Cp Bond Cleavage Research Articles

Full carbon upcycling of organophosphorus wastewater enabled by interface photolysis

The key of wastewater treatment is to reduce the toxicity of organic pollutants and ideally undergo mineralization, typically accompanying the formation of greenhouse gas CO2 in large amounts. Here, a full carbon upcycling strategy for efficient valorization of organic phosphorus (OPs) contaminants enabled by interface photolysis was developed, in which the van der Waals interface effect based on the interfacial heterojunction interaction could efficiently regulate the electron density of the UCN/CdS NPs photocatalyst interface to benefit the construction of the interface-orienteering electron pump and edge active sites. The synergistic catalysis of ·OH on the C sites and holes on the Cd sites at the photocatalyst interface edge could realize the complete photodegradation of glyphosate wastewater in 2 h to exclusively afford gas fuel CO (4124 μmol g−1) and glycine (86 %), which was likewise applicable to an extensive scope of OPs for nigh quantitative carbon upcycling. Quantum calculations elaborated that the Cd edge sites with the ability to enrich holes induced by the van der Waals interface effect could reduce the activation energy of CP bond cleavage of glyphosate activated by ·OH, resulting in CP bond scission selectivity of ca. 91.5 %, which is vital to full carbon upcycling. The oriented interface engineering offers a more eco-friendly photocatalytic protocol to facilitate both wastewater treatment and carbon resource recovery.

Efficient degradation and detoxification of antibiotic Fosfomycin by UV irradiation in the presence of persulfate

Fosfomycin (FOS) as a widely used antibiotic has been found in abundance throughout the environment, but little effort has been devoted to its treatment. In this study, we systemically looked into the degradation of FOS by ultraviolet-activated persulfate (UV/PS) in aqueous solutions. Our findings demonstrated that FOS can be degraded efficiently under the UV/PS, e.g., >90 % of FOS was degraded with 19,200 mJ cm−2 of UV irradiance and 20 μM of PS. HO was the dominant radical responsible for FOS degradation. FOS degradation increased as PS dosage increased, and higher degradation efficiency was observed at neutral pH. Natural water constitutes either promoted (e.g., Cu2+, Fe3+, and SO42−) or inhibited (e.g., humic acid, HCO3−, and CO32−) FOS degradation to varying degrees. Hydroxyl substitution, CP bond cleavage, and coupling reactions were the major degradation pathways for FOS degradation. Finally, the toxicity evaluation revealed that FOS was toxic to E. coli and S. aureus, but the toxicity of the intermediate products of FOS to E. coli and S. aureus rapidly decreased over time after UV/PS treatment. Therefore, these findings provided a fundamental understanding of the transformation process of FOS and supplied useful information for the environmental elimination of FOS contamination and its toxicity.

Microbial biotransformation mechanisms of PFPiAs in soil unveiled by metagenomic analysis

As alternatives of long-chain PFASs (Poly- and perfluoroalkyl substances), perfluoroalkyl phosphinic acids (PFPiAs) are increasingly observed in the environment, but their environmental behaviors have not been well understood. Here, the microbial biotransformation of C6/C6 and C8/C8 PFPiA in two soils (Soil N and Y) was investigated. After 252 d and 330 d of incubation with PFPiAs in Soil N and Y respectively, the levels of PFPiAs decreased distinctly, accompanied by the increasing perfluorohexaphosphonic acid (PFHxPA) or perfluorooctanophosphonic acid (PFOPA) formation, magnifying PFPiAs were susceptible to C-P cleavage, which was also confirmed by the density functional theory calculations. The half-lives of the PFPiAs were longer than one year, while generally shorter in Soil N than in Soil Y and that of C6/C6 was shorter than C8/C8 PFPiA (392 d and 746 d in Soil N, and 603 and 1155 d in Soil Y, respectively). Metagenomic sequencing analysis revealed that Proteobacteria as the primary host of the potential functional genes related to CP bond cleavage might be the crucial phyla contributing to the biotransformation of PFPiAs. Meanwhile, the more intensive interactions between the microbes in Soil N consistently contribute to its greater capacity for transforming PFPiAs.

α-Ketophosphonates in the Synthesis of α-iminophosphonates

The potentialities of condensation of α-ketophosphonates with primary amines for direct synthesis of α-iminophosphonates have been revealed. Diesters of α-ketophosphonic acids react with the primary amines by two competitive pathways: with a formation of α-iminophosphonates or a C-P bond cleavage resulting in a hydrogen phosphonate and an acylated amine. In many cases, the latter undesirable pathway is dominant, especially for more nucleophilic alkyl amines. Using metallic salts of α-ketophosphonates avoids the C-P bond cleavage, allowing direct preparation of α-phosphorylated imines by the reaction with primary amines. This strategy provides an atom economy single-stage synthesis of iminophosphonates – precursors of bio relevant phosphorus analogs of α-amino acids. Methyl sodium iminophosphonates, bearing aryl or heteryl substituents at the imino carbon atom exist in solutions at room temperature as an equilibrium mixture of Z- and E-isomers. A configuration of the C=N bond can be controlled by the solvent: changing the aprotic dipolar solvent DMSO-d6 by water or alcohols leads to the change from a predominant Z-isomer to almost an exclusive E-form. In contrast, diesters of the respective iminophosphonates exist in non-protic solvents predominantly in Econfiguration. The solvent effect on E-Z stereochemistry is demonstrated by DFT calculations.

Phosphate oxygen isotope evidence for methylphosphonate sources of methane and dissolved inorganic phosphate

The ocean is an important source of methane, however, the sources of oceanic methane and mechanisms of its release to the atmosphere have only recently begun to be understood. Recent studies have identified methylphosphonate (MPn) as a previously unknown and likely source of methane in the aerobic ocean (Karl et al., 2008), as well as shown the biosynthesis of methylphosphonic acid to be a widespread trait in marine microbes (Metcalf et al., 2012). The mechanisms and reaction pathways from MPn to free methane, however, have not been well studied. Here we present results of laboratory studies on the photo-degradation of MPn, a likely mechanism of methane release to the atmosphere and phosphate release to the surface oceans. Phosphonoacetic acid was also studied as an additional model compound for comparison. We used the multi-labeled water isotope probing (MLWIP) approach, involving 18O-labeled waters to probe the photolytic mechanism of CP bond cleavage in phosphates through analysis of P released from MPn as PO4. These studies identified distinct reaction pathways involving phosphates compared with other common organophosphorus compounds (e.g., phosphoesters), as well as suggest the involvement of both ambient water and atmospheric oxygen in CP bond cleavage. There is only a small amount of water oxygen incorporated into product PO4 after cleavage of the CP bond in MPn, suggesting atmospheric O2 or radicals formed from O2 under Ultra Violet Radiation (UVR), as the primary source of O that replaces C in the CP bond of MPn. Model calculations suggest that the δ18OP signature of phosphate released via UV-degradation of phosphates is largely (75%) inherited from the original phosphate substrate. This opens up the possibility of tracing and differentiating specific phosphate sources of dissolved phosphate from other organophosphorus (Porg) sources (e.g., phosphoesters) used in primary production, as well as for tracing specific MPn sources of atmospheric methane.

Tuning the Polymerization Behavior of Silicon-Bridged [1]Ferrocenophanes Using Bulky Substituents

Sila[1]ferrocenophanes bearing bulky nitrogen- and silicon-based substituents at the ansa bridge have been prepared by nucleophilic substitution of chloride at silicon in Fe(η5-C5H4)2SiClH (3) by Li[N(SiMe3)2] and K[Si(SiMe3)3]. The resulting compounds, Fe(η5-C5H4)2Si[N(SiMe3)2]H (4) and Fe(η5-C5H4)2Si[Si(SiMe3)3]H (5), have been fully characterized, and their ring-opening polymerization (ROP) chemistry has been explored. Upon heating for 3 h, 4 yields the polymer [(η5-C5H4)Fe(η5-C5H4)Si{N(SiMe3)2}H]n (Mn = 38 000 Da, PDI = 7.5), but 5 does not react due to the larger steric bulk of the substituent on silicon. ROP initiated by Na[C5H5] under photolytic conditions involving Fe−Cp bond cleavage occurred for both 4 and 5, to afford (η5-C5H5)Fe(η5-C5H4)[SiRH(η5-C5H4)Fe(η5-C5H4)]n−1SiRH(η1-C5H5) (R = N(SiMe3)2: n = 20 and 60; R = Si(SiMe3)3: n = 20 and 50), but anionic ROP initiated with nBuLi was unsuccessful, presumably due to the close proximity of the bulky group to the site of nucleophilic attack. The pol...

Palladium‐Catalyzed Arylation of Olefins by Triarylphosphines via CP Bond Cleavage

AbstractCH Arylation of olefins by triarylphosphines via CP bond cleavage has been achieved with either Pd0 or PdII catalysts. A variety of olefins and triarylphosphines are tolerated, and we inferred that both Pd0 and PdII could function directly without pre‐oxidation or pre‐reduction.

The enzymatic conversion of phosphonates to phosphate by bacteria

Phosphonates are ubiquitous organophosphorus compounds that contain a characteristic CP bond which is chemically inert and hydrolytically stable. Bacteria have evolved pathways to metabolize these phosphonate compounds and utilize the products of these pathways as nutrient sources. This review aims to present all of the known bacterial enzymes capable of transforming phosphonates to phosphates. There are three major classes of enzymes known to date performing such transformations: phosphonatases, the C-P lyase complex and an oxidative pathway for CP bond cleavage. A brief description of each class is presented.

Oxygen isotope signature of UV degradation of glyphosate and phosphonoacetate: Tracing sources and cycling of phosphonates

The degradation of phosphonates in the natural environment constitutes a major route by which orthophosphate (Pi) is regenerated from organic phosphorus and recently implicated in marine methane production, with ramifications to environmental pollution issues and global climate change concerns. This work explores the application of stable oxygen isotope analysis in elucidating the CP bond cleavage mechanism(s) of phosphonates by UV photo-oxidation and for tracing their sources in the environment. The two model phosphonates used, glyphosate and phosphonoacetic acid were effectively degraded after exposure to UV irradiation. The isotope results indicate the involvement of both ambient water and atmospheric oxygen in the CP bond cleavage and generally consistent with previously posited mechanisms of UV-photon excitation reactions. A model developed to calculate the oxygen isotopic composition of the original phosphonate P-moiety, shows both synthetic phosphonates having distinctly lower values compared to naturally derived organophosphorus compounds. Such mechanistic models, based on O-isotope probing, are useful for tracing the sources and reactions of phosphonates in the environment.

An iron-cyclopentadienyl bond cleavage mechanism for the thermal ring-opening polymerization of dicarba[2]ferrocenophanes

In order to gain insight into the mechanism for the thermal ring-opening polymerization of strained dicarba[2]ferrocenophanes, the thermal reactivity of selected examples of these species with different substitution patterns has been explored. When heated at 300 °C dicarba[2]ferrocenophanes meso/rac-[Fe(η5-C5H4)2(CHPh)2] (mesomeso/racrac-7) and meso-[Fe(η5-C5H4)2(CHCy)2] (mesomeso-13) were found to isomerize or to undergo disproportionation, respectively. These processes are apparently general for dicarba[2]ferrocenophanes with one or more non-hydrogen substituents at each carbon atom in the dicarba bridge and both appear to involve homolytic cleavage of the C–C bond in the bridge as a key step. In striking contrast, derivatives containing either one or no non-hydrogen substituents on the bridge such as {Fe[η5-C5H4]2[CH(Ph)CH2]} (15) and [Fe(η5-C5H4)2(CH2)2] (17) undergo thermal ring-opening polymerization (ROP) under similar conditions (300 °C, 1 h). Thus, thermolysis of 15 yielded polyferrocenylethylene {Fe[η5-C5H4]2[CH(Ph)CH2]}n (16a) with a broad molecular weight distribution (Mw = 13,760, PDI = 3.27). Analysis of 16a by MALDI-TOF mass spectrometry suggested that the material was macrocyclic. Thermal treatment of linear polyferrocenylethylenes {Fe[η5-C5H4]2[CH(Ph)CH2]}n with narrow molecular weight distributions (prepared by photocontrolled ROP) at 300 °C confirmed that the macrocycles detected form directly, and not as a result of depolymerization. Copolymerizations of 15 with 17 and of 15 with the deuterated species [Fe(η5-C5H4)2(CD2)2] (dd44-17) were conducted in order to probe the bond cleavage mechanism. Comparative NMR spectroscopic analysis of the resulting copolymers 18 and dd44-18, respectively, and of homopolymer 16a, indicated that thermal ROP does not occur via a homolytic C–C bridge cleavage mechanism. A series of thermolysis experiments were conducted with MgCp2 (Cp = η5-C5H5) at 300 °C, which resulted in the isolation of ring-opened species formed from 15 and 17, and indicated that the Fe–Cp bonds can be cleaved under the thermal ROP conditions employed. The studies indicated that a chain growth process that involves heterolytic Fe–Cp bond cleavage in the monomers is the most probable mechanism for the thermal ROP of dicarba[2]ferrocenophanes.

A fluorescent substrate for carbon–phosphorus lyase: Towards the pathway for organophosphonate metabolism in bacteria

Many species of bacteria can use naturally occurring organophosphonates as a source of metabolic phosphate by cleaving the carbon–phosphorus bond with a multi-enzyme pathway collectively called carbon–phosphorus lyase (CP-lyase). Very little is known about the fate of organophosphonates entering this pathway. In order to detect metabolic intermediates we have synthesized a fluorescently labelled organophosphonate and show that this is a viable substrate for the CP-lyase pathway in Escherichia coli and that the expected product of CP-bond cleavage is formed. The in vivo competence of one potential metabolic intermediate, 1-ethylphosphonate-α- d-ribofuranose, is also demonstrated.

Photoinduced FeCp Bond Cleavage and Insertion Reactions of Strained Silicon- and Sulphur-Bridged [1]Ferrocenophanes in the Presence of Transition-Metal Carbonyls

The photochemical reactions of the moderately strained sila[1]ferrocenophane [Fe(eta-C(5)H(4))(2)SiPh(2)] (1) and the highly strained thia[1]ferrocenophane [Fe(eta-C(5)H(4))(2)S] (8) with transition-metal carbonyls ([Fe(CO)(5)], [Fe(2)(CO)(9)] and [Co(2)(CO)(8)]) have been studied. The use of metal carbonyls has allowed the products of photochemically induced Fe-cyclopentadienyl (Cp) bond cleavage reactions in the [1]ferrocenophanes to be trapped as stable, characterisable products. During the course of these studies the synthesis of 8 from [Fe(eta-C(5)H(4)Li)(2)TMEDA] (TMEDA=N,N,N',N'-tetramethylethylenediamine) and S(SO(2)Ph)(2) has been significantly improved by a change of reaction solvent and temperature. Photochemical reaction of 1 with excess [Fe(CO)(5)] in THF gave the dinuclear complex [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)SiPh(2)] (9). The analogous photolytic reaction of 8 with [Fe(CO)(5)] in THF gave cyclic dimer [Fe(eta-C(5)H(4))(2)S](2) (10) and [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)S] (11), with the former being the major product. Photolysis of 1 with [Co(2)(CO)(8)] afforded the remarkable tetrametallic dimer [(CO)(2)Co(eta-C(5)H(4))SiPh(2)(eta-C(5)H(4))Fe(CO)(2)](2) (13). The corresponding photochemical reaction of 8 with [Co(2)(CO)(8)] gave a trimetallic insertion product in high conversion, [Co(CO)(4)(CO)(2)Fe(eta-C(5)H(4))S(eta-C(5)H(4))Co(CO)(2)] (14). These reactivity studies show that UV light promotes Fe-Cp bond cleavage reactions of both of the [1]ferrocenophanes 1 and 8. We have found that, whereas the less strained sila[1]ferrocenophane 1 requires photoactivation for Fe-Cp bond insertions to occur, the highly strained thia[1]ferrocenophane 8 undergoes both irradiative and non-irradiative insertions, although the latter occur at a slower rate. Our results suggest that such photoinduced bond cleavage reactions may be general and applicable to other related strained organometallic rings with pi-hydrocarbon ligands.

Synthesis and reactions of 2,2,2-trihaloethyl ?-hydroxyiminobenzylphosphonates. The influence of the ester group on the chemistry of phosphonates

Arbuzov reactions of diethyl 2,2,2-trihaloethyl phosphites (3) with benzoyl chloride afforded ethyl 2,2,2-trihaloethyl benzoylphosphonates (4). The reactions of 4 with NH2OH.HCl led to the formation of methyl benzoate and ethyl methyl H-phosphonate as a result of alcoholysis of 4, followed by alkoxy group exchange. Methanol solutions of benzoylphosphonates 4 were found by 31P NMR spectroscopy to contain considerable proportions of hemiacetals, 7, which undergo base-catalyzed CP bond cleavage. The formation of hemiacetals from benzoylphosphonates 4 is suppressed in 2-propanol, and in this solvent the corresponding oximes 2 could be obtained in good yields. Reactions of methyl benzoylphosphonochloridate (10) with 2,2,2-trihaloethanols, in CH2Cl2, gave methyl 2,2,2-trihaloethyl benzoylphosphonates (11) which could be converted directly to oximes 12 by NH2OH.HCl in a one-pot procedure. In contrast to the previously studied dimethyl (E)-α-hydroxyiminobenzylphosphonate, which underwent thermal Beckmann rearrangement to afford N-benzoylphosphoramidates, both (E) and (Z)-trihaloethyl esters 2 and 12 underwent fragmentation to benzonitrile and to the corresponding dialkyl hydrogen phosphate, reflecting the increased electrophilicity of the phosphorus in these compounds. Demethylation of methyl esters 12 was effected smoothly by iodide or bromide ions to yield benzoylphosphonate salts 15, which in turn were converted to oxime salts 14 by treatment with hydroxylamine. In contrast, attempted deethylation of ethylesters 2 in refluxing acetonitrile led to benzonitrile and pyrophosphate type product as indicated by 31P spectroscopic examination of the reaction mixture. Oxime salts 14 behaved similarly when heated. Acidification of lithium 2,2,2-trifluoroethyl α-hydroxyiminobenzylphosphonate (14a) gave the corresponding hydrogen trifluoroethyl phosphonate (19a). The fragmentation of 19a in 0.6 N ethanolic hydrogen chloride to ethyl trifluoroethyl hydrogen phosphate and benzonitrile at room temperature had a T1/2 value of approx 18 hours, which is greater by a factor of 2 than that of the corresponding methyl ester. When the fragmentation of 19 was carried out in solvent mixtures of either water with methanol or 2-propanol, or methanol with tbutanol, the composition of the solvents was reflected in the products, indicating a dissociative type mechanism, involving metaphosphate as reactive intermediates.