Chain-Selective and Regioselective Ethylene and Styrene Dimerization Reactions Catalyzed by a Well-Defined Cationic Ruthenium-Hydride Complex: New Insights on the Styrene Dimerization Mechanism

The cationic ruthenium hydride complex [(η6-C6H6)(PCy3)(CO)RuH]+BF4− was found to be a highly regioselective catalyst for the ethylene dimerization reaction to give 2-butene products (TOF = 1910 h−1, \u3e95% selectivity for 2-butenes). The dimerization of styrene exclusively produced the head-to-tail dimer (E)-PhCH(CH3)CH═CHPh at an initial turnover rate of 2300 h−1. A rapid and extensive H/D exchange between the vinyl hydrogens of styrene-d8 and 4-methoxystyrene was observed within 10 min without forming the dimer products at room temperature. The inverse deuterium isotope effect of kH/kD = 0.77 ± 0.10 was measured from the first-order plots on the dimerization reaction of styrene and styrene-d8 in chlorobenzene at 70 °C. The pronounced carbon isotope effect on both vinyl carbons of styrene as measured by using Singleton’s method (13C(recovered)/13C(virgin) at C1 = 1.096 and C2 = 1.042) indicates that the C−C bond formation is the rate-limiting step for the dimerization reaction. The Eyring plot of the dimerization of styrene in the temperature range of 50−90 °C led to ΔH⧧ = 3.3(6) kcal/mol and ΔS⧧ = −35.5(7) eu. An electrophilic addition mechanism has been proposed for the dimerization of styrene

Regioselective Intermolecular Coupling Reaction of Arylketones and Alkenes Involving C-H Bond Activation Catalyzed by an \u3cem\u3ein Situ\u3c/em\u3e Formed Cationic Ruthenium-Hydride Complex

The cationic ruthenium hydride complex, formed in situ from the treatment of the tetranuclear ruthenium hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} with HBF4·OEt2, was found to be a highly effective catalyst for the intermolecular coupling reaction of arylketones and 1-alkenes to give the substituted indene and ortho-C−H insertion products. The formation of the indene products resulted from the initial alkene isomerization followed by regioselective ortho-C−H insertion of 2-alkene and dehydrative cyclization. The preliminary mechanistic studies revealed a rapid and reversible ortho-C−H bond activation followed by the rate-limiting C−C bond formation step for the coupling reaction

Efficient Dehydrogenation of Amines and Carbonyl Compounds Catalyzed by a Tetranuclear Ruthenium-μ-oxo-μ-hydroxo-hydride Complex

The tetranuclear ruthenium-μ-oxo-μ-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was found to be a highly effective catalyst for the transfer dehydrogenation of amines and carbonyl compounds. For example, the initial turnover rate of the dehydrogenation of 2-methylindoline was measured to be 1.9 s−1 with a TON of 7950 after 1 h at 200 °C. The extensive H/D scrambling patterns observed from the dehydrogenation reaction of indoline-N-d1 and indoline-α-d2 suggest a monohydride mechanistic pathway with the C−H bond activation rate-limiting step

Aqueous Phase C-H Bond Oxidation Reaction of Arylalkanes Catalyzed by a Water-Soluble Cationic Ru(III) Complex [(pymox-Me\u3csub\u3e2\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3eRuCl\u3csub\u3e2\u3c/sub\u3e]\u3csup\u3e+\u3c/sup\u3eBF\u3csub\u3e4\u3c/sub\u3e\u3csup\u3e-\u3c/sup\u3e

The cationic complex [(pymox-Me2)RuCl2]+BF4− was found to be a highly effective catalyst for the C−H bond oxidation reaction of arylalkanes in water. For example, the treatment of ethylbenzene (1.0 mmol) with t-BuOOH (3.0 mmol) and 1.0 mol % of the Ru catalyst in water (3 mL) cleanly produced PhCOCH3 at room temperature. Both a large kinetic isotope effect (kH/kD = 14) and a relatively large Hammett value (ρ = −1.1) suggest a solvent-caged oxygen rebounding mechanism via a Ru(IV)-oxo intermediate species

Intermolecular Dehydrative Coupling Reaction of Arylketones with Cyclic Alkenes Catalyzed by a Well-Defined Cationic Ruthenium-Hydride Complex: A Novel Ketone Olefination Method via Vinyl C–H Bond Activation

The cationic ruthenium−hydride complex [(η6-C6H6)(PCy3)(CO)RuH]+BF4− was found to be a highly effective catalyst for the intermolecular olefination reaction of aryl ketones with cycloalkenes. The preliminary mechanistic analysis revealed that an electrophilic ruthenium−vinyl complex is the key species for mediating both vinyl C−H bond activation and the dehydrative olefination steps of the coupling reaction

Reactivity of acyclic (pentadienyl)iron(1+) cations: Synthetic studies directed toward the frondosins

A short, 4-step route to the scaffold of frondosin A and B is reported. The [1-methoxycarbonyl-5-(2′,5′-dimethoxyphenyl)pentadienyl]Fe(CO)3+ cation was prepared in two steps from (methyl 6-oxo-2,4-hexadienoate)Fe(CO)3. Reaction of this cation with isopropenyl Grignard or cyclohexenyllithium reagents affords (2-alkenyl-5-aryl-1-methoxycarbonyl-3-pentene-1,5-diyl)Fe(CO)3 along with other addition products. Oxidative decomplexation of these (pentenediyl)iron complexes, utilizing CuCl2, affords 6-aryl-3-methoxycarbonyl-1,4-cycloheptadienes via the presumed intermediacy of a cis-divinylcyclopropane

Reactivity of Acyclic (pentadienyl)iron(1+) Cations with Phosphonate Stabilized Nucleophiles: Application to the Synthesis of Oxygenated Metabolites of Carvone

The addition of phosphonate stabilized carbon nucleophiles to acyclic (pentadienyl)iron(1+) cations proceeds predominantly at an internal carbon to afford (pentenediyl)iron complexes. Those complexes bearing an electron withdrawing group at the σ-bound carbon (i.e., 13/14) are stable and isolable, while complexes which do not contain an electron withdrawing group at the σ-bound carbon undergo CO insertion, reductive elimination and conjugation of the double bond to afford cyclohexenone products (21/22). Deprotonation of the phosphonate 13/14 or 21 and reaction with paraformaldehyde affords the olefinated products. This methodology was utilized to prepare oxygenated carvone metabolites (±)-25 and (±)-26

Putative spin liquid in the triangle-based iridate Ba3_3IrTi2_2O9_9

We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$, which constitutes a new frustration motif made up a mixture of edge- and corner-sharing triangles. In spite of strong antiferromagnetic exchange interaction of the order of 100~K, we find no hint for long-range magnetic order down to 23 mK. The magnetic specific heat data unveil the $T$-linear and -squared dependences at low temperatures below 1~K. At the respective temperatures, the zero-field muon spin relaxation features a persistent spin dynamics, indicative of unconventional low-energy excitations. A comparison to the $4d$ isostructural compound Ba$_3$RuTi$_2$O$_9$ suggests that a concerted interplay of compass-like magnetic interactions and frustrated geometry promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte

Inhibition of REV-ERBs stimulates microglial amyloid-beta clearance and reduces amyloid plaque deposition in the 5XFAD mouse model of Alzheimer\u27s disease

A promising new therapeutic target for the treatment of Alzheimer\u27s disease (AD) is the circadian system. Although patients with AD are known to have abnormal circadian rhythms and suffer sleep disturbances, the role of the molecular clock in regulating amyloid-beta (Aβ) pathology is still poorly understood. Here, we explored how the circadian repressors REV-ERBα and β affected Aβ clearance in mouse microglia. We discovered that, at Circadian time 4 (CT4), microglia expressed higher levels of the master clock protein BMAL1 and more rapidly phagocytosed fibrillary A

Charge-spin correlation in van der Waals antiferromagenet NiPS3

Strong charge-spin coupling is found in a layered transition-metal trichalcogenide NiPS3, a van derWaals antiferromagnet, from our study of the electronic structure using several experimental and theoretical tools: spectroscopic ellipsometry, x-ray absorption and photoemission spectroscopy, and density-functional calculations. NiPS3 displays an anomalous shift in the optical spectral weight at the magnetic ordering temperature, reflecting a strong coupling between the electronic and magnetic structures. X-ray absorption, photoemission and optical spectra support a self-doped ground state in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide magnets are a useful candidate for the study of correlated-electron physics in two-dimensional magnetic material.Comment: 6 pages, 3 figur