Thermal isomerization of ruthenium hydride compounds containing asymmetric bidentate pyrrole‐imine ligands

A series of ruthenium hydride compounds containing substituted bidentate pyrrole‐imine ligands were synthesized and characterized. Reacting RuHCl(CO)(PPh₃)₃ with one equivalent of [C₄H₃NH(2‐CH=NR)] in ethanol in the presence of KOH gave compounds {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NR)]} where trans‐Py‐Ru‐H 1, R = CH₂CH₂C₆H₉; cis‐Py‐Ru‐H 2, R = Ph‐2‐Me; and cis‐Py‐Ru‐H 3, R = C₆H₁₁. Heating trans‐Py‐Ru‐H 1 in toluene at 70°C for 12 hr resulted a thermal conversion of the trans‐Py‐Ru‐H 1 into its cis form, {RuH(CO)(PPh₃)₂[C₄H₃N(2‐CH=NCH₂CH₂C₆H₉)]} (cis‐Py‐Ru‐H 1) in very high yield. The ¹H NMR spectra of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 2, cis‐Py‐Ru‐H 3, and cis‐Py‐Ru‐H 1 all show a typical triplet at ca. δ–11 for the hydride. The trans and cis form indicate the relative positions of pyrrole ring and hydride. The geometries of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 1, and cis‐Py‐Ru‐H 3 are relatively similar showing typical octahedral geometries with two PPh₃ fragments arranged in trans positions.     

cis/trans Isomerism of Hydroalumination and Hydrogallation Products—Reflections on Stability and Rearrangement Mechanism

Treatment of (silylalkynyl)benzenes with (Me₃C)₂Ga? H afforded stable cis‐addition products, for example, (Me₃C)₂Ga? C(SiMe₃)?C(H)? C₆H₅ ( 1 ), while spontaneous cis/trans rearrangement was observed for sterically less shielded gallium hydrides. The corresponding trans‐di(tert‐butyl)gallium compounds ( 13 , 14 ) were obtained by the reaction of C₆H_6?n[C(H)?C(SiMe₃)GaCl₂]_n ( 11 , 12 ) with LiCMe₃. In contrast, spontaneous isomerization took place upon reaction of (Me₃C)₂Al? H with phenyltrimethylsilylethyne. In this case the cis isomer ( 17 ) was detected only at low temperature, while the trans product ( 18 ) formed quantitatively above 0 °C. Quantum‐chemical calculations showed that the trans forms are thermodynamically favored, essentially caused by a better mesomeric interaction of the C?C double bonds with the phenyl groups, a smaller steric stress in the molecules, and a short bonding contact of the coordinatively unsaturated Al or Ga atoms to C? H bonds of the aromatic rings. The rotation about the C?C double bonds follows a zwitterionic mechanism, and the relatively small rotational barrier is further lowered by an interaction to a Lewis acidic lithium cation.     

Light‐Harvesting Photocatalysis for Water Oxidation Using Mesoporous Organosilica

An organic‐based photocatalysis system for water oxidation, with visible‐light harvesting antennae, was constructed using periodic mesoporous organosilica (PMO). PMO containing acridone groups in the framework (Acd‐PMO), a visible‐light harvesting antenna, was supported with [Ru^II(bpy)₃²⁺] complex (bpy=2,2′‐bipyridyl) coupled with iridium oxide (IrO_x) particles in the mesochannels as photosensitizer and catalyst, respectively. Acd‐PMO absorbed visible light and funneled the light energy into the Ru complex in the mesochannels through excitation energy transfer. The excited state of Ru complex is oxidatively quenched by a sacrificial oxidant (Na₂S₂O₈) to form Ru³⁺ species. The Ru³⁺ species extracts an electron from IrO_x to oxidize water for oxygen production. The reaction quantum yield was 0.34 %, which was improved to 0.68 or 1.2 % by the modifications of PMO. A unique sequence of reactions mimicking natural photosystem II, 1) light‐harvesting, 2) charge separation, and 3) oxygen generation, were realized for the first time by using the light‐harvesting PMO.     

trans‐Di­chloro­tetrakis(4‐methylpyrimidine‐N1)­ruthenium(II)

The title compound, trans‐[Ru^IICl₂(N¹‐mepym)₄] (mepym is 4‐methylpyrimidine, C₅H₆N₂), obtained from the reaction of trans,cis,cis‐[Ru^IICl₂(N¹‐mepym)₂(SbPh₃)₂] (Ph is phenyl) with excess mepym in ethanol, has fourfold crystallographic symmetry and has the four pyrimidine bases coordinated through N¹ and arranged in a propeller‐like orientation. The Ru—N and Ru—Cl bond distances are 2.082 (2) and 2.400 (4) Å, respectively. The methyl group, and the N³ and Cl atoms are involved in intermolecular C—H?N and C—­H?Cl hydrogen‐bond interactions.     

Ruthenium‐Catalyzed Cascade CH Functionalization of Phenylacetophenones

Three orthogonal cascade C? H functionalization processes are described, based on ruthenium‐catalyzed C? H alkenylation. 1‐Indanones, indeno indenes, and indeno furanones were accessed through cascade pathways by using arylacetophenones as substrates under conditions of catalytic [{Ru(p‐cymene)Cl₂}₂] and stoichiometric Cu(OAc)₂. Each transformation uses C? H functionalization methods to form C? C bonds sequentially, with the indeno furanone synthesis featuring a C? O bond formation as the terminating step. This work demonstrates the power of ruthenium‐catalyzed alkenylation as a platform reaction to develop more complex transformations, with multiple C? H functionalization steps taking place in a single operation to access novel carbocyclic structures.     

Copper‐Catalyzed C(sp3)−H Amidation: Sterically Driven Primary and Secondary C−H Site‐Selectivity

Undirected C(sp³)?H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C?H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C?H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C?H bonds over tertiary and benzylic C?H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C?H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N₃. Mechanistic and DFT studies indicate that C?H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ²‐N,O‐NC(O)Ar) to provide carbon‐based radicals R^. and copper(II)amide intermediates [Cu^II]‐NHC(O)Ar that subsequently capture radicals R^. to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C?H amidation selectivity in the absence of directing groups.     

Non‐Heme‐Type Ruthenium Catalyzed Chemo‐ and Site‐Selective C−H Oxidation

Herein, we developed a Ru(II)(BPGA) complex that could be used to catalyze chemo‐ and site‐selective C?H oxidation. The described ruthenium complex was designed by replacing one pyridyl group on tris(2‐pyridylmethyl)amine with an electron‐donating amide ligand that was critical for promoting this type of reaction. More importantly, higher reactivities and better chemo‐, and site‐selectivities were observed for reactions using the cis‐ruthenium complex rather than the trans‐one. This reaction could be used to convert sterically less hindered methyne and/or methylene C?H bonds of a various organic substrates, including natural products, into valuable alcohol or ketone products.     

Dehydrogenative Carbon–Carbon Bond Formation Using Alkynyloxy Moieties as Hydrogen‐Accepting Directing Groups

In the presence of a catalyst system consisting of Pd(OAc)₂, PCy₃, and Zn(OAc)₂, the reaction of alkynyl aryl ethers with bicycloalkenes, α,ß‐unsaturated esters, or heteroarenes results in the site‐selective cleavage of two C? H bonds followed by the formation of C? C bonds. In all cases, the alkynyloxy group acts as a directing group for the activation of an ortho C? H bond and as a hydrogen acceptor, thus rendering the use of additives such as an oxidant or base unnecessary.     

Isocyanate‐ and Isothiocyanate‐Derived RuIV‐Based Alkylidenes: Synthesis,Structure, and Activity

The synthesis and characterization of a series of isocyanate‐ and isothiocyanate‐derived second generation Grubbs–Hoveyda‐type ruthenium–alkylidene complexes, that is, [Ru(N?C?O)₂(IMesH₂)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 1 ), [Ru(N?C?O)₂(1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(=CH‐2‐(2‐PrO)‐C₆H₄)] ( 2 ), [Ru(N?C?S)₂(IMesH₂)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 3 ), and [Ru(N?C?S)₂(1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 4 ), and their activity in various metathesis reactions are described. Compounds 1 – 4 were prepared by reaction of the parent complexes [RuCl₂(IMesH₂)(?CH‐2‐(2‐PrO)C₆H₄)] ( 5 ) (IMesH₂=1,3‐bis‐(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) and [RuCl₂(1,3‐dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene)(?CH‐2‐(2‐PrO)‐C₆H₄)] ( 6 ) with silver cyanate and thiocyanate, respectively. The X‐ray structure of 1 was determined, confirming the isocyanate‐type bonding of the ligand. The isothiocyanate‐type bonding in 3 and 4 was unambiguously confirmed by IR and ¹³C NMR spectroscopy. The isocyanate‐derived complexes 1 and 2 were found to be excellent catalysts for the ring‐opening metathesis polymerization (ROMP) of cis‐cycloocta‐1,5‐diene (COD). Both 1 and 2 yielded poly(COD) with a trans‐content of about 80 %. First‐order kinetics with unprecedentedly high rate constants of polymerization (k_p=0.068 and 0.26 s^?1, respectively) were observed. Compounds 3 and 4 were also active initiators for the ROMP of COD, however, they generated poly(COD) with a cis‐content of 80 and 67 %, respectively. Complexes 1 and 2 also showed good catalytic activity in cross‐metathesis (CM) reactions. Finally, 1 – 4 were also found to be excellent catalysts for the regioselective cyclopolymerization of diethyl 2,2‐dipropargylmalonate (DEDPM), resulting in poly(DEDPM) almost entirely based on five‐membered repeat units, that is, cyclopent‐1‐ene‐1,2‐vinylenes.     

Application of carbon arc‐generated Mo‐ and W‐based catalyst systems to the ROMP of norbornene

This study focuses on the application of the carbon arc‐generated molybdenum‐ and tungsten‐based catalyst systems, MoCl₅? C and WCl₆? C, to effect ring‐opening metathesis polymerization (ROMP) of bicyclo[2.2.1]hept‐2‐ene (norbornene). The results are compared with those previously obtained by the electrochemically generated MoCl₅? ē? Al? CH₂Cl₂ and WCl₆? ē? Al? CH₂Cl₂ systems. The polymer products are characterized using ¹H and ¹³C NMR, gel permeation chromatography, differential scanning calorimetry and thermo gravimetric analysis. According to NMR spectra analyses, the molybdenum‐based catalyst system produced polynorbornene with ca 48% cis structure whereas tungsten system produced ca 56% cis structure polynorbornene and in both cases the polynorbornene had a blocky distribution. Copyright © 2009 John Wiley & Sons, Ltd.     

Ruthenium Nanoparticles on Nano‐Level‐Controlled Carbon Supports as Highly Effective Catalysts for Arene Hydrogenation

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with [Ru₃(CO)₁₂] in toluene heated at reflux provided the corresponding CNF‐supported ruthenium nanoparticles, Ru/CNFs (Ru content=1.1–3.8 wt %). TEM studies of these Ru/CNFs revealed that size‐controlled Ru nanoparticles (2–4 nm) exist on the CNFs, and that their location was dependent on the surface nanostructures of the CNFs: on the edge of the graphite layers (CNF‐P), in the tubes and on the surface (CNF‐T), and between the layers and on the edge (CNF‐H). Among these Ru/CNFs, Ru/CNF‐P showed excellent catalytic activity towards hydrogenation of toluene with high reproducibility; the reaction proceeded without leaching of the Ru species, and the catalyst was reusable. The total turnover number of the five recycling experiments for toluene hydrogenation reached over 180 000 (mol toluene) (mol Ru)^?1. Ru/CNF‐P was also effective for the hydrogenation of functionalized benzene derivatives and pyridine. Hydrogenolysis of benzylic C? O and C? N bonds has not yet been observed. Use of poly(ethylene glycol)s (PEGs) as a solvent made possible the biphasic catalytic hydrogenation of toluene. After the reaction, the methylcyclohexane formed was separated by decantation without contamination of the ruthenium species and PEG. The insoluble PEG phase containing all of the Ru/CNF was recoverable and reusable as the catalyst without loss of activity.     

Chiral Lithiated Allylic α‐Sulfonyl Carbanions: Experimental and Computational Study of Their Structure,Configurational Stability,and Enantioselective Synthesis

X‐ray crystal structure analysis of the lithiated allylic α‐sulfonyl carbanions [CH₂?CHC(Me)SO₂Ph]Li ? diglyme, [cC₆H₈SO₂tBu]Li ? PMDETA and [cC₇H₁₀SO₂tBu]Li ? PMDETA showed dimeric and monomeric CIPs, having nearly planar anionic C atoms, only O?Li bonds, almost planar allylic units with strong C?C bond length alternation and the s‐trans conformation around C1?C2. They adopt a C1?S conformation, which is similar to the one generally found for alkyl and aryl substituted α‐sulfonyl carbanions. Cryoscopy of [EtCH?CHC(Et)SO₂tBu]Li in THF at 164 K revealed an equilibrium between monomers and dimers in a ratio of 83:17, which is similar to the one found by low temperature NMR spectroscopy. According to NMR spectroscopy the lone‐pair orbital at C1 strongly interacts with the C?C double bond. Low temperature ⁶Li,¹H NOE experiments of [EtCH?CHC(Et)SO₂tBu]Li in THF point to an equilibrium between monomeric CIPs having only O?Li bonds and CIPs having both O?Li and C1?Li bonds. Ab initio calculation of [MeCH?CHC(Me)SO₂Me]Li ? (Me₂O)₂ gave three isomeric CIPs having the s‐trans conformation and three isomeric CIPs having the s‐cis conformation around the C1?C2 bond. All s‐trans isomers are more stable than the s‐cis isomers. At all levels of theory the s‐trans isomer having O?Li and C1?Li bonds is the most stable one followed by the isomer which has two O?Li bonds. The allylic unit of the C,O,Li isomer shows strong bond length alternation and the C1 atom is in contrast to the O,Li isomer significantly pyramidalized. According to NBO analysis of the s‐trans and s‐cis isomers, the interaction of the lone pair at C1 with the π* orbital of the CC double bond is energetically much more favorable than that with the “empty” orbitals at the Li atom. The C1?S and C1?C2 conformations are determined by the stereoelectronic effects n_C–σ_SR* interaction and allylic conjugation. ¹H DNMR spectroscopy of racemic [EtCH?CHC(Et)SO₂tBu]Li, [iPrCH?CHC(iPr)SO₂tBu]Li and [EtCH?C(Me)C(Et)SO₂tBu]Li in [D₈]THF gave estimated barriers of enantiomerization of ΔG^≠=13.2 kcal mol^?1 (270 K), 14.2 kcal mol^?1 (291 K) and 14.2 kcal mol^?1 (295 K), respectively. Deprotonation of sulfone (R)‐EtCH?CHCH(Et)SO₂tBu (94 % ee) with nBuLi in THF at ?105 °C occurred with a calculated enantioselectivity of 93 % ee and gave carbanion (M)‐[EtCH?CHC(Et)SO₂tBu]Li, the deuteration and alkylation of which with CF₃CO₂D and MeOCH₂I, respectively, proceeded with high enantioselectivities. Time‐dependent deuteration of the enantioenriched carbanion (M)‐[EtCH?CHC(Et)SO₂tBu]Li in THF gave a racemization barrier of ΔG^≠=12.5 kcal mol^?1 (168 K), which translates to a calculated half‐time of racemization of t_1/2=12 min at ?105 °C.     

Origin of the color of π‐conjugated columnar polymers: Poly(p‐n‐octylthiophenyl)acetylene prepared using a [Rh(norbornadiene)Cl]2 catalyst

Highly stereospecific polymerization of a novel sulfur containing aromatic acetylenes, that is, (p‐n‐octylthiophenyl)acetylene (pOctSPA), was successfully performed using the Rh complex, [Rh(norbornadiene)Cl]₂‐TEA, catalyst in the presence of various solvents under mild conditions. The resulting polymers were characterized in detail by ¹H NMR, ESR, laser Raman, diffuse reflective UV‐Vis (DRUV‐Vis), and wide angle X‐ray diffraction methods. The data showed that the resulting polymers bear cis‐transoid form, which can induce the cis‐to‐trans isomerization when the cis polymers are subjected to pressure at room temperature under vacuum, breaking rotationally the cis C?C bonds in the main‐chain giving two kinds of π‐radicals, the so‐called cis radical and trans radical as the origin of a polymer magnet like a novel spin glass material. Further, the resulting cis poly(acetylene)s were found to have a helical main‐chain, which is packed in pseudohexagonal crystal called π‐conjugated columnar or nano π‐conjugated columnar as a novel color controllable material. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2836–2850, 2005     

Ruthenium‐Catalyzed Oxidative Coupling/Cyclization of Isoquinolones with Alkynes through C?H/N?H Activation: Mechanism Study and Synthesis of Dibenzo[a,g]quinolizin‐8‐one Derivatives

The mechanism of [{RuCl₂(p‐cymene)}₂]‐catalyzed oxidative annulations of isoquinolones with alkynes was investigated in detail. The first step is an acetate‐assisted C? H bond activation process to form cyclometalated compounds. Subsequent mono‐alkyne insertion of the Ru? C bonds of the cyclometalated compounds then takes place. Finally, oxidative coupling of the C? N bond of the insertion compounds occurs to afford Ru⁰ sandwich complexes that undergo oxidation to regenerate the catalytically active Ru^II complex with the copper oxidant and release the desired dibenzo[a,g]quinolizin‐8‐one derivatives. All of the relevant intermediates were fully characterized and determined by single crystal X‐ray diffraction analysis. The [{RuCl₂(p‐cymene)}₂]‐catalyzed C? H bond functionalization of isoquinolones with alkynes to synthesize dibenzo[a,g]quinolizin‐8‐one derivatives through C? H/N? H activation was also demonstrated.     

2‐Iodo‐N‐(3‐nitrobenzyl)aniline and 3‐iodo‐N‐(3‐nitrobenzyl)aniline exhibit entirely different patterns of supramolecular aggregation

In 2‐iodo‐N‐(3‐nitro­benzyl)­aniline, C₁₃H₁₁IN₂O₂, the mol­ecules are linked into a three‐dimensional structure by a combination of C—H?O hydrogen bonds, iodo–nitro interactions and aromatic π–π‐stacking interactions, but N—H?O and C—H?π(arene) hydrogen bonds are absent. In the isomeric 3‐iodo‐N‐(3‐nitro­benzyl)­aniline, a two‐dimensional array is generated by a combination of N—H?O, C—H?O and C—H?π(arene) hydrogen bonds, but iodo–nitro interactions and aromatic π–π‐stacking interactions are both absent.     

Highly Effective Ru/BaCeO3 Catalysts on Supports with Strong Basic Sites for Ammonia Synthesis

BaCeO₃‐a and BaCeO₃‐b, with strong basic sites, were synthesized by using a co‐precipitation method at different calcination temperatures, and used as supports to evaluate their performance in ammonia synthesis. The ammonia synthesis rate with the 1.25 % Ru/BaCeO₃‐a catalyst is 24 mmol g^?1 h^?1, which is higher than that of 1.25 % Ru/BaCeO₃‐b catalyst (18 mmol g^?1 h^?1) at 3 MPa and 450 °C. Moreover, the performance of the 4 % Cs‐1.25 % Ru/BaCeO₃‐a catalyst was further improved to 28 mmol g^?1 h^?1, and no sign of deactivation was observed after a reaction time of 120 h. The XPS and H₂ temperature‐programmed reduction analyses indicated that the Ru/BaCeO₃‐a catalyst has more oxygen vacancies than the Ru/BaCeO₃‐b catalyst. In addition, the average Ru particle size of the Ru/BaCeO₃‐a catalyst is closer to 2 nm than the Ru/BaCeO₃‐b catalyst, which promotes the generation of B₅‐type sites (the active site for N₂ dissociation). The CO₂ temperature‐programmed desorption analysis indicates that BaCeO₃‐a has a high basic density, which is beneficial for electron transfer to Ru and further facilitates the dissociation of N≡N bonds.     

手性Ru复合物催化剂的固载化及其不对称氢转移反应催化应用

Chiral Ru-BsDPEN, (1R,2R)-N-p-benzenesulfonyl-1,2-diphenylethylenediamine, catalyst has been immobilized on a mesoporous molecular sieve of MCM-41 type successfully. A hybrid mesoporous molecular sieve was synthesized using a precursor bearing benzene group, which in organosilica were sulfonylated and reacted with (1R,2R)-l,2-diphenylethylenediamine and [RuC1E(p-cymene)]2 successively to afford immobilized catalyst. The Brunauer-Emmett-Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size decreased after immobilization of catalyst onto the mesoporous material. Enantioselective transfer hydrogenation of ketones catalyzed by immobilized catalyst showed the highest yield of 22.36% and e.e. value of 31.47% by using acetophenone as substrate when reaction time was 48 and 16 h respectively.     

Ru‐Catalyzed Branched versus Linear Selective C3‐Alkylation of 2‐Aroylbenzofurans with Acrylates via CH Activation

The carbonyl‐directed C3?H activation and alkylation of 2‐aroylbenzo[b]furans with acrylates occurs selectively either in a linear or branched fashion, depending on the catalyst employed; [Ru(p‐cymene)Cl₂]₂ or Ru(PPh₃)₃Cl₂, respectively. Two alternate pathways—funded upon the differences in steric and electronic preferences of these two complexes—is proposed for the selectivity of linear versus branched products.     

Cadmium(II) Complexes with Mixed cis‐Epoxysuccinate and 2,2′‐Bipyridyl‐Like Ligands: Syntheses,Crystal Structures,and Luminescent Properties

Two new Cd^II complexes, [Cd( ces )(phen)]_∞ ( 1 ) and {[Cd( ces )(bpy)(H₂O)](H₂O)}₂ ( 2 ), were prepared by slow solvent evaporation methods from mixtures of cis‐epoxysuccinic acid and Cd(ClO₄)₂ · 6H₂O in the presence of phen or bpy co‐ligand ( ces = cis‐epoxysuccinate, phen = 1,10‐phenanthroline, and bpy = 2,2′‐bipyridine). Single‐crystal X‐ray diffraction analyses show that complex 1 has a one‐dimensional (1D) helical chain that is further assembled into a two‐dimensional (2D) sheet, and then an overall three‐dimensional (3D) network by the interchain C–H ··· O hydrogen bonds. Complex 2 features a dinuclear structure, which is further interlinked into a 3D supramolecular network by the co‐effects of intermolecular C–H ··· O and C–H ··· π hydrogen bonds as well as π ··· π stacking interactions. The structural differences between 1 and 2 are attributable to the intervention of different 2,2′‐bipyridyl‐like co‐ligands. Moreover, 1 and 2 exhibit intense solid‐state luminescence at room temperature, which mainly originates from the intraligand π→π* transitions of aromatic co‐ligands.