were initiated by using two competing chiral ligands bearing opposite configurations. The absolute configuration of the resulting highly enantioenriched product reflects the different efficiencies of the two catalysts. Thus, our method provides a simple and efficient way to compare the asymmetric power of chiral ligands for enantioselective catalysis both qualitatively and quantitatively.     

Lanthanide complexes of new nonadentate imino-phosphonate ligands derived from 1,4,7-triazacyclononane: synthesis, structural characterisation and NMR studies

The polyamino ligand 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane (1) has been used to synthesise two new ligands by Schiff-base condensation with methyl sodium acetyl phosphonate to give ligand L and methyl sodium 4-methoxybenzoyl phosphonate to give ligand L1 in the presence of lanthanide ion as templating agent to form the complexes [Ln(L)] and [Ln(L1)](Ln = Y, La, Gd, Yb). Both ligands L and L1 have nine donor atoms comprising three amine and three imine N-donors and three phosphonate O-donors and form Ln(III) complexes in which the three pendant arms of the ligands wrap around the nine-coordinate Ln(III) centres. Complexes with Y(III), La(III), Gd(III) and Yb(III) have been synthesised and the complexes [Y(L)], [Gd(L)] and [Gd(L1)] have been structurally characterised. In all the complexes the coordination polyhedron about the lanthanide centre is slightly distorted tricapped trigonal prismatic with the two triangular faces of the prism formed by the macrocyclic N-donors and the phosphonate O-donors. Interestingly, given the three chiral phosphorus centres present in [Ln(L)] and [Ln(L1)] complexes, the three crystal structures reported show the presence of only one diastereomer of the four possible. 1H, 13C and 31P NMR spectroscopic studies on diamagnetic [Y(L)] and [La(L)] and on paramagnetic [Yb(L)] complexes indicate the presence in solution of all the four different diastereomers in varying proportions. The stability of complexes [Y(L)] and [Y(L1)] in D2O in both neutral and acidic media, and the relaxivity of the Gd(III) complexes, have also been investigated.     

从碳中心到硅中心:手性螺环双膦配体研究的发展

手性螺环配体和催化剂已被公认是一类优势手性配体和催化剂。手性螺环配体的相关研究，促进了不对称催化领域的发展。根据螺环骨架类型进行分类，分别讨论具有螺[4.4]壬烷骨架、螺二氢茚骨架、螺[4.4]壬二烯骨架以及螺二色烷骨架的手性螺环双膦配体的合成及在不对称催化反应中的应用，为今后发展新的不对称催化体系提供了重要参考。     

Insight into substrate binding in Shibasaki's Li3(THF)n(BINOLate)3Ln complexes and implications in catalysis

Heterobimetallic Lewis acids M 3(THF) n (BINOLate) 3Ln [M = Li, Na, K; Ln = lanthanide(III)] are exceptionally useful asymmetric catalysts that exhibit high levels of enantioselectivity across a wide range of reactions. Despite their prominence, important questions remain regarding the nature of the catalyst-substrate interactions and, therefore, the mechanism of catalyst operation. Reported herein are the isolation and structural characterization of 7- and 8-coordinate heterobimetallic complexes Li 3(THF) 4(BINOLate) 3Ln(THF) [Ln = La, Pr, and Eu], Li 3(py) 5(BINOLate) 3Ln(py) [Ln = Eu and Yb], and Li 3(py) 5(BINOLate) 3La(py) 2 [py = pyridine]. Solution binding studies of cyclohexenone, DMF, and pyridine with Li 3(THF) n (BINOLate) 3Ln [Ln = Eu, Pr, and Yb] and Li 3(DMEDA) 3(BINOLate) 3Ln [Ln = La and Eu; DMEDA = N, N'-dimethylethylene diamine] demonstrate binding of these Lewis basic substrate analogues to the lanthanide center. The paramagnetic europium, ytterbium, and praseodymium complexes Li 3(THF) n (BINOLate) 3Ln induce relatively large lanthanide-induced shifts on substrate analogues that ranged from 0.5 to 4.3 ppm in the (1)H NMR spectrum. X-ray structure analysis and NMR studies of Li 3(DMEDA) 3(BINOLate) 3Ln [Ln = Lu, Eu, La, and the transition metal analogue Y] reveal selective binding of DMEDA to the lithium centers. Upon coordination of DMEDA, six new stereogenic nitrogen centers are formed with perfect diastereoselectivity in the solid state, and only a single diastereomer is observed in solution. The lithium-bound DMEDA ligands are not displaced by cyclohexenone, DMF, or THF on the NMR time scale. Use of the DMEDA adduct Li 3(DMEDA) 3(BINOLate) 3La in three catalytic asymmetric reactions led to enantioselectivities similar to those obtained with Shibasaki's Li 3(THF) n (BINOLate) 3La complex. Also reported is a unique dimeric [Li 6(en) 7(BINOLate) 6Eu 2][mu-eta (1),eta (1)-en] structure [en = ethylenediamine]. On the basis of these studies, it is hypothesized that the lanthanide in Shibasaki's Li 3(THF) n (BINOLate) 3Ln complexes cannot bind bidentate substrates in a chelating fashion. A hypothesis is also presented to explain why the lanthanide catalyst, Li 3(THF) n (BINOLate) 3La, is often the most enantioselective of the Li 3(THF) n (BINOLate) 3Ln derivatives.