Manganese Carbonyl Research Articles

Synthesis and structure of rhenium and manganese carbonyl complexes bearing a thiosaccharinate ligand

The reactions of [M2(CO)8(NCMe)2] (M = Re, Mn) with thiosaccharin (tsacH) have been investigated. TsacH reacts with [Re2(CO)8(NCMe)2] at room temperature to furnish [Re2(CO)8(μ‐H)(μ‐sac‐κN,S)] (1) and [Re(CO)5(sac‐κS)] (2), while a similar reaction with [Mn2(CO)8(NCMe)2] affords only [Mn(CO)5(sac‐κS)] (3). The dinuclear 1 contains a bridging tsac ligand coordinated to both rhenium centers using the nitrogen and thiocarbonylic sulfur atoms, while the tsac ligand is bonded to the metal center only through the sulfur atom in mononuclear 2 and 3. The molecular structures of 1‐3 have also been determined by X‐ray crystallography.

Microenvironment-Activatable Probe for Precise NIR-II Monitoring and Synergistic Immunotherapy in Rheumatoid Arthritis.

Rheumatoid arthritis (RA) represents an insidious autoimmune inflammatory disorder that severely lowers the life quality by progressively destructing joint functions and eventually causing permanent disability, posing a serious public health problem. Here, an advanced theranostic probe is introduced that integrates activatable second near-infrared (NIR-II) fluorescence imaging for precise RA diagnosis with multi-pronged RA treatments. A novel molecular probe comprising a long-wavelength aggregation-induced emission unit and a manganese carbonyl cage motif is synthesized, which enables NIR-II fluorescence activation and concurrently releasing therapeutic carbon monoxide (CO) gas in inflamed joint microenvironment. This molecular probe self-assembles into a biocompatible nanoprobe, which is subsequently conjugated with anti-IL-6R antibody to afford active-targeting ability of RA. The nanoprobe exhibits significant turn-on NIR-II fluorescence signal at the RA lesion, enabling highly sensitive RA diagnosis and real-time therapeutic monitoring. The combination of ROS scavenging, on-demand CO gas release, and IL-6 signaling blockade results in potent therapeutic effect and synergistic immunomodulation impact, significantly alleviating the RA symptoms and preventing joint destruction. This research introduces a novel paradigm for the development of high-performance, activatable theranostic strategies to facilitate precise detection and enhanced treatment of RA-related diseases.

Group 7 carbonyl complexes of a PNN-heteroscorpionate ligand.

A series of rhenium and manganese carbonyl complexes of a heteroscorpionate ligand with an atypical N2P-donor set has been prepared to better understand their electronic and CO releasing properties. Thus, the ligand, pz2TTP, with an a,a-bis(pyrazol-1-yl)tolyl group decorated with an ortho-situated di(p-tolyl)phosphanyl reacts with carbonyl group 17 reagents to give [fac-(κ2NP-pz2TTP)Re(CO)3Br], 1, and [fac-(κ3N2P-pz2TTP)M(CO)3](OTf = O3SCF3), 2-M (M = Re, Mn), if care is taken during the preparation of the manganeses derivative. When heated in CH3CN, 2-Mn slowly transforms to [fac,cis-(κ3N2P-pz2TTP)Mn(CO)2(NCCH3)](OTf), 3-Mn. In contrast, the corresponding 3-Re can only be prepared from 2-Re using Me3NO; pure 3-Mn can also be prepared by this method. Experimental and density functional calculations at the M06L/Def2-TZVP/PCM(CH3CN) level show that the replacement of a carbonyl with an acetonitrile solvent decreases the oxidation potential by around 0.8 V per carbonyl released, making decarbonylated species potent reductants. At the same time, the electronic spectrum broadens and undergoes a red-shift, making dicarbonyl complexes more susceptible to photo-initiated decarbonylation reactions than tricarbonyls. When 2-Mn or 3-Mn are irradiated in with 390 nm LED light in aerated solutions, [trans-Mn(pz2TTP = O)2](OTf)2, 4, along with insoluble manganese oxides are rapidly formed.

Influence of the Bis-Carbene Ligand on Manganese Catalysts for CO2 Electroreduction.

First row transition metal complexes have attracted attention as abundant and affordable electrocatalysts for CO2 reduction. Manganese complexes bearing bis-N-heterocyclic carbene ligands defining 6-membered ring metallacycles have proven to reduce CO2 to CO selectively at very high rates. Herein, we report the synthesis of manganese carbonyl complexes supported by a rigid ortho-phenylene bridged bis-N-heterocyclic carbene ligand (ortho-phenylene-bis(N-methylimidazol-2-ylidene), Ph-bis-mim), which defines a 7-membered ring metallacycle. We performed a comparative study with the analogues complexes bearing an ethylene-bis(N-methylimidazol-2-ylidene) ligand (C2H4-bis-mim) and a methylene-bis(N-methylimidazol-2-ylidene) ligand (CH2-bis-mim), and found that catalysts comprising a seven-membered metallacycle retain similar selectivity and activity as those with six-membered metallacycles, while reducing the overpotential by 120-190 mV. Our findings reveal general design principles for manganese bis-N-heterocyclic carbene electrocatalysts, which can guide further designs of affordable, fast and low overpotential catalysts for CO2 electroreduction.

Cascade Reactions Catalyzed by Gold Hybrid Nanoparticles Generate CO Gas Against Periodontitis in Diabetes.

The treatment ofdiabetic periodontitis poses a significant challenge due to the presence of local inflammation characterized by excessive glucose concentration, bacterial infection, and high oxidative stress. Herein, mesoporous silica nanoparticles (MSN) are embellished with gold nanoparticles (Au NPs) and loaded with manganese carbonyl to prepare a carbon monoxide (CO) enhanced multienzyme cooperative hybrid nanoplatform (MSN-Au@CO). The Glucose-like oxidase activity of Au NPs catalyzes the oxidation of glucose to hydrogen peroxide (H2O2) and gluconic acid，and then converts H2O2 to hydroxyl radicals (•OH) by peroxidase-like activity to destroy bacteria. Moreover, CO production in response to H2O2, together with Au NPs exhibited a synergistic anti-inflammatory effect in macrophages challenged by lipopolysaccharides. The underlying mechanism can be the induction of nuclear factor erythroid 2-related factor 2 to reduce reactive oxygen species, and inhibition of nuclear factor kappa-B signaling to diminish inflammatory response. Importantly, the antibacterial and anti-inflammation effects of MSN-Au@CO are validated in diabetic rats with ligature-induced periodontitis by showing decreased periodontal bone loss with good biocompatibility. To summarize, MSN-Au@CO is fabricate to utilize glucose-activated cascade reaction to eliminate bacteria, and synergize with gas therapy to regulate the immune microenvironment, offering a potential direction for the treatment of diabetic periodontitis.

Development of Manganese Carbonyl Loaded Upconversion Nanoparticles for Near‐Infrared‐Triggered Carbon Monoxide and Mn2+ Delivery

Photoactivatable carbon monoxide‐releasing molecules (CORMs), typically based on transition‐metal carbonyl complexes, have reliance on activation by UV or visible light that restricts their biomedical applications. To address this limitation, a near‐infrared (NIR)‐responsive nanoplatform is presented based on upconversion nanoparticles (UCNPs) loading with manganese carbonyl complex Mn2(CO)10 that concurrently releases CO and manganese ion (Mn2+). With the UCNPs, the more tissue‐penetrable NIR is used to locally generate UV light for photodecomposition of Mn2(CO)10 into CO and manganese oxide (MnOX), after which MnOX is reduced to Mn2+ by the overexpressed glutathione in cancer cells. Moreover, the released Mn2+ can serve as a magnetic resonance imaging contrast agent to monitor the NIR‐controlled corelease of CO and Mn2+ in real time. Therefore, this nanoplatform can provide a potential strategy for NIR‐enabled spatiotemporally release of CO and Mn2+, enhancing the controlled delivery and biomedical application of CORMs.

Unveiling Mechanistic Complexity in Manganese-Catalyzed C-H Bond Functionalization Using IR Spectroscopy Over 16 Orders of Magnitude in Time.

ConspectusAn understanding of the mechanistic processes that underpin reactions catalyzed by 3d transition metals is vital for their development as potential replacements for scarce platinum group metals. However, this is a significant challenge because of the tendency of 3d metals to undergo mechanistically diverse pathways when compared with their heavier congeners, often as a consequence of one-electron transfer reactions and/or intrinsically weaker metal-ligand bonds. We have developed and implemented a new methodology to illuminate the pathways that underpin C-H bond functionalization pathways in reactions catalyzed by Mn-carbonyl compounds. By integrating measurements performed on catalytic reactions with in situ reaction monitoring and state-of-the-art ultrafast spectroscopic methods, unique insight into the mode of action and fate of the catalyst have been obtained.Using a combination of time-resolved spectroscopy and in situ low-temperature NMR studies, we have shown that photolysis of manganese-carbonyl precatalysts results in rapid (<5 ps) CO dissociation─the same process that occurs under thermal catalytic conditions. This enabled the detection of the key states relevant to catalysis, including solvent and alkyne complexes and their resulting transformation into manganacycles, which results from a migratory insertion reaction into the Mn-C bond. By systematic variation of the substrates (many of which are real-world structurally diverse substrates and not simple benchmark systems) and quantification of the resulting rate constants for the insertion step, a universal model for this migratory insertion process has been developed. The time-resolved spectroscopic method gave insight into fundamental mechanistic pathways underpinning other aspects of modern synthetic chemistry. The most notable was the first direct experimental observation of the concerted metalation deprotonation (CMD) mechanism through which carboxylate groups are able to mediate C-H bond activation at a metal center. This step underpins a host of important synthetic applications. This study demonstrated how the time-resolved multiple probe spectroscopy (TRMPS) method enables the observation of mechanistic process occurring on time scales from several picoseconds through to μs in a single experiment, thereby allowing the sequential observation of solvation, ligand substitution, migratory insertion, and ultimate protonation of a Mn-C bond.These studies have been complemented by an investigation of the "in reaction flask" catalyst behavior, which has provided additional insight into new pathways for precatalyst activation, including evidence that alkyne C-H bond activation may occur before heterocycle activation. Crucial insight into the fate of the catalyst species showed that excess water played a key role in deactivation to give higher-order hydroxyl-bridged manganese carbonyl clusters, which were independently found to be inactive. Traditional in situ IR and NMR spectroscopic analysis on the second time scale bridges the gap to the analysis of real catalytic reaction systems. As a whole, this work has provided unprecedented insight into the processes underpinning manganese-catalyzed reactions spanning 16 orders of magnitude in time.

Acid‐Unlocked Switch Controlled the Enzyme and CO In Situ Release to Induce Mitochondrial Damage via Synergy

AbstractCO gas therapy has attracted enormous attention in tumor therapy due to the abilities of mitochondrial damage and inhibition of cellular respiration. However, the inefficient and random release of CO greatly limit its application. Taking this into account, the study constructs an acid‐unlocked nanostructure based on MPDA‐MnCO‐GOx@DSNPs, designated as MMGD. The nanostructure enables tumor microenvironment (TME) specific enzyme and CO prodrug (manganese carbonyl, MnCO) cascade reaction, thus facilitating CO release in situ. Mesoporous polydopamine (MPDA) can provide the space for MnCO and glucose oxidase (GOx) loading. Especially, lanthanide (Ln3+)‐doped down‐shifting luminescent nanoparticles (DSNPs) can not only serve as the near‐infrared II (NIR‐II) fluorescence imaging probe, but also act as the acid‐unlocked gating switch. The slightly acidic TME can render the dissociation of DSNPs, thus exposing GOx and releasing MnCO. The catalytic reaction of GOx can produce H2O2 and create a more acidic environment, which facilitates the CO generation in situ, leading to mitochondrial damage by reducing cytochrome c oxidase activity and adenosine triphosphate (ATP) levels. Meanwhile, MPDA has the NIR light absorption capability for photothermal therapy (PTT). This study provides an ingenious strategy for efficient and controllable CO gas, starvation, and PTT of tumor guided by NIR‐II fluorescence imaging.

Syntheses, paramagnetism, and semiconducting characteristics of polynuclear manganese carbonyl chalcogenide anions: A review

Syntheses, paramagnetism, and semiconducting characteristics of polynuclear manganese carbonyl chalcogenide anions: A review

H2O2-triggered CO release based on porphyrinic covalent organic polymers for photodynamic/gas synergistic therapy.

A novel H2O2-responsive carbon monoxide nanogenerator was designed by effectively encapsulating a manganese carbonyl prodrug into porphyrinic covalent organic polymers for realizing the combined CO gas and photodynamic therapy under near infrared light irradiation.

Dual-Modality Imaging-Guided Manganese-Based Nanotransformer for Enhanced Gas-Photothermal Therapy Combined Immunotherapeutic Strategy Against Triple-Negative Breast Cancer.

Activating the stimulator of the interferon gene (STING) is a promising immunotherapeutic strategy for converting "cold" tumor microenvironment into "hot" one to achieve better immunotherapy for malignant tumors. Herein, a manganese-based nanotransformer is presented, consisting of manganese carbonyl and cyanine dye, for MRI/NIR-II dual-modality imaging-guided multifunctional carbon monoxide (CO) gas treatment and photothermal therapy, along with triggering cGAS-STING immune pathway against triple-negative breast cancer. This nanosystem is able to transfer its amorphous morphology into a crystallographic-like formation in response to the tumor microenvironment, achieved by breaking metal-carbon bonds and forming coordination bonds, which enhances the sensitivity of magnetic resonance imaging. Moreover, the generated CO and photothermal effect under irradiation of this nanotransformer induce immunogenic death of tumor cells and release damage-associated molecular patterns. Simultaneously, the Mn acts as an immunoactivator, potentially stimulating the cGAS-STING pathway to augment adaptive immunity, resulting in promoting the secretion of type I interferon, the proliferation of cytotoxic T lymphocytes and M2-macrophages repolarization. This nanosystem-based gas-photothermal treatment and immunoactivating therapy synergistic effect exhibit excellent antitumor efficacy both in vitro and in vivo, reducing the risk of triple-negative breast cancer recurrence and metastasis; thus, this strategy presents great potential as multifunctional immunotherapeutic agents for cancer treatment.

Activated Mn-MACHO Complexes Form Stable CO2 Adducts.

Manganese(I) carbonyl complexes bearing a MACHO-type ligand (HN(CH2 CH2 PR2 )2 ) readily react in their amido form with CO2 to generate 4-membered {Mn-N-C-O} metallacycles. The stability of the adducts decreases with the steric demand of the R groups at phosphorous (R=isopropyl>adamantyl). The CO2 -adducts display generally a lower reactivity as compared to the parent amido complexes. These adducts can thus be interpretated as masked forms of the active amido catalysts and potentially play important roles as off-loop species or branching points in catalytic transformations of carbon dioxide.

Synthesis, Characterization, and Reactivity of a (PPP) Pincer-Ligated Manganese Carbonyl Complex: Polarity Reversal Imparted by the Electrophilic Nature of a Planar Mn-P(NR2)2 Fragment.

The bonding interactions of a synthesized pincer-ligated manganese dicarbonyl complex featuring an N-heterocyclic phosphenium (NHP+) central moiety are explored. The pincer ligand [PPP]Cl was coordinated to a manganese center using Mn(CO)5Br and 254 nm light to afford the chlorophosphine complex (PPClP)Mn(CO)2Br (2) as a mixture of halide exchange products and stereoisomers. The target dicarbonyl species (PPP)Mn(CO)2 (3) was prepared by treatment of 2 with 2 equiv of the reductant KC8. Computational investigations and analysis of structural parameters were used to elucidate multiple bonding interactions between the Mn center and the PNHP atom in 3. The generation of a product of formal H2 addition, (PPHP)Mn(CO)2H (4), was achieved through the dehydrogenation of NH3BH3, affording a 2:1 mixture of 4syn:4anti stereoisomers. The nucleophilic nature of the Mn center and the electrophilic nature of the PNHP moiety were demonstrated through hydride addition and protonation of 3 to produce K(THF)2[(PPHP)Mn(CO)2] (6) and (PPClP)Mn(CO)2H (5), respectively. The observed reactivity suggests that 3 is best described as a Mn-I/NHP+ complex, in contrast to pincer-ligated dicarbonyl manganese analogues typically assigned as MnI species.

The chemistry of rhenium and manganese carbonyl complexes bearing heterocyclic thiolate ligands: Mono‒, di‒, tri‒, and tetranuclear complexes

The chemistry of rhenium and manganese carbonyl complexes bearing heterocyclic thiolate ligands: Mono‒, di‒, tri‒, and tetranuclear complexes

NNN Pincer-Manganese-Catalyzed Guerbet-Type β-Alkylation of Alcohols under Microwave Irradiation

A series of manganese carbonyl complexes based on bis(imino)pyridine ligands of the type R2NNN (R = Cy, iPr, Ph, p-FC6H4) were synthesized. While the complex appears to be an NN bidentate-Mn(I) triscarbonyl species in the solid state, in solution, there is a gradual loss of carbon monoxide leading first to an NNN pincer-Mn(I) biscarbonyl complex, which finally disproportionates to an NNN pincer-Mn(II) dibromide and an NNN pincer-Mn(0) complex. Evidence for this transformation has been obtained from single-crystal X-ray diffraction, IR, EPR, and HRMS analysis. The loss of carbon monoxide is apparently faster with a cyclohexyl-substituted complex than with others. The considered complexes (0.05 mol %) were utilized for catalyzing the β-alkylation of secondary alcohols at 140 °C in air under conventional heating (12 h), as well as under microwave heating (2 h) in the presence of 2.5 mol % of NaOtBu. Among the considered complexes, the catalyst (p-FC6H4NNN)Mn(CO)2Br was found to be highly efficient. While under conventional heating, a maximum of 92% (1840 TON at 153 TOs/h) of the β-alkylated product was obtained; microwave heating provided the β-alkylated product in 85% yield (1700 TON at 850 TOs/h) in just 2 h. The catalytic system has been successfully implemented to alkylate several other secondary alcohols, as well (35 examples). IR, EPR, and HRMS analyses indicate the intermediates in the catalytic cycle to be based both on NNN pincer-Mn(I) biscarbonyl species and on an NNN pincer-Mn(II)/Mn(0) couple. Deuterium labeling studies point to the involvement of C–H bond activation in the rate-determining step (RDS) with a kinetic isotope effect (KIE) of 9.0.

Low-energy high-spin binuclear hexamethylbenzene manganese carbonyl structures with partially bonded benzene rings

The geometries and energetics of binuclear hexamethylbenzene manganese carbonyls (Me6C6)2Mn2(CO)n (n = 4, 3, 2, 1), including the experimentally known tetracarbonyl, have been examined using density functional theory. Relatively low- energy structures include trans- and cis-(η6-Me6C6)2Mn2(CO)2(µ-CO)2 doubly bridged tetracarbonyl structures and a triplet (η6-Me6C6)2Mn2(µ-CO)3 triply bridged structure analogous to experimentally known isoelectronic binuclear cyclopentadienyliron carbonyls. However, in addition, a series of low-energy quintet spin state structures (η10–2n-Me6C6)Mn(CO)n–Mn(η6-C6Me6) (n = 4, 3, 2) is found. The tetracarbonyls and tricarbonyl of this series have partially bonded hexamethylbenzene rings suggesting a certain fragility of the hexamethylbenzene-manganese linkage not found in the isoelectronic cyclopentadienyliron compounds. For the dicarbonyl and monocarbonyl (Me6C6)2Mn2(CO)n (n = 2, 1) systems, singlet structures having the triple or quadruple manganese-manganese bonds necessary to give each manganese atom the favored 18-electron configuration are very high-energy structures relative to isomeric triplet and quintet spin state structures.

The manganese carbonyl complex [Mn(CO)3(tqa-κ3N)]Br: A novel antimicrobial agent with the potential to treat avian pathogenic Escherichia coli (APEC) infections

The development of alternatives to antibiotics is essential for the treatment of animal infections and as a measure to reduce the selective pressure on antibiotics that are critical for human medicine. Metal complexes have been highlighted for their antimicrobial activity against several bacterial pathogens. In particular, manganese carbonyl complexes have shown efficacy against multidrug-resistant Gram-negative pathogens, and relatively low cytotoxicity against avian macrophages and in wax moth larval models. They are thus potential candidates for deployment against Avian Pathogenic Escherichia coli (APEC), the aetiological agent of avian colibacillosis, which results in severe animal welfare issues and financial losses worldwide. This study aimed to determine the efficacy of [Mn(CO)3(tqa-κ3N)]Br in Galleria mellonella and chick models of infection against APEC. The results demonstrated in vitro and in vivo antibacterial activity against all antibiotic-resistant APEC test isolates screened in the study.

Stimulus-Detonated Biomimetic "Nanobomb" with Controlled Release of HSP90 Inhibitor to Disrupt Mitochondrial Function for Synergistic Gas and Photothermal Therapy.

Photothermal therapy (PTT) is considered a promising treatment for tumors; however, its efficacy is restricted by heat shock proteins (HSPs). Herein, a stimuli-responsive theranostic nanoplatform (M/D@P/E-P) is designed for synergistic gas therapy and PTT. This nanoplatform is fabricated by a load of manganese carbonyl (MnCO, CO donor) in dendritic mesoporous silicon (DMS), followed by the coating with polydopamine (PDA) and loading of epigallocatechin gallate (EGCG, HSP90 inhibitor). Upon near-infrared (NIR) irradiation, the photothermal effect of PDA can kill tumor cells and allow for the controlled drug release of MnCO and EGCG. Moreover, the acidity and H2 O2 -rich tumor microenvironment enable the decomposition of the released MnCO, accompanied by the production of CO. CO-initiated gas therapy can realize to disrupt the mitochondrial function, which will accelerate cell apoptosis and down-regulate HSP90 expression by decreasing intracellular ATP. The combination of EGCG and MnCO can significantly minimize the thermo-resistance of tumors and improve PTT sensitivity. In addition, the released Mn2+ enables T1 -weighted magnetic imaging of tumors. The therapeutic efficacy of the nanoplatform is methodically appraised and validated both in vitro and in vivo. Taken together, this study affords a prime paradigm for applying this strategy for enhanced PTT via mitochondrial dysfunction.

Nanodrug Augmenting Antitumor Immunity for Enhanced TNBC Therapy via Pyroptosis and cGAS-STING Activation.

Pyroptosis is a proinflammatory form of programmed cell death that results in the release of cellular contents and activation of immune responses. However, GSDME (a pyroptosis-executed protein) is suppressed in many cancers. Herein, we constructed a nanoliposome (GM@LR) for codelivering the GSDME-expressing plasmid and manganese carbonyl (MnCO) into TNBC cells. MnCO generated Mn2+ and carbon monoxide (CO) in the presence of H2O2. The CO-activated caspase-3, which cleaved the expressed GSDME, converting apoptosis to pyroptosis in 4T1 cells. In addition, Mn2+ promoted maturation of dendritic cells (DCs) by the activation of STING signaling pathway. The increased proportion of intratumoral mature DCs brought about massive infiltration of cytotoxic lymphocytes, leading to a robust immune response. Besides, Mn2+ could be applied for magnetic resonance imaging (MRI)-guided metastasis detection. Taken together, our study showed that GM@LR nanodrug could effectively inhibit tumor growth via pyroptosis and STING activation combined immunotherapy.

Gas therapy potentiates aggregation-induced emission luminogen-based photoimmunotherapy of poorly immunogenic tumors through cGAS-STING pathway activation

The immunologically “cold” microenvironment of triple negative breast cancer results in resistance to current immunotherapy. Here, we reveal the immunoadjuvant property of gas therapy with cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway activation to augment aggregation-induced emission (AIE)-active luminogen (AIEgen)-based photoimmunotherapy. A virus-mimicking hollow mesoporous tetrasulfide-doped organosilica is developed for co-encapsulation of AIEgen and manganese carbonyl to fabricate gas nanoadjuvant. As tetra-sulfide bonds are responsive to intratumoral glutathione, the gas nanoadjuvant achieves tumor-specific drug release, promotes photodynamic therapy, and produces hydrogen sulfide (H2S). Upon near-infrared laser irradiation, the AIEgen-mediated phototherapy triggers the burst of carbon monoxide (CO)/Mn2+. Both H2S and CO can destroy mitochondrial integrity to induce leakage of mitochondrial DNA into the cytoplasm, serving as gas immunoadjuvants to activate cGAS-STING pathway. Meanwhile, Mn2+ can sensitize cGAS to augment STING-mediated type I interferon production. Consequently, the gas nanoadjuvant potentiates photoimmunotherapy of poorly immunogenic breast tumors in female mice.