Organometallics最新文献

Using density functional theory (B3LYP-D3(BJ)/def2-TZVP), we explored the origin of the reaction barriers and reactivity for the elimination of one sulfur atom from propylene sulfide by methylene-linked geminal intramolecular G13/G15-based (G13 = group 13 element and G15 = group 15 element) frustrated Lewis pair (FLP) molecules. In contrast to the traditional understanding validated by previous theoretical examinations, our B3LYP computational results demonstrate that the elimination reactions with intramolecular geminal FLP-type molecules in this study proceed through multiple steps rather than a one-step concerted process. Our B3LYP computations reveal that during the multistep process the second transition state, G13/G15-TS2, serves as the rate-determining step, featuring a nucleophilic attack by the Lewis base at the G15 center on the least hindered sulfur atom of propylene sulfide, leading to the release of a propylene molecule. Based on our theoretical investigations using the activation strain model, the activation barrier of the essential second transition step is primarily determined by the structural deformation energy of the intramolecular geminal G13/G15-type FLP fragment, characterized by its flexible linear bent structure, as opposed to the rigid structure of the propylene sulfide fragment.

Palladium-mediated site-selective C–H bond activations of 9(10H)-acridinone, resulting in the formation of 4- and 1-arylated 9(10H)-acridinones, are presented through the use of both stoichiometric and catalytic experiments. In the stoichiometric reactions, two distinct classes of acridinone palladacycles are generated via C (4)–H and C (1)–H bond activations, with the pyridine and ketone groups serving as the directing group, respectively. The constitutional conformation and thermal stability of these palladacycles were elucidated through both X-ray crystallography and NMR spectroscopy. Additionally, an investigation was conducted into the interconversion of C (4 and 1)–H bond-activated palladacycles in trifluoroacetic acid and acetic acid. During the course of C (1)–H bond arylation, a serendipitous discovery led to the isolation of a chromeno [4,3,2-kl] acridinone compound as a byproduct, showcasing good fluorescence properties. Controlled experiments, kinetic isotope effect study, key palladacycles, and the formation of corresponding products support the proposed mechanisms for these presented reactions. Finally, the pyridinyl group can serve as a removable directing group and can be readily eliminated from both 4- and 1-arylated 9(10H)-acridinones.

Synthesis of Ru(III)-aNHC complexes 1a’ and 1b’ has been achieved in the aqueous acid medium at ambient temperature. The abnormal binding mode of NHC through this method was undoubtedly confirmed by the synthesis of Ru(III)-aNHC complex 2a’ from the C(2)-methylated ligand precursor. The conversion of abnormal to normal NHC complexes (1a and 1b) was observed in the reaction medium. A pyridine-rollover mechanism for the conversion of abnormal to normal NHC has been proposed and validated by suitable substitution at the ligand backbone. Complexes 3a (Ru-nNHC) and 3a’ (Ru-aNHC) were prepared with the bidentate ligand precursor having a Me-substituted pyridine to prohibit the “pyridine-rollover” pathway. The conversion of abnormal NHC complex 3a’ to the normal NHC complex 3a was found to be suppressed in aqueous solutions at room temperature as the λ_max for 3a’ remained the same even after 15 days, suggesting the role of C(3)-H of pyridine in the process. An investigation of this synthetic protocol in various aqueous acid/salt solutions indicates that Cl^– ions are required to form the complexes, indicating a halide-assisted C–H activation pathway. All complexes have been characterized using various spectroscopic techniques. The molecular structures of complexes 1a’, 1b, 2a’, and 3a have been determined using the single-crystal X-ray diffraction technique.

A Ni-catalyzed, ZnCl₂-assisted domino coupling of enones and alkyne-tethered vinylcyclopropanes (VCPs) was developed. The reaction proceeds through the following steps: (1) oxidative cyclization of a Ni(0) complex with an enone and the alkyne component of the alkyne-tethered VCP in the presence of ZnCl₂, (2) carbonickelation of the VCP moiety, (3) β-C elimination leading to C–C bond cleavage of the cyclopropane moiety, and (4) β-H elimination to stereoselectively obtain (E)-1,3-diene as the coupling product. The optimal reaction conditions and scope of enones and alkyne-tethered VCPs were systematically explored. The reaction mechanism was investigated by performing deuterium-labeling experiments and density functional theory (DFT) calculations on the model compounds. The results clarify that the β-C elimination process occurs readily, and the Ni(0) precatalyst is regenerated via the 1,4-addition of H–Ni(II) species, generated by β-H elimination, to an excess of enone, followed by Zn reduction of the formed 1,4-adduct.

A multiscale computational approach was used to investigate the interaction, adsorption, and diffusion of three anticancer drugs, 5-fluorouracil (5-FU), busulfan (BU), and cisplatin (CIS), within the pores of a 2D flexible Zn-based MOF (Zn(BTTB)-MOF) functionalized with –NH₂, –NO₂, −OH, and -SH groups. The DFT analysis results indicated that adding functional groups to the H₃BTTB organic linker created additional binding sites, resulting in stronger interactions between the drugs and the modified structures by 17.5% for NO₂–Zn(BTTB)-MOF···5-FU to 115% for OH-Zn(BTTB)-MOF···BU in binding energies. Our grand canonical Monte Carlo (GCMC) studies revealed that both functionalized and pristine structures exhibited a high drug-loading capacity, increasing to ∼13, 15, and 24% for CIS, 5-FU, and BU, respectively. Molecular dynamics (MD) simulations indicated a decrease in the dynamics of the modified structures as a function of simulation time, with calculated diffusion coefficients ranging from (0.78–15.4) × 10^–12 m²·s^–1, consistent with previous findings in drug release. The study highlights the significance of adding functional groups to the Zn(BTTB)-MOF organic linker, as it significantly enhances the binding energy of anticancer drugs. Functionalized Zn(BTTB)-MOF enhances drug interactions due to additional binding sites, increasing drug-loading capacity and resulting in slower drug diffusion, making it more effective for anticancer drug delivery.

Herein, we synthesized water-soluble ruthenium complexes [(η⁶-p-cymene)Ru(κ²-L)]⁺ ([C-1]–[C-5]) ligated with substituted bis-imidazole methane-based ligands (L1–L5) and the molecular structures of the representative complexes [C-2] and [C-4] were established by single-crystal X-ray diffraction. We screened the synthesized complexes for the catalytic dehydrogenation of formic acid (FA) in water, where substitution on the bis-imidazole methane ligands was found to exert a significant impact on the catalytic activity of the complexes. The results inferred that, among the screened catalysts, [C-5] outperformed others with an initial turnover frequency (TOF) of 1831 h^–1 at 90 °C. One of the most notable features of [C-5] was its exceptional long-term stability, as it maintained efficient H₂ production from FA for 35 catalytic runs and remained active even after 60 days without any significant deactivation, reaching a turnover number (TON) of 35,000. Furthermore, reaction kinetics and the influence of various reaction parameters are thoroughly examined; comprehensive mass and NMR investigations under both catalytic and control conditions are conducted, and theoretical studies are performed to gain more insights into the reaction pathway of FA dehydrogenation over the studied catalysts.

The performance of six ruthenium catalysts and two iron catalysts were evaluated toward the acceptorless dehydrogenation of benzylamine. All catalysts shared the common structure [M(Cp/Cp*)(P^R₂N^R’₂)(MeCN)]PF₆ (M = Fe, Ru; Cp = cyclopentadienyl; Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; P^R₂N^R’₂ = 1,5-R′-3,7-R-1,5-diaza-3,7-diphosphacyclooctane) in which the P^R₂N^R’₂ ligands contain a pendant tertiary amine that enables cooperative catalytic mechanisms. Catalytic activity and selectivity were evaluated to identify the optimal catalyst structural features. The iron catalyst [Fe(Cp)(P^Ph₂N^Ph₂)(MeCN)]PF₆ demonstrated near-exclusive selectivity for the acceptorless dehydrogenative coupled product, N-benzylidenebenzylamine. The absence of the hydrogen-borrowed (dibenzylamine) product indicates that this iron catalyst strongly favors dehydrogenation pathways over hydrogenation. This was confirmed through the control reactions. The performance of [Fe(Cp)(P^Ph₂N^Ph₂)(MeCN)]PF₆ was optimized, but the catalyst was ineffective toward a broader scope of substrates.

Our interest in the design of ambiphilic ligands and their coordination to gold has led us to synthesize an indazol-3-ylidene gold chloride complex functionalized at the 4-position of the indazole backbone by a stibine functionality. The antimony center of this new complex cleanly reacts with o-chloranil to afford the corresponding stiborane derivative. Structural analysis indicates that the stiborane coordination environment is best described as a distorted square pyramid whose open face is oriented toward the gold center, allowing for the formation of a long donor–acceptor, or pnictogen, Au → Sb bonding interaction. The presence of this interaction, which has been probed computationally, is also manifested in the enhanced catalytic activity of this complex in the cyclization of N-propargyl-4-fluorobenzamide.

Our interest in the design of ambiphilic ligands and their coordination to gold has led us to synthesize an indazol-3-ylidene gold chloride complex functionalized at the 4-position of the indazole backbone by a stibine functionality. The antimony center of this new complex cleanly reacts with o-chloranil to afford the corresponding stiborane derivative. Structural analysis indicates that the stiborane coordination environment is best described as a distorted square pyramid whose open face is oriented toward the gold center, allowing for the formation of a long donor-acceptor, or pnictogen, Au → Sb bonding interaction. The presence of this interaction, which has been probed computationally, is also manifested in the enhanced catalytic activity of this complex in the cyclization of N-propargyl-4-fluorobenzamide.

Development of hydrogen energy carriers is crucial for society. Reversible (de)hydrogenation using carbon-based materials, particularly formic acid (FA), has been widely studied. Typically produced under basic conditions through CO₂ hydrogenation, formate salt is an energetically favorable form, but its dehydrogenation is challenging. This study found an equilibrium between formic acid dehydrogenation (FADH) and CO₂ hydrogenation under high-pressure conditions, facilitated organic solvent suppression of dehydrogenation, and accelerated hydride formation on an Ir catalyst. These conditions allow for the direct production of FA from CO₂ and H₂ in nonbasic 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) using a pentamethylcyclopentadienyl iridium (Cp*Ir) catalyst featuring a 4,4′-diamino-2,2′-bipyridine ligand (4DABP). Under mild conditions (50 °C, 1 MPa; CO₂:H₂ ratio = 1:1), the catalyst achieved a turnover number (TON) of 2084 in 2 h. The use of supercritical CO₂ further increased the TON to 6100, producing a 0.12 M FA solution after 96 h. This study presents a novel method for the direct production of formic acid from CO₂ and H₂, indicating new possibilities in the development of hydrogen energy carriers.