Osmaindenes: Synthesis and Reversible Mechanochromism Characteristics

A series of novel osmaindenes 1 - 6 bearing different substituents (CF 3 , H, I, Br, OCH 3 , N(Ph) 2 ) has been synthesized by nucleophilic reaction of water with the corresponding aromatic osmanaphthalyne complexes. All osmaindenes 1 - 6 have been characterized by elemental analysis (EA) and nuclear magnetic resonance (NMR) spectroscopy, although the low solubilities of 3 and 4 precluded the accumulation of their 13 C NMR spectra. Osmaindenes 2 , 3 and 5 have also been characterized by single-crystal X-ray diffraction analysis. Subsequently, through solid-state fluorescence spectroscopy, mechanochromic studies, and powder X-ray diffraction (XRD) analysis, we found that osmaindenes 1 - 6 fluoresce at wavelengths in the range 500-800 nm, while also displaying reversible mechanochromic properties. The solid-state fluorescence emission of 1 after grinding extends into the near-infrared region. This research provides new insight into the design and synthesis of metallic materials with excellent mechanochromic properties.

Nucleophilic Reactions of Osmanaphthalynes with PMe3 and H2 O

Members of a new class of complexes, 2(CF₃ ), 2(H), 2(Br), 2(I), and 2(OCH₃ ), have been synthesized in a one-pot method involving the treatment of osmanaphthalynes bearing corresponding substituents (1(CF₃ ), 1(H), 1(Br), 1(I), and 1(OCH₃ )) with trimethylphosphine (PMe₃ ) and water. The main reaction process involves two steps, namely a ligand-exchange with trimethylphosphine and nucleophilic addition of water to the Os≡C bond of the osmanaphthalyne. The substituents have a significant influence on the rate of the reaction, as befits a nucleophilic addition. Fortunately, the key intermediate [1(OCH₃ )]' could be successfully captured, and the detailed reaction mechanism has been explored with the aid of density functional theory (DFT) calculations, which were in excellent agreement with the experimental findings. All of the target complexes have been fully characterized by ¹ H, ³¹ P{¹ H}, and ¹³ C{¹ H} NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis.

Extension of the Simmons-Smith reaction to metal-carbynes: efficient synthesis of metallacyclopropenes with σ-aromaticity

The Simmons-Smith reaction offers a direct route for conversion of an alkene into a cyclopropane with a zinc carbenoid as the active intermediate. Zinc carbenoids, however, have never delivered a methylene unit to substrates with metal-carbon multiple bonds. Herein, we describe this type of reaction and the construction of three-membered rings has now been applied in organometallic systems by combining classical zinc carbenoid reagents with a range of structurally and electronically diverse metal carbynes. A variety of metallacyclopropene derivatives prepared in this way represent rare examples with σ-aromaticity in an unsaturated three-membered ring. The structures of such products are supported by experimental observations and theoretical calculations.

Synthesis and Characterization of Cyclopropaosmanaphthalenes Containing a Fused σ-Aromatic Metallacyclopropene Unit

Metalla-aromatics are important complexes that show unique properties owing to their highly conjugated systems, which show Hückel or Möbius aromaticity. Recently, several metalla-aromatics showing spiro-aromaticity or σ-aromaticity have been reported. Herein, we report the isolation of the first cyclopropametallanaphthalenes, in which the metallacyclopropene ring shows σ-aromaticity and weak hyperconjugative aromaticity. The reaction of OsCl₂ (PPh₃ )₃ with o-ethynylphenyl alkynes in the presence of PPh₃ followed by protonation with HCl yielded the first cyclopropametallanaphthalenes. The reaction mechanism and the aromaticity were also investigated by density functional theory studies.

Access to Metal-Bridged Osmathiazine Derivatives by a Formal [4+2] Cyclization

Treatment of osmacyclopentadiene derivatives 1 with phenyl or isopropyl isothiocyanate gave the fused five and six-membered osmacycles 2-5 by a formal [4+2] cyclization. The facile protonation of the newly generated exocyclic imine in complexes 2-5 afforded conjugation-extended osmacycle derivatives 6-9. Compounds 2-9 each contain two main-group heteroatoms (N and S) in the fused six-membered ring located at the ortho (for S) and para (for N) positions relative to the osmium centre; these species can be regarded as rare osma-1,3-thiazine derivatives and represent the first fused metallathiazine derivatives. In contrast to the non-planar organic 6H-1,3-thiazine, nearly coplanar metallathiazines 8 and 9 can be achieved by tuning the groups on the two nitrogen atoms. These unique metal-bridged osma-1,3-thiazine derivatives exhibit remarkable stabilities, broad spectral absorptions spanning the visible spectra, and considerable photothermal properties, which suggests their potential applications in material science.

Activatable probes for diagnosing and positioning liver injury and metastatic tumors by multispectral optoacoustic tomography

Optoacoustic tomography (photoacoustic tomography) is an emerging imaging technology displaying great potential for medical diagnosis and preclinical research. Rationally designing activatable optoacoustic probes capable of diagnosing diseases and locating their foci can bring into full play the role of optoacoustic tomography (OAT) as a promising noninvasive imaging modality. Here we report two xanthene-based optoacoustic probes (C1X-OR1 and C2X-OR2) for temporospatial imaging of hepatic alkaline phosphatase (or β-galactosidase) for evaluating and locating drug-induced liver injury (or metastatic tumor). The probes rapidly respond to the disease-specific biomarkers by displaying red-shifted NIR absorption bands and generate prominent optoacoustic signals. Using multispectral optoacoustic tomography (MSOT), we can precisely localize the focus of drug-induced liver injury in mice using C1X-OR1, and the metastatic tumors using C2X-OR2. This work suggests that the activatable optoacoustic chromophores may potentially be applied for diagnosing and localizing disease foci, especially smaller and deeper ones.

Black-Phosphorus-Incorporated Hydrogel as a Sprayable and Biodegradable Photothermal Platform for Postsurgical Treatment of Cancer

Photothermal therapy (PTT) is a fledgling therapeutic strategy for cancer treatment with minimal invasiveness but clinical adoption has been stifled by concerns such as insufficient biodegradability of the PTT agents and lack of an efficient delivery system. Here, black phosphorus (BP) nanosheets are incorporated with a thermosensitive hydrogel [poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PDLLA-PEG-PDLLA: PLEL)] to produce a new PTT system for postoperative treatment of cancer. The BP@PLEL hydrogel exhibits excellent near infrared (NIR) photothermal performance and a rapid NIR-induced sol-gel transition as well as good biodegradability and biocompatibility in vitro and in vivo. Based on these merits, an in vivo PTT postoperative treatment strategy is established. Under NIR irradiation, the sprayed BP@PLEL hydrogel enables rapid gelation forming a gelled membrane on wounds and offers high PTT efficacy to eliminate residual tumor tissues after tumor removal surgery. Furthermore, the good photothermal antibacterial performance prevents infection and this efficient and biodegradable PTT system is very promising in postoperative treatment of cancer.

Recent Advances in Metallaaromatic Chemistry

Metallaaromatics can be broadly defined as aromatic compounds in which one of the ring atoms is a transition metal. The metallabenzenes are one important class of these compounds that has undergone extensive study recently. Closely related species such as fused-ring metallabenzenes, heterometallabenzenes, π-coordinated metallabenzenes and metallabenzynes have also attracted considerable attention. Although many metallaaromatics can be considered as metalla-analogues of classic organic aromatic compounds, this is not always the case. Recent seminal studies have shown that metallapentalenes and metallapentalynes, which are metalla-analogues of the anti-aromatic compounds pentalene and pentalyne, are in fact aromatic and highly stable. Very unusual spiro-metallaaromatic compounds have also recently been isolated. In this concepts article, key features of all these intriguing metallaaromatic compounds are discussed with reference to the structural, spectroscopic, reactivity and theoretical studies that have been undertaken. These compounds continue to generate much interest, not only because of the contributions they make to fundamental chemical understanding, but also because of the promise of possible practical applications.

Syntheses of Amino-Substituted Iridabenzofurans and Subsequent Selective N-Functionalisation

The first examples of amino-substituted fused-ring metallabenzenes, the cationic iridabenzofuran [Ir(C₇ H₄ O{NH₂ -2}{OMe-7})(CO)(PPh₃ )₂ ][O₃ SCF₃ ] (5) and neutral analogue Ir(C₇ H₄ {NH₂ -2}{OMe-7})Cl(PPh₃ )₂ (6), can be prepared by reduction of the corresponding nitro-substituted iridabenzofurans with zinc and concentrated hydrochloric acid. N-functionalised derivatives of 5 and 6 are formed through alkylation, sulfonylation or acylation. Thus, consecutive treatments with methyl triflate and base gives the corresponding trimethylammonium-substituted iridabenzofurans while sulfonamide derivatives are formed with p-toluenesulfonyl chloride. N-Acylation of 5 or 6 with acid chlorides, however, selectively form either amide or imide products depending on the charge on the metal and the steric size of the acid chloride. Cationic 5 gives amide substituted products regardless of the conditions whereas neutral 6 rapidly undergoes di-N-acylation with excess benzoyl chloride under mild conditions to give the imide-substituted product Ir(C₇ H₄ O{N[C(O)Ph]₂ -2}{OMe-7})Cl(PPh₃ )₂ (13). Selective mono-acylation of 6 can be achieved with one equivalent of benzoyl chloride or with excess of the sterically congested pivaloyl chloride.

In Vivo Imaging-Guided Photothermal/Photoacoustic Synergistic Therapy with Bioorthogonal Metabolic Glycoengineering-Activated Tumor Targeting Nanoparticles

Developing multifunctional phototheranostics with nanoplatforms offers promising potential for effective eradication of malignant solid tumors. In this study, we develop a multifunctional phototheranostic by combining photothermal therapy (PTT) and photoacoustic therapy (PAT) based on a tumor-targeting nanoagent (DBCO-ZnPc-LP). The nanoagent DBCO-ZnPc-LP was facilely prepared by self-assembling of a single lipophilic near-infrared (NIR) dye zinc(II)-phthalocyanine (ZnPc) with a lipid-poly(ethylene glycol) (LP) and following modified further with dibenzyl cyclootyne (DBCO) for introducing the two-step chemical tumor-targeting strategy based on metabolic glycoengineering and click chemistry. The as-prepared DBCO-ZnPc-LP could not only convert NIR light into heat for effective thermal ablation but also induce a thermal-enhanced ultrasound shockwave boost to trigger substantially localized mechanical damage, achieving synergistic antitumor effect both in vitro and in vivo. Moreover, DBCO-ZnPc-LP can be efficiently delivered into tumor cells and solid tumors after being injected intravenously via the two-step tumor-targeting strategy. By integrating the targeting strategy, photoacoustic imaging, and the synergistic interaction between PTT and PAT, a solid tumor could be accurately positioned and thoroughly eradicated in vivo. Therefore, this multifunctional phototheranostic is believed to play an important role in future oncotherapy by the enhanced synergistic effect of PTT and PAT under the guidance of photoacoustic imaging.

Biodegradable black phosphorus-based nanospheres for in vivo photothermal cancer therapy

Photothermal therapy (PTT) offers many advantages such as high efficiency and minimal invasiveness, but clinical adoption of PTT nanoagents have been stifled by unresolved concerns such as the biodegradability as well as long-term toxicity. Herein, poly (lactic-co-glycolic acid) (PLGA) loaded with black phosphorus quantum dots (BPQDs) is processed by an emulsion method to produce biodegradable BPQDs/PLGA nanospheres. The hydrophobic PLGA not only isolates the interior BPQDs from oxygen and water to enhance the photothermal stability, but also control the degradation rate of the BPQDs. The in vitro and in vivo experiments demonstrate that the BPQDs/PLGA nanospheres have inappreciable toxicity and good biocompatibility, and possess excellent PTT efficiency and tumour targeting ability as evidenced by highly efficient tumour ablation under near infrared (NIR) laser illumination. These BP-based nanospheres combine biodegradability and biocompatibility with high PTT efficiency, thus promising high clinical potential.

Synthesis of aromatic ruthenabenzothiophenes via C–H activation of thiophenes

The first ruthenabenzothiophenes have been achievedviathe C–H activation of thiophene.

Triplet State Aromaticity: NICS Criterion, Hyperconjugation, and Charge Effects

Aromaticity, one of the most important concepts in organic chemistry, has attracted considerable interest from both experimentalists and theoreticians. It remains unclear which NICS index is best to evaluate the triplet-state aromaticity. Here, we carry out thorough density functional theory (DFT) calculations to examine this issue. Our results indicate that among the various computationally available NICS indices, NICS(1)zz is the best for the triplet state. The correlations can be improved from 0.840 to 0.938 when only neutral species are considered, demonstrating the significant effect of the charge on the triplet-state aromaticity. In addition, calculations suggest that five-membered cyclic species with "hyperconjugative" aromaticity (and antiaromaticity) in the S0 state will become antiaromatic (and aromatic) in the T1 state, indicating an important role of hyperconjugation. Finally, a moderate correlation (r(2) =0.708) is identified between the NICS(1)zz values and spin distributions.

The Clar Structure in Inorganic BN Analogues of Polybenzenoid Hydrocarbons: Does it Exist or Not?

The Clar structure of polybenzenoid hydrocarbons (PBHs) have attracted considerable interest of both theoretical and experimental chemists since it was proposed in the 1950s. However, it remains unclear whether the Clar structure could exist in inorganic PBHs, the boron nitride (BN) analogues where the alternate boron and nitrogen atoms are used to replace the carbon atoms of PBHs. Here, we carry out thorough density functional theory (DFT) calculations to probe the possibility of Clar structures in BN analogues of PBHs. A strong correlation (r(2) =0.975) between the ring number (n=3-10) of BN analogues of [n]acenes and energy differences between the most and least stable isomers is identified, suggesting the existence of Clar structures in inorganic PBHs. In addition, the slightly weaker correlations in comparison to that (r(2) =0.989) of the organic PBHs is rationalized by the reduced aromaticity, which is revealed by two aromatic indices: ELFπ and SCI.

Mechanisms of large Stokes shift and aggregation-enhanced emission of osmapentalyne cations in solution: combined MD simulations and QM/MM calculations

The large Stokes shift and aggregation-enhanced emission of OCs are caused by the photoexcitation-induced chromophore's symmetrical variation and molecular aggregation in solutions, respectively.