Donor-Flexible Bis(pyridylidene amide) Ligands for Highly Efficient Ruthenium-Catalyzed Olefin Oxidation

An exceptionally efficient ruthenium-based catalyst for olefin oxidation has been designed by exploiting N,N′-bis(pyridylidene)oxalamide (bisPYA) as a donor-flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson-type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state-of-the-art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h⁻¹ and turnover numbers of several millions.     

Non-cross-linked Polystyrene Supported Cyclosulfamide:A New Chiral Auxiliary for Highly Stereoselective Alkylation Reactions

The asymmetric alkylation reactions induced by non-cross-linked polystyrene supported cyclosulfamide chiral auxiliary occurred in moderate to good yields with a very high stereoselectivity（e.e.〉99%）. Compared to non-supported cyclosulfamide chiral auxiliary, this chiral auxiliary can be recovered by simple precipitation and filtration, and could be reused at least four cycles without appreciable reduction in the yield or stereoselectivity.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph₂P‐N‐PPh₂ at Group 4 metallocenes is presented herein. Coordination of N,N‐bis(diphenylphosphino)amine ( 1 ) to [(Cp₂TiCl)₂] (Cp=η⁵‐cyclopentadienyl) generated [Cp₂Ti(Cl)P(Ph₂)N(H)PPh₂] ( 2 ). The heterometallacyclic complex [Cp₂Ti(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Ti ) can be prepared by reaction of 2 with n‐butyllithium as well as from the reaction of the known titanocene–alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with the amine 1 . Reactions of the lithium amide [(thf)₃Li{N(PPh₂)₂}] with [Cp₂MCl₂] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp₂M(Cl){κ²‐N,P‐N(PPh₂)₂}] ( 4 Zr and 4 Hf ). Reduction of 4 Zr with magnesium gave the highly strained heterometallacycle [Cp₂Zr(κ²‐P,P‐Ph₂P‐N‐PPh₂)] ( 3 Zr ). Complexes 2 , 3 Ti , 4 Hf , and 3 Zr were characterized by X‐ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)methanide Ligands

A study of the coordination chemistry of different bis(diphenylphosphino)methanide ligands [Ph₂PC(X)PPh₂] (X=H, SiMe₃) with Group 4 metallocenes is presented. The paramagnetic complexes [Cp₂Ti{κ²‐P,P‐Ph₂PC(X)PPh₂}] (X=H ( 3 a ), X=SiMe₃ ( 3 b )) have been prepared by the reactions of [(Cp₂TiCl)₂] with [Li{C(X)PPh₂}₂(thf)₃]. Complex 3 b could also be synthesized by reaction of the known titanocene alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with Ph₂PC(H)(SiMe₃)PPh₂ ( 2 b ). The heterometallacyclic complex [Cp₂Zr(H){κ²‐P,P‐Ph₂PC(H)PPh₂}] ( 4 aH ) has been prepared by reaction of the Schwartz reagent with [Li{C(H)PPh₂}₂(thf)₃]. Reactions of [Cp₂HfCl₂] with [Li{C(X)PPh₂}₂(thf)₃] gave the highly strained corresponding metallacycles [Cp₂M(Cl){κ²‐P,P‐Ph₂PC(X)PPh₂}] ( 5 aCl and 5 bCl ) in very good yields. Complexes 3 a , 4 aH , and 5 aCl have been characterized by X‐ray crystallography. Complex 3 a has also been characterized by EPR spectroscopy. The structure and bonding of the complexes has been investigated by DFT analysis. Reactions of complexes 4 aH , 5 aCl , and 5 bCl did not give the corresponding more unsaturated heterometallacyclobuta‐2,3‐dienes.     

Synthesis of New Chiral Bis(BINOL) Substituted 2,2''''-Bipyridine Ligands

Chiral 2,2'-bipyridines have been reported to be highly efficient catalysts and useful building blocks of supramolecular.[1,2] Chirality of bipyridines was introduced by chiral substituents. Because 1,1'-binaphthyl (BINOL) and its derivatives belong to the most important components of asymmetric catalysts, we would like to synthesize 5,5'-and 6,6'-positions substituted chiral bipyridine-type ligands, the chiral moieties of ligands originate from enationpure 1, 1'-binapthyl units.     

Asymmetric Induction of Chiral 1,1''''-Bis(oxazolinyl)ferrocenes as Ligands in Metal-Catalyzed Cyclopropanation and Diels-Alder Reactions

Bis(oxazoline) ligands1 have been successfully used in a variety of metal-catalyzed asymmetric reactions, such as cyclopropanation, allylic oxidation reactions, etc; Chiral ferrocene derivatives2 have also been proved as effective ligands in numerous asymmetric reactions, for example, chiral ferrocenylphosphines exhibited high enantioselectivity for the reduction of olefins, Heck reactions and Aldol reactions of aldehydes. These results stimulated us to study the behaviour the bis(oxazoline) …     

Introduction of a New Class of Ligands for the Metal-Catalyzed Enantioselective Synthesis

Protected thiosugars were prepared as ligands for the metal-catalyzed enantioselective synthesis. The protecting groups in these ligands were varied to test a proposed new concept for the metal-catalyzed enantioselective synthesis. This new concept centres on the use of a stair-like ligand with a large substituent on one side and a small substitutent on the other rather than the commonly employed ligands which have C₂ symmetry (see Fig.3). In such a ligand, both substituents should have a major influence on the coordination of a prochiral substrate. To test this proposal, 3-thio-α-D -glucofuranose derivatives with the following substituents were synthesized: 1,2-O-isopropylidene-5,6-O-methylidene (see 24 ), 1,2:5,6-di-O-isopropylidene (see 2 ), 5,6-O-cyclohexylidene-1,2-O-isopropylidene (see 23 ), 1,2-O-cyclohexylidene-5,6-O-isopropylidene (see 14 ), 1,2:5,6-di-O-cyclohexylidene (see 13 ), 5,6-O-(adamantan-2-ylidene)-1,2-O-isopropylidene (see 21 ), and 1,2:5,6-di-O-(adamantan-2-ylidene) (see 25 , Table 2). As a representative of the allofuranoses, 1,2:5,6-di-O-isopropylidene-3-thio-α-D -allofuranose ( 6 ) was chosen. The following derivatives of 1,2-O-isopropylidene-α-D -xylofuranose were also synthesized: 1,2-O-isopropylidene-5-deoxy-3-thio-α-D -xylofuranose ( 29 ), 1,2-O-isopropylidene-3-thio-α-D -xylofuranose ( 28 ) and 5-O-[(tert-butyl)-diphenylsilyl]-1,2-O-isopropylidene-3-thio-α-D -xylofuranose ( 15 , see Table 2). The proposed concept was tested using the copper-catalyzed 1,4-addition of BuMgCl to cyclohex-2-en-1-one. The enantioselectivity was very dependent on the ligand used and was up to 58%.     

手性双噁唑啉配体的合成进展

总结了近年来用于不对称催化的各种双噁唑啉配体的合成方法,包括丙二酸酯类、酒石酸类、吡啶类、联苯、联萘及二茂铁类等多种双噁唑啉配体的合成.另外,还讨论了苯甲醚类、二联苯噁二唑类、联苯胺类与氮杂类等新型双噁唑啉配体的合成.     

Aluminum Bis(trifluoromethylsulfonyl)amides: New Highly Efficient and Remarkably Versatile Catalysts for C - C Bond Formation Reactions

Superacid-derived aluminum catalysts R(2)AlNTf(2) (2 - 5 mol%) are highly efficient and versatile and are suitable promoters for the allylation and pentadienylation of aldehydes, aldol reactions, aldol cross-coupling of ketones, and Michael additions (several products are shown). Furthermore, they can be converted into chemoselective Lewis acids. Tf=trifluoromethanesulfonyl.     

负载化的手性双(口,恶)唑啉配体在不对称催化中应用

负载化的手性双唑啉配体广泛应用于不对称催化领域,具有小分子配体所不具备的可回收再利用的特点。本文主要介绍了不同类型的负载化手性双唑啉配体以及它们在不对称催化领域中的应用。     

衍生于手性双二茂铁乙胺的单齿亚磷酰胺配体在不对称催化氢化中的应用

研究了衍生于手性双二茂铁乙胺的手性单齿亚磷酰胺配体的铑络合物催化剂在烯酰胺、β-脱氢氨基酸酯、衣康酸酯以及α-脱氢氨基酸酯的不对称氢化中的应用,结果显示该催化剂具有较好的催化性能,对烯酰胺类底物最高获得了96%的ee值,对β-脱氢氨基酸酯类底物最高获得了86%的ee值,对衣康酸酯最高获得了75%的ee值,对α-脱氢氨基酸酯类底物最高获得了95%的ee值.     

Derivatives of Bis(diphenylphosphino)maleic Anhydride as Ligands in Polynuclear Gold(I) Complexes

Based on the new binuclear gold(I) complex [(AuCl)₂(L1)] (1) (L1?=?2,3-bis(diphenylphosphino)maleic anhydride) four new polynuclear compounds were synthesized by reactions of 1 with E(SiMe₃)₂ (E?=?S, Se). During the formation of these new compounds the initial ligand L1 undergoes various transformations (e.g. substitution, hydration or hydrogenation) leading to the new ligands: trans-2,3-bis(diphenylphosphino)succinic anhydride (L2), 2-diphenylphosphino-3-mercapto-maleic anhydride anion (L3), 2-diphenylphosphino-3-selenolato-maleic anhydride anion (L4) and 2,3-bis(diphenylphosphino)succinic acid (L5). In case of using the sulfur species S(SiMe₃)₂ a pentanuclear cluster, [Au₅(PPh₂)₃(L3)₂] (2), and a 24-nuclear cluster, [Au₂₄S₆(PPh₂)₄(L3)₈] (3), could be obtained. With Se(SiMe₃)₂ the binuclear complex, [(AuCl)₂(L2)] (4), and the dodecanuclear cluster, [Au₁₂Se₄(L4)₄(L5)₂] (5), were yielded.     

Donor‐Flexible Bis(pyridylidene amide) Ligands for Highly Efficient Ruthenium‐Catalyzed Olefin Oxidation

An exceptionally efficient ruthenium‐based catalyst for olefin oxidation has been designed by exploiting N,N′‐bis(pyridylidene)oxalamide (bisPYA) as a donor‐flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson‐type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state‐of‐the‐art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h^?1 and turnover numbers of several millions.     

Bis(diphenylphosphino)Alkane / Co(II)/Tetrahydroborate and Cyanotrihydroborate Reactions: Formation of Unusual Bis(diphenylphosphino)methane Complexes and the Influence of Carbon Monoxide

Abstract

Reactions between Co(II), bis(diphenylphosphino)methane (dppm) and either NaBH₄ or NaBH₃CN have been studied. They follow pathways which are in marked contrast to those followed by Ph₂P(CH₂)nPPh₂ (n=2?6) in the presence of NaBH₄ in which the final product is normally CoH(phosphine)₂ although binuclear BH₄-bridged complexes may sometimes be obtained. The products obtained with dppm are Co₂X₃(dppm)₂ (X=Cl,Br) (I), CoCl(dppm)₃ (II), {CoHX(dppm)₂}Y (X=Cl, Br, I, BH₃CN; Y=Cl,BH₃CN,BPh₄,Clo₄) (III), and Co₂H₂(dppm)₃ (IV). While a binuclear A-frame structure can be proposed for the Co(I)-Co(II) species (I), crystal twinning has so far prevented an X-ray determination. However, X-ray studies on (II) and (IV) have shown that (II) contains tetrahedral Co(I) to which one chloro and three monodentate dppm ligands are attracted while (IV) is a binuclear species containing bridging dppm ligands and two terminal hydrides. The compounds (III) are octahedral Co(III) complexes. Possible mechanisms for the formation of these in strongly reducing environments will be discussed.     

Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes ( 1 a : (S)-BINAP; 1 b : (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex ( 1 c : (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]₂ and [Rh(cod)₂]⁺[BF₄]⁻ upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.     

A Library Approach to the Development of BenzaPhos: Highly Efficient Chiral Supramolecular Ligands for Asymmetric Hydrogenation

A library of chiral supramolecular ligands, named BenzaPhos, of straightforward preparation (two steps from commercially or readily available starting materials) and modular structure, was designed and synthesized. The ligands were screened in the search for new rhodium catalysts for the enantioselective hydrogenation of several benchmark and industrially relevant substrates. Once a series of hits were identified, structural modifications were introduced on three of the best ligands and a small second-generation library was created. Members of the latter library showed outstanding levels of activity and enantioselectivity in the hydrogenation of challenging olefins, such as enamide S4 and β-dehydroamino ester S5 (>99?%?ee: best value ever reported in both cases). A series of control experiments were undertaken to clarify the role of hydrogen bonding in determining the catalytic properties of the new ligands. The results of these experiments, together with those of computational studies carried out on four dihydride complexes involved in the catalytic hydrogenation of substrate S4, strongly suggest that a substrate orientation takes place in the catalytic cycle by formation of a hydrogen bond between the ligand amide oxygen atom and the substrate amide NH atom.