Organometallics最新文献

Thermodynamic hydricity $(\Delta {G^{°}}_{H^{-}})$ is the free energy for loss of hydride from a molecule such as a transition metal hydride or an organohydride. Knowledge of hydricity values for hydride donor and hydride acceptor molecules can be used to predict whether hydride transfer reactions are thermodynamically favorable. In this report, a fast and operationally simple approach to the measurement of hydricity values is demonstrated, using open-circuit potential measurements. The method employs only materials and reagents that are commonly available, such as Pt wire and H₂ gas. Low concentration of samples (0.5 to 2 mM) can be used, and a measurement can be completed in about 2 h. Results are presented for transition metal and organohydride molecules with hydricity values spanning a range of ∼20 kcal mol^–1, with $\Delta {G^{°}}_{H^{-}}$ from 59.3 ± 0.3 up to 74.8 ± 0.1 kcal mol^–1. An average error of 0.01 V based on replicate data collected was obtained, and this corresponds to an average uncertainty in hydricity of about 0.4 kcal mol^–1.

A series of (pro)ligands based on {PN(H)P} and {PN(H)P(O)} frameworks, as well as their MeO-aryl-functionalized analogues {PN(H)P^OMe} and di(thio)oxidized {P(O)N(H)P(O)^OMe} and {P(S)N(H)P(S)^OMe}, were synthesized in good yields, and their solution and solid-state structures were confirmed by multinuclear NMR spectroscopy (¹H, ³¹P{¹H}, ¹³C{¹H}) and X-ray diffraction. The coordination chemistry of these (pro)ligands with Ni(II), Ni(0), and Pd(II) precursors was explored. A range of different products was obtained in moderate to high yields and characterized in solution and in the solid state by using NMR spectroscopy and single-crystal X-ray diffraction. Regardless of the nature of the aryl substitution, the alkyl–Ni complexes exhibited remarkable instability in solution, undergoing rapid decomposition. Preliminary ethylene polymerization studies were conducted under homogeneous conditions using the prepared Ni and Pd complexes with selected activators, including MAO, Et₂AlCl, [Ph₃C]⁺[B(C₆F₅)₄]⁻, Na⁺[B(C₆F₅)₄]⁻, and [H(OEt₂)₂]⁺[NH₂{B(C₆F₅)₃}₂]⁻. DFT studies were undertaken to help decipher the oligo- and polymerization results obtained with the Ni-based systems.

1,2-Benzisothiazol-3(2H)-one (bitH) reacts with [Os₃(CO)₁₀(NCMe)₂] to afford triosmium [Os₃(CO)₁₀(μ-H)(μ-N,O-bit)] (1) and tetraosmium [{Os₂(CO)₅(μ-N,O-bit)}₂(μ₃-N,O,S-bit)₂] (2). Oxidative decarbonylation of 1 using Me₃NO gives the hexaosmium [Os₆(CO)₁₈(μ-H)₂(μ₃-N,O,S-bit)₂] (3). The benzisothiazolinate (bit) ligand displays two different coordination modes (μ-N,O and μ₃-N,O,S) at these polyosmium centers, and the μ₃-N,O,S coordination mode observed in 2 and 3 is unprecedented.

A new database predicted with theoretical chemistry of organometallic star-like compounds with a central planar carbon atom, named Star-Database, is presented. Planar star-like structures with D_3h, D_4h, and D_5h symmetries are considered, where the central carbon atom is three-, tetra-, or penta-coordinated in a single plane. Combinations of atoms ranging from hydrogen to bismuth (excluding noble gases, lanthanides, and actinides) were considered along with charges of +1, 0, and −1. The systems have been generated through a systematic geometric and energetic screening, employing a multistep optimization and filtering protocol based on density functional theory (DFT), DFT-D3, and Møller–Plesset (MP2 and MP4) methods. All the molecules in the Star-Database satisfy three geometrical criteria: (a) planarity, (b) star-like geometry (the peripheral atoms arranged symmetrically around the central carbon resembling a star), and (c) coordination. There are 40-D_3h, 19-D_4h, and 10-D_5h star-like planar molecules in the Star-Database. The elemental abundance with symmetry is analyzed. The most abundant elements in the first coordination sphere are metals (Pd, Pt), and in the second coordination are nonmetals (Se, I) > Te > H > F, Cl. The Star-Database provides atomic coordinates, HOMO–LUMO energy gaps and orbitals, and XY-NICS maps of aromaticity. Only 19 star-molecules are potentially aromatic.

In accordance with the constraints by Hückel’s and Baird’s rules, species generally exhibit aromaticity in one state (the lowest singlet state S₀ or the lowest triplet state T₁). Consequently, species with adaptive aromaticity (being aromatic in both the S₀ and T₁ states) are particularly rare. In this study, density functional theory (DFT) was employed to investigate adaptive aromaticity in 14e^–, 16e^– and 18e^– metallabenzenes. Based on bond length, fuzzy bond order (FBO), multicenter index (MCI), delocalized bond electron density (EDDB) analyses, magnetically induced current-density (MICD) analysis, and isomerization stabilization energy (ISE), 14e^– ruthenabenzenes are found to possess adaptive aromaticity. A reduction in the delocalization of the spins in the six-membered ring of metallabenzenes will facilitate the maintenance of their T₁ aromaticity. The ligand’s effect on adaptive aromaticity in 14e^– ruthenabenzenes was conducted by principal component analysis (PCA), one of the most commonly used unsupervised machine learning algorithms, which suggests that electron-deficient ligands are detrimental to adaptive aromaticity. A supervised machine learning method, multiple linear regression (MLR), was employed to develop a quantitative equation for predicting aromaticity in the T₁ state. This study demonstrates the first example of a metallabenzene with adaptive aromaticity, which is a valuable contribution to the field of aromatic chemistry.

The controlled sequential CO and isocyanide insertions into rhenium–carbon bonds, affording a series of novel acyl, iminoacyl, and carbene complexes, are described. The reaction of Re(III) alkyl and benzyl complexes with CO under mild conditions yields reversible Re–acyl intermediates. These species do not undergo further reaction with CO to yield α-dicarbonyl products. In contrast, the reaction of Re(III) alkyl and benzyl complexes with aryl isocyanides yields double isocyanide insertion products. Sequential exposure of acyl intermediates to CO and isocyanide results in the formation of rare mixed CO–CNR-inserted carbene complexes, as confirmed by multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and DFT (APFD) calculations. Computational studies reveal a clear energetic preference for isocyanide insertion into Re–acyl bonds over CO insertion into Re–iminoacyl bonds, rationalized by the greater nucleophilicity of the iminoacyl nitrogen relative to the acyl oxygen. These findings provide new mechanistic insights into heteroallene activation and demonstrate the cooperative reactivity of CO and isocyanide ligands in the construction of C–C and C–heteroatom bonds at rhenium centers.

While normally reluctant toward oxidation, SbBr₃ can be oxidized with 3,4,5,6-tetrachloro-1,2-benzoquinone (o-chloranil) in the presence of a Lewis base like the bromide anion or triphenylphosphine oxide (PPh₃O) to form the tetrachlorocatecholate (cat^Cl) derivatives [SbBr₄(cat^Cl)]⁻ ([2-Br]⁻) and SbBr₃(cat^Cl)•OPPh₃ (2•OPPh₃), respectively. Structural, spectroscopic, and computational data indicate that the SbBr₃(cat^Cl) fragment is similarly, if slightly less, Lewis acidic than the previously reported SbCl₃(cat^Cl) fragment. The SbBr₃/o-chloranil system, as well as its previously reported counterpart SbCl₃/o-chloranil, were tested as Lewis acid catalysts for C–O bond metathesis and polycarbonate depolymerization. These results identified SbX₃/o-chloranil pairs (X = Cl, Br) as simple main-group platforms for C–O bond cleavage chemistry.

Cr(CO)₆, Mo(CO)₆, W(CO)₆, and Fe(CO)₅ undergo an aza-Wittig reaction with triphenylphosphinazine [(Ph₃P)₂N₂]. These reactions address exclusively one CO ligand, yielding (isocyanoimino)triphenylphosphorane metal complexes [(CO)_xMCN₂(PPh₃)] (1: M = Cr, x = 5; 2: M = Mo, x = 5; 3: M = W, x = 5, 4: M = Fe, x = 4). We present selective CO ligand deoxygenation at a metal center by an aza-Wittig reagent in the broad context of metallaheterocumulene fragmentation for carbon atom transfer.

Alkene isomerization holds significant importance in organic chemistry and various chemical industries; however, achieving a high selectivity remains a major challenge. This comprehensive computational investigation delves into the mechanistic parameters governing alkene isomerization catalyzed by a modular Ni(0)/silane system. By systematically analyzing electronic and steric influences of both the substrate and catalyst, the study unveils critical insights into factors that modulate catalytic selectivity and productivity of the isomerized products. In particular, the [3,1]-hydrogen migration pathway in olefins is studied, with a focus on E/Z stereoselectivity. Overall, our findings elucidate the subtle interplay between catalyst design and substrate structure, offering potential design principles for the development of more efficient nickel-catalyzed alkene isomerization processes within synthetic and industrial contexts.

In this study, we present a facile synthetic methodology for the synthesis of 7-(2-biaryl)-substituted pyrazolo[1,5-a]pyridines directly from 7-arylpyrazolo[1,5-a]pyridines via palladium-mediated ortho-C–H activation/arylation. This transformation can be readily accomplished under both catalytic and stoichiometric conditions, facilitated by the intrinsic directing ability of the pyrazolo[1,5-a]pyridine scaffold. Through the stoichiometric reactions, key 7-phenylpyrazolo[1,5-a]pyridine-derived palladacycles bearing acetate or trifluoroacetate ligands were isolated and structurally characterized by X-ray crystallography. To gain mechanistic insight into the C–H bond cleavage step, both parallel and intermolecular kinetic isotope effect (KIE) studies were conducted, providing evidence in support of the proposed reaction pathway. Finally, the developed methodology enables the practical synthesis of 7,7′-bis(2-biaryl)-substituted 3,3′-bipyrazolo[1,5-a]pyridines via an intermolecular C–H/C–H cross-coupling reaction, affording a new class of aggregation-induced enhanced emission (AIEE)-active luminogens.