N-杂环卡宾Ru配合物的合成及其在Suzuki偶联反应中的催化应用

合成了两个新的氮杂环卡宾金属钌配合物1和2,通过核磁共振氢谱、核磁共振碳谱、红外光谱和元素分析对其结构进行了表征,同时,X射线单晶衍射确证了配合物2的结构为cis(I)顺式构型.化合物1和2均能在温和的反应条件下有效催化卤代芳烃和苯硼酸的Suzuki偶联反应,并表现出较高的催化活性.     

双N-杂环卡宾螯合配合物研究进展

本文综述了由各种基团桥连的双N-杂环卡宾螯合配合物研究的最新进展,着重讨论了这些配合物对各种化学反应的催化性能。     

氮杂环卡宾-铁配合物催化碳-碳偶联反应的研究进展

作为传统贵金属催化剂的理想替代品,铁具有来源广泛、毒性低和环境兼容性好等特点,目前被用于多种环境友好的催化过程。近年来,氮杂环卡宾(NHC)由于其独特的空间和电子性质,常作为配体,不仅能够被应用于贵金属(如钯、镍和铑等)催化,在铁催化中也得到了广泛的应用。本文综述了氮杂环卡宾及铁配合物催化剂的特点,并重点讨论了近十年其催化的碳-碳偶联包括芳基-芳基交叉偶联、芳基-烷基交叉偶联、烷基-烷基交叉偶联等反应中的研究进展。     

Pd-NHC络合物催化交叉偶联反应的新进展

钯催化的交叉偶联反应能非常有效且方便构建碳-碳键并应用于农药、医药、新型材料和有机中间体等领域.多年来,各种不同结构的配体以及新型的催化体系被不断开发出来.其中N-杂环卡宾(NHC)配体毒性低,稳定性好,同时在反应过程中具备良好的配位能力,因而被作为新一代催化体系应用于各种不同的交叉偶联反应中.根据NHC结构特点综述了近年来新开发的Pd-NHC催化剂及其在多种交叉偶联反应中的应用.     

N-杂环卡宾铜配合物在催化领域中的应用进展

N-杂环卡宾已经成为金属有机化学、无机配位化学等领域广泛使用的优良配体,尤其是其过渡金属配合物在催化领域中取得了丰硕的成果。其中N-杂环卡宾铜配合物的相关报道虽然出现较晚,但相比于含Ru、Pd等贵金属催化剂及以有机膦为配体的过渡金属配合物,其不仅有价格低廉、低毒等优势,还在共轭加成、[3+2]环加成等反应中表现出优良的催化活性,成为目前的研究热点。本文总结了近年来N-杂环卡宾铜配合物在催化领域中的研究进展。     

N-杂环卡宾的反应及应用

自从1991年Arduengo第一次分离得到稳定的游离N-杂环卡宾以后,N-杂环卡宾金属络合物的研究在近几年来得到了迅速的发展。N-杂环卡宾的反应性能较高,它们与周期表中几乎所有的元素都能发生反应。N-杂环卡宾金属络合物对许多反应有催化作用,它们是一类有潜在应用价值的催化剂。本文对近年来相关的研究成果进行了综述。     

Pd-N-杂环卡宾化合物催化的Heck反应、Suzuki反应进展

Pd催化的C—C键偶联反应是形成碳—碳单键的重要反应之一.传统上,使用膦化合物为配体来调整催化活性及选择性.但大多数Pd-膦化合物对空气稳定性差,容易被氧化;在溶液中易于解离出膦配体而降低催化剂稳定性,通常需要给反应体系中加入较多的膦配体以保持催化剂的稳定性和活性.1991年发现的稳定N-杂环卡宾(NHC)类配体具有富含电子、给电子能力强,对金属配位能力强,结构易修饰等特点,使得金属-NHC化合物成为金属有机化学、催化等领域研究新的焦点.Pd-NHC化合物已经可催化多类有机反应,是继传统Pd-膦催化剂外的又一类高效催化剂.综述了近年来不同结构的NHC如单齿简单NHC、双齿NHC、含其它配位原子的NHC等配体与Pd的配合物在Heck反应、Suzuki反应等偶联反应中的应用.     

氮杂环卡宾催化二氧化碳羧化反应的研究进展

二氧化碳是一种来源丰富的可再生资源,科研工作者一直致力于开发能够高效转化二氧化碳的催化体系。氮杂环卡宾在有机化学中是一类非常重要的催化剂,利用氮杂环卡宾-过渡金属配合物催化实现二氧化碳的高效化学转化受到了人们的广泛关注。本文主要根据氮杂环卡宾-过渡金属配合物进行分类,总结归纳了近年来氮杂环卡宾-过渡金属配合物催化二氧化碳羧化反应的研究进展。     

氮杂环卡宾-钯配合物催化Buchwald-Hartwig偶联反应最新研究进展*

钯催化的Buchwald-Hartwig偶联反应是用于构建C-N键非常直接有效的方法。氮杂环卡宾-钯配合物具有性能稳定、催化活性高等优点,是Buchwald-Hartwig偶联反应的高效催化剂。对这一领域近3年的研究进展作简要介绍。     

官能团化N,C双齿N-杂环卡宾配合物研究进展

综述了官能团化N,C双齿N-杂环卡宾金属配合物研究的最新进展,着重讨论了这些配合物对各种化学反应的催化性能.     

Remote Electronic Tuning of Chiral N-Heterocyclic Carbenes

Our recent efforts to develop novel N-Heterocyclic carbene (NHC)-catalyzed asymmetric reactions are described. During our investigation for development of the acylation reactions via acylazoliums generated by the reactions of NHCs and α-oxidized aldehydes, we have observed significant effects of substitution at a remote site of the carbene carbon of NHCs. In addition, we also observed a significant enhancement of the enantioselectivity by the addition of carboxylate anions. From this observation, we proposed a novel working hypothesis involving a formation of a complex of the substrate and additive to reinforce the recognition of the catalyst for enhancement of the catalytic performance of the asymmetric N-heterocyclic carbene system. By applying this concept, we achieved the kinetic resolutions of both cyclic and acyclic alcohols in excellent enantioselectivities. The effects of the remote substitution were also observed in intramolecular Stetter reaction and intermolecular benzoin reaction. In these reactions, the comparison of the catalytic performance of the NHCs bearing variable remote substitutions provided insights into the reaction mechanism because the remote substitution tuned the electronic nature of NHCs without affecting the steric and electrostatic factors around the reaction site. We also developed an intramolecular benzoin condensation involving two aldehydes, which is challenging to realize. Using the substrates bearing proper protecting groups, we succeeded in the stereo divergent synthesis of a variety of inososes, which are important intermediates for the synthesis of biologically active cyclitols.     

N-Heterocyclic Carbenes Carrying Weakly Coordinating Anions

In this Concept article we provide a brief overview of the design and preparation of N-heterocyclic carbenes carrying weakly coordinating anions (WCA-NHCs). The anionic charge in these ligand systems is located on an exocyclic group, for example, B(C₆F₅)₃, tethered to the backbone of the imidazole ring, thus resembling a weakly coordinating moiety. With the general guiding principle behind the application of WCA-NHCs being the conversion of otherwise cationic NHC complexes into their overall neutral congeners, numerous transition metal as well as main group element complexes were isolated during the last decade, which are summarized herein.     

Identification of the Active Catalyst for Nickel-Catalyzed Stereospecific Kumada Coupling Reactions of Ethers

A series of nickel complexes in varying oxidation states were evaluated as precatalysts for the stereospecific cross-coupling of benzylic ethers. These results demonstrate rapid redox reactions of precatalysts, such that the oxidative state of the precatalyst does not dictate the oxidation state of the active catalyst in solution. These data provide the first experimental evidence for a Ni⁰–Ni^II catalytic cycle for a stereospecific alkyl–alkyl cross-coupling reaction, including spectroscopic analysis of the catalyst resting state.     

Bidentate Donor-Functionalized N-Heterocyclic Carbenes: Valuable Ligands for Ruthenium-Catalyzed Transfer Hydrogenation

Ruthenium complexes are by far the most studied compounds that catalyze hydrogen transfer reactions. In this review, we describe the use in this field of ruthenium complexes bearing bidentate donor-functionalized N-heterocyclic carbene ligands. The review specifically covers the application in transfer hydrogenations of (κ²-C_NHC,Y)-ruthenacyclic compounds where the Y donor atom is a N, P, O, or S atom, and where the N-heterocyclic carbene ligand is a classical imidazol-2-ylidene, a benzimidazol-2-ylidene, a mesoionic 1,2,3-triazolylidene, or an imidazol-4-ylidene ligand. Tridentate donor-functionalized N-heterocyclic carbene complexes thus fall outside the scope of the review. Applications in (asymmetric) transfer hydrogenation of ketones, aldehydes, imines, alkenes, and nitrobenzene are discussed.     

Tricyanoborane-Functionalized Anionic N-Heterocyclic Carbenes: Adjustment of Charge and Stereo-Electronic Properties

The 1-methyl-3-(tricyanoborane)imidazolin-2-ylidenate anion ( 2 ) was obtained in high yield by deprotonation of the B(CN)₃-methylimidazole adduct 1 . Regarding charge and stereo-electronic properties, anion 2 closes the gap between well-known neutral NHCs and the ditopic dianionic NHC, the 1,3-bis(tricyanoborane)imidazolin-2-ylidenate dianion ( IIb ). The influence of the number of N-bonded tricyanoborane moieties on the σ-donating and π-accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2 , IIb , and 1,3-dimethylimidazolin-2-ylidene (IMe, IIa ). Therefore NHC 2 , which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)₄] yielding alkylated imidazoles 3 and 4 , the anionic selenium adduct 5 , and the anionic nickel tricarbonyl complex 8 , respectively. The results of this study prove that charge, number of coordination sites, buried volume (%V_bur) and σ-donor and π-acceptor abilities of NHCs can be effectively fine-tuned via the number of tricyanoborane substituents.     

氮杂环卡宾在有机催化中的研究进展

介绍了氮杂环卡宾作为有机催化剂的发展历史和催化机理,综述了近年来氮杂环卡宾在有机催化领域中的研究成果.     

Ligand-Facilitated Reductive Coupling of Benzyl Chlorides with Aryl Chlorides Catalyzed by Well-Defined Heteroleptic Ni (II)-NHC Complexes

Novel heteroleptic Ni (II) complexes bearing a highly hindered yet flexible IPr^* ligand, Ni (IPr^*)(PPh₃)Br₂ ( 1 ) and Ni (IPr^*)(PCy₃)Br₂ ( 2 ) (IPr^* = 1,3-bis(2,6-bis (diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene), were easily prepared in 78% and 89% yield, respectively. Both were characterized by elemental analysis and NMR spectroscopy, and 1 was subjected to X-ray crystallography. Compared with 2 and its analogue bearing a less sterically demanding IPr ligand (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), complex 1 exhibited superior catalytic activity in the magnesium-mediated reductive coupling of benzyl chlorides with aryl chlorides, featuring outstanding tolerance of both coupling partners with steric demand. This study discloses a ligand-facilitated reductive coupling of benzyl chlorides with aryl chlorides, which provides a new and practical synthetic tool for the synthesis of diarylmethanes.     

二茂铁咪唑盐的合成及其在Suzuki-Miyaura反应中的应用

合成了硫醚官能化、膦官能化及未官能化的二茂铁咪唑盐,并研究了以其作为N-杂环卡宾配体前体对Pd催化的Suzuki-Miyaura偶联反应的影响,发现在4-甲基溴苯与苯硼酸偶联反应中以膦官能化的配体对催化性能提高有利,而硫醚官能化不利于催化性能提高。