In Situ Generation of Ruthenium Carbonyl Phosphine Complexes as a Versatile Method for the Development of Enantioselective C−O Bond Arylation

We report here a method for in situ generation of various ruthenium carbonyl phosphine catalysts for arylation via cleavage of inert aromatic carbon–oxygen bonds. The use of catalyst systems consisting of [RuCl₂(CO)(p-cymene)], CsF, styrene, and phosphines enabled facile screening of phosphine ligands. Asymmetric C–O arylation was also achieved for atropo-enantioselective biaryl synthesis using a chiral monodentate phosphine ligand.     

Ruthenium‐Catalyzed CC Bond Cleavage in Lignin Model Substrates

Ruthenium–triphos complexes exhibited unprecedented catalytic activity and selectivity in the redox‐neutral C? C bond cleavage of the β‐O‐4 lignin linkage of 1,3‐dilignol model compounds. A mechanistic pathway involving a dehydrogenation‐initiated retro‐aldol reaction for the C? C bond cleavage was proposed in line with experimental data and DFT calculations.     

Ruthenium-catalyzed chemoselective N-allyl cleavage: novel Grubbs carbene mediated deprotection of allylic amines

A novel application of the Grubbs carbene complex has been discovered. The first examples of the catalytic deprotection of allylic amines with reagents other than palladium catalysts have been achieved through Grubbs carbene mediated reaction. Significantly, the catalytic system directs the reaction toward the selective deprotection of allylic amines (secondary as well as tertiary) in the presence of allylic ethers. A variety of substrates, including enantiomerically pure multifunctional piperidines, are also usable. The new method is more convenient, chemoselective, and operationally simple than the palladium-catalyzed method. The current mechanistic hypothesis invokes a nitrogen-assisted ruthenium-catalyzed isomerization, followed by hydrolysis of the enamine intermediate. We believe that the reactive species involved in the reaction may be an Rubond;H species rather than the Grubbs carbene itself. Thus, the isomerization may occur according to the hydride mechanism. The synthetic utility of this ruthenium-catalyzed allyl cleavage is illustrated by the preparation of indolizidine-type alkaloids.     

A practical ruthenium-catalyzed cleavage of the allyl protecting group in amides, lactams, imides, and congeners

A convenient methodology for the deprotection of N-allylic amide-like moieties was developed. The first examples accounting for the ruthenium-catalyzed deallylation of amides, lactams, imides, pyrazolidones, hydantoins, and oxazolidinones have been achieved by the sequential use of Grubbs carbene (isomerization step) and RuCl(3) (oxidation step). A variety of substrates, including enantiopure multifunctional beta- and gamma-lactams, can be employed.     

A visible-light-mediated oxidative cn bond formation/aromatization cascade: photocatalytic preparation of N-arylindoles

Just add light and air: Structurally diverse N-arylindoles can be prepared from readily prepared o-styryl anilines through visible-light photocatalysis. The reaction, which is conducted open to air, is mediated by [Ru(bpz)(3) ](PF(6) )(2) (bpz=2,2'-bipyrazine) and involves both C?N bond formation and aromatization. Using suitably substituted substrates, a 1,2-carbon shift can be also incorporated into this cascade reaction.     

Aqueous-Phase Nitrile Hydration Catalyzed by an In Situ Generated Air-Stable Ruthenium Catalyst

RuCl₂(PTA)₄ (PTA=1,3,5-triaza-7-phosphaadamantane) is an active, recyclable, air-stable, aqueous-phase nitrile hydration catalyst. The development of an in situ generated aqueous-phase nitrile hydration catalyst (RuCl₃⋅3 H₂O+6 equivalents PTA) is reported. The activity of the in situ catalyst is comparable to RuCl₂(PTA)₄. The effects of [PTA] on the activity of the reaction were investigated: the catalytic activity, in general, increases as the pH goes up, which shows a positive correlation with [PTA]. The pH effects were further explored for both the in situ and RuCl₂(PTA)₄ catalyzed reaction in phosphate buffer solutions with particular attention given to pH 6.8 buffer. Increased catalytic activity was observed at pH 6.8 versus water for both systems with turnover frequency (TOF) up to 135 h⁻¹ observed for RuCl₂(PTA)₄ and 64 h⁻¹ for the in situ catalyst. Catalyst loading down to 0.001 mol % was examined with turnover numbers as high as 22 000 reported. Similar to the preformed catalyst, RuCl₂(PTA)₄, the in situ catalyst could be recycled more than five times without significant loss of activity from either water or pH 6.8 buffer.     

钌配合物断裂DNA及其机理研究

DNA是遗传信息的携带者和基因表达的物质基础,金属配合物与DNA的相互作用研究受到广泛关注,成为生物无机化学的重要研究内容之一.与其他类型金属配合物相比,钌配合物具有良好的热力学稳定性以及丰富的光化学、光物理和氧化还原特性,其作为DNA断裂试剂也引起人们的极大兴趣.以近年一些代表性的研究工作为例,本文对钌配合物在DNA断裂作用机制方面的研究进展进行了综述.     

Atom‐Transfer Radical Addition Reactions Catalyzed by RuCp* Complexes: A Mechanistic Study

Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom‐transfer radical reactions catalyzed by the complexes [RuCl₂Cp*(PPh₃)] and [RuClCp*(PPh₃)₂] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero‐order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate‐limiting step of the reaction.     

Ruthenium‐Catalyzed Synthesis of 2,3‐Cyclo[3]dendralenes and Complex Polycycles from Propargyl Alcohols

Ruthenium‐catalyzed cascade transformations for the synthesis of 2,3‐cyclo[3]dendralenes and multicomponent processes based thereon to generate complex polycycles are presented. The combination of allylation–cyclization sequences with diene‐transmissive Diels–Alder reactions allows the rapid and selective construction of natural‐product‐like motifs from easily accessible starting materials in a one‐pot process and provides a new method to access potential drug candidates.     

Stepwise Metal–Ligand Cooperation by a Reversible Aromatization/Deconjugation Sequence in Ruthenium Complexes with a Tetradentate Phenanthroline‐Based Ligand

The synthesis and reactivity of ruthenium complexes containing the tetradentate phenanthroline‐based phosphine ligand 2,9‐bis((di‐tert‐butylphosphino)methyl)‐1,10‐phenanthroline (PPhenP) is described. The hydrido chloro complex [RuHCl(PPhenP)] ( 2 ) undergoes facile dearomatization upon deprotonation of the benzylic position, to give [RuH(PPhenP‐H)] ( 4 ). Addition of dihydrogen to 4 causes rearomatization of the phenanthroline moiety to trans‐[Ru(H)₂(PPhenP)] ( 5 ), followed by hydrogenation of an aromatic heterocycle in the ligand backbone, to give a new dearomatized and deconjugated complex [RuH(PPhenP*‐H)] ( 6 ). These aromatization/deconjugation steps of the coordinated ligand were demonstrated to be reversible and operative in the dehydrogenation of primary alcohols without the need for a hydrogen acceptor. This aromatization/deconjugation sequence constitutes an unprecedented mode of a stepwise cooperation between the metal center and the coordinated ligand.