The Mechanism of the Intramolecular Hydrocarbyl Metathesis within a Planar Triruthenium Cluster: Combining Core Flexibility with Hydride Mobility

The transition metal catalysed formation and cleavage of C−C bonds is of utmost importance in synthetic chemistry. While most of the existing homogeneous catalysts are mononuclear, knowledge of the behaviour of polynuclear species is much more limited. By using computational methods, here we shed light into the mechanistic details of the thermally-induced isomerization of Cp*₃Ru₃(μ-H)₂(μ₃-η²-pentyne)(μ₃-pentylidyne) ( 2 ) into Cp*₃Ru₃(μ-H)₂(μ₃-η²-octyne)(μ₃-ethylidyne) ( 3 ), a process that involves the migration of a C₃ fragment between the hydrocarbyl ligands and across the plane formed by the three Ru centres. Our results show this to be a complex transformation that comprises of five individual rearrangements in an A→B→A→B→A order. Each so-called rearrangement A consists of the CH migration from the μ₃-η²-alkyne into the μ₃-alkylidine ligand in the other side of the Ru₃ plane. This process is facilitated by the cluster's ability to adopt open-core structures in which one Ru−Ru bond is broken and a new C−C bond is formed. In contrast, rearrangements B do not involve the formation or cleavage of C−C bonds, nor do they require the opening of the cluster core. Instead, they consist of the isomerization of the μ₃-η²-alkyne and μ₃-alkylidyne ligands on each side of the triruthenium plane into μ₃-alkylidyne and μ₃-η²-alkyne, respectively. Such transformation implies the migration of three H atoms within the hydrocarbyl ligands, and in this case, it is aided by the cluster's ability to behave as a H reservoir. All in all, this study highlights the plasticity of these Ru₃ clusters, whereby Ru−Ru, Ru−C, Ru−H, C−C, and C−H bonds are formed and broken with surprising ease.     

钌催化C-H键活化构建C-C键反应的研究进展

根据定位基团类型并结合其反应机理,介绍了近几年来钌催化的C-H键活化构建C-C键的研究进展.参考文献40篇.     

Isolation of Bis- and Mono-Cyclometallated Ru−IMes Complexes upon Reaction of [Ru(PPh3)3HCl], IMes and ZnMe2

Addition of an excess of ZnMe₂ to a mixture of [Ru(PPh₃)₃HCl] and IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) yields the bis-cyclometallated complex, [Ru(IMes)“(PPh₃)₂] 2 , together with the mono-cyclometallated, Ru−Zn heterobimetallic complex [Ru(IMes)′(PPh₃)₂(ZnMe)] 3 . Treatment of 2 with H₂, PhSiH₃ or pinacolborane yields the previously reported complex, [Ru(IMes)′(PPh₃)₂H] 1 , the synthesis of which has been reinvestigated. Further studies of small molecule reactivity show that 1 adds H₂ to give [Ru(IMes)(PPh₃)₂H₄] 4 , whilst 2 reacts with catecholborane to give [Ru(IMes-Bcat)′(PPh₃)₂H] 5 , in which (IMes-Bcat)′ signifies a borylated NHC ligand that is singly-metallated onto Ru. Treatment of 2 with CO gives the 18-electron dicarbonyl product [Ru(IMes)”(PPh₃)(CO)₂] 6 . Compounds 1 – 3 , 5 and 6 have been structurally characterised.     

[Co(TPP)]-Catalyzed Formation of Substituted Piperidines

Radical cyclization via cobalt(III)-carbene radical intermediates is a powerful method for the synthesis of (hetero)cyclic structures. Building on the recently reported synthesis of five-membered N-heterocyclic pyrrolidines catalyzed by Co^II porphyrins, the [Co(TPP)]-catalyzed formation of useful six-membered N-heterocyclic piperidines directly from linear aldehydes is presented herein. The piperidines were obtained in overall high yields, with linear alkenes being formed as side products in small amounts. A DFT study was performed to gain a deeper mechanistic understanding of the cobalt(II)-porphyrin-catalyzed formation of pyrrolidines, piperidines, and linear alkenes. The calculations showed that the alkenes are unlikely to be formed through an expected 1,2-hydrogen-atom transfer to the carbene carbon. Instead, the calculations were consistent with a pathway involving benzyl-radical formation followed by radical-rebound ring closure to form the piperidines. Competitive 1,5-hydrogen-atom transfer from the β-position to the benzyl radical explained the formation of linear alkenes as side products.     

Ruthenium(II)-Catalyzed Double Annulation of Quinones: Step-Economical Access to Valuable Bioactive Compounds

Double ruthenium(II)-catalyzed alkyne annulations of quinones were accomplished. Thus, a strategy is reported that provides step-economical access to valuable quinones with a wide range of applications. C−H/N−H activations for alkyne annulations of naphthoquinones provided challenging polycyclic quinoidal compounds by forming four new bonds in one step. The singular power of the thus-obtained compounds was reflected by their antileukemic activity.     

Ru/CNFs 催化剂催化氨分解制氢

 研究了鱼骨式碳纤维 (CNFs) 和管式碳纤维 (CNTs) 负载 Ru 催化剂的氨分解反应活性. 结果表明, Ru/CNFs 催化剂上氨分解活性高于 Ru/CNTs 催化剂. 通过改变 Ru 负载量或载体表面的含氧基团来调节 Ru 的粒径. Ru 的活性位随着 Ru 颗粒尺寸的增大而增加. CNFs 上的含氧基团对 Ru 颗粒的氨分解活性影响很大. 在相同粒径的 Ru 颗粒上, CNFs 表面的含氧基团增加了 Ru 的活性.     

Photo-Induced Ruthenium-Catalyzed C−H Benzylations and Allylations at Room Temperature

The ruthenium-catalyzed synthesis of diarylmethane compounds was realized under exceedingly mild photoredox conditions without the use of exogenous photocatalysts. The versatility and robustness of the ruthenium-catalyzed C−H benzylation was reflected by an ample scope, including multifold C−H functionalizations, as well as transformable pyrazoles, imidates and sensitive nucleosides. Mechanistic studies were indicative of a photoactive cyclometalated ruthenium complex, which also enabled versatile C−H allylations.     

Mild,Selective Ru-Catalyzed Deuteration Using D2O as a Deuterium Source

A method for the selective deuteration of polyfunctional organic molecules using catalytic amounts of [RuCl₂(PPh₃)₃] and D₂O as a deuterium source is presented. Through variation of additives like CuI, KOH, and various amounts of zinc powder, orthogonal chemoselectivities in the deuteration process are observed. Mechanistic investigation indicates the presence of different, defined Ru-complexes under the given specific conditions.     

Ru上有氧条件下氨分解的动力学研究

IthasbeenshownthatRuisvalidforthesyn thesisanddecompositionofammonia[1,2 ] .FurtherstudyofammoniaadsorptionanditsdecompositionproductsdesorptiononRuwillbeimportant .Previ ousstudiesofammoniaadsorptiononRumainlyfo cusedontheammoniasynthesisandhydrogenpro ductionintheabsenceofoxygen[3] ,onlyafewinves tigationsonammoniadecompositioninthepresenceofoxygenhavebeenreported[4 ,5] ,andtheeffectofad sorbedoxygenontheratesofammoniadecompositionandproductformationonRuarestillnotwellunder stood .Inthispa…     

Ni原子活化氨分子理论研究

在UB3LYP/6-311＋＋G(3df,3pd)水平下, 详细研究了Ni活化NH₃分子的单重态和三重态势能面, 并用分子中的原子量子理论(Quantum Theory of Atom-in-Molecular, QTAIM)计算了势能面上所有驻点的性质. 计算结果表明, 单重态势能面有两条反应途径, 而三重态势能面仅有一条反应途径. 第一个N—H断开的活化能较低, 为99.96 kJ/mol, 活化自由能为100.86 kJ/mol,在常温下就可以进行; 第二个N—H键断裂所需能量高达200 kJ/mol, 不容易进行. 在合适温度下, Ni可以活化NH₃得到三重态HNiNH₂, 这表明Ni可以作为活化NH₃分子的良好催化剂.     

Hydrogen Isotope Exchange Catalyzed by Ru Nanocatalysts: Labelling of Complex Molecules Containing N-Heterocycles and Reaction Mechanism Insights

Ruthenium nanocatalysis can provide effective deuteration and tritiation of oxazole, imidazole, triazole and carbazole substructures in complex molecules using D₂ or T₂ gas as isotopic sources. Depending on the substructure considered, this approach does not only represent a significant step forward in practice, with notably higher isotope uptakes, a broader substrate scope and a higher solvent applicability compared to existing procedures, but also the unique way to label important heterocycles using hydrogen isotope exchange. In terms of applications, the high incorporation of deuterium atoms, allows the synthesis of internal standards for LC-MS quantification. Moreover, the efficacy of the catalyst permits, even under subatmospheric pressure of T₂ gas, the preparation of complex radiolabeled drugs owning high molar activities. From a fundamental point of view, a detailed DFT-based mechanistic study identifying undisclosed key intermediates, allowed a deeper understanding of C−H (and N−H) activation processes occurring at the surface of metallic nanoclusters.     

Rh-Catalyzed Decarbonylative Cross-Coupling between o-Carboranes and Twisted Amides: A Regioselective,Additive-Free,and Concise Late-Stage Carboranylation

The convenient cross-coupling of sp² or sp³ carbons with a specific boron vertex on carborane cage represents significant synthetic values and insurmountable challenges. In this work, we report an Rh-catalyzed reaction between o-carborane and N-acyl-glutarimides to construct various B_cage−C bonds. Under the optimized condition, the removable imine directing group (DG) leads to B(3)− or B(3,6)−C couplings, while the pyridyl DG leads to B(3,5)−Ar coupling. In particular, an unexpected rearrangement of amide reagent is observed in pyridyl directed B(4)−C(sp³) formation. This scalable protocol has many advantages, including easy access, the use of cheap and widely available coupling agents, no requirement of an external ligand, base or oxidant, high efficiency, and a broad substrate scope. Leveraging the Rh^I dimer and twisted amides, this method enables straightforward access to diversely substituted and therapeutically important carborane derivatives at boron site, and provides a highly valuable vista for carborane-based drug screening.     

Framework Effects on Activation and Functionalisation of Methane in Zinc-Exchanged Zeolites

The first selective oxidation of methane to methanol is reported herein for zinc-exchanged MOR (Zn/MOR). Under identical conditions, Zn/FER and Zn/ZSM-5 both form zinc formate and methanol. Selective methane activation to form [Zn-CH₃]⁺ species was confirmed by ¹³C MAS NMR spectroscopy for all three frameworks. The percentage of active zinc sites, measured through quantitative NMR spectroscopy studies, varied with the zeolite framework and was found to be ZSM-5 (5.7 %), MOR (1.2 %) and FER (0.5 %). For Zn/MOR, two signals were observed in the ¹³C MAS NMR spectrum, resulting from two distinct [Zn-CH₃]⁺ species present in the 12 MR and 8 MR side pockets, as supported by additional NMR experiments. The observed products of oxidation of the [Zn-CH₃]⁺ species are shown to depend on the zeolite framework type and the oxidative conditions used. These results lay the foundation for developing structure–function correlations for methane conversion over zinc-exchanged zeolites.     

π-Extended Polyaromatic Hydrocarbons by Sustainable Alkyne Annulations through Double C−H/N−H Activation

The widespread applications of substituted diketopyrrolopyrroles (DPPs) call for the development of efficient methods for their modular assembly. Herein, we present a π-expansion strategy for polyaromatic hydrocarbons (PAHs) by C−H activation in a sustainable fashion. Thus, twofold C−H/N-H activations were accomplished by versatile ruthenium(II)carboxylate catalysis, providing step-economical access to diversely decorated fluorogenic DPPs that was merged with late-stage palladium-catalyzed C−H arylation on the thus-assembled DPP motif.     

Small Molecule Activation with Intramolecular “Inverse” Frustrated Lewis Pairs

The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1-BR₂-2-[(Me₂N)₂C=N]-C₆H₄ ( 3 – 6 ) [BR₂=BMes₂ ( 3 ), BC₁₂H₈, ( 4 ), BBN ( 5 ), BBNO ( 6 )] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X-ray analysis. These novel types of pre-organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via an ortho-phenylene linker, are capable of activating H−H, C−H, N−H, O−H, Si−H, B−H and C=O bonds. 4 and 5 deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1-(RC≡C-BR₂)-2-[(Me₂N)₂C=NH]-C₆H₄ (R=Ph, H) and reacted with ammonia, BnNH₂ and pyrrolidine, to generate the FLP adducts 1-(R₂HN→BR₂)-2-[(Me₂N)₂C=NH]-C₆H₄, where the N-H functionality is activated by intramolecular H-bond interactions. In addition, 5 was found to rapidly add across the double bond of H₂CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise, 5 is capable of cleaving H₂, HBPin and PhSiH₃ to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules.     

氮掺杂碳纳米管对其负载的Ru催化剂上合成氨的促进作用

以乙腈为碳源和氮源,采用化学气相沉积法制备了氮掺杂的碳纳米管.电子显微镜观察表明,样品形貌为中空的多壁纳米管,管腔大小10～15 nm,壁厚10～20 nm.X射线光电子能谱结果表明,氮已掺杂到碳纳米管结构中,主要以吡啶型氮和取代型氮存在.结合X射线衍射和拉曼光谱结果发现,随着制备温度的升高,氮掺杂量减少,但纳米管的石...     

用水合肼还原的Ru／AC氨合成催化剂的制备

 用RuCl3水溶液浸渍BET比表面积为1020m2／g的椰壳活性炭（AC）载体，制备了钌含量为6％的Ru／AC氨合成催化剂．在添加助剂前，分别用水合肼水溶液、水合肼蒸气和H2还原催化剂，然后分别浸渍Ba（NO3）2和KOH．催化剂中的Ru∶K∶Ba摩尔比为1∶3∶0．3．用N2物理吸附、XPS和CO化学吸附等方法对催化剂进行了表征．结果表明，用不同还原方法制备的催化剂上的钌以不同的化学状态存在，它的活性与其比表面积和金属钌的分散度相关．用水合肼水溶液还原的催化剂S1中的钌在大气气氛下以金属态存在，它的BET比表面积和金属分散度较大，低温低压下催化活性最高．以水合肼蒸气还原的催化剂S2中的钌在大气气氛下以RuO3形态存在，它的BET比表面积和金属分散度小，催化活性最低．用H2还原的催化剂S3中的钌在大气气氛下以RuO2形态存在，其BET比表面积和金属分散度与S1催化剂相当，催化活性也与S1相近．     

2-Fluoro-5-nitrophenyldiazonium: A Novel Sanger-Type Reagent for the Versatile Functionalization of Alcohols

As a novel Sanger-type reagent, 2-fluoro-5-nitrophenyldiazonium tetrafluoroborate enabled the versatile functionalization of primary and secondary aliphatic alcohols. Based on a mild nucleophilic aromatic substitution of the fluorine atom under unprecedented, base-free conditions, the diazonium unit on the aromatic core of the resulting aryl-alkyl ether could be employed for such diverse transformations as radical C−H activation and cyclization, as well as palladium catalyzed cross-coupling reactions.