Organometallics最新文献

A wide range of gold-catalyzed reactions has continued to increase based on a dual activation mechanism. Herein, the diaurate-catalyzed synthesis mechanism of benzofulvenes through C(sp³)–H activation is thoroughly investigated by density functional theory (DFT). A few scenarios are highlighted, including the mode of catalyst transfer, the catalysis mechanism contrast between the Au center and two centers, and the manner of σ-gold coordinated diyne formation. Three mechanistic pathways were computed: (a) a dual-catalysis pathway of precatalyst (pathway a), (b) a single-catalysis pathway (pathway b), and (c) a dual-catalysis pathway including 9,8-H transfer (pathway c). As for the reasonable pathway a, NTf₂^– abstracts a proton from the π-gold complex, generating a σ-coordinated monogold complex. Subsequently, another catalyst coordinates, forming a σ,π-digold complex, which undergoes two consecutive cyclization steps to give non-gem-diaurated species. The reaction subsequently can proceed via three possible routes: (a₁) undergo π-system slippage to yield gem-c, which then undergoes gold transfer and protonation with a substrate to afford benzofulvenes; (a₂) intermolecular protodeauration to generate σ-monoaurated species, followed by protonation with HNTf₂; and (a₃) protonation by HNTf₂ occurs to generate π-monoaurated species, which undergoes intermolecular protodeauration to form benzofulvenes.

Ruthenium(II) polypyridyl complexes can be harnessed for photodynamic therapy. In this work, diprotic ligands which can be deprotonated to change the metal complexes from dicationic to neutral are combined with extended π systems for light absorption at longer wavelengths. Herein, the diprotic ligands are 4,4′-dhbp = 4,4′-dihydroxybipyridine or 4,7-dhphen = 4,7-dihydroxy-1,10-phenanthroline and the π-expanded ligands are bphen = bathophenanthroline, dppz = dipyrido[3,2-a:2′,3′-c]phenazine, and dppn = benzodipyrido[3,2-a:2′,3′-c]phenazine. This report describes the synthesis and characterization of [(bphen)₂Ru(4,4′-dhbp)]Cl₂ (1_A), [(dppz)₂Ru(4,4′-dhbp)]Cl₂ (2_A), [(dppn)₂Ru(4,4′-dhbp)]Cl₂ (3_A), [(bphen)₂Ru(4,7-dhphen)]Cl₂ (4_A), [(dppz)₂Ru(4,7-dhphen)]Cl₂ (5_A), and [(dppn)₂Ru(4,7-dhphen)]Cl₂ (6_A). Single crystal X-ray diffraction data are reported for 1_A, 2_A, and two known precursor compounds: [(η⁶-p-cymene)RuCl(diprotic ligand)]Cl (P1, P2 where diprotic ligand = 4,4′-dhbp and 4,7-dhphen, respectively). Compounds 1_A–6_A have been studied for their photocytotoxicity vs breast and melanoma cancer cells, lipophilic vs hydrophilic properties, thermodynamic acidities (pK_a values), singlet oxygen quantum yields, and luminescence which is heavily influenced by the nature of the π expanded ligand. Four compounds (bearing bphen and dppn ligands) have promising photocytotoxicity including activity with green light and one compound has a phototherapeutic index (PI) as high as 145.

Structural confirmation of an iodine(V) analogue of Weiss’s reagent, [ArI-O(Pyr)₂]²⁺, is reported using monodentate pyridine ligands and a nitro-substituted arene to provide protection from electrophilic aromatic substitution. The new complex is found to act as a source of electrophilic oxygen.

The naphthalen-1,8-diyl and dihydroacenaphthen-5,6-diyl platforms have been widely utilized as rigid aromatic scaffolds to support a myriad of p-block elements. This is especially true for boron, where several 1,8-diboryl naphthalene derivatives have been reported. Of the many diboryl compounds in the scientific literature, 1,8-bis(halo(aryl)boryl) and 5,6-bis(halo(aryl)boryl) naphthalenes and dihydroacenapthenes are unknown, which prompted the work described herein. Here, we report on the synthesis and full characterization, including multinuclear NMR spectroscopy and single-crystal X-ray diffraction, of 1,8-bis(chloro(mesityl)boryl)-naphthalene and 5,6-bis(chloro(mesityl)boryl)-1,2-dihydro-acenaphthene, compounds 1 and 2, respectively. We have also explored the chemistry of 1 and 2 with methylene triphenylphosphorane to afford two novel 1,1-diboryl phosphorus ylides, 3 and 4, which have also been fully characterized. The structure and bonding in these diboryl ylides were further interrogated using computational methods.

Imidazo[1,5-b]pyridazin-7-ylidene, which is composed of a carbene site and a proximate 2e-σ-donor N-heteroaromatic site, was developed as a rigid scaffold for constructing multinuclear metal complexes. Gold(I) chloride was introduced to the carbene site, giving an η¹-carbene-gold(I) complex containing a noncoordinated N-σ-donor site. The chloride ligand on the gold(I) complex was then abstracted by a cationic silver salt, enabling the N-σ-donor to coordinate to another cationic gold center and affording a tetranuclear gold(I) complex. SC-XRD analysis revealed that the tetranuclear gold complex had a bent square Au₄ core bearing gold(I)–gold(I) interactions. These interactions were further assessed using DFT calculations. The catalytic performance of the tetranuclear gold complexes was evaluated in four types of nucleophilic addition reactions to alkynes.

Multiple insertions of diphenylsilylene into the Si–O and Si–H bonds of Me₂PhSi–Y (Y = OMe or H) were achieved by a transition-metal-free diphenylsilylene (Ph₂Si:) transfer from Ph₂(Et₂N)Si–B(pin). This reaction proceeded at 135 °C in toluene, yielding up to seven diphenylsilylene-linked silicon chains.

Herein, we report the [5,5]-rearrangement of aryl sulfoxides with readily available α,β-unsaturated nitriles, furnishing γ-aryl α,β-unsaturated nitriles with excellent regioselectivity. This transformation proceeds under mild reaction conditions and exhibits high chemo- and regioselectivity, excellent functional-group compatibility, and a broad substrate scope. Notably, no ortho-cyanoalkylated products arising from competing [3,3]-rearrangements were detected. Interestingly, mechanistic investigations elucidate the crucial role of tropinone, which acts both as a Lewis base in its Mannich-type addition to the in situ-generated α,β-unsaturated sulfonium imine species and as a Bronsted base in promoting γ-deprotonation of LB-addition sulfonium imine species to form the rearrangement precursor.

Mixed carbene-phosphine complexes are known to be beneficial in many catalytic reactions. However, synergistic catalysis employing such complexes utilizing two metal centers, each possessing a combination of mesoionic carbene (MIC) and phosphine ligands, is very rare. This report describes the synthesis of the first dinuclear palladium(II) complex utilizing a combination of MIC and PCy₃ ligands, and the same has been characterized by using standard spectroscopic techniques. The aforementioned complex appeared to be an efficient precatalyst, working at a very low catalyst loading for the Suzuki–Miyaura coupling of aryl chlorides and copper-free intermolecular α-arylation reactions. In addition, the catalytic outcomes of the dinuclear MIC/PCy₃ complex are superior when compared to the catalytic outcomes of the corresponding mononuclear MIC/PCy₃ complex under identical reaction conditions, indicating potential metal–metal cooperativity during catalysis. The Pd•••Pd separation is crucial in synergistic catalysis, and the same in the dinuclear MIC/PCy₃ complex has been compared with the distances reported for dinuclear Pd^II–NHC complexes.

Reactions of three aryl-substituted bismuth cations, [BiPh₂(SbF₆)], [BiMes₂(SbF₆)], and [BiDipp₂(SbF₆)], with the Pt⁰ complex Pt(PCy₃)₂ have been investigated (Mes = 2,4,6-trimethyl-phenyl; Dipp = 2,6-di-iso-propyl-phenyl; Cy = cyclohexyl). Unexpectedly, and in contrast with the reactivity of the recently reported methyl analogue [BiMe₂(SbF₆)], the formation of isolable metal-only Lewis pairs [(Cy₃P)₂Pt→BiAr₂(SbF₆)] is not observed (Ar = aryl). Instead, an unprecedented bismuth-to-platinum oxidative aryl transfer is witnessed to give the Pt^II complexes [PtAr(PCy₃)₂(SbF₆)], along with the suggested bismuthinidene intermediates BiAr. Attempts to trap these fleeting intermediates with an ortho-quinone led to a Pt^II semiquinone radical complex.

Leishmaniasis, a neglected tropical disease, is an epidemic and a public health concern in at least 98 countries. The currently available treatments impose several limitations, including high toxicity, reduced activity, and drug resistance, demanding a quest for novel and effective therapeutics. Since silver and gold-NHC complexes generally display promising biological applications evading drug resistance, in this research work, we have reported the synthesis, structures, structural characterizations, and in vitro antileishmanial activities of a novel series of Ag(I), Au(I), and Au(III) complexes of quinoxaline-wingtip N-heterocyclic carbene (NHC) ligands. The proligands and metal complexes were synthesized and fully characterized by using different spectroscopic techniques and solid-state single-crystal XRD analysis. All the synthesized complexes are investigated for their in vitro antileishmanial potential against intracellular amastigotes of different Leishmania species. Surprisingly, only Au(I) and Au(III)-NHC complexes are effective and display promising antileishmanial activity with IC₅₀ values varying between 0.3 and 17.5 μM. Structure–activity and toxicity relationships demonstrate the dicationic Au(III)-NHC complex encompassing the phenanthroline ligand as the lead candidate, exhibiting both a high activity and an excellent selectivity index (SI = 157), especially against L. amazonenis. These findings highlight the promising potential of these compounds as alternative therapeutic candidates for the treatment of leishmaniases.