Organometallics最新文献

First-row transition metal catalysis continues to provide innovative and sustainable advances for synthetic chemistry. However, these metals can be challenging to screen efficiently in optimization campaigns due to the limited knowledge of catalyst assembly, stability, and speciation. In this report we demonstrate the use of thermogravimetric analysis (TGA) as a promising tool in evaluating the formation and properties of an Fe precatalyst, fac-Fe(dpa)Cl₃. Using TGA it was possible to identify the generation of distinct Fe complexes that could form in situ from prestirring the commercial metal salt iron trichloride (FeCl₃) and di(2-picolyl)amine (dpa) in different organic solvents. Upon applying these prestirred mixtures to the reaction between methionine and benzyl acrylate, it was determined that distinct complexes gave distinct TGA profiles. Similar TGA profiles yielded similar reaction yields, while distinct TGA profiles tended to give rise to unique yields. Utilizing this approach, a more informed first-row metal catalyzed reaction strategy can be realized.

The synthesis of a lithium disilenide and its reaction with CO are described. Reaction of NHB-substituted dilithiodisilene NHB(Li)Si═Si(Li)NHB (1, NHB = diazaborolyl) with Me₃SiCl resulted in the formation of the lithium disilenide NHB(Me₃Si)Si═Si(Li)NHB (2). Disilenide 2 reacts with 1 atm. of CO, leading to the C–C coupling of two molecules of CO with the formation of a disilacyclobutenone dimer bridged by two lithium ions, which are coordinated to the three exocyclic oxygen atoms.

Xanthene-derived ligands, such as Xantphos, and related scaffolds are pivotal in contemporary organometallic chemistry, delivering wide-bite-angle diphosphines and frustrated Lewis pairs (FLPs) with applications in catalysis and main-group reactivity. 4,5-Dibromo-9,9-dimethyl-9H-xanthene serves as a common gateway intermediate for perisubstitution, yet literature reports on its synthesis are inconsistent. In our hands, direct bromination of 9,9-dimethylxanthene afforded exclusively the 2,7-dibromo regioisomer in 72% yield, as confirmed by single-crystal X-ray diffraction. A modified literature procedure employing an ortho-lithiation protocol with n-BuLi/TMEDA followed by bromination yielded the desired 4,5-dibrominated product in 65% on gram scale. This work resolves ambiguities in prior reports, providing a reliable, reproducible protocol to facilitate access to xanthene-based frameworks.

Two novel half-sandwich organometallic complexes, [(p-cymene)M(XY)Cl], XY = L-BSO, M = Ru^II (Ru-LBSO), Os^II (Os-LBSO), containing the amino acid L-buthionine sulfoximine (L-BSO), as well as their XY = glycine analogs (Ru-Gly and Os-Gly), have been synthesized, characterized and their solution chemistry investigated. L-BSO is an inhibitor of the enzyme γ-glutamyl cysteine synthetase and, hence, glutathione synthesis. The diastereomers of Ru-LBSO and Os-LBSO were also characterized by DFT calculations which suggested the higher stability of [S_M,r_S] and [S_M,s_S] compared to [R_M,r_S] and [R_M,s_S] configurations [chirality at M(II), chirality at sulfur of L-BSO]. Interestingly, glycine complexes are non-toxic toward both cancer and normal cells, whereas Os-LBSO was cytotoxic toward human IGROV-1 ovarian cancer cells, but not toward lung and cervical cancer cells. Os-LBSO, but not Ru-LBSO, demonstrated glutathione inhibition. These studies on Ru-LBSO and Os-LBSO complexes demonstrate the challenges of making progress toward the development for clinical use of organometallic complexes that contain multiple chiral centers. However, they offer exciting possibilities for discovery of novel drugs with new mechanisms of action.

A Sc(II) pentamethylcyclopentadienyl (Cp*) complex such as “Cp*₂Sc” has not been isolable, although the Sc(II) metallocenes, Cp^ttt₂Sc (Cp^ttt = C₅H₃^tBu₃) and (C₅Me₄SiMe₂^tBu)₂Sc can be crystallographically characterized and Cp^ttt₂Sc forms the Sc(II) CO and CNR adducts Cp^ttt₂Sc(CO) and Cp^ttt₂Sc(CNXyl) (Xyl = C₆H₃-2,6-Me₂). However, the dark-teal Sc(II) metallocene Cp*₂Sc(CNXyl)₂ can be isolated from the Sc(III) reduced dinitrogen complex (Cp*₂Sc)₂(μ-η¹:η¹-N₂) through its reaction with 2 equiv of CNXyl. Density functional theory analysis based on the X-ray crystal structure is used to evaluate the electronic structure of this complex, which allows its isolation, and the low 36.3 MHz (13.0 G) hyperfine coupling in the eight-line EPR spectrum of Cp*₂Sc(CNXyl)₂.

The synthesis of a new Cp*Co(III) complex bearing a bis-carbene ligand (1,1′-dimethyl-4,4′-bi-1,2,4-triazol-5,5′-ylidene, bitz) is reported. The synthetic approach utilizes a Co(I) precursor and a bis-triazolium salt without the need for a base or an external oxidant. The electrochemical properties of the complex have been studied.

This paper reports on a synthetic approach to 1,2-disubstituted carboxonium derivatives [1,2-B₁₂H₁₀O₂CR]⁻ that combines acylation and (diacetoxyiodo)benzene-promoted cyclization reactions. The formation pathway of the carboxonium ring fused to the closo-dodecaborate was examined using DFT calculation and it was found that the reaction includes two main transition states corresponding to the deprotonation-iodination of the cluster and intramolecular cyclization. It was established that the nature of the R-substituent significantly affects the stability of the carboxonium ring to opening processes initiated by water and alcohols. It was also demonstrated that, depending on the nucleophilicity of the reagent, both mixed derivatives with hydroxy and acyloxy groups and dihydroxy derivatives can be obtained.

We report the synthesis and characterization of a new p-dimethylamino-substituted thiapyridinophane ligand (^pNMe2NCHS2) and its palladium complexes. The electron-rich dimethylamino groups engender the palladium compounds with several unusual properties compared to the parent unsubstituted NCHS2 ligand. A facile room-temperature C(sp²)–H activation of the ^pNMe2NCHS2 ligand was observed, which is facilitated by the p-dimethylamino group acting as an internal base. NMR spectroscopic and mechanistic studies were conducted to gain insight into the possible mechanism of the C–H activation process.

The reduction of carbon dioxide mediated by N-phosphinoamidinato silylenes was described. The reaction of an N-phosphinoamidinato chlorosilylene 1 with CO₂ afforded carbon monoxide and a dioxo-bridged siloxane 2. Compound 1 was then reduced with KC₈ to form base-stabilized disilyne 5, where the interconnected silylene centers reduce CO₂ to form CO and carbonate(dioxo)-bridged siloxane derivative 6. In the CO₂ reduction, the N-phosphinoamidinate ligand interchanges between N,N′- and N,P-chelate, showing the hemilabile character depending on the oxidation state of the silicon center.

The use of pyrylium and related catalysts for sp³ C–O bond reduction is reported. Studies on a cationic, divalent Ge complex ([Cp*Ge⁺][B(C₆F₅)₄^–]) used for deoxygenation reactions reveal that O₂ is required for the oxidation of the complex into an active pyrylium catalyst. Reactivity screens show pyrylium, flavylium, and xanthylium catalysts are active, leading to a diverse, bench-stable, and highly tunable catalyst library.