Organometallics最新文献

The reactions between 1,3-bis((diphenylphosphaneyl)methyl)imidazolidine L1 or 1,3-bis((di-tert-butylphosphaneyl)methyl)imidazolidine L2 and [PdCl₂(COD)], in the presence or absence of KPF₆ in CH₃CN, afforded complexes [(^PhPCP)PdCl]PF₆ 1, [(^tBuPCP)PdCl]Cl 2, and [(^tBuPCP)PdCl]PF₆ 3 in excellent isolated yields. Interestingly, the reaction between L2 and [PdCl₂(COD)] in CH₂Cl₂ yielded the unexpected noncarbene amine-nitrogen-coordinated complex [(^tBuPNP)PdCl] PF₆ 4. Complexes 1 and 3 react with PhSNa to give their thiolate complexes, [(^PhPCP)Pd(SPh)]PF₆ 5 and [(^tBuPCP)Pd(SPh)]PF₆ 6, in good yields. Complex 3 reacts with an excess amount of NaBH₄ in THF to give the hydride complex [(^tBuPCP)Pd(H)]PF₆, 7. Of these, the palladium thiolate and the previously reported analogous nickel thiolate complexes were found to be efficient catalysts for the hydroboration of CO₂ with 9-BBN to selectively give methoxyborane in excellent yields under mild conditions, compared to the corresponding halide and hydride complexes. Complex 6 and complex 8, [(^tBuPCP)Ni(SPh)]PF₆, exhibit TONs of over 25,000 and 7,000, respectively. A combined proposed mechanism, based on control experiments, shows that the thiolate complexes form reactive adducts, exhibit two pathways for MeOBBN formation, and hence outperform the hydride complexes.

The Rh-catalyzed conversion of olefins and arenes to alkenyl arenes using [(η²-C₂H₄)₂Rh(μ-OPiv)]₂ as the catalyst precursor and 12 ortho- and para-substituted benzoquinone derivatives as the in situ oxidant is reported. Included are comparative studies of the quinone derivatives for (1) rate of styrene production from benzene and ethylene, (2) Markovnikov to anti-Markovnikov selectivity for reactions of benzene and propylene, and (3) ortho/meta/para selectivity when using tert-butylbenzene as the arene. Cyclic voltammetry was utilized to measure reduction potentials for each quinone to determine any possible influence of the quinone redox potential on arene alkenylation rate and selectivity. While significant differences in selectivity are observed between ortho-quinone derivatives, such differences are minimal when para-substituted quinones are utilized. These results suggest that ortho-benzoquinone derivatives likely serve as bidentate ligands, which explains the stronger influence on catalyst activity of ortho-benzoquinone identity compared to para-benzoquinones. Although ortho-benzoquinones generally give styrene production rates faster than those of para-benzoquinones, 3,5-di-tert-butyl-ortho-benzoquinone and ortho-chloranil react with ethylene to form bicyclo[2.2.2]oct-5-ene-2,3-dione derivatives as a significant side product.

The present work studies the role half-salen cobalt-complexes in the oxa-6π electrocyclizations of O’Donnell’s Schiff bases. Based on chemical modulations of the electronic nature of half-salen cobalt complexes catalyzing the oxa-6π electrocyclization of Schiff bases to benzoxazines, a series of mechanistic investigations, including reaction rate measurements, deuterium-labeling studies, and linear-free energy relationships, reveal a fine-tuned mechanism consisting of three fundamental chemical steps. These chemical steps resembles the operating mechanism in the galactose oxidase enzyme.

Herein, three NNO-Ru complexes were synthesized and demonstrated to be efficient catalysts for the selective alkylation of indoles with various alcohols via the interrupted borrowing hydrogen (IBH) strategy. A diverse array of bisindolylmethane derivatives, including several structurally important compounds such as Turbomycin B, Arundone, and anticancer agents were achieved in good to excellent yields. The reactions were conducted in an atom- and step-economical manner under mild conditions, accommodating both primary and secondary alcohols.

Toward the development of earth-abundant catalysts for carbon dioxide (CO₂) reduction, we prepared nine new nickel CNC pincer complexes incorporating N-heterocyclic carbenes (NHCs) and a central pyridine ring. The wingtips were varied between long-chain olefin wingtips (1_R), a macrocyclic monounsaturated ring (2_R), and a macrocyclic saturated ring (3_R). The para-position on the pyridine was varied with R = H, Me, or OMe, giving nine combinations. Two crystal structures for 1_Me and 2_OMe are reported, thus confirming the geometry of the Ni(II) pincer. The catalytic activity of all nine nickel complexes was evaluated for CO₂ reduction in the presence of a photosensitizer, (Ir(ppy)₃) (ppy = 2-phenylpyridine), and formate was identified as the major product with CO as a minor product. The catalytic activity increased in the order R = OMe > Me > H, which reflects an electron donor group facilitating CO₂ reduction, and the saturated macrocyclic wingtip was optimal (maximum TON_HCO2– = 207 for 3_OMe at 24 h). Excited-state lifetimes for two compounds are reported using transient absorption spectroscopy (TAS), and these are related to the catalytic behavior. Overall, these catalysts are moderately active in the presence of a photosensitizer, but they are unable to perform self-sensitized catalysis.

We describe the synthesis and characterization of a Cu(I) complex, {Q₃Sb(o-chlor)}Cu(OTf) (Q = 8-quinolinyl; OTf = trifluoromethanesulfonate; o-chlor = o-choranil), supported by the Sb(V) ligand Q₃Sb(o-chlor). The complex {Q₃Sb(o-chlor)}Cu(OTf) was experimentally characterized via ¹H, ¹³C{¹H}, and ¹⁹F{¹H} NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) as well as examined computationally with density functional theory (DFT) calculations. Variable temperature ¹H NMR spectroscopy (20 to −110 °C) indicates temperature-dependent fluxional processes for {Q₃Sb(o-chlor)}Cu(OTf) and uncoordinated Q₃Sb(o-chlor). The electron density of Cu for {Q₃Sb(o-chlor)}Cu(OTf) was probed by comparing Cu^II/Cu^I redox potential and Cu 2p electron binding energies, using XPS, with a related non-Sb-containing complex, (TMQA)Cu(OTf) (TMQA = tris(quinolin-2-ylmethyl)amine). The E_1/2 of the Cu^II/Cu^I redox of {Q₃Sb(o-chlor)}Cu(OTf) is shifted 670 mV more positive than that of (TMQA)Cu(OTf). XPS spectra of {Q₃Sb(o-chlor)}Cu(OTf) and (TMQA)Cu(OTf) indicate a 0.8 eV higher Cu 2p binding energy for {Q₃Sb(o-chlor)}Cu(OTf). Computational studies of the molecular orbitals and localized natural bonding orbitals (NBOs) are consistent with a weak Cu(I) → Sb(V) interaction for {Q₃Sb(o-chlor)}Cu(OTf), for which Sb(V) acts as a Z-type ligand.

Although a Ru(II)-containing complex exhibits a good catalytic performance in the asymmetric reductive amination of levulinic acid (LA) to chiral 5-methyl-2-pyrrolidone (MPD), the underlying reaction mechanism remains unclear. For the asymmetric reductive amination of LA to MPD catalyzed by [LRu(PL)Cl]Cl (L= (R)-2,2′-bis(diphenylphosphanyl)-1,1′-binaphthalene, PL = p-cymol) with H₂ as the H-source and NH₄OAc as the N-source in a trifluoroethanol (TFE) solution, the catalytic mechanism has been studied at the M06/def2-TZVP, 6–311++G (d,p) theoretical level. Upon dissociation in the TFE solution with NH₄OAc, the [LRu(PL)Cl]Cl compound can form a stable complex LRu(OAc)₂ as the initial catalytically active species. The conversion of LA to MPD catalyzed by LRu(OAc)₂ is kinetically predominant through the reductive amination of the ketonic carbonyl (–C═O) group of LA. The rate-determining step is associated with C═N bond formation for ring-closure, and the chirality-controlling step is concerned with C═H bond formation for hydrogenation. In protic solvents, the higher catalytic activity of LRu(OAc)₂ is associated with a lower solvent dielectric constant. The above theoretical results are in good agreement with the experimental findings reported. The current research should provide some theoretical clues for designing novel catalysts for the asymmetric reductive amination of ketone carbonyl-containing compounds to a chiral product.

Low-valent germanium compounds, such as germylenes, can undergo a variety of activation reactions, but the development of related catalytic processes is hindered by a challenging reductive elimination step. A possible way to overcome this obstacle is element-ligand cooperativity (ELC), which allows generation of reactive species without an oxidation state change at the element center. Here, we report the reactivity of the bicyclic germanide K[(tmim)Ge] (tmimH₃ = tris(3-methylindol-2-yl)methane) with a phenolic O–H bonds which, instead of formal oxidative addition, undergoes a reversible O–H addition reaction coupled with cage opening to generate a Ge(II) phenoxide via element-ligand cooperativity.

A synthetic method was developed that provides access to free phenylene-bridged di-N-heterocyclic carbenes with sterically unencumbered substituents. Two free dicarbenes, p-phenylene-bridged 1a and m-phenylene-bridged 1b, were synthesized and isolated up to 86% yield. Free dicarbene 1a was synthesized and found to be highly crystalline, making it isolable in high purity and yield. Additionally, p-phenylene free dicarbene 1a was structurally characterized by SC-XRD. These free dicarbenes were used to synthesize neutral metal complexes in the absence of halogens, silver salts, or anionic counterions. A Mo bimetallic complex 3 was synthesized in 94% yield without oxidation of the metal center and was isolated and characterized spectroscopically. Using the m-phenylene free dicarbene 1b, the synthesis of (^nBuCⁱCⁱC^nBu) Zr trisamido complexes was improved from previous reports to obtain Zr pincer complex 4 in high purity. The free dicarbene method required only stoichiometric Zr(NMe₂)₄ and eliminated the halogens from the reaction mixture and the formation of complexes with mixed coordination spheres (monoamido and diamido).

The Suzuki–Miyaura cross-coupling reaction is widely used in organic synthesis. However, its reactivity and selectivity remain unsatisfactory for some functionalized substrates, and the synthetic efficiency for many functional molecules urgently needs improvement. Developing palladium catalysts compatible with this reaction to address these challenges and expand its practical applications holds significant research value. This paper reports a divalent palladacycle complex catalyst based on the cyclopropane monophosphine ligand TPhos and systematically investigates its application in the Suzuki–Miyaura cross-coupling reaction. Studies show that this catalyst exhibits exceptionally high reactivity, with a maximum turnover number (TON) of up to 192,000, along with excellent functional group tolerance. Notably, for substrates containing reactive functional groups such as alkenyl, alkynyl, and aldehyde groups, it effectively suppresses competitive side reactions such as Heck coupling, Sonogashira coupling, and disproportionation, thereby yielding the desired cross-coupled products with high chemoselectivity. Furthermore, the catalytic system developed herein was successfully applied to the gram-scale synthesis of various pharmaceutical intermediates, demonstrating a substantial reduction in catalyst loading compared with literature reports.